The Influence of gingival Biotypes on Tooth Movement and Periodontal Tissue in Anterior Retraction Phase / Pannapat Chanmanee

Abstract

Introduction: Protrusion of maxillary anterior teeth was usually found inorthodontic patients with highly esthetic demands. The gingival biotypes were the outcome predictors in several dental fields. Until now, no clinical prospective studies revealed the importance of gingival biotypes in orthodontic perspective. Objectives: Part I: To compare gingival thicknesses and five alveolar bone parameters on the labial and palatal sides between thick and thin gingival biotypes in anterior dentoalveolar protrusion teeth Part II: To compare the changes of gingival thicknesses and five alveolar bone parameters on the labial and palatal sides between thick and thin gingival biotypes in en masse retraction phase. Material and methods: Part I: The study included 240 anterior teeth from 40 healthy patients with skeletal Class I malocclusion with dentoalveolar protrusion. The thick (n = 108) and thin (n = 132) gingival biotypes were assessed by probe transparency. The gingival thicknesses and five alveolar bone parameters from cone beam computed tomography were measured. The differences between the thick and thin gingival biotype parameters were statistically analyzed by Mann-Whitney U test. Part II: The 32 adult subjects with protrusion of the upper anterior teeth (thick gingival biotype = 16, thin gingival biotype = 16) who were planned with bilaterally extraction of the maxillary first premolars. An 0.018x0.022-inch stainless steel wire anterior slots 0.018x0.025 inch and posterior slots 0.022x0.028 -inch slot. The en masse retraction was used NiTi coil spring delivery force 150 grams from upper canine to upper first molars bilaterally until 16 weeks period of observation. The Lateral cephalograms, study models were taken at pre-retraction (T1) and after 16 weeks of retraction (T2). The cone-beam compute tomograms were scanned after T2 3 months for bone remodeling. Non-parametric tests were used to analyze the data. Results: Part I: Gingival thickness and palatal bone gradually increased toward the apical area while the labial bone thickness was almost even in both gingival biotypes. The thick gingival biotype showed thicker gingiva and alveolar bone than in the thin gingival biotype. The thick gingival biotype showed a shorter distance from the alveolar crest to the cementoenamel junction and lower palatal cortical bone height than the thin gingival biotype. Cancellous bone was detected only at the palatal side in both gingival biotypes which started 4 mm above the crestal bone level toward the root apex in the thick gingival biotype and 8 mm in the thin gingival biotype. Additionally, the thick gingival biotype showed significantly greater palatal cancellous bone than the thin gingival biotype (P < 0.01). Part II: The thin gingival biotype showed faster rate of tooth movement and more upper incisors inclination change than the thick gingival biotype. Both gingival biotypes showed thickening of gingiva and labial alveolar bone and decreasing of palatal bone. The significant decreasing of palatal bone height that composed of pure cortical bone was observed in thin gingival biotype. Conclusion: Part I: Patients with anterior dentoalveolar protrusion teeth presented both thick and thin gingival biotypes. The thick gingival biotype showed more favorable alveolar bone parameters than the thin gingival biotype. Part II: The thick gingival biotype showed slow rate of tooth movement, less tipping movement of upper incisors and less palatal bone loss than thin gingival biotype.