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Nozad Mojaver Y, Tawadros P, Moura Ferreira P, Whittle T, Murray GM. Threshold variations of medial pterygoid single motor units during vertical or horizontal force tasks. J Oral Rehabil 2021; 48:1314-1326. [PMID: 34510487 DOI: 10.1111/joor.13257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 08/19/2021] [Accepted: 09/01/2021] [Indexed: 11/28/2022]
Abstract
OBJECTIVES To test the hypotheses that (a) the force thresholds at onset of medial pterygoid muscle single motor unit (SMU) activity do not decrease with an increase in the rate of force generation in standardised vertical or horizontal jaw-force tasks, and (b) there is evidence for functional heterogeneity within the medial pterygoid muscle. METHODS In 14 healthy participants, electromyographic recordings of the right medial pterygoid muscle were performed with intramuscular fine-wire electrodes during four isometric force tasks: vertical, horizontal contralateral, horizontal protrusion and horizontal ipsilateral, performed at two rates of force development (slow ramp, fast ramp). Computer tomography scans confirmed electrode location within the muscle, which was divided into medial and lateral parts. Force thresholds of onset of discriminated SMUs were compared between rates in each task; significance accepted at p < 0.05. RESULTS Of 45 SMU force thresholds studied in one or more tasks, there was no significant difference between slow and fast ramp within each force task, except slow ramp thresholds from the lateral part during the vertical force task were significantly higher than fast ramp thresholds. Reversals of recruitment order between tasks provided evidence for functional heterogeneity within the muscle. Force thresholds of the vertical tasks (range: 1-292.6 N) were mostly higher than for the horizontal tasks (range: 0.1-12.5 N). CONCLUSION The data are consistent with the proposal that the medial pterygoid muscle stabilises the jaw in the vertical plane during isometric force generation in the jaw closing, as well as horizontal directions.
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Affiliation(s)
- Yalda Nozad Mojaver
- Faculty of Medicine and Health, Sydney Dental School, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, Australia
| | - Paul Tawadros
- Faculty of Medicine and Health, Sydney Dental School, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, Australia
| | - Polyana Moura Ferreira
- Faculty of Medicine and Health, Sydney Dental School, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, Australia
| | - Terry Whittle
- Faculty of Medicine and Health, Sydney Dental School, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, Australia
| | - Greg M Murray
- Faculty of Medicine and Health, Sydney Dental School, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, Australia
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Sritara S, Tsutsumi M, Fukino K, Matsumoto Y, Ono T, Akita K. Evaluating the morphological features of the lateral pterygoid insertion into the medial surface of the condylar process. Clin Exp Dent Res 2021; 7:219-225. [PMID: 33205570 PMCID: PMC8019758 DOI: 10.1002/cre2.353] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 10/11/2020] [Accepted: 10/13/2020] [Indexed: 11/09/2022] Open
Abstract
OBJECTIVE The lateral pterygoid is vital in coordinating multidimensional jaw movements. Since a vector in three-dimensional (3D) space is defined by two 3D points, the role of the lateral pterygoid in 3D jaw movements is defined by its origin and insertion. Reportedly, the lateral pterygoid is inserted into not only the pterygoid fovea but also into the medial surface of the condylar process. The objective was to investigate the morphological features of the region of the lateral pterygoid that inserted into the medial surface of the condylar process. MATERIAL AND METHODS Ten head halves of seven cadaveric donors were analyzed. In all specimens, the insertion area on the medial surface of the condylar process was measured based on microcomputed tomography images. Muscle fibers were separated into ≥50 small bundles, and positional relationships between the origins and insertions were investigated. RESULTS Overall, 28.8 ± 5.0% of the insertion area of the lateral pterygoid was situated on the medial surface of the condylar process. Moreover, muscle fiber arrangement revealed that origins of the muscle bundles inserting into the medial surface in seven specimens posteriorly occupied the lateral plate of the pterygoid process longitudinally, whereas those in three specimens mainly occupied the posteroinferior portion. CONCLUSIONS Muscle bundle inserting on the medial surface of the condylar process had a broad insertion area and a distinct origin on the posterior region of the lateral plate of the pterygoid process. This muscle bundle could act as one of the significant subunits within the lateral pterygoid. Therefore, anatomical coordination mechanisms underlying jaw movement cannot be elucidated without considering this subunit.
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Affiliation(s)
- Sasin Sritara
- Department of Orthodontic Science, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
| | - Masahiro Tsutsumi
- Department of Clinical Anatomy, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
| | - Keiko Fukino
- Department of Orthodontic Science, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
| | - Yoshiro Matsumoto
- Department of Orthodontic Science, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
| | - Takashi Ono
- Department of Orthodontic Science, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
| | - Keiichi Akita
- Department of Clinical Anatomy, Graduate School of Medical and Dental SciencesTokyo Medical and Dental UniversityTokyoJapan
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Chen H, Whittle T, Gal J, Klineberg IJ, Murray GM. Functional properties of single motor units in the human medial pterygoid muscle: Thresholds. J Oral Rehabil 2020; 48:132-142. [PMID: 33068481 DOI: 10.1111/joor.13115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 10/01/2020] [Accepted: 10/06/2020] [Indexed: 11/30/2022]
Abstract
BACKGROUND Little is known regarding the functional properties of single motor units (SMUs) in the medial pterygoid muscle (MPt) during jaw movements. OBJECTIVES The aims are (a) to report the thresholds of onset of MPt SMUs during 4 goal-directed jaw movement tasks, and (b) to determine whether the threshold of onset of SMU activation varies with the velocity of jaw movement and the location within the muscle. METHODS Intra-muscular electrodes were inserted in the right MPt of 18 participants performing ipsilateral (right), contralateral, protrusive and opening-closing jaw movements recorded at 2 velocities. Task phases were as follows: BEFORE, OUT, HOLDING, RETURN and AFTER. SMU onset thresholds were determined from the displacement (mm) of the lower mid-incisor point. Electrode location within 4 arbitrary muscle divisions was determined with computer tomography. Statistical tests: Spearman's correlations, Kruskal-Wallis tests; significance accepted at P < .05. RESULTS A significant inverse relation occurred between velocity and threshold for the RETURN of the ipsilateral movement (n = 62 SMU thresholds), while a significant positive relation occurred for the OUT of the contralateral movement (n = 208); there were no significant associations for the protrusive (n = 131) and opening-closing (n = 58) tasks. Significant threshold differences occurred across the 4 muscle divisions only during the OUT of the contralateral and protrusive movements. Some evidence was provided for gender differences in MPt SMU properties. CONCLUSIONS The absence of a significant inverse relation between velocity and SMU threshold for most recorded movements suggests the MPt acts as a stabilizer of the jaw in horizontal and opening-closing jaw movements.
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Affiliation(s)
- Hui Chen
- Jaw Function and Orofacial Pain Research Unit, Faculty of Medicine and Health, Sydney Dental School, Level 2, Westmead Hospital Centre for Oral Health, University of Sydney, Sydney, NSW, Australia
| | - Terry Whittle
- Jaw Function and Orofacial Pain Research Unit, Faculty of Medicine and Health, Sydney Dental School, Level 2, Westmead Hospital Centre for Oral Health, University of Sydney, Sydney, NSW, Australia
| | - John Gal
- Jaw Function and Orofacial Pain Research Unit, Faculty of Medicine and Health, Sydney Dental School, Level 2, Westmead Hospital Centre for Oral Health, University of Sydney, Sydney, NSW, Australia
| | - Iven J Klineberg
- Jaw Function and Orofacial Pain Research Unit, Faculty of Medicine and Health, Sydney Dental School, Level 2, Westmead Hospital Centre for Oral Health, University of Sydney, Sydney, NSW, Australia
| | - Greg M Murray
- Jaw Function and Orofacial Pain Research Unit, Faculty of Medicine and Health, Sydney Dental School, Level 2, Westmead Hospital Centre for Oral Health, University of Sydney, Sydney, NSW, Australia
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Nozad Mojaver Y, Tawadros PB, Moura Ferreira P, Whittle T, Murray GM. Single motor units from the medial pterygoid muscle can be active during isometric horizontal and vertical forces. J Oral Rehabil 2019; 46:998-1008. [PMID: 31206789 DOI: 10.1111/joor.12831] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 05/30/2019] [Accepted: 06/09/2019] [Indexed: 12/27/2022]
Abstract
OBJECTIVES To determine (a) whether the medial pterygoid muscle is active in an isometric vertical force task and in isometric horizontal force tasks in the contralateral, protrusion and ipsilateral directions; (b) whether the same single motor units (SMUs) could be active across different directions of isometric force generation; and (c) whether different regions of the medial pterygoid muscle exhibit different patterns of SMU activation during the generation of any one direction of isometric force. METHODS Intramuscular electromyographic (EMG) recordings were made from the right medial pterygoid muscle in 15 healthy participants during isometric force tasks: vertical and horizontal contralateral, protrusion and ipsilateral. A computed tomography scan divided the EMG recording site into a medial or lateral part in each participant. Single motor units were discriminated in each task. RESULTS Medial pterygoid SMU activity was recorded in 100% of participants for the vertical biting tasks, 86% of participants for the horizontal contralateral and horizontal protrusion tasks and 57% of the horizontal ipsilateral tasks. Of the 72 SMUs that were discriminated, 36% were active in all tasks; 18% were active only in the vertical tasks and 17% were active in the vertical, horizontal contralateral and horizontal protrusion tasks. The proportion of SMUs that was active in at least 1 horizontal task in the lateral part (33/39) was significantly higher than the proportion (21/33) in the medial part (Chi-Square, P < 0.05). CONCLUSION The data are consistent with a stabilisation role for the medial pterygoid muscle in isometric jaw forces in the vertical and horizontal planes.
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Affiliation(s)
- Yalda Nozad Mojaver
- Jaw Function and Orofacial Pain Research Unit, Sydney Dental School, Faculty of Medicine and Health, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, New South Wales, Australia
| | - Paul B Tawadros
- Jaw Function and Orofacial Pain Research Unit, Sydney Dental School, Faculty of Medicine and Health, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, New South Wales, Australia
| | - Polyana Moura Ferreira
- Jaw Function and Orofacial Pain Research Unit, Sydney Dental School, Faculty of Medicine and Health, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, New South Wales, Australia
| | - Terry Whittle
- Jaw Function and Orofacial Pain Research Unit, Sydney Dental School, Faculty of Medicine and Health, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, New South Wales, Australia
| | - Greg M Murray
- Jaw Function and Orofacial Pain Research Unit, Sydney Dental School, Faculty of Medicine and Health, Westmead Hospital Centre for Oral Health, The University of Sydney, Westmead, New South Wales, Australia
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Butts R, Dunning J, Perreault T, Mettille J, Escaloni J. Pathoanatomical characteristics of temporomandibular dysfunction: Where do we stand? (Narrative review part 1). J Bodyw Mov Ther 2017; 21:534-540. [DOI: 10.1016/j.jbmt.2017.05.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Ruangsri S, Whittle T, Wanigaratne K, Murray GM. Functional Activity of Superior Head of Human Lateral Pterygoid Muscle during Isometric Force. J Dent Res 2016; 84:548-53. [PMID: 15914593 DOI: 10.1177/154405910508400612] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
There is controversy as to the jaw tasks for which the superior head of the human lateral pterygoid muscle (SHLP) becomes active. The aim was to describe the functional activities of SHLP single motor units (SMUs) during horizontal isometric force tasks. In 11 subjects, 48 SMUs were recorded from computer-tomography-verified SHLP sites during generation of horizontal isometric force in the contralateral (CL), protrusive (P), and ipsilateral (IL) directions and intermediate directions (CL-P, IL-P). In eight subjects, SHLP SMUs were active in CL, CL-P, and P. Qualitatively, SHLP EMG activity increased with increased isometric force. Forty-two SMUs were active in directions other than IL; 6 exhibited activity at IL and other directions. The similarity of these data to previous human lateral pterygoid (IHLP) data supports the notion that SHLP and IHLP should be regarded as a single muscle, with activities shaded according to the biomechanical demands of the task.
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Affiliation(s)
- S Ruangsri
- Faculty of Dentistry, Khonkaen University, Mittraphab Rd., Muang, Khonkaen, 40002 Thailand
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Shumway KR, Porfirio DJ, Bailey EF. Phonation-related rate coding and recruitment in the genioglossus muscle. Exp Brain Res 2015; 233:2133-40. [PMID: 25899868 DOI: 10.1007/s00221-015-4284-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 04/10/2015] [Indexed: 11/26/2022]
Abstract
Motor unit recruitment was assessed in two muscles with similar muscle fiber-type compositions and that participate in skilled movements: the tongue muscle, genioglossus (GG), and the hand muscle, first dorsal interosseous (FDI). Our primary objectives were to determine in the framework of a voluntary movement whether muscle force is regulated in tongue as it is in limb, i.e., via processes of rate coding and recruitment. Recruitment in the two muscles was assessed within each subject in the context of ramp force (FDI) and in the tongue (GG) during vowel production and specifically, in the context of ramp increases in loudness, and subsequently expressed relative to the maximal. The principle findings of the study are that the general rules of recruitment and rate coding hold true for both GG and FDI, and second, that average firing rates, firing rates at recruitment and peak firing rates in GG are significantly higher than for FDI (P < 0.001) despite tasks performed across comparable force ranges (~2-40 % of max). The higher firing rates observed in the tongue within the context of phonation may be a function of that muscle's dual role as (prime) mover and hydrostatic support element.
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Affiliation(s)
- K R Shumway
- Department of Physiology, College of Medicine, The University of Arizona, Tucson, AZ, 85721-0093, USA
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3-Dimensional Physiologic Postural Range of the Mandible: A Computerized-Assisted Technique—A Case Study. Case Rep Med 2013; 2013:698397. [PMID: 24194764 PMCID: PMC3806511 DOI: 10.1155/2013/698397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 07/10/2013] [Accepted: 08/23/2013] [Indexed: 11/29/2022] Open
Abstract
Previous studies demonstrated that while the mandible assumes its resting position in space, antagonistic muscles should assume minimal muscle activity within a spatial range. This zone of mandibular rest has been mapped using physiologic parameters of muscle activity and incisal spatial kinematics. This case study expands on previous research by monitoring incisal and posterior jaw position and includes lateral pterygoid muscle activity, thus allowing for determining the spatial range including additional relevant coordinates and muscle activity. Four positions were evaluated: a maximum physiologic open position, a maximum physiologic closed position, physiologic rest position, and maximum physiologic protrusion position. Within the physiologic zone of rest formed by these 4 positions, the vertical and anterior borders of the envelope of function may be documented for the incisal and posterior mandible in true 3-dimensional fashion to assist the clinician in determining a physiologic interocclusal freeway space and vertical dimension of occlusion. Advantages and limitations are discussed.
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Davies J, Charles M, Cantelmi D, Liebgott B, Ravichandiran M, Ravichandiran K, Agur A. Lateral pterygoid muscle: A three-dimensional analysis of neuromuscular partitioning. Clin Anat 2011; 25:576-83. [DOI: 10.1002/ca.21298] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2011] [Revised: 09/22/2011] [Accepted: 10/11/2011] [Indexed: 11/11/2022]
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Yamaguchi S, Itoh S, Watanabe Y, Tsuboi A, Watanabe M. Quantitative analysis of masticatory activity during unilateral mastication using muscle fMRI. Oral Dis 2010; 17:407-13. [PMID: 21114592 DOI: 10.1111/j.1601-0825.2010.01767.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Quantitative analysis of the activities of all masticatory muscles is required to elucidate the mechanism of stomatognathic dysfunction. Electromyography can be used to record the activity of masticatory muscles, but quantification of the overall activity of every masticatory muscle has not been accomplished because of methodological limitations. In this study, we used muscle functional magnetic resonance imaging for simultaneous quantification of the overall activities of the masseter, medial pterygoid and lateral pterygoid muscles during unilateral gum chewing. METHODS Seven healthy male volunteers participated in the study. We evaluated changes in the mean proton transverse relaxation time in the bilateral masseter, medial pterygoid and lateral pterygoid muscles before and after unilateral gum chewing, and to quantify the overall activity of these muscles simultaneously during unilateral gum chewing. RESULTS After 5 min of chewing, the activity of the ipsilateral masseter was highest among the six muscles, followed by the ipsilateral medial pterygoid, contralateral lateral pterygoid and contralateral masseter muscles. CONCLUSION These results affirm the importance of the ipsilateral masseter muscle and quantitatively demonstrate the important contribution of the ipsilateral medial pterygoid and contralateral lateral pterygoid muscles during unilateral mastication.
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Affiliation(s)
- S Yamaguchi
- Division of Aging and Geriatric Dentistry, Tohoku University Graduate School of Dentistry, Sendai, Japan.
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Peck CC, Wirianski A, Murray GM. Jaw motor plasticity in health and disease. Comput Methods Biomech Biomed Engin 2010; 13:455-8. [DOI: 10.1080/10255840903453090] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Cioffi I, van Ruijven LJ, Michelotti A, Langenbach GE. Degree of Mineralization at the Attachment of Lateral Pterygoid. Anat Rec (Hoboken) 2010; 293:1387-92. [DOI: 10.1002/ar.21178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Bhutada MK, Phanachet I, Whittle T, Peck CC, Murray GM. Regional properties of the superior head of human lateral pterygoid muscle. Eur J Oral Sci 2008; 116:518-24. [DOI: 10.1111/j.1600-0722.2008.00582.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Ruangsri S, Whittle T, Murray GM. Superior head of human lateral pterygoid muscle: Single motor unit firing rates during isometric force. Arch Oral Biol 2007; 52:995-1001. [PMID: 17448438 DOI: 10.1016/j.archoralbio.2007.02.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Revised: 02/14/2007] [Accepted: 02/28/2007] [Indexed: 11/26/2022]
Abstract
The superior head of the human lateral pterygoid muscle (SHLP) has been classically considered to have functions that are independent of the inferior head of the lateral pterygoid (IHLP). Recent evidence however suggests that some of the functional properties of the SHLP are similar to those of the IHLP. The aim was to determine whether the functional properties in terms of single motor unit (SMU) firing rates within the SHLP vary with horizontal isometric force (400-800gwt) and direction (i.e., contralateral (CL), protrusive (P), ipsilateral (IL) and intermediate directions, CL-P, IL-P) in a manner similar to those identified for the IHLP, and as would be expected if both SHLP and IHLP should be regarded as one muscle. In eight subjects, the firing rates of 40 SMUs were recorded from computer tomography (CT)-verified SHLP sites while each subject exerted horizontal isometric forces with their lower jaw onto a force transducer in the five directions. Firing rates increased significantly with horizontal isometric force from 400 to 800gwt. Firing rates also changed significantly (p<0.01) with direction with CL, CL-P and P having comparable firing rates (13.3, 12.6 and 12.6impulses/s, respectively) which were significantly higher than IL-P. The similarity of these data to previous IHLP data, provide additional support for the hypothesis that the SHLP and the IHLP should be regarded as two parts of one muscle.
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Affiliation(s)
- Supanigar Ruangsri
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia
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Bhutada MK, Phanachet I, Whittle T, Peck CC, Murray GM. Activity of superior head of human lateral pterygoid increases with increases in contralateral and protrusive jaw displacement. Eur J Oral Sci 2007; 115:257-64. [PMID: 17697164 DOI: 10.1111/j.1600-0722.2007.00461.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The hypothesis was that the superior head of human lateral pterygoid muscle (SHLP) plays a similar role in jaw movement as the inferior head of human lateral pterygoid muscle (IHLP). The aims were to determine the functional properties of SHLP single motor units (SMUs) and root mean square activity (RMS) of the SHLP during contralateral and protrusive jaw movement tasks and to compare these features with those identified previously for the IHLP. In 22 human subjects, SMUs were recorded intramuscularly from computer tomography-verified sites within the SHLP during standardized contralateral and protrusive jaw movement tasks recorded by a jaw-tracking device. Of the 50 SMUs discriminated, 39 were active during contralateral and 29 during protrusive jaw movements. The firing rates and RMS of the SHLP motor units increased with an increase in jaw displacement. The RMS activity across the entire trial during contralateral jaw movement was significantly greater than that during protrusion. Similarly to conclusions previously identified for the IHLP, the data are consistent with an important role for the SHLP in the control of contralateral and protrusive jaw movements. The similarities in SHLP and IHLP functional properties support the proposal that both heads should be regarded as a system of fibers acting as one muscle.
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Affiliation(s)
- Manish K Bhutada
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Westmead Center for Oral Health, Westmead Hospital, Darcy Road, Westmead, NSW 2145, Australia
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Murray GM, Bhutada M, Peck CC, Phanachet I, Sae-Lee D, Whittle T. The human lateral pterygoid muscle. Arch Oral Biol 2007; 52:377-80. [PMID: 17141177 DOI: 10.1016/j.archoralbio.2006.10.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Revised: 10/05/2006] [Accepted: 10/05/2006] [Indexed: 11/21/2022]
Abstract
One of the jaw muscles particularly implicated in temporomandibular disorders (TMD), a common form of non-dental chronic orofacial pain, is the human lateral pterygoid muscle. The precise role of this muscle in TMD is unclear as is the nature of the interaction between pain and motor function particularly involving this muscle. This research group has adopted a two-stage approach to studying the effects of pain on motor function. The first is to study normal orofacial motor function through recordings of jaw movement and electromyographic (EMG) activity from a number of jaw muscles (including recordings from the lateral pterygoid muscle; verification of electrode location achieved through computer tomography imaging) during a number of standardised jaw movements. These studies have defined the detailed functional properties of, in particular, the lateral pterygoid muscle, whose physiology and function is not well understood. In summary, the data are consistent with the hypothesis previously proposed that the lateral pterygoid should be regarded as a system of fibres that acts as one muscle, with varying amounts of evenly graded activity throughout its entire range, and with the distribution of activity within the muscle being determined by the biomechanical demands of the task. Our second approach has been to study the effects of experimental masseter muscle pain on the detailed functional properties (e.g., root-mean-square EMG activity) of the jaw muscles, especially the lateral pterygoid muscle. Preliminary data from these pain studies point towards significant effects of human experimental muscle pain on jaw muscle activity and jaw movement.
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Affiliation(s)
- Greg M Murray
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia.
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Bailey EF, Rice AD, Fuglevand AJ. Firing patterns of human genioglossus motor units during voluntary tongue movement. J Neurophysiol 2006; 97:933-6. [PMID: 17021024 DOI: 10.1152/jn.00737.2006] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The tongue participates in a range of complex oromotor behaviors, including mastication, swallowing, respiration, and speech. Previous electromyographic studies of the human tongue have focused on respiratory-related tongue muscle activities and their role in maintaining upper airway patency. Remarkably, the activities of human hypoglossal motor units have not been studied during the execution of voluntary maneuvers. We recorded single motor unit activity using tungsten microelectrodes in the genioglossus muscle of 10 healthy human subjects performing both slow tongue protrusions and a static holding maneuver. Displacement of the tongue was detected by an isotonic transducer coupled to the lingual surface through a customized lever arm. For protrusion trials, the firing rate at recruitment was 13.1 +/- 3 Hz and increased steeply to an average of 24 +/- 6 Hz, often with very modest increases in tongue protrusion. For the static holding task, the average firing rate was 16.1 +/- 4 Hz, which is surprisingly high relative to limb motor units. The average coefficient of variation of interspike intervals was approximately 20% (range, 10-28%). These are the first recordings of their type obtained in human subjects and provide an initial glimpse into the voluntary control of hypoglossal motoneurons during tongue movements presumably instigated by activity in the motor cortex.
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Affiliation(s)
- E Fiona Bailey
- Department of Physiology, College of Medicine, University of Arizona, Tucson, AZ 85721-0093, USA.
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Huang BY, Whittle T, Murray GM. A working-side change to lateral tooth guidance increases lateral pterygoid muscle activity. Arch Oral Biol 2006; 51:689-96. [PMID: 16513080 DOI: 10.1016/j.archoralbio.2006.01.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 01/15/2006] [Accepted: 01/16/2006] [Indexed: 10/25/2022]
Abstract
UNLABELLED The inferior head of lateral pterygoid (IHLP) is thought to play a critical role in the generation and control of lateral jaw movements. AIM The aim was to test the hypothesis that a change to the lateral tooth guidance (working-side occlusal alteration, OA) results in a significant change in the electromyographic (EMG) activity of the IHLP during standardised lateral jaw movements (laterotrusion) tracked by a jaw-tracking system. METHODS Ten trials of right laterotrusion were repeated under: control 1 (before occlusal alteration), OA (after occlusal alteration placement), and control 2 (after occlusal alteration removal) conditions in 14 subjects while recording left IHLP, bilateral anterior and posterior temporalis, masseter and submandibular muscles. RESULTS IHLP activity was significantly (p<0.05) increased with the occlusal alteration during the outgoing (movement from intercuspal position to approximately 5mm right) and return phases of laterotrusion. The other muscles demonstrated no change or a significant decrease in activity. CONCLUSIONS These findings suggest that a change to the occlusion on the working-side in the form of a steeper guidance necessitates an increase in IHLP activity to move the mandible down the steeper guidance. It must be emphasised that these data cannot be used as justification for occlusal therapy.
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Affiliation(s)
- B Y Huang
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Westmead Centre for Oral Health, Westmead, NSW 2145, Australia
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Aoki S, Uchida S, Inoue H. Fatigue-related changes in discharge patterns of motor units in the inferior head of the lateral pterygoid muscle in humans. Arch Oral Biol 2005; 50:727-37. [PMID: 15958204 DOI: 10.1016/j.archoralbio.2004.12.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2004] [Accepted: 12/28/2004] [Indexed: 11/30/2022]
Abstract
OBJECTIVE To investigate single motor unit (SMU) firing patterns of the inferior head of the human lateral pterygoid muscle (IHLP) during sustained isometric contractions, and to examine IHLP fatigability. DESIGN In 5 subjects, EMG was recorded from the right IHLP during generation of horizontal isometric mandibular force towards left side. Subjects tracked a target on an oscilloscope, slowly increasing the force to 25% of maximum voluntary contraction, and then maintained that force for 120 s (endurance task). Subjects rested for 30 s after each test, and three 10s recovery tests were performed every 30 s (recovery task). Fatigue data were obtained from 23 SMUs. RESULTS Twelve of 23 SMUs (52.2%) continued to fire throughout the 120 s, and each subject had at least one of these units. These units were classified as tonic pattern (T-unit). The firing rate of 6 of the 12 T-units (50.0%) decreased gradually with time. Comparison of the mean firing rate and coefficient of variance (CV) of interspike interval (ISI) of the 12 T-units between pre-fatigue, post-fatigue and the three recovery tasks showed that the mean firing rate decreased and CV of ISI increased after fatigue. Mean firing rate and CV of ISI recovered after 30 s of rest after the endurance task. CONCLUSIONS The firing patterns of IHLP units changed with the passing of time during sustained isometric contractions leading to fatigue.
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Affiliation(s)
- S Aoki
- Department of Removable Prosthodontics and Occlusion, Osaka Dental University, Japan
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Huang BY, Whittle T, Murray GM. Activity of inferior head of human lateral pterygoid muscle during standardized lateral jaw movements. Arch Oral Biol 2005; 50:49-64. [PMID: 15598417 DOI: 10.1016/j.archoralbio.2004.08.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/24/2004] [Indexed: 11/29/2022]
Abstract
OBJECTIVE (a) To describe the changes in electromyographic (EMG) activity from selected jaw muscles during a standardized lateral jaw movement with the teeth together, and (b) to investigate the effects on jaw muscle activity of changes in both the rate of lateral jaw movement and the relative magnitude of jaw-closing force. DESIGN In 16 healthy volunteers, recordings were made using a jaw-tracking system, of mid-incisor point (MIPT) movements, as well as EMG activity from the contralateral inferior head of the lateral pterygoid muscle (IHLP), and bilateral anterior and posterior temporalis, masseter and submandibular muscles, during lateral jaw movement tasks at two speeds and two closing force levels with the teeth together. RESULTS The IHLP was the only muscle to show a consistent increase in activity in association with the outgoing phase of the task and a decrease during the return phase. Under high closing force at slow speed, the EMG activities of the IHLP and bilateral anterior temporalis and masseter muscles were significantly (p < 0.05) higher than those under a low closing force, while there was no significant change (p > 0.05) in bilateral posterior temporalis and submandibular muscles. The change from slow to fast lateral movement at low force did not significantly (p > 0.05) alter the mean activity except for the IHLP (increase in activity) and the contralateral anterior temporalis (decrease in activity). CONCLUSIONS The data suggest that the IHLP is one of the principal jaw muscles involved in a lateral jaw movement with the teeth together while the other jaw muscles may play a contributory or facilitatory role.
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Affiliation(s)
- B Y Huang
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Westmead Centre for Oral Health, Westmead, NSW 2145, Australia
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Murray GM, Phanachet I, Uchida S, Whittle T. The human lateral pterygoid muscle: A review of some experimental aspects and possible clinical relevance. Aust Dent J 2004; 49:2-8. [PMID: 15104127 DOI: 10.1111/j.1834-7819.2004.tb00042.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The clinical notion that some disturbance to the activity of the lateral pterygoid muscle plays a role in the aetiology of temporomandibular disorders (TMD) is still widely accepted and influences management strategies. However, there is no rigorous scientific evidence to support this clinical notion and the role of the lateral pterygoid muscle in normal function is still controversial. The classically defined functions of each head of the muscle are that the superior head is active on closing, retrusion, and ipsilateral jaw movements, while the inferior head is active on opening, protrusion and contralateral jaw movements. However, recent data indicate that these concepts are too simplistic. For example, recent evidence suggests that parts of the superior head may also be active on opening, protrusion and contralateral jaw movements, and that the superior head may consist of three mediolaterally arranged functional zones. Given these complexities, the proposal that clicking and/or locking conditions arise in the temporomandibular joint through some form of lack of co-ordination between the two heads of the muscle needs re-evaluation. Despite earlier reports to the contrary, both heads of the lateral pterygoid muscle appear to be electrically silent at the postural or resting jaw position, and therefore appear to play no role in the anteroposterior positioning of the jaw at the postural position. An important role has also been demonstrated electromyographically for progressive changes in activity in the inferior head as the direction of horizontal jaw force shifts from one side to the other. This suggests an important role for the lateral pterygoid muscle in the generation of side-to-side and protrusive jaw forces. The lateral pterygoid muscle is likely therefore to play an important role in parafunctional excursive jaw movements and also possibly a role in influencing jaw position in patients where the maxillomandibular relationship records change from session to session. The above data provide new insights into the normal function of the lateral pterygoid muscle. The proposal that the lateral pterygoid muscle plays some role in the aetiology of TMD needs now to be rigorously tested.
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Affiliation(s)
- G M Murray
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, The University of Sydney.
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Phanachet I, Whittle T, Wanigaratne K, Murray GM. Minimal tonic firing rates of human lateral pterygoid single motor units. Clin Neurophysiol 2004; 115:71-5. [PMID: 14706471 DOI: 10.1016/s1388-2457(03)00315-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
OBJECTIVE The minimal tonic firing rates (the lowest firing rates at which motor units fire regularly; MTFR) of single motor units (SMUs) within the lateral pterygoid muscle have not been widely investigated. The aims of this study were (a) to identify MTFR of SMUs within the inferior head (IHLP) and superior head (SHLP) of the lateral pterygoid muscle during horizontal jaw movements, and (b) to determine whether these MTFR vary with movement direction. METHODS Twenty subjects moved the jaw to maintain SMU firing at the lowest continuous firing rate. SMU activity was recorded from computer-tomography-verified sites within the IHLP or SHLP. RESULTS In the IHLP, the mean (+/-SD) MTFR for contralateral movement (15.6+/-2.3 imp/s; n=22 SMUs) were not significantly different from those during protrusion (16.3+/-3.4 imp/s; n=19). In the SHLP, the mean (+/-SD) MTFR for contralateral, ipsilateral movement, and protrusion were 14.7+/-2.5 imp/s (n=10), 13.2+/-2.1 imp/s (n=8), and 16.2+/-3.7 imp/s (n=2), respectively. CONCLUSIONS Lateral pterygoid SMUs have greater MTFR than previously reported in the masseter and IHLP, namely 5-8 and 8-10 imp/s, respectively. The MTFR did not vary with the task within each muscle head. SIGNIFICANCE Some physiological properties of lateral pterygoid SMUs may be different from those in other jaw muscles.
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Affiliation(s)
- I Phanachet
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia
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Uchida S, Whittle T, Wanigaratne K, Murray GM. Activity in the inferior head of the human lateral pterygoid muscle with different directions of isometric force. Arch Oral Biol 2002; 47:771-8. [PMID: 12446184 DOI: 10.1016/s0003-9969(02)00116-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The aim was to test the hypothesis that this head of the muscle plays a part in the generation and fine control of horizontal mandibular forces in a range of directions. Electromyographic activity was recorded from the inferior head of the lateral pterygoid of eight individuals during the generation such forces to a target in contralateral, ipsilateral and protrusive directions, and in two intermediate directions (contralateral-protrusive, ipsilateral-protrusive). The mean electromyographic activity and the mean firing rates of 21 single-motor units were significantly affected by direction, with the highest activity being contralateral, and graded decreases occurring as the direction shifted to the ipsilateral. Firing rates were significantly correlated with force magnitude. The data suggest that the inferior head of the human lateral pterygoid is involved in the creation and fine control of mandibular forces in different horizontal directions.
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Affiliation(s)
- S Uchida
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Professorial Unit, Westmead Centre for Oral Health, NSW 2145, Westmead, Australia
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