Influence of Unilateral Masseter Muscle Atrophy on Craniofacial Morphology in Growing Rabbits

Kwon, Tae-Geon; Park, Hyo-Sang; Lee, Sang-Han; Park, In-Sook; An, Chang-Hyeon

doi:10.1016/j.joms.2006.10.059

« Previous Next »Journal of Oral and Maxillofacial Surgery
Volume 65, Issue 8 , Pages 1530-1537, August 2007

Influence of Unilateral Masseter Muscle Atrophy on Craniofacial Morphology in Growing Rabbits

Tae-Geon Kwon, DDS, PhD
- Associate Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry, Kyungpook National University, Daegu, Korea.
- Address correspondence and reprint requests to Dr Kwon: Department of Oral and Maxillofacial Surgery, School of Dentistry, Kyungpook National University, Samduck 2 Ga, Jung Gu, Daegu, 700-421, Korea
Hyo-Sang Park, DDS, PhD
- Professor, Department of Orthodontics, School of Dentistry, Kyungpook National University, Daegu, Korea.
Sang-Han Lee, DDS, PhD
- Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry, Kyungpook National University, Daegu, Korea.
In-Sook Park, DDS, MS
- Instructor, Department of Dentistry and Oral Surgery, School of Medicine, Keimyung University, Daegu, Korea.
Chang-Hyeon An, DDS, MS
- Assistant Professor, Department of Oral and Maxillofacial Radiology, School of Dentistry, Kyungpook National University, Daegu, Korea.

Purpose

The purpose of the study was to evaluate whether the induction of unilateral masticatory muscle dysfunction can alter the skeletal growth patterns.

Materials and Methods

Twenty-one white male New Zealand rabbits (4 weeks old) were divided into 3 groups of 7 subjects: group 1 served as the control to study normal craniofacial growth. In groups 2 and 3, rabbits were injected with 5 units and 15 units of Botulinum toxin A (BTXA) into the right masseter muscle, respectively. The effect of a neuromuscular blockade of masseteric activity on craniofacial growth was evaluated with 3 samples of serial computed tomography (CT) scans with a slice thickness of 0.625 mm, taken at 4 weeks (base line), 8 weeks (endpoint of prepubertal craniofacial growth), and 24 weeks (after pubertal growth).

Results

The ipsilateral mandibular ramus height, zygomatic arch length, and masseteric length did not develop as much as those of the contralateral side after pubertal growth. At age 24 weeks, the masseter muscle volume asymmetry index reached −13.8% (group 2), −18.4% (group 3), and −1.6% for the control group. The ipsilateral side of the hemimandible showed less bone volume after 8 weeks but it showed partially recovered symmetry at 24 weeks. The maxillomandibular incisor midline and transverse molar discrepancies were not evident in any of the groups.

Conclusions

The BTXA injection can be an effective method in inducing site-specific muscular hypofunctions so that masticatory muscle-craniofacial bone interaction can be investigated efficiently. The result showed that the unilateral atrophy of the masseter muscle in the growing subjects influenced the morphology of the local skeletal sites. This did not, however, result ultimately in mandibular midline asymmetry or right–left asymmetry in hemimandibular volume after growth. The results imply that alterations in specific masticatory muscle function can be compensated by the growth of other structural components.