Photoactivated dentin bonding with N-phenyliminodiacetic acid

The overall objective of this study was to correlate adhesive resin and polymerization initiator chemistry with bonding to dentin that had been treated with N-phenyliminodiacetic acid (PIDAA), a self-etching primer with initiator and co-initiator potential. The hypotheses to be tested were that: (1) the nature of the adhesive resin and (2) the type of polymerization initiator system are critical factors that can influence the bonding of composite restoratives to dentin.

Three types of bonding resins: (A) a non-carboxylic acid bonding resin (BisGMA/HEMA); (B) a carboxylic acid monomer (PMDM, the control); and (C) a combination system (BisGMA/HEMA/PMDM), along with two types of initiator systems: (1) a self-curing chemical initiator system based on PIDAA and (2) a dual-cure system involving camphorquinone, PIDAA, and visible light irradiation, were tested with a randomized 3 x 2 full factorial design. Solutions of each resin in acetone were tested with and without camphorquinone. Solution (A) was a 50% solution of 1:1 BisGMA/HEMA; Solution (B), a 10% solution of PMDM; and Solution (C), a 50% solution of 2:2:1 BisGMA/HEMA/PMDM in the ratio of 2:2:1. All percents were on a mass basis. (The photoactivated solutions of A, B, and C also contained 0.5% camphorquinone based on the mass of the resin.) Ninety composite-to-dentin specimens were prepared by a 2-step protocol: 1) 60 s application of 20 microL of 0.3 mol/L PIDAA in 1:1 v/v acetone/H2O; 2) 60 s application of 20 microL of one of the six resin solutions, followed by 60 s visible light irradiation. A visible light-activated composite (Silux, 3M) was then applied to each treated surface and irradiated for 60 s. Specimens were stored in distilled H2O (22 degrees C, 24 h) before shear bond testing. The summary statistics were calculated and a two-way ANOVA and Duncan's Multiple Range test were used to discern if the two factors significantly affected the mean shear bond strength.

Mean shear bond strengths and standard deviations were obtained (with and without camphorquinone, respectively): (A), 11.0 MPa +/- 3.9 and 4.1 MPa +/- 4.9; (B), 27.0 MPa +/- 5.3 and 13.7 MPa +/- 5.6; (C), 18.3 MPa +/- 5.3 and 7.0 MPa +/- 5.2. The use of camphorquinone significantly enhanced the mean shear bond strengths obtained with the carboxylic, non-carboxylic and combination monomer based adhesive systems (p < 0.0001). For PIDAA-treated dentin, moderate shear bond strengths were obtained with a non-carboxylic acid resin solution containing camphorquinone. The addition of both PMDM and camphorquinone to this resin further improved the shear bond strengths. The highest mean shear bond strength was obtained with the combination of PMDM and camphorquinone (p < 0.05).

These results suggest that formulations based on PIDAA, PMDM and camphorquinone are more effective as bonding systems than those formulations without PMDM and camphorquinone. PIDAA, a self-etching primer with initiator and co-initiator abilities, appears to interact positively with both carboxylic acid monomers such as PMDM and the photooxidant camphorquinone.