The Structure of Surface Enamel with Special Reference to Occlusal Surfaces of Primary and Permanent Teeth

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Abstract
Clinical studies have shown that fissure sealants are not retained by primary teeth as well as they are by permanent teeth, presumably due to the presence (of a surface layer of prismless enamel in primary teeth. In order to compare the enamel structure and main crystallite orientation on occlusal surfaces, sections from primary molars and permanent premolars were examined by polarized light microscopy. Crystallite orientation to the enamel surface was measured at various distances from the fissure entrance. It was found that the crystallites were arranged almost perpendicular to the enamel periphery whilst the prisms formed an acute angle with the periphery. Only on rare occasions was prismless surface enamel observed. It was concluded that main crystallite orientation and prism arrangement were alike in primary and permanent occlusal enamel, and that the poor retention of sealants on primary teeth cannot be explained by the presence of a prismless surface.