Biomechanics in removable partial denture
Download as PPTX, PDF113 likes39,683 views
The document discusses the application of biomechanics in prosthodontics, focusing on the mechanical principles that affect removable partial dentures (RPDs). Key factors include stress types (vertical, horizontal, torsion) and resistance strategies (tooth-based and tooth-tissue based). It also introduces concepts such as the lever principle and the snow shoe principle to optimize prosthesis design for stress distribution.
Biomechanics in removable partial denture
- 1. TASEEF HASAN FAROOK, BDS (final year)
- 2. What is Biomechanics in Prosthodontics? Application of mechanical principles on biological tissues while studying the biology from a functional viewpoint and then using these principles to design a stable prosthesis.
- 3. Biomechanical considerations: The RPD and their associated structures are subjected to various forms of stress. Their ability to resist them depend on: Direction, Duration, Magnitude and frequency of the Stress (Force) being applied onto the denture and denture bearing areas Capacity of these areas to resist these forces/stress Changes due to resistance over time The type of Resistance Generated: 1. Tooth based 2. Tooth and Tissue based
- 4. Types of Stress (Force) acting on an RPD within the oral cavity: These stresses can be classified into: 1. Vertical - a) Displacing Force b) Dislodging Force 2. Horizontal 3. Torsion Resistance to stress can be divided into: 1. Tooth based resistance contributes mainly to resisting Horizontal Stress (direct retainers) 2. Tooth-Tissue based resistance contributes to resisting Vertical Stress and Torsion (major connectors and indirect retainers)
- 6. Factors contributing to the amount of Stress on the RPD: • The length of edentulous span (example: Kennedy Classification III usually exhibit no lever action) • Quality of Ridge Support (example: Wider ridges disperse more stress due to the Snow Shoe Principle) • Quality of Oral Mucosa (example: Healthy mucosa are able to withstand much greater force than weak flabby mucosa) • Clasp Design (flexibility, length and material used) • Occlusal Harmony
- 7. Principles of Mechanical forces (According to McCraken):
- 8. Mechanical Force Principles to be considered within the oral cavity: 1. Lever Principle (Further divided into Orders I, II and III) 2. Inclined Plane Principle 3. Wheel and Axle (Rotation) Are of prime concern while designing an RPD LEVER PRINCIPLE INCLINED PLANE PRINCIPLE
- 9. WHEEL AND AXLE PRINCIPLE (along horizontal axis) WHEEL AND AXLE (along Saggital Axis)
- 10. Types of lever Action: There are 3 types of mechanical lever action based on: 1.the position of the fulcrum 2.The location of the load along the fulcrum line. 3.The area from which the effort to displace is exerted
- 11. First Order Lever Action (Class I):
- 12. Example of 1st Order Lever Action In cantilever type of Removable Partial Denture where There is Distal Extension. If there is bone Resorption of the residual alveolar ridge under the distal extension, it will result in an effort leading to first order lever movement along the fulcrum line.
- 13. Second Order Lever Action (Class II)
- 14. Third Order Lever Action (Class III)
- 15. Example of third order Lever action: Usually seen in the tooth supported RPD. Upon consuming sticky food, the food exerts pulling effort on the prosthetic teeth while the natural teeth and retainers exert counteracting forces from both sides.
- 16. Biomechanics of Inclined Planes: The rest will ‘slip off’ the inclined rest seat However, flattening the rest seat will aid in the retention of the direct retainer on the tooth surface and resist horizontal forces
- 17. Wheel and Axle Principle: (Rotation) The Partial denture can rotate along one of 3 planes: A. The saggital plane B. The frontal plane C. The horizontal Plane And along one of 3 axes: 1. Saggital axis 2. Vertical axis 3. Horizontal axis.
- 19. Rotation of Frontal Plane along Saggital Axis Rotation of Horizontal Plane along Vertical Axis
- 20. Saggital Plane and Horizontal Axis Rotation
- 21. Frontal Plane Rotation Along the saggital Axis
- 22. Snow Shoe Principle The basis of the principle is to distribute stress/forces onto as large an area as possible in order to counteract the stresses applied to a partial denture.
- 23. Snow Shoe Principle In order to overcome the forces acting against the RPD, the prosthesis must take full advantage of all the primary and secondary stress bearing areas. Ex. Buccal shelf area are the primary stress bearing areas in the mandible because of their position on the occlusal plane. Not extending the denture to the shelf area will result in displacing forces and horizontal forces during mastication.
- 24. References: • McCraken’s Removable Partial Prosthodontics , 11th and 12th editions • Stewart’s Clinical Removable Prosthodontics, 3rd edition • Basic Principles of removable partial denture, Abbasi Begum, online journal, slideshare.net, 06-06-2016 • RPD biomechanics, Foundation for Oral Facial Rehabilitation, online journal, ffofr.org • Biomechanics of removable partial denture, Dr Ann Winchy, Dept. of Oral Health and rehabilitation, University of Louisville, 17-05-2014.