Effect of Repair Gap Width on the Strength of Denture Repair: An In Vitro Comparative Study

To evaluate the effect of repair gap width on the flexural strength and impact strength of a repaired acrylic denture with and without thermal cycling.

A total of 240 heat-polymerized acrylic resin specimens were fabricated in dimensions of 65 × 10 × 2.5 ± 0.2 mm and 55 × 10 × 10 ± 0.2 mm for flexural strength and impact strength testing, respectively. All specimens were sectioned into halves then divided into 6 groups according to repair gap width (n = 10). The repair gap of the control group was 2.5 mm at the base, while the repair gaps of the test groups were prepared as 2.0, 1.5, 1.0, 0.5, and 0 mm at the base. All specimens were prepared with a 45° bevel joint. Each specimen was placed into the mold that retained the original length of the specimen and modified only the repair gap, which was packed with repair resin. After polymerization, specimens were finished and polished, and half of the specimens were thermal cycled for 5000 cycles. Three-point bending test and Charpy impact test were used to determine the flexural strength and impact strength, respectively. ANOVA and Tukey's HSD test were used for statistical analysis, where α was set at 0.05.

Decreasing repair gap significantly increased the flexural strength in comparison to control group (p < 0.05); 0.5-mm repair gap showed the highest flexural strength values. Changing the repair gap significantly increased the impact strength of groups 2.0- and 1.5-mm (p < 0.05). Thermal cycling significantly decreased the flexural strength of all tested groups as well as impact strength for groups with wide repair gaps (2.5-, 2.0-, and 1.5-mm) (p < 0.05), while other tested groups had nonsignificant effect on impact strength (p > 0.05).

Decreasing repair gap increased the flexural and impact strengths of repaired acrylic resin. A repair gap of 0-, 0.5-, or 1.0-mm with beveled repair surface is recommended to improve repair strength and overcome the drawbacks of increased amounts of autopolymerized repair resin.