The study aimed to analyze the shear bond strength of aged silorane composite repaired with the same substrate or a conventional methacrylate-based composite after different mechanical and adhesive surface treatments.
Silorane composite specimens were aged by thermal cycling (5000 cycles, 5–55 °C) and randomly assigned to different surface treatments (each group n = 16): diamond bur abrasion, aluminum oxide sandblasting, silica coating, or hydrofluoric acid etching. Then, an adhesive system corresponding to the repair composite or a combination of silane agent and the respective adhesive was applied. Silorane composite or a nanofiller composite were adhered onto the conditioned surfaces. In the control group ( n = 16), silorane composite was adhered to fresh substrate (incremental build up). After further thermal cycling, shear bond strength was tested and failure modes were assessed. Data were analyzed by ANOVA/post hoc tests, Weibull statistics and Chi 2 -test ( p ≤ 0.05).
Incremental shear bond strength (control group: 21.0 ± 10.5 MPa) was achieved by all groups except those etched with hydrofluoric acid or samples abraded with diamond bur and repaired with the nanofiller composite without silane application. Generally, the application of the silane agent improved repair bond strength of the nanofiller but not of the silorane composite. Cohesive failure was observed more frequently than adhesive failure when the silane agent was applied or when silorane composite was used for repair.
Silorane composite can be repaired with either the same substrate or a methacrylate-based nanofiller composite but requires mechanical surface treatment and – in case of the methacrylate-based composite – silanization prior to adhesive application.
Polymerization shrinkage is considered as one of the main shortcomings of conventional methacrylate-based composites. Silorane composites were shown to overcome this problem to a certain extent as they are undergoing a photocationic ring-opening polymerization instead of a radical polymerization reaction, which results in polymerization shrinkage below 1% and a decrease of shrinkage stress by 27% compared to methacrylate-based composites . Furthermore, silorane composites were shown to present an increased hydrophobicity, which reduces water uptake and enhances hydrolytic stability . As silorane composites were marketed quite recently, information about their clinical performance is scarce and limited to one study with an observation period of 12 months. In this study, it was hypothesized that reduced polymerization stress would improve marginal performance, but marginal adaptation of silorane class II restorations was inferior compared to a methacrylate-based material .
In vitro studies showed that physical properties, such as flexural strength, dynamic and static moduli of elasticity, hardness and wear resistance of silorane composites are in the range of conventional methacrylate-based composites. Thus, longevity of silorane composite restorations might also be affected by mechanical or chemical degradation processes leading to clinical failures in the form of chipping, wear, discoloration or secondary caries, and requiring further operative treatment.
For the last years, it was shown that new techniques and materials in adhesive dentistry allow the repair of pre-existing restorations instead of their complete replacement . This approach is considered as conservative and cost-reducing method as the intact part of the restoration can be maintained and unnecessary removal of dental hard tissues and repeated irritations or injuries to the pulp can be avoided . The repairability of silorane composites was analyzed recently in several in vitro studies , but only few studies tested the ability of methacrylate-based composites to repair silorane restorations . These studies investigated either the effect of the adhesive intermediate agent or the impact of surface preparation on silorane repair. A systematic investigation combining both different surface pretreatments (mechanical and chemical) and different adhesive conditioning methods (adhesive, silane agent) was not done so far.
Thus, the objective of the present in vitro study was to evaluate the effect of various combinations of surface pretreatments and adhesive conditioning methods on shear bond strength of aged silorane repairs in order to determine the optimum repair method when either the same substrate or a conventional methacrylate-based composite is used. The null hypotheses tested were (1) the type of surface pretreatment does not affect shear bond strength, (2) the use of silane does not affect shear bond strength and (3) the kind of adhesive/repair composite does not influence shear bond strength.