Repairability of polyacid-modified composite resin.

The purpose of this study was to evaluate the effect of time and surface treatment on the resulting shear bond strength of a repaired polyacid-modified composite resin restorative material (VariGlass VLC). Seventy-two specimens of VariGlass were prepared in cavities (2 mm X 7 mm) cut into acrylic resin cylinders. The specimens were then divided into three groups of 24. For each of the three groups, 12 of the specimens were repaired 5 minutes after the cavities were initially filled, while 12 specimens were repaired 1 week after the initial fill. The VariGlass surfaces were treated in one of the following ways: no treatment; primer (30 seconds) and adhesive (light activated for 10 seconds); or 37% phosphoric acid etchant (30 seconds), primer (30 seconds), and adhesive (light activated for 10 seconds). Repairs were made using a split polytetrafluoroethylene mold (3 mm X 5 mm) mounted over the exposed VariGlass surface. After bonding a cylinder of VariGlass to the treated surfaces, the specimens were thermocycled 500 times (5 degrees C and 55 degrees C water baths), stored in distilled water for 1 week, and loaded to failure in shear at 0.5 mm/min. Data were analyzed using two-way ANOVA and a Student-Newman-Keuls multiple comparison test. Results indicated that the bond strength of specimens repaired at 5 minutes was significantly higher when no surface treatment was used prior to repair. Bond strength of specimens repaired at 1 week was unaffected by surface treatment. Time of repair significantly affected the no-treatment and the primer-adhesive groups.