Changes in the periodontal membrane due to apical periodontitis.

Teeth with an apical inflammatory lesion were studied by light microscopic morphometrical procedures to estimate the volumetric density of periodontal ligament tissues by point counting. Sixty-four root surfaces were investigated from coronal to apical. The observed tissue changes were similar in groups with and without bacteria, except for an elevated volumetric density of inflammatory cells in the first group. The attachment was lost apically. Principal fibers running to the root surface and extensions in the cementum decreased from coronal to apical, but were replaced by fibers running parallel to cementum and fibers oriented in a network. We suggest that acellular extrinsic fiber cementum was lost, whereas cellular mixed stratified cementum was built. The cellular mixed stratified cementum synthesis was by inclusion of the remaining fibers from the acellular extrinsic fiber cementum. We suspect that the changes were the result of the anti-inflammatory reaction caused by the periapical lesion.