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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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Chen H, Whittle T, Gal JA, Murray GM, Klineberg IJ. The medial pterygoid muscle: a stabiliser of horizontal jaw movement. J Oral Rehabil 2017; 44:779-790. [PMID: 28664577 DOI: 10.1111/joor.12542] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/25/2017] [Indexed: 11/30/2022]
Abstract
There is limited information of the normal function of the human medial pterygoid muscle (MPt). The aims were to determine whether (i) the MPt is active throughout horizontal jaw movements with the teeth apart and (ii) whether single motor units (SMUs) are active during horizontal and opening-closing jaw movements. Intramuscular electrodes were placed in the right MPt of 18 participants who performed five teeth-apart tasks: (i) postural position, (ii) ipsilateral (i.e. right) jaw movement, (iii) contralateral movement, (iv) protrusive movement and (v) opening-closing movement. Movement tasks were guided by a target and were divided into BEFORE, OUT, HOLDING, RETURN and AFTER phases according to the movement trajectories recorded by a jaw tracking system. Increased EMG activity was consistently found in the OUT, HOLDING and RETURN phases of the contralateral and protrusive movement tasks. An increased RETURN phase activity in the ipsilateral task indicates an important role for the MPt in the contralateral force vector. Of the 14 SMUs active in the opening-closing task, 64% were also active in at least one horizontal task. There were tonically active SMUs at the postural jaw position in 44% of participants. These new data point to an important role for the MPt in the fine control of low forces as required for stabilisation of vertical mandibular position not only to maintain postural position, but also throughout horizontal jaw movements with the teeth apart. These findings provide baseline information for future investigations of the possible role of this muscle in oro-facial pain conditions.
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Affiliation(s)
- H Chen
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, Westmead Hospital Centre for Oral Health, University of Sydney, Westmead, NSW, Australia
| | - T Whittle
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, Westmead Hospital Centre for Oral Health, University of Sydney, Westmead, NSW, Australia
| | - J A Gal
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, Westmead Hospital Centre for Oral Health, University of Sydney, Westmead, NSW, Australia
| | - G M Murray
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, Westmead Hospital Centre for Oral Health, University of Sydney, Westmead, NSW, Australia
| | - I J Klineberg
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, Westmead Hospital Centre for Oral Health, University of Sydney, Westmead, NSW, Australia
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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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De Santis R, Gloria A, Russo T, D'Amora U, Varriale A, Veltri M, Balleri P, Mollica F, Riccitiello F, Ambrosio L. Reverse engineering of mandible and prosthetic framework: Effect of titanium implants in conjunction with titanium milled full arch bridge prostheses on the biomechanics of the mandible. J Biomech 2014; 47:3825-9. [PMID: 25468297 DOI: 10.1016/j.jbiomech.2014.10.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 04/08/2014] [Accepted: 10/16/2014] [Indexed: 11/27/2022]
Abstract
This study aimed at investigating the effects of titanium implants and different configurations of full-arch prostheses on the biomechanics of edentulous mandibles. Reverse engineered, composite, anisotropic, edentulous mandibles made of a poly(methylmethacrylate) core and a glass fibre reinforced outer shell were rapid prototyped and instrumented with strain gauges. Brånemark implants RP platforms in conjunction with titanium Procera one-piece or two-piece bridges were used to simulate oral rehabilitations. A lateral load through the gonion regions was used to test the biomechanical effects of the rehabilitations. In addition, strains due to misfit of the one-piece titanium bridge were compared to those produced by one-piece cast gold bridges. Milled titanium bridges had a better fit than cast gold bridges. The stress distribution in mandibular bone rehabilitated with a one-piece bridge was more perturbed than that observed with a two-piece bridge. In particular the former induced a stress concentration and stress shielding in the molar and symphysis regions, while for the latter design these stresses were strongly reduced. In conclusion, prosthetic frameworks changed the biomechanics of the mandible as a result of both their design and manufacturing technology.
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Affiliation(s)
- Roberto De Santis
- Institute of Polymers, Composites and Biomaterials, National Research Council of Italy, V.le J.F. Kennedy 54, Mostra d׳Oltremare (PAD. 20), 80125 Naples, Italy
| | - Antonio Gloria
- Institute of Polymers, Composites and Biomaterials, National Research Council of Italy, V.le J.F. Kennedy 54, Mostra d׳Oltremare (PAD. 20), 80125 Naples, Italy.
| | - Teresa Russo
- Institute of Polymers, Composites and Biomaterials, National Research Council of Italy, V.le J.F. Kennedy 54, Mostra d׳Oltremare (PAD. 20), 80125 Naples, Italy
| | - Ugo D'Amora
- Institute of Polymers, Composites and Biomaterials, National Research Council of Italy, V.le J.F. Kennedy 54, Mostra d׳Oltremare (PAD. 20), 80125 Naples, Italy
| | - Angelo Varriale
- Department of Oral Surgery and Implantology, University of Siena, Via Banchi di Sotto 55, 53100 Siena, Italy
| | - Mario Veltri
- Department of Oral Surgery and Implantology, University of Siena, Via Banchi di Sotto 55, 53100 Siena, Italy
| | - Piero Balleri
- Department of Oral Surgery and Implantology, University of Siena, Via Banchi di Sotto 55, 53100 Siena, Italy
| | - Francesco Mollica
- Department of Materials Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italy
| | - Francesco Riccitiello
- Department of Oral and Maxillofacial Sciences, University of Naples "Federico II", Via Pansini 5, 80131 Naples, Italy
| | - Luigi Ambrosio
- Institute of Polymers, Composites and Biomaterials, National Research Council of Italy, V.le J.F. Kennedy 54, Mostra d׳Oltremare (PAD. 20), 80125 Naples, Italy
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Salame TH, Peck CC, Murray GM. A new method for lateral pterygoid electromyographic electrode placement. J Prosthet Dent 2007; 98:224-31. [PMID: 17854624 DOI: 10.1016/s0022-3913(07)60059-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
STATEMENT OF PROBLEM Making electromyographic recordings of the lateral pterygoid muscle (LP) is difficult because of potential electrode damage to, for example, the maxillary artery and long buccal nerve, and because of pain and reduced jaw mobility characteristic of many orofacial pain patients. PURPOSE The purpose of this study was to develop a reliable intraoral placement technique for the inferior head of the lateral pterygoid (IHLP) that minimizes jaw displacement. MATERIAL AND METHODS In 2 dried skulls and 7 human cadavers, it was estimated that, with the mandible in an ipsilateral closed position, a straight needle could be used to position fine-wire electrodes into the midportion of IHLP by inserting the needle through the mucosa adjacent to the distal root of the maxillary second molar, towards the external auditory meatus and parallel to the buccal alveolar bone of the maxilla. The needle avoided the maxillary artery and long buccal nerve. Using this approach in 5 adults, 2 fine-wire electrodes were placed into the IHLP. Placement was verified by computer tomography (CT) and electromyography. RESULTS In all subjects, the ideal insertion depth to place the electrodes in the middle of IHLP was 29 mm. CONCLUSIONS This technique is a reliable method for IHLP electrode placement for patients with impaired jaw function, minimizing risk of damage to major structures.
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Affiliation(s)
- Talal H Salame
- Faculty of Dentistry, University of Sydney, Sydney, Australia
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Bhutada MK, Phanachet I, Whittle T, Wanigaratne K, Peck CC, Murray GM. Threshold properties of single motor units in superior head of human lateral pterygoid muscle. Arch Oral Biol 2007; 52:552-61. [PMID: 17270143 DOI: 10.1016/j.archoralbio.2006.12.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 11/22/2006] [Accepted: 12/05/2006] [Indexed: 11/20/2022]
Abstract
UNLABELLED The superior head of the human lateral pterygoid muscle (SHLP) may play a similar role in jaw movement as the inferior head (IHLP). OBJECTIVE The aim was to determine whether threshold properties of single motor units (SMUs) within SHLP during jaw tasks were comparable to those identified for IHLP. DESIGN In 24 human subjects, SMUs were recorded intramuscularly from computer-tomography verified sites within SHLP during standardised jaw tasks recorded by a jaw-tracking device. RESULTS Of the 69 SMUs discriminated, 54 were active during contralateral, 52 during protrusive and 8 during ipsilateral jaw movements. The thresholds, at which SMUs commenced firing, decreased (p<0.05) as speed of contralateral or protrusive tasks increased. The data suggest an important role for SHLP in generation and control of contralateral and protrusive jaw movements. A number of lines of evidence were consistent with functional heterogeneity within SHLP. CONCLUSIONS 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 Kumar Bhutada
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Level 3, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW, Australia
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De Santis R, Mollica F, Zarone F, Ambrosio L, Nicolais L. Biomechanical effects of titanium implants with full arch bridge rehabilitation on a synthetic model of the human jaw. Acta Biomater 2007; 3:121-6. [PMID: 16997642 DOI: 10.1016/j.actbio.2006.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2005] [Revised: 06/06/2006] [Accepted: 07/06/2006] [Indexed: 11/22/2022]
Abstract
A composite model of the mandible, constituted by an inner polymeric core and a glass fibre reinforced outer shell, has been developed and equipped with six ITI titanium implants and a full gold alloy arch bridge prosthesis. The effects of this oral rehabilitation on the biomechanics of the mandible are investigated through a simulation of the lateral component of the pterygoid muscles. These muscles are involved as the mouth is opened and closed, hence their activity is very frequent. An increase of the mandible stiffness due to the prosthesis is observed; moreover, the coupling of the relatively stiff rehabilitation devices with the natural tissue analogue leads to stress-shielding and stress-concentration in the incisal and molar regions, respectively. Although the amplitude of the force generated by pterygoid muscles is quite small, high strains over the incisal region are measured. A stress-shielding effect, of about 20%, is observed at the symphysis as the full arch bridge prosthesis is fixed on the implants. Therefore, the presence of the prosthesis leads to significant modification of the stress field experienced by the mandible, and this may be relevant in relation to the biomechanics of mandibular bone remodelling.
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Affiliation(s)
- Roberto De Santis
- Institute for Composite and Biomedical Materials, National Research Council, Piazzale Tecchio 80, 80125 Napoli, Italy
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Sae-Lee D, Wanigaratne K, Whittle T, Peck CC, Murray GM. A method for studying jaw muscle activity during standardized jaw movements under experimental jaw muscle pain. J Neurosci Methods 2006; 157:285-93. [PMID: 16765448 DOI: 10.1016/j.jneumeth.2006.05.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 04/05/2006] [Accepted: 05/02/2006] [Indexed: 11/28/2022]
Abstract
This paper describes a method for studying superficial and deep jaw muscle activity during standardized jaw movements under experimental jaw muscle pain. In 22 healthy adults, pain was elicited in the right masseter muscle via tonic infusion of 4.5% hypertonic saline and which resulted in scores of 30-60 mm on a 100-mm visual analogue scale. Subjects performed tasks in five sessions in a repeated measures design, i.e., control 1, test 1 (during hypertonic or isotonic saline infusion), control 2 (without infusion), test 2 (during isotonic or hypertonic saline infusion), control 3 (without infusion). During each session, subjects performed maximal clenching and standardized jaw tasks, i.e., protrusion, lateral excursion, open/close, chewing. Mandibular movement was recorded with a 6-degree-of-freedom tracking system simultaneously with electromyographic (EMG) activity from the inferior head of the lateral pterygoid muscle with fine-wire electrodes (verified by computer tomography), and from posterior temporalis, the submandibular muscle group and bilateral masseter muscles with surface electrodes. EMG root mean square values were calculated at each 0.5 mm increment of mandibular incisor movement for all tasks under each experimental session. This establishes an experimental model for testing the effects of pain on jaw muscle activity where the jaw motor system is required to perform goal-directed tasks, and therefore should extend our understanding of the effects of pain on the jaw motor system.
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Affiliation(s)
- Daraporn Sae-Lee
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Professorial Unit, Level 3, Westmead Hospital Centre for Oral Health, Westmead, NSW 2145, Australia
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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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Huang BY, Whittle T, Peck CC, Murray GM. Ipsilateral interferences and working-side condylar movements. Arch Oral Biol 2006; 51:206-14. [PMID: 16154529 DOI: 10.1016/j.archoralbio.2005.07.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Revised: 07/12/2005] [Accepted: 07/20/2005] [Indexed: 10/25/2022]
Abstract
UNLABELLED There is limited knowledge of the effects of the occlusion on temporomandibular joint function. AIM The aim was to investigate the influence of a working-side occlusal alteration (OA, i.e. interference) on trajectories of working-side condylar points during standardized lateral jaw movements (laterotrusion) tracked by a jaw-tracking system. METHODS Ten trials of right laterotrusion were repeated under: control 1 (before OA), OA (immediately after placement of a working-side interference) and control 2 (immediately after removal of OA) conditions. RESULTS During right jaw movement, the paths of the working-side condylar points under OA were significantly more inferior and anterior to those under control at the same amount of mid-incisor-point displacement from the intercuspal position. The OA significantly reduced the rotation of the mandible about the antero-posterior and supero-inferior axes and significantly increased the opening angle. Controls 1 and 2 were not significantly different. CONCLUSIONS A working-side interference has an immediate, significant effect on working-side condylar movement.
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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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De Santis R, Mollica F, Esposito R, Ambrosio L, Nicolais L. An experimental and theoretical composite model of the human mandible. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2005; 16:1191-7. [PMID: 16362221 DOI: 10.1007/s10856-005-4728-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Accepted: 08/19/2005] [Indexed: 05/05/2023]
Abstract
The purpose is to design and manufacture a composite mandible replicate suitable for testing the influence of prosthetic materials on the stress distribution of bone. Composite mandibles made of a poly(methylmethacrylate) core and a glass reinforced outer shell are manufactured and characterised through mechanical tests assisted by the finite element analysis. The mandible replicate has been conveniently equipped with strain gauges, moreover a video extensometer has also been used in order to measure the arch width change during loading. A close agreement is found between the experimental data and the theoretical predictions. By laterally loading the mandibles the maximum values of stress and strain take place in the premolar-incisal region. By varying technological parameters such as the fiber volume fraction and orientation, it is easy to replicate the behaviour of mandibles having different stiffnesses. The results obtained by laterally loading the composite mandibles through the condyles or through the gonion regions are consistent with literature data relative to the arch width decrease of natural jaws during opening and closing. This novel synthetic system coupled with the Finite Element model constitutes an experimental-theoretical model suitable to investigate the biomechanical effects of oral rehabilitations on mandibular bone.
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Affiliation(s)
- R De Santis
- Institute of Composite and Biomedical Materials-National Research Council, Piazzale Tecchio 80, Napoli, 80125, Italy.
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12
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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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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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Phanachet I, Whittle T, Wanigaratne K, Klineberg IJ, Sessle BJ, Murray GM. Functional heterogeneity in the superior head of the human lateral pterygoid. J Dent Res 2003; 82:106-11. [PMID: 12562882 DOI: 10.1177/154405910308200206] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The activity of the superior head of the human lateral pterygoid muscle (SHLP) is controversial. Given the non-parallel alignment of some SHLP fibers, the SHLP may be capable of differential activation. The aims were to clarify SHLP activity patterns in relation to location within SHLP. In 18 subjects, SHLP single motor units were intramuscularly recorded at computer-tomography-verified sites during horizontal (e.g., protrusion) and vertical (e.g., opening) jaw tasks (recorded by a jaw-tracking device) and at resting postural jaw position. None of 92 units was active at the resting postural position. Medially located units (21) showed activity during contralateral movement, protrusion, and opening; 5 were also active on jaw closing. There was a significant association between unit location and the number of units active during vertical tasks (i.e., jaw closing and clenching). Analysis of the data suggests differential activation within SHLP and raises the possibility of functional heterogeneity within SHLP.
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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, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia
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POINT (CRITIQUE). IMPLANT DENT 2002. [DOI: 10.1097/00008505-200207000-00002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Phanachet I, Whittle T, Wanigaratne K, Murray GM. Functional properties of single motor units in the inferior head of human lateral pterygoid muscle: task firing rates. J Neurophysiol 2002; 88:751-60. [PMID: 12163527 DOI: 10.1152/jn.2002.88.2.751] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The precise function of the inferior head of the human lateral pterygoid muscle (IHLP) is unclear. The aim of this study was to clarify the normal function of the IHLP. The hypothesis was that an important function of the IHLP is the generation and fine control of horizontal (i.e., anteroposterior and mediolateral) jaw movements. The activities of 50 single motor units (SMUs) were recorded from IHLP (14 subjects) during two- or three-step contralateral movement (n = 36) and/or protrusion (n = 33). Most recording sites were identified by computer tomography. There was a statistically significant overall increase in firing rate as the magnitude of jaw displacement increased between the holding phases (range of increments: 0.3-1.6 mm). The firing rates during the dynamic phases for each unit were significantly greater than those during the previous holding phases but less than those during the subsequent holding phases. For the contralateral step task at the intermediate rate, the cross-correlation coefficients between jaw displacement in the mediolateral axis and the mean firing rate of each unit ranged from r = 0.29 to 0.77; mean +/- SD; r = 0.49 +/- 0.13 (protrusive step task: r = 0.12-0.74, r = 0.44 +/- 0.14 for correlation with anterior-posterior axis). The correlation coefficients at the fast rate during the contralateral step task and the protrusive step task were significantly higher than those at the slow rate. The firing rate change of the SMUs per unit displacement between holding phases was significantly greater for the lower-threshold than for the higher-threshold units during contralateral movement and protrusion. After dividing IHLP into four regions, the SMUs recorded in the superior part exhibited significantly greater mean firing rate changes per unit displacement during protrusion than for the SMUs recorded in the inferior part. Significantly fewer units were related to the protrusive task in the superior-medial part. These data support previously proposed notions of functional heterogeneity within IHLP. The present findings provide further evidence for an involvement of the IHLP in the generation and fine control of horizontal jaw movements.
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Affiliation(s)
- I Phanachet
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Westmead Centre for Oral Health, Westmead Hospital, Australia
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Uchida S, Whittle T, Wanigaratne K, Murray GM. The role of the inferior head of the human lateral pterygoid muscle in the generation and control of horizontal mandibular force. Arch Oral Biol 2001; 46:1127-40. [PMID: 11684032 DOI: 10.1016/s0003-9969(01)00077-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The aim was to test the hypothesis that the inferior head (IH) of the human lateral pterygoid muscle (LP) is involved in the generation and fine control of horizontal isometric mandibular force. Although previous studies provided some evidence for this, they had limitations that necessitate a re-examination. In eight participants, electromyographic (EMG) activity was recorded from the IHLP unilaterally, as well as bilateral surface recordings from the masseter (M) and anterior temporalis (AT), and the submandibular group of muscles (SUBM), during the generation of horizontal isometric mandibular force in a direction contralateral to the side of the IHLP recording. Isometric force at 5-8 mm open from the intercuspal position was exerted on a transducer (attached by a bar to the upper teeth) by a rod attached to the lower teeth. Participants tracked a target on a video screen that required 5-s holding periods at each 100 gwt (0.98 N) between 400 gwt (3.92 N) and 800 gwt (7.84 N). The mean of multi-unit EMG activity from all muscles during the most stable 2-s force-holding periods increased significantly with each force increment (GLM repeated measures: P<0.0001). When normalized, the multi-unit data from the IHLP exhibited the steepest rate of increase. The mean firing rates of 21 IHLP single motor units (SMUs) significantly increased with force (GLM repeated measures: P<0.0001). Two SMUs fired in advance of force onset, which suggests a role in force initiation. There were close associations between fluctuations in force and in IHLP SMU firing rates and multi-unit activity, but a similar correspondence was not as clear for the other recorded jaw muscles. These findings suggest that the IHLP is important in the generation and fine control of contralaterally directed, horizontal jaw forces.
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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, Westmead, NSW 2145, Australia
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Phanachet I, Whittle T, Wanigaratne K, Murray GM. Functional properties of single motor units in inferior head of human lateral pterygoid muscle: task relations and thresholds. J Neurophysiol 2001; 86:2204-18. [PMID: 11698512 DOI: 10.1152/jn.2001.86.5.2204] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of this study was to clarify the normal function of the inferior head of the human lateral pterygoid muscle (IHLP). The hypothesis was that an important function of the IHLP is in the fine control of horizontal jaw movements. The activities of 99 single motor units (SMUs) were recorded from IHLP (22 recordings from 16 subjects). Most recording sites were identified by computer tomography (CT). All 99 SMUs were active during contralateral jaw movements with the teeth apart, and protrusive jaw movements with the teeth apart, and 81% (48 of 59 units studied during all 3 tasks) were active during submaximal jaw-opening movements. None were active on maximal ipsilateral or retrusive jaw movements with the teeth apart nor on jaw closing/clenching in intercuspal position; nor were they spontaneously active when the jaw was at the clinically determined postural jaw position. Thresholds of SMUs ranged from <0.2 mm of contralateral or protrusive horizontal displacements to 61-89% of the maximum contralateral or protrusive displacement, respectively. For the 35 units continuously active during the contralateral task, 23 (66%) were recruited within 2 mm of contralateral displacement [25 (63% of 40 units) for protrusion]. Recruitment thresholds (mm) of some of the units were rate dependent with thresholds significantly decreasing with increasing rate of horizontal jaw movement in protrusion and contralateral movements. At eight recording sites where up to six SMUs were able to be discriminated, the average thresholds of successively recruited SMUs were within a 1-mm increment of horizontal jaw displacement. After dividing IHLP into four regions, the SMUs recorded in the superior-medial zone exhibited significantly lower mean threshold values than for the SMUs recorded in the other zones (no units were recorded in the inferior-lateral zone). This provides suggestive evidence supporting previously proposed notions of functional heterogeneity within IHLP. Taken together, the data suggest that specific regions of the IHLP are capable of selective activation in a finely controlled manner to allow the application of the appropriate force vector (magnitude and direction) to effect the required condylar movement needed for the generation and control of horizontal jaw movements.
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Affiliation(s)
- I Phanachet
- Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, University of Sydney, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia
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