RESTS AND
REST SEATS
The Component Parts
of Removable Partial Dentures
Denture Base
Artificial Teeth
Supporting Rests
Connectors: Major Connectors
Retainers
Minor Connectors
Direct retainers
Indirect Retainers
Clasp assembly
REST
Rests: Are rigid extensions of a
Partial Denture, Placed in
Rest Seats, Which are
prepared on either the
Occlusal, Lingual surfaces
or Incisal edges of the teeth,
providing Support to the
Partial Denture
Support
The
Quality of the Prosthesis
to Resist Displacement
Towards Denture Supporting
Structures
•Functions Of The Rests
1.
2.
3.
4.
5.
Support
Transmitting
vertical
stress
along the long axis of the tooth
Secure the clasp in its proper
position
Distributing the Occlusal Load
It
May
Act
As
Indirect
Retention.
SUPPORT & FORCE
TRANSMISSION
1-Support
Transmitting Vertical Stress Along The
Long Axis Of The Tooth
3-Secure the clasp arms in
their proper position
Secure the Clasp in Its
Proper Position
4-Distributing the Occlusal Load
5-May Act As Indirect
Retention
6-Restore occlusion of the abutment
that show tilting or infra-occlusion
(overlay rest)
Tipped molar (Mesially inclined
mandibular molar)
Onlay
(reduce cusp angle)
7-Direct food away from
tooth contact and
embrasure area
Embrasure Rest
A Gap Between Two Molars
8-Resistance to Lateral Displacement of the
Prosthesis but applying damaging horizontal
forces on abutment teeth
Types of rests:A- Rests are either a part of
a Clasp Assembly
(primary rest)
Or
An Auxiliary Rest
Clasp assembly
Auxiliary rest

1.
2.
B-According to
the relations to
edentulous
span: Adjacent to the
saddle
Away from the
saddle

1.
2.
3.
C- According to positions: Occlusal rest{ molarspremolar}
Lingual rests{ cingulam of
canines-or casted lingual
restorations}
Incisal rests {caninesincisors}
I- Occlusal Rest
A Rigid Extension of
a RPD That Contacts
the Occlusal Surface
of a Posterior Tooth
or Restoration, on a
Rest Seat Specially
Prepared to Receive
it.
Forms and Requirements
of Rest Seat Preparation
1- Should Be Rounded
Triangular in Shape the
Base of the Triangle at
the Marginal Ridge
About 2.5 mm in Width,
and Its Rounded Apex Is
Directed Towards the
Center of the Tooth
Rest Seat
1
m
m
2-The Marginal Ridge Is Lowered Approximately 1 to 1.5
Mm of Teeth in Relation to a Vertical Line (permit
sufficient bulk )
3- The floor of the rest
seat should be spoon
shaped
Forms and Requirements of
Rest Seat Preparation
4- The angle between the minor
connector and the rest should be
less than 90˚
Prevent Slippage of the Prosthesis
Creating an Orthodontic Like Force
To Direct the Forces Along the
Long Axis of the Tooth
Rest Seat
1
m
m
4- Spoon Shaped Inclined Apically As It Approaches
the Center of the Tooth
Forms And Requirements Of Rest
Seat Preparation
5-Rest seats are prepared in sound enamel,
existing restorations or in crowns and
inlays
6-If an amalgam restoration is present, it
could be replaced by a cast restoration
(Occlusal rests can be prepared in an old
amalgam restoration
7-Preparations for the occlusal rest must
precede making master cast and follow
proximal preparation (guiding planes and
elimination of undesirable undercuts)
GUIDING PLANES
Requirements of the
Occlusal Rest
I-O.R. must
fit the tooth ( minimize
food collection and preserve their
location in relation to the tooth
2- It must be strong enough to
withstand the loads without deform
3-It must not
raise the vertical
dimension of occlusion
Not Raise the
Vertical
Dimension
Special Considerations
1- Boxed shaped occlusal rest
• Employed Only on a
Perfectly Periodontally
Healthy Tooth
• Helps in Preventing
Lateral Movement of
the Denture
Rests
I- Occlusal Rest
II- Lingual Rests
III. Incisal Rest
II-Lingual Rests
A- Cingulum Rest
(inverted V Rest)
B. Ball Rest
C. Canine Ledge
II-Lingual Rests
C. Canine Ledge
A- Cingulum
Rest ( V Rest)
B. Ball Rest
Half -Moon Shaped
V- Shaped
Ling
D
M
Lab
2 mm
1- 1.5 mm
A
Adequate
Tooth
Preparation
Directs
Forces
Down the
Long Axis
of Tooth
III- Incisal Rest seat
1.5mm
2mm
2mm
1.5mm
III- Incisal Rest
•Rigid Extension
•More Applicable on
Mandibular Teeth
•Used Predominantly As
Auxiliary Rests or As Indirect
Retainers
•2.5 mm Wide and 1.5 mm Deep
The Lingual Rest Is
Preferable to an Incisal Rest
• Placed Closer to the Center
of Rotation of the Abutment
Tooth
•More Esthetic
• Less Bothersome to a
Curious Tongue
Lingual
Rest Will
Exert Less
Leverage
and
Reducing
Its
Tendency
to Tipping
Post Is More
Readily
Removed by
Application of
Force Near
Its Top Than
by Applying
Same Force
Nearer
Ground Level
IV- Embrasure Hooks
Placed in Embrasures Between Teeth
Extending Over the Buccal or Labial
Surface but Never Extend Below
Survey Line.
IV- Embrasure Hooks
•Resistance to Lateral
and Anteroposterior
Movement
• Act As Indirect Retainer
IV- Embrasure Hooks
• Poor Esthetics and Wedging
Action on Teeth