biomechanics in rpd

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a short presentation on the biomechanics in Removable Partial Denture.... a very important topic to be understood completely for easy designing of cast framework and also to know the problems in already treated conditions


  • 1. Biomechanics ofRemovable partialdenture

2. INTRODUCTIONBiomechanics basically deals with application ofmechanical principles to biological tissues. In the oral cavity one would find a number of sources of stressgeneration, the human body is built in such a manner that it learns to adapt to any stressful situation. However when we try to create an artificialreplacement of that natural component which is lost,we are at a loss in making it fully functional and adaptable. 3. Biomechanics (GPT 7): 1: the application of mechanical laws to livingstructures, specifically the locomotor systems of thebody. 2: the study of biology from the functional viewpoint. 3: An application of the principles of engineeringdesign as implemented in living organisms. 4. Mechanical principles applicable in Removable Prosthodontics Lever principle Inclined plane Snowshoe principle 5. Lever: A simple machine consisting of a rigid bar pivoted on a fixed point and used to transmit force, as in raising or moving a weight at one end by pushing down on the other. 6. LeverClass I 7. Class II 8. Class III 9. Inclined plane Inclined plane Forces against an inclined plane may result in deflection of that which is applying the forces or may result in movement to the inclined plane, neither of these is desirable. 10. Snowshoe principle This principle is based on distribution of forces to as large an area aspossible. Like in a snow shoe which is designed to distribute forces onthe entire base area of the shoe, a partial denture should covermaximum area possible within the physiologic limits so as todistribute the forces over a larger area. 11. Stress consideration in a partial dentureThe stresses can be divided as: Vertical1.Displacing stresses2. Dislodging stresses Horizontal Torsional 12. Displacing stress Those forces which are the result of stresses along the longaxis of the teeth in a crown to apex direction and therelatively vertical stresses on the ridge mucosa. These arethe least harmful and are born well if within physiologiclimits. 13. Dislodging stress These are the forces which tend to lift the partial denture from itsrest position. Reciprocal dislodging action occurs when wideedentulous spaces are interrupted by few teeth thus inviting anantero-posterior or lateral tilt of prosthesis. 14. Horizontal stress They originate as a component of rhythmic chewingstroke. These forces are effective in mesio-distal andbuccolingual direction. These lateral stresses are mostdamaging. 15. Torsional stressIt is a twisting rotational type of force. Its a combination ofvertical and horizontal force. Torsion is noted most frequentlywhere a long segment acts upon the first abutment it engages.Where the ridge mucosa has higher resiliency torque is higher.Torque applies rotation about a fixed point. 16. Biomechanical considerationof individual componentPerpetual preservation of what is remaining is moreimportant than meticulous replacement of what is lost De Van 17. Major connector Connects parts of prosthesis located on one sideof the arch with those on the opposite side Should be rigid: Distribution of force Effectiveness of other components If flexible forces concentrated on individual teeth orridge damaging. 18. Direct retainer 19. RestRelation between rest andabutment should be suchthat forces should bedirected apically downalong the long axis of thetooth Stress absorbed byfibers of PDL withoutgetting damaged. 20. Indirect retainerTo prevent the DEB frommoving away from its seatbecause of cheek andtongue forces, sticky food.It uses mechanicaladvantage of leverage bymoving the fulcrum linefarther from the force. 21. Contributes to support andstability of the partial denturecounteracts horizontal forcesapplied to the denture. Longspan mandibular lingual barmajor connector (even iftooth supported), IR providesadditional support and rigidityfor lingual bar. Preventsimpingement of the lingualbar on the mucosa duringfunction. 22. Factors influencingmagnitude of stress 23. Length of span 24. Quality of ridge 25. Type of mucosa 26. Clasp type 27. Clasp design 28. Amount of tooth contact 29. Occlusion 30. Control stress by design consideration 31. 1. Retention as a means of stress control A) forces of adhesion and cohesion B) atmospheric pressure C) Frictional contact D) Neuromuscular control 32. Strategic clasp positioninga) Quadrilateral configurationb) Tripod configurationc) Bilateral configuration 33. Clasp designa) circumferential claspb) bar claspc) combination clasp 34. 4 Indirect retention5 Functional basing6 occlusion a) harmonious occlusion b) size of food table c) occlusal pattern of posterior teeth 35. 7 Denture base a) Size & configuration b) accuracy of adaptation of base to the tissues 36. Removable partial dentures by design are intended to be removed from and replaced into the mouth. Because of this, they are not rigidly connected to the teeth or tissues, which means that they are subjected to movement in response to functional loads. These movement can cause generation of stresses which if not controlled , can damage the remaining teeth and supporting bone.Efforts must be always directed towards minimizing the harmful forces on the remaining teeth by proper designing of the RPD. 37. THANK YOU