Evaluation of Marginal Adaptation of Onlay Restorations constructed from Two types of Glass Ceramics: An In vitro study

Objective: Marginal fit is crucial for the success of glass-ceramic onlay restorations, but limited data exists on one pressable zirconia-reinforced lithium disilicate's (ZL) marginal fit. This in vitro study assessed onlays from two materials: monolithic lithium disilicate (LD) and newly developed monolithic zirconia-reinforced lithium disilicate (ZL). Material and methods: Twenty-four onlay ceramic restorations were constructed on epoxy dies, divided into LD and ZL groups, and cemented with self-adhesive resin. Vertical marginal gaps were measured with a stereo electron microscope. The samples underwent thermomechanical fatigue loading (TML) in a chewing simulator and were re-evaluated. Results: ZL had a non-significant mean marginal gap of 46.42 μm before TML (p=0.086) and a significant mean gap of 57.28 μm after TML (p=0.00). LD exhibited marginal gap values of 41.16 μm before TML and 46.63 μm after TML. Conclusions: Marginal gap values for onlays before and after TML within clinically acceptable ranges. The marginal gap before TML was not significantly affected by the materials, but TML negatively impacted the marginal gap for both materials