Use of Hydroxy Acids for Etching: Dentin Adhesion and Collagen Degradation

Objectives: To test the use of hydroxy acids in the bonding procedure as alternatives to the aggressive phosphoric acid etchant.
Methods: Mid-coronal dentin surface of intact human molars was flattened with a carbide bur and etched with 35% phosphoric acid, glycolic acid, tartaric acid, gluconic acid, or gluconolactone for 15 sec (N=8/per group). OptiBond FL adhesive was applied to the dentin surface and teeth were restored with 5mm of resin composite (Filtek Supreme Ultra) applied incrementally and light-cured. Dumbbell-shaped resin-dentin beams were prepared and evaluated under the microtensile bond strength method. Failure pattern was recorded and classified in adhesive, cohesive in composite, cohesive in dentin or mixed. Collagen degradation was indirectly assessed by percent dry weight loss of dentin completely demineralized with the different etchants (n=10 per group; size: 6 x 2 x 1mm) after storage in incubation media at 37°C for 30 days. Mineralized beams were used as negative control. Statistical analysis was performed by one-way ANOVA and post-hoc Tukey-Kramer tests (α=0.05).
Results: The highest mean bond strength was observed for tartaric acid (57.03 MPa), with no statistically significant differences (p>0.05) to glycolic acid (52.77 MPa), phosphoric acid (50.69 MPa), and gluconic (49.03 MPa) acids. Demineralization with gluconolactone (39.22 MPa) resulted in bond strength significantly lower than tartaric acid (p = 0.0133). Tartaric acid and gluconolactone etching resulted mainly in dentin and adhesive failures, respectively. Significant lower collagen degradation was observed for gluconolactone (2.28%) and gluconic acid (0.46%), while phosphoric acid (-13.79%) resulted in statistically significant higher collagen degradation when compared to other acids (p<0.05).
Conclusions: Use of glycolic and gluconic acids resulted in adequate bond strength to dentin and reduced collagen degradation. Both acids are potential alternative etchants to phosphoric acid in the bonding procedures.