Modificação do flúido dentinário afeta a composição do biofilme formado sobre a superfície de lesão cariosa natural de esmalte

Abstract

According to the most influential view, there is a barrier of dentin sclerosis between the healthy dentin / pulp and the natural carious lesion of enamel, so that the dentinal fluid would negligibly affect the pores of the carious enamel and its surface. However, such a view is based on the aspect of the dentin under stereomicroscopy, which is ambiguous with respect to the dentin condition (healthy or carious), being open the possibility of the dentin fluid to affect the surface of the enamel and what is in contact with it. In this context, the objective of this in vitro study was to test the hypothesis that the type of enamel surface (healthy or naturally carious, with either chlorhexidine or NaCl in the underlying dentinal fluid) affects the single species biofilm composition. For this purpose, 10 crowns of human premolars were selected that presented two types of enamel surface (inactive natural enamel lesion, white spot lesion and ICDAS score 2, and normal enamel, ICDAS 0 score) on their proximal surfaces. Through three-dimensional computerized microtomography (microCT) analysis, teeth with cracks and / or incipient cavitated carious lesions were excluded. After removal of the pulp tissue, a single species biofilm (Streptococcos mutans) was formed on each type of enamel surface, the underlying dentin of which changed its dentin fluid. The paired groups were: (I) noncavitated inactive enamel carious lesion (ICDAS 2) with chlorhexidine solution in the pulp chamber (LECLX); (II) noncavitated inactive enamel carious lesion (ICDAS 2) with 0.9% sodium chloride solution in the pulp chamber (LECNACL); (III) normal enamel surface (ICDAS 0) with chlorhexidine solution in the pulp chamber (ENCLX); and (IV) normal enamel surface (ICDAS 0) with sodium chloride solution in the pulp chamber (ENNACL). After sterilization (with ethylene oxide) of the teeth, one of the liquids was inserted into the pulp chamber and a 5 day biofilm formation period was performed using TYE culture medium and sucrose. To ensure that the outcome was related only to the factor, in the LECLX and LECNACL groups the crown was isolated with nail varnish, so that only the lesion was exposed. Similarly, in the ENCLX and ENNACL groups only one region of the healthy enamel of equal size to that of the lesion was exposed and the remainder of the crown was isolated. After each biofilm formation period, the extracellular polysaccharides (PEC) were quantified. After the assays of all groups were completed, the samples were infiltrated in the pulp chamber with aqueous contrast solution (Thoulet solution with

xi refractive index of 1.47) for 24 h and submitted to microCT analysis. The results showed that the factor had an effect on the amount of both soluble PEC (repeated measures ANOVA: p <0.001, eta squared of 36.7%, power 97.8%) and insoluble PEC (repeated measures ANOVA: p <0.01; eta squared of 29.3%, power of 90.8%). As for the group paired analysis (paired T test): for soluble PECs, the LECLX group had the least amount (with a large effect size: Hedge G of 1.5 to 1.92; p <0.001; power > 90%), whereas the LENACL group had smaller amounts than the ENCLX and ENNACL groups, also with a large effect size (Hedge G of 1.2 to 1.3; p <0.05; power > 90%) and the normal enamel groups did not have a conclusive difference (51% power). For insoluble PEC, the results were similar, except that the LENACL and ENNACL groups had no conclusive difference. Through microCT the path of the contrast solution from the pulp chamber to the body of the enamel carious lesion was verified, not affecting the normal enamel. It was concluded that the modification of the dentin fluid altered the composition of the biofilm formed on the surface of the enamel, indicating the existence of a facilitated pathway between the pulp chamber and the natural enamel carious lesion, not affecting the normal enamel, with important implications on the pathogenesis and treatment of enamel caries.