Collagen crosslinking Additives in Dental Adhesives

Objectives: Collagen crosslinkers improve bond strengths to dentin. So far, relatively long application times have been used to ensure substantivity. This study aims at elucidating the effectiveness of crosslinkers added directly to the adhesive.

Methods: BisGMA/HEMA (2-Hydroxyethyl methacrylate) (60/40mol%) were mixed with camphorquinone/EDMAB (0.2/0.8wt%), and 40wt% ethanol. Riboflavin (B2), grape seed extract (GSE) and chitosan (CHT) were added at 0 (control) 0.05, 0.1, 0.25, 0.5, 1.0 or 2.0wt%. Crosslinkers were also added at 0 (control) or 1wt% to one commercial adhesive (Adper Single Bond). A QTH light (600mW/cm²x40s) was used for all experiments. Degree of conversion (near IR, 6165cm^-1) and flexural strength/modulus (FM, GPa, 3-point bending, stored dry or in distilled water for 7 days) were evaluated. Caries-free human teeth with exposed occlusal dentin were restored with each adhesive (n=5) and Filtek Z250, stored in water (37°C/24h), then sectioned in 1x1 mm sticks for microtenstile bond strength (MTBS) testing (1mm/min). Results were analyzed with one-way ANOVA/Tukey's test (α=5%).

Results: FM (dry or wet) was not affected by the crosslinkers up to 1.0% concentration. Above that, FM significantly decreased for all crosslinkers, except for CHT, possibly due to light attenuation in B2/GSE groups. Conversion was only reduced for B2 at 1 or 2wt%. For materials formulated with BisGMA/HEMA, the addition of crosslinkers did not affect MTBS in comparison to the control, for every concentration. When added to the commercial adhesive at 1%, MTBS was statistically higher than the control for CHT.

Conclusions: Even though, in general, conversion and mechanical properties were not affected by the presence of crosslinkers up to a concentration of 1%, MTBS did not improve in the experimental materials. However, the addition of chitosan at 1% directly to the commercial etch-and-rinse adhesive statistically improved MTBS. Further studies will evaluate crosslinkers added directly to other classes of commercial adhesives.