Preparation of ultrathin translucent zirconia laminate veneers using 3D printing reduction guides

Minimizing and controlling the amount of tooth reduction during the preparation of ultrathin laminate veneers is a challenge for minimally invasive dentistry. The use of reduction guides is advised to reach the optimal space required for the definitive restoration without excessive reduction. The digital production of a reduction guide used to control tooth preparation for ultrathin laminate veneers is described.

Translucency of recent zirconia materials and material-related variables affecting their translucency: a systematic review and meta-analysis

BACKGROUND

Recent forms of translucent zirconia material have been developed, offering a wide range of options and varieties for enhancing aesthetics, making it a preferred choice in the field of prosthetic dentistry. However, there is insufficient understanding regarding the recent types of zirconia materials and their optical behavior. Understanding the variables that influence the translucency of zirconia and identifying strategies to enhance its esthetics are crucial.

PURPOSE

The current systemic review highlights a comprehensive understanding of different zirconia generations in relation to their optical characteristics and evaluates material-related variables affecting their translucency.

METHODS

The present review studied in-vitro studies that evaluated the optical characteristics of different yttria content of yttria stabilized materials. The topics explored were: (1) the different zirconia material generations and their optical behavior; (2) material-related factors that affect their translucency. The research was restricted to online publication in the English language from July 1, 2010, to July 31, 2023, using PubMed, Scopus, and Science Direct resources. The search key terms and their combinations were "zirconia," "translucent zirconia," "cubic zirconia," "highly translucent zirconia," "yttria partially stabilized zirconia," "monolithic zirconia," "translucency," "optical properties," and "light transmission."

RESULTS

The data obtained from fifty-three studies addressed the optical characteristics of various zirconia generations. They reported that changing yttria content had a significant impact on translucency. Different kinds of zirconia ceramics of the same generation have varying translucencies. Achieving optimum aesthetics with monolithic zirconia is challenging due to factors related to material aspects such as the presence of additives, point defects, microstructure, thickness, phase distribution, and sintering conditions.

CONCLUSIONS

Newly developed monolithic dental zirconia ceramics have improved aesthetics and translucency. However, additional research is necessary to evaluate their performance and long-term durability.

TRIAL REGISTRATION

This systematic review was registered in PROSPERO, under number CRD42023474482.

Effect of surface treatments on biaxial flexural strength, fatigue resistance, and fracture toughness of high versus low translucency zirconia

BACKGROUND

Mechanical surface treatments can deteriorate the mechanical properties of zirconia. This study evaluated and compared the biaxial flexural strength, fracture toughness, and fatigue resistance of high translucency (HT) to low translucency (LT) zirconia after various mechanical surface treatments.

METHODS

Four hundred eighty zirconia discs were prepared by milling and sintering two HT (Katana and BruxZir) and LT (Cercon and Lava) zirconia blocks at targeted dimensions of 12 mm diameter × 1.2 mm thickness. Sintered zirconia discs received one of the following surface treatments: low-pressure airborne particle abrasion (APA) using 50 µm alumina particles, grinding using 400 grit silicon carbide paper, while as-sintered specimens served as control. Internal structure and surface roughness were evaluated by scanning electron microscope (SEM) and a non-contact laser profilometer, respectively. Half of the discs were tested for initial biaxial flexural strength, while the rest was subjected to 10⁶ cyclic fatigue loadings, followed by measuring the residual biaxial flexural strength. Fractured surfaces were examined for critical size defects (c) using SEM to calculate the fracture toughness (K_IC). The effect of surface treatments, zirconia type, and cyclic fatigue on the biaxial flexural strength was statistically analyzed using three-way analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05). Weibull analysis was done to evaluate the reliability of the flexural strength for different materials.

RESULTS

The initial biaxial flexural strength of LT zirconia was significantly higher (p < 0.001) than that of HT zirconia in all groups. While low APA significantly increased the biaxial flexural strength of LT zirconia, no significant change was observed for HT zirconia except for Katana. Surface grinding and cyclic fatigue significantly reduced the flexural strength of all groups. High translucency zirconia reported higher fracture toughness, yet with lower Weibull moduli, compared to LT zirconia.

CONCLUSION

LT zirconia has higher biaxial flexural strength, yet with lower fracture toughness and fatigue resistance, compared to HT zirconia. Low-pressure APA has significantly increased the biaxial flexural strength in all zirconia groups except BruxZir. Grinding was deteriorating to biaxial flexural strength and fracture toughness in all zirconia types. Cyclic fatigue has significantly decreased the biaxial flexural strength and reliability of HT and LT zirconia.

Retention of different CAD/CAM endocrowns bonded to severely damaged endodontically treated teeth: An in vitro study

Aim:

Assess the retention of endocrowns fabricated of different CAD/CAM materials.

Settings and Design:

In vitro - comparative study.

Material and Methods:

Root canal treated mandibular first molars were prepared in a standardized method. Standardized endocrowns were manufactured using four CAD-CAM blocks: resin infiltrated ceramic (Vita Enamic), partially stabilized tetragonal zirconia (Katana), lithium disilicate ceramic (IPS e.max CAD), and polyether-ether-keton (PEEK, BioHPP). After proper surface treatment, the restorations were cemented using a resin cement (Panavia F2.0) and were connected to a special attachment unit and secured to a universal testing machine. The amount of axial load required to dislodge the restoration from the tooth structure was measured (n = 12, α = 0.05). Failures were classified as adhesive debonding from the tooth structure without damaging the supporting tooth structure and cohesive fracture of the supporting tooth structure

Statistical Analysis Used:

One-way analysis of variance,Tukey's post hoc test.

Results:

The retention of Vita Enamic (61 ± 11 N) and IPS e.max CAD (58 ± 9 N) was significantly higher (F = 123, P < 0.01) than Katana (33 ± 13) and Peek restorations (23 ± 11). Vita Enamic and IPS e.max CAD were associated with fractured tooth segments during debonding while Katana and PEEK specimens were adhesively debonded from the remaining tooth structure.

Conclusions:

Within the limitations of this study, using lithium disilicate ceramics and resin infiltrated ceramics as restorative materials to fabricate endocrowns to restore severely damaged endodontically treated teeth, recorded significantly higher retention values. Meanwhile, using yttrium partially stabilized zirconia and polyether ether ketones for the same purpose recorded a favorable mode failure which avoided the possibility of tooth fracture.

Bone marrow-derived mesenchymal stem cells and extracellular vesicles enriched collagen chitosan scaffold in skin wound healing (a rat model)

BACKGROUND

Over the past ten years, regenerative medicine has focused on the regeneration and the reconstruction of damaged, diseased, or lost tissues and organs. Skin, being the largest organ in the human body, had attained a good attraction in this field. Delayed wound healing is one of the most challenging clinical medicine complications. This study aimed to evaluate the collagen chitosan scaffold's effect alone, or enriched with either bone marrow-derived mesenchymal stem cells (BM-MSCs) or their secreted extracellular vesicles (EVs) on the duration and quality of skin wound healing.

METHODS

A full-thickness skin wound was induced on the back of 32 adult male Sprague-Dawley rats. The wounds were either covered with collagen chitosan scaffolds alone, scaffolds enriched with stem cells, or extracellular vesicles. Unprotected wounds were used as control. Healing duration, collagen deposition and alignment, CD 68+ macrophage count, and functional tensile strength of healed skin were assessed (α = 0.05, n = 8).

RESULTS

The rate of skin healing was significantly accelerated in all treated groups compared to the control. Immuno-histochemical assessment of CD68+ macrophages showed enhanced macrophages count, in addition to higher collagen deposition and better collagen alignment in EVs and BM-MSCs treated groups compared to the control group. Higher tensile strength values reflected the better collagen deposition and alignment for these groups. EVs showed higher amounts of collagen deposition and better alignment compared to MSCs treated group.

CONCLUSION

The collagen chitosan scaffolds enriched with MSCs or their EVs improved wound healing and improved the quantity and remodeling of collagen with a better assignment to EVs.

Influence of fatigue loading on fracture resistance of endodontically treated teeth restored with endocrowns

PURPOSE

This in vitro study aimed to evaluate the influence of fatigue loading on fracture resistance of endodontically treated molars restored with endocrowns using different machinable blocks.

METHODS

Endodontically treated mandibular first molars were prepared using a standardized method. Specimens were divided into 4 groups (n = 10).Anatomically shaped endocrowns groups were manufactured using VITA ENAMIC (VE) and KATANA Zirconia (KZ). Layered endocrowns groups were manufactured using IPS e.max CAD (EM) and BioHPP (BH). Half of the specimens of each group were subjected to fracture resistance test, while the other half were subjected to thermocycling and chewing simulation. After fatigue loading, specimens were loaded until failure. Specimens were examined using stereomicroscopy. Data were analyzed using ANOVA analysis of variance and Bonferroni post hoc test (α=0.05).

RESULTS

KZ group had the highest initial fracture resistance value (1810.20± 119.56 N) and BH had the lowest value (579.50± 76.15 N). The reduction of fracture resistance after fatigue loading was significant for KZ group (1588.30±216.25 N) and BH group (502.60±11.53 N) and non-significant to VE group (1101.70±77.05 N) and EM group (1112.10±74.12 N). Failure modes of KZ and EM groups showed high percentage of non-restorable fractures, while VE and BH groups showed high percentage of restorable fractures.

CONCLUSIONS

Within the limitations of this study, the following can be concluded: Poly infiltrated ceramics should be considered as a proper material to be used as an endocrown material because of its ability to be restorable if failure occurred.

The effect of fusion sputtering surface treatment on microshear bond strength of zirconia and MDP-containing resin cement

PURPOSE

The aim of this study is to evaluate the effect of fusion sputtering surface treatment on the microshear bond strength of zirconia and self-adhesive MDP-containing resin cement.

MATERIALS

Thirty-six zirconia discs received one of the following treatments: fusion sputtering, airborne particle abrasion with 50-μm aluminum oxide particles, while as-sintered specimens served as a control. Four treated zirconia samples from each group were examined using 3D laser scanning microscope to assess the surface roughness and scanning electron microscope to study the surface topography. The specimens of each group were bonded to composite micro discs using MDP-containing self-adhesive resin cement (Panavia SA cement plus). The specimens were thermocycled for 5000 cycles between 5 and 55 °C. Microshear bond strength test was performed using universal testing machine until bonding failure. Failure modes and fracture surfaces was evaluated using scanning electron microscope.

RESULTS

The fusion sputtering surface treatment significantly influenced zirconia-resin bond strength (p < 0.001). The highest mean microshear bond strength value was observed in fusion sputtering treatment (23.18 ± 4.38). The lowest value was observed in as-sintered zirconia surfaces (7.23 ± 6.26).

SIGNIFICANCE

Fusion sputtering surface treatment enhanced the microshear bond strength of zirconia and resin cement.

Bioactive-hybrid-zirconia implant surface for enhancing osseointegration: an in vivo study

Background

Zirconia is characterized by a hard, dense, and chemically inert surface which requires additional surface treatments in order to enhance osseointegration. The proposed hypothesis of the study was that combination of a nano-porous surface infiltrated with a bioactive material may enhance osseointegration of zirconia implants.

Methods

Custom-made zirconia implants (3.7 mm × 8 mm) were designed, milled, and sintered according to manufacturer recommendations. All implants received selective infiltration etching (SIE) technique to produce a nano-porous surface. Surface porosities were either filled with nano-hydroxy apatite particle- or platelet-rich plasma while uncoated surface served as a control (n = 12, α = 0.05). New surface properties were characterized with mercury porosimetry, XRD analysis, SEM, and EDX analysis. Implants were inserted in femur head of rabbits, and histomorphometric analysis was conducted after healing time to evaluate bone–implant contact percentage (BIC%).

Results

Selective infiltration etching produced a nano-porous surface with interconnected surface porosities. Mercury porosimetry revealed a significant reduction in total porosity percent after application of the two coating materials. XRD patterns detected hexagonal crystal structure of HA superimposed on the tetragonal crystal phase of zirconia. Histomorphometric analysis indicated a significantly higher (F = 14.6, P < 0.001) BIC% around HA–bioactive–hybrid surface (79.8 ± 3%) and PRP-coated surface (71 ± 6 %) compared to the control (49 ± 8%).

Conclusions

Bioactive–hybrid–zirconia implant surface enhanced osseointegration of zirconia implants.

Microtensile Bond Strength of Resin-bonded Hightranslucency Zirconia Using Different Surface Treatments

PURPOSE

To evaluate the effect of a novel surface treatment intended to improve bond strength to high-translucency zirconia.

MATERIALS AND METHODS

Fully sintered high-translucency zirconia disks (Incoris TZI) were divided into four groups according to the surface treatment received: modified fusion sputtering technique, selective infiltration etching, low pressure particle abrasion using 30-μm alumina particles, while 50-μm particle abrasion served as control. Surface roughness was evaluated quantitatively using a contact profilometer. The disks were bonded to pre-aged composite resin disks using a light-polymerized adhesive resin (RelyX ultimate). The bilayered disks were sectioned into microbars and zirconia-resin bond strength was evaluated using the microtensile bond strength test (MTBS). The test was repeated after 3 months of water storage (37°C). Scanning electron microscopic examination of the zirconia resin interface was performed at different magnifications. A repeated measures ANOVA and Bonferroni post-hoc test were used to analyze the data (n = 20, α = 0.05).

RESULTS

One-way ANOVA revealed significant differences in average surface roughness (Ra) between the tested groups (p < 0.001). The highest Ra value was recorded for fusion sputtering (12.23 ± 0.11 μm), followed by 50-μm particle abrasion (6.400 ± 0.887), then low pressure 30-μm particle abrasion (2.4 ± 0.15 μm), while the lowest surface roughness was recorded for the selective infiltration group (0.368 ± 0.04 μm). Modified fusion sputtering and selective infiltration etching produced significantly higher MTBS values at each of the tested intervals (p < 0.001) compared to particle abrasion using different particle sizes. Water storage resulted in reduction in the bond strength of 30-μm abraded specimens, which was attributed to structural defects observed at the zirconia/ resin interface. Scanning electron microscopic examination revealed a nanoporous surface characteristic of selective etching surface treatment, and modified fusion sputtering resulted in the creation of surface-fused microbeads.

CONCLUSION

Within the limitations of this study, selective infiltration etching and modified fusion sputtering techniques established a strong, stable, durable bond to high-translucency zirconia.

Fracture resistance of three-unit zirconia fixed partial denture with modified framework

Obtaining ideal prosthetic framework design is at times hindered by anatomical limitations in the posterior region that might increase the risk for zirconia restoration fracture. Modification such as increasing the bulk thickness especially in the connector region could result in strengthening the zirconia framework. Three-unit zirconia fixed partial dentures replacing mandibular molars were fabricated using the following two techniques: CAD/CAM technology and manual copy milling. Modified framework with unveneered full thickness connectors were designed and fabricated with the aforementioned methods. Conventional frameworks (0.5 mm thick with rounded 3 mm connectors) served as control (N = 20). After cementation on epoxy dies, the frameworks were loaded to fracture in a universal testing machine. Fractured surfaces were prepared for examination using scanning electron microscopy. Statistical analysis revealed significant differences in fracture resistance between conventional and modified framework design for both fabrication techniques tested. SEM examination indicated that critical crack originated at the tensile surface of the connectors for conventional frameworks. The critical crack for modified frameworks occurred on the axial wall of the abutments. The modification of the zirconia framework design presented significant improvement of the fracture resistance compared to the conventional design.

Color management of the cervical region using different framework materials

BACKGROUND

  Color-matching of the cervical area between natural teeth and different crown prostheses is a common clinical problem.

PURPOSE

  The purpose of this study was to compare the color of the cervical region of five commercially available crown systems to an extracted natural tooth and to each other.

MATERIALS AND METHODS

  The color of the cervical region of an extracted maxillary incisor was measured by means of a colorimeter (ShadeVision, X-Rite). Fifty master dies were fabricated, divided into five groups (N=10) according to the framework material; group 1: high-noble gold alloy, group 2: same as group 1 but treated with gold paste material, group 3: precious reinforced alloy, group 4: white zirconium oxide substructure (Lava 3M ESPE), and group 5: shaded zirconium oxide (Lava). A direct comparison of L*, a*, and b* parameters was accomplished between the control natural tooth and the five crown systems, and the mean color differences (ΔE) was calculated. The data were statistically analyzed with one-way analysis of variance and post hoc multiple comparison (α=0.05).

RESULTS

  Compared to the natural tooth, the mean color differences (ΔE) values were clinically unacceptable for all groups (ΔE > 3.7). The detected color differences, among different porcelain systems, were not visually perceptible (ΔE < 3.7).

CONCLUSIONS

  Within the limitations of this study, the cervical color of an extracted natural tooth could not be duplicated using different crowns systems.

CLINICAL SIGNIFICANCE

Color-matching of the cervical region of different crown systems with natural tooth remains a difficult task.

Allocation of color space for different age groups using three-dimensional shade guide systems

PURPOSE

To determine the color space and the coverage error of two manual shade guide systems in four age groups of a selected population.

MATERIAL AND METHODS

A total of 174 patients were divided into four age groups and the shade of their natural teeth was measured (2067 teeth) with a spectrophotometer (Vita Easyshade). Color parameters in terms of L*, a*, b* values, chroma, and hue were recorded for each tooth. Color difference (ΔE*min) between each natural tooth and the closest match using two manual shade guide systems were calculated (3D Master shade guide standard and 3D Master shade guide with intermediate values). A Wilcoxon test was used to assess statistical differences between mean ΔE*min values for each system (α = 0.05).

RESULTS

The recoded ΔE of the two tested manual systems was 6.19 for 3D Master shade guide (standard) and 6.02 for 3D Master shade guide (intermediate values). A statistically significant difference (P < 0.001) was found between the mean ΔE*min of the two systems. 47% of natural teeth presented a best match with intermediate value and chroma shade tabs. The mean ΔE*min was influenced by the age group of the patients (5.15, 5.23, 6.58, and 6.69, respectively).

CONCLUSION

Using intermediate value and chroma did not improve shade match, nor the coverage error of the tested population. Nevertheless, better coverage error was observed in younger age groups compared to older anterior teeth.

Color management of porcelain veneers: influence of dentin and resin cement colors

OBJECTIVE

Porcelain veneers have become an interesting treatment option to correct the shape and color of anterior teeth. Because of their limited thickness and high translucency, achieving a good color match is influenced by several variables. The aim of this work was to investigate the influence of natural dentin and resin cement colors on final color match of porcelain veneers.

METHOD AND MATERIALS

A preselected shade tab (A1) was chosen as the target color for a maxillary central incisor, and its color parameters (L*a*b*) were measured using a digital spectrophotometer (SpectroShade, MHT). Nine natural dentin colors (Natural Die Material, Ivoclar Vivadent) representing a wide range of tooth colors were used to prepare resin replicas of the maxillary central incisor with a standard preparation for porcelain veneers. The prepared porcelain veneers (IPS Empress Esthetic, A1, 0.6 mm thick, Ivoclar Vivadent) were cemented on the resin dies (nine groups of natural dentin colors) using seven shades of resin cement (Variolink Veneers, Ivoclar Vivadent). The L*a*b* values of the cemented veneers were measured, and DE values were calculated against the preselected target color (A1). DE greater than 3.3 was considered as a significant color mismatch detectable by the human eye.

RESULTS

The seven shades of resin cement had no significant influence on the final color of the veneers, as the measured DE values were almost identical for every test group. On the other hand, the color of natural dentin was a significant factor that influenced final color match. None of the 63 tested combinations (nine natural dentin colors and seven resin cement colors) produced an acceptable color match.

CONCLUSION

Thin porcelain veneers cannot mask underlying tooth color even when different shades of resin cement are used. Incorporation of opaque porcelain (high chroma) may improve final color match.