[Measuring and analysis of the shoulder circumferences of 840 adults' permanent teeth crown preparations]

Objective: To measure and analyze the shoulder circumferences of adults' permanent teeth crown preparations based on data collected through the intraoral scanning, so as to provide dental anatomy data for clinical diagnosis and analysis. Methods: Intraoral scanning data of 840 complete crown preparations were collected, and were entrusted to the World Dental Laboratory Co., Ltd. in Fuzhou between March 2021 and June 2022. Except the data of the third molar, the rest data were categorized in terms of 14 tooth positions in the upper and lower jaw (each category involved 30 samples from male group and 30 samples from female group). Image measurement software was used to measure the shoulder circumferences of permanent teeth crown preparations. And analysis was conducted to reveal the difference of shoulder circumference diameters between male and female groups. And then they were grouped according to the mean value at each tooth position, on the premise that the difference between the maximum and minimum values and the mean value of the entire group was≤±1.00 mm. Analysis were further conducted to determine the differences of shoulder circumference diameters between each dental position and the differences between male and female in the same groups. Results: Bivariate analysis of variance showed that gender had no effect on the shoulder circumference of full crown preparations (F=0.55, P=1.457), while tooth position had a significant impact on the shoulder circumference of full crown preparations (F=273.15, P<0.001). The samples were classified into 5 groups according to the mean values of shoulder circumference diameters relating to each tooth position. Statistical analysis showed that Group 1, covering maxillary lateral incisor, mandibular central incisor and mandibular lateral incisor, had shoulder circumference with diameters of (16.62±2.21) mm; Group 2, consisting of maxillary central incisor, maxillary cusp, mandibular cusp, mandibular first premolar and mandibular second premolar, had diameters of (20.78±2.48) mm; Group 3, consisting of maxillary first premolar and maxillary second premolar, had diamerters of (22.09±2.72) mm; Group 4, covering maxillary first molar, maxillary second molar and mandibular first molar, had diamerters of (30.21±2.67) mm; while Group 5, with mandibular second molar alone its member, had diamerters of (31.34±3.18) mm. The difference among the 5 groups was statistically significant (P<0.05). Conclusions: Significant differences of shoulder circumference diameters could be found between different tooth positions, while at the same tooth position, the differences between male and female are not significant. The 14 tooth positions could be grouped into 5 groups according to their shoulder circumference diameters. Future research could take the grouping as reference.