[Four-year follow-up study of onlay and occlusal veneer restorations on posterior teeth]

OBJECTIVE

To investigate the survival rate and clinical failure reasons of onlay and occlusal veneer restorations retrospectively, and to put forward valuable suggestions for the selection of clinical indications.

METHODS

A total of 102 patients and 124 teeth treated by one of the authors from 2016 to 2019 were subjected to CAD/CAM lithium silicate reinforced glass-ceramic onlay or veneer restorations of premolars and molars, including 43 teeth with pulp vitality, 81 endodontic treated teeth, and occlusal thickness of restoration was 1.5 mm. After four years of restoration, retrospective surveys were conducted to record the survival rate of restorations, the causes of restoration failure, and patient satisfaction rates, and the survival rate of restorations between vital teeth and endodontic treated teeth and among restored teeth was statistically analyzed by Chi-square test.

RESULTS

The survival rates of restorations on vital teeth and endodontic treated teeth were 95.5% and 90.0%, respectively, the average survival rate was 90.2%. The survival rates of vital teeth were higher than those of endodontic treated teeth without statistical difference. There was also no statistically significant difference among the tooth locations. The causes of failure included the cracking of the restoration, the loss of the restoration, the fracture of the abutment teeth, secondary caries below the adjacent contact point, and food impaction caused by the loosening of the adjacent contact point. The overall patient satisfaction rate was 91.5%.

CONCLUSION

The 4-year survival rate of glass-ceramic onlays and occlusal veneers is lower than that of the full crown restoration, and there are more complications than that of the single-crown restorations. The design of the restoration should be carefully selected based on the vitality of the abutment tooth and the remaining amount of tooth tissue. When there is too little tooth structure left, a post and crown should be selected for restoration. Adequate strength and thickness of the restoration should be ensured to prevent food impaction. Due to the small amount of abutment tooth preparation, it has the advantages of less stimulation of the pulp and periodontal tissue, and can be recommended as a trial restoration.

Ethnobotanical, ecological and health risk assessment of some selected wild medicinal plants collected along mafic and Ultra Mafic rocks of Northwest Pakistan

The current study investigated wild plant resources and health risk assessment along with northern Pakistan's mafic and ultramafic regions. Ethnobotanical data was collected through field visits and semi-structured questionnaire surveys conducted from local inhabitants and healers. Six potentially toxic elements (PTEs) such as lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr), manganese (Mn), and zinc (Zn) were extracted with acids and analyzed using atomic absorption spectrophotometer (AAS, Perkin Elmer-7000) in nine selected wild medicinal plants. Contamination factor (CF), pollution load index (PLI), estimated daily intake (EDI), target hazard quotient (THQ), and hazard index (HI) were used to determine the health risk assessment of the studied medicinal plants. The results showed that the selected medicinal plants were used for the treatments of cough, joint swelling, cardiovascular disorders, toothaches, diabetes, and skin pimples by the local inhabitants due to their low-cost and easy accessibility. The concentrations of Pb (3.4-53 mg kg-1), Cd (0.03-0.39 mg kg-1), Ni (17.5-82 mg kg-1), Cr (29-315 mg kg-1), Mn (20-142 mg kg-1), and Zn (7.4-64 mg kg-1) in the studied medicinal plants were found above the safe limits (except Zn) set by WHO/FAO/USEPA (1984/2010). The Pb contamination factor was significantly (p < 0.05) higher in A. modesta (7.84) and D. viscosa (6.81), and Cd contamination factor was significantly higher in C. officinalis (26.67), followed by A. modesta (8.0) mg kg-1. Based on PTE concentrations, the studied plants are considered not suitable for human consumption purposes. Pollution load index values for A. modesta, A. barbadensis, A. caudatus, A. indica, C. procera (2.93), D. viscosa (2.79), and C. officinalis (2.83), R. hastatus (3.12), and Z. armatum were observed as 1.00, 2.80, 2.29, 2.29, 2.93, 2.79, 2.83, 3.12 and 2.19, respectively. Hazard index values were in order of R. hastatus (1.32 × 10-1) ˃ C. procera (1.21 × 10-1) ˃ D. viscosa (1.10 × 10-1) ˃ A. caudatus (9.11 × 10-2) ˃ A. barbadensis (8.66 × 10-2) ˃ Z. armatum (7.99 × 10-2) ˃ A. indica (6.87 × 10-2) ˃ A. modesta (5.6 × 10-2) ˃ C. officinalis (5.42 × 10-2). The health risk index values suggested that consumption of these plants individually or in combination would cause severe health problems in the consumers. Pearson's correlation results showed a significant correlation (p ≤ 0.001) between Zn and Mn in the studied medicinal plants. The current study suggests that wild medicinal plants should be adequately addressed for PTEs and other carcinogenic pollutants before their uses in the study area. Open dumping of mining waste should be banned and eco-friendly technology like organic amendments application should be used to mitigate PTEs in the study area.

Genome assemblies of two species of porcelain crab, Petrolisthes cinctipes and Petrolisthes manimaculis (Anomura: Porcellanidae)

Crabs are a large subtaxon of the Arthropoda, the most diverse and species-rich metazoan group. Several outstanding questions remain regarding crab diversification, including about the genomic capacitors of physiological and morphological adaptation, that cannot be answered with available genomic resources. Physiologically and ecologically diverse Anomuran porcelain crabs offer a valuable model for investigating these questions and hence genomic resources of these crabs would be particularly useful. Here, we present the first two genome assemblies of congeneric and sympatric Anomuran porcelain crabs, Petrolisthes cinctipes and Petrolisthes manimaculis from different microhabitats. Pacific Biosciences high-fidelity sequencing led to genome assemblies of 1.5 and 0.9 Gb, with N50s of 706.7 and 218.9 Kb, respectively. Their assembly length difference can largely be attributed to the different levels of interspersed repeats in their assemblies: The larger genome of P. cinctipes has more repeats (1.12 Gb) than the smaller genome of P. manimaculis (0.54 Gb). For obtaining high-quality annotations of 44,543 and 40,315 protein-coding genes in P. cinctipes and P. manimaculis, respectively, we used RNA-seq as part of a larger annotation pipeline. Contrarily to the large-scale differences in repeat content, divergence levels between the two species as estimated from orthologous protein-coding genes are moderate. These two high-quality genome assemblies allow future studies to examine the role of environmental regulation of gene expression in the two focal species to better understand physiological response to climate change, and provide the foundation for studies in fine-scale genome evolution and diversification of crabs.

Factors Influencing Dentists' Choice of Restorative Materials for Single-Tooth Crowns: A Survey Among Saudi Practitioners

BACKGROUND Material selection is crucial in restorative dentistry, influenced by aesthetics, material properties, and tooth location. This understanding is key for advancing dental practices and patient outcomes. The present study aimed to assess dentists' preferences for restorative materials in single-tooth crowns (SC) and how abutment tooth location and preparation margins influence these choices. MATERIAL AND METHODS A web-based pre-validated questionnaire survey was conducted among 811 actively practicing dentists in Saudi Arabia. RESULTS In posterior teeth, we found that ceramic was the most preferred material for SC regardless of the abutment tooth location and location of margins, followed by porcelain fused to metal (PFMs). In anterior teeth, ceramics were preferred, followed by CAD/CAM-based resin SC. Among the choice of ceramics in teeth for both supra-gingival margins, monolith zirconia was the most-preferred material for SC fabrication in posterior teeth, followed by zirconia-reinforced lithium silicate ceramic. Similarly, for sub-gingival margins, monolith zirconia crowns were the most popular option in posterior teeth among the respondents, with the highest in the mandibular molar region. In the anterior region, layered zirconia was the least preferred, and lithium disilicate ceramics was the most-favored option. A statistically significant difference existed between supra- and subgingival preparation for teeth 11 (P=0.01), 16 (P=0.03), and 34 (P=0.02). CONCLUSIONS Ceramic was the material of choice among Saudi dentists for replacement of SC, irrespective of the location and preparation margin. Monolith zirconia was usually selected for posterior teeth and lithium disilicate ceramics was the top choice in anterior teeth.

Ultrathin lithium disilicate and translucent zirconia crowns for posterior teeth: Survival and failure modes

PURPOSE

To evaluate the reliability and failure modes of ultrathin (0.5 mm) lithium disilicate, translucent and ultra-translucent zirconia crowns for posterior teeth restorations.

MATERIALS AND METHODS

Fifty-four mandibular first molar crowns of three ceramic materials: (1) Lithium disilicate (e.max CAD, Ivoclar Vivadent), (2) 3Y-TZP (Zirconn Translucent, Vipi), and (3) 5Y-PSZ (Cercon XT, Dentsply Sirona), with 0.5 mm of thickness were milled and cemented onto composite resin abutments. Eighteen samples of each group were tested under mouth-motion step-stress accelerated life testing in a humid environment using mild, moderate, and aggressive profiles. Data was subjected to Weibull statistics. Use level curves were plotted and reliability was calculated for a given mission of 100,000 cycles at 100, 200, and 300 N. Fractographic analyses of representative samples were performed in scanning electron microscope.

RESULTS

Beta (β) values suggest that failures were dictated by material's strength for lithium disilicate and by fatigue damage accumulation for both zirconias. No significant differences were detected in Weibull modulus and characteristic strength among groups. At a given mission of 100,000 cycles at 100 N, lithium disilicate presented higher reliability (98% CB: 95-99) regarding 3Y-TZP and 5Y-PSZ groups (84% CB: 65%-93% and 79% CB: 37&-94%, respectively). At 200 N, lithium disilicate reliability (82% CB: 66%-91%) was higher than 5Y-PSZ (20% CB: 4%-44%) and not significantly different from 3Y-TZP (54% CB: 32%-72%). Furthermore, at 300 N no significant differences in reliability were detected among groups, with a notable reduction in the reliability of all materials. Fractographic analyses showed that crack initiated at the interface between the composite core and the ceramic crowns due to tensile stress generated at the intaglio surface.

CONCLUSIONS

Ultrathin lithium disilicate crowns demonstrated higher reliability relative to zirconia crowns at functional loads. Lithium disilicate and zirconia crown's reliability decreased significantly for missions at higher loads and similar failure modes were observed regardless of crown material. The indication of 0.5 mm thickness crowns in high-load bearing regions must be carefully evaluated.

CLINICAL SIGNIFICANCE

Ultraconservative lithium disilicate and zirconia crowns of 0.5 mm thickness may be indicated in anterior restorations and pre-molars. Their clinical indication in high-load requirement regions must be carefully evaluated.

Effect of a modified laminate veneer preparation design on absolute margin discrepancy and marginal overhang

STATEMENT OF PROBLEM

Veneer preparation designs impact veneer accuracy. However, whether a modified design could reduce absolute margin discrepancy and marginal overhangs is unclear.

PURPOSE

The purpose of this in vitro study was to investigate whether a modified veneer preparation design enhances the absolute margin discrepancy and marginal overhang.

MATERIAL AND METHODS

The absolute margin discrepancy and the marginal overhang of 3 different veneer preparation designs on a typodont tooth (n=20): feather edge, shoulder, and shoulder with wings were measured. The feather edge design was prepared first and subsequently modified to create the shoulder and shoulder with wings preparations. Ceramic veneers were fabricated using computer-aided design and computer-aided manufacture with each veneer assessed for fit before cementation. Ten specimens were cut vertically, and 10 were cut horizontally in each group. The absolute margin discrepancy and marginal overhangs were measured for each cross-section with scanning electron microscopy. Descriptive data analysis and hypothesis testing were conducted using the nonparametric Kruskal Wallis test (α=.05).

RESULTS

On the vertical sections, the shoulder with wings preparation had the best absolute margin discrepancy and overhang. The design was also best for mesial overhang and mesial absolute margin discrepancy when measuring horizontally.

CONCLUSIONS

The shoulder with wings preparation design produced the smallest cervical absolute margin discrepancy and overhang. This design also produced absolute margin discrepancy and overhangs comparable with those of the shoulder design in the proximal areas.

Influence of ceramic thickness and dental substrate on the survival rate and failure load of non-retentive occlusal veneers after fatigue

OBJECTIVE

To investigate the effect of ceramic thickness and dental substrate (enamel vs. dentin/enamel) on the survival rate and failure load of non-retentive occlusal veneers.

MATERIALS AND METHODS

Human maxillary molars (n = 60) were divided into five test-groups (n = 12). The groups (named DE-1.5, DE-1.0, DE-0.5, E-1.0, E-0.5) differed in their dental substrate (E = enamel, DE = dentin/enamel) and restoration thickness (standard: 1.5 mm, thin: 1.0 mm, ultrathin: 0.5 mm). All teeth were prepared for non-retentive monolithic lithium-disilicate occlusal veneers (IPS e.max Press, Ivoclar). Restorations were adhesively cemented (Syntac Classic/Variolink II, Ivoclar) and exposed to thermomechanical fatigue (1.2 million cycles, 1.6 Hz, 49 N/ 5-55°C). Single load to failure was performed using a universal testing-machine. A linear-regression model was applied, pairwise comparisons used the Student-Newman-Keuls method (p < 0.05).

RESULTS

Three dentin-based occlusal veneers (one DE-1.0, two DE-0.5) revealed cracks after fatigue exposure, which corresponds to an overall-survival rate of 95%. Load to failure resulted in the following ranking: 2142 N(DE-0.5) > 2105 N(E-1.0) > 2075 N(E-0.5) > 1440 N(DE-1.5) > 1430 N(DE-1.0). Thin (E-1.0) and ultrathin enamel-based occlusal veneers (E-0.5) revealed high failure loads and surpassed the standard thickness dentin-based veneers (DE-1.5) significantly (p = 0.044, p = 0.022).

CONCLUSION

All tested monolithic lithium disilicate occlusal veneers obtained failure loads above physiological chewing forces. Thin and ultrathin enamel-based occlusal veneers outperformed the standard thick dentin-based occlusal veneers.

CLINICAL SIGNIFICANCE

Minimally invasive enamel-based occlusal veneer restorations with non-retentive preparation design may serve as a conservative treatment option.

Development of zirconia-based polymer-infiltrated ceramic network for dental restorative material

Polymer-infiltrated ceramic network (PICN) materials have gained considerable attention as tooth restorative materials owing to their mechanical compatibility with human teeth. However, the mechanical strength of contemporary PICN materials is lower than those of conventional resin composites and ceramics. This study aims to develop novel high-strength PICN for use as a dental restorative material. Zirconia-based PICN (EXP) was fabricated using 3 mol% yttria tetragonal polycrystalline zirconia powder and resin monomers via slip casting, followed by sintering and polymer infiltration. Comprehensive analyses of the microstructure, mechanical properties, and physicochemical properties of EXP were performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, inorganic content measurements, three-point bending test, Vickers hardness test, two-body wear test, shear bond strength (SBS) test, surface free energy analysis, and water sorption/solubility test. Commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) materials, including resin composite (CERASMART), silicate-based PICN (ENAMIC), and zirconia ceramic (e.max ZirCAD), were used for comparison. The analyses highlight the dual network structure of EXP, which comprised a zirconia skeleton and an infiltrated resin phase. EXP exhibits a flexural strength of 346.0 ± 46.0 MPa, flexural modulus of 44.0 ± 3.7 GPa, and Vickers hardness of 440.1 ± 51.2 VHN. The mechanical properties of EXP are significantly higher than those of CERASMART and ENAMIC but lower than those of ZirCAD. Notably, the EXP hardness closely mimics that of the human enamel. The wear volume, SBS, and water sorption/solubility of EXP are comparable to those of CERASMART and ENAMIC. Therefore, EXP has potential applications as a tooth restorative material.

Characteristic fatigue strength and reliability of dental glass-ceramics: Effect of distinct surface treatments - Hydrofluoric acid etching and silane treatment vs one-step self-etching ceramic primer

The aim of this study was to mechanically characterize through flexural fatigue test two CAD-CAM glass-ceramics according to distinct surface etching protocols. To do so, feldspathic (FELD) and lithium disilicate (LD) glass ceramics were subjected to different surface treatments: (1) control - no treatment (Ctrl); (2) conventional protocol etching with 5% hydrofluoric acid followed by silane coupling agent application (HF + SIL; Monobond N, Ivoclar); or (3) using a self-etching ceramic primer (E&P; Monobond Etch & Prime, Ivoclar). Ceramic discs (N = 120; Ø = 12 mm; thickness = 1.2 mm) were produced from CAD-CAM blocks, with 60 being from FELD (VITABLOCS Mark II, Vita Zahnfabrik) and 60 from LD (IPS e.max CAD, Ivoclar). Next, 20 disks of each ceramic were allocated into three groups: Ctrl, HF + SIL, or E&P. Surface roughness data were collected on all samples before and after surface treatments (except for Ctrl). Cyclic fatigue (n = 15) biaxial flexural strength tests were performed by the piston-on-three-balls geometry (ISO 6872) considering the test parameters established from a monotonic test (n = 5). The monotonic test was carried out at a 1 mm/min loading rate and 500 kgf loading cell until fracture to obtain the failure data. The cyclic fatigue test was executed underwater at a frequency up to 20 Hz, with the first stress being 25% of the monotonic test for 5000 cycles, followed by increments of 5% of the monotonic test at each step of 10,000 cycles until failure (fracture). Complementary fractography, topography and Atomic Force Microscopy (AFM) analyses were performed. Characteristic Fatigue Strength (CFS) and Weibull modulus were analyzed by Weibull analysis using the fatigue test data. Roughness and complementary analysis data were analyzed by one-way ANOVA. The statistical results exhibited similar CFS among Ctrl, HF + SIL and E&P for both glass-ceramics. The survival analysis corroborates the findings, however the Weibull modulus pointed out superior structural reliability of FELD treated with the E&P group compared to HF + SIL. According to the complementary analyses, HF + SIL exhibited a higher surface area than E&P and Ctrl for FELD (p = 0.001). Roughness showed statistically significant differences among conditions for FELD (E&P < Ctrl = HF + SIL; p < 0.05) and no difference for LD (p > 0.05). Therefore, the CFS were not influenced by any condition evaluated for FELD and LD glass-ceramics; however, superior structural reliability (higher Weibull modulus) for the feldspathic ceramic treated with the E&P was observed.

Wear of lithium disilicate opposed by various ceramic materials

OBJECTIVES

To compare volumetric wear of lithium disilicate against different ceramic (3 mol% yttria-stabilized (3Y) zirconia, 5 mol% yttria-stabilized (5Y) zirconia, lithium disilicate, porcelain and enamel antagonists).

MATERIALS AND METHODS

Forty lithium disilicate (e.max CAD) specimens (n = 8/antagonist) were wet sanded to 1200grit SiC and mounted into a UAB wear device. Antagonist spheres (diameter = 4.75 mm) were made from polished 3Y zirconia, 5Y zirconia, lithium disilicate, porcelain and human enamel. A two-body wear test was performed with 20 N load and 1.5 mm slide for 400,000 cycles at 1 Hz. 33% glycerin was used as a lubricant. Wear facets were measured with optical profilometry. Wear scar areas of antagonists were measured with digital microscopy. Scanning electron microscopy was performed on wear facets and scars. Vicker's microhardness was measured of all antagonist materials. All data were compared with 1-way ANOVA and Tukey post-hoc analysis.

RESULTS

Significant differences in lithium disilicate volumetric wear (mm3 ) occurred with various antagonist materials: 0.38 ± 0.01a (3Y zirconia), 0.33 ± 0.01b, (5Y zirconia), 0.16 ± 0.01c (lithium disilicate), 0.11 ± 0.03d, (enamel), and 0.07 ± 0.01e (porcelain). The lithium disilicate antagonist demonstrated a larger wear scar than other materials. Zirconia was the hardest material and enamel the least hard.

CONCLUSIONS

Zirconia causes significant wear on lithium disilicate and lithium disilicate causes significant wear against itself.

CLINICAL SIGNIFICANCE

When selecting a material to oppose an existing lithium disilicate crown, a porcelain or lithium disilicate surface would cause significantly less wear to the existing crown. If an existing zirconia crown exists opposed to a prepared tooth, lithium disilicate may not be an ideal material selection to restore the tooth.

Influence of different surface finishing procedures of strength-gradient multilayered zirconia crowns on two-body wear and fracture load: Lithium silicate or leucite glazing versus polishing?

OBJECTIVES

To examine the influence of different finishing procedures on the surface roughness, wear resistance and fracture load of strength-gradient multilayered zirconia.

MATERIALS AND METHODS

Zirconia crowns (Multilayer 3D pro; n = 96) were manufactured and treated with a lithium-silicate- (LISI_S), leucite-based glaze spray (LEU_S), leucite-based glaze mass (LEU_M) or polished (POL). Natural molars (CG; n = 24) acted as a control. Roughness was determined on flat glazed specimens (n = 28). Two-body wear was examined by digitalizing and matching the occlusal surface before and after thermo-mechanical aging (6,000 thermal and 1,200,000 chewing cycles). The groups were split to measure fracture load initially and after aging. Kolmogorov-Smirnov, Spearman correlation, Kruskal-Wallis-H, Levene's test, one-way ANOVA with Scheffé post-hoc and Weibull modulus were computed.

RESULTS

POL presented the lowest and LEU_S the highest roughness. Following POL, no ceramic loss was observed. LISI_S, LEU_S and LEU_M showed lower ceramic wear than the CG. The lowest wear of the antagonist was observed for the CG. LISI_S showed a lower antagonistic wear than LEU_S, LEU_M and POL. LISI_S, LEU_S, LEU_M and POL showed higher fracture load values and Weibull moduli than the CG. Artificial aging did not impact the fracture load or Weibull moduli.

SIGNIFICANCE

With glazed groups showing height losses closer to the CG, glazing should be preferred to polishing when approximating the wear behavior of a natural dentition. Finishing of monolithic zirconia by glazing with a lithium silicate-based spray is recommended to preserve the antagonists. All examined zirconia crowns presented sufficient mechanical properties to withstand masticatory forces, even after prolonged aging.

Biomechanical behavior and Weibull survival of CAD-CAM endocrowns with different marginal designs: A 3D finite element analysis

OBJECTIVES

To evaluate and compare the effect of tooth preparation designs and different CADCAM. materials on stress distribution and Weibull survival probability of endocrowns. applied to root canal-treated lower first permanent molar using the 3D finite element. analysis method.

METHODS

A root canal-treated lower first permanent molar was prepared for endocrowns with a. butt joint or with a ferrule design by placing, circumferentially, a 1-mm wide shoulder. finish line. The prepared molar was scanned for the two designs and modeled on a 3D. Finite element model. Monolithic zirconia (IPS e.max ZirCAD MT, FCZ), lithium. disilicate (IPS e.max CAD, EX), and nano-ceramic resin composite (Lava Ultimate, LU). CAD-CAM materials were used for each preparation to design the virtual endocrown. A. total of six models were built according to the different tooth preparation designs and. endocrown materials. An occlusal load of 600 N and a transverse load of 20 N in. magnitude that simulates the average occlusal load was directed toward the occlusal. surfaces. von Mises and maximum principle values were evaluated Weibull risk-ofrupture. analysis was used to analyze the survival probability of the restorations and. tooth in the different models.

RESULTS

The highest von Mises were found in the butt joint design for FCZ, EX, and LU (45.3. MPa, 35.2 MPa, and 24.2 MPa, respectively) compared to the ferrule design for the. same materials (42.6 MPa, 31.2 MPa, and 23.6 MPa, respectively). For von Mises. stress distribution in the remaining part of tooth structure (dentin), the highest stresses. were found in LUFerrule which was closely similar to LUButt joint (135.4 MPa and. 134.7 MPa, respectively), followed by EXFerrule and FCZFerrule (132.2 MPa and. 131.7 MPa, respectively), while the lowest stresses were found in EXButt joint and. FCZButt joint (129.0 MPa and 128.4 MPa, respectively). Shear stresses within the. resin cement were the highest in FCZ and EX compared to LU. EX was found to be the. most reliable material with the highest survival probability, while FCZ showed the. lowest survival probability according to the Weibull risk-of-fracture results.

SIGNIFICANCE

Materials with high elastic modulus transfer more stresses to the endocrown and less. to the remaining tooth structure. Endocrown tooth preparation with ferrule design has. better stress distribution and magnitude compared to the butt joint design.

Effect of abutment screw-access hole on the fatigue performance of implant-supported lithium-disilicate luted simplified restorations

The present study aimed to evaluate the impact of the existence of an abutment screw-access hole and the filling effects on the fatigue mechanical behavior of a luted lithium-disilicate glass-ceramic. Seventy-two discs (Ø = 10 mm, 1.0 mm in thickness) of lithium disilicate (IPS e.max CAD, Ivoclar AG) were obtained from prefabricated blocks. Thirty-six abutment specimens of an opaque zirconia (Yz - IPS e.max ZirCAD, Ivoclar AG) and titanium (Ti - Luminesse Ti-Cam discs, Talladium Inc.) were confectioned, and allocated according to 6 groups: Yz and Ti rigid (without screw access hole); Yz unfilled, Yz filled, Ti unfilled and Ti filled (with the screw access (Ø = 2.5 mm) in the center). For the unfilled groups, only a polytetrafluoroethylene tape was used. Resin composite (Tetric N-Ceram, Ivoclar AG) was applied to the screw access hole for the filled groups (Yz and Ti). A cyclic fatigue test was carried out (load of 200 N, 10,000 cycles each; 20 Hz of frequency, step size of 100 N until failure detection (radial/cone crack). The fatigue failure load (FFL) and number of cycles until failure (CFF) were recorded for statistical purposes. The stress distribution (MPa) was evaluated by finite element analysis. A statistically positive effect of the abutment material and the presence of the screw access hole was observed (p ≤ 0.05). The rigid groups (without screw access holes) depicted almost 100% of survival after the fatigue tests. Among the other groups, the Yz-filled group showed the best performance (p ≤ 0.05), followed by the Yz unfilled group. The Ti groups depicted lower values of FFL and CFF, with the Ti unfilled group showing the most unfavorable fatigue behavior (p ≤ 0.05). The lowest tensile stress concentration in the restorative material was observed with the use of rigid abutments, the filled groups depicted intermediate values, while unfilled groups showed the highest stress concentration (Yz rigid = 306.3 MPa; Ti rigid = 310.4 MPa < Yz filled = 490.7 MPa; Ti filled = 498.9 MPa < Yz unfilled = 707.6 MPa; Ti unfilled = 719.7 MPa). Therefore, the presence of a screw-access hole decreases the mechanical performance of a lithium disilicate ceramic regardless of the abutment material. In the presence of a screw-access hole, zirconia abutments depicted a higher fatigue failure load when compared with titanium. The filling of the abutment screw-access hole with resin composite increased the mechanical performance of the simulated restoration.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.

CAD/CAM leucite-reinforced glass-ceramic for simulation of attrition in human enamel in vitro

OBJECTIVE

Investigate attrition simulation using CAD/CAM leucite-reinforced glass-ceramic antagonists on occlusal vs. buccal enamel.

METHODS

Three dental materials with known wear rates (resin-modified glass-ionomer, micro-filled, and fine particle composites) validated the wear simulator (CAD/CAM glass-ceramic antagonists, 200 cycles, 80 N load, deionised water irrigation, 0.7 mm sliding movement). Following this, human molars were sectioned into paired occlusal and buccal polished samples (n = 8/gp). Exposed 1.5 mm Ø enamel areas were subjected to attritional wear with and without pre-immersion in citric acid (5 min, 0.3%, pH 3.8). Profilometry measured step-height enamel wear and surface microhardness at different depths was calculated using Vickers indentation at 0.1 N and 0.5 N loads.

RESULTS

Dental material wear using the CAD/CAM antagonists showed consistency with previous data: mean (SD) resin-modified glass ionomer material loss of 177.77 (16.89) µm vs. 22.15 (1.30) µm fine particle hybrid composite resin wear vs. 13.63 (1.02) µm micro filled composite resin wear (P < 0.001). The coefficient of variation was less than 10%. Following validation, enamel sample wear was significantly increased when attrition was introduced (P < 0.001) independent of buccal vs. occlusal sample location (P < 0.05). Attrition resulted in occlusal wear of 26.1 ± 4.5 µm vs. buccal 26.3 ± 1.2 µm and attrition/erosion resulted in occlusal wear of 26.05 ± 4.46 µm vs. buccal 25.27 ± 1.16 µm. Whereas erosion-alone resulted in occlusal wear of 1.65 ± 0.13 µm and buccal 1.75 ± 0.03 µm. Microhardness testing at different loads revealed significantly greater hardness reductions in occlusal enamel vs. buccal enamel for 0.1 KgF indentations (P < 0.001) whereas in contrast 0.5 KgF indentations showed no differences.

SIGNIFICANCE

Wear simulation with CAD/CAM glass ceramic antagonists produced consistent wear in dental materials and human enamel, regardless of enamel surface origin. Lighter (0.1 KgF) hardness testing of occlusal vs. buccal origin revealed damage to the mechanical integrity of the superficial worn enamel.

Fusion machine learning model predicts CAD-CAM ceramic colors and the corresponding minimal thicknesses over various clinical backgrounds

OBJECTIVES

This study has developed and optimized a machine learning model to accurately predict the final colors of CAD-CAM ceramics and determine their required minimum thicknesses to cover different clinical backgrounds.

METHODS

A total of 120 ceramic specimens (2 mm, 1 mm and 0.5 mm thickness; n = 10) of four CAD-CAM ceramics - IPS e.max, IPS ZirCAD, Upcera Li CAD and Upcera TT CAD - were studied. The CIELab coordinates (L*, a* and b*) of each specimen were obtained over seven different clinical backgrounds (A1, A2, A3.5, ND2, ND7, cobalt-chromium alloy (CC) and medium precious alloy (MPA)) using a digital spectrophotometer. The color difference (ΔE) and lightness difference (ΔL) results were submitted to 39 different models. The prediction results from the top-performing models were used to develop a fusion model via the Stacking integrated learning method for best-fitting prediction. The SHapley Additive exPlanation (SHAP) was performed to interpret the feature importance.

RESULTS

The fusion model, which combined the ExtraTreesRegressor (ET) and XGBRegressor (XGB) models, demonstrated minimal prediction errors (R2 = 0.9) in the external testing sets. Among the investigated variables, thickness and background colors (CC and MPA) majorly influenced the final color of restoration. To achieve perfect aesthetic restoration (ΔE<2.6), at least 1.9 mm IPS ZirCAD or 1.6 mm Upcera TT CAD were required to cover the CC background, while two tested glass-ceramics did not meet the requirements even with thicknesses over 2 mm.

SIGNIFICANCE

The fusion model provided a promising tool for automate decision-making in material selection with minimal thickness over various clinical background.

Tooth morphology, internal fit, occlusion and proximal contacts of dental crowns designed by deep learning-based dental software: A comparative study

OBJECTIVES

This study compared the tooth morphology, internal fit, occlusion, and proximal contacts of dental crowns automatically generated via two deep learning (DL)-based dental software systems with those manually designed by an experienced dental technician using conventional software.

METHODS

Thirty partial arch scans of prepared posterior teeth were used. The crowns were designed using two DL-based methods (AA and AD) and a technician-based method (NC). The crown design outcomes were three-dimensionally compared, focusing on tooth morphology, internal fit, occlusion, and proximal contacts, by calculating the geometric relationship. Statistical analysis utilized the independent t-test, Mann-Whitney test, one-way ANOVA, and Kruskal-Wallis test with post hoc pairwise comparisons (α = 0.05).

RESULTS

The AA and AD groups, with the NC group as a reference, exhibited no significant tooth morphology discrepancies across entire external or occlusal surfaces. The AD group exhibited higher root mean square and positive average values on the axial surface (P < .05). The AD and NC groups exhibited a better internal fit than the AA group (P < .001). The cusp angles were similar across all groups (P = .065). The NC group yielded more occlusal contact points than the AD group (P = .006). Occlusal and proximal contact intensities varied among the groups (both P < .001).

CONCLUSIONS

Crowns designed by using both DL-based software programs exhibited similar morphologies on the occlusal and axial surfaces; however, they differed in internal fit, occlusion, and proximal contacts. Their overall performance was clinically comparable to that of the technician-based method in terms of the internal fit and number of occlusal contact points.

CLINICAL SIGNIFICANCE

DL-based dental software for crown design can streamline the digital workflow in restorative dentistry, ensuring clinically-acceptable outcomes on tooth morphology, internal fit, occlusion, and proximal contacts. It can minimize the necessity of additional design optimization by dental technician.

Quantitative analysis of the color in six CAD-CAM dental materials of varied thickness and surface roughness: An in vitro study

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) monochromatic restorative materials are gaining popularity because of their convenience and efficiency. However, studies that quantitatively analyzed color change associated with thickness and surface roughness are sparse.

PURPOSE

The purpose of this in vitro study was to quantitatively evaluate the color of 6 CAD-CAM monochromatic materials of different thickness and surface roughness using the CIELab color system.

MATERIAL AND METHODS

A total of 150 12×12-mm square specimens of 6 different CAD-CAM monochromatic materials (VITA Enamic HT [VE], IPS e.max CAD HT [LS], LAVA Ultimate HT [LU], Telio CAD HT [TE], VITA Suprinity HT [VS], and Celtra Duo HT [CD]) in shade A2 and 5 different thicknesses (from 0.5 mm to 2.5 mm, with 0.5-mm increments) were fabricated (n=5). After 3 different surface treatments (polished, roughened by SiC P800-grit, and P300-grit), CIELab color parameters (L*, a* and b*) were measured using a spectrophotometer (VITA Easyshade V), and surface roughness was measured with a profilometer (VK-X200). Color variation was quantified by ΔE00 and 50:50% acceptability and perceptibly thresholds. Data analyses were performed using MANOVA, 2-way ANOVA, post hoc Tukey-Kramer test, and the 1-sample t test (α=.05).

RESULTS

The L*, a*, and b* of the monochromatic specimens were significantly influenced by material type, thickness, and surface roughness (P<.001). An overall increase in the L* (from 61.90 to 82.2), a* (from -4.22 to 1.16), and b* (from 5.48 to 43.22) of the specimens was observed with increased thickness. The roughened specimens exhibited lower L* and higher a* and b* than the polished ones (P<.001). The use of P300-grit for roughening resulted in greater ΔE00 compared with P800-grit (P<.001). As thickness decreased or surface roughness increased, the ΔE00 increased and exceeded the acceptability and perceptibly thresholds for color difference.

CONCLUSIONS

Material type, thickness, and surface roughness were major factors affecting the color of CAD-CAM monochromatic materials. Variations in thickness of 0.5 mm or more, as well as roughening treatments, may lead to clinically unacceptable color changes.

In-vitro evaluation of wear characteristics, microhardness and color stability of dental restorative CAD/CAM materials

The aim of this study was to demonstrate the vertical and volumetric wear characteristics of CAD/CAM materials. The microhardness and color stability were evaluated. A polymer infiltrated ceramic network CAD/CAM block, resin nanoceramic CAD/CAM blocks, a resin composite, and enamel tissue were investigated. Samples were loaded in a chewing simulator. Other samples were aged and immersed in coffee. Color change was evaluated using the digital image analysis and a spectrophotometer. The data were analyzed using Kolmogorov-Smirnov, Kruskal Wallis, Mann Whitney U, Friedman, Spearman's rho tests (p<0.05). The lowest level of wear was obtained in enamel tissue group 0.20 (Q1:0.14; Q3:0.27μm). Resin composite group 2.48 (Q1:2.12; Q3:2.92) showed lower level of discoloration. No agreement was obtained between the digital image analysis and spectrophotometer data (Spearman's rho -0.314, p=0.014). Similar wear rate to the natural enamel tissue was obtained for Vita Enamic. Digital image analysis was considered a promising technique for monitoring the color change.

Comparison of discoloration of ceramic containing 3D printable material and CAD/CAM blocks

This study aimed to clarify aspects of the color and translucency of 3D printed dental material with CAD/CAM blocks. Three different ceramic-containing, resin-based CAD/CAM blocks and a 3D printable resin were evaluated after thermocycled and assessed for their degree of discoloration based on colorant types and storage times. Data were analyzed using repeated-measures analysis of variance followed by Tukey's post-hoc test. All materials in red wine had ∆E00 values higher than the clinically accepted threshold value. At 1 week and 1 month, the 3D material was statistically significantly more discolored than the other 3 materials (p<0.05). None of the materials exceeded the acceptable threshold value at any time point. The color changes increased over time in resin-based CAD/CAM blocks and 3D printable dental materials. After 1 week and 1 month, there was a statistically significant difference in the color change between the 3D printed material and the CAD/CAM blocks.

Extended porcelain veneers in the maxillary anterior region. A retrospective study with an up to 27-year follow-up

AIM

The aim of the present retrospective study was to evaluate the long-term results, including technical and biologic outcomes, of maxillary extended porcelain veneers with an incisal edge thickness above 2 mm.

MATERIALS AND METHODS

Patients treated with extended porcelain veneers performed by a single clinician at University of Geneva between 1990 and 2003 were identified and invited to an examination. Of the 37 identified patients, 10 patients with 50 veneers agreed to be examined and were included. A clinical examination was performed to assess survival rates as well as technical and biologic outcomes (modified United States Public Health Services criteria). Patient records were also reviewed to retrieve patient and reconstruction data and every complication event. Patient-reported outcome measures (PROMs) were evaluated using a visual analog scale to measure esthetic satisfaction, functional and phonetic comfort, masticatory improvement, tooth sensitivity, and acceptance of restoration replacement in case of failure. Data were descriptively analyzed, and Kaplan-Meier survival estimators were computed for survival rates and complication events.

RESULTS

The survival rate of the veneers was 96% after a mean follow-up of 20.7 ± 3.7 years in function. The technical complication rate amounted to 30%, including two failures, nine repairable fractures, three cracks, and one displacement due to trauma. No cavitated caries lesions or endodontic complications were registered. PROMs were very high for esthetic satisfaction and phonetic comfort.

CONCLUSIONS

Within the limitations of the present retrospective study, extended porcelain veneers appear to be a successful long-term treatment option in terms of clinical outcomes and patient satisfaction.

Two‑year clinical performance of indirect restorations fabricated from CAD/CAM nano hybrid composite versus lithium disilicate in mutilated vital teeth. A randomized controlled trial

TRIAL DESIGN

This is a randomized, controlled, superiority, double-blinded, parallel-group, two-arms trial with an allocation ratio of 1:1. The aim of this trial was to compare the two-year clinical performance of partial indirect restorations fabricated from CAD/CAM nano-hybrid composite and ceramic lithium disilicate blocks using the modified USPHS criteria.

METHODS

In two parallel groups (n = 50 restorations), fifty participants having mutilated vital teeth with a minimum of two remaining walls were randomly enrolled in this trial and received indirect restorations of either nano-hybrid composite resin blocks (Brilliant, Coltene, Switzerland) or Lithium Disilicate (IPS Emax CAD). The restorations were assessed using modified USPHS criteria by two independent blinded assessors at baseline, six months, one-year and two years follow-up visits. Categorical and ordinal data were presented as frequencies and percentages. Categorical data were analyzed using the chi-square test. Ordinal data were analyzed using the Mann-Whitney U test for intergroup comparisons and Freidman's test followed by the Nemenyi post hoc test for intragroup comparisons. Numerical data were presented as mean and standard deviation values. They were analyzed for normality using the Shapiro-Wilk test. Data were found to be normally distributed and were analyzed using the independent t-test. The significance level was set at p ≤ 0.05 within all tests.

RESULTS

Forty-eight participants received the allocated intervention and completed the follow-up periods. There was a statistically significant difference between both tested materials for all USPHS criteria regarding Marginal integrity and Marginal discoloration at six-months Follow-up, but with no statistically significant difference at one- and two-year follow-up.

CONCLUSIONS

Both materials showed an acceptable, successful clinical performance along the two-years follow-up period.

CLINICAL RELEVANCE

The CAD/CAM nano-hybrid composite blocks are as reliable as Lithium disilicate for restoring mutilated vital teeth.

Biomechanical behavior of all-ceramic endocrowns fabricated using CAD/CAM: A systematic review

PURPOSE

This study performed a systematic review to assess the biomechanical behavior of all-ceramic endowcrowns fabricated using computer-aided design and computer-aided manufacturing (CAD/CAM) for the restoration of endodontically treated teeth.

STUDY SELECTION

Three electronic databases (PubMed, Web of Science, and Scopus) were searched by operators specializing in health sciences databases searches to answer the following focused question based on the Population, Intervention, Comparison, Outcome (PICO) format: "Whether all-ceramic CAD/CAM endocrowns (Intervention) used to restore human endodontically treated teeth (Population) exhibit superior fracture resistance (Outcome) compared to non-CAD/CAM all-ceramic or non-ceramic endocrowns (Comparison)." The methodological quality assessment was performed using previously conducted systematic reviews of in vitro studies. The outcomes were expressed as the mean ± the standard deviation (SD).

RESULTS

Seventeen in vitro studies were included. The materials used in these studies were lithium disilicate glass-ceramic, polymer-infiltrated ceramic, zirconia-reinforced lithium silicate glass-ceramic, resin/hybrid nanoceramics, zirconia-reinforced lithium silicate ceramics, and feldspathic ceramic. The fracture resistance of endocrowns using different ceramics varied as follows: (i) IPS e.max CAD (2863.62 ± 51.47 N), (ii) Vita Enamic (1952 ± 378 N), (iii) Vita Suprinity (1859 ± 588 N), (iv) Cerasmart (1981 ± 169.5 N), (v) LAVA Ultimate (2484 ± 464 N), (vi) Celtra Duo (1618.30 ± 585.00 N), and (vii) Cerec Blocs (236.29 ± 32.12 N).

CONCLUSIONS

CAD/CAM all-ceramic endocrowns can withstand occlusal forces in the posterior region. All-ceramic endocrowns improve the fracture strength of endodontically treated teeth. Lithium disilicate crowns were commonly and successfully used in the included studies. More in vitro investigations that implement uniformity in material and measurement approaches are required to strengthen the evidence currently available in the literature regarding the durability of all-ceramic endocrowns.

Initial damage and failure load of zirconia-ceramic and metal-ceramic posterior cantilever fixed partial dentures

OBJECTIVES

The aim of this study was to compare failure load and initial damage in monolithic, partially veneered, and completely veneered (translucent) zirconia cantilevered fixed partial dentures (CFPDs), as well as completely veneered metal-ceramic CFPDs under different support and loading configurations.

MATERIALS AND METHODS

Eight test groups with anatomically congruent CFPDs (n = 8/group) were fabricated, differing in CFPD material/support structure/loading direction (load applied via steel ball (Ø 6 mm) 3 mm from the distal end of the pontic for axial loading with a 2-point contact on the inner cusp ridges of the buccal and oral cusps and 1.3 mm below the oral cusp tip for 30° oblique loading): (1) monolithic zirconia/CoCr abutment teeth/axial, (2) monolithic zirconia/CoCr abutment teeth/oblique, (3) partially veneered zirconia/CoCr abutment teeth/axial, (4) partially veneered zirconia/CoCr abutment teeth/oblique, (5) completely veneered zirconia/CoCr abutment teeth/axial, (6) completely veneered CoCr/CoCr abutment teeth/axial (control group), (7) partially veneered zirconia/implants/axial, and (8) partially veneered zirconia/natural teeth/axial. Restorations were artificially aged before failure testing. Statistical analysis was conducted using one-way ANOVA and Tukey post hoc tests.

RESULTS

Mean failure loads ranged from 392 N (group 8) to 1181 N (group 1). Axially loaded monolithic zirconia CFPDs (group 1) and controls (group 6) showed significantly higher failure loads. Oblique loading significantly reduced failure loads for monolithic zirconia CFPDs (group 2). Initial damage was observed in all groups except monolithic zirconia groups, and fractography revealed design flaws (sharp edges at the occlusal boundary of the veneering window) in partially veneered zirconia CFPDs.

CONCLUSIONS

Monolithic zirconia CFPDs might be a viable alternative to completely veneered CoCr CFPDs in terms of fracture load. However, oblique loading of monolithic zirconia CFPDs should be avoided in clinical scenarios. Design improvements are required for partially veneered zirconia CFPDs to enhance their load-bearing capacity.

CLINICAL RELEVANCE

Monolithic zirconia may represent a viable all-ceramic alternative to the established metal-ceramic option for CFPD fabrication. However, in daily clinical practice, careful occlusal adjustment and regular monitoring should ensure that oblique loading of the cantilever is avoided.

Bond Strength to Lithium-Disilicate Ceramic after Different Surface Cleaning Approaches

PURPOSE

To evaluate the effect of different lithium-disilicate (LiSi) glass-ceramic surface decontamination procedures on the shear bond strength (SBS) to resin cement.

MATERIALS AND METHODS

Seventy CAD/CAM LiSi ceramic specimens (IPS e.max CAD, Ivoclar) were cut and sintered. Fifty specimens were treated with 5% hydrofluoric acid (HF) for 20 s, while 20 were left untreated. All 70 specimens were then contaminated with human saliva and try-in silicone paste. The following surface cleaning methods were investigated (n = 10): C: water rinsing (control); PA: 37% H3PO4 etching for 20 s; E: 70% ethanol applied for 20 s; CP: cleaning paste (Ivoclean, Ivoclar) brushed for 20 s; HFSEP: self-etching ceramic primer (Monobond Etch&Prime, Ivoclar) rubbed for 20 s; HF: 5% HF applied for 20 s or no HF etching prior to contamination; SEP: self-etching ceramic primer rubbed for 20 s and no HF etching prior to contamination. Composite cylinders were created and luted with an adhesive resin cement to the decontaminated surfaces. After storage for 24 h at 37°C, the SBS test was conducted. Two fractured specimens per group were observed under SEM to perform fractographic analysis. The data were statistically analyzed with p set at <0.05.

RESULTS

The type of surface cleaning approach influenced bond strength (p < 0.001). HFSEP, SEP, and HF attained higher SBS (p < 0.001) compared to other groups. None of the approaches were able to completely remove contaminants from the ceramic surfaces. SEM images showed residual traces of contaminants on CP-treated surfaces.

CONCLUSIONS

The self-etching ceramic primer enhanced bond strength to contaminated LiSi ceramic surfaces, irrespective of previous treatment with hydrofluoric acid.

Clinical performance of monolithic lithium disilicate hybrid abutment crowns over at least 3.5 years

PURPOSE

Hybrid abutment crowns (HACs) made from monolithic ceramics represent an efficient option for single restorations on implants. However, long-term data are scarce. The purpose of this clinical trial was to evaluate the survival and complication rates of CAD-CAM fabricated HACs over a time period of at least 3.5 years.

MATERIALS AND METHODS

Twenty-five patients with a total of 40 HACs made of monolithic lithium disilicate ceramic bonded to a titanium base CAD-CAM abutment were retrospectively evaluated. All implants and screw-retained restorations were placed and manufactured in the same department of a university hospital. Only crowns that had been in service for more than 3.5 years were included in the study. HACs were evaluated regarding technical and biological complications. Functional Implant Prosthodontic Scores (FIPS) were obtained.

RESULTS

The mean observation time was 5.9 ± 1.4 years. Implant survival was 100%, and HAC survival was 97.5%. Over the observation period, one crown fracture was observed, necessitating refabricating of the restoration. Three minor biological complications were found. The overall mean FIPS score was 8.69 ± 1.12 points.

CONCLUSIONS

Within the limitations of this study, monolithic screw-retained HACs milled from lithium disilicate ceramics and bonded to titanium bases appeared to be a reliable treatment option over more than 3.5 years due to their low biological and technical complication rates.

INFLUENCE OF AGING, BEVERAGES, AND MOUTH WASH SOLUTIONS ON THE MICROSTRUCTURAL AND COLOR STABILITY OF DIFFERENT DENTAL CERAMICS: AN IN VITRO STUDY

Рurроse - to evaluate the influence of aging, beverages, and mouthwash solutions on the microstructural and color stability of three CAD/CAM ceramic materials. In total, 87 specimens (7×5×1.5 mm) were prepared from 3 CAD/CAM ceramic groups, Lithium Disilicate glass ceramic (IPS e.max CAD), Extra translucent zirconia (VITA YZ), and Resin Nanoceramic (Cerasmart 270). All the materials were A2 or equivalent shades. After hydrothermal aging in distilled water at 5 C to 55 C for (10.000 cycles). The samples were randomly allocated into 3 groups (n=27) and immersion (staining) for one week in 3 different solutions coffee, green tea, and chlorhexidine. The baseline measurements of ceramic discs were recorded for color change and 2 samples of each group sent for SEM (microstructure) images before aging and staining. The second measurement was recorded after 10000 thermocycling and immersion in staining agents for 7 days. Statistical analysis were performed with an independent Kruskal-wallis test . The significant level was set at P≤0.05. ∆E values for lithium Disilicate after immersion in coffee, green tea and chlorhexidine gluconate were 3.167, 1.847 and 2.022, respectively. corresponding ∆E values for VITA XT were 3.438, 4.201 and 2.267. meanwhile Cerasmart shows more sensitivity for staining than LD and VITA of 4.454, 2.926 and 2.933. Within limitation of this study lithium disilicate showed the best color stability with values less than perception threshold. VITA and Cerasmart show higher sensitivity for staining with VITA more affected by green tea (Higher than clinically accepted threshold) and Cerasmart more affected by coffee (higher than clinically accepted threshold).

Effect of final temperature and heating rate on the mechanical and optical properties of a zirconia veneering ceramic

PURPOSE

To evaluate the effect of firing temperature and heating rate on the volumetric shrinkage, translucency, flexural strength, hardness, and fracture toughness of a zirconia veneering ceramic.

MATERIAL AND METHODS

Zirconia veneering ceramic specimens (N = 45) with varying final temperatures (730 °C, 750 °C, and 770 °C) and heating rates (70 °C/min, 55 °C/min, and 40 °C/min) were fabricated (n = 5). Each specimen's shrinkage, translucency, flexural strength, hardness, and fracture toughness were determined. Two-way analysis of variance, Scheffé test, and Pearson's correlation analysis were used to evaluate data (α = 0.05).

RESULTS

The shrinkage (44.9 ± 3.1-47.5 ± 1.6 vol%) and flexural strength (74.1 ± 17.4-107.0 ± 27.1 MPa) were not affected by tested parameters (P ≥ 0.288). The interaction between the main factors affected the translucency, hardness, and fracture toughness of the specimens (P ≤ 0.007). Specimens with 770 °C final temperature and 70 °C/min heating rate had the lowest (21.8 ± 3.2 %) translucency (P ≤ 0.039). The hardness ranged between 4.98 ± 0.51 GPa (730 °C; 70 °C/min) and 5.60 ± 0.37 GPa (770 °C; 70 °C/min). Fracture toughness ranged between 0.54 ± 0.04 MPa√m and 0.67 ± 0.08 MPa√m with the highest values for specimens fired at 730 °C with 70 °C/min (P ≤ 0.001). There was a positive correlation between translucency and hardness (r = 0.335, P = 0.012), and a negative correlation between fracture toughness and all parameters other than shrinkage (translucency: r = -0.693/P < 0.001, flexural strength: r = -0.258/P = 0.046, hardness: r = -0.457/P < 0.001).

CONCLUSIONS

Heating rate and final temperature should be considered while fabricating veneered zirconia restorations with tested ceramic as they affected the translucency, hardness, and fracture toughness.

Ultrathin Feldspathic Ceramic Veneers: A Pilot SEM Evaluation of Etched Intaglio Surfaces

Ultrathin ceramic veneers are a viable therapeutic option to manage esthetic challenges in the anterior zone. Proper conditioning of the intaglio surface of porcelain veneers is essential to achieve an adequate bonding. In clinical practice, this is typically done with chemical etching using an acid-containing agent, such as hydrofluoric acid. While it is well established that the etching effect is dependent on etching time and the acid concentration, little is known about the impact of etching time and the veneer fabrication method. The purpose of this pilot study was to evaluate, using scanning electron microscopy (SEM), the effect that different etching-time protocols have on the intaglio surface characteristics of ultrathin ceramic veneers fabricated with either the platinum foil technique or the refractory die technique. Several replicas of an ultrathin feldspathic ceramic veneer for a maxillary central incisor were fabricated. Individual specimens were processed according to different intaglio surface-etching protocols: no etching, etching for 90 seconds, etching for 120 seconds, and etching for 150 seconds (9.6% hydrofluoric acid used for all etching groups). It was observed that the 120-second etching protocol resulted in a favorable microroughness surface pattern in the platinum foil group. This pattern was comparable to that obtained by etching for 90 seconds with hydrofluoric acid the intaglio surface of veneers fabricated with the refractory die technique. Increasing the etching time to 150 seconds did not result in a more favorable roughness pattern.

Effect of partially stabilized zirconia thickness on the translucency and microhardness of resin cement

STATEMENT OF PROBLEM

Partially stabilized zirconia has been introduced as a more translucent iteration. However, knowledge of the effect of the thickness of partially stabilized zirconia on the microhardness of resin cement is sparse.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of thickness and material type on the translucency of partially stabilized zirconia and the microhardness of the resin cement polymerized beneath.

MATERIAL AND METHODS

Specimens were prepared from 2 translucent zirconias with different yttrium content (Ceramil Zolid HT+ [HT] and Ceramil Zolid FX [SHT]) and a lithium disilicate glass-ceramic (e.max CAD [EX]) of different thicknesses (0.5, 1, 1.5, and 2 mm) (n=10). Color coordinates were recorded by using a spectrophotometer, and the relative translucency parameter (RTP) was calculated by using the CIEDE2000 formula. The microhardness of the resin cement polymerized under ceramic specimens was measured. Two-way analysis of variance, the Tukey honestly significant difference, and independent samples t tests were used to analyze the data (α=.05).

RESULTS

Material type (P<.001), thickness (P<.001), and their interaction significantly affected the RTP (P=.001) and hardness values (P<.001). Regardless of the thickness, EX had the highest RTP (P≤.027), and the resin cements polymerized under EX showed the highest microhardness (P≤.002). However, the difference between HT and SHT for RTP (P≥.082) and resin cement hardness (P≥.984) was not significant. Specimens of 0.5 mm resulted in higher RTP (P≤.001) and resin cement hardness (P≤.006) than the 1.5- and 2-mm specimens of each ceramic.

CONCLUSIONS

Increasing material thickness reduced the translucency of the partially stabilized zirconia and the hardness of the resin cements polymerized beneath.

Efficacy of two polishing systems in reestablishing the surface smoothness of posterior monolithic lithium disilicate restorations: One-year results of a split-mouth randomized controlled clinical trial

STATEMENT OF PROBLEM

Selecting the optimal polishing procedure to reestablish surface smoothness after occlusal adjustment is essential for the long-term success of glass-ceramic restorations. While in vitro studies have shown different effective polishing protocols, clinical trials are lacking.

PURPOSE

The purpose of this split-mouth controlled clinical trial was to evaluate the effectiveness of 2 polishing systems in reestablishing the surface smoothness of posterior monolithic lithium disilicate ceramic restorations.

MATERIAL AND METHODS

Ninety-six restorations that required occlusal adjustment after bonding were randomized into 2 groups: Forty-eight restorations were polished by using the Exa Cerapol polishing kit, and the other 48 restorations were polished by using the Shofu polishing kit. The restorations were replicated with epoxy resin at 3 study times-after bonding (t1), after occlusal adjustment (t2), and after polishing (t3)-for quantitative roughness analysis (Ra). Representative specimens from each group were qualitatively analyzed by using a confocal laser microscope. Clinical analyses were performed after the polishing procedure and at 30, 180, and 365 days after the polishing procedure by following the United States Public Health Service (USPHS) criteria. ANOVA and the Tukey multiple comparisons parametric tests were computed (α=.05). The Kaplan-Meier test was used to analyze the survival rate of restorations.

RESULTS

No statistically significant difference was found between the Exa Cerapol and Shofu groups (P=.086). A statistically significant difference was found between study times t1 and t2 and between t2 and t3 (both P<.001) in both experimental groups. No statistically significant difference was found between study times t1 and t3 (P=.181) in either experimental group. For the clinical criterion "integrity of restorations," all the elements analyzed indicated an alfa grade at all study times. The survival rate of the restorations was 100%.

CONCLUSIONS

Both polishing kits were effective in reestablishing the surface smoothness of restorations after occlusal adjustment.

Accuracy of three digital waxing-guided trial restoration protocols for controlling the depths of tooth preparation for ceramic veneers

STATEMENT OF PROBLEM

The accuracy of digital waxing-guided trial restoration protocols that have been implemented with ceramic veneers has not been reported.

PURPOSE

The purpose of this in vitro study was to evaluate the accuracy of 3 digital trial restorations fabricated from digital waxing for ceramic veneers.

MATERIAL AND METHODS

A uniform 0.3-mm digital waxing added to the facial surface of 30 maxillary central typodont incisors was created in a software program. The trial restorations were fabricated on typodont teeth with autopolymerizing acrylic resin by using a silicone index based on 3-dimensionally printed casts designed from the digital waxing. The 30 maxillary central incisors were divided into 3 groups: the depth cutter (0.5 mm, Komet) (DC) group, the round bur (1.5 mm, Diatech) (RB) group, and the specially designed calibrated depth bur (laser mark of 0.5 mm, Gaofeng) (CD) group. The 3 groups were randomly prepared with a random number table by 2 experienced prosthodontists aiming to produce an even facial clearance of 0.5 mm. The dimensional differences in the standard tessellation language (STL) files between the surfaces of the original teeth, digital waxing, trial restorations, and prepared teeth in the software program were measured and analyzed at the same 9 points on the labial surface. One-way ANOVA with a post hoc test was used to identify significant discrepancies between trial restorations and waxing and differences in the reduction depth of typodont teeth (RDT) and the reduction depth (RD) among the 3 techniques (α=.05). The mean relative differences (MRDs) were calculated to determine the accuracy (%).

RESULTS

The thickness of the trial restorations was significantly greater than that of the digital waxings, with a discrepancy of 0.20 ±0.14 mm, especially at the cervical site. With the use of a trial restoration, the RDTs of the middle (-0.01 ±0.11 mm) and cervical locations (0.09 ±0.20 mm) showed significantly smaller preparation depths than did the other locations. Significant differences in RD were found among the 3 guided techniques (P<.05). Group DC presented the most accurate result of 0.51 ±0.08 mm with an MRD of 2%, whereas the results of 0.57 ±0.10 mm with an MRD of 14% and 0.60 ±0.11 mm with an MRD of 20% were obtained from group RB and group DC, respectively.

CONCLUSIONS

The trial restoration was significantly thicker than its corresponding waxing. The DC technique presented the most accurate reduction result among the 3 protocols examined.

Clinical management of vital and non-vital discolored tooth preparation stump shades: A clinical case series

OBJECTIVE

Traditional and modern-day laboratory techniques can be used to mask vital and non-vital discolored teeth.

CLINICAL CONSIDERATIONS

Two clinical case reports are presented showing different treatment approaches to differing clinical scenarios of partial coverage veneer and full coverage crown restorations, respectively.

CONCLUSIONS

Feldspathic ceramics should be considered when customization of stump shade correction and equalization is required with minimum facial reduction with veneer restorations. Translucent zirconia (5 mol% Y2 O3 ) can be used to mask metal posts and core restorations on non-vital teeth using an opaquer material that is infused into the intaglio surface in the green state.

CLINICAL SIGNIFICANCE

Different clinical scenarios will present to the clinician in regard to discolored stump shades where understanding what laboratory material treatment options are available that will help guide definitive restoration types and ultimately tooth preparation design.

Fracture resistance evaluation of CAD/CAM zirconia and composite primary molar crowns with different occlusal thicknesses

OBJECTIVE

To evaluate the effect of different CAD/CAM materials and occlusal thicknesses on the fracture resistance of primary molar crowns.

METHODS

Sixty extracted primary molar teeth were prepared and randomly divided into six experimental groups according to the material and thickness. Primary molar crowns with a central groove thickness of 0.3 and 0.5 mm were fabricated from CAD/CAM zirconia (group Z), zirconia-reinforced lithium silicate (group ZLS), and pre-polymerized composite resin blocks (group C). Each crown was cemented with self-adhesive resin cement on the prepared tooth. All specimens were subjected to fracture tests until fracture. Fracture load values were recorded in Newtons (N). Data were statistically analyzed using a two-way analysis of variance (ANOVA) followed by Tukey multiple comparison test.

RESULTS

The highest fracture load values were obtained in group Z at 0.5 mm occlusal thickness and were significantly higher compared with the other experimental groups (p < 0.05). Although the lowest fracture load values were obtained in group ZLS at 0.3 mm occlusal thickness, all the tested CAD/CAM primary molar crowns at both thicknesses demonstrated fracture load values exceeding reported chewing force in pediatric patients.

CONCLUSION

CAD/CAM primary molar crowns with reduced occlusal thickness may be used for the full-coverage restoration of primary molar teeth.

Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study

AIM

To evaluate the effect of thermo-mechanical cycling (TMC) on fracture resistance of different computer-aided design/computer-aided manufacture (CAD/CAM) crowns.

MATERIALS AND METHODS

A total of 42 CAD/CAM crowns were fabricated on epoxy resin maxillary first premolar teeth and divided into three groups (n = 14) according to the material used: IPS e.max CAD (Ivoclar Vivadent) lithium disilicate (LD), Vita ENAMIC (VE) (VITA Zahnfabrik), Tetric CAD (Ivoclar Vivadent). Also, each group was subdivided into two equal subgroups according to TMC (n = 7). Subgroups (O) without TMC and subgroup (W) with TMC (5-55°C, 30 second, 75,000 cycles). All samples in each group were cemented with a universal bond (Tetric N bond universal) and adhesive resin cement (Variolink Esthetic DC) (Ivoclar Vivadent). Subsequently, the samples were loaded to failure in a universal testing machine at a crosshead speed of 1 mm/min, and the fracture pattern and the fracture resistance in each group were recorded.

RESULTS

Fracture resistance was analyzed by one-way analysis of variance (ANOVA) test, followed by Tukey's post hoc test for pairwise comparison. Fracture resistance showed a significant difference between the tested groups before and after TMC; IPS e.max CAD has the highest value (1233.35 ± 97.72, 1165.73 ± 199.54 N) followed by Tetric CAD (927.62 ± 42.5, 992.04 ± 53.46 N) and Vita ENAMIC has lowest value (506.49 ± 74.24, 354.69 ± 90.36 N).

CONCLUSION

Thermo-mechanical cycling affected the fracture resistance of both polymer-based CAD/CAM crowns.

CLINICAL SIGNIFICANCE

For dental practitioners, both IPS e.max CAD and Tetric CAD can be used clinically for posterior teeth, providing satisfactory results and resistance to fracture. How to cite this article: Elmokadem MI, Haggag KM, Mohamed HR. Effect of Thermo-mechanical Cycling on Fracture Resistance of Different CAD/CAM Crowns: An In Vitro Study. J Contemp Dent Pract 2024;25(1):29-34.

A step-by-step technique to create an ideal color match, form, and surface texture to all-ceramic restorations

OBJECTIVES

Although the presence of a chairside CAD/CAM system in the dental office saves time and cost, it deprives the dentist from the dental technologist' skills and experience. The dentist now has to gain and acquire knowledge and skills about how to finish, characterize, stain, and glaze ceramic restorations. The main objectives of this article is to teach novel and reproducible techniques for surface color, texture, glaze and polish for either the chairside or laboratory fabricated indirect ceramic restoration.

CLINICAL CONSIDERATIONS

A protocol for intraoral characterization of monolithic ceramics; the "Triple R" protocol for tooth color mimicking was followed. It consist of three steps: (1) "Recognize" tooth color shapes, (2) "Record" the present color shapes in the patient dentition by drawing a color map for the color shapes extension and determine which luster paste stain to be used for replicating them, and (3) "Replicate" intraorally the recorded color shapes guided by the adjacent natural teeth using low fusing ceramic pastes (shades and stains) for color shape replication. Also, the final touch technique was followed to shape, texture and final surface finish of dental restorations. It is composed of 5 basic levels which we call dental "micro-esthetics that define shape, texture, and surface luster.

CONCLUSIONS

Following the steps of both; the "Triple R" protocol and the "FINAL TOUCH" technique will help to reproduce the final shade of the restoration to create the illusion of a natural tooth to the observer.

CLINICAL SIGNIFICANCE

This article shows how combining two practical methodologies to record and replicate both color shapes and surface texture of natural teeth may extend mimicking, that is, step by step natural tooth shade beyond the limitations of the available commercial shade guides.

Marginal and internal fit of porcelain laminate veneers: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Marginal integrity and internal adaptation are key to the long-term success of porcelain laminate veneers. Evidence for their marginal and internal fit is unclear, and the factors affecting such fit have not been identified.

PURPOSE

The purpose of this systematic review and meta-analysis was to summarize the scientific literature assessing the effects of various parameters on the marginal and internal fit of porcelain laminate veneers.

MATERIAL AND METHODS

An electronic search was conducted to identify all relevant published articles on the fit accuracy of ceramic veneers between January 2000 and June 2021 in the PubMed-MEDLINE, Scopus, Embase, Google Scholar, and Web of Science databases. Information, including the study outcomes, in terms of the mean marginal gap, internal gap, and absolute marginal discrepancies of porcelain laminate veneers, was extracted from the selected studies. The inverse-variance random effects model was used to analyze the pooled results and estimate the overall effect based on the heterogeneity of studies (α=.05).

RESULTS

Twenty-one studies were selected for analysis, 2 clinical and 19 in vitro. The risk of bias was "medium" for most studies (19 of 21), and only 2 studies were classified as "high risk." A mean difference of -4.53 μm (95% CI: -21.46 to 12.41) was found, with no statistically significant difference in marginal gap between the pressed and milled fabrication modes (P=.600). As for the internal gap, significant differences were found (mean difference=-40.56 μm; 95% CI: -76.54 to -4.58), with pressed veneers performing better (P=.030). Butt joint preparation design produced significantly (P=.002) lower marginal gaps than the palatal chamfer (mean difference=-14.02 μm; 95% CI: -23.07 to -4.98).

CONCLUSIONS

No significant differences were found between the pressed and milled porcelain laminate veneers for marginal gap, but for the internal gap, the differences were significantly in favor of the pressed type. The butt joint veneer preparation design was significantly better than the palatal chamfer design in terms of marginal fit.

Oviposition Deterrent Activity of Some Wild Plants for Adult Females of Chrysomya albiceps with Medical and Veterinary Importance

<b>Background and Objective:</b> <i>Chrysomya albiceps</i> is widely spread worldwide, causing myiasis in both humans and animals and playing a mechanical role in the spreading of helminths, viruses and bacteria. Searching for new and safe alternative control methods is very important to eliminate the transmission of pathogens. This study aims to determine the oviposition-deterrent activity of <i>Juniperus procera</i>, <i>Artemisia absinthium</i>, <i>Rosmarinus officinalis</i> and <i>Hypoestes forskaolii</i> wild plants against adult <i>Chrysomya albiceps</i>. <b>Materials and Methods:</b> The effect of plant extracts from <i>Juniperus procera</i>, <i>Artemisia absinthium</i>, <i>Rosmarinus officinalis</i> and <i>Hypoestes forskaolii</i> plants were tested against adult females of <i>Chrysomya albiceps</i> for oviposition deterrent or repellency. These extracts resulted in oviposition deterrent efficacy for adult females of <i>C. albiceps</i> based on the plant type, plant part (leaves or stems), extract type (methanol, acetone and petroleum ether) and tested dose. <b>Results:</b> The highest anti-oviposition activity against <i>C. albiceps</i> females presented from <i>A. absinthium</i> stems acetone extract at a dose of 1 mg cm² by 100 %, while at 0.5 mg cm² recorded remarkable repellency by 86.7% as compared with the control treatment. According to the dose-response relationship, <i>A. absinthium</i> methanol and acetone extracts were ED₅₀ values of 0.85, 0.319 mg cm² (leaves) and 1.88, 0.576 mg cm² (stems), followed by <i>J. procera</i> methanol extract by 0.983 mg cm² (leaves) and 0.98 mg cm² (stems), respectively achieved highest oviposition deterrent efficiency as compared with other extracts. <b>Conclusion:</b> The high repellency activities of these extracts can be utilized to stop <i>C. albiceps</i> flies from laying eggs on wounds and transmitting myiasis diseases to humans and animals and could potentially replace pesticides used in the future control programs of flies.

Fracture Resistance of Chairside CAD/CAM Lithium Disilicate-reinforced Ceramic Occlusal Veneers With and Without Margin and Full Coverage Crowns

OBJECTIVE

The aim of this investigation was to compare the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate-reinforced ceramic occlusal veneers with and without margin and traditional full coverage premolar crowns.

METHODS AND MATERIALS

A total of 60 chairside CAD/CAM lithium disilicate-reinforced ceramic (Amber Mill, Hass Bio) restorations were designed and fabricated with a chairside CAD/CAM system (CEREC Dentsply Sirona). The restorations were divided into three groups (n=20): 1) occlusal veneer with 1.0-mm uniform occlusal thickness and with chamfer margin; 2) occlusal veneer with 1.0-mm uniform occlusal thickness and without margin; and 3) full coverage crown with uniform occlusal thickness and gingival margin. Occlusal veneers and crowns were cemented with dual cured resin luting cement (Multilink, Ivoclar Vivadent) to printed resin dies, load cycled (5 million load cycles at 1 Hz with 275 N force), and then loaded until fracture. Load at break (LB) and peak load (PL) until fracture were recorded. Scanning electron microscope images of the tested restorations on the abutments were obtained.

RESULTS

Fracture strengths were different depending on the design of the restoration. There was no significant difference in fracture strength between the two types of occlusal veneer (LB: 1132.45 N; PL: 1143.30 N for veneers with margin; LB: 1149.25 N; PL: 1219.05 N for veneers without margin). Full coverage crowns showed the lowest fracture resistance (LB: 936.26 N, PL: 976.42 N), which was significantly lower than both designs of occlusal veneer.

CONCLUSIONS

The fracture resistance of the CAD/CAM lithium disilicate-reinforced ceramic restorations was influenced by the design. Occlusal veneers with and without margin displayed higher fracture resistance than traditional crowns.

Minimally invasive CAD/CAM lithium disilicate partial-coverage restorations show superior in-vitro fatigue performance than single crowns

OBJECTIVE

To analyze the influence of restoration design (partial-coverage restoration vs. crown) and ceramic layer thickness on the performance and failure loads of CAD/CAM-fabricated lithium disilicate (LDS) reconstructions on molars after fatigue.

MATERIALS AND METHODS

Seventy-two posterior monolithic CAD/CAM-fabricated LDS restorations (IPS e.max CAD, Ivoclar Vivadent) with different occlusal/buccal ceramic layer thicknesses (1.5/0.8, 1.0/0.6, and 0.5/0.4 mm) and restoration designs (PCR: non-retentive full-veneer/partial-coverage restoration, C: crown,) were investigated and divided into six groups (n = 12, test: PCR-1.5, PCR-1.0, PCR-0.5; control: C-1.5, C-1.0, C-0.5). LDS restorations were adhesively bonded (Variolink Esthetic DC, Ivoclar Vivadent) to dentin-analogue composite dies (Z100, 3M ESPE). All specimens were subjected to thermomechanical loading (1.2 million cycles, 49 N, 1.6 Hz, 5-55°C) and exposed to single load to failure testing. Failure analysis was performed with light and scanning electron microscopies. Data were statistically analyzed using ANOVA, Tukey-Test, and t-test (p < 0.05).

RESULTS

Eight crown samples (C-0.5) and one PCR specimen (PCR-0.5) revealed cracks after fatigue, resulting in an overall success rate of 87.5% (crowns: 75%, PCRs: 96.88%). Direct comparisons of PCRs versus crowns for thicknesses of 0.5 mm (p < 0.001) and 1.0 mm (p = 0.004) were significant and in favor of PCRs. Minimally invasive PCRs (0.5 and 1.0 mm) outperformed crowns with the identical ceramic thickness. No difference was detected (p = 0.276) between thickness 1.5 mm PCRs and crowns.

CONCLUSIONS

Minimally invasive monolithic CAD/CAM-fabricated posterior LDS PCRs (0.5 and 1.0 mm) resulted in superior failure load values compared to minimally invasive crowns. Minimally invasive crowns (0.5 mm) are prone to cracks after fatigue.

CLINICAL SIGNIFICANCE

Minimally invasive CAD/CAM-fabricated LDS PCR restorations with a non-retentive preparation design should be considered over single crowns for molar rehabilitation.

The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading

AIM

This study aimed to investigate the effect of modified framework (MF) design on the fracture resistance of IPS e.max Press anterior single crown after thermocycling and cyclic loading.

MATERIALS AND METHODS

Two types of IPS e.max Press frameworks were designed (n = 10); standard framework (SF) with a 0.5 mm uniform thickness and MF with a lingual margin of 1 mm in thickness and 2 mm in height connected to a proximal strut of 4 mm height and a 0.3 mm wide facial collar. The crowns were cemented to resin dies, subjected to 5,000 cycles of thermocycling, and loaded 10,000 cycles at 100 N. A universal testing machine was used to load specimens to fracture, and the modes of failure were determined.

RESULTS

The mean and standard deviation (SD) of fracture resistance were 219.24 ± 110.00 N and 216.54 ±120.02 N in the SF and MF groups. Thus, there was no significant difference (p = 0.96). Mixed fracture was the most common failure mode in both groups. We found no statistically significant difference between the groups (p = 0.58).

CONCLUSION

The MF design did not increase the fracture resistance of IPS e.max Press crown.

CLINICAL SIGNIFICANCE

Framework design is an essential factor for the success of all-ceramic restorations and its modification might be regarded as an approach to increase fracture resistance. Furthermore, the modified design was evaluated in metal-ceramic or zirconia crowns while less attention was paid to the IPS e.max Press crowns. How to cite this article: Golrezaei M, Mahgoli HA, Yaghoobi N, et al. The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading. J Contemp Dent Pract 2024;25(1):79-84.

Recent advances in glass-ceramics: Performance and toughening mechanisms in restorative dentistry

The use of glass-ceramics in the medical field has grown significantly since the 1980s. With excellent aesthetic properties, semi-translucency, outstanding mechanical properties, corrosion resistance, wear resistance and great biocompatibility and workability glass-ceramics is one of the most commonly used materials in restorative dentistry and is widely used in veneers, inlays, onlays, all-ceramic crowns, and implant abutments. This review provides an overview of the research progress of glass-ceramics in restorative dentistry, focusing on the classification, performance requirements, toughening mechanisms and their association with clinical performance, as well as the manufacturing and fabrication of glass-ceramics in restorative dentistry. Finally, the developments and prospects of glass-ceramics in restorative dentistry are summarized and discussed.

Effect of different surface treatment protocols on the bond strength between lithium disilicate and resin cements

Because the use of hydrofluoric acid (HF) poses health risks if handled improperly, many clinicians prefer to have the ceramic restorations pre-etched in dental laboratories. However, during the try-in procedure, the pre-etched glass-ceramic restorations may be contaminated with saliva resulting in reduced bond strength. This in-vitro study aimed to investigate the effect of different surface treatments on the bond strength of lithium disilicate (LD) glass-ceramic restorations (IPS e.max Press, Ivoclar Vivadent) to two resin cements. One-hundred eighty blocks (4X4X3mm) of LD glass-ceramic were divided into twelve groups (n = 15), of which six received Variolink Esthetic DC (VE) cement and six received RelyX Ultimate (RU) cement, following the surface treatments: G1) Control: Hydrofluoric Acid + Silane (HF + Sil); G2) Hydrofluoric Acid + Saliva + Silane (HF + S + Sil); G3) Hydrofluoric Acid + Saliva + Ivoclean + Silane (HF + S + IC + Sil); G4) Hydrofluoric Acid + Saliva + Phosphoric Acid + Silane (HF + S + P + Sil); G5) Hydrofluoric Acid + Saliva + Monobond Etch & Prime (HF + S + EP); G6) Monobond Etch & Prime (EP). Following treatment, a resin-cement cylinder (2.3 mm diameter) was built on the glass-ceramic surface, photocured (20 s), stored in distilled water (37 °C, 24 h) and submitted to the shear bond strength test. Bond strength data (MPa) were subjected to two-way ANOVA and Tukey (α = 0.01). Cement type and surface treatment had a significant effect on the bond strength (p < 0.001) (Table 4). Single-step Monobond Etch & Prime (EP) significantly improved the bond strength of resin-cements to glass-ceramic with and without saliva contamination.

A Comparative Analysis of Marginal Adaptation Values between Lithium Disilicate Glass Ceramics and Zirconia-Reinforced Lithium Silicate Endocrowns: A Systematic Review of In Vitro Studies

This systematic review aimed to identify and analyze in vitro studies on the marginal adaptation values of computer-aided-design/computer-aided-manufacturing (CAD/CAM) and heat-pressed lithium disilicate glass ceramics and zirconia-reinforced lithium silicates and endocrown restorations. A full literature search was conducted in Web of Science, PubMed/Medline, EMBASE, Scopus, Cochrane Library, Google Scholar, and ProQuest electronic databases. The following keywords: endocrown [(marginal adaption) or (marginal fit) or internal fitting)], endocrown [(molar(s)) or (premolar(s) or (posterior teeth) or (maxillary arch) or (mandibular arch)] and ceramic materials as [(lithium disilicate glass ceramic CAD/CAM) or (zirconia) or (heat-press)] were used. Articles were manually searched utilizing their reference lists. Study selection was restricted or limited to the time of publication but not to the type of tested teeth or ceramic material, endocrown design, system of endocrown construction, abutment scanning, and system of the marginal adaption measurement. A total of 17 in vitro studies published between 2016 and 2023 were included in this systemic review. Less than half of the studies were published during 2023. Most studies used lithium disilicate glass ceramic and zirconia-reinforced lithium silicate all-ceramic materials by CAD/CAM or heat-press systems. Marginal adaptation, or marginal gap, was almost equal in the 2 materials, while it was slightly or marginally higher in the heat-press than in the CAD/CAM system. All-ceramic lithium disilicate glass ceramic and/or zirconia endocrowns fabricated for posterior teeth in both arches using CAD/CAM or heat-press had recorded marginal adaptation values within an acceptable range.

Polyphenols-Rich Extract of Calotropis procera Alone and in Combination with Trichoderma Culture Filtrate for Biocontrol of Cantaloupe Wilt and Root Rot Fungi

Fungal diseases have always been a major problem for cantaloupe crops; however, synthetic fungicides are hazardous to humans and the environment. Consequently, a feasible alternative to fungicides without side effects could be by using bio agents and naturally occurring plants with antibacterial potential. This study has achieved a novel procedure for managing wilt and root rot diseases by potentially using Trichoderma sp. culture filtrates in consortium with plant extract of Calotropis procera, Rhizoctonia solani, Fusarium oxysporum, and Pythium ultimum, which were isolated from infected cantaloupe roots with identified root rot symptoms. The antagonistic activity of four Trichoderma isolates and analysis of antibiotics and filtrate enzymes of the most active Trichoderma isolate were determined as well as phytochemical analysis of C. procera plant extract using HPLC-UV. The obtained results showed that all Trichoderma isolates considerably lowered the radial growth of P. ultimum, R. solani, and F. oxysporum in varying degrees. The scanning electron micrographs illustrate the mycoparasitic nature of Trichoderma sp. on F. oxysporum. The phytochemical analysis of C. procera indicated that phenolic contents were the major compounds found in extracts, such as vanillin (46.79%), chlorogenic acid (30.24%), gallic acid (8.06%), and daidzein (3.45%) but including only a low amount of the flavonoid compounds rutin, naringenin, and hesperetin. The Pot experiment's findings showed that cantaloupe was best protected against wilting and root rot diseases when it was treated with both Trichoderma sp. culture filtrates (10%) and C. procera extract of (15 mg/mL), both alone and in combination. This study demonstrates that the application of bio agent Trichoderma spp. filtrate with C. procera phenol extract appears useful for controlling wilting and root rot disease in cantaloupe. This innovative approach could be used as an alternative to chemical fungicide for the control of wilting and rot root diseases.

Toothbrushing effects on the surface roughness and cement volume loss of bonded enamel-ceramic interface

This study evaluated the effect of toothbrushing on enamel-cementing material-ceramic bonded interfaces, using different cementing materials.

MATERIALS AND METHODS

Thirty enamel and thirty ceramic blocks were bonded with cementing materials to produce the samples that were bonded with three types of cementing materials: 1- RelyX Ultimate resin cement (REXU), 2- RelyX Unicem 2 self-adhesive resin cement (REU2) and 3- heated Z100 restorative composite (60°C). Bonded interfaces of the samples were toothbrushed and the surfaces of the 3 cementing materials were evaluated for roughness (RG, in µm), roughness profile (RP, in µm), and volume loss (VL, in µm3) (baseline and after 20,000 and 60,000 toothbrushing cycles). Data were evaluated by Generalized Linear Analysis (two factors: "material" and "toothbrushing cycle") and Bonferroni test (α=0.05).

RESULTS

REXU and Z100 exhibited lower RG than that presented by REU2, except after 60,000 toothbrushing cycles when only Z100 differed from REU2. The increase in toothbrushing cycles increased the RG and RP for all materials. REU2 also showed higher RP than those showed by REXU and Z100 when it was analyzed regarding the enamel. The VL of Z100 was the lowest with 20,000 toothbrushing cycles, regarding the enamel and ceramic. For 60,000 cycles, REXU showed the lowest VL regarding the ceramic, and REU2 had the highest VL regarding the enamel and ceramic.

CONCLUSION

In general, REXU and Z100 showed the best results regarding the evaluations performed and the REU2 exhibited the highest RG, RP, and VL.

Fracture Resistance of Chairside CAD/CAM Molar Crowns Fabricated with Different Lithium Disilicate Ceramic Materials

PURPOSE

To compare the fracture resistance of five different groups of chairside CAD/CAM molar crowns fabricated from various lithium disilicate ceramic materials (LDC): one conventional precrystallized CAD/CAM LDC, two novel precrystallized LDCs, and one fully crystallized LDC tested both with and without optional sintering.

MATERIALS AND METHODS

A total of 60 chairside CAD/CAM lithium disilicate molar crowns (n = 12 per group) with 1.5-mm occlusal thickness and a 1.0-mm chamfer finish were designed and fabricated with a chairside CAD/CAM system (CEREC, Dentsply Sirona). The restorations were divided into five groups: (1) IPS e.max CAD; (2) Amber Mill; (3) Straumann n!ce; (4) Straumann n!ce with optional sintering; and (5) Supreme CAD. Restorations were cemented using conventional resin luting cement and primer system to 3D-printed resin dies. Bonded restorations were loaded for 100,000 cycles with 275-N force, and the load at break (LB) and peak load (PL) until fracture were measured. SEM images of fracture surfaces on the printed dies were obtained.

RESULTS

Fracture resistance was significantly different depending on the material. Supreme CAD showed the highest fracture resistance (LB: 1,557.2 N; PL: 1,785.8 N), followed by Amber Mill (LB: 1,393.0 N; PL: 1,604.2 N) and IPS e.max CAD (LB: 1,315.7 N; PL: 1,461.9 N). Straumann n!ce without (LB: 862.4 N; PL: 942.9 N) and with the optional sintering (LB: 490.4 N; PL: 541.0 N) showed significantly lower fracture resistance than the others.

CONCLUSION

The fracture resistance of chairside CAD/CAM lithium disilicate molar crowns varied depending on the material, and the novel materials did not perform as well as the conventional equivalents. Fully crystallized lithium disilicate ceramic block materials showed lower fracture resistance than precrystallized counterparts and should be used with caution in the clinic, especially with optional sintering.

[Influence of cavity design on quality of margin and marginal adaptation and microleakage of all-ceramic CAD/CAM inlays]

OBJECTIVE

To investigate the influence of 135° and 90° cavity design on quality of margin and marginal adaptation and microleakage of all-ceramic computer aided design/computer aided manufacturing (CAD/CAM) inlays.

METHODS

One hundred extracted human molars were prepared by criteria of buccal occlusal (BO) inlay. On the buccal, the mesial margin was prepared as 135° bevel while the distal margin was prepared as butt-joint. All-ceramic restorations were made in the Sirona CEREC AC CAD/CAM system with VitaBlocs Mark Ⅱ, Upcera UP.CAD, IPS e.max CAD, Upcera Hyramic and Lava Ultimate. The gaps between each inlay's mesial margin-abutment and distal margin-abutment were recorded under an optical microscope. Each inlay was adhered to the abutment and aged by thermal cycling for 10 000 times. Each specimen was cut into 3 slices after staining. Dye penetration was evaluated under an optical microscope for mesial and distal margins.

RESULTS

Mean marginal integrity rate, mean marginal gap value and mean depth of microleakage of 135° margin of Group Upcera Hyramic and Lava Ultimate were significantly better than those of Group VitaBlocs Mark Ⅱ, Upcera UP.CAD and IPS e.max CAD(P < 0.05). Mean marginal gap value, mean depth of microleakage and scale of mean depth of microleakage of 90° margin of Group Upcera Hyramic and Lava Ultimate were significantly better than those of Group Upcera UP.CAD and IPS e.max CAD (P < 0.05) while mean marginal integrity rate was not significantly different (P>0.05). Mean marginal integrity rate of 90° margin was significantly better than that of 135° margin in each group (P < 0.05) while mean depth of microleakage between different margins was not significantly different in each group (P>0.05). Mean marginal gap value of 90° margin of Group VitaBlocs Mark Ⅱ and IPS e.max CAD was significantly better than that of 135° margin (P < 0.05) while there was not significant difference in other 3 groups between 90° and 135° margin (P>0.05). Scale of mean depth of microleakage of 135° margin of Group Upcera Hyramic and Lava Ultimate was significant better than that of 90° margin (P < 0.05) while there was not significantly different in other 3 groups between 90° and 135° margin (P>0.05).

CONCLUSION

The mesial and distal margins of abutement of all-ceramic inlay should be prepared as butt-joint.

Effect of Thermomechanical Fatigue Loading on the Internal and Marginal Adaptation of Endocrowns Utilizing Different CAD/CAM Restorative Materials

PURPOSE

To assess the impact of fatigue loading on the internal and marginal fit of CAD/CAM-fabricated endocrowns for restoring endodontically treated molars using different machinable blocks.

MATERIALS AND METHODS

A total of 72 mandibular first molars were prepared using a standardized method and were divided into four groups (n = 18), each restored with a different CAD/CAM material: group V = polymer-infiltrated ceramic (Vita Enamic); group K = partially stabilized tetragonal zirconia (Katana); group E = lithium disilicate ceramic (IPS e.max CAD; and group B = polyetheretherketone (BioHPP). Endocrowns were subjected to thermomechanical fatigue loading. Internal and marginal adaptation of the endocrowns were examined at 66 points using the sectioning technique and a stereomicroscope. Data were analyzed using one-way ANOVA and Tukey post hoc test (α = .05).

RESULTS

Statistical tests showed that adhesive cementation resulted in significantly increased marginal and internal gap values in all regions in all four tested groups (P < .001). After thermomechanical fatigue loading, all regions in groups B and K showed a statistically significant difference, while no significant differences were found in the regions in group V (P > .05). In group E, the marginal (F = 71.00) and pulpal (F = 28.065) regions showed statistically significant differences (P < .001).

CONCLUSION

Polymer-infiltrated ceramics showed the lowest gap even after thermomechanical fatigue loading and may therefore provide enhanced clinical survival of the restored tooth, favoring the use of this material for fabricating endocrown restorations.

Are Tooth and Ceramic Fractures Different Sides of the Same Coin? A Report of Two Clinical Cases

Two clinical cases involving the fracture of a natural tooth and one of a ceramic crown are presented and discussed based on fractography principles. In the first case, a patient reported intense pain in a sound third molar where a longitudinal fracture was identified, and the tooth was extracted. In the second case, a posterior rehabilitation using a lithium silicate ceramic crown was carried out, and the patient returned after 1 year with a fractured piece of the crown. Both were analyzed under microscopy to identify the origins of fractures and their causes. The fractures were critically analyzed so that relevant information could be generated from the laboratory to the clinic.