Streptococcus mutans biofilm formation on chlorhexidine-containing dentin bonding agents

Purpose: The aim of this study was to assess the influence of different chlorhexidine diacetate (CHX)-containing experimental and commercially available dentin bonding agents (DBAs) on in vitro Streptococcus mutans (SM) biofilm formation. The null hypothesis was that the tested CHX-containing DBAs had no effect on in vitro SM biofilm formation when compared to the neat DBA counterparts without CHX addition. Methods and materials: Specimens were prepared from the following DBAs: (1) Adper Scotchbond 1XT (SB1XT; 3M-ESPE); (2) SB1XT + 0.2% CHX (experimental version); (3) Peak LC Bond (Ultradent); (4) Peak Universal Bond (Ultradent; containing 0.2%CHX). A constant amount of uncured resin was dispensed from each DBA into a circular mould (6.4 mm × 1.5 mm); photo-activation was performed for 120 s at 800 mW/cm2 in a nitrogen atmosphere. A modified drip-flow reactor (MDFR) was used to culture SM on the surfaces of the samples and in vitro biofilm formation was evaluated after 24 h using the MTT assay. Two samples from each of the tested DBAs were coloured with fluorescent dyes (LIVE/DEAD) and observed using laser confocal microscopy (CLSM). Data were statistically analyzed according to one-way ANOVA model and Student post-hoc t-test with a significance level of p < 0.05. Results: The null hypothesis was rejected, since the effect of CHX addition was adhesive-dependent. SB1XT + CHX showed a significant increase in biofilm formation compared to its CHX-free counterpart (p < 0.0001); Peak Universal Bond showed significantly lower biofilm development when compared to Peak LC Bond (p = 0.0011). CLSM data showed that biofilms developed on the surfaces of SB1XT, SB1XT + CHX and Peak LC Bond provided an almost complete surface coverage with mostly live micro-organisms. Specimens of Peak Universal Bond exhibited low biofilm formation with a prevalence of red-stained (i.e. dead) micro-organisms. Conclusion: Within the tested experimental conditions, CHX addition to DBAs influences biofilm development depending on the DBA composition.