Objective:To digitally measure the three-dimensional (3D) size of primary tooth crowns and the dimensions of the dental arch in children with individual normal primary dentition, preliminarily obtaining baseline data on the 3D size of primary tooth crowns as well as the length and width of the dental arch, and their influence factors. This study aims to provide a data foundation for the design of reference models for primary dentition.Methods:From May to June 2021, 122 caries-free children aged 3.5-4.5 years with individual normal occlusion were selected from five kindergartens in Haidian District, Beijing. Impressions were taken and plaster models were cast. After preliminary screening, 67 eligible models were scanned to obtain digital dental models. Digital measurement software was used for landmark-based measurements. Parameters included 3D crown dimensions (mesiodistal diameter, buccolingual diameter, and occlusogingival height), dental arch dimensions (length and width at specific regions), and occlusal measurements (overjet and overbite at the primary central incisors, and Bolton index for anterior and full dentition). Gender differences in crown dimensions and bilateral symmetry of homologous teeth, as well as the correlations between arch dimensions and gender, height, weight, and body mass index (BMI) were analyzed.Results:The homonymous teeth of 67 children exhibited strong bilateral symmetry in all 3D dimensions ( P>0.05). Gender differences were observed in the buccolingual dimension for all deciduous molars except for the right mandibular first deciduous molar ( P<0.05). For the occlusogingival dimension, gender differences were found in the right maxillary first and second deciduous molars, left maxillary first deciduous molar, and left mandibular first and second deciduous molars ( P<0.05). For the mesiodistal dimension, only the left mandibular second deciduous molar and right mandibular deciduous canine showed gender differences ( P<0.05). All significant differences above indicated larger dimensions in boys compared to girls. In both maxillary and mandibular arches, the lengths and widths at various locations were significantly larger in boys than in girls ( P<0.05). Univariate correlation analysis revealed that body weight was positively correlated with the width of the terminal plane in both the maxilla and mandible and the total length of the mandibular dental arch, while BMI was positively correlated with the width of the maxillary terminal plane and the widths at all measured sites in the mandible ( P<0.05). Multiple regression analysis demonstrated that, after controlling for relevant variables, BMI was a significant positive predictor for the lengths and widths at various sites of the dental arch ( P<0.05), and height was a positive predictor for dental arch length ( P<0.05), as well as body weight was a positive predictor for the width in the molar region ( P<0.05). Overjet at the primary central incisors was 2.28 (1.57, 2.66) mm, and overbite was 1.13 (0.75, 1.92) mm. The anterior Bolton index was 0.79±0.03, and the overall Bolton index was 0.94±0.03. Conclusions:Primary tooth crowns of individual normal occlusion children demonstrate strong bilateral symmetry in homologous teeth. Most primary molars exhibit gender differences in buccolingual and occlusogingival dimensions, with larger values in boys. Arch dimensions (length and width) are consistently larger in boys.

Objective:To digitally measure the three-dimensional (3D) size of primary tooth crowns and the dimensions of the dental arch in children with individual normal primary dentition, preliminarily obtaining baseline data on the 3D size of primary tooth crowns as well as the length and width of the dental arch, and their influence factors. This study aims to provide a data foundation for the design of reference models for primary dentition.Methods:From May to June 2021, 122 caries-free children aged 3.5-4.5 years with individual normal occlusion were selected from five kindergartens in Haidian District, Beijing. Impressions were taken and plaster models were cast. After preliminary screening, 67 eligible models were scanned to obtain digital dental models. Digital measurement software was used for landmark-based measurements. Parameters included 3D crown dimensions (mesiodistal diameter, buccolingual diameter, and occlusogingival height), dental arch dimensions (length and width at specific regions), and occlusal measurements (overjet and overbite at the primary central incisors, and Bolton index for anterior and full dentition). Gender differences in crown dimensions and bilateral symmetry of homologous teeth, as well as the correlations between arch dimensions and gender, height, weight, and body mass index (BMI) were analyzed.Results:The homonymous teeth of 67 children exhibited strong bilateral symmetry in all 3D dimensions ( P>0.05). Gender differences were observed in the buccolingual dimension for all deciduous molars except for the right mandibular first deciduous molar ( P<0.05). For the occlusogingival dimension, gender differences were found in the right maxillary first and second deciduous molars, left maxillary first deciduous molar, and left mandibular first and second deciduous molars ( P<0.05). For the mesiodistal dimension, only the left mandibular second deciduous molar and right mandibular deciduous canine showed gender differences ( P<0.05). All significant differences above indicated larger dimensions in boys compared to girls. In both maxillary and mandibular arches, the lengths and widths at various locations were significantly larger in boys than in girls ( P<0.05). Univariate correlation analysis revealed that body weight was positively correlated with the width of the terminal plane in both the maxilla and mandible and the total length of the mandibular dental arch, while BMI was positively correlated with the width of the maxillary terminal plane and the widths at all measured sites in the mandible ( P<0.05). Multiple regression analysis demonstrated that, after controlling for relevant variables, BMI was a significant positive predictor for the lengths and widths at various sites of the dental arch ( P<0.05), and height was a positive predictor for dental arch length ( P<0.05), as well as body weight was a positive predictor for the width in the molar region ( P<0.05). Overjet at the primary central incisors was 2.28 (1.57, 2.66) mm, and overbite was 1.13 (0.75, 1.92) mm. The anterior Bolton index was 0.79±0.03, and the overall Bolton index was 0.94±0.03. Conclusions:Primary tooth crowns of individual normal occlusion children demonstrate strong bilateral symmetry in homologous teeth. Most primary molars exhibit gender differences in buccolingual and occlusogingival dimensions, with larger values in boys. Arch dimensions (length and width) are consistently larger in boys.