[Anatomic-roentgenologic study of the mandibular canal in atrophic mandible].

This study analyses the changes observed with atrophy of the mandibular foramen and mental foramen, as well as the mandibular canal. All 43 left halves of the examined mandibles were systematized according to the classification of the reduction of residual ridges by Atwood. This classification allows a precise description of the rate of atrophy. An evaluation of the results of computed tomography and X-ray, as well as measurements of the mandibles showed a number of significant atrophic changes. With extreme reduction of residual ridges the mental canal is significantly shortened. Increasing atrophic change causes the mental foramen to approach both the alveolar ridge and the basic tangent line. The distance of the mandibular canal to the lingual and buccal surface remains constant, whereas the distance to the cranial and caudal surface is markedly reduced according to the degree of atrophy. The mass of compact and spongy bone tissue is reduced to a level of 50% or less of the original volume. In general, the cortical lamina around the mandibular canal is more often found on the caudal side than on the cranial side. At extreme rates of reduction of residual ridges the mandibular canal is enclosed by compact bone tissue. The visibility of the mandibular canal and the mental foramen on X-ray is significantly reduced by extreme rates of resorption.