Some periodontal tissue reactions to orthodontic tooth movement in monkeys

Abstract The purpose of the experiment reported was to study soft tissue changes at teeth which were orthondontically moved into areas with varying thickness and quality of periodontal tissues. The maxillary central incisors and first premolars in 5 adult monkeys were used as experimental teeth. 6 months prior to the start of the orthodontic treatment phase, the maxillary second premolars were extracted. By surgical means, areas with varying width of the keratinized gingiva were established in the incisor and premolar region. Following a clinical baseline examination which involved assessments of gingival width, location of the gingival margin in relation to cemento‐enamel junction and probing attachment level, fixed orthodontic appliances were inserted in order to bodily move (1) the two contral incisors in labial direction through the alveolar bone envelope and (2) the first premolars in distal direction into contact with the first molars. Orthodontic forces were applied for a period of 3‐4 months. The lateral incisors and first molars were selected as non‐moved control teeth. After the experimental teeth had been retained in their new positions for 1 month, the clinical examination was repeated. Tissue blocks containing test and control specimens were subsequently dissected and prepared for microscopic analysis. The analysis included histometric assessments of loss of connective tissue attachment and height of alveolar bone. The results showed that at every second labially moved incisor, the gingival margin had become displaced in apical direction. The degree of displacement, however, was small and only at 2 teeth accompanied by loss of connective tissue attachment. Throughout the study, these particular teeth also showed obvious signs of gingival inflammation. In the incisor tooth regions, no relationship was found between the initial width of the keratinized gingiva and the degree of apical displacement of the gingival margin during orthodontic therapy. Furthermore, there was no statistically significant difference in terms of loss of connective tissue attachment between premolars which had been bodily moved into areas of the jaw bone lined by alveolar mucosa or keratinized gingiva. These observations suggest that plaque‐induced inflammation and the thickness (volume) of the marginal soft tissue, rather than the apico‐coronal width of the keratinized and attached gingiva, are determining factors for the development of gingival recession and attachment loss during orthodontic tooth movement.