Interaction between GIC and S. sanguis biofilms: antibacterial properties and changes of surface hardness

The aim of this study was to investigate the interaction of Streptococcus sanguis with two glass-ionomer formulations (GIC:A containing fluoride and GIC:B without fluoride) with particular reference to bacterial growth and changes in hardness of the cement with respect to time.

Discs of two water activated glass-ionomer cements were prepared according to the manufacturer's instruction. Hydroxyapatite discs (HA) were used as controls. 3D laser scanning technique was used to characterize surface roughness and area of the substrate prior to growing biofilms. Surface hardness was evaluated before and after biofilm growth. A constant depth film fermenter system (CDFF) was used to grow S. sanguis biofilms on the specimens in a similar manner to that described previously by Wilson et al. in 1995. For susceptibility measurement, specimens were removed from CDFF aseptically over periods up to 14d after the first colonization with bacteria. Counts of viable bacterial in the accumulating biofilm layer on each surface were measured and converted to colony forming units per unit surface area. To determine the effect of storage media, hardness discs were exposed to distilled water, lactic acid pH 4, lactic acid pH 5, citric acid pH 5, artificial saliva and S. sanguis biofilms. Twenty-four hours after preparing and subsequent autoclaving, specimens were transferred to a vessel containing 40 ml storage medium. The specimens were investigated for periods up to 7d.

The viable counts of S. sanguis per mm2 on GIC:A were significantly less than those on HA and GIC:B during the first 5d (p<0.05). The viable counts of bacteria on the surface of GIC:B were lower during the initial 5d when compared to HA. Exposure of GIC:A and GIC:B to different medium produced softening to the surface of cement. It is apparent that the effects of the biofilms are significantly greater than storage in water but similar to storage in lactic acid pH 5.

This investigation showed that the growth of S. sanguis biofilms were significantly affected by both glass-ionomer formulations, the greater reduction being noted on the surface of the fluoride containing GIC. S. sanguis biofilms produced reduction on the surface hardness of the cement equivalent to that seen after immersion in lactic acid at pH 5. This indicates that while S. sanguis biofilm is affected by the GIC, there is also a decrease in hardness of the cement indicating some cement degradation.