This document discusses biomechanical considerations for removable partial dentures. It explains that dentists must consider the direction, duration, frequency and magnitude of forces when placing partial dentures. Removable partial dentures function using simple machines like levers, wedges and screws. The location of stabilizing and retentive components is important in relation to the horizontal axis of rotation of the abutment teeth. Indirect retainers help prevent displacement of the denture base through lever action. Partial dentures are subject to three main movements: rotation around a transverse axis through the back teeth, rotation around a longitudinal axis, and rotation around a vertical axis. Indirect retainers do not control movement toward the tissues.

1. BIOMECHANICAL
CONSIDERATIONS OF
REMOVABLE PARTIAL
DENTURES
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2. INTRODUCTION
Maxfield stated, “ Common observation clearly
indicates that the ability of living things to
tolerate force is largely dependent upon the
magnitude or intensity of the force”
Dentist must consider direction, duration and
frequency of force application, as well as the
magnitude of the force
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3. SIX SIMPLE MACHINES
LEVER
WEDGE
SCREW
WHEEL
AXLE
PULLEY
INCLINED PLANE
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4. Principle of Levers
FF
EERR
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5. CANTILEVER
It is beam supported only at one
end can act as a first – class
lever
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6. Location of stabilizing and retentive components in relation to
the horizontal axis of rotation of the abutment becomes
extremely important
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7. The axial surface contours of abutment teeth must be altered to
locate components of direct retainer assemblies more favorably in
relation to the abutment’s horizontal axis
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8. Mechanical Advantage= Effort Arm
Resistance Arm
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9. POSSIBLE MOVEMENTS OF
PARTIAL DENTURE
 One movement is rotation about an axis
through the most posterior abutments
 A second movement is rotation about a
longitudinal axis as the distal extension base
– moves in a rotary direction about the
residual ridge
 A third movement is rotation about an
imaginary vertical axis located near the
center of the dental arch
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10. ROTATION AROUND AROTATION AROUND A
TRANSVERSE AXISTRANSVERSE AXIS
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11. ROTATION AROUND A
LONGITUDINAL AXIS
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12. ROTATION AROUND A
VERTICAL AXIS
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13. “The component of a removable partial denture
that assists the direct retainer(s) in preventing
displacement of the distal extension denture
base by functioning through lever action on
the opposite side of the fulcrum line when the
denture base moves away from the tissues in
pure rotation around the fulcrum line.”-GPT
INDIRECT RETAINER
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14. An indirect retainer does not control the movement of
the denture base in the tissueward direction
Amount of movement =amount of compressible
mucosa
Fulcrum line runs between the most posterior rests.
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15. Movement away from ridge
 Sticky foods
 Functions of tissues at the borders
 Gravity (maxillary denture)
Fulcrum line runs through retentive tip of direct retainer
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16. Types of Fulcrum Lines
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17. www.asiandentalacademy.org

18. Comparision of Tooth -supported
and Tissue-supported partial
dentures
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19. REFERENCES
 A.A.Grant and W.Johnson,Removable denture Prosthodontics,
ed 2.1992,Churchill livingstone Inc.
 Ernest L.Miller and Joseph E.Grasso,Removable Partial
Prosthodontics, ed 2. 1979,Williams and Willkins.
 Glen P. Mcgivney, Alan B. Carr.Mccraken’s Removable Partial
Prosthodontics, ed10. St. Louis ;2000 ,The C.V. Mosby Co.
 Stewart ,Rudd and Keubker, Clinical Removable Partial
Prosthodontics,ed 2.1997,Ishiyaku EuroAmerica Inc. U.S.A
 William E. Avant.Indirect retention In partial denture Design.J
Prosthet Dent.16:1103-1110
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