Statics of partial denture.
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The document discusses the principles of statics in relation to partial dentures, highlighting the importance of equilibrium and the effects of forces on teeth structures. It covers design planning criteria, potential advantages and disadvantages of various denture designs, and the mechanics involved in ensuring proper support and balance. Additionally, it emphasizes the need for consideration of aesthetics, comfort, and hygiene in denture construction while outlining various design alternatives for achieving effective denture support.
Statics of partial denture.
- 1. Statics of Partial Dentures Professor Dr. Kyaw Tint B.D.S.(IDM), M.D.Sc.(UDM), Ph.D(TMDU) Dip.Med.Ed (UOPH) ,Cert. in Higher Education(IIE,USA) Attached to IADR, JBI, PFA 1st September 2018, Grand Han Thar Hospital
- 3. • Statics is the study of the equilibrium of forces acting on a rigid body • In statics, rigid bodies are structures that deform so little when loaded by forces that the points of application of force undergo minimal displacement • Equilibrium refers to the state when a rigid body is at rest or in uniform motion
- 4. force is characterized by • Magnitude, number, and unit (eg, 30 N) • Direction, represented by the vector arrow, in which the tip points the direction and the length represents the measure of forc • Position of the line of action on which the force can be moved
- 5. Forces that have a common line of action can be combined by simple addition or subtraction. The resultant force lies on this same line of action.
- 6. If two forces are not parallel but have a common point of application, the resultant force is determined by means of a parallelogram of forces The resultant of several nonparallel forces is determined by means of a polygon of forces
- 7. If a force acting on a tooth is not in the direction of the tooth axis or runs at a distance from the axis, a torque acts on the tooth
- 8. In multiple-rooted teeth, eccentric forces can be absorbed to a certain degree. In tilted teeth, forces encountered have disastrous effects when they produce torques that tip the tooth
- 9. • In equilibrium, any force (action force or input force) causes a counterforce (reaction force or output force) that is equal and in the opposite direction (Newton’s third law).
- 10. 1.Stable equilibrium exists when a body seeks to return to its initial position if displaced by external forces. 2. Neutral equilibrium exists when any displacement brings the body into a new equilibrium position. 3.Unstable equilibrium exists when a body tries to leave its original position.
- 11. • In a statically indeterminate system, the equilibrium conditions are insufficient to calculate support reactions; • In a statically determinate system, the support reactions can be ascertained from its equilibrium conditions alone
- 12. Forces Acting on the Residual Dentition • When constructing partial dentures, it is important to ensure that the remaining teeth are not exposed to any eccentric action of force by the retainers. • Sagittal Force • Transverse Force • Vertical Masticatory Force • Spring Force and Friction
- 13. Mixed Support • If a free-end saddle has mixed support, the mechanical system is no longer at rest and can no longer be calculated by statics methods. • For this purpose, kinetics analysis criteria should be used
- 14. • Mucosa-borne dentures can be interpreted as rigid bodies that rest on floating bearings or springs; all compressive, tensile, shearing, and tipping forces will tilt, twist, displace, or tip the rigid body • This is a statically indeterminate system.
- 15. A clasp denture for restoring a free-end saddle is always a statically indeterminate system because it has mixed support
- 17. Different periodontal support areas are formed • Polygonal support areas for alternating edentulous spaces • Square (trapezoidal) support areas • Triangular support areas • Linear supports • Punctiform supports
- 18. Triangular support area Square support area Polygonal support area
- 19. If denture is supported by one tooth, result in the saptial axes, A line between two rests always represent the axis of rotation.
- 20. An axis of rotation also arises when the support line divides the denture body
- 21. Visco-elastic bedding • The compressibility of the mucosa is also influenced by the shape of the support: - Parts that are subject to punctiform loading will sink more deeply (up to 3 mm) than - Edges with linear loading (up to 2 mm), - Extensive saddle areas undergo relatively little sinking (up to 0.5 mm) • Therefore, viscoelastic bedding of the denture should be assumed
- 22. Spring Force and Friction Spring force = Spring constant × Spring deflection (or) F = c × s Friction force = Friction coefficient × Normal force (or ) F = μ × Fn ClaspsHooke’s Law
- 24. Action and Resistance Levers AL= Action lever RL= Resistance Lever Arm
- 25. If the teeth on a denture are set up slightly outside the alveolar ridge on the vestibular side, lever effects may occur, and the denture may be tipped off. The distance from the point of force application to the center of the alveolar ridge is regarded as the action lever arm. Clasping the denture on the opposite side of the jaw counteracts the tipping as a resistance lever arm.
- 26. Design Planning Criteria • Analysis of static relationships • Analysis of physiologic conditions • Cost-effectiveness analysis • Support, Connector, Saddle • Asthetics, Comfort, Efficiency, Hygiene
- 27. Analysis of static relationships • Try to get complete periodontal support • Defined retentive forces of anchoring elements • One clasp with occlusal support, close to saddle • Denture design must actively support to residual dentition through splinting
- 28. Analysis of physiologic conditions • Observe the principles of periodontal hygiene • Design denture frameworks to be stable, slim, and clear of the periodontium and tongue • Make handling and cleaning easy for the patient • Allow for the possibility of periodontal treatment • Avoid using a diversity of materials. • Use biocompatible materials. • Relate esthetic concerns to the patient’s needs
- 29. Cost-effectiveness analysis • Choose simple and effective anchoring elements • Use of prefabricated structural components • Reasonable technical effort and materials • Aftercare, reparability, and extension possibilities etc…
- 30. Residual Dentition Situations and Design Descriptions
- 31. Design 1
- 32. • All of the remaining teeth undergo coronal restoration, and teeth that are close together are subject to primary splinting. • The edentulous gaps are fitted with closed, intracoronal parallel attachments, and the free-end gap is fitted with a T- attachment and a double-arch shear distributor. As a result, secondary splinting of the abutment teeth is achieved
- 33. Static, Advant: & Disadvant:
- 34. STATICS •The statics of a partial denture that is combined with rigid anchoring and supporting elements are balanced. •The free-end saddle may only sink by means of the periodontal resilience of the abutment teeth. •All of the masticatory forces are transferred to the periodontium. •The denture sits absolutely firmly, the periodontal hygiene conditions are favorable, and the result is a reliable long-term restoration
- 35. Advantages • Secure, firm seating in the mouth • Rigid denture–residual dentition connection • No mucosal loading • Worn parts can be replaced • Excellent esthetic quality • Favorable conditions for periodontal hygiene due to intracoronal placement of attachments
- 36. Disadvantages • If artificial and natural teeth are unbalanced, there is a risk of permanent overloading of the abutments • misleads people into demanding too much from the restoration • handling of this construction is problematic • This denture is not a good value for the money
- 37. Design 1: Model cast-clasp denture
- 38. Statics, Advantage&Disadvantage • S: Polygonal support, full clasping • A: Most cost-effective, easy to handle • D: - Mechanical loading to Enamel of abutments, plaque accumulation - Need to prepare guiding plane
- 39. Design 1: Alternative solutions 1 For esthetic reasons, the canines and first premolars on both sides are fitted with Bonwill clasps. The static relationships are comparable if the anterior rests close to the saddle are placed so they can tilt when the free-end saddle is loaded.
- 40. Design 1: Alternative Solutions 2 Fixed partial denture to which a double-arch circular notch at the free-end saddle is created for the shear distribution arm of a monoreducer, More expensive
- 41. Design 2
- 42. Design 2: Alternative solution closed parallel attachments together with double-arch circular notches with shear distributors at the free-end saddles
- 43. Design 3 To identify the rest points The rest points establish the path of the clasps
- 44. An anterior palatal strap or a sectioned plate may be designed, but it does not meet the requirement for tongue clearance. The pressure and fricative field is covered and may impede tongue function (eg, phonetics and taste); in addition, the device is less comfortable to wear. The shaping of the denture framework allows for periodontal Hygiene and tongue clearance
- 45. Full clasping of the remaining teeth offers good splinting effects, providing the horizontal positional stability The diagonal tipping line establishes four resistance levers, which are active against the action lever on the free-end saddle The esthetics are deficient, and periodontal hygiene is adequate
- 46. Design 3: Alternative Solution 14-pontic partial denture in which the free-end pontics are supported on at least one implant placed in the gap A fixed partial denture from the right second molar to the left first premolar is supplemented by a monoreducer in the free-end area, which is secured via a lock attachment and supported by a double-arch shear distributor in a circular notch
- 47. Please take a break…..
- 48. A given force can be resolved if the magnitudes of the single forces are known. To do this, a polygon of forces is constructed by drawing arcs of circles at the origin and at the tip of the force being resolved, along with the radius of the components. The intersection of the arcs establishes the apices of the components