Assessment of the survival and success rates of lithium disilicate crowns after different surface finishing procedures: An in vitro study

Abstract

Statement of problem: Evidence is limited for the impact of clinical adjustments and polishing on the longevity of glazed lithium disilicate restorations.

Purpose: The purpose of this in vitro study was to evaluate the influence of surface finishing on the survival and success rates of lithium disilicate restorations based on fatigue resistance and failure mode.

Material and methods: Lithium disilicate (IPS e.max CAD) maxillary premolar crowns (N=54) were cemented on a dentin analog. The restorations were divided into 3 groups: overglaze (OG), abrasion (GA), and abrasion and polishing (AP). The crowns were submitted to cyclic fatigue in 37 ^oC water at 100 N and 2 Hz in 2 lifetimes. The load was applied to the occlusal surface by using anatomic pistons to simulate a clinical tripod occlusal contact. After cycling, the crowns were examined for failure (cracking, chipping, or catastrophic fractures) under optical and scanning electron microscopy. Cracking was considered either a structural failure (success analysis) or a survival (clinical criteria - survival analysis). Data were analyzed by using the log rank Kaplan-Meier and Holm-Sidak tests (α=.05).

Results: Surface finishing had no influence on the structural integrity of lithium disilicate, with similar success rates (P=.720). The calculated survival rate was higher for AP than that for other groups (P=.028). Cracking was found for GA and AP crowns, mostly initiating from the external surface. Chipping occurred in all experimental groups, and AP crowns did not show catastrophic failures.

Conclusions: Although surface treatments had no influence on the success of lithium disilicate, polishing showed a positive effect on the survival rate of the crowns based on the clinical implications of cracking (no need for replacement).