Development of a novel antibacterial quaternary ammonium silane cavity disinfectant

Abstract

During cavity preparations, clinicians have used various disinfectant materials for removal of surface contaminants and biofilms from dentine structure. This thesis consists of studies which examined antimicrobial, cytotoxic, and protease inhibitory properties of a partially condensed Quaternary Ammonium Silane (QAS) cavity disinfectant. The effect of QAS disinfectant on dentine bond durability and nanoleakage of simplified etch-and-rinse adhesives will also be evaluated.

The current project was designed to answer five research questions. The first research question aimed to analyze whether there is antimicrobial efficacy and potency of QAS against Streptococcus mutans with a systematic review. In conclusion, QAS showed antimicrobial efficacy to eliminate Streptococcus mutans.

The effect on host-derived proteases in dentine was conducted to answer the second research question of this project. The percentage of dry mass loss, used as an indirect measurement of dissolution of demineralized dentine matrix by endogenous matrix-bound proteases, increased with time and was significantly lower in the chlorhexidine (CHX) and QAS groups when compared to the control at 14 days. The rate of C-terminal cross-linked telopeptides (ICTP) and C-terminal peptide (CTX) release used to measure degradation of demineralized collagen matrix was lower in the CHX and QAS groups, when compared to the uninhibited control at 7 and 14 days. Dentinal MMP-2 and cathepsin-K activities of CHX and QAS groups were significantly reduced after demineralized dentine was pretreated with QAS. Hence, QAS was shown to be a good inhibitor of MMP and cathepsin-K activities in demineralized dentine.

The third research question investigated the application of QAS on cariogenic biofilm formation and dentine substrate changes onto which multi-species biofilms have been grown using Raman spectroscopy. Confocal laser scanning microscopy showed confluent biofilms in the control group, but increased dead cell count in the QAS groups. Log CFU (single/dual-species) biofilms was lower in the QAS groups than the control. Metabolic activities of biofilms also decreased with increasing QAS exposure time. Increased Raman shifts were seen in functional and aromatic groups of dentine with CH2-1450-1455 cm-1 bending, responding to treatment with shifts at 1450 cm-1, 1453 cm-1, 1457 cm-1, 1460 cm-1 and 1462 cm-1 for the control, 2% CHX, 2%, 5% and 10% QAS specimens. Thus, QAS was shown to possess antimicrobial activities and inhibit the growth of cariogenic biofilms.

The fourth research question was to evaluate the transdentinal cytotoxicity and macrophage phenotype response to QAS. The 2% QAS does not have a cytotoxic effect on 3T3 NIH mouse fibroblast cells and its application is associated with a constructive remodeling effect on macrophages.

The purpose of the last research question was to evaluate whether the application of QAS cavity disinfectant has any effect on long-term dentine bond strength and nanoleakage expression of two simplified etch-and-rinse adhesives. At the end of 12 months, 2% QAS was shown to preserve dentine bond stability and reduce interfacial nanoleakage.

In conclusion, the use of 2% QAS cavity disinfectant preserved dentine bond strength and enhanced bond durability. The cavity disinfectant is not cytotoxic and showed both antibacterial as well as anti-protease properties. (498 words)