Abstract
It is conventionally taught that the carious lesion in dentin undermines the enamel due to lateral spread of the lesion at the enamel-dentin junction (EDJ). The aim of the present study was to challenge this hypothesis by testing an alternative hypothesis, that lateral spread is related to advanced lesions where the dentin is infected. Selected points in the groove-fossa system of 100 unrestored occlusal surfaces were examined and the teeth divided into five groups (scores 0-4) depending on the clinical appearance of the lesion. Teeth were sectioned through these sites and texture of the dentin was assessed by probing. Colour slides of the section face with the more extensive changes in the dentin were projected and the dimensions of the lesions at the EDJ were assessed by three examiners on two separate occasions. Inter- and intra-examiner reproducibility was assessed and found acceptable. Results showed that in 47 teeth demineralisation had not reached the EDJ. In the remaining teeth the presence or absence of lateral spread of the lesion at the EDJ was related to the clinical features of the lesion. Lateral spread was rarely found in lesions with an apparently intact enamel surface (scores 0-2). However, 32% of sites with microcavitation (score 3) and 63% of sites with obvious cavitation (score 4) showed lateral spread. Of those 31 sections which were judged to have soft dentin, 80% had lateral spread. In conclusion, the phenomenon of lateral spread of caries at the FDJ is related to advanced lesions with cavity formation where the dentin is soft and infected.