10-MDP-based dentin bonding systems: why is chlorhexidine not worth to be used adjunctively?

The introduction of 10-methacryloyloxy-decyl-dihydrogen phosphate (10-MDP) has advanced the use of self-etching dentin bonding systems (DBS). For these cases, their use associated with chlorhexidine (CHX) to reach a long-lasting performance still was uncertain. The aim of this study was to determine the role of 2% CHX digluconate in combination with MDP-based DBS in terms of degree of conversion (DC) and bond strength (BS). Five DBSs were tested: Clearfil SE Bond-CSE, Clearfil Protect Bond-CPB, Adper Scotchbond Universal-SU were compared with MDP-free DBSs, Adper Single Bond2-SB2 and Adper Scotchbond Multipurpose-MP. For DC, a drop of each DBS (n = 6), mixed or not with 2% CHX was assessed. For BS, 100 human third molars were divided into the 5 groups (n = 20). Half of the teeth were treated with water and the other half with 2% CHX. Data was analyzed using two-way and three-way ANOVA, respectively, for DC and BS, and Tukey tests, in which DBS and CHX were significant factors for both tests. Regarding DC, CHX significantly affected MP and CSE. For BS, CHX impaired the performance of SU. Conclusions: CHX affected both the DC and BS of MDP-based and MDP-free DBS due to different mechanisms. For MDP-based systems, it was clearly impaired. Therefore, it can be concluded that MDP-based systems may compete with CHX for dentin calcium and its interaction may early impair their bonding properties.