The Hard Tissue Morphology In Maxillary Aesthetic Zone Of67Young Adults With Normal Occlusion Measured By CBCT

ObjectiveTo investigate the hard tissue morphology in maxillary aesthetic zone of67young adults with normal occlusion,in order to provide some basis to the clinical treatment.Methods67eligible Chinese Han national young volunteers are scanned by cone-beam computed tomography(CBCT). Then measured and analyzed the hard tissue morphology in maxillary aesthetic zone after reconstruction. The measurements included:the labial(buccal) and palatal bone thickness of maxillary anterior teeth and premolars, the alveolar bone thickness, alveolar height, the labial(buccal) and palatal alveolar crest height, the labial-lingual gradient of the maxillary anterior teeth, the labial bony curvature angle below root apex, the distance between root apex and the deepest point of buccal bony curvature. Statistical analysis was used by SPSS18.0soft after measurement.Results1. The labial(buccal) and palatal bone thickness:The buccal bone is thicker than palatal bone only at2mm and4mm apical to the cemento-enamel junction(CEJ) of the maxillary second premolars. Thin labial(buccal) bone(＜1.00mm) exists at each reference line of all measured tooth.The labial(buccal) bone thickness is0.00mm at some points, the percents at the middle of the root and1/4length of the root from the apex of roots in maxillary anterior teeth are more than80.00%.2. The alveolar thickness:The mean alveolar thickness is less than6.00mm only at2mm apical to the cemento-enamel junction of the maxillary first premolars.The alveolar bone thinner than6.00mm exists in all measured teeth except maxillary canines. The percent of alveolar thickness not less than6.00mm is more than80.00%in maxillary anterior teeth and the second premolars.3. The alveolar height: The mean alveolar bone height of all measured teeth is more than10.00mm in normal occlusion youth，it’s even more than20.00mm in maxillary anterior teeth. The percent of alveolar bone height less than15.00mm is less than5.00%.4. The labial(buccal) and palatal alveolar ridge crest height: The mean buccal alveolar ridge crest height of the maxillary first premolars is more than2.00mm only,the mean labial(buccal) and palatal alveolar ridge crest height of other teeth are all less than2.00mm.There is a negative correlation between the labial(buccal) alveolar ridge crest height and the labial(buccal) bone thickness at2mm apical to CEJ of the maxillary anterior teeth and premolars (P＜0.05),the absolute value of the correlation coefficient is between0.6and0.8.5. The labial-lingual gradient of the anterior teeth: the mean labial-lingual gradient of the female maxillary central incisor is less than15.00°, yet the mean gradient of the other teeth is range from15.00°to20.00°. The mean labial-lingual gradient of the maxillary central incisor is less than other anterior teeth in female (P＜0.01)，yet the mean labial-lingual gradient of the maxillary central incisor is less than lateral incisor in male (P=0.012).6. The labial bony curvature angle below root apex is (141.46±17.11)°in maxillary central incisor zone, and (142.23±12.01)°in lateral incisor zone. There is no significant deference between the two teeth (P2=0.569).7. The mean distance between root apex and the deepest point of buccal bony curvature is2.80±1.38mm in central incisor,2.29±1.18mm in lateral incisor. The deference between the two teeth is significant (P2＜0.01).Conclusion1. The labial(buccal) bone thickness is thin in maxillary aesthetic zone of normal occlusion youth, and bone defect can be found at some sites in different degrees, especially at the middle of the root and1/4length of the root from the apex of roots of anterior teeth.2. The alveolar bone height is sufficient especially in the zone of anterior teeth and first premolars.3. The distance between labial(buccal) crest and labial(buccal) CEJ is larger at the maxillary first premolars,and the thinner the labial(buccal) crest is,the larger the distance is.4. There is angle between the long axis of the anterior teeth and the alveolar bone and the labial-lingual gradients of the anterior teeth are different.5. The percents of the youth with obvious curvature in the labial bone below incisor root apex and thin bone at the labial of axis are little, but the aesthetic risk markedly increases in the implant operation, so the classification should be assessed carefully before the clinical treatment.