Influence of restoration thickness and dental bonding surface on the fracture resistance of full-coverage occlusal veneers made from lithium disilicate ceramic

Objectives. The purpose of this in-vitro study was to evaluate the influence of ceramic thickness and type of dental bonding surface on the fracture resistance of non-retentive full-coverage adhesively retained occlusal veneers made from lithium disilicate ceramic. Methods. Seventy-two extracted molars were divided into three test groups (N=24) depending on the location of the occlusal veneer preparation: solely within enamel, within enamel and dentin or within enamel and an occlusal composite resin filling. For each test group, occlusal all-ceramic restorations were fabricated from lithium disilicate ceramic blocks (IPS e.max CAD) in three subgroups with different thicknesses ranging from 0.3 to 0.7 mm in the fissures and from 0.6 to 1.0 mm at the cusps. The veneers were etched (5% HF), silanated and adhesively luted using a self etching primer and a composite luting resin (Multilink Primer A/B and Multilink Automix). After water storage at 37 degrees C for 3 days and thermal cycling for 7500 cycles at 5-55 degrees C, specimens were subjected to dynamic loading in a chewing simulator with 600,000 loading cycles at 10 kg combined with thermal cycling. Unfractured specimens were loaded until fracture using a universal testing machine. Statistical analysis was performed using Kruskal-Wallis and Wilcoxon tests with Bonferroni-Holm correction for multiple testing. Results. Only specimens in the group with the thickest dimension (0.7 mm in fissure, 1.0 mm at cusp) survived cyclic loading without any damage. Survival rates in the remaining subgroups ranged from 50 to 100% for surviving with some damage and from 12.5 to 75% for surviving without any damage. Medians of final fracture resistance ranged from 610 to 3390 N. In groups with smaller ceramic thickness, luting to dentin or composite provided statistically significant (p <= 0.05) higher fracture resistance than luting to enamel only. The thickness of the occlual ceramic veneers had a statistically significant (p <= 0.05) influence on fracture resistance. Significance. The results suggest to use a thickness of 0.7-1 mm for non-retentive full-coverage adhesively retained occlusal lithium disilicate ceramic restorations. (C) 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.