The biomechanics of stresses induced by removable partial denture/ fixed orthodontic training

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  • The biomechanics of stresses induced by removable partial denture/ fixed orthodontic training

    1. 1. 11 THE BIOMECHANICSTHE BIOMECHANICS OF STRESSES INDUCEDOF STRESSES INDUCED BY REMOVABLEBY REMOVABLE PARTIAL DENTUREPARTIAL DENTURE INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.comwww.indiandentalacademy.com
    2. 2. www.indiandentalacademy.comwww.indiandentalacademy.com 22 CONTENTSCONTENTS IntroductionIntroduction What Is StressWhat Is Stress Simple machinesSimple machines Development of forcesDevelopment of forces Forces acting on the removable partial dentureForces acting on the removable partial denture Distribution of stress between the teeth andDistribution of stress between the teeth and tissuetissue Induced stresses to be recognizedInduced stresses to be recognized Consequence of inefficient management of stressesConsequence of inefficient management of stresses ConclusionConclusion BibliographyBibliography
    3. 3. www.indiandentalacademy.comwww.indiandentalacademy.com 33 INTRODUCTIONINTRODUCTION  Nature has designed theNature has designed the StomatognathicStomatognathic system to dissipate the forces of masticationsystem to dissipate the forces of mastication to the supporting structures.to the supporting structures.  In a partially edentulous situation theIn a partially edentulous situation the mechanism of dissipating the force by themechanism of dissipating the force by the dentition is compromised due to the breach indentition is compromised due to the breach in integrity of the dental arches.integrity of the dental arches.
    4. 4. www.indiandentalacademy.comwww.indiandentalacademy.com 44
    5. 5. www.indiandentalacademy.comwww.indiandentalacademy.com 55  When a removable partial denture is usedWhen a removable partial denture is used to restore the missing natural teeth and toto restore the missing natural teeth and to maintain the continuity of the dental archesmaintain the continuity of the dental arches it is important for the dentist to consider theit is important for the dentist to consider the direction ,duration and frequency of thedirection ,duration and frequency of the force application as well as the magnitude.force application as well as the magnitude.
    6. 6. www.indiandentalacademy.comwww.indiandentalacademy.com 66 What is stress?What is stress? An internal force that resists an externallyAn internal force that resists an externally applied load or force. GPTapplied load or force. GPT Different types of stresses areDifferent types of stresses are Compressive stressCompressive stress Tensile stressTensile stress Shear stressShear stress
    7. 7. www.indiandentalacademy.comwww.indiandentalacademy.com 77 SimpleSimple machinesmachines With the introduction of the removable partial denturesWith the introduction of the removable partial dentures into the oral cavity certain simple machines come intointo the oral cavity certain simple machines come into play. These canplay. These can magnifymagnify the stresses .It is thereforethe stresses .It is therefore important to know its functioning to maintain the health ofimportant to know its functioning to maintain the health of the oral structures.the oral structures. LeverLever WedgeWedge ScrewScrew Wheel and axleWheel and axle PulleyPulley Inclined planeInclined plane
    8. 8. www.indiandentalacademy.comwww.indiandentalacademy.com 88 Development of forcesDevelopment of forces The most commonly encountered simpleThe most commonly encountered simple machines in removable partial denture are:machines in removable partial denture are: LeverLever Inclined planeInclined plane It should be borne in mind that the success of aIt should be borne in mind that the success of a removable partial denture lies in avoiding theseremovable partial denture lies in avoiding these to the greatest extent possibleto the greatest extent possible..
    9. 9. www.indiandentalacademy.comwww.indiandentalacademy.com 99 LeverLever AA lever is a rigidlever is a rigid bar that rests on abar that rests on a fulcrum (a fixedfulcrum (a fixed point.)point.) The farther the forceThe farther the force is from the fulcrum,is from the fulcrum, the easier it is tothe easier it is to work the leverwork the lever There areThere are threethree classesclasses of levers.of levers.
    10. 10. www.indiandentalacademy.comwww.indiandentalacademy.com 1010 Class IClass I AA class-1class-1 leverlever has itshas its fulcrum locatedfulcrum located somewhere betweensomewhere between the effort and thethe effort and the resistanceresistance E.g. Distal extensionE.g. Distal extension removable partialremovable partial denturedenture
    11. 11. www.indiandentalacademy.comwww.indiandentalacademy.com 1111 Class IIClass II With aWith a class-2 leverclass-2 lever,, the fulcrum is at onethe fulcrum is at one end, the effort is at theend, the effort is at the other end and theother end and the resistance is in theresistance is in the middlemiddle Seen as indirectSeen as indirect retention in removableretention in removable partial denturepartial denture
    12. 12. www.indiandentalacademy.comwww.indiandentalacademy.com 1212 Class IIIClass III In aIn a class-3 leverclass-3 lever. The. The fulcrum is at one end andfulcrum is at one end and the effort is appliedthe effort is applied between the fulcrum andbetween the fulcrum and the resistance.the resistance. Not encountered inNot encountered in partial denturespartial dentures TMJ muscles and teethTMJ muscles and teeth act as a class III leveract as a class III lever
    13. 13. www.indiandentalacademy.comwww.indiandentalacademy.com 1313 Inclined PlaneInclined Plane Forces against theForces against the inclined plane may resultinclined plane may result in deflection of thatin deflection of that which is applying thewhich is applying the force or may result inforce or may result in the movement of thethe movement of the inclined plane .inclined plane . Neither of these resultsNeither of these results are desirableare desirable E.g Cingulum rest seatE.g Cingulum rest seat on cuspidson cuspids
    14. 14. www.indiandentalacademy.comwww.indiandentalacademy.com 1414 Forces acting on the partialForces acting on the partial denture.denture.
    15. 15. www.indiandentalacademy.comwww.indiandentalacademy.com 1515 Forces acting during placementForces acting during placement and removal of the partialand removal of the partial denturedenture 1)1) When a contacting rigid area of a removableWhen a contacting rigid area of a removable partial denture passes over the surface bulge ofpartial denture passes over the surface bulge of the abutment teeth.the abutment teeth. 2)2) Movement of the retentive clasp out of theMovement of the retentive clasp out of the infrabulgeinfrabulge area and over the abutment height ofarea and over the abutment height of contour.contour.
    16. 16. www.indiandentalacademy.comwww.indiandentalacademy.com 1616 Forces acting on tooth and tissueForces acting on tooth and tissue borne removable partial dentureborne removable partial denture Forces acting on a distal extension partialForces acting on a distal extension partial denture are a result of a composite of forcesdenture are a result of a composite of forces arising from the three principal fulcrums.arising from the three principal fulcrums. 1) Fulcrum on the1) Fulcrum on the horizontal plane.horizontal plane. 2) Fulcrum on the2) Fulcrum on the sagittal plane.sagittal plane. 3) Fulcrum on the3) Fulcrum on the vertical plane.vertical plane.
    17. 17. www.indiandentalacademy.comwww.indiandentalacademy.com 1717 Fulcrum on theFulcrum on the horizontal planehorizontal plane Extends through theExtends through the two principaltwo principal abutments, one onabutments, one on each side of the dentaleach side of the dental arch.arch. Controls rotationalControls rotational movement of themovement of the denture in the sagittaldenture in the sagittal plane.plane.
    18. 18. www.indiandentalacademy.comwww.indiandentalacademy.com 1818 Fulcrum on theFulcrum on the Sagittal PlaneSagittal Plane Extends through theExtends through the occlusal rest on the terminalocclusal rest on the terminal abutment and along theabutment and along the crest of the residual ridgecrest of the residual ridge on one side of the archon one side of the arch The fulcrum controls theThe fulcrum controls the rotational movement of therotational movement of the denture in the vertical planedenture in the vertical plane
    19. 19. www.indiandentalacademy.comwww.indiandentalacademy.com 1919 Fulcrum on theFulcrum on the vertical planevertical plane Located in the vicinity ofLocated in the vicinity of the midline just lingualthe midline just lingual to the anterior teeth.to the anterior teeth. Controls the rotationalControls the rotational movement of themovement of the denture in the horizontaldenture in the horizontal direction.direction.
    20. 20. www.indiandentalacademy.comwww.indiandentalacademy.com 2020 Forces acting on tooth supportedForces acting on tooth supported removable partial dentureremovable partial denture Kennedy’s Class III situationKennedy’s Class III situation Supported by abutmentsSupported by abutments Force against it are transmittedForce against it are transmitted down the long axisdown the long axis of the abutment teethof the abutment teeth
    21. 21. www.indiandentalacademy.comwww.indiandentalacademy.com 2121 Distribution of stress betweenDistribution of stress between teeth and tissue?teeth and tissue? Two schools of thought exists in the matter ofTwo schools of thought exists in the matter of allocating the proportionate share of stress thatallocating the proportionate share of stress that is to be sustained by the tooth and the residualis to be sustained by the tooth and the residual ridge.ridge.
    22. 22. www.indiandentalacademy.comwww.indiandentalacademy.com 2222 Stressbreaker SchoolStressbreaker School Residual ridgeResidual ridge bearbear the stresses and teeth bethe stresses and teeth be spared.spared. Use of flexible or movable joint between theUse of flexible or movable joint between the teeth and the metal framework.teeth and the metal framework.
    23. 23. www.indiandentalacademy.comwww.indiandentalacademy.com 2323 Wide Distribution of StressWide Distribution of Stress SchoolSchool Support provided by aSupport provided by a combinationcombination ofof abutment tooth and the mucosa.abutment tooth and the mucosa. Various clinical techniques and designVarious clinical techniques and design variations have been tried so as to exploit thevariations have been tried so as to exploit the maximum load bearing capacity of each.maximum load bearing capacity of each.
    24. 24. www.indiandentalacademy.comwww.indiandentalacademy.com 2424 Induced stresses to beInduced stresses to be recognizedrecognized
    25. 25. www.indiandentalacademy.comwww.indiandentalacademy.com 2525 Stress resulting from applianceStress resulting from appliance inaccuraciesinaccuracies Orthodontic stressOrthodontic stress MalocclusionMalocclusion Impingement of subbasalImpingement of subbasal structuresstructures
    26. 26. www.indiandentalacademy.comwww.indiandentalacademy.com 2626 Stress from interference toStress from interference to appliance insertionappliance insertion Intermittent disturbance of tooth alignment .Intermittent disturbance of tooth alignment . Contacting rigid area of a removable prosthesisContacting rigid area of a removable prosthesis passes over the surface bulge of the abutmentpasses over the surface bulge of the abutment tooth.tooth.
    27. 27. www.indiandentalacademy.comwww.indiandentalacademy.com 2727 Gingival impingement by theGingival impingement by the removable applianceremovable appliance Gingivae most susceptible to injury by anyGingivae most susceptible to injury by any pressure induced by a removable prosthesis.pressure induced by a removable prosthesis.
    28. 28. www.indiandentalacademy.comwww.indiandentalacademy.com 2828 Stress on a sloping tooth surfaceStress on a sloping tooth surface for the support of an abutmentfor the support of an abutment occlusal rest.occlusal rest. Seen while using cuspid tooth for abutmentSeen while using cuspid tooth for abutment services with steep lingual surface.services with steep lingual surface. Appliance slips as occlusal load is appliedAppliance slips as occlusal load is applied which can cause gingival irritation.which can cause gingival irritation.
    29. 29. www.indiandentalacademy.comwww.indiandentalacademy.com 2929 Stress resulting in the impingementStress resulting in the impingement by a major connectorby a major connector Trauma from flexingTrauma from flexing Trauma from lateral appliance movementTrauma from lateral appliance movement Trauma from connector settlement.Trauma from connector settlement.
    30. 30. www.indiandentalacademy.comwww.indiandentalacademy.com 3030 Factors influencing magnitude ofFactors influencing magnitude of stress transmitted to thestress transmitted to the abutment teethabutment teeth
    31. 31. www.indiandentalacademy.comwww.indiandentalacademy.com 3131 Length Of SpanLength Of Span Longer Edentulous SpanLonger Edentulous Span==Longer DentureLonger Denture BaseBase==Greater Force to the Abutment TeethGreater Force to the Abutment Teeth The fulcrum is located at or near the occlusalThe fulcrum is located at or near the occlusal rest of the terminal abutment tooth.rest of the terminal abutment tooth. The denture base determines how muchThe denture base determines how much force the abutment tooth must withstand.force the abutment tooth must withstand.
    32. 32. www.indiandentalacademy.comwww.indiandentalacademy.com 3232 Quality of support of ridgeQuality of support of ridge Large well formed ridges areLarge well formed ridges are capable of absorbing greatercapable of absorbing greater amounts of stress than are smallamounts of stress than are small thin or knife edged ridges.thin or knife edged ridges. Broad ridges with parallel sidesBroad ridges with parallel sides  longer flanges on denturelonger flanges on denture basebase stabilizes the denturestabilizes the denture against the lateral forcesagainst the lateral forces
    33. 33. www.indiandentalacademy.comwww.indiandentalacademy.com 3333 Approximately 1mm thick mucoperiosteumApproximately 1mm thick mucoperiosteum can bear greater functional loads thancan bear greater functional loads than atrophic mucosa.atrophic mucosa. Soft flabby displaceable tissue allowsSoft flabby displaceable tissue allows excessive movement.excessive movement.
    34. 34. www.indiandentalacademy.comwww.indiandentalacademy.com 3434 Qualities of claspQualities of clasp The more flexible the retentive arm of the clasp ,The more flexible the retentive arm of the clasp , the less stress is transmitted to the abutmentthe less stress is transmitted to the abutment tooth.tooth. A passive clasp will exert less force than anA passive clasp will exert less force than an active clasp.active clasp.
    35. 35. www.indiandentalacademy.comwww.indiandentalacademy.com 3535 Flexibility can be increased byFlexibility can be increased by lengtheninglengthening the clasp.the clasp. Clasp length is increased by using a curvedClasp length is increased by using a curved path on an abutment tooth.path on an abutment tooth. Gold clasps will exert less stress on theGold clasps will exert less stress on the abutment than chrome alloy.abutment than chrome alloy.
    36. 36. www.indiandentalacademy.comwww.indiandentalacademy.com 3636 Abutment tooth surfaceAbutment tooth surface The surface of a gold crown or restoration givesThe surface of a gold crown or restoration gives more frictional resistance to clasp armmore frictional resistance to clasp arm movement than the enamel surface of the tooth.movement than the enamel surface of the tooth. Hence greater stress is exerted on a toothHence greater stress is exerted on a tooth restored with gold than on a tooth with intactrestored with gold than on a tooth with intact enamel.enamel.
    37. 37. www.indiandentalacademy.comwww.indiandentalacademy.com 3737 Occlusal harmonyOcclusal harmony Disharmonious occlusionDisharmonious occlusion generates horizontalgenerates horizontal forcesforces Partial denturePartial denture constructed to opposeconstructed to oppose natural dentition will facenatural dentition will face more stresses.more stresses.
    38. 38. www.indiandentalacademy.comwww.indiandentalacademy.com 3838 If the occlusalIf the occlusal loadload is applied to the baseis applied to the base adjacent to the abutment toothadjacent to the abutment tooth , there will be, there will be less movementless movement of the denture base asof the denture base as compared if the load was applied to the distalcompared if the load was applied to the distal end.end. The occlusal load should be applied in theThe occlusal load should be applied in the center of the denture bearing area.center of the denture bearing area.
    39. 39. www.indiandentalacademy.comwww.indiandentalacademy.com 3939 Consequence of inefficient management ofConsequence of inefficient management of stresses induced by partial denturestresses induced by partial denture GreaterGreater stressesstresses Abutment ToothAbutment Tooth OrthodonticOrthodontic movement.movement. Malocclusion.Malocclusion. Residual RidgeResidual Ridge Inflammation,Inflammation, Edema of residualEdema of residual ridge mucosa.ridge mucosa. Resorptive loss ofResorptive loss of adjacent alveolaradjacent alveolar process .process .
    40. 40. www.indiandentalacademy.comwww.indiandentalacademy.com 4040 CONCLUSIONCONCLUSION Removable Partial Dentures can be aRemovable Partial Dentures can be a boon or a bane based on theboon or a bane based on the understanding of its biomechanicalunderstanding of its biomechanical principles.principles. Blindly done, the removable partialBlindly done, the removable partial denture can act as a potentiallydenture can act as a potentially destructive device which could inducedestructive device which could induce more harm than than the good it wasmore harm than than the good it was intended for.intended for.
    41. 41. www.indiandentalacademy.comwww.indiandentalacademy.com 4141 BibliographyBibliography Removable partial prosthodonticsRemovable partial prosthodontics - McCRACKEN- McCRACKEN Clinical Removable Partial ProsthodonticsClinical Removable Partial Prosthodontics - STEWART- STEWART Essentials Of Removable Partial Denture ProsthesisEssentials Of Removable Partial Denture Prosthesis - APPLEGATE- APPLEGATE Partial denturesPartial dentures -JOHN-JOHN OSBORNEOSBORNE Removable Partial ProsthodonticsRemovable Partial Prosthodontics -GRASSO-GRASSO Removable Denture ProsthodonticsRemovable Denture Prosthodontics - GRANT- GRANT
    42. 42. www.indiandentalacademy.comwww.indiandentalacademy.com 4242 AcknowledgementsAcknowledgements I would like to thankI would like to thank Dr Geetha K PatilDr Geetha K Patil Dr Malathi DayalanDr Malathi Dayalan Dr Nagaraj K.RDr Nagaraj K.R Dr Shilpa ShettyDr Shilpa Shetty Dr Manjunath .S.BDr Manjunath .S.B Dr Bharath ShettyDr Bharath Shetty Without whose help and support thisWithout whose help and support this presentation would not have been possiblepresentation would not have been possible
    43. 43. www.indiandentalacademy.comwww.indiandentalacademy.com 4343

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