The objective of this study was to evaluate the biomechanical and thermal behavior of a proposed preparation design as a conservative treatment option that aims to preserve both gingival and tooth health structures through a comparative finite element analysis with non-preparation and conventional designs. 3D solid models of laminate veneers with different preparation designs were obtained using cone-beam computed tomography (CBCT) scanning of the maxillary incisor. A 100-Newton load was applied with angulations of 60° and 125° to the longitudinal axis of the tooth to determine the stresses during mastication. In addition, transient thermal analysis was performed to compare the temperature and thermal distribution of the restored tooth models when subjected to thermal loads of 5 °C and 55 °C. Teeth prepared with the proposed design showed lower stress distributions and a repairable failure mode, followed by the non-preparation design, while teeth prepared with the conventional design showed the highest stress concentrations. Furthermore, cold thermal loading yielded larger thermal stress distributions than hot thermal loading, independent of the preparation type, and the effect of temperature changes were within the critical limit near the pulp and dentin regions. Thus, the preparation design geometry affects the long-term success of laminate restoration, and the proposed design yields more uniform and appropriate stress distributions than the other techniques.

Background: To measure adequate enamel thickness of maxillary incisors in planning enamel reduction for a porcelain laminate veneer restoration in relation to chronological age and sex by using cone beam computed tomography (CBCT) in an Iraqi subpopulation. Methods: From 81 CBCT images, 324 maxillary incisors were examined. Enamel thickness was measured at both mesial and distal regions of the tooth in three different levels: cervical, middle, and incisal (occlusal) 1/3 at a sagittal section. Measurements were made for the following tooth areas using CBCT: facial enamel thickness at 1, 3, and 5 mm from the cementoenamel junction (CEJ), palatal enamel thickness at 5 mm from the CEJ (5 mm P), facial and palatal enamel thickness at the incisal edge (IFP), mid incisal enamel thickness (IET), and the incisal edge enamel-pulp distance (IEPD). Relationships of enamel thickness with age and sex were evaluated using Independent t-test, Mann–Whitney U-test and the Pearson correlation coefficient, a simple linear regression analysis used for statistical analysis. Results: Significant differences (P < 0.05) were found in terms of an inverse association between enamel thickness and chronological age at all measurements above the CEJ and the regression model for the mid-incisal enamel thickness was (R2 of 0.4). In contrast, there was an increase in IFP, palatal, and IPED enamel thickness with age. Also, significant differences were found in enamel thickness between males and females, the enamel being thicker in females in relation to facial enamel thickness, enamel palatal thickness above CEJ and IET, while for IEPD, the enamel thickness was greater in males compared to females. Conclusion: The measurements for enamel thickness outcome variables in relation to chronological age revealed significant differences for each measured distance and there were statistically significant differences in enamel thickness between males and females at all measurements except at IFP. These results demonstrate that CBCT can be used for noninvasive, accurate measurements of enamel thickness in both sex.

Background: The restorative material used to seal the screw access channel in screw-retained implant-supported crowns may influence the biomechanical behavior and mechanical performance of the restoration. Objective: To evaluate the influence of different screw access channel restorative materials on stress distribution and deformation in porcelain-fused-to-metal (PFM) and monolithic zirconia implant-supported crowns using three-dimensional finite element analysis (FEA). Materials and Methods: Three-dimensional finite element models of screw-retained PFM and monolithic zirconia implant-supported crowns were developed. Four restorative materials—direct composite resin, resin matrix ceramic (RMC), lithium disilicate (LDS), and zirconia inlays—were used to restore the screw access channel. Each model was subjected to 200 N vertical and oblique occlusal loads. Equivalent von Mises (EVM) stress and total deformation were calculated and compared among the different restorative materials and crown types. Results: In PFM crowns, lithium disilicate and zirconia inlays produced lower stress transfer under vertical loading than direct composite resin and resin matrix ceramic. Under oblique loading, the differences in stress distribution among restorative materials were less pronounced. Zirconia inlays exhibited the highest internal stress concentrations but the lowest deformation, whereas direct composite resin demonstrated the greatest deformation. In monolithic zirconia crowns, deformation values were comparable among zirconia, lithium disilicate, and resin matrix ceramic inlays, indicating that the high stiffness of the zirconia crown largely governed the biomechanical response. Conclusions: Both the crown material and the restorative material used to seal the screw access channel affected the biomechanical performance of implant-supported restorations. Lithium disilicate and zirconia demonstrated more favorable mechanical behavior than direct composite resin, which exhibited greater deformation. These findings suggest that indirect restorative materials may provide biomechanical advantages over direct composite resin, particularly in restorations subjected to higher occlusal loads.