Abstract
This study investigates the repair bond strength of aged resin composites after removing different thicknesses, determine the repair performance using the same or different resin composites and describe the treated surfaces after ageing. Seventy simulated class I cavities were prepared in extracted human third molars were randomly divided into two groups and restored with a nanofilled (Filtek Z350) or a microhybrid (Clearfil APX) composite. Five specimens without ageing in each group acted as a positive control for microtensile bond strength (MTBS) test. After thermocycling, each group was randomly divided into two subgroups: Group RT1, 1 mm removed and Group RT3, 3 mm removed, followed by roughening. Ten specimens in each subgroup were repaired with the same or different composites, and MTBS tests were conducted. The surface roughness (Sa), and water contact angle of the remaining five specimens in each subgroup were measured. In every combination group, Group RT3 showed significantly higher MTBS values than Group RT1, and identical composite was not compulsory for higher repair bond strength. Removal thickness had no significant effect on the Sa in same composite group. In both the Z350 and APX groups, the water contact angle decreased with increasing removal thickness.
Highlights
Resin composites are extensively used in the treatment of dental defects because of their excellent aesthetic properties and physical properties
Brosh et al indicated that the repair bond between the original and newly added resin composite could be influenced by chemical and mechanical mechanisms: reaction with the surface resin matrix and exposed inorganic fillers could account for chemical bonding and macro/micromechanical attachment could account for mechanical bonding (Loomans et al, 2011; Pilo et al, 2016), when we repair the aged resin composites that had defects, such as fracture defects, discolouration, treatments are needed to create a surface for better adhesive between aged composite substrate and newly added composite
Three-way analysis of variance (ANOVA) revealed that the aged resin composite factor (F 9.130, p 0.003) and removal thickness (F 346.419, p 0.000) factor had significant impacts on the microtensile bond strength (MTBS) value
Summary
Resin composites are extensively used in the treatment of dental defects because of their excellent aesthetic properties and physical properties. Kanzow and Wiegand’s retrospective study indicated that among repaired restorations, the rate of Dental Resin Repair Removal Thickness failure of the repaired part was still higher than that of the remaining parts of the original restoration (Kanzow and Wiegand, 2020) It has been widely investigated inin vitro studies that an increase in roughness of the aged composite surface through etching, air abrasion, polishing, and laser irradiation results in a considerable improvement in the bond strength (Barcellos et al, 2015; Valente et al, 2015; Yokokawa et al, 2015; Pilo et al, 2016; Nagano et al, 2018; Flury et al, 2019; Kanzow et al, 2019; Martos et al, 2019). The interface between the aged resin composite and the new repair part may be still the weakest link in the assembly (Valente et al, 2016), and a gold standard for the treatment of aged resin composites is absent
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