Efeito do material endodôntico na cariogenicidade do biofilme formado in vitro sobre lesões iniciais de cárie radicular natural

Abstract

Currently, it is believed that a dentine sclerosis barrier exits subjacent to initial natural root caries lesions (IRC), making it difficult the transport of materials from the pulp to the IRC. However, this view is based on two-dimensional analyzes that do not take into account the entire dentinal volume underlying IRC. In addition, there are evidences indicating a facilitated transport pathway between the pulp chamber and the IRC surface. In this context, the aim of this in vitro study was to test a hypothesis that the composition of the endodontic material (irrigating solution with chlorhexidine) affects the cariogenicity of S.mutans biofilm formed on IRC surface in endodontically treated teeth. Three studies (with paired samples) were performed: (1) intracanal application of 2% chlorhexidine irrigating solution (n = 8; G1: IRC and G2: sound root surface); (2) intracanal application of irrigating solutions with different chlorhexidine concentrations (0.0%; 0.25%; 0.5%) (n = 24; surfaces with IRC); and (3) application of radiographic contrast solution for 24 h, either on the IRC surface and in the pulp chamber at two distinct moments (n = 8). All teeth were human anterior permanent uniradicular teeth with single root canal presenting both sound (control) and IRC (experimental) surfaces (as selected by a calibrated examiner: Kappa 0.97). Computed microtomography (microCT) analysis excluded teeth with cracked or fractured roots, internal root resorption and cavitated root carious lesion. Occlusal access to the pulp chamber, root canal instrumentation, and occlusal restoration with composite resin were performed on all teeth, and then the teeth were sterilized with ethylene oxide. Subsequently, the teeth were subjected for 5 days to Streptococcus mutans UA159 biofilm formation on the root surface (control or experimental), while other root areas were protected by acid-resistant varnish. After each biofilm formation period, colony forming units (CFUs), soluble extracellular polysaccharides (PECs) and insoluble polysaccharides (PECi) were quantified. For study 3, each tooth received application of an aqueous radiographic contrast solution for 24 h, either applied on the IRC surface or in the pulp chamber, and then submitted to histopathological analysis under MicroCT. The results showed that, in study 1, the biofilms formed on IRC presented lower cariogenicity based on all parameters: CFU (p <0.0001; Hedge g = -5.3; 95% CI = -7.8 / -2, 8), PECs (p <0.0001; Hedge g = -1.51; 95% CI = -2.8 / -0.17), and PECi (p <0.0001; Hedge g = 1.80 95% CI = -3.2 / -0.4). The chlorhexidine concentration in the intracanal irrigating solution was negatively correlated with the UFC amount formed on IRC surface (p = 0.0068; R = -0.537; 95% CI = -0.17 / -0, 77; power = 87.3%). All lesions in study 3 presented a facilitated path between surface and root canal, regardless the contrast solution application site. We conclude that the chlorhexidine irrigation solution applied in the root canal negatively affected the cariogenicity of the S. mutans biofilm formed on the IRC surface due to a facilitated transport pathway between the root canal and the IRC.