Adverse effects on periodontal tissues have been associated with surgical techniques used to expose impacted teeth that are to undergo orthodontic tooth movement. The purpose of this study was to compare the effects on the periodontium of two of the more commonly used surgical techniques for labially impacted canines--(1) exposure of the entire labial aspect of the anatomic crown with total excision of all keratinized tissue (the window approach) and (2) a technique which exposes only 4 to 5 mm of the most superficial portion of the labial aspect of the cusp tip while maintaining 2 to 3 mm of keratinized tissue. Twelve patients were selected who had undergone comprehensive orthodontic therapy for a unilateral labial impaction of an upper canine, and who had the impacted canine surgically exposed with a window approach. This group's periodontal status after orthodontic therapy was compared to that of another group of twelve patients who had also undergone comprehensive orthodontic therapy for a unilaterally impacted labial upper canine but in whom the surgical exposure of the impacted tooth had been performed in a manner which preserved 2 to 3 mm of keratinized tissue on the labial aspect. The results indicated that the twelve subjects in whom the window approach had been used had statistically more gingival recession, gingival inflammation, and loss of attachment on the labial and labioproximal surfaces of the impacted teeth than the other group that had 2 to 3 mm keratinized tissue maintained after surgical exposure (p less than 0.05).