Desenvolvimento de um modelo de biofilme para estudos de desmineralização do esmalte

Abstract

The aims of this study were to evaluate enamel demineralization response to cariogenic conditions induced by several sucrose regimens in microcosm biofilms, and to test the model with a dose-response evaluation to chlorhexidine. Microcosm biofilms derived from plaque enriched saliva were grown on bovine enamel discs in multi-well plates fed with defined medium enriched with mucin (DMM), which was supplemented with sucrose concentrations that ranged from 0.075% to 1%. Sucrose exposure occurred all day in batch culture or in a semi-continuous fed (40 min to 6h). Plates were incubated anaerobically for up to 10 days at 37°C. DMM was replaced daily. Data from acidogenicity of biofilms were collected as pH readings from medium supernatants and the percentual surface hardness change (%SHC) was obtained by enamel surface hardness readings before and after treatments. The results from sucrose regimens indicated that acidogenicity of biofilms affected, enamel surface hardness. Under low sucrose concentration exposures (batch- 0.075%) enamel hardness was not affected. Exposures to 0.15% sucrose were timedependent, as enamel surface experienced mineral loss in batch but not in semicontinuous (6 h) fed. With 0.5% sucrose concentration a time-dependent exposure effect was also observed in enamel hardness change.Exposures from 40 min to 3 h sucrose-fed (up to 10 days) did not caused significant %SHC in enamel, but increasing the exposure time to 6 h induced significant mineral loss. Under 0.5%- batch severe damage to enamel surface was noted, irrespective of the time-points evaluated (4, 7 and 10 days). The resulting eroded surfaces excluded the possibility of SH evaluation, and suggested that the constant low pH (4.3) would promote erosion lesions instead of subsurface carious lesions. Exposures to 0.5% and 1% in 6 h sucrose-fed induced significant %SHC in enamel. The dose-response evaluation was performed in one regimen - semi-continuous 1% sucrose. After 24h of grown, biofilms were treated with chlorhexidine in concentrations that ranged from 0.012 to 0.12% or a control (sterile saline solution) during 1 min. Treatment was applied before sucrose-fed for 3 days. Biofilm acidogenicity and the changes in enamel hardness were dose-responsive to chlorhexidine treatments. In conclusion, within the limitations of laboratorial studies the biofilm model assessed promoted doseresponse effect to chlorhexidine and to different sucrose feeding protocols, being suitable as a pre-clinical model for testing the anticariogenic potential of treatments and for demineralization studies