FRACTURE RESISTANCE OF LITHIUM DISILICATE OVERLAYS WITH DIFFERENT PROXIMAL BOX DESIGNS

Abstract

This study aimed to evaluate the effects of varying proximal box dimensions on the fracture resistance of overlay restorations. Maxillary premolars of similar dimensions were prepared with flat occlusal surfaces and proximal boxes of different sizes. Buccolingual width of 3 or 4.5 mm and proximal depth of 1 or 1.5 mm were created on both the mesial and distal aspects. Cylindrical overlays (1.5 mm thick) were designed using the 3Shape dental system (3Shape, Copenhagen K, Denmark), milled from lithium disilicate blocks, and bonded with Panavia V5 resin cement (Kuraray Noritake Dental, Tokyo, Japan). After simulated aging via thermocycling, fracture load was tested, and fracture patterns were examined using the built-in camera of a 3D profilometer. Overlay preparation designs without proximal boxes exhibited statistically significantly higher fracture load than those with proximal boxes measuring 4.5 mm in buccolingual width and 1.5 mm in proximal depth. No statistically significant differences were observed among the groups with proximal boxes. In conclusion, while variations in buccolingual width and proximal depth did not affect the fracture load of the overlay restorations, preparations without proximal boxes tended to exhibit higher fracture load and more severe fracture patterns compared to those with proximal boxes.

Keywords: Overlay, Lithium Disilicate, Proximal Box, Fracture Resistance, Fracture Mode