Novel Zirconia Materials in Dentistry

Durability of resin bonding to translucent zirconia materials: An in vitro study

STATEMENT OF PROBLEM

How the yttria content (3Y-PSZ, 4Y-PSZ and 5Y-PSZ) affects the tensile bond strength of luting resin to translucent zirconia ceramics is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate whether the bond strength of resin to translucent zirconia ceramics and its durability are influenced by the yttria content (3Y-PSZ, 4Y-PSZ and 5Y-PSZ).

MATERIAL AND METHODS

Sixty-four disk-shaped specimens of zirconia ceramics were randomly allocated to 4 groups (n=16) with respect to the yttria concentration: GHT: 3 mol% yttria-partially stabilized zirconia 3Y-PSZ; GHTML: 3 mol% yttria-partially stabilized multilayered zirconia 3Y-PSZ; GSTML: 4 mol% yttria-partially stabilized zirconia 4Y-PSZ; and GUTML: 5 mol% yttria-partially stabilized zirconia 5Y-PSZ. For bonding, acrylic resin tubes were filled with composite resin and bonded to the zirconia disks using adhesive luting resin by following manufacturer's instructions. Half of each main group (n=8) was stored in water for 3 days at 37 °C. The other half was stored in water for 150 days with 37 500 thermocycles (5 to 55 °C). The tensile bond strength test was determined with a universal testing machine at a crosshead speed of 2 mm/minute using a chain loop for alignment.

RESULTS

The tensile bond strength was not significantly affected by the yttria concentration of different zirconia materials (3Y-PSZ, 4Y-PSZ, and 5Y-PSZ, P=.17). The mean ±standard deviation failure loads for groups ranged from 24.1 ±2.6 MPa for the ultratranslucent multilayered zirconia (with thermocycling) to 52.7 ±5.4 MPa for the high translucent multilayered zirconia (without thermocycling). However, artificial aging adversely affected the tensile bond strength values for all tested zirconia systems (P<.001). Scanning electron microscope evaluation showed that cohesive fracture was the predominant failure mode, while few specimens exhibited adhesive failure at the interface.

CONCLUSIONS

The yttria concentration (3Y-PSZ, 4Y-PSZ, and 5Y-PSZ) had no significant effect on the bond strength of different zirconia ceramics (P=.17), whereas the artificial aging procedures led to a statistically significant decrease in tensile bond strength (P<.001).

Novel bilayered zirconia systems using recycled 3Y-TZP for dental applications

OBJECTIVE

To synthesize bilayer zirconia systems based on commercial or recycled 3Y-TZP obtained from non-milled remnants and to compare their optical and mechanical properties before and after aging.

METHODS

Bilayer zirconia samples were fabricated using either recycled 3Y-TZP (3Y-R/4Y and 3Y-R/5Y) or commercial powders (3Y/4Y and 3Y/5Y). Microstructure and phase composition were analyzed using ScanningElectronMicroscopy (SEM) and X-Ray Diffraction (XRD). Optical and mechanical properties were assessed via reflectance and biaxial flexural strength tests (BFS), followed by fractographic analysis. Optical properties and BFS data were analyzed using two-way ANOVA and Tukey test, and Weibull statistics, respectively.

RESULTS

Recycled powder exhibited particle sizes < 2.07μm. SEM micrographs depicted dense surfaces with largest grains in the 5Y, followed by recycled-3Y, 4Y, and commercial-3Y. XRD analysis revealed tetragonal peaks in commercial and recycled 3Y-TZPs, and tetragonal and cubic phases in the 4Y and 5Y surfaces. Aging induced significant phase transformation in 4Y (∼40 %), commercial- (58 %) and recycled-3Y (53 %), with no effect in 5Y surfaces. Commercial bilayers exhibited higher translucency and strength (∼1130 MPa) compared to recycled bilayers (∼935 MPa), with no significant differences within commercial, nor within recycled groups. Aging decreased contrast ratio for recycled groups and increased the strength of all groups. While all groups presented high reliability up to 500MPa, commercial bilayers outperformed recycled systems at 800-MPa.

SIGNIFICANCE

The synthesis of bilayered systems using recycled-3Y was successful, resulting in high reliability in missions up to 500MPa. Bilayers based on commercial powder demonstrated superior translucency, strength, and reliability at 800MPa compared to their recycled counterparts.

Effect of different finishing/polishing techniques and glaze application on the flexural strength of ultratranslucent zirconia after hydrothermal aging

PURPOSE

To evaluate the effect of different finishing/polishing procedures and glaze on the surface roughness, flexure strength, and microstructure of an ultratranslucent zirconia (UZ) submitted aging.

METHODOLOGY

Two hundred and forty (240) UZ bars were sintered (8 × 2 × 1 mm) and treated according to the factors (n = 15): Type of finishing/polishing procedure (Control - Ctrl; Ultra-fine Diamond Burr - FG; Medium grit diamond burr- MG; Stone Bur - Stone; Rubber - Rub; FG + Rub; MG + Rub; Stone + Rub), and "Glaze" (Without and With - Gl). The bars were hydrothermally degraded (24 h, 127 °C, 1.7 bar), submitted to roughness analysis and 3-point mini flexural strength (FS) test. Scanning Electron Microscopy (SEM), X-ray Diffraction (XDR), and Weibull analysis were performed. Data were analyzed by 2-way ANOVA and Tukey test (5%).

RESULTS

Finishing/Polishing' and its interaction with 'Glaze' were statistically significant (P < 0.0001) for FS, unlike 'Glaze' alone (P = 0.8827). Rub (602.11 MPaA), Stone + Rub (555.50 MPaAB), and Ctrl (621.72 MPaA) showed superior FS, while FG_GL showed the lowest FS. Stone + Rub showed the highest Weibull modulus (13.15a). Ctrl_Gl (0.18 ± 0.02F μm) and Ctrl + Rub_Gl (0.29 ± 0.07F μm) showed the lowest roughness. Glaze (0.48B) reduced the roughness of the groups that did not receive it (1.56A), with MG (2.60 ± 0.69A μm) and FG (2.50 ± 0.7A μm) exhibiting rougher surfaces.

CONCLUSIONS

Rubber polishers are ideal for minor adjustments to UZ while Stone followed by rubber is effective for greater abrasion without compromising mechanical strength. The application of glaze did not reduce mechanical strength and resulted in lower surface roughness compared to the non-glazed groups, with the exception of the FG groups.

Zirconia in fixed prosthodontics: a review of the literature

The purpose of this narrative review is to organize information and knowledge about the properties of the clinical evidence of zirconia-applied dental restorations and to provide relevant information to establish application methods to obtain long-term clinical prognosis of zirconia-applied dental prostheses. From PubMed and manual searches, found "zirconia," "crown," "survival," and "success" keywords were searched. Case reports, case series, reviews, abstracts, in vitro studies, and observational studies were excluded. Additionally, implant superstructures not supported by the periodontal ligament and partially covered crowns were excluded. A total of 42 studies were identified. According to the studies in this review, the most common complication of porcelain-layered zirconia restorations is porcelain fracture, but the long-term prognosis is stable. However, complications of monolithic zirconia restorations include crown fractures and fractures of the abutment tooth and root, and long-term clinical evidence is not available yet. Additionally, bruxism can be a complication factor with both types of restorations, so it is important to carefully examine the oral habits, including bruxism, before treatment. Therefore, the success of zirconia-based restorations in clinical practice requires a careful approach in addition to accurate knowledge of the zirconia material and identification of applicable cases.

Fracture toughness and subcritical crack growth analysis of high-translucent zirconia prepared by stereolithography-based additive manufacturing

The objective was to study the subcritical crack growth phenomena and determine the fracture toughness of two yttria-partially-stabilized zirconia ceramics. One of the two materials evaluated was a commercially available 5 mol% yttria partially stabilized zirconia (5Y-PSZ), and the other was an experimental partially stabilized zirconia made from a mixture of 3 mol% and 8 mol% yttria stabilized zirconia powder (3Y+8Y-PSZ), with the final samples prepared by the Stereolithography (SLA) process. The samples in water were tested by three-point bending experiments at different stress rates to obtain Weibull and SCG parameters. The results show that 3Y+8Y-PSZ has higher Weibull modulus(m = 11.54) and characteristic strength(σ0 = 812.27 MPa) compared to 5Y-PSZ (m = 8.57, σ0 = 647.25 MPa). SCG parameters n obtained for 5Y-PSZ and 3Y+8Y-PSZ tested in water were 26.03, 37.94, respectively. The strength of 5Y-PSZ and 3Y+8Y-PSZ (Pf = 5%) was reduced by 56.49%, 45.30% after 10 years of simulated use. Regarding the fracture toughness of both materials, 3Y+8Y-PSZ had higher values regardless of the method used to determine it. However, the fitting correction factor of the Vickers indentation method was not applicable to either 5Y-PSZ or 3Y+8Y-PSZ. Determining the SCG parameters of two materials and predicting their lifetimes using constant stress rate testing is an effective way to evaluate materials.

Experimental bilayer zirconia systems after aging: Mechanical, optical, and microstructural characterization

OBJECTIVES

To characterize two experimental zirconia bilayer materials compared to their monolithic controls, before and after hydrothermal aging.

METHODS

Commercial zirconia powders were utilized to fabricate two bilayer materials: 3Y-TZP+ 5Y-PSZ (3Y+5Y/BI) and 4Y-PSZ+ 5Y-PSZ (4Y+5Y/BI), alongside control groups 3Y-TZP (3Y/C), 4Y-PSZ (4Y/C), and 5Y-PSZ (5Y/C). Compacted specimens were sintered (1550 °C- 2 h, 3 °C/min), and half of them underwent hydrothermal aging (134 °C-20h, 2.2 bar). Characterizations were performed through scanning-electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, reflectance tests and biaxial flexural strength test (ISO:6872). Weibull statistics were applied to determine the characteristic strength and Weibull modulus. Grain size and optical properties were analyzed using two-way ANOVA followed by the Tukey test.

RESULTS

Degradation regions and monoclinic phase were observed at aged 3Y-TZP and 4Y-PSZ surfaces. Significant differences were observed in the evaluation of optical properties between the bilayer and control groups. The bilayer materials presented intermediate characteristic strength values compared to their controls and aging significantly increased the strength of some groups.

SIGNIFICANCE

Experimental bilayer materials presented lower mechanical properties than monolithic controls, 3Y/C and 4Y/C. Hydrothermal aging increased the characteristic strength of bilayered and monolithic controls, except for 5Y-PSZ. Both experimental bilayer systems, as well as monolithic controls, met the ISO 6872:2015 requirements for single-unit crowns (100 MPa), 3-unit fixed dental prostheses (FDPs) up to premolars (300 MPa), and 3-unit FDPs involving molars (500 MPa). However, for FDPs with four or more units, only monolithic 3Y-TZP and 4Y-PSZ, and bilayered 3Y+5Y met the required minimum flexural strength (≥800 MPa).

Impact of liner treatment on the translucency of CAD/CAM multi-colored lithium disilicate and multi-layered zirconia implant-supported crowns, and evaluation of fracture strength of ceramic crowns

This study aimed to evaluate the optical properties of liner-treated CAD/CAM Multi-colored lithium disilicate (Amber Mill Direct; AMD) and multi-layered zirconia (Omega multi; OM) implant-supported crowns, as well as their effect on the fracture strength of Ti or Zr abutments to which they were applied. After sintering AMD and OM ceramic blocks, they were classified into three groups: untreated, liner-treated, and liner-treated with added color. Optical properties were evaluated by analyzing color differences using background materials to assess translucency and the masking ability of liner-treated ceramics. Subsequently, the fracture strength of implant-supported crowns applied to Ti or Zr abutments was measured, and statistical analysis was conducted using Weibull statistics. Untreated AMD exhibited the highest translucency. Liner treatment reduced translucency in both ceramics, while color-added liner treatment increased translucency. Liner-treated AMD showed greater color difference compared to OM, whereas color-added liner treatment reduced the color difference. Fracture strength was highest in Ti abutment-OM crowns (548.03 N) and lowest in Zr abutment-AMD crowns (283.58 N). Additionally, the Weibull coefficient was over twice as high in Ti abutment-AMD crowns (m = 17.500). Color liners can adjust the high translucency of lithium disilicate ceramics to block discoloration, providing natural tooth-like color and enabling the creation of esthetic restorations. Furthermore, lithium disilicate ceramic crowns applied to Ti abutments exhibited high Weibull coefficients and fracture strengths.

Zirconia Barriers in Bone Regeneration Procedures: A Scoping Review

PURPOSE

To identify the current status and development of zirconia barriers in bone augmentation procedures in the maxillofacial area of adult human patients.

MATERIALS AND METHODS

Two independent reviewers conducted an electronic literature search in PubMed/MEDLINE, Web of Science, Scopus, EBSCO, the Cochrane Library, and LILACS databases, as well as a manual search to identify eligible clinical studies up to April 15, 2024. The protocol was designed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews guidelines.

RESULTS

The initial electronic search resulted in 240 studies. The systematic application of inclusion and exclusion criteria resulted in 6 articles that met the purpose of the study. The included articles were 5 clinical case series and 1 case report, published between 2016 and 2023. Only 4 articles reported histological studies. A total of 40 sites regenerated with zirconium barriers were reported in 30 patients. Results were obtained with variability in bone gain values, between 0.9-8.0 mm horizontally and 1.4-12.0 mm vertically, in addition to a 30% complication rate.

CONCLUSIONS

Although the results obtained in the studies included in this scoping review are favorable with respect to the amount of bone formation and the reduced surgical time required, the number of complications is considered high. Moreover, due to a limited number of patients included in the case series and the short duration of follow-up, additional studies including a control group are required.

Influence of surface treatment before glazing on wear and flexural strength of translucent zirconia

OBJECTIVES

To determine whether the surface treatment of translucent zirconia prior to glazing affects wear and flexural strength.

METHODS

Translucent zirconia disks were either left as-sintered, polished, or sandblasted. Half of the specimens within these three groups were glazed. Human enamel and dentin substrates were prepared as control. The wear volume and depth, as well as surface roughness parameters, were obtained after chewing simulation (n = 8 per group). Biaxial flexural strength of zirconia specimens was measured and fractures were analyzed. Statistics was performed with multifactorial ANOVAs (α = 0.05).

RESULTS

The overall wear volume was significantly higher on glazed surfaces (0.020 ± 0.007 mm3) compared to non-glazed zirconia (0.001 ± 0.001 mm3; p < 0.001). No significant difference in wear volume was found among different surface treatments (p = 0.368). Nevertheless, wear volume significantly increased when rough antagonists were used for zirconia and tooth substrates (both p < 0.001). The lowest wear volume was measured on polished zirconia (< 0.001 ± < 0.001 mm3) and highest on dentin (2.327 ± 1.686 mm3). The flexural strength was significantly higher for polished zirconia surfaces (652 ± 135 MPa) than for all other groups (p < 0.001).

SIGNIFICANCE

Lowest wear and highest flexural strength of a translucent zirconia restoration can be expected when the surface is polished. When applying glaze, the prior surface treatment does not affect wear. Applied to clinical situations, perfect surface polishing after occlusion adjustments is recommended to prevent increased wear of the antagonist.

Shear bond strength of resin cement to additively manufactured zirconia with customized surface texture and porosity: Part 1

STATEMENT OF PROBLEM

The additive manufacturing of zirconia has been reported to present promising mechanical properties. However, studies on bonding to additively manufactured (AM) zirconia are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effect of customized porosity and surface texture on the shear bond strength (SBS) of resin cement to 3-dimensionally (3D) printed zirconia.

MATERIAL AND METHODS

A total of 60 zirconia disks (Ø12×5 mm) were designed with different surface porosity using a computer-aided design (CAD) software program and manufactured via stereolithography (SLA) 3D printing. The disks were divided into 4 groups (n=15) based on surface texture and porosity: Control (no designed porosities), G1:50 (50×50-µm pores 200 µm apart), G2:100 (100×100-µm pores 400 µm apart), and G3:200 (200×200-µm pores 800 µm apart). The specimens were cleaned, and the binder removed before sintering. The microstructural analysis of the specimen's surface before SBS was performed using a profilometer to determine surface texture (n=5). SBS was measured using a universal testing machine, and thermal cycling was performed to simulate aging (n=10). Data for SBS were analyzed using 2-way ANOVA (α=.05).

RESULTS

Surface texture and porosities were confirmed by profilometry. In all comparisons, the G3:200 group demonstrated the highest mean SBS with 8.78 MPa (P<.001); however, it was similar to the Control group, which had a mean of 8.41 MPa (P=.631). The G1:50 showed significantly lower SBS values at 3.90 MPa (P<.001), followed by the G2:100 group with 5.14 MPa (P<.001). Thermal cycling generally decreased SBS in all groups (P<.001).

CONCLUSIONS

Customized surface textures can improve bond strengths, with larger pores (200×200 µm) providing values comparable with those of traditional mechanical pretreatments surfaces, while smaller pores resulted in lower bond strengths. This approach avoids surface damage and phase transitions caused by traditional treatments. These findings provide a foundation for future research aimed at developing more durable and reliable zirconia restorations, ultimately enhancing clinical outcomes.

Changes in the Properties of Different Zones in Multilayered Translucent Zirconia Used in Monolithic Restorations During Aging Process

This study assessed the changes in the mechanical and surface properties of the transition zone in multilayered translucent monolithic zirconia subjected to long-term hydrothermal aging. A total of 360 disk-shaped specimens (diameter: 15.0 mm; thickness: 1.2 mm) were prepared using conventional (3Y-TZP in LT; ZL, 4Y-TZP in MT; ZM) and multilayered translucent zirconia (5Y-TZP in MT Multi; ZT, 3Y/5Y-TZP in Prime; ZP) among IPS e.max ZirCAD blocks. Specimens were divided into three groups (n = 30) and aged in the autoclave at 134 °C under 0.2 MPa for 0 h (control group), 5 h (first aged group), and 10 h (second aged group). The mechanical and surface properties of the transition zone in the multilayered translucent zirconia were investigated, followed by statistical analysis (α = 0.05). Before and after aging, ZL (1102.64 ± 41.37 MPa) and ZP (1014.71 ± 139.86 MPa) showed the highest biaxial flexural strength (BFS); ZL showed the highest Weibull modulus (31.46) and characteristic strength (1121.63 MPa); and ZT exhibited the highest nanoindentation hardness (20.40 ± 1.80 GPa) and Young's modulus (284.90 ± 20.07 GPa). After aging, ZL (116.75 ± 9.80 nm) exhibited the highest surface roughness (Ra); the monoclinic phase contents in ZL and ZP increased; and surface uplifts, microcracks, and irregular defects caused by phase transformation appeared on ZL and ZP surfaces. The 3Y/5Y-TZP transition zone exhibited flexural strength, Vickers hardness, phase distribution changes, and surface microstructure changes similar to those of 3Y-TZP before and after aging; however, the surface roughness was lower than that of 3Y-TZP and higher than those of 4Y-TZP and 5Y-TZP after aging. The mechanical and surface characteristics, excluding BFS and Vickers hardness, were influenced by the yttrium oxide content in each zone and the aging process.

Evaluation of Surface Roughness of Multilayered Monolithic Zirconia Following Chairside Adjustment with 3 Different Polishing Systems Sterilized for Multiple Cycles: An In Vitro Study

BACKGROUND Chairside grinding, finishing, and polishing are essential for smoothing multilayered monolithic zirconia (MMLZ) restorations. Due to rubber matrix hardening, repeated sterilization of finishing and polishing instruments reduces their abrasive effectiveness. This study aimed to evaluate the effects of sterilization cycles on the effectiveness of 3 commercial polishing kits on the surface roughness of MMLZ crown restorations. MATERIAL AND METHODS One hundred milled, disc-shaped zirconia specimens (10 mm diameter, 3 mm thickness) were divided into 3 groups (n=30) based on the polishing kit used [EVE Diacera, SS White, Ultradent Jiffy]. Each group was further subdivided based on 1, 5, or 10 flash sterilization cycles (n=10). Profilometers measured average surface roughness while objective qualitative analysis was performed by scanning electron microscopy. A one-way ANOVA (Kruskal-Wallis) rank test and a post-hoc Dunn test with Bonferroni correction were used to determine the significance of median values and mean rank scores. The significance threshold for probability 'P' value was set at P≤0.05. RESULTS After 5 autoclaving cycles, the EVE Diacera group had a statistically significant increase in surface roughness (P=0.0009), which decreased somewhat after 10 cycles. The Ultradent Jiffy reduced surface roughness after repeated autoclaving, but SS White did not. Surface roughness did not change across groups after multiple autoclaving cycles, according to post-hoc analysis. CONCLUSIONS MMLZ surface roughness produced by all 3 polishing systems was clinically acceptable after 10 flash sterilization cycles. Ten flash sterilization cycles did not affect the efficiency of any of the polishing systems to produce a smooth surface on the MMLZ specimens.

Light-curing of restorative composite through milled and 3D-printed full-contour zirconia for adhesive luting

OBJECTIVES

To evaluate the effect of different zirconia compositions and manufacturing processes on the light irradiance (LI), to measure the degree of conversion (DC) of solely light-curing restorative composite underneath these zirconia grades and to evaluate the respective zirconia microstructures.

METHODS

Six dental zirconia grades (GC HT, GC UHT [GC]; Katana HT, Katana UTML [Kuraray Noritake]; Lava Esthetic, Lava Plus [3 M Oral Care]) were cut and sintered per manufacturer instructions. One 3D-printed zirconia grade (XJet [XJET]) was prepared according to previous research. Zirconia plates were ground to four thicknesses (0.5, 1.0, 1.5, 3.0 mm). The LI through these zirconias was measured using light spectrometry using two light-curing units (Demi Plus [Kerr], Bluephase G4 [Ivoclar]). Restorative composite (Clearfil AP-X [Kuraray Noritake]) was light-cured through the zirconia plates and the DC was determined by micro-Raman spectrometry 5 min, 24 h and 1 w after light-curing. Statistical analysis of LI and DC data involved linear mixed-effects modelling and multi-way ANOVA. Microstructural analysis of zirconia was performed by scanning electron microscopy.

RESULTS

Zirconia type and thickness, and LCU had a significant effect on LI (p < .0001). DC significantly increased over time (p < .0001) and was not influenced by curing-light attenuation if LI reached at least 40 mW/cm². Increased yttria content resulted in an increased zirconia grain size.

SIGNIFICANCE

Despite significant light attenuation, DC of composite light-cured through zirconia at almost all thicknesses, approached DC measured without zirconia interposition for five out of seven zirconia grades. Additionally, the manufacturing process did not seem to influence LI or DC.

Implant-Supported Cantilever Fixed Dental Prosthesis in the Anterior Region: Effect of Implant Type and Aging In Vitro

OBJECTIVES

To investigate if the fracture load of implant-supported cantilever fixed dental prostheses (ICFDPs) in the anterior region is affected by the implant type and the aging protocol.

MATERIALS AND METHODS

Sixty ICFDPs were prepared using multilayer monolithic zirconia for restoring bone-level (BL) and tissue-level (TL) titanium-zirconium implants. Fracture load was measured at baseline (no aging) or after aging in a chewing simulator loading the implant crown or the cantilever in a 30° angle (n = 10 per group). A two-way ANOVA was applied (α = 0.05) for the effects of implant type and aging protocol.

RESULTS

Implant type (p < 0.001) and aging (p < 0.001) had a significant effect on fracture load values. Baseline specimens of both BL (665 ± 62 N) and TL (554 ± 23 N) had significantly higher mean fracture load values than those of aged specimens(BL implant crown 545 ± 46 N, BL cantilever 563 ± 45 N, TL implant crown 455 ± 32 N, TL cantilever 476 ± 24 N) (p < 0.001). The loading position during aging did not affect fracture load values for BL (p = 0.980) nor TL (p = 0.749). BL implants failed by cement fracture and abutment deformation, while for TL the transmucosal part of the implant deformed.

CONCLUSIONS

The fracture load values of anterior ICFDPs decrease with aging in a chewing simulator. BL implants are preferable over TL implants for anterior ICFDPs as higher fracture load values were achieved, and no implant deformation occurred.

The effects of restorative material and connector cross-section area on the stress distribution of fixed partial denture: a finite element analysis

BACKGROUND

This study aimed to evaluate the effects of restorative materials and connector cross-section areas (CSAs) on the stress distribution of monolithic fixed partial dentures (FPDs).

METHODS

FPDs, abutment teeth, periodontal ligament (PDL), and alveolar bone were modeled by computer-aided design. Four materials with varied elastic modulus (3 mol% yttria-stabilized tetragonal zirconia polycrystals [Zr], lithium disilicate [LD], polymer-infiltrated ceramic network [PICN], and resin composite [RC]) and five CSA of connectors (4, 6, 8, 10, and 12 mm2) were set as FPD variables for finite element analysis (FEA). The stress distribution on FPDs, abutment teeth, PDL, and alveolar bone was analyzed under two different loading modes (three-point loading and pontic loading). The results of FEA were further verified by photoelastic test.

RESULTS

Both FPD material and CSA influenced the stress distribution of the FPD-tooth-bone complex. At a constant CSA of 8 mm², Zr, with the highest elastic modulus, exhibited the lowest stress on abutment teeth (2.4177 MPa). As the materials' elastic modulus decreased, the stress increased by 2.37%, 7.67%, and 13.16% for LD, PICN, and RC, respectively. Increasing the CSA from 4 mm² to 12 mm² reduced stress on abutments by 1.65% and 1.54% in the Zr and PICN groups, respectively. However, in the RC group, the stress increased significantly by 115.63%.

CONCLUSION

Materials with a higher elastic modulus tend to confine stress within the FPDs, reducing the downward transmission of stress. As the CSA increases, stress might be more evenly distributed from FPD to the periodontium, potentially reducing stress concentration.

Effect of simulated tooth brushing on the surface gloss of monolithic all-ceramic restorations: an in vitro study

AIM

The surface gloss of restorative materials can be greatly impacted by abrasion from tooth brushing. This study aimed to evaluate the effect of simulated tooth brushing using regular and abrasive toothpaste on the surface gloss of glazed monolithic all-ceramic restorations.

MATERIALS AND METHODS

In this, in vitro study, four different monolithic all-ceramic materials were used: Cerec Tessera (advanced lithium disilicate), Celtra Due (zirconia reinforced lithium silicate), Cerec Zirconia+ (Translucent Zirconia), and Cerec Blocs (Feldspathic). Eighty rectangular shaped specimens were made (20 of each material) using a low-speed diamond disc with the following dimensions (12/10/ 1 mm). The samples were polished using polishing kit & paste (DIAPOL, EVE). A glaze (Universal overglaze, Dentsply Sirona) was applied to all the samples then a toothbrushing simulator was used for 10.000 cycles using two different toothpastes. Surface gloss was assessed before and after simulated tooth brushing using glossmeter.

RESULTS

The results showed a significant reduction in the mean surface gloss of the four materials after the use of regular and abrasive toothpastes (P < 0.001). In all materials, the use of abrasive toothpaste was associated with more reduction of surface gloss (P < 0.001).

CONCLUSION

Simulated tooth brushing and toothpaste type affect the surface gloss of glazed monolithic all-ceramic materials.

CLINICAL SIGNIFICANCE

The surface characteristics of monolithic all-ceramic materials is affected by abrasion from toothbrushing which could impact the surface of the materials and possibly alter the glaze coating, compromising the restoration's longevity and esthetics. This effect was greater with the use of abrasive toothpaste.

Textured Intaglio Micropores Improve the Properties of 3D-Printed Zirconia Crowns

Monolithic zirconia crowns fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) via subtractive manufacturing (SM) exhibit limited bonding properties compared with other ceramics. Traditional methods such as air abrasion can improve bonding but may negatively affect the mechanical stability of zirconia. Nanoparticle jetting (NPJ), an emerging 3-dimensional-printing technology for zirconia restorations, offers the potential to create intricate structures, such as porous surfaces, with high precision. This study aimed to demonstrate that NPJ-manufactured monolithic zirconia crowns with an intaglio porous design can enhance bonding properties while maintaining mechanical strength. Standard NPJ zirconia crowns and commercially available SM zirconia crowns (SZC) were used as control groups. The surface roughness, fracture load, 2-body wear, and shear bond strength (SBS) were evaluated. The NPJ intaglio porous crowns (NIPC) with an intaglio porous design exhibited satisfactory and comparable fracture strength to SZC (within 1-mm occlusal thickness). Although the NIPC retained a relatively high original surface roughness, it demonstrated similar occlusal surface roughness, 2-body wear, and aging resistance to SZC after thorough polishing. Furthermore, the NIPC showed significantly superior intaglio surface roughness and SBS compared with conventionally air-abraded zirconia. Overall, this study successfully demonstrated the potential of NIPC as a viable restorative option, offering robust bonding and reliable mechanical properties.

Effect of Staining, Glazing and Polishing on the Survival Probability of Monolithic Zirconia Crowns

OBJECTIVE

The purpose of this in vitro study was to evaluate the effect of staining, glazing, and polishing on the survival probability of monolithic crowns manufactured with preshaded stabilized zirconia with 5 mol% of yttrium oxide (5Y-TZP).

MATERIALS AND METHODS

Monolithic crowns in the shape of an upper canine (1.5 mm of thickness) were manufactured by CAD/CAM, adhesively cemented on metallic foundation, and divided into 6 groups (n = 21): C (control), S (staining), G (glazing), P (polishing), SG (staining and glazing), and SP (staining and polishing). The survival probability was determined by step-stress accelerated life testing with a load applied to the palatine concavity of the crown. First, the specimens were subjected to a single-load to fracture test (SLF) and next to the fatigue test (5 Hz, thermocycling immersed in water varying 5-55°C), including the light (n = 9), moderate (n = 6), and aggressive (n = 3) loading profiles (load ranged between 20% and 60% of SLF). The survival probability was calculated considering the cycles for failure (CFF) and fatigue failure load (FFL) and illustrated using a Kaplan-Meier graph. The comparison among groups was performed using a Log-Rank test (α = 0.05).

RESULTS

The mean value of SLF was 586.7 N. There was no difference among groups in survival probability, considering CFF and FFL.

CONCLUSION

Staining, glazing, and polishing can be performed safely without damaging the mechanical behavior of 5Y-TZP monolithic crowns.

CLINICAL SIGNIFICANCE

Staining is used to characterize and improve the esthetic of zirconia monolithic crowns. It can be used to reproduce the color gradient in the cervical region of the crown and pigmented grooves. This study showed that staining, glazing, and polishing did not affect the survival probability and the use of finishing procedures (glazing or polishing) after staining did not improve the survival probability of zirconia monolithic crowns.

Optical and Mechanical Properties of the Multi-Transition Zones of a Translucent Zirconia

OBJECTIVE

To characterize the composition, flexure resistance, and optical properties of a multilayer translucent zirconia in relation to its multi-transition zones.

MATERIALS AND METHODS

A multilayer zirconia (5Y/4Y) and a conventional 3 mol% yttria partially stabilized zirconia (3Y) were investigated. Bar-shaped specimens were obtained from the enamel and dentin layers, and the vertical cross-section of 5Y/4Y (N = 10). A four-point flexural (σf) test was performed using a universal testing machine (1.0 mm/min). Plate-shaped specimens (N = 6) were also produced from the enamel, transition 1, transition 2, and dentin layers. Translucency parameters (TPab and TP00) were determined using a dental spectrophotometer (N = 6). X-ray fluorescence and X-ray diffraction techniques were used to analyze elemental (N = 2) and phase compositions (N = 2), respectively. Data were analyzed using analysis of variance (ANOVA) and Tukey's test (α = 0.05).

RESULTS

The yttrium content and σf varied between layers of 5Y/4Y. 3Y had the highest σf, followed by dentin. Enamel and cross-section showed lower and statically similar σf. 3Y and dentin groups had similar but statistically lower TPab and TP00 than the enamel.

CONCLUSIONS

Different layers of multilayered zirconia have distinct compositions, which affect their mechanical and optical properties. The weak enamel layer compromises the mechanical properties of cross-sectional specimens.

CLINICAL SIGNIFICANCE

The development of novel cubic-containing multilayer zirconia ceramics to produce monolithic restorations brings new challenges to dental clinicians and laboratory technicians. The CAD/CAM design of multilayered 5Y/4Y restorations should consider the esthetic and mechanical requirements of each clinical case, as different properties are found in the different layers of these materials.

Effect of Grinding and Polishing Protocols on Surface Roughness, Flexural Strength, and Phase Transformation of High-Translucent 5 mol% Yttria-Partially Stabilized Zirconia

OBJECTIVES

 This study evaluated surface roughness, biaxial flexural strength, and phase transformation of 5Y-PSZ after grinding and polishing with different protocols.

MATERIAL AND METHODS

 Two commercial 5Y-PSZ, Lava Esthetic (L) and Cercon xt (C), were used and divided into 3 groups: LC and CC represented unpolished control groups; LE and CE were polished with protocol I (EVE DIASYNT® PLUS HP following with EVE DIACERA RA); and LJ and CJ were polished with protocol II (Superfine diamond bur following with Jota ZIR Gloss polishing kit). Surface roughness was evaluated after polishing step-by-step with a contact-type profilometer. After high-gross polishing, the specimens were subjected to biaxial flexural strength test, crystallographic microstructure analysis using an X-ray diffractometer (XRD), and surface micro-topography using scanning electron microscopy (SEM).

STATISTICAL ANALYSIS

Surface roughness differences after each step and biaxial flexural strength between groups were evaluated with one-way ANOVA, followed by Bonferroni post-hoc analysis. Changes in surface roughness across four different time points within groups were assessed using one-way repeated measures ANOVA, followed by Bonferroni post-hoc analysis.

RESULTS

 After high-gross polishing, both polishing protocols showed significantly lower surface roughness than the grinding group (p < 0.05). The LE and CE groups exhibited the highest surface roughness values, which were significant differences from the LJ and CJ groups (p < 0.05). The LE group showed significantly lower biaxial flexural strength compared to the LC group (p < 0.05). However, there was no statistically significant difference in the CE and CJ groups compared to the control group (p > 0.05). Furthermore, all polishing protocols did not change the phase transformation of zirconia.

CONCLUSION

 Polishing protocol II provided a smoother surface than the protocol I after high-gross polishing, while the biaxial flexural strength of materials remained unaffected.

Two-step sintering suppresses grain growth and improves flexural strength of dental zirconia

OBJECTIVES

This study aimed to elucidate the effect of various two-step sintering (TSS) protocols on the physical, mechanical, and optical properties of partially stabilized zirconia with different yttria dopant concentrations (Y-PSZ).

METHODS

Disc-shaped specimens were obtained from most widely used commercial dental zirconia powders of various Y contents (Tosoh Corp.) by uniaxial pressing followed by cold-isostatic pressing. Densification was carried out using TSS protocols with varying temperatures for both sintering steps. Relative density (ρRel), microstructure, and phase content were analyzed. Biaxial flexural strength (σ) and translucency parameter (TP) were evaluated.

RESULTS

The TSS results were compared with optimized conventional sintering (CS) results from a previous study for the same Y-PSZ compositions. TSS 3Y-PSZ and 4Y-PSZ reached similar ρRel to those of their CS counterparts, whereas 5Y-PSZ failed to achieve that regardless of TSS protocol. TSS yielded less cubic phase compared to CS, especially for 3Y-PSZ and for higher temperatures. TSS suppressed the grain growth throughout the temperature range investigated, promoting smaller grains than CS (p < 0.05). The TP values for TSS Y-PSZ were lower than those of CS (p ≤ 0.0001), except for 3Y-PSZ. The σ values for TSS Y-PSZ were significantly higher than those of CS (p ≤ 0.0002).

SIGNIFICANCE

TSS increased strength without significantly jeopardizing the optical properties of various Y-PSZ compositions relative to their CS counterparts. This alternative sintering method appears to be a promising technique for controlling grain growth while eliminating porosities in dental Y-PSZ ceramics, thus potentially enhancing the clinical longevity of zirconia restorations.

Biaxial Flexural Strength and Vickers Hardness of 3D-Printed and Milled 5Y Partially Stabilized Zirconia

This study compares the mechanical properties of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) materials, designed for 3D printing or milling. Three 5Y-PSZ materials were investigated: printed zirconia (PZ) and two milled zirconia materials, VITA-YZ-XT (MZ-1) and Cercon xt (MZ-2). PZ samples were made from a novel ceramic suspension via digital light processing and divided into three subgroups: PZ-HN-ZD (horizontal nesting, printed with Zipro-D Dental), PZ-VN-Z (vertical nesting, printed with Zipro-D Dental) and PZ-VN-Z (vertical nesting, printed with Zipro Dental). Key outcomes included biaxial flexural strength (ISO 6872) and Vickers hardness (n ≥ 23 samples/subgroup). Microstructure and grain size were analyzed using light and scanning electron microscopy. Printed specimens exhibited biaxial flexural strengths of 1059 ± 178 MPa (PZ-HN-ZD), 797 ± 135 MPa (PZ-VN-ZD), and 793 ± 75 MPa (PZ-VN-Z). Milled samples showed strengths of 745 ± 96 MPa (MZ-1) and 928 ± 87 MPa (MZ-2). Significant differences (α = 0.05) were observed, except between vertically printed groups and MZ-1. Vickers hardness was highest for PZ-VN-Z (HV0.5 = 1590 ± 24), followed by MZ-1 (HV0.5 = 1577 ± 9) and MZ-2 (HV0.5 = 1524 ± 4), with significant differences, except between PZ and MZ-1. PZ samples had the smallest grain size (0.744 ± 0.024 µm) compared to MZ-1 (0.820 ± 0.042 µm) and MZ-2 (1.023 ± 0.081 µm). All materials met ISO 6872 standards for crowns and three-unit prostheses in posterior regions.

Impact of surface pre-treatment on bond strength between cement and zirconia: A systematic review and network meta-analysis

STATEMENT OF PROBLEM

The optimal zirconia pretreatment, contingent upon the type of cement used, warrants further research.

PURPOSE

The purpose of this investigation was to evaluate the influence of various surface pretreatments on the bonding efficacy of cement to zirconia.

MATERIAL AND METHODS

A comprehensive search was conducted across the PubMed, Embase, Scopus, and Web of Science databases for in vitro studies related to bonding with zirconia up to April 2024, supplemented by a manual search. A network meta-analysis was executed to compare different types of cement.

RESULTS

Of the 6118 articles screened, 21 were selected for inclusion in this review. These studies examined various surface pretreatment techniques, primers, resin cements, aging protocols, and bond strength testing methods. The highest bond strengths were observed with 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based cements. The network meta-analysis indicated that mechanical and mechano-chemical pretreatments yielded superior results across all cement types.

CONCLUSIONS

The existing evidence indicates that both surface pretreatments and the specific type of cement should be considered when interpreting the findings of in vitro studies for their application in clinical practice.

Evaluation of Extra-High Translucent Dental Zirconia: Translucency, Crystalline Phase, Mechanical Properties, and Microstructures

Highly translucent zirconia (TZ) is frequently used in dentistry. The properties of several highly translucent zirconia materials available in the market require an in-depth understanding. In this study, we assessed the translucency, crystalline phase, mechanical properties, and microstructures of three newly developed highly translucent zirconia materials (Zpex 4. m, 4 mol% yttria-stabilized zirconia: 4YSZ; Zpex Smile.m, 5YSZ; ZR Lucent ULTRA, 6YSZ). The translucency parameter (TP) was analyzed using the CIELAB system. X-ray diffraction was conducted for the crystalline phase analysis, followed by Rietveld refinement. A biaxial flexural strength test using the Weibull analysis was performed to evaluate the mechanical properties. Scanning electron microscopy, grain size distribution, and average grain size were used to analyze the microstructures. The TP content of the ZR Lucent ULTRA was the highest among the samples investigated. The Rietveld analysis revealed that the cubic zirconia phase content of the ZR Lucent ULTRA was the highest. The biaxial flexural strength of the ZR Lucent ULTRA was the lowest (622.9 MPa). The average grain size and proportion of large grains (1.0 µm < x) were the highest in ZR Lucent ULTRA. Therefore, extra-high translucent zirconia has the potential for use in anterior monolithic restorations owing to its esthetics and strength.

Determination of streptococcus mutans retention in acidic and neutral pH artificial saliva environment of all-ceramic materials with different surface treatment

BACKGROUND

Although surface finishing processes are effective against Streptococcus mutans biofilm, the mechanism of action of saliva with different acidity values ​​has not been studied in detail. This study aims to produce four different all-ceramic materials in a single session with CAD/CAM devices and apply two different surface finishing processes, glazing and polishing, and then determine the retention of Streptococcus mutants on the surfaces of the materials in saliva with varying levels of acidity.

METHODS

Zirconia-reinforced lithium silicate (Vita Suprinity, Vita Zahnfabrik, Bad Saöckingen, Germany), monochromatic feldspar (Vitablocs Mark 2, Vita Zahnfabrik, Bad Saöckingen, Germany), leucite glass ceramic (IPS Empress CAD, Ivoclar Vivadent, Liechtenstein), and monolithic zirconia (Incoris TZI (Cerec) Sirona, Germany) were used in the study. The surface roughness values ​​of all samples were measured with a profilometer before the application of S. mutans biofilm. A modified Fusayama artificial saliva model was prepared to reflect the oral environment. S. mutans bacterial biofilm growth rate was determined for each group with tetrazolium dye (MTT) assay and the colony-forming unit (CFU/mL). Scanning electron microscopy was used to compare the efficacy of all-ceramic materials against bacterial biofilm.

RESULTS

The surface treatment applied with polishing rubber (Ra 0.18-0.33) resulted in a slightly less rough surface than the glaze (Ra 0.32-0.35) treatment. S. mutans showed less retention in ceramic samples treated with the pH 5 saliva compared to the pH 7 ones. When this group's percentage growth rates, colony-forming units, and scanning electron microscopy images colored with ImageJ were examined, the Glaze application reduced growth (65.02 - 91.38%) and colony formation (6.1 × 1010 - 7.8 × 1010) in all samples except for Vita Suprinity compared to the Polishing Rubber application (p < 0.05).

CONCLUSION

The pH of the salivary, the surface roughness, and the chemical content of the ceramic samples may directly affect the S. mutans biofilm formations. The Polishing Rubber of the surface treatment type should only be suggested for Vita Suprinity, whereas the Glaze of the surface treatment type should be proposed for Vita Block Mark II and InCoris TZI in an acidic salivary environment. A surface treatment method other than Glaze and Polishing Rubber should be preferred for IPS Empress CAD.

Effect of low-temperature degradation treatment on hardness, color, and translucency of single layers of multilayered zirconia

STATEMENT OF PROBLEM

Evaluating the effect of low-temperature degradation (LTD) on multilayered zirconia blocks is important for the long-term life of zirconia restorations.

PURPOSE

The purpose of this in vitro study was to analyze the changes in color, translucency, and hardness of a single layer of multilayered zirconia after an LTD treatment.

MATERIAL AND METHODS

Ninety multilayered 10×10×1.0-mm zirconia specimens (3M Lava Esthetic) were designed using Auto CAD 2006 (Autodesk) and divided into 6 groups (n=15) based on LTD (no treatment, LTD treatment) and the inherent layer type (incisal, transition, and body). The hardness of each specimen was measured using a microVickers hardness tester. The CIELab color coordinates were measured using a spectrophotometer, and the data were used to calculate the color difference and translucency (TP). Data were analyzed using 2-way ANOVA and the Scheffé test (α=.05).

RESULTS

LTD treatment did not alter the hardness of multilayered zirconia (P=.572). A significant difference was found in the hardness between the layers of multilayered zirconia (P<.001). LTD treatment did not alter the b∗ or L∗ values (P=.773, P=.701) but did change the a∗ values (P<.001). On LTD treatment, the a∗ value was found to decrease. The L∗, a∗, and b∗ values differed based on the respective layer within the material (P<.001). As layers progress from the incisal to the body, the L∗ value decreased and the a∗ and b∗ values increased. In all groups, the color difference values were highest in the following order: the incisal and transition layers < the transition and body layers < the incisal and body layers. On LTD treatment, the color difference between the layers decreased. The LTD treatment did not affect the TP value (P=.208), but the TP value for each layer showed a significant difference (P<.001).

CONCLUSIONS

LTD treatment did not affect the optical properties or hardness of the multilayered zirconia. The hardness of the multilayered zirconia increased from the incisal to the body layer. In multilayered zirconia, the brightness decreased from the incisal to the body layer, and red and yellow color changes were observed. The TP of multilayered zirconia increased from the incisal to the body layer.

Trueness and adaptation of screw-retained implant-supported monolithic zirconia crowns fabricated using 3-dimensional gel deposition

STATEMENT OF PROBLEM

Implant-supported monolithic zirconia restorations manufactured using the additive 3-dimensional (3D) gel deposition technique have been introduced. However, studies determining the trueness and adaptation of implant-supported crowns made with the technique are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the trueness and adaptation of implant-supported zirconia crowns fabricated using additive 3D gel deposition in comparison with zirconia crowns made with the widely used subtractive milling technique.

MATERIAL AND METHODS

Crowns were fabricated for wide-diameter titanium implants and wide-neck abutments. Self-glazed zirconia (SGZ) crowns were fabricated using 3D gel deposition (n=10) and from 2 brands of zirconia blanks, Wieland and Upcera, using subtractive milling (WMZ and UMZ, n=10). All crowns were digitalized by a scanner, and then 3D deviation analysis was applied. The trueness was assessed by root mean square (RMS). Marginal and internal adaptations were evaluated using the direct-view technique (DT) and replica technique (RT). The results were analyzed by using the 1-way ANOVA and Kruskal-Wallis statistical tests (α=.05).

RESULTS

The RMS and marginal discrepancy of SGZ exhibited the lowest values among the 3 groups (P<.05), and the 2 types of milled zirconia crowns had comparable RMS and marginal discrepancy values (P>.05). The internal discrepancy values of SGZ were significantly lower than those of WMZ and UMZ in all regions (P<.05). Compared with the WMZ, UMZ showed comparable internal discrepancy values in the axial and axio-occlusal transition regions (P>.05) but had significantly lower internal discrepancy value in the occlusal region (P<.05).

CONCLUSIONS

The adaptation of 3 types of wide-diameter implant-supported zirconia crowns can meet the clinical requirements. Compared with the subtractive milling process, 3D gel deposition produced implant-supported zirconia crowns with improved trueness and adaptation.

Effect of occlusal adjustment and subsequent repolishing on the surface roughness and volumetric wear of different types of glazed monolithic zirconia after chewing simulation

The objective was to evaluate the effect of material (four monolithic zirconia) and surface condition [glazed (G) versus polished after simulation of occlusal adjustment (GAP)] on roughness and volumetric wear (VW) of dental zirconia after chewing simulation (CS). Zirconia specimens (ZS) were fabricated with an approximate diameter of 12.0 mm and a thickness of 1.0 mm. The four types of monolithic zirconia utilized were Prettau 4 Anterior (PA), Lava Plus (LP), Cercon hT (hT), and Cercon xT (xT). All specimens were coated with a thin and uniform layer of Prettau Plus glaze. Additionally, half of the ZS underwent a simulation of occlusal adjustment followed by clinical polishing. The sliding wear test was performed using a chewing simulator set at 30 N, 2 Hz, and 500,000 cycles, employing steatite specimens (SS) to simulate opposing dentition. ZS and SS underwent topographic analysis through optical profilometry to assess volumetric wear (VW) and surface roughness. The average roughness values (μm) of the zirconia ranged from 0.38h (PA-G before CS) to 2.55a (PA-GAP after CS), while for the antagonist the values ranged from 1.3b (LP-G before CS) to 2.6a (PA-GAP after CS). The VW values (mm3) of the ZS ranged from 0.7b (LP-G) to 2.5a (LP-GAP), while for the antagonist the values ranged from 0.17a (xT-GAP) to 0.33a (LP-G). The CS increased the roughness of all materials tested, regardless of the surface condition. The glazed condition showed lower roughness than the glazed/occlusal adjustment/polishing condition before the CS for three zirconia (PA, LP and xT) and after the CS for all materials. The surface condition did not significantly influence volumetric wear (VW) for three materials (PA, hT, and xT); however, for the Lava Plus (LP) group, the glazed condition resulted in reduced VW. The VW of the SS was unaffected by the material type or surface condition. In summary, zirconia specimens that underwent occlusal adjustment followed by repolishing demonstrated increased surface roughness compared to the glazed ones, while their wear behavior varied depending on the type of zirconia used.

Impact of speed sintering on the mechanical and optical properties of multilayered zirconia

STATEMENT OF PROBLEM

Speed sintering techniques have been introduced to shorten the sintering time of zirconia ceramics, yet their impact on multilayered zirconia properties remains understudied.

PURPOSE

The purpose of this in vitro study was to assess the effect of speed sintering on the optical properties and the mechanical flexural strength of multilayered zirconia materials.

MATERIAL AND METHODS

A total of 360 disks (Ø14 ±2 mm ×1.2 ±0.02 mm) were fabricated by following the International Organization for Standardization (ISO) 6872:2015 standard using 2 types of Vita A2 shade multilayered zirconia materials: IPS e.max ZirCAD Prime (ZP) and IPS e.max ZirCAD Prime Esthetic (ZPE). Each material comprised translucent (Tr), gradient l (Gr), and dentin (De) layers, with 60 disks per layer. Half were sintered using a standard sintering protocol and half using a speed sintering protocol. Biaxial flexural strength was accessed using a universal testing machine equipped with the Blue Hill Universal software program by following the ISO 6872:2015 standard, with 20 disks per subgroup. The spectrophotometric analysis of optical properties (contrast ratio [CR], translucency parameter [TP], and total transmittance [Tt%]) was performed using a dual-beam spectrophotometer (Ultrascan VIS) in accordance with the ISO 7491:2000 standard, with 10 disks per subgroup. The comparison of the optical properties and the mechanical flexural strength between the speed and standard protocol was analyzed using an unpaired t test (α=.05).

RESULTS

Speed sintering reduced biaxial flexural strength in all ZP layers (P<.05) and in ZPE-Gr (P<.05). A statistically significant difference in the CR was observed in the ZP-Tr, ZP-Gr, and ZPE-Gr layers (P<.05). The TP of the ZP-Gr, ZP-De, and ZPE-Gr layers was significantly lower when using the speed sintering protocol. Tt% was significantly lower with speed sintering for both materials (P<.05).

CONCLUSIONS

Speed sintering statistically changed both the optical (CR, TP, Tt%) and mechanical (flexural strength) properties of multilayered zirconia materials, but the differences may not be clinically relevant.

Improving osteogenic properties of zirconia ceramic via glow discharge plasma-enhanced deposition of amine organic compound

Background/purpose

Osseointegration potential is greatly depended on the interaction between bone cells and dental implant surface. Since zirconia ceramic has a bioinert surface, functionalization of the surface with an organic compound allylamine was conducted to overcome its drawback of minimal interaction with the surrounding bone.

Materials and methods

The zirconia surface was initially treated with argon glow discharge plasma (GDP), then combined with amine plasma at three different conditions of 50-W, 75-W and 85-W, to prepare the final samples. The surface characteristics and cell biocompatibility were then evaluated.

Results

Surface morphology analysis revealed a bulbous pattern on allylamine-treated sample groups. The aromatic C-H, C-O, N-H, C ˆ C, and C-H stretching and functional groups have been identified. Surface roughness increased, and hydrophilicity improved after surface modification. Cell viability analysis showed the highest result for the allylamine 50-W (A50) group. Alkaline phosphatase (ALP) assay indicated the A50 group had the highest activity, subsequently promoting late-stage mineralization at day 21. The reverse transcription-quantitative polymerase chain reaction (RT-qPCR) data demonstrated a significant upregulation of osteogenic gene expressions from day 1 to day 21.

Conclusion

The allylamine-treated surface demonstrates immense enhancement in the surface hydrophilicity as well as in the viability, differentiation, and osteogenic properties of osteoblast-like cells. This makes it a promising candidate for future dental implant applications.

Shear bond strength of porcelain to milled and stereolithography additively manufactured zirconia with and without surface treatment: An in vitro study

STATEMENT OF PROBLEM

Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength.

MATERIAL AND METHODS

A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (α=.05) RESULTS: A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001).

CONCLUSIONS

Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.

Bonding super translucent multilayered monolithic zirconia to different foundation materials: an invitro study

BACKGROUND

The objective of this study was to investigate the effect of bonded substrate, zirconia surface conditioning and the interaction between them on the shear bond strength of monolithic zirconia.

METHODS

Forty-eight monolithic zirconia discs were CAD-CAM fabricated and divided into two groups according to surface treatment either as milled and universal primer application (Monobond N, Ivoclar-Vivadent) (P) or sandblasting then universal primer application (Monobond N) (SP). Each main group was further divided into three test groups according to the bonded substrate: dentin (DSP, DP), composite (CSP, CP) or resin modified glass ionomer (RMGI) (GSP, GP). Adhesive resin cement (Multilinik automix, Ivoclar-Vivadent) was used for bonding. Specimens were stored in water bath for six months before thermal cycling for 10,000 cycles to mimic intra oral condition. All specimens underwent shear bond strength test (SBS) using a universal testing machine. Two and one-way ANOVA and Bonferroni Post Hoc tests were used for statistical analyses.

RESULTS

The means ± SD SBS of all test groups were recorded in (MPa). DSP group showed the highest mean SBS (22.65 ± 2.0) followed by DP group (18.61 ± 2.55). Meanwhile, GSP and GP groups showed the lowest mean SBS (4.77 ± 0.09, 4.57 ± 0.73 respectively).

CONCLUSION

Sandblasting with priming is recommended as a monolithic zirconia surface treatment method. Dentin is the most reliable substrate followed by composite.

Prospective clinical study of enamel wear caused by monolithic zirconia resin-bonded inlay-retained and wing-retained fixed partial dentures over 5 years

OBJECTIVES

To prospectively evaluate the wear of posterior zirconia resin-bonded fixed partial dentures (RBFPDs) with polished occlusal surfaces and their natural enamel antagonists compared to contralateral controls in an enamel-enamel contact over 5 years.

MATERIALS AND METHODS

In six patients with either an inlay- or wing-retained RBFPD made of monolithic 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), wear was evaluated indirectly using baseline and annual polyvinyl siloxane impressions. Resulting gypsum models were digitized and aligned by unchanged surface areas. Wear was analyzed by depth and area. For each parameter, descriptive statistics were used to express the degree of wear observed at yearly intervals for each group. A linear mixed regression analysis was performed to compare the enamel opposing 3Y-TZP group and the enamel-enamel controls at tooth level. All statistical tests were conducted at the 5% significance level.

RESULTS

After 5 years, the mean enamel wear depth of teeth opposing 3Y-TZP was 77 μm, compared to 54 μm for control teeth. No wear was observed on the 3Y-TZP RBFPDs. Maximum enamel wear depth and wear area were 229 μm and 9 mm², respectively, for teeth opposing 3Y-TZP, and 135 μm and 5 mm² for control teeth. Significant differences in mean enamel wear depth emerged after 2 years of observation.

CONCLUSIONS

Polished 3Y-TZP caused more enamel wear than natural antagonists over 5 years, but the wear remained within the range reported for other commonly used indirect restorative materials.

CLINICAL RELEVANCE

The clinical use of polished 3Y-TZP restorations appears to be justified in terms of natural antagonist wear behavior.

Fatigue behavior of sintered, glazed and glass-infiltrated surfaces of 5Y-PSZ bonded plates

This study evaluated the effect of different occlusal surface finishes (glaze and silica glass infiltration) on surface characteristics and fatigue behavior of partially stabilized zirconia (PSZ) plates adhesively bonded onto epoxy resin discs. PSZ disc specimens (n = 15; Katana blocks STML, Kuraray Noritake Dental) were produced (Ø = 10 mm; thickness = 1.2 mm) and allocated into 3 groups: As sintered (S), silica glass infiltration (SGI), and glaze application (G). The PSZ intaglio surface was air-abraded with 50-µm alumina powder followed by bonding agent application. All produced PSZ were adhesively cemented onto dentin analogue discs made of epoxy resin material (Ø = 10 mm; thickness = 2 mm). Step stress fatigue test was performed (load ranging from 200 to 1800 N; step size 100 N and 10,000 cycles; 20 Hz). The topographic, microstructural, and fractographic analyses were performed by scanning electron microscopy. Results: No statistically significant difference in fatigue behavior was detected among the groups. All failures started at the bonding surface. Silica glass-infiltration and glaze layer application provided a smoothing effect, while the sintered group had a surface with grooves. The occlusal surface finishing method (silica glass infiltration or glazing) had no deleterious effect on fatigue behavior of adhesively bonded PSZ plates.

Influence of different cutting instruments and rotational speeds on heat generation and cutting efficiency when sectioning different types of zirconia

PURPOSE

The purpose of this study was to evaluate the temperature generated on the intaglio surface and efficiency when cutting different types of zirconia with different rotary instruments and rotational speeds.

METHODS

A conventional diamond rotary instrument (Brasseler, grit size 107 μm) and special diamond rotary instrument marketed to cut zirconia (4 ZR, Brasseler, grit size 126 μm) were tested on 3Y-TZP and 4Y-TZP zirconia with a rotation speed of 100,000 rpm and 200,000 rpm. Zirconia specimens were cut under water cooling (110 mL/min) in a custom-made holder attached to a universal testing machine. The temperature was recorded with infrared sensors pointing at the intaglio surface of the zirconia specimens.

RESULTS

A rotation speed of 200,000 rpm resulted in significantly shorter cutting times, but also in significantly higher temperatures at the intaglio surface of the zirconia specimens compared with a rotation speed of 100,000 rpm. Significantly shorter cutting times were observed for the conventional diamond rotary instrument than for the special rotary instrument marketed to cut zirconia. Using the special rotary instrument, significantly longer cutting times were recorded for 3Y-TZP than for 4Y-TZP.

CONCLUSIONS

A conventional diamond rotary instrument was more efficient than a special rotary instrument. However, to avoid high temperatures when cutting zirconia clinically, a rotation speed of 100,000 rpm is recommended.

Classification system for maxillary fixed dental prostheses

PURPOSE

To present an addendum to existing fixed dental prostheses (FDPs) classification system for maxillary prostheses. The new classification identifies the relationships between FP-1 (fixed prostheses) designs and newly developed clinical interdental gingival contours.

MATERIALS AND METHODS

Clinical and laboratory descriptions of the various types of full-arch fixed prostheses are described with photographic illustrations. Benefits and limitations of the various prosthetic designs are explained. Surgical differences in the amount of alveolectomy are illustrated. One clinical case is demonstrated.

RESULTS

A new classification system for maxillary implant fixed complete dentures is presented. The new system will serve as an improved communication aid for clinicians, patients, and laboratory technicians. Treatment of patients with edentulous maxillae and/or terminal dentitions and implant fixed complete dentures include several options relative to design and materials. Restorative space can have a major impact on prosthesis design and longevity. Early on in dental implant therapy, prostheses were generally made with cast metal frameworks, denture bases and denture teeth. Prosthetic complications were widely reported. With increased clinical experience and improved materials, computer-aided design and computer-aided manufacturing (CAD-CAM) protocols were developed that allowed stronger prostheses to be constructed in reduced or small restorative volumes. FP-1 ceramic implant-supported fixed prostheses (CISFPs) are designed to replace only the dental hard tissues and to promote preservation and rehabilitation of gingival soft tissues. The physical properties and minimum thickness requirements in full arch prostheses are influenced by several factors including distances between implants and rigid connector sizes.

CONCLUSION

FP-1 CISFPs may be the closest prostheses the profession can offer edentulous patients that mimic the look, feel, and function of missing dentitions. Aesthetic outcomes of FP-1 CISFPs are variable and depend on a multitude of factors. This article presented a classification system that builds on existing classification by identifying the level of papilla heights achieved with FP-1 CISFPs.

Effect of simulated intraoral adjustment on the color and translucency of gradient multilayered monolithic zirconia

STATEMENT OF PROBLEM

The use of multilayered monolithic zirconia ceramics is becoming popular because it simplifies the production of esthetic restorations. The effect of clinical adjustment on the optical properties of these ceramics, especially strength-gradient zirconia, remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the color and translucency of gradient multilayered zirconia brands after grinding and polishing.

MATERIAL AND METHODS

Sixty 10×10×1-mm monolithic zirconia specimens were milled from 6 zirconia brands (Ceramill Zolid HT White, Ceramill Zolid HT Preshade, Ceramill Zolid FX Multicolor, VITA YZ XT Multicolor, IPS e.max ZirCAD Prime, and KATANA YML). The zirconia specimens were milled to include all layers of A2 preshaded multilayered zirconia blanks (A2 shade) except Ceramill Zolid HT White and Ceramill Zolid HT Preshade. Ceramill Zolid HT White specimens were milled from a white zirconia blank with subsequent shading. The color coordinates and the relative translucency parameter after glazing and after grinding and polishing were determined with a reflectance spectrophotometer, and the relative translucency parameter and contrast ratio were measured. The differences in color and translucency were calculated. The data were analyzed using 2-way ANOVA and 1-way ANOVA tests followed by the post hoc Tukey test (α=.05).

RESULTS

Statistically significant changes (P<.001) in the color coordinates measured before and after grinding and polishing were detected for each zirconia brand except for the KATANA YML that showed no significant difference (P=.686) in lightness. The highest color difference after grinding and polishing was detected in group KATANA YML. The 2-way ANOVA test showed a statistically significant interaction (P<.001) between the zirconia brand and the grinding and polishing regarding the relative translucency parameter. The zirconia brand had a significant impact on the relative translucency parameter before and after grinding and polishing (both P<.001).

CONCLUSIONS

Except for KATANA YML, the color change in multilayered zirconia after clinical adjustment with polishing was not beyond the clinically acceptable limit of the color difference. Although clinical adjustment with polishing reduced the translucency of gradient zirconia, the change in translucency was below the clinically detectable threshold value of the translucency difference.

Assessment of Dual-Cure Resin Cement Properties of Microhardness and Water Sorption/Solubility through Various Shades of Monolithic Zirconia

Background

It is important to evaluate the physical properties of dual-cure resin cement in different shades of monolithic zirconia because such an understanding is necessary for its clinical application.

Materials and Methods

For this in vitro study, 60 specimens of dual-cure resin cement were prepared and grouped into three sets (n = 20) according to monolithic zirconia shade: light, medium, and dark. Two-millimeter-thick discs of each shade were used as substrates for curing the resin cement. A Vickers hardness tester was employed for measuring microhardness, while ISO 4049 standards were followed for examining water sorption and solubility. Measurements were recorded at 24 hours, baseline, and 1 week after curing.

Results

The highest mean value of microhardness (85 HV) was observed in the light shade zirconia group, whereas medium and dark shades exhibited average values equal to 80 HV and 75 HV, respectively. The dark shade showed maximum water sorption among other groups with a mean value of 35 μg/mm³, followed by medium (30 μg/mm3) and light (25 μg/mm3) shades. In relation to solubility, the dark shade also had the highest value, which was approximately 3.5 μ/mm3, while the medium shade showed around 2.5 μg/mm3 and the light shade exhibited nearly 1.5 μg/mm3.

Conclusion

Microhardness and water sorption/solubility are significantly affected by the shade variation of monolithic zirconias combined with dual-cured resins. Lighter shades result in higher microhardness and lower water absorption and solubility, leading to better performance and longer lifespan.

Zirconia crowns manufactured using digital light processing: Effects of build angle and layer thickness on the accuracy

OBJECTIVES

This study investigated the effects of build angle and layer thickness on the trueness and precision of zirconia crowns manufactured using digital light processing (DLP) technology.

MATERIALS AND METHODS

Single crowns were fabricated from zirconia using DLP technology. The crowns were manufactured with three different representative build angles (0°, 45°, and 90°) and two different layer thicknesses (30 μm and 50 μm). After printing, the specimens were non-contact-scanned, and their accuracy was assessed using a 3D analysis software. Root mean square (RMS) values were used to determine trueness and precision. Color maps were generated to detect deviations within the specimens. Statistical analyses were conducted using two-way ANOVA.

RESULTS

Build angle and layer thickness significantly affected trueness and precision (p < 0.05). At a 30-μm layer thickness, the crowns printed at angles of 0° (32.2 ± 3.2 μm) and 45° (33.9 ± 2.4 μm) demonstrated the best marginal trueness compared to those in other groups (p < 0.05). Notably, those printed at an angle of 90° exhibited the best intaglio surface trueness (37.4 ± 4.0 μm). At a 50-μm layer thickness, the crowns printed at an angle of 90° exhibited the lowest accuracy concerning marginal and intaglio surface aspects (27.7 ± 8.2 μm).

CONCLUSIONS

Both the build angle and layer thickness significantly affected the dimensional accuracy of DLP-printed zirconia crowns, with the 30-μm layer thickness offering superior trueness. Optimal results were achieved using build angles of 0° and 45° in conjunction with thinner layers, minimizing marginal defects.

CLINICAL SIGNIFICANCE

All zirconia crowns produced at different build angles and layer thicknesses satisfied clinical requirements. Specific combinations of these factors realized the fabrication of single crowns that possessed the highest accuracy.

Fatigue strength of bilayer yttria-stabilized zirconia after low-temperature degradation

This study examined the impact of interfacial interactions on bilayer yttria-stabilized zirconia (YSZ) used in dental restorations. In-house bilayer structures of 3YSZ and 5YSZ composition underwent hydrothermal degradation to compare the properties of control and low-temperature degradation (LTD) treated groups. Biaxial flexural strength via piston-on-three-balls, staircase fatigue strength over 106 cycles at 15 Hz, phase characterization and quantification through XRD and Rietveld refinement, and fractography were conducted. Weibull analysis was employed to determine the Weibull modulus and characteristic strength. Results demonstrated an enhancement in the mechanical performance of 3YSZ composition after LTD treatment, whereas the mechanical properties of 5YSZ remained largely unaffected post-degradation. Fractographic analysis revealed that failure originated at the surface tensile location across all specimen groups. These findings offer insights into the mechanical behavior of bilayer zirconia structures and reinforce the significance of hydrothermal treatment in enhancing their performance, particularly in the case of 3Y compositions.

Effect of air-particle abrasion and methacryloyloxydecyl phosphate primer on fracture load of thin zirconia crowns: an in vitro study

The study aimed to investigate the effects of airborne-particle abrasion (APA) and 10-methacryloxydecyl dihydrogen phosphate (10-MDP primer) surface treatments on the fracture load of thin zirconia crowns made from 3Y-TZP and 5Y-PSZ zirconia. Eighty full-contour zirconia crowns of 0.5 mm thickness were fabricated from 3Y-TZP and 5Y-PSZ zirconia. Crowns of each material were divided into four groups based on the surface treatment applied to the fitting surface (n = 10): Group 1 (control), Group 2 (10-MDP Primer Only), Group 3 (APA Only), and Group 4 (10-MDP Primer + APA). Crowns were cemented using self-adhesive resin cement and subjected to thermocycling. Fracture load tests were performed using a universal testing machine with a hemispherical indenter. Statistical analysis was performed using one-way ANOVA, Tukey's post hoc test, and independent samples T-test (α = 0.05). The fracture load of 3Y-TZP was significantly higher than 5Y-PSZ crowns across all groups (P ≤ 0.001). Group 1 had the lowest fracture load, while Group 4 had the highest for both materials. In 3Y-TZP, the fracture load of Group 2 increased by 40% (P = 0.002) and Group 3 by 50% (P < 0.001) compared to Group 1. Group 4 showed a 90% increase over Group 1 (P < 0.001). For 5Y-PSZ, fracture load of Group 4 increased by 70% compared to Group 1 (P < 0.001). It was concluded that applying a 10-MDP primer or APA significantly increases the fracture load of thin 3Y-TZP zirconia crowns, with the combination of both treatments yielding the highest values. For 5Y-PSZ, a significant increase in fracture load is observed only when both APA and the 10-MDP primer are used together.

Survival Analysis of Prefabricated Zirconia Crowns with and Without Pulpotomy in Primary Teeth: A Retrospective Cohort Study

BACKGROUND

Prefabricated Zirconia Crowns (PZCs) are increasingly preferred for restoring primary teeth due to their esthetic appeal and retention. However, their rigid, unmodifiable design requires precise tooth preparation, often leading to aggressive reduction and potential pulp exposure. Pulpotomy, a standard treatment for reversible pulpitis and mechanical pulp exposure, is sometimes employed before PZCs. While pulpotomy is not routinely performed, its use raises important considerations about the interplay between restorative procedures and pulp therapy in pediatric dentistry, particularly regarding the long-term restoration outcomes of PZCs.

PURPOSE

This study aimed to investigate the impact of pulpotomy on the success rate of PZCs.

METHODS

We examined 81 anterior upper primary teeth treated with PZCs in children aged 2-5 years over a two-year period. Cases were divided into groups with and without pulpotomy. Follow-ups occurred at 6-month intervals, assessing clinical and radiographic outcomes. Analyses were performed using SPSS 25.0 software. The statistical significance was p < 0.05.

RESULTS

A total of 81 anterior primary teeth were included. Chi-square analysis showed no association between pulp therapy and PZC success (χ2 = 0.051, p = 0.822). The Kaplan-Meier survival analysis revealed comparable survival curves and the log-rank test showed no statistically significant difference in survival time between pulpotomy-treated and untreated groups (χ2 = 0.051, p = 0.821).

CONCLUSIONS

Pulpotomy did not significantly affect the success rate of PZCs within 2 years.

In Vitro Wear of Human Enamel Against Monolithic Zirconia After Staining, Glazing and Polishing Treatments

OBJECTIVE

To evaluate the effect of staining, glazing, and polishing of stabilized zirconia with 5 mol% of yttrium oxide (5Y-TZP) on the wear behavior of opposing tooth enamel.

MATERIALS AND METHODS

The plane specimens of 5Y-TZP were divided into 6 groups (n = 10), according to surface treatment: as sintered, staining, glazing, polishing, staining followed by glazing, and staining followed by polishing, and positioned against tooth enamel during the two-body wear test (20 N, 2 Hz, until completing 300,000 cycles). The wear rates of tooth enamel were evaluated using a profile projector and a digital pachymeter as a measure of vertical height loss. The data were analyzed by one-way ANOVA and a Tukey post hoc test (α = 0.05).

RESULTS

Polishing reduced the vertical height loss (p < 0.001) while there was no difference among other groups.

CONCLUSION

Polishing is recommended as a finishing procedure to reduce the wear rates of tooth enamel, and finishing procedures (glazing or polishing) performed after staining did not affect the vertical height loss of tooth enamel.

CLINICAL SIGNIFICANCE

Polishing is the recommended finishing procedure for preshaded 5Y-TZP to reduce the wear rates of opposing tooth enamel. Staining is applied to the occlusal surface to reproduce the pigmented groove appearance, and glazing or polishing performed after staining did not affect the wear rates of opposing tooth enamel.

Effects of Er:YAG laser debonding on changes in the properties of dental zirconia

OBJECTIVES

To investigate changes in the optical and mechanical properties of novel zirconia ceramics applied in dentistry after Er:YAG laser debonding and to evaluate the feasibility and value of reusing zirconia restorations debonded by an Er:YAG laser.

METHODS

Four types of zirconia ceramics were investigated: self-glazed zirconia (SGZ), 3Y-TZP, 4Y-PSZ and 5Y-PSZ. Forty rectangular (25 mm*8 mm*1.5 mm) specimens were fabricated for each zirconia type, and a total of 160 specimens were manufactured. The zirconia specimens were divided into four subgroups according to the applied Er:YAG laser debonding process: the control group, 4 W laser group, 5 W laser group, and 6 W laser group. For each subgroup, 10 specimens were subjected to color tests (color difference (△E) and transparency parameter (TP) tests) and subsequent mechanical tests (flexural strength (FS), elastic modulus (EM), Vickers hardness (VH) and surface roughness (Ra) tests). The △E, TP, FS, EM, VH and Ra values were measured and calculated. One random sample from each subgroup was observed by SEM. Statistical analyses were performed by one-way ANOVA followed by post hoc comparisons (α = 0.05).

RESULTS

The △E and TP values after Er:YAG laser debonding were not significantly different among the subgroups (P > 0.05). However, the 6 W laser group had the highest △E and lowest TP. The ranges of changes in △E and TP were below the clinically detectable threshold (△E = 1.2, △TP = 1.33). In terms of the mechanical properties, there were no significant differences in the FS, EM, VH or Ra among the subgroups. No obvious microcracks were detected on the surfaces of the zirconia specimens during SEM.

CONCLUSIONS

Er:YAG laser debonding does not obviously affect the optical or mechanical properties of novel zirconia ceramics in dentistry. Moreover, it is potentially feasible and valuable to reuse zirconia restorations after Er:YAG laser debonding.

Survival and Complication Rates of Feldspathic, Leucite-Reinforced, Lithium Disilicate and Zirconia Ceramic Laminate Veneers: A Systematic Review and Meta-Analysis

OBJECTIVES

To analyze survival and complication rates for anterior and premolar laminate-veneers out of different ceramic materials (feldspathic, leucite-reinforced glass-ceramic [LRGC], lithium-disilicate [LDS] and zirconia).

MATERIAL AND METHODS

A systematic literature search was conducted across multiple databases for clinical studies on ceramic laminate-veneers with a minimum-follow-up of ≥ 1 year. The date of last search was on February 19, 2024. Survival, technical, esthetic and biological events were assessed for different laminate-veneer materials at three observation periods (short- [1-3 years], mid- [4-6 years] and long-term [≥ 7 years]).

RESULTS

Twenty-nine studies were included. Meta-analysis revealed a pooled survival-rate of 96.13% for feldspathic, 93.70% for LRGC and 96.81% for LDS at 10.4 years. No difference was found between materials. Complication rates (technical/esthetic/biological) were as follows: Feldspathic: 41.48%/19.64%/6.51%; LRGC: 29.87%/17.89%/4.4%; LDS: 6.1%/1.9%/0.45% at 10.4 years. Zirconia showed a 100% survival-rate with no complications at 2.6 years. No long-term data was available for zirconia.

CONCLUSIONS

Feldspathic, LRGC and LDS laminate-veneers showed high survival-rates at long-term observation. LDS slightly outperforms feldspathic and LRGC laminate-veneers with lower long-term complication rates. More studies providing long-term data on zirconia laminate-veneers are needed.

CLINICAL SIGNIFICANCE

Ceramic laminate-veneers are a reliable treatment option. LDS may be preferred as a restorative material for long-term success.

Influence of the preparation design on the retentive strength of resin-bonded attachments

OBJECTIVES

The study investigated the influence of retention grooves and material thickness of the retainer wing on the retentive strength of resin-bonded attachments (RBAs).

MATERIALS AND METHODS

Sixty-four extracted human molars were used. Each tooth received a preparation limited to the enamel for the retainer wings of the RBAs. The specimens were divided into eight groups, each containing eight specimens. The groups varied based on the number of conical retention grooves (0, 1, 2, or 4) and the thickness of the CoCr retainer wings (0.4 mm and 0.8 mm). Before testing the retentive strength of the RBAs, the specimens underwent 37,500 thermal cycles followed by dynamic loading of 1,200,000 cycles on the RBAs' patrices using a chewing simulator. The debonding test was conducted using a universal testing machine at a crosshead speed of 2 mm/min.

RESULTS

The mean retentive strength ranged from 326 ± 96 N to 440 ± 77 N. Only a small portion of specimens (10.9%) exhibited adhesive failure, while the remainder demonstrated cohesive failure within the tooth structure. Neither the number of retention grooves, the thickness of the retainer wings, nor the size of the bonding surface significantly affected retentive strength.

CONCLUSIONS

The findings suggest that reducing the number of retention grooves and the material thickness does not influence the retentive strength of RBAs.

CLINICAL RELEVANCE

The retention of RBAs appears promising, supporting the clinical application of this treatment modality.

Survival, technical and biological outcome of fixed tooth- and implant-supported restorations: A retrospective analysis of a patient cohort treated in an undergraduate dental education program

OBJECTIVES

There is a paucity of data on the outcome of fixed tooth- and implant-supported porcelain-fused-to-metal (PFM) and ceramic-based (CB) restorations fabricated during undergraduate dental education. Therefore, this retrospective study examined the outcome of fixed restorations placed in patients participating in an undergraduate program.

METHODS

Patient records were searched for data on fixed PFM and CB restorations. For these restorations, the functional period in situ and technical and biological complications, namely restoration fracture, decementation, screw loosening, secondary caries, and loss of vitality, were recorded. Periodontal parameters were also documented. Kaplan-Meier survival and complication estimates after 1 and 5 years were calculated for restoration types, materials, designs (veneered/non-veneered), cementation/retention modes and localizations with group sizes ≥ 15. Regression models were used to analyze the influence of demographic data and abovementioned restoration characteristics on restoration survival, technical and biological outcome.

RESULTS

1196 restorations with a mean observation time of 5 years were included in the analysis. The different restoration types exhibited survival rates of > 90.8% after 5 years, accompanied by a favorable biological outcome. However, monolithic resin-matrix or feldspathic ceramic restorations were found to have a higher fracture rate than lithium disilicate or zirconium dioxide ceramic restorations resulting in lower survival rates for these restorations. Additionally, resin-matrix ceramic restorations showed a higher decementation rate than lithium disilicate restorations.

CONCLUSIONS

Fixed tooth- and implant-supported CB restorations fabricated from lithium disilicate and zirconium dioxide ceramics demonstrated better survival and lower complication rates than restorations fabricated from resin-matrix or feldspathic ceramics in an undergraduate dental education program.

CLINICAL SIGNIFICANCE

Due to the more favorable outcome of CB restorations fabricated from lithium disilicate or zirconium dioxide ceramics, undergraduate dental education should focus on the application of these ceramics to increase restoration survival by reducing technical complications.

Monolithic zirconia as a valid alternative to metal-ceramic for implant-supported single crowns in the posterior region: A systematic review and meta-analysis of randomized controlled trials

STATEMENT OF PROBLEM

Technical complication rates of standard metal-ceramic implant-supported posterior restorations are relatively high. Whether monolithic zirconia crowns represent a more successful alternative is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the clinical outcomes of posterior monolithic zirconia and metal-ceramic implant-supported single crowns.

MATERIAL AND METHODS

A search was conducted in MEDLINE, Scopus, Embase, Web of Science, and CENTRAL databases for randomized controlled trials up to April 2023 with a follow-up time of at least 1 year. Restoration and implant survival and failure rates, marginal bone loss (MBL), bleeding on probing (BOP), and technical complications were analyzed by 2 reviewers. Statistical analyses were conducted using the R-statistics software program. The risk of bias was assessed by the Cochrane Risk of Bias Tool 2 (RoB 2), and the certainty of evidence by the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.

RESULTS

A total of 11 out of 2030 records were identified by title and abstract, and 4 records were included after full-text analysis. The statistical analysis revealed no significant difference in MBL (MD -0.11, 95% CI: [-0.25; 0.03]), BOP (OR 0.66, 95% CI: [0.25; 1.77]), or implant failure (OR 1.30, 95% CI: [0.24; 7.08]). Monolithic zirconia presented significantly less chipping over 1 year (OR 0.17, 95% CI: [0.03; 0.99]). The chipping rate was 0% for monolithic zirconia and 7.61% for metal-ceramic. Based on a narrative review, the restoration survival rate was 97.5% in the monolithic zirconia group and 99.1% in the metal-ceramic group.

CONCLUSIONS

Monolithic zirconia showed favorable short-term survival rates and had significantly less chipping over 1 year. Regarding MBL, BOP, and failure rates, both restoration types presented similar results at the 1-year follow-up.

Nonthermal Atmospheric Plasma Promotes Bonding Between Adhesive Monomers and Zirconia

OBJECTIVE

To investigate whether nonthermal atmospheric plasma (NTAP) can promote bonding between commonly used adhesive monomers and zirconia.

MATERIALS AND METHODS

The zirconia surface and monomers (HEMA, BisGMA, TEGDMA, and MDP) were treated with different NTAP approaches (10 w, 30 s), and the surface characteristics and chemical structures between the zirconia surface and monomers were verified by the contact angle, scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectroscopy, and x-ray photoelectron spectroscopy (XPS). Scotchbond Universal adhesive with two different resin cements, RelyX Ultimate and RelyX Unicem 2, was applied, followed by NTAP-aided clinical procedures, and then microtensile bond strength test (μTBS) and failure mode evaluation were tested for preliminary mechanical properties assessment. One-way ANOVA was employed for the statistical analysis.

RESULTS

The contact angle analysis, SEM, and ATR-FTIR confirmed that NTAP can promote the polymerization of BisGMA, TEGDMA, and MDP on the zirconia surface, while XPS confirmed that NTAP can induce a chemical reaction between MDP and zirconia.

CONCLUSIONS

Nonthermal atmospheric plasma can increase the affinity between selected monomers and zirconia and promote the chemical bonding strength between phosphate monomers and zirconia; besides, it can enhance the bonding strength of two different adhesive systems.

CLINICAL SIGNIFICANCE

The mechanism of how NTAP improved common adhesive monomers interacting with zirconia surfaces was revealed in this study. NTAP, as a relatively high energy-boosting method, could not only improve the surface affinity of zirconia and chemical bonding in-between monomers and zirconia but also enhance the polymerization of different monomers onto zirconia, resulting in improved bonding properties. Thus, further exploration of versatile bonding materials and/or onto different dental substrates could take this into account.