THE RESPONSE OF SUPRAALVEOLAR GINGIVAL COLLAGEN TO ORTHODONTIC ROTATION MOVEMENT IN DOGS

An orthodontically rotated tooth relapses toward its pretreatment posi tion. Explanations for this phenomenon have been given after light mic roscopic studies, according to which it lad been assumed that stretche d supraalveolar gingival fibers pulled back the tooth and brought abou t relaxation of the stretched fibers. The rotational relapse, however, can be prevented by supraalveolar fiberotomy of the gingiva around th e tooth. This investigation was initiated to reevaluate the validity o f the hitherto assumed causes for the relapse, by obtaining ultrastruc tural data on the response of collagen fibers after orthodontic interv ention, Lateral maxillary incisors in the dog were rotated with bonded fixed appliances. The teeth were divided into groups according to dif ferent orthodontic procedures. Scanning and transmission electron micr oscopic analyses were performed on gingival samples after proper proce ssing. Analyses of the untreated control samples showed well-organized , parallel, and densely packed thick bundles of collagen fiber;, inter connected with thin fibers. After rotation-followed-by-retention, the gingival fibers were torn, ripped, disorganized, and laterally spaced and of increased diameter. Thus it was concluded that all these patter ns are incompatible with stretching. Also, an increased number of elas tic: fibers were seen in proximity to the torn collagen fibers. After gingival fiberotomy, most fibers resumed the appearance of the organiz ed pattern of large fiber bundles similar to those seen in tie control s.