Effect of 35% sodium ascorbate treatment on microtensile bond strength after nonvital bleaching

According to previous reports, adverse effects of tooth bleaching on bond strength can be reversed by delaying bonding for 1-3 weeks or by applying 10% sodium ascorbate (SA) for 3 hours or more. This study evaluated the effectiveness of the short-term application of 35% SA to counteract the effects of a 7-day 35% hydrogen peroxide (H2O2) bleaching regimen on bond strength.

Forty extracted third molars were mounted and sectioned to obtain a flat dentin surface and then randomly assigned into 4 groups: group 1: restored, no bleach; group 2: bleached, bonded immediately; group 3: bleached, treated with two 1- minute 35% SA applications before bonding; and group 4: bleached, treated with two 5-minute 35% SA applications before bonding. For bleach treatment in groups 2-4, flattened dentin surfaces were exposed to H2O2 for 7 days at 37°C. Subsequent to respective treatments, dentin surfaces were built up with composite (TPH3 and Prime &Bond NT, Dentsply Caulk, Milford, DE). After 24 hours of storage (100% humidity, 37°C), the specimens were sectioned into 1-mm(2) dentin-composite beams. Four beams from each tooth (n = 40/group) were subjected to microtensile bond strength testing.

Results were as follows: group 1: 18.1 ± 8.1MPa, group 2: 11.3 ± 5.7MPa, group 3: 11.2 ± 5.2MPa, and group 4: 12.6 ± 6.1MPa. A 1-factor analysis of variance and the Tukey post hoc test (α = 0.05) indicated that bleaching had a detrimental effect on bond strength and that short-term SA treatments after bleaching did not significantly improve bond strength.

The application of 35% SA in a clinically relevant timeframe was not effective at reversing bleaching effects on bond strength. Bonding procedures should be delayed following tooth bleaching.