Statement of problem:Abfraction incidence is usually challenging and difficult to be identified accurately, especially, in case of existing restoration. Aim of the study:This study aimed to evaluate the influence of laminate veneer design on abfraction incidence in maxillary central incisor with different loading protocols using finite element analysis.Materials and methods: Maxillary central incisor was subjected to Computerized tomography (CT) scan to obtain 3D finite element model. Tooth without restoration (control) was subjected to a load of 100 N at 60° and 125°, the same load was applied with the previous directions on the tooth model with lithium disilicate laminate veneer using three preparation designs: veneer is taken up to the incisal edge level but the edge, is not reduced (Feather) (FP), design (FP) is prepared with 0.5mm incisal reduction without palatal overlapping (Butt joint.) (BJP) and (POP) in which, design (FP) is prepared with 2 mm incisal reduction and 0.5 mm palatal overlap. Results:In feather preparation (FP) design, stress values were slightly higher than that in control model in enamel and dentin at both load directions. While, but joint preparation (BJP) design exhibited the lowest stress in both layers and direction of load. ConclusionHighest stresses were concentrated at the cement -enamel junction in all loading scenarios, butt joint preparation (BJP) design in both load conditions developed lower stresses than that in other designs, and feather preparation (FP) design suggested the probability of abfraction formation.

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 labiopalatal extension with 1.5 free median extension, 30.95 Mpa) where The lowest stress value was recorded in Model 7 (veneer with 2 mm labiopalatal 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 labiopalatal extension with 1.5 free median extension, 53.61 Mpa) where The lowest stress value was recorded in Model 7 (veneer with 2 mm labiopalatal 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-labioincisal 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.

Statement of problem: Degree of marginal discrepancy determines effectively success and failure of fixed restorations. Purpose: To evaluate the effect of porcelain veneering techniques on the marginal fit of bi-layered zirconia crown using four marginal designs. Materials and Methods: A 40 Plaster replicas were made from two master dies and divided into two main groups (20 for each) according to type of finish line. Each group subdivided into two subgroups (10 for each) to obtain the following groups {A1} shoulder without cervical collar {A2} shoulder with 1 mm cervical collar. {B1} chamfer without cervical collar {B2} chamfer with 1 mm cervical collar. Zirconia blanks were milled using CAD/CAM system to produce 40 zirconia copings. Then, Veneering of the copings was done. Vertical gap distances were measured at 18 predetermined points. Results: Veneering with porcelain exhibited statistical significant difference in mean values of marginal gap in both group {A1} and {B1}, while veneering with porcelain did not exhibit significant difference in both group {A2} and {B2} in comparison with the pre veneering state. Correlations based on the finish line design exhibited significant difference in mean values of marginal gap between all tested groups. Correlations based on presence or absence of cervical zirconia collar did not exhibited statistical significant difference between tested groups. On other hand, there were significant differences in mean values of marginal gap between tested groups in post veneering state, at the level of P value < 0.05. Conclusions: Marginal fit of the final crowns with chamfer finish lines were better than that with shoulder, however, veneering with porcelain significantly raised marginal gap distance of crowns with collarless shoulder and chamfer preparations, while in that designs with cervical collar, veneering was not significantly affected on the marginal gap distance for both finish line designs (2556)