Zhenyan Lin

Classification of the Root Position of the Maxillary Central Incisors and its Clinical Significance in Immediate Implant Placement.

Purpose:The aim was to classify the relationship of the sagittal root positions of the maxillary central incisor to alveolar bone using cone beam computed tomography (CBCT). Methods:CBCT images of 934 maxillary central incisors were retrospectively reviewed included 542 men and 392 women. The sagittal root position in the alveolar bone was classified as buccal, middle, or palatal. The sagittal buccal type was further classified into 3 subtypes: I, II, and III. Results:The root position type was buccal in 95.4% of the 934 incisors, middle in 4.4%, and palatal in 0.2%. In the buccal type, 47.5%, 44.2%, and 8.3% were subtypes I, II, and III, respectively. There was no significant difference in the major and subtypes of root position between the male and female subjects (both P > 0.05). Conclusions:In Chinese adults, the predominant type of sagittal root position of the maxillary central incisor is buccal. This classification system is useful in planning the implant site for immediate placement in the maxillary esthetic zone.

Comparative analysis of the stress distribution in five anatomical types of maxillary central incisor

BACKGROUND The maxillary central incisor is one of the most important anatomical indicators in esthetics, and stress distribution may vary among its five anatomical views (labial, palatal, mesial, distal, and incisal). OBJECTIVE To compare stress distribution among the five anatomical views of the maxillary central incisor under loading force at five angles and to observe and analyze the stress distribution in the dentin and periodontal ligament. METHODS We established three-dimensional finite element models of the five different views, which simulated the bite force with a static load force at 0∘, 30∘, 45∘, 60∘, and 90∘. The stress and displacement values for the cementoenamel junction (CEJ)-apical labial, palatal, mesial, and distal and the equivalent stress values on the periodontal ligament of the maxillary central incisor were calculated. RESULTS As the angle increased, the equivalent stress on the periodontal ligament, overall tooth displacement, equivalent stress, and displacement over the four views increased. The peaks of equivalent stress over the four views appeared within 0.8-17 mm below the CEJ, although all equivalent stress values decreased while approaching the peak. Within 1-19 mm below the CEJ, the equivalent stress over the M1 and P1 views of the maxillary central incisor decreased substantially. CONCLUSION The peaks of the equivalent stress over the M1 and P1 views of the maxillary central incisor and their stress distribution were lower than those of the other three types. Our findings provided theoretical data on the biomechanics of this esthetically important tooth, which may be useful during implantation of missing maxillary central incisors.