PURPOSE: To evaluate the repair bond strength of a laboratory processed composite treated with hydrofluoric acid gels of different acid concentrations and for various etching times and repaired with a flowable composite. METHODS: 75 specimens of a laboratory composite (Targis) were prepared in a split metal mold and stored for 24 hours in an incubator at 37 degrees C and 100% relative humidity. The laboratory composite surfaces were then etched for 5, 10, 15, 30, and 60 seconds using three hydrofluoric acid concentrations (5%, 8%, and 9.5%). The repair composite (Tetric Flow) was light-cured in two increments for 40 seconds each in an inverted, truncated cone mold. Storage conditions of specimens before debonding were 24 hours at 37 degrees C and 100% relative humidity. Tensile bond strengths were determined using a testing machine at a crosshead speed of 0.5 mm/minute. A two-way ANOVA was used to determine significant differences. Failure sites were classified. The morphological aspects of the etched composite surfaces were evaluated qualitatively by scanning electron microscopy.

RESULTS: There were no differences in the repair bond strengths with respect to the three different acid concentrations or the five etching times tested. The minimum etching time to observe an etched pattern was at 60 seconds with the highest concentration of hydrofluoric acid (9.5%).