Fatigue Loading of Lithium Disilicate Crowns with Different Axial Heights

Objectives: Monolithic all-ceramic crowns have become increasingly popular because of optimal esthetics and superior mechanical strength. However, limited data exist regarding the effect of axial wall height (AWH) when factoring in adhesive cementation of crowns and bonding between tooth and lithium disilicate (LD) surfaces. The purpose of this in-vitro study was to evaluate the effect of various AWH on the debonding of LD crowns under fatigue loading.
Methods: Extracted maxillary third molars were prepared for all-ceramic crown at 20-degrees using a customized jig. Samples were divided into four groups (0 mm, 1 mm, 3 mm, 4 mm) and scanned using the 3Shape TRIOS3 Scanner. Crowns were then designed, milled, and cemented with PANAVIA SA Cement and Clearfil Universal Bond Quick following manufacturer protocol. Samples were subjected to fatigue loading with 100N at 30-degree inclination on the functional cusp using a chewing simulator (SD Mechatronik CS-4). Number of cycles until failure and mode of failure were recorded. Debonded samples were examined under microscopy and optical coherence tomography (OCT).
Results: No tooth or crown fractures were observed during 2 months of continuous loading in this study. The 0 mm group debonded under 250,000 cycles, 1 mm group debonded after 5 million cycles, 3 mm group debonded after 6.25 million cycles, while 4 mm group remained intact beyond this stage. Microscopic evaluation of debonded specimen revealed that debonding had mainly occurred at the cement and LD interface, and the majority of cement remained on the dentin surface. OCT imaging confirmed microscopy findings in all debonded samples.
Conclusions: Adhesively cemented LD crowns with a short (1 mm) AWH resisted debonding for 5 million cycles which was less than that of 3 mm (6.25 million) and 4 mm preparations; however, it could be considered as clinically acceptable. Preparation of tooth for bonded restorations should consider tooth tissue preservation over excessive reduction for optimal resistance.