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Int J Physiother Res 2014;2(6):772-76. ISSN 2321-1822 772

Review Article

IS MASTICATORY FORCE AT MOLAR REGION ANALOGICAL TOSTAPLING MECHANICS AND BOTH BELONGING TO ANUNIDENTIFIED LEVER SYSTEM?R.Vinodh Rajkumar.

Founder: PALEOLITHICX, Physiotherapist & Functional Fitness Training Instructor (Freelance),Bangalore, Karnataka, India.

For easy and clear understanding of biomechanics, the inter-relationships of simple machines andmusculoskeletal functions have always been attempted and established. The masticatory biomechanics is stillunder research because there is wide range of findings on masticatory muscles including the lack of completeclarity on their line of actions and lever arms too. As a prospective contribution to advanced research onmastication and management of Temporomandibular joint, there are two innovative concepts discussed in thisarticle; (1) Strong correlation between stapling mechanics and Temporomandibular joint biomechanics atmolar region (2) Scope for a new unidentified lever system named as fourth class lever. The principal intent ofthis article is to share these two innovative concepts to be explored further for practical applications in thefield of Physical therapy, Dentistry and Engineering.KEYWORDS: Stapling mechanics, Mastication at molar region, unidentified lever system.

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International Journal of Physiotherapy and ResearchISSN 2321- 1822

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ABSTRACT

INTRODUCTION

Address for correspondence: R.Vinodh Rajkumar, # 638, 1st Floor, Jakkuramma Building, BehindEswara Temple, 1st Cross, 1st Main, Mathikere, Bangalore-560054, Karnataka, India.Mobile: 9008424632 E-Mail: [email protected]

International Journal of Physiotherapy and Research,Int J Physiother Res 2014, Vol 2(6):772-76. ISSN 2321-1822

DOI: 10.16965/ijpr.2014.692

The functions of some simple machines and thethree identified lever systems are commonlycorrelated for better understanding ofmusculoskeletal biomechanics. It appears thatthe stapling mechanics and the masticatory actat the molar region are similar, that may alsobelong to an unidentified lever system. Chewingor Occlusion, in a dental context is thephenomenon of interaction of mandible andmaxillary teeth, bones, and muscles and thisprocess is also called as mastication and theforce acting during this process is known asmasticatory force or biting force.1 Bite force is

an important variable to investigate oralfunction related to occlusal factor, dentition,dentures, and treatment with implants,orthognathic surgery, temporo-mandibulardisorders and neuromuscular changes.2 It wasalso observed that the biting force was higherin the posterior pairs of teeth and comparativelylower in the anterior pairs.3

The anatomy and biomechanics of Tempo-romandibular joint (TMJ) is elaboratelydiscussed in various textbooks for PhysicalTherapists which makes it obvious the role ofPhysical Therapists in some aspects pertinentto Dentistry. Exercise therapy has long beenused in the treatment of TMJ disorders and

DOI: 10.16965/ijpr.2014.692

Accepted : 11-11-2014Published (O): 23-11-2014Published (P): 11-12-2014

Received: 31-10-2014Peer Review: 31-10-2014Revised: None

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R.Vinodh Rajkumar. IS MASTICATORY FORCE AT MOLAR REGION ANALOGICAL TO STAPLING MECHANICS AND BOTH BELONGING TO ANUNIDENTIFIED LEVER SYSTEM?

therapeutic exercise interventions are prescribedto address specific TMJ impairments and toimprove the function of the TMJ andcraniomandibular system.4 The lack of clarity insome aspects of TMJ functions and the demandfor detailed researches in the management ofTMJ disorders have also been reported. Thereis a clear need for well-designed controlled trialsexamining physical therapy interventions for TMJdisorders.5 The line of action of masticatorymuscles is still not clear and the lever actionadvocates do not always agree on how toanalyze the chewing apparatus.6 Various suchliteratures indicate the requirement for furtherbetter understanding of the TMJ and themasticatory functions. As a prospectivecontribution to this requirement, there are twoinnovative concepts discussed in this article; (1)Strong correlation between stapling mechanicsand Temporomandibular joint biomechanics atmolar region (2) Scope for a new unidentifiedlever system named as fourth class lever. Theprincipal intent of this article is to share thesetwo innovative concepts to be explored furtherfor practical applications in the field of Physicaltherapy, Dentistry and Engineering.Mechanical-Biomechanical analysis andinterpretationsStaplers are used in putting together varioussheets of paper. Photograph 1 shows a simplestapler version that can be operated chieflybetween thumb and index finger as shown inPhotograph 2 but it may also demand theauxiliary role of other fingers based on thethickness of sheets to be stapled as shown inPhotograph 3. The force requirement is directlyproportional to the thickness of the sheetsplaced at the stapling ends. To understand thelever system of the stapler, the three accreditedlever systems should be recalled at this juncture- Figure 1a, 1b, 1c & 1d. The relative locationsof the applied force, the resistance, and thefulcrum or axis of rotation determine leverclassifications.7 Lever arm is used to describethe distance from the axis to the point at whicha force is applied to the lever, hence effort arm(EA) refers to the lever arm of effort force andresistance arm (RA) refers to the lever arm ofthe resistance.8 Resistance arm is also namedas load arm (LA) by some authors.9 All

these three lever systems usually possessunequal lengths of effort arm (EA) and load arm(LA) but the first class lever system of somemachines like see-saw possess equal lengthsof EA and LA- Figure 1a. Mechanical advantageis the ratio of the effort arm to the load arm,thus it is directly proportional to EA and inverselyproportional to LA. A lever system is said to be100% mechanically efficient if the leverage ofEA and LA are equal whilst EA>LA can increasethe mechanical efficiency beyond 100% (stilldepending on the load) and EA<LA can decreasethe mechanical efficiency below 100%. If weclosely examine the stapler (Photograph-1), itpossesses a unique feature as shown in Figure-2 with equal leverages of EA & LA on the sameside that is quite different from all the threeaccredited lever systems. The points ofapplication of efforts by the thumb and indexfinger are in line with the point at which the loadgets placed. Not only that, the line joining thepoints of effort and the point of load also tendsto intersect the stapler perpendicularly(Photograph 4 & 5).

Photograph 1: F- Fulcrum of the stapler, E - Effortapplying points for the thumb and the index finger,

L- place for Load (sheets of paper) at the stapling ends,EA - Effort arm, LA - Load arm.

Photograph 2: Role of the thumb and the index fingerwhen only few sheets of paper are to be stapled.



Photograph 3: Auxiliary role of other fingers whenmany sheets of paper are to be stapled.

Fig. 1: (a) First class lever with equal lever arms (b)Second class lever (c) Third class lever (d) First class

lever with unequal lever arms. F- Fulcrum, E - Effort, EA- Effort arm, L- Load, LA - Load arm.

Fig. 2: Effort arm = Load arm, but different from thefunctions of first class lever shown in Figure 1a.

Fig. 3a,3b,3c: Schematically shows the of molarregion, maxilla, mandible, Temporomandibular joint

(TMJ).

Fig. 4a,4b,4c: 4a & 4b schematically shows the equalleverages of load arm and effort arm of the Masseterthat should be matched with Figure-2. Also to be notedis the action line of Masseter perpendicular to man-dible. 4c schematically shows the increased load armas the food particle is placed in the incisor region whilethe effort arm of the Masseter remains unchanged (Thirdclass lever with unequal lever arms)

Photograph 4: The sheets of paper (L) and the placewhere the efforts (E) are applied.

Photograph 5: The line joining load (L) and the pointsof efforts (E) looks perpendicularly intersecting the

stapler.

All these interpretations of stapling mechanicsshould be compared with TMJ function at molarregion. The TMJ is one of the most complex,delicate and highly used joints in a humanbody.10 Mandibular elevation predominantlyhelps in mastication at different distances fromTemporomanibular joint for different purposes



with the bite forces ranging from very soft tohighly forceful. Measuring maximum bite forceis an attempt to quantify the force that mandibleelevator muscles can make.11 The role of theMasseter muscle in the mastication is wellestablished. The masseter muscle closes themouth and is the main muscle used inmastication.12 The Masseter is a powerfulmuscle of mastication that elevates mandible.13

Mansour and Reynik (1975) interpret thebehavior of the mandible as a lever system andnoticed load & effort on the same side withmechanical advantage at the more posteriorportion (molar region).14 All these literaturereviews aptly corresponds with the intendedbiomechanical analysis at molar region chieflyusing the Masseter muscle.Lever systems of mandible and variations in thelength of the load arm have been shownschematically in sagittal view (Figure-3).Thelocation of the food substance from the TMJdetermines the length of the load arm which inturn determines the masticatory forcerequirements. The length of the effort arm andthe masticatory force are inversely proportionaland also belong to third class lever system. Bitingforce is inversely varying to the distance of toothpair from the temporomandibular joint.3 Also atmolar region, better mechanical advantage wasnoticed by Mansour and Reynik.14

Apart from all these foundation knowledge, it isalso possible that the concentration of efforttaken by Masetter (E) and the food substance(L) in the molar region may be at equal distancefrom the TMJ with the action line of Masseterperpendicularly intersecting the mandible. Ifsuch biomechanical arrangement is naturallypossible, then the function of TMJ at molarregion will be an unidentified lever systemanalogical to stapling mechanics (Figure 2,3&4).Hence, the major difference of this unidentifiedlever system is the presence of load and efforton the same side with equal lever arms or le-verages and the line of action of Masseter per-pendicular to the mandible lever. The anatomi-cal location of Masseter in the molar region, asshown in various textbooks and search engines,increases the chance of this line of action ofMasseter and unidentified lever system with100% mechanical advantage as long as the

Masseter effort (E) can overcome the resistanceof the food (L) masticated at the molar regionbut this has to be experimented because theresearches on chewing apparatus and mastica-tory muscles are still ongoing. The externalmorphology of the masseter muscle does notmatch that described in anatomical atlases andtextbooks.15 Studies have reported differencesin the morphological disposition of the humanmasseter muscle stating variations in course andorientation.16 Thickness and the strength of themasseter correlated significantly with facialmorphology.17 The variations in the structuraldisposition of the deep and superficial fibresduring mastication have been described by someauthors.18 Many difficulties will have to be over-come if the goal of the TMJ research is todevelop systems aimed at predicting the TMJloading and stress analysis during mandibularmovements during normal or abnormalneuromuscular control.19 The mean biting forceat molars were found to be the highest ascompared to central incisors, lateral incisors,canine and premolar regions.3 A finer gradationof force and contraction speeds is possible inmasticatory muscles than in limb and in trunkmuscles.20 The motor unit territories are smalland restricted to specific areas in animal andhuman masseter and such an organizationpermits the differential control of separatemuscle portions and also the production ofinternal force vectors with different directionsand magnitudes in muscles with broad attach-ment areas and heterogeneous skeletal leverarms, resulting in differential mechanicalactions.21

CONCLUSION

TMJ kinetics and masticatory functions can befurther researched on the basis of this mechani-cal-biomechanical analysis and interpretations.Masseter as a whole or certain portion ofMasseter with or without possible role of anyother masticatory muscles may be linked to thisstapling mechanics at the molar region. A simpleextra-oral and intra-oral palpation of Massetercontraction during a biting action also confirmstremendous anterior motion of this muscletowards the molar region (in fact the posteriormotion of this muscle also can be felt at the


same time during an extra-oral palpation),perhaps to enhance its sagittal plane dimensionand perpendicular orientation to the mandible.Stapling mechanics analogy to understand theTMJ biomechanics at molar region can beemphasized in the learning systems of PhysicalTherapists and Dentists. The new views aboutthe features of an unidentified lever system withequal lever arms on the same side can also beseriously taken in to consideration for consen-sus, practical applications and accreditation as‘fourth class lever’.

REFERENCES

Conflicts of interest: None

10. Alomar X, Medrano J, Cabratosa J, Clavero J, LorenteM, Serra I, Monill J, Salvador A, Anatomy of thetemporomandibular joint. Seminars in Ultrasound,CT, and MRI 2007;28:170-183.

11. L J Pereira M.B Gavião, L R Bonjardim, P M Casteloand S Andrade Ada. Ultrasonography andelectromyography of masticatory muscles in agroup of adolescents with signs and symptoms ofTMD. Journal of Clinical Pediatric Dentistry2006;30:314-319.

12. Hylander W. L. An experimental analysis oftemporomandibular joint reaction force inmacaques. American Journal of PhysicalAnthropology 1979;51:433-456.

13. Drake R, Vogl AW, Mitchell A, Grays Anatomy forStudents, 927, 2009.

14. Mansour and Reynik. In vivo occlusal forces andmoments. I. Forces measured in terminal hingeposition and associated moments, J Dent Res.1975;54(1):114-20.

15. Ju-Young Lee, Jeong-Nam Kim, Ja-Young Yoo, Kyung-Seok Hu, Hee-Jin Kim, Wu-Chul Song and Ki-SeokKoh, Topographic anatomy of the masseter musclefocusing on the tendinous digitations, ClinicalAnatomy 2012;25(7):889–892.

16. Goto TK, Langenbach ER, Hannam AG. Length changesin the human masseter muscle after jaw movement.Anat Records 2001;262(3):293-300.

17. Weijs WA, Hillen B. Correlation between cross-sectional area of jaw muscles and craniofacial sizeand shape. American journal of physicalAnthropology 1986;70:423-431.

18. Newton J P, Abel E W, Robertson E M, Yemm R. Changesin human masseter and medial pterygoid muscleswith age: a study by computed tomography.Gerodontics. 1987;3:151–154.

19. E.Tanaka, J.H.Koolstra, Biomechanics of theTemporomandibular joint. J Dent Res.2008;87(11):989-991.

20. T.M.J.J Van Eijden, S.J.J. Turkawsk. Morphology andPhysiology of Masticatory Muscle Motor Units,T.M.G.J. Sage publications 2001;12:76.

21. Van Eijden TMGJ, Klok EM, Weijs WA, Koolstra JH.Mechanical capabilities of the human jaw musclesstudied with a mathematical model, Arch Oral Biol.1988;33:819-826.

1. Bakke M. Bite Force and Occlusion. Seminars inOrthodontics, 12:120-26, 2006.

2. A Vander Bilt, A Tekamp., H Van der Glas and J Ab-bink. Bite force and electromyography duringmaximum unilateral and bilateral clenching.European Journal of Oral Sciences. 2008;116:217-222.

3. B K Biswas S Bag & S Pal. Biomechanical analysisof normal and implanted tooth using biting forcemeasurement. International Journal of Engineeringand Applied Sciences 2013;4(2) ISSN 2305-8269.

4. Hertling D, Dussault L. The Temporomandibularjoint. In: Hall CM, Brody LT, eds. TherapeuticExercise: Moving Toward Function. Philadelphia,Pa: Lippincott Williams & Wilkins; 499– 520, 1999.

5. Margaret L McNeely,Susan Armijo Olivo and DavidJ Magee. A Systematic Review of the Effectivenessof Physical Therapy Interventions forTemporomandibular Disorders, Physical Therapy2006;86(5):710-725.

6. Lin Wang. Biomechanical analysis in Humanmasticatory system. Applied mechanics andmaterials 2013;249-250:1294-1300.

7. Susan J Hall, Basic Biomechanics, Chapter-13,Equilibrium and Human movement, Brown & Benchmark, 1991.

8. Cynthia C Norkin and Pamela K Levangie, Jointstructure and function, Chapter 1, Page-33, JaypeeBrothers, 2nd Edition).

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How to cite this article:R.V inodh Rajkumar. IS MASTICATORY FORCE AT MOLAR REGIONANALOGICAL TO STAPLING MECHANICS AND BOTH BELONGING TO ANUNIDENTIFIED LEVER SYSTEM? Int J Physiother Res 2014;2(6):772-776.DOI: 10.16965/ijpr.2014.692


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