Study On The Hard Tissue Morphology Of The Middle Teeth In The Early Teeth

Cone beam computed tomography (CBCT) has been increasingly used in orthodontics. Comparing with traditional two dimensional imaging, CBCT enables to diagnose patients by using the three dimensional approach. All the landmarks were defined by using Multi-plane reconstruction (MPR) which makes the measurement of spatial distance or angle possible. Based on the obtained cross-sectional images of teeth and surrounding bone along the defined direction, we can observe the tooth morphology and measure the amount of the surrounding periodontal bone. Patients in early permanent dentition ranging from 11 years old to 14 years old was selected in this study because most orthodontic patients received treatment around that age. The hard tissue morphology of maxillary and mandibular central incisors was targeted because adaptive changes of surrounding periodontal bone could be significantly impacted by proclination of maxillary and mandibular central incisors. Three dimensional landmarks were developed by using CBCT MPR to measure bone defect around maxillary and mandibular central incisors. The results could be used as clinical analysis indicators which could guide orthodontic treatment, prevent the root absorption and the alveolar bone defects, and reduce periodontal damage.Objective:To study the hard tissue morphology of the area around maxillary and mandibular central incisors in orthodontic patients who were in early permanent dentition, and also to explore the correlation between the hard tissue morphology and the cephalometric analysis indicators using CBCT MPR as well. To discuss whether the results obtained from 3D measurement could be used in the 2D cephalometric analysis results.Methods:1) 100 orthodontic patients in early permanent dentition were chosen to study the incidence of the dehiscence and fenestration around alveolar bone of maxillary and mandibular incisors. Depending on the Quartiles method, the results of 3D cephalometric analysis were divided into six groups including Class Ⅲ tendency, Class Ⅱ tendency, low mandibular-plane angle tendency and high mandibular-plane angle tendency, central incisors with lingual inclination and central incisors with labial inclination. To compare the incidence of the alveolar bone defect between each two groups and to study the correlation between the results of the cephalometric analysis and the incidence of the alveolar bone defect.2) Selection of 100 patients is the same as method 1). To study the thickness of apical alveolar bone of maxillary and mandibular central incisors, and the correlation between the results of the cephalometric analysis and the thickness of apical alveolar bone.3) Selection of 100 patients is the same as method 1). To study the crown-root angulation of maxillary and mandibular central incisors, and the correlation between the results of the cephalometric analysis and the crown-root angulation of maxillary and mandibular central incisors.4) Selection of 100 patients is the same as method 1). To do the cephalometric analysis with 3D and 2D methods, and to analyze the difference and the fitting degree between the two methods.Results:1) The incidence of alveolar bone defect of maxillary central incisor at labial side was 5.5%, the incidence of dehiscence at lingual side was 3.0%; the incidence of alveolar bone defect of mandibular central incisor at labial side was 74.5%, the incidence of dehiscence atlingual side was 16.0%. The more maxillary central incisors inclined labially, the more apical lingual alveolar bone attached. The more mandibular central incisors inclined lingually, the more apical lingual alveolar bone attached, and the higher likelihood of occurrence of alveolar bone defect (especially fenestration) showed at labial side. The alveolar attachment height of mandibular central incisor in the lingual side was averagely lower in class III tendency group. The likelihood of occurrence of the labial and lingual alveolar bone defect in mandibular incisor was higher in high mandibular-plane angle tendency group.2) The apical alveolar bone of maxillary and mandibular central incisor in men is thicker than that in women. The apical alveolar bone of mandibular central incisors at labial side was thicker than maxillary central incisors. The apical alveolar bone of mandibular central incisors at lingual side was thinner than maxillary central incisors. The total thickness of apical alveolar bone of mandibular central incisors was lesser than maxillary central incisors, and the range of the movement of the teeth was more limited in mandibular central incisors. The apex of maxillary central incisor was closer to the labial side. The apex of mandibular central incisors was almost in the center of the alveolar bone. The more labial inclination of maxillary central incisors was, the more thickness of the apical alveolar bone of maxillary central incisors at labial side showed, and the lesser thickness at lingual side and the total thickness showed. The more lingual inclination of maxillary central incisors was, the more total thickness of the apex showed, and the apex was closer to the labial cortical bone.The more lingual inclination of mandibular central incisor was, the lesser labial and total thickness of the apex showed. The high mandibular-plane angle tendency group had the narrower alveolar bone between mandibular central incisors’ apex area.3) The more lingual inclination of maxillary and mandibular central incisor was, the smaller crown-root angulation showed. There was a negative correlation between the crown-root angulation of mandibular central incisor and the fenestration of the labial side.4) The differences between the two cephalometric analysis measurements were statistically significant (P<0.05),7 indexes had the good fitting and 1 index had the moderate fitting. There was the correlation between the two cephalometric analysis measurements.Conclusion:There was the different degree of correlation between the hard tissue morphology of maxillary and mandibular central incisors and the cephalometric analysis indicators using CBCT MPR in malocclusion patients in early permanent dentition. The results obtained from 3D measurement could be used in the 2D cephalometric analysis results.