6. PRINCIPLES OF DESIGNING REMOVABLE PARTIAL DENTURE

7. All tooth supported RPD
Tooth and tissue supported RPD

8. All tooth supported RPD

9. Tooth and tissue supported RPD
Class I
Class II
Class IV

10. The forces generated in RPD’s can be understood by analyzing the action of two simple machines.
Liver and fulcrum
Inclined plane

11. Liver and fulcrum First - class lever Second - class lever
Third - class lever

12. Inclined plane

13. Forces acting on partial denture
This fulcrum controls the movement of denture in sagittal plane.
Movement is greatest in magnitude

14. The second fulcrum line extends from occlusal rest of terminal abutment and along the crest of the ridge.
Controls movement in vertical plane.
Most damaging

15. The third fulcrum is located in the vicinity of midline just lingual to the anterior teeth.

16. Every effort should be made to design the RPD to control or minimize rotational movement related to these three fulcrum lines

17. Factors influencing magnitude of stresses transmitted to abutment teeth
Length of span
Quality of support of the ridge
Qualities of the clasp
Clasp design
Length of clasp
Material used
Abutment tooth surface
Occlusal harmony

18. Thorough knowledge of mechanical & biological factors
BASIC PRINCIPLES
Thorough knowledge of mechanical & biological factors
Complete examination & diagnosis of patients
Restoration of form & functions of oral cavity
A removable partial denture is a form of treatment & not cure

19. PHILOSOPHY OF DESIGN
Various philosophies have been suggested related to removable partial denture, none has proved to be clinically advantageous over another
All of them have produced excellent results if physiological limit of supporting structures is observed
Occlusal forces should be distributed evenly and equally over the large supporting area. .

20. Main factor which influences the design of removable partial denture is type of denture support; whether tooth supported or tissue supported or combination of both.
Accordingly, impression procedures will differ for both of them.

22. THREE BASIC APPROCHES TO DISTRIBUTE OCCLUSAL FORCES
1. STRESS EQUALIZATION
2. PHYSIOLOGIC BASING
3. BROAD STRESS DISTRIBUTION

23. So it advocates use of Stress Director Or Stress Equalizer
1. STRESS EQUALIZATION
According to this concept compressibility & resiliency of tooth periodontal ligament & mucosal tissue is different
It causes an unequal distribution of stress on abutment teeth & alveolar ridge resulting in weakening of abutment teeth
So it advocates use of Stress Director Or Stress Equalizer

25. 2. PHYSIOLOGIC BASING
This theory denies use of stress breaker in removable partial denture
It advocates use of functional impression procedure to record the tissue in its functional form
It will compress tissue even at rest, so occlusal loading can’t compress tissue further
Due to the rebound action of mucosa it will position the artificial teeth above occlusal plane

26. ADVANTAGES Simplicity of design Good adaptation to underlining mucosa
Minimum direct retention required
It decreases functional stresses on abutment teeth

27. DISADVANTAGES Tissues are always in state of compression
It increases rate of Resorption of ridge
Denture teeth are always slightly above plane of occlusion
It causes instability of denture due to less number of retentive components
It does not provide stability against lateral forces

28. 3. BROAD STRESS DISTRIBUTION
It advocates use of maximum soft tissue area & maximum no of teeth for even distribution of stress
It is achieved by use of additional rest, direct retainer & by increasing denture base area

29. Broad stress distribution

30. It reduces forces on abutment teeth
ADVANTAGES
It reduces forces on abutment teeth
Health of oral tissues & abutment teeth maintained.
Additional rest seats or direct retainers reduces lateral forces on abutment teeth
It also acts as a splint

31. DISADVANTAGES
Due to greater amount of soft tissue coverage, it causes discomfort to patient
Difficult to maintain oral hygiene properly

32. ESSENTIALS OF DESIGNING
Key factors to be considered while designing of removable partial denture
Direct Retainers
Rest
Indirect Retainers
Major Connector
Minor Connector
Type Of Occlusion
Artificial Teeth

33. Indirect retainer It is employed to neutralize unseating forces
Should be located as far anterior of fulcrum line as possible
Class I design -- Two indirect retainers
Class II design -- one on opposite side

36. Class I
Class II

37. CLASS III DESIGN 1. Quadrilateral positioning of direct retainer
2. Bracing arm should be rigid

38. Rests
Prepared next to edentulous space
Indirect retention
Not required
Major & minor connectors
Same as class I & class II
Occlusion
Denture base
Functional impression not required

39. Class IV design Preserve labial alveolar bone
Direct retention – quadrilateral configuration
Major connector –should be rigid with broad palatal coverage
Indirect retention – should be as far posterior as possible
functional impression – may required

40. Class IV

41. A. Circumferential cast clasp
DESIGNS OF CLASP
A. Circumferential cast clasp

42. Bar clasp

43. DESIGNING PROCEDURE
Dentist should have thorough knowledge of all components of removable partial denture
The design of the removable partial denture should be simple & should follow mechanical & biological standards.