A histological and ultrastructural study of equine peripheral caries.

BACKGROUND: Peripheral caries (PC) has recently been shown to affect over half of UK and Australian horses. OBJECTIVES: To examine affected cheek teeth histologically and ultrastructurally, to assess the possible route(s) of carious infection into the dental tissues and to further describe the pathological changes in affected teeth. STUDY DESIGN: Descriptive pathological study. METHODS: Four control and 16 cheek teeth with different grades of PC were examined grossly, histologically and by electron microscopy. RESULTS: Cariogenic bacteria from plaque entered peripheral cementum perpendicular to the sides of teeth alongside Sharpey's fibres or vascular channels or more horizontally alongside exposed intrinsic fibres and cemental growth lines. Subsequent intra-cemental bacterial spread created different patterns of caries including vertical and horizontal flake-like patterns; deep, large flask-shaped or smaller superficial ellipsoid-shaped lytic lesions. Cemental caries progressed to affect enamel, dentine and even pulp. Gross examination underestimated the degree of caries observed on histological evaluation. MAIN LIMITATIONS: No dental histories were available; all teeth were examined on a single occasion. CONCLUSION: Equine PC causes different patterns of cemental lesions that appear dependent on the route of cariogenic bacterial invasion. Progression of caries can lead to pulpitis and tooth loss. Gross examination can underestimate the true extent of caries.