Effect of anaerobic or/and microaerophilic atmosphere on microcosm biofilm formation and tooth demineralization

Abstract

Objective: Microcosm biofilms can reproduce the complexity of a dental biofilm. However, different forms of cultivation have been used. The impact of the culture atmosphere on the development of microcosm biofilms and their potential to cause tooth demineralization has not yet been deeply studied. This study analyzes the effects of three experimental cultivation models (microaerophile vs. anaerobiosis vs. experimental mixed) on the colony-forming units (CFU) of the cariogenic microorganisms and tooth demineralization.

Methodology: 90 bovine enamel and 90 dentin specimens were distributed into different atmospheres: 1) microaerophilia (5 days, 5% CO2); 2) anaerobiosis (5 days, jar); 3) mixed (2 days microaerophilia and 3 days anaerobiosis), which were treated with 0.12% chlorhexidine (positive control - CHX) or Phosphate-Buffered Saline (negative control - PBS) (n=15). Human saliva and McBain's saliva containing 0.2% sucrose were used for microcosm biofilm formation, for 5 days. From the second day to the end of the experiment, the specimens were treated with CHX or PBS (1x1 min/day). Colony-forming units (CFU) were counted, and tooth demineralization was analyzed using transverse microradiography (TMR). Data were subjected to two-way ANOVA and Tukey's or Sidak's test (p<0.05).

Results: CHX was able to reduce total microorganism's CFU compared to PBS (differences of 0.3-1.48 log10 CFU/mL), except for anaerobiosis and microaerophilia in enamel and dentin biofilm, respectively. In the case of dentin, no effect of CHX on Lactobacillus spp. was observed. CHX significantly reduced enamel demineralization compared to PBS (78% and 22% reductions for enamel and dentin, respectively). Enamel mineral loss did not differ when compared with the other atmospheres; however, the enamel lesion depth was greater under anaerobiosis. Dentin mineral loss was lower under anaerobiosis when compared with the other atmospheres.

Conclusion: The type of atmosphere has, in general, little influence on the cariogenic ability of the microcosm biofilm.

Figure 1. Transverse microradiography representative pictures (20×) of an enamel specimen from each group: Microaerophilia; Anaerobiosis; Mixed, after treatment with Chlorhexidine (CHX) or PBS. The arrows show the lesion area. Specimens belonging to PBS showed cavitation, regardless of the atmosphere. Specimens treated with CHX showed shallow lesion

Figure 2. Transverse microradiography representative pictures (20×) of a dentin specimen from each group: Microaerophilia; Anaerobiosis; Mixed, after treatment with Chlorhexidine (CHX) or PBS. The arrows show the lesion area. Mixed-PBS was the only one not showing some cavitation of the dentin lesion