Fracture Resistance and Failure Mode of Monolithic Zirconia, Veneered Zirconia, and Metal-Ceramic Full-Coverage Restorations: A Comparative In Vitro Study.

PURPOSE: To evaluate and compare the fracture mode and strength of monolithic zirconia to veneered zirconia and metal-ceramic full-coverage restorations following artificial aging and to test the performance of translucent zirconia in terms of load-bearing capacity. MATERIALS AND METHODS: Two mandibular first molars were prepared and scanned for their respective groups of full-coverage restorations. A total of 75 full-coverage restorations were fabricated and divided into five groups: two groups for monolithic zirconia, two groups for veneered zirconia, and one group for metal-ceramic. Then, 75 light-cured hybrid composite resin dies were fabricated to serve as abutments. Before cementation, all full-coverage restorations were subjected to accelerated aging. After cementation, all full-coverage restorations were subjected to compressive loading until fracture in an electromechanical universal testing machine. A two-way nested ANOVA and Tukey test were used to analyze the results with 95% confidence levels. RESULTS: Monolithic zirconia full-coverage restorations showed the highest mean fracture resistance of 4,201.0 N, followed by metalceramic full-coverage restorations of 3,609.3 N, and veneered zirconia full-coverage restorations showed the lowest mean fracture resistance of 2,524.6 N. The main mode of failure was cohesive bulk fracture for the monolithic zirconia group, cohesive/adhesive failure with infrastructure damage for the veneered zirconia group, and cohesive/adhesive failure without infrastructure damage for the metal-ceramic group. CONCLUSIONS: Monolithic zirconia full-coverage restorations showed superior resistance to fracture compared to metal-ceramic full-coverage restorations and are highly reliable in terms of load-bearing capacity within the posterior regions of the mouth.

Fracture resistance and failure mode of monolithic zirconia, veneered zirconia, and metal-ceramic full-coverage restorations: A comparative in vitro study.

PURPOSE: To evaluate and compare the fracture mode and strength of monolithic zirconia to veneered zirconia and metal-ceramic full-coverage restorations following artificial aging. The main concern was to test the performance of translucent zirconia in terms of load-bearing capacity. MATERIALS AND METHODS: Two mandibular first molars were prepared and scanned for their respective groups of full-coverage restorations. 75 full-coverage restorations were fabricated and divided into five groups: two groups for monolithic zirconia, two groups for veneered zirconia, and one group for metal-ceramic. 75 light-cured hybrid composite resin dies were fabricated to serve as abutments. Before cementation, all full-coverage restorations were subjected to accelerated aging. After cementation, all full-coverage restorations were subjected to compressive loading until fracture in an electromechanical universal testing machine. A two-way nested analysis of variance and Tukey test were used to analyze the results with 95% confidence levels. RESULTS: Monolithic zirconia full-coverage restorations showed the highest mean fracture resistance of 4,201 N, followed by metal-ceramic full-coverage restorations of 3,609.3 N, and the veneered zirconia full-coverage restorations showed the lowest of 2,524.6 N. The main mode of failure was cohesive bulk fracture for the monolithic zirconia group, cohesive/adhesive failure along with infrastructure damage for the veneered zirconia group and cohesive/adhesive failure without infrastructure damage for the metal-ceramic group. CONCLUSIONS: Monolithic zirconia full-coverage restorations showed superior resistance to fracture in comparison to metal-ceramic full-coverage restorations and are highly reliable in terms of load-bearing capacity within the posterior regions of the mouth.

Partial Extraction Therapy with Early Implant Placement in the Esthetic Zone: A Clinical Case Report.

Immediate replacement of teeth designated for extraction is an appealing treatment rationale for both the patient and the operator. However, it has been associated with a greater risk of facial recession and compromised soft-tissue esthetics. Partial extraction therapy (PET) or synonymously socket shield technique (SST) or root membrane technique (RMT) has been proposed to conserve the facial alveolar contour and soft-tissue esthetics. In this article, a special case is described where a root membrane was used to prevent the modeling of the facial aspect of the extraction socket. Partial extraction was performed allowing the socket with the facial root membrane in situ to partially heal for 8 weeks before implant placement. Successful integration and restoration were achieved with very minimal hard- and soft-tissue changes, accentuating satisfactory esthetic results as dictated by objective esthetic assessment. PET with early implant placement may be considered a viable treatment option for selected cases.

Analysis of the effect magnitude of different parameters on smile attractiveness.

OBJECTIVE: To evaluate the effect magnitude of different parameters on smile attractiveness. MATERIALS AND METHODS: A reference and 13 images were produced by manipulating 13 parameters. Image rating was performed with a 4-point Likert scale from least attractive (1) to most attractive (4). Image raters included laypeople, dental students, dentists, and dental specialists. Friedman and Wilcoxon image were used for estimate of effect size. Parameters were classified into small (0.10- < 0.30), medium (0.30- < 0.5), or large (≥0.50). RESULTS: A total of 1040 people participated with good consistency (α = 0.861), and moderate reliability (0.64-0.7). The reference image had the highest rank (laypeople:11.79, dental background: 12.55). For effect size; gingival margin level (-0.11, -0.01), teeth width proportion (-0.09, -0.10), inverted smile arch (-0.09, -0.21), commissure line cant (-0.15, -0.17) and low smile (-0.24, -0.23) had small effect size; occlusal plane cant (-0.36, -0.49), midline cant (-0.36, -0.48), and midline shift (-0.37, -0.49) had medium effect size; diastema (-0.55, -0.54) and color (-0.56, -0.56) had large effect size for the laypeople and dental groups. High smile (-0.42, -0.51), incisor edge symmetry (-0.46, -0.54) had medium effect size in laypeople group and large effect size in the dental group. Width to length tooth proportion (-0.26, -0.39) had small effect size in the laypeople group and medium effect size in the dental group. CONCLUSIONS: Smile parameters had different effect magnitude on smile attractiveness and were classified into small, medium, or large parameters. Neither laypeople nor professionals have a collective judgment on what constitutes a beautiful smile. CLINICAL SIGNIFICANCE: This study investigated the effect magnitudes of 13 smile parameters and presented a small, medium, and large smile parameters classification. It should provide the clinician with an insight into the expected effect each parameter has on the smile.

Optical properties of CAD-CAM monolithic systems compared: three multi-layered zirconia and one lithium disilicate system.

OBJECTIVE: this in vitro investigation aims to evaluate and compare optical properties of three types of esthetic CAD-CAM monolithic multi-layered zirconia materials with a control (conventional lithium disilicate, IPS e. max CAD). METHODS: Four monolithic CAD-CAM ceramic materials were investigated: Ceramill Zolid® FX Multilayer (ZF), IPS e. max® ZirCAD MT Multi (ZM), Katana® STML (KS) and one lithium disilicate glass-ceramics as a control (IPS e. max® CAD LT; LC). A total of 72 (15 × 15 × 1 mm) samples were CAD CAM fabricated and sintered based on sample-size power calculations, and each material comprised 18 samples. The translucency and opalescence parameters with the contrast ratio were evaluated with a dental spectrophotometer over the backgrounds of black and white. The data were analyzed by ANOVA, then Bonferroni post hoc comparison test was made between groups. The statistical significance was set at p < 0.05. RESULTS: Zirconia materials revealed lower optical properties than the lithium disilicate control LC (P < 0.05). TP values ranged from 14.174 to 20.439. No differences were detected between the zirconia products in terms of TP and CR (P = 1.000). OP values ranged from 5.068 to 10.097. The lowest OP values were found statistically significant for ZF followed by KS and ZM (P = 1.000). LC had the highest TP and OP values, as well as the lowest CR (p < 0.05). CONCLUSIONS: The optical properties of monolithic zirconia systems tested here are still lower than those of lithium disilicate glass-ceramics. The only difference observed between the monolithic CAD CAM zirconia materials, was for the low opalescence parameter for the ZF. CLINICAL SIGNIFICANCE: Multi-layered monolithic zirconia systems have better esthetics by shade layers resembling natural tooth color gradients. CAD-CAM technology allowed for in-office milling and shaping of restorations using these systems. This study reports on their optical properties affecting human vision/perception of natural tooth shade to conclude about their use in the esthetic zones.