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REST AND REST SEATSlec:4+5

Assis.Prof.Dr. Radhwan Himmadi Hasan B.D.S , M.Sc. , Ph.D 2016-2017
* * Dr.Radhwan Himmadi Hasan


Rest: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
* * Dr.Radhwan Himmadi Hasan

Rest seat:portion of a tooth prepared to receive a rest

* * Dr.Radhwan Himmadi Hasan

Functions Of The Rests

1-Support(the main function): resist displacement towards denture supporting structures which will prevent impingement of gingival tissues adjacent to the abutment
* * Dr.Radhwan Himmadi Hasan


2-maintain the components of the dentures in their positions and prevents spreading of clasp arm
* * Dr.Radhwan Himmadi Hasan

3-Distributing the Occlusal Load Along the long axis of the tooth

4-May Act As Indirect Retention
* * Dr.Radhwan Himmadi Hasan

4-Direct food away from tooth contact and embrasure area

* * Dr.Radhwan Himmadi Hasan

5- improve the existing occlusion

* * Dr.Radhwan Himmadi Hasan


Types of rest Occlusal rest{ molars- premolar} Lingual rests{ cingulam of canines} Incisal rests {canines-incisors} Embrasure Hooks
* * Dr.Radhwan Himmadi Hasan


A rigid extension of a RPD that contacts the occlusal surface of a posterior tooth or restoration, a rest seat specially prepared to receive it.
A-Occlusal Rest
* * Dr.Radhwan Himmadi Hasan

Types of occlusal rest

A- conventional B-other forms:

Box-shaped O.R. Extended O.R. Onlay O.R. Inter proximal O.R. Embrasures O.R. Internal O.R.
* * Dr.Radhwan Himmadi Hasan

Requirements of occlusal Rest Seat Preparation

1- Should be rounded triangular outline form, the base of the triangle at the marginal ridge and its rounded apex is towards the center of the tooth
* * Dr.Radhwan Himmadi Hasan

* * Dr.Radhwan Himmadi Hasan

3-The angle between the minor connector and the rest should be less than 90˚ 1- To prevent Slippage of the Prosthesis Creating an Orthodontic Like Force2- To direct the forces Along the Long Axis of the tooth * * Dr.Radhwan Himmadi Hasan

* * Dr.Radhwan Himmadi Hasan

4-the rest seat may be papered in either saucer shape or box shape Saucer shape(spoon) used more than box in cases of : free end saddle bounded cases having weak abutments
* * Dr.Radhwan Himmadi Hasan


5-Rest seats are prepared in sound enamel, or in crowns and inlays Floride gel applied to abutment
* * Dr.Radhwan Himmadi Hasan

Requirements of occlusal Rest:

1.Should have sufficient thickness of metal to prevent breakage especially over the marginal ridge.
2.It should fit the rest seat accurately with beveled margins, preventing food stagnation or impaction.
* * Dr.Radhwan Himmadi Hasan

3.It must not raise the vertical dimensions of occlusion

* * Dr.Radhwan Himmadi Hasan

4-In bounded partial denture: placed in the near zone of the occlusal surface to edentulous area In free end partial dentures: placed in the far zone of the occlusal surface to decrease torque action on abutment tooth
* * Dr.Radhwan Himmadi Hasan

Tipped molar

(Mesially inclined mandibular molar)

The rest should be designed to prevent further tipping, It must direct forces down the long axis of the tooth by either of one of these ways :
* * Dr.Radhwan Himmadi Hasan

Additional occlusal rest in distal fossa

* * Dr.Radhwan Himmadi Hasan


2. A rest preparation that extended from the mesial marginal ridge to the distal triangular fossa to minimize further tipping

* * Dr.Radhwan Himmadi Hasan

3-interproximal O.R. They are prepared as individual occlusal rest seats , except that the preparations must be extended further lingually than the ordinarily accomplished . used to avoid interproximal wedging , additionally will shunt food away from contact points
* * Dr.Radhwan Himmadi Hasan



II- Lingual Rests : A- Cingulum Rest ( inverted V Rest ). B- Ball Rest. C- Canine Ledge.
* * Dr.Radhwan Himmadi Hasan


A- Cingulam Rest (inverted Rest) Def. a portion of RPD ; placed in an enamel seat at the cingulam or just Incisal to it . Indication: no posterior tooth to place an occlusal rest . commonly used on the maxillary canines Rarely on lower anterior; due to less thickness of enamel

* * Dr.Radhwan Himmadi Hasan

Specification of Cingulum Rest Seat :1- A rounded inverted V shaped preparation(half – moon shaped).2- All sharp angles & undercuts should be eliminated .3- The rest seat is broadest at the center and merges as it approaches proximal surfaces * * Dr.Radhwan Himmadi Hasan


III- Incisal Rest : Def.: a rigid extension of a RPD , placed at the Incisal angles of anterior teeth on prepared rest seats. - commonly used as auxiliary rest or as indirect retainers . - More applicable on mandibular teeth due to lack of adequate thickness of enamel on the lingual surface.
* * Dr.Radhwan Himmadi Hasan


- A saddle shaped preparation , and the notch should extend onto the facial surface to prevent the tooth from moving labially .
* * Dr.Radhwan Himmadi Hasan


N.B.: The lingual Rest is preferable to an incisal Rest ?? because: - placed closer to the center of rotation of the abutment, thus reducing its tendency to tipping - More esthetic . - Less bothersome to tongue .
* * Dr.Radhwan Himmadi Hasan



Direct retainer: It is that component of a removable partial denture that is used to retain and prevent dislodgment, consisting of a clasp assembly or a precision attachment
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Intracoronal retainers

the intra coronal retainer is within the normal contours of the abutment. The first component or matrix and the second component or patrix. There should be parallelism between the matrix and patrix
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Clasps mainly divided 2 types Occlusally approaching which approach the undercut from the occlusal area and gingivally approaching which enter the undercut crossing the gingival margin.
Occlusally approaching
gingivally approaching
* Dr.Radhwan Himmadi Hasan
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Parts of clasp assembly
Circumferential Clasp (Retentive Arm)
Reciprocating (Bracing) Arm
Distal Occlusal Rest
Proximal Plate
* Dr.Radhwan Himmadi Hasan
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Principles of Clasp Design

1. Encirclement- more than 180 degrees in greatest circumference if the tooth engaged by the clasp assembly 2. Occlusal rest - to prevent the movement of the clasp arms cervically. 3. Each retentive terminal should be opposed by a reciprocal component.why
* Dr.Radhwan Himmadi Hasan
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1-Retentive arm -Reciprocal elements(shoulder) – junction of gingival and middle third Terminal retentive arm – gingival third2-Reciprocal arm- middle third
2-Reciprocal arm
1-retentive arm
Occl.rest
shoulder
* Dr.Radhwan Himmadi Hasan
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Functional requirements of the clasp
Retention Support Stability Reciprocation Encirclement Passivity
* Dr.Radhwan Himmadi Hasan
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Retention

Is obtained by the incorporation of a flexible element of the clasp into the undercut. Sufficient undercut to be engaged to obtain desired retention. Force from the clasp arm on flexing must be within the tolerance of the PDL and must be less to prevent deformation of the clasp arm itself.
* Dr.Radhwan Himmadi Hasan
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Support

Support is the quality of the clasp assembly to resist displacement of the prosthesis in the apical direction. a rest must contact the surface of the abutment tooth at a properly prepared surface- rest seat
* Dr.Radhwan Himmadi Hasan
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A properly prepared rest will prevent the tissue ward movement of the prosthesis. maintains the position of the clasp assembly in relation to the abutment. Transmits forces along the long axis of the abutments
* Dr.Radhwan Himmadi Hasan
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Stability

Resistance to horizontal displacement
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Reciprocation
Counteracts lateral displacement of an abutment when retentive clasp terminus passes over the height of contour
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Encirclement

Prevent movement of abutment away from associated clasp assembly More than 180 degrees
* Dr.Radhwan Himmadi Hasan
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A
B
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Passivity

Prevent the transmission of the adverse forces to the associated abutment Be passive until a dislodging force is applied
* Dr.Radhwan Himmadi Hasan
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Classification of extra-coronal retainers
Supra bulge clasps (occlusally approaching, circumferential clasps) Infrabulge clasps (gingivally approaching, projection or bar clasps) Combination clasps
* Dr.Radhwan Himmadi Hasan
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Circumferential (circlet )clasps

The cast circumferential clasp design was introduced by Dr N B Nesbitt in 1916. Simple, easy to construct- excellent support, bracing, retentive properties. Close adaptation to tooth therefore minimises food entrapment Disadvantage- covers large amount of tooth surface
* Dr.Radhwan Himmadi Hasan
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Simple Circlet clasp

Tooth support RPD Undercut remote from edentulous area Half round Disadvantages - Increase tooth coverage - compromised esthetics
Akers clasp assembly. Buccal retentive clasp arm, lingual reciprocation(bracing) and mesial occlusal rest.
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Circlet clasp. Multiple circlet clasp Embrasure clasp. Reverse action or hair pin clasp Ring clasp. Back action and reverse back action clasp
Variations of circlet clasp
* Dr.Radhwan Himmadi Hasan
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Reverse circlet clasp, Reverse action or hair pin clasp
Undercut located adjacent to edentulous area Kennedy class I ,II Disadvantages - cover considerable tooth surface - Poor esthetics
* Dr.Radhwan Himmadi Hasan
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multiple clasp

2 simple circumferential clasp joined at the terminal aspect of their reciprocal elements Indication: Principle abutment is periodontal compromised and the forces are distributed between multiple abutment teeth
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Embrasure clasp

2 simple circumferential clasp joined at bodies Used on side of the arch where there is no edentulous space Can be used only when adequate tooth preparation is possible
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

* Single isolated molar or premolar

Combination clasp

Cast metal reciprocal arm and wrought wire retentive arm Indication : abutment adjacent to Kennedy class I and II area Advantage kinder to the tooth, less force on abutment can engage greater undercut Disadvantage more prone to breakage than cast minimal stabilizing
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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Gingivally approaching clasps /Bar typeit consist of the following

Approach the undercut gingivally and have a push type of retention.
* Dr.Radhwan Himmadi Hasan
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1-Approach arm,(bar type)

It is a minor connector that connect the retentive tip to the denture base. It crosses the gingival margin at right angle and it is the only flexible minor connector. Flexibility of the clasp is controlled by the taper and length of the approach arm More esthetic
* Dr.Radhwan Himmadi Hasan
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Retentive terminal(bar type)

It should end on the surface of the tooth below the undercut.
* Dr.Radhwan Himmadi Hasan
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T-clasp
Kennedy class I and II Undercut locate adjacent edentulous area Contraindication - Severe soft tissue undercut - Height of contour locate near occlusal surface
* Dr.Radhwan Himmadi Hasan
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Modified T-clasp

No retentive horizontal projection Kennedy class I and II Undercut locate near adjacent edentulous area Canine and premolar Advantage - esthetics
* Dr.Radhwan Himmadi Hasan
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I bar

Kennedy class I and II RPI - Mesial rest - Proximal plate - I bar
* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

* Only occure in class I , II, IV

Kennedy class I, II and IV

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* Indirect retainer

Forms of indirect retainer

Auxiliary occlusal rest Canine extension from occlusal rest Continuous bar retainer & lingual plate Rugae Support Hard palate
* Dr.Radhwan Himmadi Hasan
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Determination of indirect retainer position

* Dr.Radhwan Himmadi Hasan
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* Dr.Radhwan Himmadi Hasan

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