RESTS AND REST

SEATS

Denture BaseArtificial Teeth

Supporting Rests

Retainers Direct retainers Indirect Retainers

Connectors: Major Connectors

Minor Connectors

The Component Parts of Removable Partial Dentures

Clasp assemblyClasp assembly

REST

Rests: -Rests: - AAre rigid extensions of a re rigid extensions of a Partial Denture, Placed in Partial Denture, Placed in

Rest SeatsRest Seats, Which are , Which are prepared on either the prepared on either the

Occlusal, Lingual surfaces Occlusal, Lingual surfaces or Incisal edgesor Incisal edges of the teeth, of the teeth,

providing providing SupportSupport to the to the Partial Denture Partial Denture

The Quality of the Prosthesis to Resist Displacement Towards Denture Supporting Structures

Support

•Functions Of The RestsFunctions Of The Rests

1.1. SupportSupport

2.2. Transmitting vertical stressTransmitting vertical stress along the long axis of the toothalong the long axis of the tooth

3.3. SSecure the claspecure the clasp in its proper in its proper positionposition

4.4. Distributing the Occlusal LoadDistributing the Occlusal Load

5.5. It May Act As It May Act As Indirect Indirect Retention.Retention.

1-Support

SUPPORT & FORCE SUPPORT & FORCE TRANSMISSIONTRANSMISSION

Transmitting Vertical Stress Along The Long Axis Of The Tooth

3-S3-Secure the clasp armsecure the clasp arms in in their proper positiontheir proper position

Secure the Clasp in Its Proper Position

4-Distributing the Occlusal Load

5-May Act As 5-May Act As Indirect Indirect RetentionRetention

6-Restore occlusion of the abutment 6-Restore occlusion of the abutment that show tilting or infra-occlusion that show tilting or infra-occlusion

(overlay rest) (overlay rest)

Tipped molar (Mesially inclined Tipped molar (Mesially inclined mandibular molar)mandibular molar)

OnlayOnlay(reduce cusp angle)(reduce cusp angle)

7-Direct food away from tooth contact and embrasure area

Embrasure RestEmbrasure Rest

A Gap Between Two Molars

8-Resistance to Lateral Displacement of the 8-Resistance to Lateral Displacement of the Prosthesis but applying damaging horizontal Prosthesis but applying damaging horizontal

forces on abutment teethforces on abutment teeth

A- Rests are either a part of a Clasp Assembly Assembly ((primary

rest)

Or

An Auxiliary RestAuxiliary Rest

Types of rests:-

Clasp assemblyClasp assembly

Auxiliary restAuxiliary rest

B-B-According to According to the relations to the relations to edentulous edentulous span: -span: -

1.1. Adjacent to the Adjacent to the saddlesaddle

2.2. Away from the Away from the saddlesaddle

C- C- According to positions: -According to positions: -

1.1. Occlusal restOcclusal rest{ molars- { molars- premolar}premolar}

2.2. Lingual restsLingual rests{ cingulam of { cingulam of canines-or casted lingual canines-or casted lingual restorations}restorations}

3.3. Incisal restsIncisal rests {canines- {canines-incisors} incisors}

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.

I- Occlusal Rest

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

2.5m.m

.

Rest Seat

2-The Marginal Ridge Is Lowered Approximately 1 to 1.5 Mm of Teeth in Relation to a Vertical Line (permit

sufficient bulk )

1mm

3- The floor of the rest seat should be spoon

shaped

Forms and Requirements of Rest Seat Preparation

Prevent Slippage of the Prosthesis Creating an Orthodontic Like Force

4- 4- The angle between the minor connector and the rest should be less than 90˚

To Direct the Forces Along the Long Axis of the Tooth

Rest Seat

4- Spoon Shaped Inclined Apically As It Approaches the Center of the Tooth

1mm

Forms And Requirements Of Rest Seat Preparation

5-5-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-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

3-3-It must not raise the vertical dimension of occlusion

Not Raise the Vertical

Dimension

• Employed Only on a Perfectly Periodontally Healthy Tooth

Special Considerations

• Helps in Preventing Lateral Movement of the Denture

1- Boxed shaped occlusal rest

II- Lingual Rests

I- Occlusal Rest

III. Incisal Rest

Rests

IIII-Lingual Rests-Lingual Rests

C. Canine Ledge

A- Cingulum Rest (inverted V Rest)

B. Ball Rest

IIII-Lingual Rests-Lingual Rests

C. Canine Ledge

A- Cingulum Rest ( V Rest)

B. Ball Rest

LabLing

M D2 mm

A

1- 1.5 mm

Half -Moon Shaped V- Shaped

Adequate Tooth Preparation Directs Forces Down the Long Axis of Tooth

IIIIII- Incisal Rest seat- Incisal Rest seat

1.5mm2mm

2mm

1.5mm

IIIIII- Incisal Rest- Incisal Rest

•Used Predominantly As Auxiliary Rests or As Indirect Retainers

•Rigid Extension

•More Applicable on Mandibular Teeth

•2.5 mm Wide and 1.5 mm Deep

The Lingual Rest Is Preferable to an Incisal Rest

•Less Bothersome to a Curious Tongue

•More Esthetic

•Placed Closer to the Center of Rotation of the Abutment Tooth

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

• Act As Indirect Retainer

•Resistance to Lateral and Anteroposterior Movement

IV- Embrasure Hooks

•Poor Esthetics and Wedging Action on Teeth

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