Distribution of sex and age.

Objective
To evaluate transverse maxillomandibular discrepancy and dental compensation in first molar areas in 7- to 9-year-old children with skeletal Class III malocclusion without posterior crossbite using cone-beam computed tomography (CBCT).
Methods
The sample of this retrospective study consisted of 60 children (7 to 9 years old), who were divided into the skeletal Class III malocclusion group (study group, skeletal Class III malocclusion without posterior crossbite, N = 31) and the Class I occlusion group (control group, Class I occlusion with one or two impacted teeth, N = 30). CBCT data were obtained from the database of the Department of Radiology of Hospital of Stomatology, Shandong University. For three-dimensional reconstruction of the head, the dental arch width, basal bone width, and buccolingual inclination angle were measured using MIMICS 21.0 software. Independent-sample t tests were used to compare the two groups.
Results
The mean age of the children was 8.18±0.83years. The width of the maxillary basal bone was significantly smaller in the skeletal Class III malocclusion group (59.75 ± 3.14 mm) than in the Class I occlusion group (62.39 ± 3.01 mm) (P < 0.01). The mandibular basal bone width was significantly larger in the skeletal Class III malocclusion group (60.00 ± 2.56 mm) than in the Class I occlusion group (58.19 ± 2.42 mm) (P < 0.01). The difference in the width of the maxillary and mandibular bases in the skeletal Class III malocclusion group (–0.25 ± 1.73 mm) was significantly different from that in the Class I occlusion group (4.20 ± 1.25 mm) (P < 0.01). However, there was no significant difference in the upper or lower dental arch width between the two groups (P > 0.05). The buccal inclination of the maxillary molars in the skeletal Class III malocclusion group (31.4° ± 8.9°) was significantly higher than that in the Class I occlusion group (17.64° ± 7.3°) (P < 0.01), as was the lingual inclination angle of mandibular molars (45.24° ± 8.3° vs. 37.96° ± 10.18°; P < 0.01).
Conclusion
Transverse maxillary and mandibular discrepancies in the posterior area and transverse dental compensation were found in the early mixed dentition of patients with skeletal Class III malocclusion without posterior crossbite. This suggests that even in the absence of posterior crossbite, maxillary expansion can be attempted to correct the maxillomandibular transverse discrepancy.

研究目的
采用锥形束计算机断层扫描（cone-beam computed tomography, CBCT），评估7~9岁无后牙反𬌗的骨性III类错𬌗儿童第一磨牙区的上下颌横向不调及牙齿代偿情况。

研究方法
本回顾性研究的样本共纳入60名7~9岁儿童，分为骨性III类错𬌗组（观察组，无后牙反𬌗的骨性III类错𬌗，n=31）与I类𬌗组（对照组，伴1~2颗阻生牙的I类𬌗，n=30）。CBCT数据来源于山东大学口腔医院放射科数据库。采用MIMICS 21.0软件对头颅进行三维重建，并测量牙弓宽度、基骨宽度及颊舌向倾斜角。采用独立样本t检验对两组数据进行比较。

研究结果
纳入儿童的平均年龄为8.18±0.83岁。骨性III类错𬌗组的上颌基骨宽度（59.75±3.14 mm）显著小于I类𬌗组（62.39±3.01 mm）（P<0.01）；该组下颌基骨宽度（60.00±2.56 mm）显著大于I类𬌗组（58.19±2.42 mm）（P<0.01）。骨性III类错𬌗组的上下颌基骨宽度差（-0.25±1.73 mm）与I类𬌗组（4.20±1.25 mm）相比差异具有统计学意义（P<0.01）。但两组的上下颌牙弓宽度差异无统计学意义（P>0.05）。骨性III类错𬌗组上颌磨牙的颊向倾斜角（31.4°±8.9°）显著高于I类𬌗组（17.64°±7.3°）（P<0.01），下颌磨牙的舌向倾斜角亦如此（45.24°±8.3° vs 37.96°±10.18°；P<0.01）。

研究结论
在无后牙反𬌗的骨性III类错𬌗患者的早期混合牙列中，存在后牙区上下颌横向不调及横向牙齿代偿。这提示即使无后牙反𬌗，也可尝试采用上颌扩弓矫正上下颌横向不调。