Transdentinal cytotoxic effects of different concentrations of chlorhexidine gel applied on acid-conditioned dentin substrate.

It has been demonstrated that chlorhexidine digluconate (CHX) is capable of eliminating bacteria that may remain lodged in dentin after mechanical caries removal. In addition, the use of CHX on acid-etched dentin before adhesive system application delays the resin-dentin interface degradation, maintaining the integrity of the adhesive restorations. Despite these advantages of using CHX in restorative dentistry, when applied on dentin, this chemical agent may diffuse across dentinal tubules to cause toxic effects to the pulp cells. The aim of this study was to evaluate the transdentinal cytotoxic effects caused by different concentrations of CHX gels applied on acid-conditioned dentin substrate. Dentin discs (0.2-mm and 0.5-mm thick) were cut from human third molars and mounted in artificial pulp chambers. Odontoblast-like MDPC-23 cells (50,000 cells/cm(2)) were seeded on the pulpal side of the discs, and the carbon polymer gel (natrosol) with different CHX concentrations (0.12, 0.2, 1, and 2%), 35% phosphoric acid, or pure natrosol were applied on the occlusal side of the discs, forming six treatment groups (n = 10 discs/thickness). The dentin discs in the control group (n = 10 discs/thickness) did not receive any treatment. In each group, cell metabolism was analyzed by the methyltetrazolium assay (n = 8/thickness), and cell morphology was assessed by scanning electron microscopy (n = 2/thickness). Statistical analysis showed that CHX gels had a dose-dependent toxic effect on the odontoblast-like cells. Cell metabolism decreased by 12.8, 14.6, 18.3, 26, 13.7, and 10.5% for the 0.5-mm-thick dentin discs and 23, 26.3, 28.1, 34.5, 22.5, and 19.4% for the 0.2-mm-thick dentin discs treated with 0.12% CHX, 0.2% CHX, 1% CHX, 2% CHX, H(3)PO(4), and pure natrosol, respectively. According to the experimental conditions of the current investigation, it may be concluded that the application of natrosol gel with different concentrations of CHX on acid-conditioned dentin causes mild transdentinal cytotoxic effects to the MDPC-23 cells in a dose-dependent manner. Dentin acted as a biological barrier against CHX diffusion, and this effect was directly related to dentin thickness.