Short Exposure to 1% Hydrofluoric Acid to Improve the Repair Bond Strength of Dental Resin Composites

Application of 1% hydrofluoric acid (HFA) to improve the repair bond strength of a microhybrid (Z250; 3M/ESPE) and a nanofilled dental composite (Supreme XT, 3M/ESPE) was investigated. Aged composites were etched using 1% HFA for 10, 30, or 60 s. Negative (non-etched) and positive (10% HFA for 60 s) control groups were tested. The surfaces received a layer of a silane and adhesive (Single Bond 2; 3M/ESPE). Cylinders of fresh composite (n = 15 per group) were built up and a shear bond strength test was carried out after water storage for 24 hr or 6 months. Surface topography was assessed using atomic force microscopy (AFM). For the nanofill at 24 hr, all etching regimens yielded higher bond strengths than the negative control. After 6 months, the negative and positive controls showed lower bond strength than 1% HFA for 30 s. For the microhybrid, the negative control generally showed lower bond strength at 24 hr, while all groups had similar results after 6 months. Only the positive controls showed lower bond strengths after 6 months. AFM analysis showed that the nanofill was more susceptible to acid-etch roughening. In conclusion, exposure to 1% HFA may improve the repair bond strength of dental composites.