Effect of CPP-ACP application on flexural strength of bleached enamel and dentin complex

Controversy continues over the effects of bleaching treatments on tooth structures in the literature. In addition to tooth sensitivity, a number of studies have reported adverse effects of bleaching procedures on dental hard tissues, including decreased hardness, fracture toughness, flexural strength, and other changes in the mechanical properties. The purpose of this in vitro study was to investigate the effect of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) application on the flexural strength (FS) of bleached teeth.

One hundred twenty blocks (2 × 3 × 8 mm) were prepared from the middle portion of the facial surfaces of 120 sound bovine teeth. Specimens were randomly divided into six groups (n=20). Group 1 consisted of the control group, stored in distilled water at 37 °C. The experimental groups (2 to 6) were immersed in CPP-ACP (0.5 h/d for 14 days, twice daily), 9.5% hydrogen peroxide (HP) (0.5 h/d, twice daily for 14 days), 9.5% HP+CPP-ACP, 38% HP (1 h/d, twice weekly for 2 weeks), and 38% HP+CPP-ACP, respectively. Flexural strength test was performed 24 hours after the last treatment session using a universal testing machine with a crosshead speed of 0.5 mm/min. Results were analyzed by two-way analysis of variance (ANOVA) and a post hoc Tukey's test (á=0.05).

Mean ± SD values for FS were 179.50 ± 24.16, 194.00 ± 21.31, 155.25 ± 32.7, 177.50 ± 30.15, 158.50 ± 27.49, and 177.50 ± 28.09 MPa, respectively. Statistically significant differences were observed in FS values between groups (p<0.05). Tukey analysis showed that using CPP-ACP subsequent to both bleaching techniques has a significant effect on tooth flexural strength.

Simulated in-office or at-home bleaching regimens performed in the absence of saliva decrease the FS of tooth structure. Application of CPP-ACP subsequent to both bleaching regimens could compensate for the decreased FS of the bovine enamel-dentin complex in this environment.