Role of keratinized gingiva for gingival health. Clinical and histologic study of normal and regenerated gingival tissue in dogs.

Abstract The present study was carried out in the Beagle dog in order to determine if variations of the width of the zone of keratinized gingiva occur in the canine dentition, if the width alters during the development of destructive periodontitis and if, subsequent to surgical excision of the periodontal lesion, the regenerated gingival margin differs from that of a normal, noninflamed gingiva. Five dogs were used. A baseline examination comprised assessments of dental plaque, gingival conditions and width of the zone of keratinized gingiva. Cotton floss ligatures were placed around the teeth on the right side of the jaws and plaque was allowed to accumulate in order to induce periodontal tissue breakdown. After 150 days the inflamed periodontal tissues around the experimental teeth were removed surgically using a “gingivectomy” or a flap procedure. In the “gingivectomy” procedure the entire zone of the keratinized gingiva was excised whereas the main part of the keratinized tissue was maintained with the flap procedure. During a healing period of 120 days plaque control was carried out daily. On the left side of the jaws (control side) a careful toothcleaning program was performed during the entire observation period of 270 days. Clinical examinations of all control and experimental tooth units were repeated on days 150 and 270. Biopsies were sampled from both sides of the jaws on day 270. In histological sections the free gingival tissue was subjected to histometric assessments and a stereologic analysis based on a standardized morphometric point-counting procedure. In addition, the number of leukocytes residing within the junctional epithelium was determined. The results showed that in Beagle dogs the width of the keratinized gingiva (WKG), on the facial aspect of premolars and molars, varies between 2 and 6 mm. During a period of 270 days of careful plaque control, the WKG was maintained unaltered. In comparison, a phase of experimental periodontitis resulted in a substantial decrease of the WKG. Subsequent to the excision of the inflamed periodontal tissues, which in some cases included the entire zone of the keratinized gingiva, a new free gingival unit developed. In most respects the structural composition of this regenerated gingival unit was similar to that of a normal control unit. Furthermore, in the absence of plaque, the regenerated soft tissue was free from signs of inflammation independent of presence or absence or width of the keratinized zone.