Stress Analysis of Ceramic Laminate Veneer for Diastema Closure with Different Extensions and Different Directions of Applied Load

摘要

Purpose: To analyze stress distribution on the IPS e. max (lithium di silicate) laminate veneer used for diastema closure with different free median extensions and different extensions of proximal preparation using two directions of applied force. Statement of the problem: Closure of large median diastema by laminate veneer will increase stress intensity on the unsupported mesial extension. Materials and Methods: Finite element model of unprepared maxillary central incisor was made, by deletion method, the labial surface was reduced by 0.5 mm. and is taken up to the height of the incisal edge (feather design), then, the basic geometric configurations of different laminate veneer designs and its dimensions in millimeters were introduced into the ANSYS software program to obtain the different nine models from three proximal extensions (1, 1.5 and 2 mm) and three unsupported median extensions ( 0.5, 1 and 1.5 mm), then the stress distributions were evaluated by applying load of 100 N at two angulations( 60° and 125°). Results: In case of 60° applied load the highest stress value was recorded in Model 3 (veneer with 1 mm labio – palatal extension with 1.5 free median extension, 30.95 Mpa) where The lowest stress value was recorded in Model 7 (veneer with 2 mm labio – palatal extension with 0.5 free median extension, 20.15 Mpa). Statistically, there was a significant difference between tested models (P at the level 0.05) except in cases of model 1, 4 and 7 which exhibited no statistical significant difference (P > 0.05). In case of 125° applied load the highest stress value was recorded in Model 3 (veneer with 1 mm labio – palatal extension with 1.5 free median extension, 53.61 Mpa) where The lowest stress value was recorded in Model 7 (veneer with 2 mm labio – palatal extension with 0.5 free median extension, 39.27 Mpa). Statistically, there was a significant difference between tested models (P at the level 0.05) except in cases of model 4, 5 and 8 which exhibited no statistical significant difference (P > 0.05). Conclusion: Stress is concentrated on the free median extension, incisal edge, and the mesio - labio - incisal point angle. The stress intensity increase in the following cases: - (1) increase in free median extension of the veneer, (2) increase in angulation of applied force, (3) decrease in proximal extension of laminate veneer.