Influence of unilateral masseter muscle atrophy on craniofacial morphology in growing rabbits.
OBJECTIVE
The purpose of the study was to evaluate whether the induction of unilateral masticatory muscle dysfunction can alter the skeletal growth patterns.


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.
Kwon
Tae-Geon
TG
Department of Oral and Maxillofacial Surgery, School of Dentistry, Kyungpook National University, Daegu, Korea. kwondk@mail.knu.ac.kr
Park
Hyo-Sang
HS
Lee
Sang-Han
SH
Park
In-Sook
IS
An
Chang-Hyeon
CH
D000818:Animals; D019274:Botulinum Toxins, Type A; D002508:Cephalometry; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005146:Facial Asymmetry / Q000139:chemically induced* / Q000503:physiopathology; D005147:Facial Bones / Q000254:growth & development*; D005150:Facial Hemiatrophy / Q000139:chemically induced* / Q000503:physiopathology; D007180:Incisor / Q000254:growth & development; D008297:Male; D008334:Mandible / Q000254:growth & development; D008406:Masseter Muscle / Q000187:drug effects / Q000254:growth & development*; D009465:Neuromuscular Agents; D011817:Rabbits; D014057:Tomography, X-Ray Computed; D015050:Zygoma / Q000254:growth & development
D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A