Bond Strength of a Self-etching Universal Adhesive System to Eroded Enamel and Dentin

Objectives: The aim of this study was to evaluate the influence of previous acid etching on bond strength of a self-etching universal adhesive system on sound and eroded enamel and dentin.
Methods: Bovine incisors were embedded in acrylic resin and ground until obtainment of flat enamel (n=44) and dentin (n=44) surfaces. Specimens were divided into two groups (n=22), according to the exposure to erosive conditions: sound (without erosion) and eroded (after erosive challenge). The erosive challenge consisted in the immersion of enamel in 0.3% citric acid (pH 2.6), 5 min each, 4x/day, 5 days. Each group was then divided into two subgroups (n=11), according to the application of 37% phosphoric acid (30s on enamel and 15s on dentin) on specimens’ surface before universal self-etching adhesive application (with and without previous acid etching). The adhesive system Scotchbond Universal (3M/ESPE) was applied according to manufacturer’s instructions and composite blocks were built up using Amelogen Plus composite resin (Ultradent). Sticks (1x1mm) were obtained and the bond strength was assessed with microtensile test, using a Universal Testing Machine at a speed of 1mm/min. Data were analyzed with two-way ANOVA and Tukey’s tests (p<0.05).
Results: For enamel groups, both erosive challenge (p=0.0340) and acid pretreatment (p=0.0476) factors significantly affected bond strength, but not the interaction between factors (p=0.18232). The means±SD(MPa) and results of Tukey’s test for erosive factor were: Sound- 25.02±5.82a, Eroded- 28.45±5.91b; and for acid factor were: Without- 24.89±5.39a, With- 28.58±6.23b (different letters mean significant difference). For dentin, both erosive challenge (p=0.9368) and acid pretreatment (p=0.0842) factors, as well as their interaction (p=0,1073), did not affect the bond strength.
Conclusions: The erosive challenge and previous acid etching significantly increased the bond strength of the universal adhesive tested to enamel substrate, but not to dentin.