Masseter length determines muscle spindle reflex excitability during jaw-closing movements

Naser-Ud-Din, Shazia, Sowman, Paul F., Sampson, Wayne J., Dreyer, Craig W. and Turker, Kemal Sitki (2011) Masseter length determines muscle spindle reflex excitability during jaw-closing movements. American Journal of Orthodontics and Dentofacial Orthopedics, 139 4: E305-E313. doi:10.1016/j.ajodo.2009.12.033

Author Naser-Ud-Din, Shazia
Sowman, Paul F.
Sampson, Wayne J.
Dreyer, Craig W.
Turker, Kemal Sitki
Title Masseter length determines muscle spindle reflex excitability during jaw-closing movements
Journal name American Journal of Orthodontics and Dentofacial Orthopedics   Check publisher's open access policy
ISSN 0889-5406
Publication date 2011-04
Sub-type Article (original research)
DOI 10.1016/j.ajodo.2009.12.033
Open Access Status
Volume 139
Issue 4
Start page E305
End page E313
Total pages 9
Place of publication Philadelphia, United States
Publisher Mosby
Language eng
Formatted abstract
The masticatory muscles are considered to be important determinants of facial form, but little is known of the muscle spindle reflex characteristics and their relationship, if any, to face height. The aim of this study was to determine whether spindle reflexes, evoked by mechanical stimulation of an incisor and recorded on the masseter muscle, correlated with different facial patterns.

Twenty-eight adult volunteers (16 women; ages, 19-38 years) underwent 2-N tap stimuli to their maxillary left central incisor during simulated mastication. Reflexes were recorded during local anesthesia of the stimulated tooth to eliminate the contribution from periodontal mechanoreceptors. Surface electromyograms of the reflex responses of the jaw muscles to these taps were recorded via bipolar electrodes on the masseter muscle and interpreted by using spike-triggered averaging of the surface electromyograms. Lateral cephalometric analysis was carried out with software (version 10.5, Dolphin, Los Angeles, Calif; and Mona Lisa, Canberra, Australia).

Two-newton tooth taps produced principally excitatory reflex responses beginning at 17 ms poststimulus. Correlation analysis showed a significant relationship between these muscle spindle reflexes and facial heights: specifically, shorter face heights were associated with stronger spindle reflexes. This correlation was strongest between the derived measure of masseter length and the spindle reflex strength during jaw closure (r = –0.49, P = 0.008).

These results suggest that a similar muscle spindle stimulus will generate a stronger reflex activation in the jaw muscles of patients with shorter faces compared with those with longer faces. This finding might help to explain the higher incidence of clenching or bruxism in those with short faces and also might, in the future, influence the design of orthodontic appliances and dental prostheses.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Dentistry Publications
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