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Periodontal fiber attachment and apical root resorption.

Apical root resorption is frequent after physiological and orthodontic tooth movement. Current resorption concepts emphasize a protective effect due to cell and fiber attachment to surfaces at risk. The present study investigated relationships between fiber attachment to the root surface and susceptibility to root resorption. The material comprised 10 normal mandibular second and third bicuspids with surrounding periodontia from 4 squirrel monkeys. On step-serial histological sections, defined coronal, middle and apical root surface regions were examined, and attached fiber density and diameter were quantified using computerized digitization methods. For each root surface region, the density and diameter value was used to calculate the fiber occupancy per unit root length. Analysis of variance testing between animal, tooth surface, and defined root surface region showed a significant effect for root surface region only. In the apical region of the root surface, the fiber density was significantly less and the fiber diameter was significantly greater than in the coronal and middle regions. The product of density and diameter showed that attached fiber occupancy was significantly less in the apical region (58%) than in coronal (70%) and middle (74%) regions. It was concluded that differences in attached fiber occupancy may contribute to the greater susceptibility of the root apex to resorption.