The shear bond strength of an immediate and delay repaired light-cure composite restoration (In vitro study)

Abstract

Background: Defects in composite resin restoration whether discovered at the time of placement or associated with old composite resin restoration could be repaired without replacing the entire restoration. This in vitro study was conducted to determine and compare the shear bond strength of an immediate and delay repaired light cured composite restoration. Materials and methods: Eighty acrylic blocks (25x25x15 mm) were constructed from cold cure acrylic resin; each one contained an acrylic hole (6mm diameter and 3mm depth) that filled with Helioprogress composite resin. The surface layer of the composite resin samples was light cured through plastic strip, abraded by finishing discs and rinsed with deionized distilled water for 15 sec. The eighty specimens were divided randomly into two groups according to the storage time in deionized distilled water before the repair: Group I: Stored for 15 min. (Immediate repair group) Group II: Stored for 1week. (Delay repair group) Both groups were subdivided into 4 subgroups according to the surface treatment they received: Subgroup 1: No surface treatment (control) Subgroup 2: 37% phosphoric acid etchant (15 sec.) Subgroup 3: Heliobond (light activated for 20 sec.) Subgroup 4: 37% phosphoric acid and Heliobond. Repair was done by using a standardized translucent plastic straw (3mm diameter and 6mm length) and was filled Helioprogress composite resin and light cured for 40 sec. in four directions. All the specimens were stored in deionized distilled water for 24 hr. testing was done by the Zwick testing machine by applying shearing force with specially designed chisel-shape rod. Data obtained were statistically analyzed using analysis of variance test and t-test. Results: The results showed very highly significant difference between the similar subgroups in group I vs. group II and there was non-significant difference between subgroup 1 vs. 2 and between subgroup 3 vs. 4. Conclusion: Delaying the repair procedure for 1 w resulted markedly reduced the bond strength, the surface treatment with 37% phosphoric acid slightly reduced the bond strength in the immediate repair while slightly increased it in the delay repair, Furthermore, the surface treatment with Heliobond fifth generation bonding agent markedly increased the bond strength in both repairs.