Abstract
Objective: to compare the effect of three surface treatment protocols and two intermediate agents on repairing aged composite, regarding microtensile bond strength (µTBS) and mode of fracture, at two time intervals. Material and methods: Six-month aged microhybrid composite blocks, were randomly distributed into three groups, subjected to; Fine, Super Fine grit diamond burs or Erbium- Yag Laser surface treatment. Each block had both One Coat bond SL (Bond) and Brilliant Flow flowable composite (Flow) intermediate agents, alongside. Blocks were incrementally repaired using nanohybrid composite, cut into beams, then randomly subjected either immediately (IM) to µTBS test or after thermocycling (TC) for 5000 cycle. Mode of failure was determined using stereomicroscope. Data were analyzed through three-way ANOVA followed by pairwise comparison with Bonferroni correction. Kruskal Wallis test compared groups for failure mode analysis (?=0.05)Results: Super Fine grit showed the highest mean µTBS compared to control for both intermediate agents, IM and after TC at P<0.05. No difference between Fine grit and Laser application for all groups (P>0.05). IM, Bond showed the highest µTBS compared to TC, Flow for all tested groups. Beams roughened with Fine and Super Fine burs showed significantly lower adhesive failures than those roughened with Laser. Flow suffers significantly higher adhesive failure than those with Bond. For TC tested groups; beams with Super Fine bur and Bond showed significantly lower adhesive failure at P=0.029.Conclusions: Super Fine grit and Bond provide the highest µTBS and the least adhesive failure; moreover TC resulted in significant decrease in µTBS.
Highlights
I n conservative dentistry, there is a growing trend towards repairing defective composite restorations instead of complete replacement
These surface treatments provide surface irregularities which promote micro-mechanical interlocking between the substrate surface and the repair resin. [5,7,8,9,10] In most clinical studies, partial removal of the old composite was done using coarse diamond bur [1,11,12,13], using either medium or fine grit diamond bur can produce more reliable repair bond strength than using coarse diamond bur. [13,14] on the other hand, Erbium laser has been recently suggested for surface roughness of the old composite by ablation mechanism, which can be used in the process of repair [15,16,17]
For the IM tested groups when bond SL (Bond) was used as an intermediate agent, both Fine and Super Fine grit bur roughened beams showed significantly lower adhesive failures percentage than those roughened with Laser, the latter was not significantly different than control at P=0.001
Summary
I n conservative dentistry, there is a growing trend towards repairing defective composite restorations instead of complete replacement. Due to absence of unpolymerized surface layer in aged composite restoration, several methods have been suggested to improve the composite-composite bond [6,7], such as surface roughening with diamond burs, acid etching or air abrasion with aluminum oxide particles. These surface treatments provide surface irregularities which promote micro-mechanical interlocking between the substrate surface and the repair resin. In earlier studies, promising results of composite repair were obtained using different protocols; these results were questionable as most tests were performed on non-aged substrates which didn’t represent the real clinical situation. They often depend on using the same type of composite for the substrate and the repair material [5,6,11]
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