The use of tannic acid increases dentin bond strength

Dentin collagen is a main component of the hybrid layer and its strength may have a great impact on the properties of adhesive interfaces.  Objectives: To evaluate the effect of tannic acid, a collagen cross-linking agent, on the tensile bond strength (TBS) of a total-etch adhesive system.

Methods: Fifteen human molars were polished until occlusal dentin was exposed and were randomly divided according to the surface treatment: G1 - control (no treatment); G2 - 20% tannic acid (pH: 2.8) and G3 - 20% tannic acid (pH: 7.2). Samples from G1 were etched with 37% Phosphoric acid, rinsed, blotted dried, One-Step Plus (Bisco) applied and composite resin used to build-up a “crown”. G2 and G3 were treated in the same manner, except that after etching, tannic acid was applied on the surface for 1 hour. After 24 hours, samples were sectioned into 0.8 x 0.8 mm beams and tested in tensile at a crosshead speed of 1mm/min using a universal testing machine.  Data were statistically analyzed using ANOVA and Fisher's PLSD tests (p< 0.05). 

Results: TBS values [MPa (SD)] are as follow:

Treatment	Control (no treatment)	20% Tannic Acid (pH: 2.8)	20% Tannic Acid (pH: 7.2)
Bond Strength (MPa)	54.11 B (14.21)	66.71 A (8.07)	63.17 A (9.36)
* Different letters indicate statistically significant differences.

Treatment of the surface with 20% tannic acid resulted in statistically significant increase in the TBS values when compared to a control group. The formulation of Tannic acid using different pH did no significantly affect the bond strength.

Conclusions: The presence of exogenous collagen cross-links on demineralized dentin induced by 20% tannic acid treatment resulted in improved bond strength values of a total-etch adhesive system. Supported by NIH-NIDCR #DE017740.