This document discusses principles of removable partial dentures, including factors that influence stress on abutment teeth and ways to control stress through design considerations. It covers simple machines like levers and the forces acting on partial dentures. Design factors that affect stress include length of span, ridge support quality, clasp flexibility, material used, occlusion, and components like direct retention, indirect retention, denture base, connectors and rests. Controlling stress involves minimum yet adequate retention from various components, accurate adaptation, neuromuscular control, frictional guidance, clasp position, and clasp design.

1. PRINCIPLES OF REMOVABLEPRINCIPLES OF REMOVABLE
PARTIAL DENTURESPARTIAL DENTURES

2. INTRODUCTIONINTRODUCTION
Principles Factors of stress on abutment
Forces acting
Controlling stress by design

3. Simple machines:
Inclined planes
Lever

5. Lever:
Class I
Class II
Class III

6. Forces acting on partial dentureForces acting on partial denture
 Fulcrum in horizontal plane (rotation in saggital plane)Fulcrum in horizontal plane (rotation in saggital plane)

8.  Fulcrum in saggital plane (rotation in vertical plane)Fulcrum in saggital plane (rotation in vertical plane)

9.  Fulcrum in vertical plane (rotation in horizontal plane)Fulcrum in vertical plane (rotation in horizontal plane)

10. Factors influencing magnitude of stressesFactors influencing magnitude of stresses
transmitted to abutment teethtransmitted to abutment teeth
1.1. Length of the span:Length of the span:
- α forces transmitted to abutment- α forces transmitted to abutment
2. Quality of support of ridge:2. Quality of support of ridge:
- well formed ridges- well formed ridges
- type of mucoperiosteum- type of mucoperiosteum

11. 3.3. Quality of the clasp:Quality of the clasp:
More flexible –More flexible –
 Less stress transmitted to theLess stress transmitted to the
abutment toothabutment tooth
 Less resistance to horizontalLess resistance to horizontal
stresses. Therefore lateral andstresses. Therefore lateral and
vertical forces increase on the ridgevertical forces increase on the ridge
Good periodontal support
Compromised
periodontal support
Less flexible clasp
Flexible clasp

12. Clasp design:Clasp design:
PassivePassive
FitFit
Reciprocal armReciprocal arm
Length of the clasp:Length of the clasp:
FlexibilityFlexibility
LengthLength
Curved courseCurved course
Material used:Material used:
Chrome alloyChrome alloy
GoldGold
WroughtWrought
Abutment tooth surface:Abutment tooth surface:
restorationrestoration
naturalnatural

13. Occlusal harmony:Occlusal harmony:
Deflective occlusal contactsDeflective occlusal contacts
Opposing occlusionOpposing occlusion
Area (near or away from the abutment)Area (near or away from the abutment)

14. Controlling stress by design considerationsControlling stress by design considerations
I. Direct retention
• Minimum yet provide adequate retention
• Other components are used to contribute retention
1. Adhesion and cohesion: Maximum area and
accurate adaptation
2. Neuromuscular control: Contour, extension,
patient ability

15. 3. Frictional control using guide planes

16. 4. Clasp position: Number of clasps – by classification
A) Quadrilateral configuration: Class III &
Class III mod

17. B) Tripod configuration: Class II & Class II mod

18. B) Bilateral configuration: Class I

19. 5. Clasp design:
a) Circumferential clasp: Mesiobuccal undercut
Reverse circlet

20. b) Vertical projection clasp: Mesiobuccal undercut
Distobuccal undercut
c) Combination clasp: stress breaking action

21. 6. Splinting of the teeth

22. II. Indirect retention
III. Occlusion
IV. Denture base
V. Major connector
VI. Minor connector
VII. Rests