بسم ال الرحمن الرحيم

Occlusal Rests And Similar Components

Definition

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

REST

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

Support

The Prepared Recess in a Tooth or Restoration Created to Receive Occlusal, Incisal, or Lingual Rest

Rest seat

Properly Prepared R.S. Help Control Stress by Directing Forces Transmitted to Abutment Teeth Down the Long Axis of Those Teeth. The Periodontal Ligament Is Capable of Withstanding Vertical Forces of Far Greater Magnitude Than Off-vertical, (Near Horizontal) or Torsional Force

Rest seat

Rests Are Either A Part Of A Clasp Assembly Or An Auxiliary Rest

1- Occlusal Rest2- Incisal Rest

Types of rests

3- Lingual Rest

Requirements

The rests must fulfill the following requirements:1- They must fit the tooth ( minimize food collection and

preserve their location in relation to the tooth

2- they must be strong enough to withstand the loads without deformation

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

4- ------------Transmit the stress with the long axis of the tooth

5- they must be at right angle or less to the long axis of the tooth

Fit- Strong-not Raise the Vertical Dimension

Not Raise the Vertical Dimension

Not Raise the Vertical Dimension

2-transmitting Vertical Stress Along the Long Axis of the Tooth

Functions:

6- It May Contributes to Indirect Retention7- prevent ingress of food between the abutment and the clasp

3-Secure the Clasp in Its Proper Position 4- Distributing the Occlusal Load

5- Resistance to Lateral Displacement of the Prosthesis

1-Support the denture against vertical forces ( PD without rests called Gum stripper)

1-Support

Transmitting Vertical Stress Along The Long Axis Of The Tooth

Secure the Clasp in Its Proper Position

Distributing the Occlusal Load

Resistance to Lateral Displacement of the Prosthesis but applying damaging horizontal forces on abutment

teeth

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

Apex Is Directed Towards the Center

Rounded Triangular

m2.5 mm

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

Rest Seat

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

1mm

Forms and Requirements of Rest Seat Preparation

Prevent Slippage of the Prosthesis Creating an Orthodontic Like Force

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

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

• Employed Only on a Perfectly Periodontally Healthy Tooth

Special Considerations

• Provide Guide-surfaces

• Helps in Preventing Lateral Movement of the Denture

• It Provides Increased Denture Retention

1- Boxed shaped occlusal rest

2-Tipped Molar (Mesially Inclined Mandibular Molar)

a- An Additional Occlusal Rest in the Distal Fossa

b- Molar With Rest Preparation Extended From Mesial Marginal Ridge to Distal Triangular Fossa

c- A Casting Is Required, Such As Full Veneer Crown or Onlay

c- A Casting Is Required, Such As Full Veneer Crown or Onlay

3- Interproximal Occlusal Rest Seats

4- Internal Rest (the Milled Rest, the Semiprecision Attachment)

5- Embrasure Rest

A Gap Between Two Molars

5- Embrasure Rest

One Simple Circle Clasps Jointed Together, and the Rest Recesses Should Be Fashioned on the Two Abutment Teeth

Two Simple Circle Clasps Jointed Together, and the Occlusal Rest Can Be Used to Bridge a Gap

Between Teeth

II-Lingual RestsII-Lingual Rests

C. Canine Ledge

A- Cingulum Rest (inverted V Rest)

B. Ball Rest

A- Cingulum Rest (inverted V Rest)

LabLing

M D2 mm

1- 1.5 mm

Half -Moon Shaped V- Shaped

A

Adequate Tooth Preparation Directs Forces Down Long Axis of Tooth

B. Ball Rest

No sharp line angles1.5 Mm Deep - 2.5 Mm Wide

C. Canine Ledge

1.5 mm Deep No Sharp Line Angles

A Step-like Preparation

III- Incisal Rest seatIII- Incisal Rest seat

1.5mm2mm

2mm

1.5mm

III- Incisal RestIII- 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

Used Predominantly As Auxiliary Rests or As Indirect Retainers

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 B or Lab Surface

but Never Extend Below S. L.

IV- Embrasure Hooks

• Act As Indirect Retainer

•Resistance to Lateral and Anteroposterior Movement

•Splinting of Natural Teeth

•Support

IV- Embrasure Hooks

• Poor Esthetics and Wedging Action on Teeth

Onlays: a restoration that restore the intire occlusal surfaceThey are enlarged occlusal rests covering the whole occlusal surface and extending buccally and linguallyIndication:1- increase the reduced VD2- Reduce cusp angle3-Improve balanced articulation

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