Dental decay generally starts in areas that are not easily or normally cleaned.
Figure B shows primary areas of enamel decay, between the teeth and on the
chewing surface. Spread of decay in dentin is shown in figure C; note lateral
advancement as well as progression of decay toward the pulp. With pulpal
involvement, degenerative changes result in pathology within the pulp
chamber (figure D), resulting in eventual periapical granuloma or cyst
development (figure E).
Figure 1-1. Stages in the progress of dental caries.