Impregnation with antimicrobials challenge bonding properties and water sorption behaviour of an acrylic liner.

To investigate the effect of impregnation of poly(ethyl methacrylate) and tetrahydro-furfuryl methacrylate (PEM/THFM) polymeric delivery system with chlorhexidine or fluconazole on its shear bond strength (SBS) and water sorption. For SBS testing, 16 PEM/THFM discs impregnated with chlorhexidine (CHX), pure fluconazole (FLUp) or fluconazole from capsules (FLUc) and 16 drug-free control discs were prepared and bonded to heat-cured acrylic blocks. All discs were allowed to set for 24h at room temperature. After setting, half the discs (n=8) were tested immediately (Group 1). The other half was further incubated in water for 28 days at 37 °C before testing (Group 2). To evaluate water uptake, five PEM/THFM discs impregnated with CHX, FLUp or FLUc and five drug-free control discs were prepared and incubated in water. Mass changes were measured up to six months. The mean SBS for control, FLUp, CHX and FLUc discs were 4.01, 3.85, 3.29 and 2.26 MPa, respectively for Group 1. Group 2 showed significantly lower SBS (P≤0.05). All failures were adhesive. The percentage mass change due to water sorption ranged significantly from 12% for control to 27% for FLUc (P≤0.05). A strong negative correlation between the extent of water absorption and the SBS was detected (R=0.94, P=0.05). Impregnation with antimicrobials presents a challenge to the physical and mechanical properties of a polymer. However, despite increased water uptake SBS remained acceptable for a temporary lining material and comparable to drug-free long-term lining materials. Moreover, the enhanced water uptake could contribute to improved leaching.