Effect of chlorhexidine on conversion of resins of different hydrophilicities

Objective: The use of chlorhexidine diacetate (CHX) as therapeutic primer has been reported to stabilize the adhesive interface over time. This study examined the effect of CHX content on degree of conversion (DC) of experimental adhesive blends using differential scanning calorimetry (DSC). The hypothesis tested was that DC of resin blends is affected by CHX content in relation to adhesive hydrophilicity.

Methods: Light-curing experimental adhesive blends with increasing hydrophilicity and different CHX concentrations were analyzed: R2 (70% bisGMA, 28.75% TEGDMA); R2+1%CHX; R3 (70% BisGMA, 28.75% HEMA); R3+1%CHX; R3+5%CHX; R3+10%CHX; R4 (40% BisGMA, 30% TCDM, 28.75% TEGDMA); R4+1%CHX; R4+5%CHX; R4+10%CHX; R5 (40% BisGMA, 30% BisMP, 28.75% HEMA); R5+1%CHX; R5+5%CHX; R5+10%CHX. All blends included 1% EDMAB and 0.25% CQ. CHX in higher percentages than 1% could not be dissolved in R2. The resins/chlorhexidine mixtures were placed in a DSC chamber and polymerized at 35°C under a nitrogen atmosphere using a quartz-halogen output (600mW/cm2). DC was calculated by knowing resin compositions and related to chlorhexidine percentage and time of curing. Data were analyzed with three-way ANOVA (resin type; CHX concentration; time of curing) and Tuckey's post hoc test.

Results: DSC exotherms showed that DC was influenced by resin type, CHX content and time of curing (p<.05). DC of R3 didn't show significant differences when 1% chlorhexidine was added, while it decreased for higher CHX concentrations (p<.05) R4 and R5 showed higher DC than neat counterparts for all tested CHX concentrations (p<.05). R4 showed the highest DC among all resins. Prolonged polymerization time increased DC.

Conclusions: CHX affects DC of adhesive blends in relation to their hydrophilicity: hydrophobic resins DC decreased in presence of high percentages of CHX, hydrophilic resins DC increased when CHX was added. In conclusion CHX dissolved in resin blends affected the DC depending on its concentration and resin type.