Physiology of skeletal muscle orthodontic considerations

bite raising effects muscle physiology

1. PHYSIOLOGY OF SKELETAL MUSCLE - Sakshi katyal 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

2. Contents: Introduction Development, structure of skeletal muscle. Events of muscle contraction Innervation of muscle Reflex types Methods of studying muscle activity a. Histological Muscle fiber types b. Electromyography 7. Adaptive response of jaw muscles to anatomical adaptations , physiological, pathological conditions and therapeutics. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

3. INTRODUCTION Knowledge of muscle is valuable to the science of contemporary orthodontics, is well defined by functional matrix theory. “ If neither Bone nor cartilage was the determinant for growth of the craniofacial skeleton, it would appear that the control would have to lie in the adjacent soft tissues”. -MELVIN MOSS,1960 Role of muscle in characteristic craniofacial growth pattern, malocclusion etiology and in therapeutic intervention is well known… 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

4. Skeletal muscle: Bundles of Long cylindrical Multinucleated cells Shows cross-striations Cardiac muscle: Elongated branched Individual cells Lie parell to each other Also shows cross striations At sites of end to end contact are intercalated discs Smooth muscle: Collection of fusiform cells Do not show striations Under Voluntary control Quick and forceful contraction Involuntary Vigrous and rhythmic contraction Involuntary Slow contraction 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

5. SKELETAL MUSCLE : ITS DEVELOPMENT Multinucleation results from fusion of embroynic mesenchymal cells called as myoblasts to form myotubes 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

6. SKELETAL MUSCLE : STRUCTURE AND ORGANIZATION Epimysium (surrounding entire muscle) Perimysium (Each fascicle of muscle fibers ) Endomysium ( Individual muscle fibers ) 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

7. MICROSCOPIC STRUCTURE OF MUSCLE FIBRE(SARCOMERE) 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

8. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

9. EVENTS AND MECHANISM OF SKELETAL MUSCLE CONTRACTION. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

10. Innervation of muscle: 1.Muscle receptors (spindle and tendon organ) 2. Motor unit Muscle spindle: Consists of connective tissue capsule surrounding a few thin non striated muscle fibers densely filled with nuclei.. Several sensory nuclei penetrate and wrap around individual fibers.. Detects change in length of extrafusal muscle fibers and regulates it. Golgi tendon organ : Connective sheath encapsulaion of myotendinous junction with sensory nerve penetration. Detects and regulates tension within muscle. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

11. Motor unit Number of muscle fibers innervated by one motor neuron. Fewer the muscle fibers per motor neuron.. Precise the movement.. Eg . Inferior lateral pterygoid has relatively low muscle fiber to motor neuron ratio…therefore capable of fine adjustments in length needed to adapt to horizontal changes in mandibular position.. In contrast masseter muscle has greater number of motor fibers per motor neuron which corresponds to gross function in providing force for mastication.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

12. Motor unit morphology: Heterogenous distribution of fiber types co-relates with its differential activation. More deep and anterior muscle regions contain relatively large number of slow fiber types ( erickson and thornell,1983) Similarly, more slow type fibers are present in Anterior part of temporalis and deep part of masseter . Motor unit activation : Recruitment gradation Rate gradation 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

13. REFLEX TYPES: Two types of reflex actions in masticatory system : 1 .Myotactic reflex : when a skeletal muscle is quickly stretched this protective reflex is elicited and brings about contraction of stretched muscle.. Importance in holding jaw joint against gravity.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

14. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS 2. Nociceptive reflex : is polysynaptic protective reflex to noxious stimuli. eg ,. When hard object is suddenly encountered during mastication lead to motor stimulation to jaw opening muscles and inhibition of jaw closing muscles.. Jaw quickly drops and teeth are pulled away..

15. Muscle function: Isotonic contraction : shortening under a constant load ( eg . occurs in masseter when mandible is elevated forcing the teeth through a bolus of food..) . Isometric contraction : when a proper number of motor units contract opposing a given force, resultant function muscle is to stabilize the jaw. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

16. Controlled relaxation: when stimulation of motor unit is discontinued.. muscle fibers relax.. Precise muscle lengthening occurs that allows smooth deliberate movements. Eccenteric contraction: lengthening of the muscle at the same time it is contracting. Eg . Tissue damage associated during an extension flexion injury (whiplash injury). Eg.During motor cycle accident. Cervical muscles contract to support head and resist movement however the impact is great sudden change in head inertia causes it to move . 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

17. Eccenteric contraction ( whiplash injury). 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

18. Methods of studying muscle activity ANATOMICAL (HISTOLOGICAL FIBER TYPES) Cross-section of skeletal muscle stained histochemically to detect the density of myofibrillar myosin- ATPase can be used to demonstrate the distribution of slow (S) type I fibers , intermediate (I) type IIa fibers , and fast (F) type IIb fibers . 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

19. MUSCLE FIBER TYPES AND RELEVANCE: Skeletal muscle fibers of humans are classified into three types: ( based on physiological biochemical histological charactersitics ).. Type I Slow Red oxidative fibers Many mitochondria Abundant myoglobin ( fe ++ containing protein that binds with O2 giving red color) Energy source: primarily from aerobic oxidative phosphorylation of fatty acids . Adapted for slow continuous contractions over prolonged periods.. As required in postural muscles.. TYPE IIA Fast/intermediate Oxidative glycolytic fibers Many mitochondria Much myoglobin But also considerable glycogen Energy source – both oxidative phosphorylation And anaerobic glycolysis Adapted for rapid contractions and short bursts of activity .. As required for athletics.. TYPE II B Fast , white glycolyic fibers Fewer mitochondria Less myoglobin Abundant glycogen Energy source : mainly glycolysis Adapted for rapid contractions but fatigue quickly. Typical in small muscles with large no of NMJ. Muscles that move eyes and digits.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

20. Electromyography Electromyography is the recording and study of the intrinsic electrical properties of skeletal muscle by means of electrodes in resting and contracting states The primary function of an electromyograph is to record, amplify and display a low-amplitude neuromuscular signal in the presence of high-amplitude noise and interference Parts of an EMG machine Electrodes : Sensors that detect electrical potentials. Leads : connects the recording electrode to the amplifier. Black for the Active (E1) electrode Red for Reference (E2) Green or white for Ground Differential amplifier : M agnifies the potential difference between the active(E1) and reference inputs(E2). Common mode rejection – reduce noise and increase signal- noise ratio 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

21. Electrode configuration Monopolar configuration One electrode is placed over the muscle and one electrode as the reference Bipolar Configuration Two electrodes are placed over the muscle and one electrode as reference The signal between the two electrodes over the muscle is amplified differentially respect to the reference electrode. Signal: noise radio is increased  03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

22. Surface Electrode Signals consist of a superimposed and summated action potentials from many fibers.. Disadvantage: - high Potential for cross talk from adjacent muscles Needle electrode Fine wire electrodes for insertion into belly of muscle. Advantages Specific pick-up area - Ability to test deep and small muscles without cross talk. Disadvantages Needle insertion increases the tightness or spasticity in the muscles. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

23. Electrode placement The most common inter-electrode distance is 20 mm Electrode material - Silver-silver chloride electrodes that minimize motion artefacts produced by skin potentials Electrode is placed along the longitudinal direction of muscle fibers Skin cleaned with alcohol and mild scrub M uscle function test is performed to identify the muscle belly Pancherz (1980) Yuen et al (1990) Reproducible methods for electrode replacement 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

24. Lateral pterygoid muscle: Salame et al (2007) -  Straight needle used to position fine-wire electrodes into IHLP Needle is inserted 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 .. ideal insertion depth 29. mm Electrode placement Insertion site : distance between centre of EAM to the point on skin perpendicular to the centre of muscle parallel to campers plane. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

25. P rocessing of EMG signals Filters: The EMG activity is usually filtered for the range of 10 Hz (High pass filters) to 5 KHz (low pass filters) Rectifiers T urn all the signal values integrative(Full wave) Eliminates negative values(Half wave) 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

26. Raw EMG signals Analysis of unprocessed is mostly qualitative Duration – measured from the initial deflection from baseline to the terminal deflection back to baseline It reflects the synchrony and also the muscle fiber density A mplitude Measured from peak to peak Reflect the depolarized fibers nearest to the recording electrode X-axis shows range of amplitudes Y-axis shows the percentage of time spent at any given amplitude 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

27. Chronic neuropathy Polyphasic , high amplitude and long duration MUAP M yopathic and neuromuscular junctions (NMJ) disorders MUAPs are of short duration, small amplitude and also polyphasic EMG pattern in neuromuscular disorders 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

28. Diagnostic EMG Neurological disorders (NCS) Muscle disorders Sleep apnoea Kinesiological EMG Sports physiology Movement analysis - evaluates timing of muscle activity with regard to the movements Uses of EMG 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

29. Adaptive response of jaw muscles: Anatomical adaptation Of Size MyHC isoforms . To Craniofacial morphology To physiological and pathological conditions: Nasal obstruction Occlusal relationship Response to therapeutic interventions: Myofunctional appliances Oral splints Increase in vertical dimension Mandibular advancement Orthognathic surgery Distraction osteogenesis Detachment of jaw muscles Surgical treatment of mandibular condylar fractures Aesthetic plastic surgery 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

30. Adaptive response of jaw muscles to altered functional demands : Size: fiber hypertrophy and atrophy Fiber type transistion : switching different MyHC isoforms . (SCHIARNNO AND REGGIANI, 1994) MyHC -I MyHC IIA MyHC IIX MyHC IIB (slower) (fast fiber types) Overloading elicits transistion towards slower fiber types... 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

31. #Jaw muscles and craniofacial morphology..: Ingervall and helkimo , 1978 Weak jaw muscles have greater variation in facial morphology.. Thickness of muscle: Resistance training by isometric contraction increases thickness of muscle (stores more glycogen and more mitochondria in number).. Adaptive changes in size are fully reversible. ( anderson and aagaard ;2007) Weijs and hillen , 1984 : short faced subjects.. Thicker jaw closing muscles.. Kiliardis and kalebo,1991 : long face subjects have significantly thinner muscles.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

32. Volume of muscle: Masseter muscle volume had a negative correlation with mandibular plane angle and gonial angle.. Masseter and Medial pterygoid muscle volume showed a positive correlation with posterior face height. Subjects with large masseter and medial pterygoid muscle volumes had flat mandibular and occlusal planes, and small gonial angles. Ref : Gionhaku N, Lowe AA. Relationship between jaw muscle volume and craniofacial form. J Dent Res. 1989 May;68(5):805-9. Growing patients with a dolichofacial vertical pattern present with a reduced dimension of the masseter when compared with brachyfacial and mesofacial subjects.. REF: Lione R,  Franchi L e al. Three-dimensional evaluation of masseter  muscle in different vertical facial patterns: a cross-sectional study in growing children. Ultrason Imaging. 2013 Oct;35(4):307-17. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

33. Length of muscle: Tabary and goldspink et al. 1972 muscles fibers could adapt to alterations in functional length by addition or deletion of sarcomeres to muscles fibers or by rearrangement of muscles fibers or both . Becht MP et al (2014) – evaluated the length and orientation of masseter in different types of malocclusions using CBCT. Significant differences were found in masseter length between the three vertical groups and significant differences in muscle orientation angle were found among the three anteroposterior groups The largest length was found in the normo -divergent group and shorter length in hyperdivergent group . 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

34. Craniofacial form and Proportion of fibres in medial pterygoid muscles: short faced have larger proportion of type II.. Produces max. force of short duration.. (Hunt et al., 2006) Muscle activity and craniofacial form: Adaptive changes in both maxillary and mandibular dental arch form and size occurred in response to alterations in tongue size, form, and position. Bishara and jakobsen , 1985 Long face subjects generates less jaw closing muscle activity than short faced.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

35. JAW MUSCLE RESPONSE TO PHYSIOLOGICAL AND PATHOLOGICAL CONDITIONS 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

36. A.Muscular activity and nasal obstruction: Nasal obstruction… mandible is lowered to allow breathing through mouth.. Change in posture …. Decrease in resting emg activites of temporalis and increase of suprahyoid muscles.. Jaw muscles adapt to their new functional lengths by increasing number of sarcomeres in series within each fibre to re-establish optimum overlap of contracin proteins.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

37. B.Occlusion and muscle function: Mesial jaw relation : postural emg activities of masseter and temporalis are higher( tecco et al.,2007), differnces attributed to muscular action axis and increase in gravitation component in class III malocclusions.. Distal jaw relation (class II div 1): Pancherz H. 1980 During maximal biting in intercuspal position the boys with Class II malocclusion exhibited less EMG activity in the masseter and temporal muscles be attributed to diverging dentofacial morphology and unstable occlusal contact conditions. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

38. # Laterognathism : masseter m. oriented more vertically, smaller lengths, nd volumes on deviated side.. Less myoelectrical activity during functional use(atrophy).. ( ingervall and thilander 1975; ferrario et al., 1999).. Shift towards fast fiber types.. # Deep/open bite cases : inc.in type II fibres ; ant. Open bite cases..inc in type I fibers. Emg activity greater wrt masseter nd temporalis in deep bite than open bite. # Premature contacts alter the occlusal balance and lead to smaller no of activities per hour.. Lower amplitudes of muscle activity..( ingervall and carlsson , 1982) Reduced occlusal stability weak elevator muscle activity ( bakke and michler,1991) # Edentulous patients .. Lesser cross-sectional area and muscle activity.. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

39. Jaw muscle response to various therapeutic interventions: 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

40. Response to functional appliance therapy Andresen and Haupl (1936) - Myotatic reflexes lead to isometric contractions from the activities of the jaw-closing muscles, which stimulates the protractor muscles and inhibits the retractor muscles of the mandible Selmer-Olsen(1937) and Umehara (1941) failed to observe active muscle contractions during nocturnal use of the activator and claimed that the viscoelastic properties of the muscles and the stretching of soft tissues are responsible for activator action McNamara and Carlson (1973) M odification of functional position of the mandible results in an immediate alteration of the neuromuscular activity of the orofacial muscles, particularly noticeable in the lateral pterygoid muscles. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

41. The functional appliances commonly used in growing individuals to correct sagittal and vertical malocclusions, displace mandible forwards ( anderson’s and herbst appliance) and downwards ( eg . Posterior bite blocks)cause stretching of soft tissues and muscles.. Has been linked to neuromuscular and skeletal adaptations. Acc. To functional matrix theory of moss.. Proposes that facial form is modified by function. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

42. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS Aggarwal P et al (1999) reported increase in postural & swallowing EMG activity following treatment with twin block. The increased activity was attributed to myotatic reflex of the elevator muscles which play a dominant role in the neuromuscular changes with Twin block treatment and not passive tension due to viscoelasticity of muscles M. J. Trenouth (2000) - Only maximum biting force EMG activity showed a significant increase throughout treatment. The amount of maximum biting force time throughout 24 hours is quite small which is approximately 12% of the total time Muscle response to the Twin-block appliance

43. #Muscle response to the Twin-block appliance: EMG activity of elevator muscles masseter and anterior temporalis increases in class II div 1 patients with twin block therapy at 0, 1, 3, 6 months following insertion… attributed to enhanced myotactic (stretch reflex) of elevator muscles contributing to isometric contractions and increase in active tension in the stretched muscle. Functional appliances that are worn full-time like Herbst , Jasper Jumper, and Twinblock can be expected to elicit a greater and more rapid neuromuscular response than those worn only part-time, eg , activator. Ref: . Aggarwal P 1 ,  Kharbanda OP ,  Mathur R ,  Duggal R ,  Parkash H . Muscle response to the twin-block appliance: an  electromyographic  study of the  masseter  and anterior temporal muscles. Am J Orthod Dentofacial Orthop .  1999 Oct;116(4):405-14 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

44. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

45. Evaluation of changes in the dimension of masseter muscle during various phases of Twin Block appliance using MRI Chaudhary P (2010 ) studied masseter muscle dimension during active phase of twin block therapy over 6 month using MRI . Due to mild atrophy of masseter muscle, there was an initial decrease in volume, cross-sectional area and thickness of masseter muscle in response to altered functional environment by Twin Block appliance therapy. As adaptation to altered environment continued, muscle showed a tendency towards normalization in its size but remains less than baseline at 6 months .

46. Herbst , functional regulator, twinblock …postural and functional activity of superior and inferior head of lat. Pterygoid increases after insertion of functional appliance.. Acts to stimulate increased condylar growth.. Ref: Yamin-Lacouture C 1 , Woodside DG, Sectakof PA, Sessle BJ. The action of three types of functional appliances on the activity of the masticatory musclesAm J Orthod Dentofacial Orthop .  1997 Nov;112(5):560-72. The initial condition of the masticatory muscles may partly determine treatment outcomes. Children with thinner pre-treatment masseter  muscles or weaker bite force show greater dentoalveolar changes . ref: Antonarakis GS 1 ,  Kiliaridis  S Predictive value of  masseter muscle thickness and bite force on Class II functional appliance treatment: a prospective controlled study. Eur J Orthod . 2015 Jan 11. pii : cju089 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

47. Jaw muscle response to various therapeutic interventions: Increse in vertical dimension: Initial response of jaw closing muscle to bite opening is increase in their emg activity… Approx. 1 week later muscle start to adapt by increasing MyHC TYPE 1 and IIA ( ohunki et al.2000) Although sarcomere length doesnot change permanently; adaptation of length is by increasing sarcomere number hence fiber length.. ( goldspink , 1998) Oral splints : m/c treatment provided for CMD, reorganises neuromuscular reflex activity, elongattion of jaw muscles to / near the dimension of least emg activity (resting zone); ( manns et al.,1983). Effects of splints may be transient ( hoimgren et al 1990;) 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

48. Jaw muscle activity in association wrt various surgical interventions: # Orthognathic surgery: Mandibular repositioning transiently decreases electrical activity of muscles ( raustia and oikarien 1994) likely a result of surgical trauma.. Post retention phase of surgery electrical activity of masseter , lat. Pterygoid , temporalis continue to rise till aleast 1 yr after surgery.. Crossectional areas and volumes of masseter decrease both after mandibular advancement and setback surgery ( katsumata et al 2004.) In long term digastric lengthens on mandibular advancement ; masseter and medial pterygoid on mandibular setback… stretch induced hypertrophy of their type I fibers . 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

49. Jaw muscle response to various therapeutic interventions: (continued)… 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS Mandibular advancement : by altering functional pattern of orofacial musculature of patient, muscle force is utilized to orthodontic or orthopaedic forces … emg of jaw closing dec . and that of jaw opening muscles increase ( hiyama at al. 2000, voudouris et al 2003 ).. Remain altered during about first 6 months of treatment… slowly returns to initial levels.. TypeII B transform to type I, IIA, IIX ( gedrange et al., 2001). Increase in crossectional area of TYPE I Detachment of jaw muscles: With regard to orthognathic surgery, the golden rule is that the pterygo-masseteric sling must not be stretched, otherwise relapse is likely to occur. Therefore, the masseter and medial pterygoid muscles are often temporarily detached during mandibular setback surgery in order to reduce post-operative relapse due to muscle pull.

50. Conclusion: Jaw muscles are versatile entities capable of changing their size, cross-sectional area, and fi bre properties to adapt to altered functional demands. The dynamic nature of muscle fi bres allows them to change their phenotype to optimize contractile function and energy uptake. These changes in the phenotype are refl ected in differences in the contraction velocity and the maximum force generated by the muscle. -THANKYOU . 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

51. References: Development, structure of skeletal muscle: Junqueira's Basic Histology Text & Atlas, 12e. pg: 201-218 2. Muscle function and reflex types Okeson JP. Management of temporomandibular disorders and occlusion. 6 th ed. Mosby USA; 2013. p. 25-39 3. Histologically Muscle fiber types Junqueira's Basic Histology Text & Atlas, 12e. Pg 217 Motor unit Okeson JP. Management of temporomandibular disorders and occlusion. 6 th ed. Mosby USA; 2013 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

52. ref. Elecromyography : Surface electrodes: Pullman SL, Goodin DS, Marquinez AI, Tabbal S, Rubin M. Clinical utility of surface EMG: report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology. Neurology 2000; 55(2) 171-177. Needle electrodes : Daube JR, Rubin DI. Needle electromyography. Muscle Nerve 2009; 39(2) 244-270 Merletti R, Farina D. Analysis of intramuscular electromyogram signals. Philos Transact A Math Phys Eng Sci 2009; 367(1887): 357-68. ). Skin preparation: ( Merletti and Migliorini , 1998 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

53. Electrode placement Salame TH 1 , Peck CC, Murray GM. A new method for lateral pterygoid electromyographic  electrode placement. J Prosthet Dent. 2007 Sep;98(3):224-31. Yuen SW 1 , Hwang JC,  Poon PW Changes in power spectrum of electromyograms of masseter and anterior temporal muscles during functional appliance therapy in children. Am J Orthod Dentofacial Orthop .  1990 Apr;97(4):301-7. EMG pattern in neuromuscular disorders Buchthal . Electromyography in the evaluation of muscle diseases. Methods in ClinicalNeurophysiology 1991; 2 25-45 Processing of EMG signals Leandro Ricardo Altimari . influence of Different Strategies of TreatmentMuscle Contraction and Relaxation Phases on EMG Signal Processing and Analysis During Cyclic Exercise. Pg 4 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

54. Adaptive response of jaw muscles Grünheid T 1 , Langenbach GE et al. The adaptive response of jaw muscles to varying functional demands. Eur J Orthod. 2009 Dec;31(6):596-612 Fiber type transistion : switching different MyHC isoforms Schiaffino S 1 ,  Reggiani  C. Myosin isoforms in mammalian skeletal muscle. J Appl Physiol (1985). 1994 Aug;77(2):493-501. Jaw muscles and craniofacial morphology Ingervall B, Helkimo E. Masticatory muscle force and facial morphology in man. Arch Oral Biol. 1978;23(3):203-6. Weijs WA,  Hillen  B. Relationships between masticatory muscle cross-section and skull shape. J Dent Res. 1984 Sep;63(9):1154-7. Kiliaridis S 1 ,  Kälebo P. Masseter muscle thickness measured by ultrasonography and its relation to facial morphology. J Dent Res. 1991 Sep;70(9):1262-5 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

55. Volume of muscle: Gionhaku N 1 , Lowe AA. Relationship between jaw muscle volume and craniofacial form. J Dent Res. 1989 May;68(5):805-9. Lione R 1 ,  Franchi L et al. Three-dimensional evaluation of masseter  muscle in different vertical facial patterns. Ultrason Imaging. 2013 Oct;35(4):307-17 Length of muscle: Tabary JC,  Goldspink  G. Physiological and structural changes in the cat's soleus muscle due to immobilization at different lengths by plaster casts. J Physiol. 1972 Jul;224(1):231-44. Becht MP et al Evaluation of masseter muscle morphology in different types of malocclusions using cone beam computed tomography. Int Orthod. 2014 Mar;12(1):32-48. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

56. Muscle activity and craniofacial form Bishara SE ,  Jakobsen JR . Longitudinal changes in three normal facial types. Am J Orthod.  1985 Dec;88(6):466-502 Muscular activity and nasal obstruction: Grünheid T 1 ,  Langenbach Ge et al. The adaptive response of jaw muscles to varying functional demands. Eur J Orthod.  2009 Dec;31(6):596-612. Occlusion and muscle function: Mesial jaw relation Tecco   S 1 ,  Tete S ,  Festa F . Relation between cervical posture on lateral skull radiographs and electromyographic activity of masticatory muscles in caucasian adult women: a cross-sectional study. J Oral Rehabil.  2007 Sep;34(9):652-62. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

57. Distal jaw relation Pancherz H. Activity of the temporal and masseter muscles in class II, division 1 malocclusions. An electromyographic investigation. J. Orthod. Dentofac. Orthop., 1980, 77, 679–688. Laterognathism Ingervall B, Thilander B. Activity of temporal and masseter muscles in children with a lateral forced bite. Angle Orthod. 1975 Oct;45(4):249-58. Premature contacts Ingervall B, Carlsson GE Masticatory muscle activity before and after elimination of balancing side occlusal interference. J Oral Rehabil. 1982 May;9(3):183-92. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS

58. Response to functional appliance therapy Ref: Aggarwal P 1 ,  Kharbanda OP ,  Mathur R ,  Duggal R ,  Parkash H . Muscle response to the twin-block appliance: an  electromyographic  study of the  masseter  and anterior temporal muscles. Am J Orthod Dentofacial Orthop .  1999 Oct;116(4):405-14. Yamin-Lacouture C 1 ,  Woodside DG et al., The action of three types of functional appliances on the activity of the  masticatory  muscles. Am J Orthod Dentofacial Orthop .  1997 Nov;112(5):560-72. Antonarakis GS 1 , Kiliaridis S. Predictive value of  masseter muscle thickness and bite force on Class II functional appliance treatment: a prospective controlled study. Eur J Orthod. 2015 Jan 11. pii : cju089. Paphangkorakit J, Osborn JW. Effect of jaw opening on the direction and magnitude of human incisal bite forces.J Dent Res. 1997 Jan;76(1):561-7. 03-08-2015 Department of Orthodontics and Dentofacial Deformities, CDER, AIIMS