Effects of porcelain veneering methods on conformity of the marginal and internal fit of three-unit zirconia framework

Evaluation of Marginal and Internal Adaptation of Crowns Fabricated with Three Different Zirconia CAD/CAM Materials

BACKGROUND

Marginal and internal adaptation are key factors that determine the clinical success of dental restorations.

AIM

The aim of this study is to evaluate the marginal and internal fit of crowns fabricated with three different CAD-CAM zirconia materials; two monolithic zirconia materials and one veneered zirconia copings in comparison with conventional metal-ceramic crowns.

MATERIAL AND METHODS

Ninety-six extracted molars (n = 96) were selected. Teeth were randomly divided into four groups (n = 24), and the following restorations were fabricated: Metal-ceramic crowns (Control group) (Group CG); monolithic zirconia crowns (GC initial) (Group MZ1); monolithic zirconia crowns (InCoris TZI),(Group MZ2); bilayered zirconia crowns, cores (InCoris ZI) veneered with a low-fusing glass-ceramic (IPS Emax Ceram),(Group BZ). Internal and marginal adaptations were evaluated using the silicone replica technique. A total of 20 points were recorded for every tooth under the light microscope at 20x magnifications. Results were compared using one-way analysis of variance (ANOVA) and the posthoc Tukey's test at a significance level of 0.01.

RESULTS

Marginal, marginal-internal, axial, and occlusal gaps between CG, MZ1, MZ2, and BZ crowns showed statistically significant differences (P < 0.01).

CONCLUSION

Monolithic zirconia groups showed better marginal adaptation compared with the veneered zirconia crowns.

Evaluation of the Marginal Fit of Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) Zirconia Bridges Fabricated With Different Firing Cycles of Veneering Porcelain: An In Vitro Study

Introduction Zirconia provides adequate mechanical strength to be used as a framework for all ceramic prostheses. Such prostheses must be covered with suitable porcelain to obtain good aesthetic results. The aim To study the effect of the firing cycle numbers of veneering ceramics (one cycle, two cycles, and three cycles) on the marginal fit of computer-aided design (CAD) and computer-aided manufacturing (CAM) zirconia bridges. Materials and methods The sample consisted of 30 full ceramic zirconia bridges, designed by CAD/CAM on a metal bridge model that was designed for this purpose. The sample was divided into three groups (N = 10); group A underwent a single firing cycle, group B underwent two cycles, and group C underwent three cycles. The copper model of the bridge was prepared to be a three-unit bridge, and the impressions of the metal models were taken to make zirconia cores. After that, the veneering ceramic layer and the micro-marginal gap were measured (in microns) on both the buccal and lingual surfaces of each bridge in the sample using the replica technique. A one-way ANOVA test was used to detect statistically significant differences between the groups. Results There were no significant differences between the studied groups in binary comparison; however, the arithmetic mean values of the marginal gap in group C were greater than all the studied groups. Conclusion Within the limitations of the current work, we found that increasing the number of firing cycles of zirconia cores affects the marginal fit; thus, it is recommended to follow the two firing cycle protocol for better adaptation of the CAD/CAM zirconia bridges.

Comparative Stress Evaluation between Bilayer, Monolithic and Cutback All-Ceramic Crown Designs: 3D Finite Element Study

Different all-ceramic crown designs are available to perform indirect restoration; however, the mechanical response of each model should still be elucidated. The study aims to evaluate the stress distribution in three different zirconia crown designs using finite element analysis. Different three-dimensional molar crowns were simulated: conventional bilayer zirconia covered with porcelain, a monolithic full-contour zirconia crown, and the cutback modified zirconia crown with porcelain veneered buccal face. The models were imported to the computer-aided engineering (CAE) software. Tetrahedral elements were used to form the mesh and the mechanical properties were assumed as isotropic, linear and homogeneous materials. The contacts were considered ideal. For the static structural mechanical analysis, 100 N occlusal load was applied and the bone tissue was fixed. Maximum principal stress showed that the stress pattern was different for the three crown designs, and the traditional bilayer model showed higher stress magnitude comparing to the other models. However, grayscale stress maps showed homogeneous stress distribution for all models. The all-ceramic crown designs affect the stress distribution, and the cutback porcelain-veneered zirconia crown can be a viable alternative to adequate function and esthetic when the monolithic zirconia crown cannot be indicated.