Design, formulation, and evaluation of isocyanatoacrylate copolymer dental adhesives

Biocompatible alkyl cyanoacrylates and their derivatives as bio-adhesives

Cyanoacrylate adhesives and their homologues have elicited interest over the past few decades owing to their applications in the biomedical sector, extending from tissue adhesives to scaffolds to implants to dental material and adhesives, because of their inherent biocompatibility and ability to polymerize solely with moisture, thanks to which they adhere to any substrate containing moisture such as the skin.

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 (delta delta) 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 < 0.001) with shear bond strength values. Crosslinker addition studies with IEM/4-META: (a) at 5-9 mol% reduced the setting time of IEM polymerization by 79%; and (b) at 6 mol% reduced initiator level requirements 60-70% to achieve a comparable setting time, and decreased setting times by ca. 75% for a given initiator level with selected IEM/methacrylate adhesive systems.

SIGNIFICANCE

The shear bond strengths of isocyanatomethacrylate-based dental adhesives can be enhanced by using reactive primers; their setting times and initiator requirements can be improved using a dimethacrylate crosslinker. Approximated permeability coefficients may be useful as indicators of bonding performance for dentin adhesive systems.