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: -

A

re 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 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

Retention.

Act As

Indirect

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 { molars premolar} Lingual rests restorations} { cingulam of canines-or casted lingual Incisal rests incisors} {canines-

I- Occlusal Rest

A Rigid Extension of a RPD That Contacts the Occlusal Surface of a Posterior Tooth or Restoration , on a Rest Seat Prepared to Receive it.

Specially

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

1 m m Rest Seat 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 Ling V- Shaped Lab M D 2 mm 1- 1.5 mm A

Adequate Tooth Preparation Directs Forces Down the Long Axis of Tooth

III- Incisal Rest seat

2mm 1.5mm

1.5mm

2mm

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