Effect of immediate and delayed dentin sealing on the fracture strength, failure type and Weilbull characteristics of lithiumdisilicate laminate veneers

Objectives. Adhesion on dentin is less reliable than on enamel, which could affect the durability of laminate veneers (LV). Immediate dentin sealing (IDS) is suggested instead of delayed dentin sealing (DDS) to overcome hypersensitivity and prevent debonding from dentin. This study evaluated the effect of IDS and DDS on the durability of Li2Si2O5 laminate veneers in vitro. Methods. Window preparations were made on the labial surfaces of sound maxillary central incisors (N=50). They were randomly divided into five groups: Group 1: Enamel only + H3PO4 Adhesive (control); Group 2: <1/4 dentin + H3PO4 DDS (2 weeks later); Group 3: Complete dentin + H3PO4 DDS (2 weeks later); Group 4: <1/4 dentin + H3PO4 IDS; Group 5: Complete dentin + H3PO4 + IDS. Li2Si2O5 laminate veneers (e.max Press) were bonded to the labial surfaces of the teeth with adhesive resin cement (Variolink Veneer). IDS layers were silicacoated (CoJet System) and silanized (ESPE-Sil). The teeth with their bonded laminates were thermocycled (10.000x cycles) and then subjected to static loading (1 mm/min). Failure type and location after debonding were classified. Data were analyzed using ANOVA and Tukey's post hoc test (alpha = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (o), values were calculated. Results. Mean fracture strength (N) per group in descending order was as follows: Group 5 (576 +/- 254), Group 4 (478 +/- 216), Group 1 (473 +/- 159), Group 2 (465 +/- 186), and Group 3 (314 +/- 137). The presence of complete dentin exposure sealed with DDS after 2 weeks on the bonded surface (Group 3) resulted in significantly lower fracture strength results than those in group 5 with IDS (p = 0.034). Weibull distribution presented higher shape (o) for Group 1 (3.67), than those of other groups (2.51-2.89). Failure types were predominantly adhesive failure between the cement and the laminate veneer in Groups 1, 2, 4 whereas Group 3 presented more often complete adhesive failures between the cement and dentin. In Group 5, failures showed some IDS and cement with or without ceramic fracture attached on the tooth. Significance. When laminate veneers are bonded to a large dentin substrate, application of immediate dentin sealing improves adhesion and thereby, the fracture strength of Li2Si2O5 laminate veneers. (C) 2016 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.