Objectives

To analyze the anatomical limitations and characteristics of maxillary and mandibular retromolar regions affecting molar distalization using cone-beam computed tomography (CBCT).

Materials and Methods

A total of 120 qualifying patients were classified into equal groups of skeletal Class II and Class III and stratified by vertical growth pattern, age, sex, and third molar presence. The available distance along the axis of distalization and cortical bone thickness (CBT) were measured in the maxillary and mandibular retromolar regions of Class II and Class III patients, respectively. One-way analysis of variance was used to examine the effects of the factors on the measured data.

Results

The minimum available distance of the Class II maxilla was observed at a level 3 mm from the cementoenamel junction (CEJ), while that of the Class III mandible was at a level 9 mm from the CEJ. The average available distance at the limit level was 4.06 ± 1.93 mm in the Class II maxilla, and the average corresponding CBT was 1.00 mm. The average available distance at the limit level in the Class III mandible was 2.80 ± 1.96 mm, and the corresponding CBT was 2.24 mm. In both skeletal Class II and Class III patients, hyperdivergent groups had the least available distance for molar distalization.

Conclusions

The limit for available distance in the Class II maxilla is closer to the coronal level, while that of the Class III mandible is closer to the apical level. A hyperdivergent growth pattern in a patient is indicative of less potential for molar distalization. Axial slices of CBCT images provide valuable evaluation for molar distalization regarding limit levels.

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Author notes

a

Postgraduate Student, Department of Orthodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.

b

Postgraduate Student, Department of Cariology and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.

c

Undergraduate Student, School of Stomatology, Shanxi Medical University, Taiyuan, China.

d

Lecturer, Department of Orthodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.

e

Professor, Department of Orthodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China.

The first two authors contributed equally to this paper.