N-phenyliminodiacetic acid as an etchant/primer for dentin bonding

Effective composite-to-dentin bonding has been achieved by the sequential use of dilute aqueous nitric acid (HNO3) and acetone solutions of N-phenylglycine and a carboxylic acid monomer, e.g., p-PMDM. Both the HNO3 pre-treatment and the surface-initiated polymerization that results from reaction of infused N-phenylglycine and PMDM have been identified as key elements of this bonding system. In this study, N-phenyliminodiacetic acid, a unique imino acid derivative with acidic and chelating potential, was evaluated as a dual etchant/primer for dentin bonding. A randomized, 2(3) factorial design was used to study the effects of 3 factors on tensile bond strength (TBS): conditioner (HNO3 vs. no HNO3), primer (N-phenylglycine vs. N-phenyliminodiacetic acid), and primer solvent (acetone vs. acetone:H2O). The three-step protocol consisting of HNO3, N-phenylglycine in acetone, and PMDM in acetone served as the control. The hypothesis tested was that N-phenyliminodiacetic acid could act as both an effective conditioner (i.e., etchant) and as a primer. Two-step protocols that included only N-phenyliminodiacetic acid and PMDM were compared with the control. TBS (n = 10 per group) were determined after 24-hour storage in H2O and analyzed by ANOVA and Duncan's Multiple Range test. Primer solvent was critical for obtaining significant bonding to dentin when HNO3 was omitted. N-phenyliminodiacetic acid in acetone without prior HNO3 etching gave the lowest ranking mean TBS (95% CI, 3.8 +/- 1.9 MPa). In contrast, the mean TBS obtained from samples treated with N-phenyliminodiacetic acid in acetone:H2O without prior HNO3 etching was not statistically different (p > 0.05) from the mean TBS for the control (95% CI, 9.3 +/- 1.8 and 9.8 +/- 1.9 MPa, respectively). Due to its dual function as etchant and primer, N-phenyliminodiacetic acid in acetone:H2O provides for a simplified bonding technique that yields strong, PMDM-mediated adhesion to dentin.