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

Impact of deglazing on biaxial flexural strength of high translucent zirconia: effect of hydrothermal aging, pH-cycling, and load-cycling

BACKGROUND

To compare the effect of deglazing and aging on biaxial flexural strength (FS) of high translucent (HT) zirconia.

METHODS

40 disc-shaped specimens (12 × 1.2 mm) of HT zirconia (3Y-PSZ, Upcera HT) were sintered after milling, glazed(G) and randomly assigned equally into 4 experimental groups: G) glazing; G-A) glazing, aging; DG-A) deglazing, aging; and NG-A) non-glazing, aging. A sequence of three methods was used for aging; hydrothermal, pH-cycling, and load cycling. FS(flexural strength) of all specimens was measured and one specimen from each group underwent X-ray diffraction (XRD) for assessment of phase transformation (t-m). Distribution of data was evaluated using the Kolmogorov -Smirnov test, and with respect to the confidence interval of 95%, data were analyzed using 1-way ANOVA with statistical software (IBM SPSS Statisticsv20.0) to compare the mean flexural strength values among the 4 groups. When significant differences were found, the mean values were compared using Tukey's honest significant difference (HSD) test (α = 0.05).

RESULTS

FS of glazed specimens (1092.78 ± 175.40 MPaa) did not decrease after aging (1141.11 ± 117.43 MPa, P = 0.872a). FS of DG-A (1338.22 ± 175.13 MPab) and NG-A (1320.44 ± 77.44 MPab) groups was significantly higher than that of G and GA groups (P < 0.005). XRD revealed monoclinic phase in DG-A (4.23%) and NG-A (7.63%) groups.

CONCLUSION

Loss of glaze layer and no glazing had no significant effect on FS of high translucent Y-PSZ after aging.

Effect of preparation designs and CAD-CAM materials on step-stress fatigue survival of premolar partial coverage restorations: An in-vitro study with fractographic analysis

OBJECTIVES

The growing trend of minimally invasive approaches has encouraged the application of partial coverage designs in restorative dentistry. This study aimed to evaluate the cyclic fatigue performance of different CAD-CAM materials used in various partial coverage designs for premolar restorations.

METHODS

A freshly extracted upper premolar was prepared using a high-speed handpiece to create mesio-occluso-distal (MOD) cavities with standardized dimensions. Three preparation designs were investigated: onlay, overlay, and vonlay. CAD software was used to create digital models of the restorations, which were milled into one of four CAD-CAM materials: Zr - zirconia polycrystals (4Y-PSZ); EX - lithium disilicate glass-ceramic; VS - zirconia-reinforced lithium silicate glass-ceramic; GB - nanohybrid composite. Partial coverage restorations were bonded to tooth replicas and subjected to step-stress cyclic fatigue testing using a chewing simulator device (n = 10). The number of cycles-to-failure and fatigue fracture resistance (N) were recorded and analysed with Kaplan-Meier survival statistics and Weibull analysis, respectively. Fracture surfaces were analysed using fractography.

RESULTS

Zr exhibited significantly higher number of cycles-to-failure and greater characteristic fracture load (L0) than the other materials, for onlay and overlay designs. For vonlay design, Zr, VS and EX had similar and greater number of cycles-to-failure than GB. When comparing different designs for the same material, Zr had lower number of cycles-to-failure for vonlay in comparison to onlay and overlay, while the other materials had similar values among the different designs. Weibull modulus was similar among experimental groups.

SIGNIFICANCE

The findings of this study emphasize the critical role of material selection and preparation design in optimizing the mechanical performance and clinical success of partial coverage restorations. 4Y-PSZ is recommended for high-stress areas due to its superior fatigue and fracture resistance. Overlay designs provide better fatigue resistance, making them more suitable for clinical scenarios requiring higher durability. Understanding the fatigue performance of different materials and designs aids in making informed decisions to enhance the longevity and success of partial coverage restorations in premolars.

Fracture strength of porcelain veneer on surface-treated zirconia

In this study, we investigated the effects of surface treatment on the fracture strength of porcelain-veneered zirconia. Highly translucent 4 mol% yttria-stabilized zirconia disks (KATANA HT, Kuraray Noritake Dental) were divided into three surface-treatment groups: 1)as-sintered, 2) alumina sandblasted, and 3) ground. Crystallographic and surface-roughness analyses were conducted for each group. Veneering ceramics (Cerabien ZR, Kuraray Noritake Dental) were applied to the zirconia surfaces. The fracture strengths of the porcelain-veneered zirconia disks were measured using biaxial flexural-strength tests. Crystallographic analysis revealed that grinding and sandblasting increased the fractions of the monoclinic and rhombohedral zirconia phases. The ground specimens had a higher surface roughness than the sandblasted specimens. Weibull analysis showed no significant differences in biaxial flexural strength among the three groups. The results suggest that these surface treatments do not affect the fracture strength of porcelain-veneered zirconia.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

Comparison of Regular and Speed Sintering on Low-Temperature Degradation and Fatigue Resistance of Translucent Zirconia Crowns for Implants: An In Vitro Study

BACKGROUND

Although there are a few studies which compare fast and slow sintering in normal zirconia crowns, it is essential to compare the cracks and load-bearing capacity in zirconia screw-retained implant crowns between regular and speed sintering protocols. This research aimed to compare the surface structure, cracks, and load-bearing capacity in zirconia screw-retained implant crowns between regular sintering (RS) and speed sintering (SS) protocol with and without cyclic loading (fatigue).

METHODS

A total of 60 screw-retained crowns were fabricated from zirconia (Katana STML Block) by the CAD/CAM system. Then, 30 crowns were subjected to the RS protocol and 30 crowns were subjected to the SS protocol. Cyclic loading was done in half zirconia crowns (15 crowns in each group) using a chewing simulator CS-4.8/CS-4.4 at room temperature. The loading force was applied on the middle of the crowns by a metal stylus underwater at room temperature with a chewing simulator at an axial 50 N load for 240,000 cycles and lateral movement at 2 mm. Scanning electron microscopy was done to study the surface of the crowns and the cracks in the crowns of the regular and speed sintering protocols, with and without fatigue.

RESULTS

For the speed sintering group, the surface looks more uniform, and the crack lines are present at a short distance compared to regular sintering. The sintering protocol with a larger Weibull module and durability increases the reliability. It showed that the Speed group showed the maximum fracture load, followed by the regular, speed fatigue, and regular fatigue groups. The fracture load in various groups showed significant differences.

CONCLUSIONS

It was found that the speed group showed the maximum fracture load followed by the regular, speed fatigue, and regular fatigue. The crack lines ran from occlusal to bottoms (gingiva) and the arrest lines were perpendicular to the crack propagations.