Odontoblast layer structure alteration as a response to carious lesions

Background: Dental caries is a bacterial disease affecting the hard tissue of the teeth as well as the pulp. The human dental pulp consists of odontoblast which are organized as a densely packed cell layer. Odontoblasts is located at the periphery of the pulp; therefore, they are the first cells encountered by cariogenic bacteria and their products that are represented in the carious lesion. Purpose: This study aimed to elucidate the effect of cariogenic bacteria to odontoblasts of human teeth. Methods: Five intact third molars and 15 third molars with occlusal caries at various stages of decay were extracted because of orthodontic or therapeutic reasons. The tooth specimens were fixed, decalcified with 10% EDTA solution (pH 7.4), and embedded in paraffin. Serial sections of 5 μm thickness were cut and stained with haematoxylin eosin and Gram’s, in addition to nestin immunohistochemistry. The specimens were then examined under light microscopy. Results: In normal teeth, odontoblast layer were aligned along the pulp chamber showing normal morphology of the cells. Slight disorganization of odontoblast layer was seen in the cases of carious lesions confined to enamel. In the cases of carious lesions confined to dentin, odontoblast layer was not observed in the areas subjacent to the lesions, only single cells showing flattened cell morphology were found. Odontoblasts beneath the lesion suffered severe damage and diminished nestin immunoreaction were observed in all cases of carious lesions with pulp exposure. Conclusion: Cariogenic bacteria invasion may damage the odontoblasts by affecting the morphology and vitality of the cells. The severity of the damage of the odontoblasts may increase as the bacterial invasion progresses toward the pulp.