Novel priming and crosslinking systems for use with isocyanatomethacrylate dental adhesives

Objectives: (a) to design, formulate and evaluate prototype primers and a crosslinking agent for use with isocyanatomethacrylate-based comonomer adhesives and (b) to establish correlations between bond strength and solubility parameter differences between the adhesives and etched dentin, and the permeability coefficients of the adhesives. Methods: Equimolar mixtures of 2-isocyanatoethyl methacrylate (IEM) and a methacrylate comonomer were formulated with tri- n-butyl borane oxide (TBBO) as the free radical initiator to have cure times of 6–10 min. Shear bond strengths to dentin were determined for each adhesive mixture ( n=7) using standard testing protocols. Shear bond strengths for the three systems were also determined after application of “reactive primers” to the dentin surface. The “reactive primers” contained 10–20 parts by weight of the respective comonomer mixture and 3.5 parts by weight TBBO in acetone. Solubility parameters difference values (Δ δ) and permeability coefficients ( P) were approximated for each adhesive system and correlated with shear bond strength values. Additionally, a crosslinking agent was prepared by bulk reaction of an equimolar mixture containing IEM and a methacrylate comonomer. The effects of crosslinker addition on: (a) the setting time of IEM; and (b) the setting times and initiator requirements of selected IEM/comonomer mixtures were determined. Results: Shear bond strength values (MPa): IEM/HEMA 13.6±2.0 (no primer), 20.1±2.0 (with primer); IEM/HETMA 9.3±3.3 (no primer), 20.8±8.1 (with primer); IEM/AAEMA 13.6±1.9 (no primer), 17.3±3.2 (with primer). Also, approximated permeability coefficients showed a significant correlation ( r=+0.867, p