Nature and attachment of cementum formed under guided conditions in human teeth. An electron microscopic study.

In an attempt at characterizing the nature and attachment of cementum formed under conditions of guided tissue regeneration (GTR) in humans, front teeth from 4 patients aged 42 to 72 years were examined at the electron microscopic level. All teeth were affected by complex periodontitis associated with advanced loss of periodontal support. Roots were surgically planed and notched, but not chemically conditioned. Either the mesial or distal surface of each tooth represented the experimental site and was covered with a biodegradable polyglactin 910 barrier, while the opposite approximal surface served as control. Following 3 months of healing, teeth were removed together with surrounding periodontal tissues including some alveolar bone. These blocks were fixed histologically, decalcified, embedded in epoxy, and sectioned for examination in the scanning (backscatter mode) and transmission electron microscope. Both experimental and control sites disclosed 2 types of regenerative cementum that seemed to be formed by cells resembling cementoblasts. The first type was characterized by a thin fringe of collagen fibrils which were arranged perpendicular to the root surface and appeared mineralized in a zone extending about 1 to 3 microm from the dentin. The second type occurred as thick patches which revealed scattered cementocytes and sheets of collagen fibrils oriented mainly parallel to the root surface, running both circularly and axially. In both situations, a continuous, thin, electrondense layer was interposed between newly formed cementum and preexisting radicular hard tissues. Interdigitation of collagen fibrils from cementum and dentin, such as observed along the natural cemento-dentinal junction, did not occur. Thus, regenerative cementum laid down in humans under guided conditions on previously diseased and planed, but not otherwise treated root surfaces shares some morphologic features with cementum formed during spontaneous repair of root resorptions. However, unlike in the course of such repair, a fibrous attachment of new cementum resembling the natural cemento-dentinal junction does not seem to be regenerated under guided conditions.