Matrix metalloproteinases (MMPs) bound to dentin have been thought to contribute to the progressive degradation of collagen fibrils in hybrid layers. Inhibition of host-derived MMPs may slow the degradation over time. Chlorhexidine (CHX) has been shown to have an anti-MMP activity and contains two cationic quaternary ammonium groups which seems to be responsible for this activity. However, CHX is water soluble which might compromise the long term effect.

Objectives : This study evaluated the effect of six different commercially available quaternary ammonium methacrylates (QAMs), CHX or artifical saliva (AS) immersion on the modulus of elasticity (E), dry mass loss and release of solubilized collagen from demineralized dentin beams.

Methods : Dentin beams (1 mm × 2 mm × 6.0 mm) were completely demineralized in 10% phosphoric acid. After baseline measurements of dry mass and E (3 point bending, 15% strain), beams were divided into 8 groups ( n = 10): 0.2 wt% CHX; 0.2 wt% QAM-1, 30 wt% QAM-2, 30 wt% QAM-3, 30 wt% QAM-4, 30 wt% QAM-5, 30 wt% QAM-6 all in AS, and AS only (control). Beams were incubated in their respective solutions in a shaking bath at 37 °C for 30 d and retested. The incubation media was hydrolized to amino acids to permit quantitation of hydroxyproline (HOP) for solubilized dentin collagen. Data were statistically analyzed using ANOVA and Tukey HSD tests ( p < 0.05).

Results : The beams incubated in AS only showed 35% decrease in E, a 32% decrease in dry mass ( p < 0.05). The groups incubated with experimental QAMs or CHX showed either slight increases or decreases in E, however, no significant change was observed ( p > 0.05). The dry mass loss followed the same trend ranging from 0.2% to 5% among experimental QAMs or CHX. Significantly more solubilized collagen was detected from AS group ( p < 0.05) compared to the other test mediums.

Conclusions : The use of experimental QAMs showed comparable inhibition of dentin MMP activity to CHX and might increase the durability of resin dentin bonds.

Supported, in part, by ROI DE051306 from the NIDCR and by Academy of Finland.

• QAM-1: [3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxypropyl]trimethyl ammonium chloride,

• QAM-2: Methacryloyloxyethyltrimethyl ammonium chloride,

• QAM-3: Methacryloylcholine methyl sulfate,

• QAM-4: [3-(Methacryloylamino)propyl]trimethylammonium chloride,

• QAM-5: Diallyldimethyl ammonium chloride,

• QAM-6: 2-Acryloxyethyltrimethyl ammonium chloride.