The effect of orthodontic treatment on periodontal bone support in patients with advanced loss of marginal periodontium.

Loss of periodontal bone support was examined in 24 patients orthodontically treated for pathologic tooth migration in one jaw. Prior to orthodontic realignment of the front teeth, the patients had received periodontal treatment. Active appliance therapy was not given until inflammation was eliminated and the patients demonstrated a high level of oral hygiene. A 0.020-inch spiral wire was bonded to each adjacent realigned tooth for retention. The levels of marginal bone of the front teeth in the treated and untreated jaws were measured in percentage of "maximum bone height" on periapical radiographs made before and after treatment. Relapse was evaluated from study models. Mean averaged loss of periodontal bone from the period before to after orthodontic treatment was 4.94% (SD 4.03, P less than 0.001) and 2.69% (SD 3.66, P less than 0.001) of the treated and untreated front teeth, respectively. The mean difference in averaged loss between treated and untreated front teeth was 2.24% (SD 3.28, P less than 0.01). The majority of the sites showed little or no loss. Maximum loss (35%) was observed in one site only. No association was found between initial bone loss and bone loss during orthodontic treatment. Spaces from 0.1 to 1.8 mm opened up adjacent to the retainer in seven patients. Relapse within the retained segment was associated with failures of the retainer. Of the 19 patients who had been in retention for more than 4 months (mean 16.0, SD 12.1), ten failures were recorded in nine patients. The failure mode was loosening of one or two teeth between wire and composite.