Analysis of pathogenesis and topography of replacement root resorption (ankylosis) after replantation of mature permanent incisors in monkeys.

The pathogenesis and topography of replacement root resorption (ankylosis) after replantation of incisors was examined in green Vervet monkeys (Cercopithecus aethiops). Incisors were replanted after 0,18 or 120 min. storage and examined histometrically for replacement resorption after 2, 4 and 8 weeks. There was a significant preference for certain locations upon the root surface. Thus, ankylosis was found significantly more often on the rounded labial and lingual surfaces than on the flat or concave proximal surfaces, and on the apical portion of the root in contrast to the coronal portion. At two-weeks' observation periods, two types of initial ankylosis were seen after 120 min. dry storage. In the cervical areas and on the labial and lingual surfaces, the most common finding was a complete mineralization of the entire periodontal ligament, while on the remaining parts of the root surface, the initial ankylosis area consisted of a layer of bone deposited upon the root surface and socket wall with an intervening soft connective tissue zone. These two zones were in some areas united by bony bridges formed along the Sharpey's fiber bundles. It is suggested that the first type of initial ankylosis represents areas where both the cemental and alveolar parts of the periodontal ligament are avital; whereas the second type represents areas where only the cemental part of the periodontal ligament is avital (i.e., from dry storage). It is concluded that ankylosis after replantation is presumably a response in the periodontium to areas of the periodontal ligament and/or the root surface damaged by the extraction procedure or storage conditions prior to replantation.