[Contraction peculiarity of the muscles that control the moving of the jaw of rat in different growing time].
OBJECTIVE
This study was aimed to evaluate the effect of functional change in oral cavity on the contraction peculiarity of the muscles that control the moving of the jaw in different time of growth.


METHODS
Fifteen male Wistar rats 4, 6 and 8 weeks old were used in this experiment. After deep anesthesia, the masseter muscles(MM), digastric muscles(DM) and lateral pterygoid muscles(LPM) were stimulated in the apartment made by the present authors. The curves that express the relations of force with electric stimulation were recorded, and the relationships between the speed and force of twitch were analyzed.


RESULTS
The maximal forces of twitch of the 8-week-old rats' MM, DM, LPM were 61.7 +/- 14.4 g, 86.4 +/- 25.1 g and 175.3 +/- 39.4 g respectively. When a single electric stimulus stimulated the muscles, the speed of twitch increased with the growth of the rats. As for MM and LPM, the speed markedly increased with the growing of rats from 4 weeks old to 6 weeks old; as for DM, it increased in rats growing from 6 weeks old to 8 weeks old.


CONCLUSIONS
The quickest time of growth of the muscles that control the moving of the jaw of rat is a period from 6 weeks to 8 weeks old and the forces of contraction and twitch increase markedly.
Chen
Mengshi
M
Department of Mechanics, Sichuan University, Chengdu 610065, China.
Li
Liang
L
Song
Yiping
Y
Li
Shujin
S
Wu
Wenchao
W
D000818:Animals; D004558:Electric Stimulation; D008297:Male; D008334:Mandible; D008410:Masticatory Muscles / Q000254:growth & development / Q000502:physiology*; D009119:Muscle Contraction; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors