removable partial dentures direct retiner

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Removable Partial Dentures Direct Retainers By:Ahmed Ali Abbas theoptimalsmile.wix.com

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Page 1: Removable partial dentures direct retiner

Removable Partial Dentures

Direct Retainers

By:Ahmed Ali Abbas

theoptimalsmile.wix.com

Page 2: Removable partial dentures direct retiner

There are two types of direct retainersThere are two types of direct retainers

11..Intra-coronalIntra-coronalWithin the contour of the crown e.g. precision attachmentWithin the contour of the crown e.g. precision attachment

22..Extra-coronalExtra-coronalOutside the contour of the crown of the tooth e.g. claspOutside the contour of the crown of the tooth e.g. clasp

Page 3: Removable partial dentures direct retiner

Intracoronal retainer consists of a key and

keyway

Page 4: Removable partial dentures direct retiner

Extracoronal circumferential direct retainer

Page 5: Removable partial dentures direct retiner

Basic RequirementsBasic Requirements

All clasps must be designed so that they satisfy the All clasps must be designed so that they satisfy the following six basic requirementsfollowing six basic requirements::

11..RetentionRetention22..SupportSupport33..StabilityStability

44..ReciprocationReciprocation55..EncirclementEncirclement

66..PassivityPassivity

Page 6: Removable partial dentures direct retiner

11..RetentionRetention

Retention is provided by the retentive arm Retention is provided by the retentive arm which prevents the partial denture from which prevents the partial denture from displacement away from the tissues displacement away from the tissues toward the occlusal.While the partial toward the occlusal.While the partial denture is seated the retentive tip must be denture is seated the retentive tip must be passive. However, it should touch the passive. However, it should touch the

tooth in the undercut areatooth in the undercut area . .

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22..SupportSupport

Support in a clasp is generally provided by Support in a clasp is generally provided by the rest. Thus, while chewing food the rest the rest. Thus, while chewing food the rest prevents tissueward movement of the prevents tissueward movement of the clasp assembly, plus directs the force clasp assembly, plus directs the force along the long axis of the tooth, thus along the long axis of the tooth, thus

reduces periodontal tissue damagereduces periodontal tissue damage . .

Page 8: Removable partial dentures direct retiner

33..BracingBracing

Bracing is the resistance to horizontal forcesBracing is the resistance to horizontal forces..

This provided by the rest, minor connector and This provided by the rest, minor connector and bracing arm. Actually, the bracing arm mainly bracing arm. Actually, the bracing arm mainly provides reciprocation which is resistance to provides reciprocation which is resistance to

force applied by retentive tipforce applied by retentive tip . .

Page 9: Removable partial dentures direct retiner

44..EncirclementEncirclement

There must be more than 180 degrees There must be more than 180 degrees crown coverage otherwise, the clasp can crown coverage otherwise, the clasp can slip-off the abutment toothslip-off the abutment tooth..

55..PassivityPassivityThe retentive clasp arm should be passive The retentive clasp arm should be passive (no active force) until a dislodging force is (no active force) until a dislodging force is appliedapplied..

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Page 11: Removable partial dentures direct retiner

Factors that determine the amount of retention provided by a particular clasp arm

11..The size of the angle of the cervical convergenceThe size of the angle of the cervical convergence..22..How far into the cervical convergence the clasp terminal is How far into the cervical convergence the clasp terminal is

placedplaced..33..Flexibility of the clasp armFlexibility of the clasp arm..

Flexibility of the clasp armFlexibility of the clasp arm::

11..The length of the clasp armThe length of the clasp arm..22..The diameter of the clasp armThe diameter of the clasp arm..

33..The cross-sectional formThe cross-sectional form..44..The type of metal usedThe type of metal used..

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Other factors about clasp design:11..In a clasp only the tip of the retentive arm should be flexible, the other In a clasp only the tip of the retentive arm should be flexible, the other

components are rigidcomponents are rigid

22..Selection of clasp will depend on the survey line (height of contour), Selection of clasp will depend on the survey line (height of contour), retention area available, type of partial denture i.e. whether it is tooth-retention area available, type of partial denture i.e. whether it is tooth-supported or distal extention removable partial denturesupported or distal extention removable partial denture..

33..Flexibility of clasp arm can be increased by curving and/or lengthening the Flexibility of clasp arm can be increased by curving and/or lengthening the armarm..

44..The thickness of the retentive clasp arm tip should be ½ the thickness at its The thickness of the retentive clasp arm tip should be ½ the thickness at its attachment to the body of the clasp armattachment to the body of the clasp arm

55..The greater the diameter of the clasp arm, the lesser will be the flexibility The greater the diameter of the clasp arm, the lesser will be the flexibility and vice versaand vice versa..

66..Wrought metal is more flexible than cast metalWrought metal is more flexible than cast metal..

77..If buccal retention is used on the left side of the arch, buccal retention must If buccal retention is used on the left side of the arch, buccal retention must be used on the right side of the archbe used on the right side of the arch

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Classification of extra-coronal retainersClassification of extra-coronal retainers:: 11..Supra bulge clasps (occlusally approaching, Supra bulge clasps (occlusally approaching,

circumferential or encircling clasps)circumferential or encircling clasps)..

The retentive arm approaches the undercut area from the The retentive arm approaches the undercut area from the suprabulge directionsuprabulge direction..

22..Infrabulge clasps (gingivally approaching, projection or Infrabulge clasps (gingivally approaching, projection or bar clasps)bar clasps)

The retentive arm approaches the undercut from the The retentive arm approaches the undercut from the infrabulge direction,e.g.Bar clasp arm (I-Bar etc.)infrabulge direction,e.g.Bar clasp arm (I-Bar etc.)

33..Combination claspsCombination clasps

a. ½ clasp is circlet and ½ clasp is Bar type ora. ½ clasp is circlet and ½ clasp is Bar type or

b. Combination of two types of metals-Chrome-cobalt an b. Combination of two types of metals-Chrome-cobalt an wrought wirewrought wire

Page 14: Removable partial dentures direct retiner

Types of circumferential claspsTypes of circumferential clasps

11..Circlet claspCirclet clasp..

22..Half & half claspHalf & half clasp..

33..Fish hook or hairpin claspFish hook or hairpin clasp..

44..Reverse circlet claspReverse circlet clasp..

55..Embrasure claspEmbrasure clasp..

66..Ring claspRing clasp..

77..Back action and reverse back action claspBack action and reverse back action clasp..

Page 15: Removable partial dentures direct retiner

11..Circlet claspCirclet clasp..

- -Is the most common clasp used for Is the most common clasp used for removable partial dentures removable partial dentures . .

- -The least complex in designThe least complex in design.. - -It has a rigid reciprocal arm, a rest, a It has a rigid reciprocal arm, a rest, a

proximal plate approximating the proximal plate approximating the edentulous area, and a flexible retentive edentulous area, and a flexible retentive arm ending in an undercut of 0.01 incharm ending in an undercut of 0.01 inch..

- -It may be used on canines, premolars, and It may be used on canines, premolars, and molars molars . .

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Variations of circlet clasp areVariations of circlet clasp are::

a) Back action clasp: Provides poor bracing due to a) Back action clasp: Provides poor bracing due to its length. It is used on premolars (use .02 its length. It is used on premolars (use .02

inch undercut) inch undercut)

b) Reverse back action: Minor connector is on b) Reverse back action: Minor connector is on buccal, otherwise similar to back action buccal, otherwise similar to back action..

c) Ring clasp: Variation of back action clasp c) Ring clasp: Variation of back action clasp usually used on upper buccally tilted and usually used on upper buccally tilted and

lower lingually tilted molars lower lingually tilted molars . .

d) Other variations of simple circlet clasp “ C ” clasp d) Other variations of simple circlet clasp “ C ” clasp or hair-pin clasp or hair-pin clasp . .

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The half and half clasp:The half and half clasp: 22..

The half and half clasp is a modification of The half and half clasp is a modification of the circlet clasp with the reciprocal arm the circlet clasp with the reciprocal arm coming from one direction and the coming from one direction and the retentive arm from the other. Two rests are retentive arm from the other. Two rests are used for this clasp. It is used on molars used for this clasp. It is used on molars and premolars. The retentive tip is placed and premolars. The retentive tip is placed into a 0.01 inch undercutinto a 0.01 inch undercut..

Page 18: Removable partial dentures direct retiner
Page 19: Removable partial dentures direct retiner

33 . .The fish hook or hair-pin claspThe fish hook or hair-pin clasp

The fishhook or hairpin clasp is another The fishhook or hairpin clasp is another modification of the circlet clasp. It is mostly modification of the circlet clasp. It is mostly used on teeth with long crowns. It is rarely used on teeth with long crowns. It is rarely used because so much of the teeth is used because so much of the teeth is covered by the retentive arm. The other covered by the retentive arm. The other difficulty is lack of flexibility of the retentive difficulty is lack of flexibility of the retentive tip because of the bulk of the clasptip because of the bulk of the clasp..

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44 . .The reverse circlet claspThe reverse circlet clasp::

The reverse circlet clasp is used when the The reverse circlet clasp is used when the retentive undercut is located on the retentive undercut is located on the surface of the abutment tooth adjacent to surface of the abutment tooth adjacent to the edentulous spacethe edentulous space..

It is indicated in class I & class II distal It is indicated in class I & class II distal extension partial dentures where deep extension partial dentures where deep tissue undercut precludes the use of tissue undercut precludes the use of infrabulge claspinfrabulge clasp..

Page 22: Removable partial dentures direct retiner

55 . .Embrasure claspEmbrasure clasp..

The embrasure clasp is used when there is The embrasure clasp is used when there is no modification spaces in the portion of no modification spaces in the portion of the arch that needs retention. The clasp is the arch that needs retention. The clasp is in fact two circlet clasps back-to-back. It in fact two circlet clasps back-to-back. It may be used on two molars, a molar and may be used on two molars, a molar and premolar or two premolars. Preparation of premolar or two premolars. Preparation of the double rest and channel going from the double rest and channel going from the lingual to the buccal of the teeth needs the lingual to the buccal of the teeth needs to be deep enough for strength and not to be deep enough for strength and not

compromised by the opposing occlusioncompromised by the opposing occlusion . .

Page 23: Removable partial dentures direct retiner
Page 24: Removable partial dentures direct retiner

66 . .The ring claspThe ring clasp..

The ring clasp is used on molars. Some The ring clasp is used on molars. Some designers advocate its use for tipped designers advocate its use for tipped mandibular molars where there is only a mandibular molars where there is only a mesial undercut on the tooth. It has mesial mesial undercut on the tooth. It has mesial and distal rests and the reciprocal arm is and distal rests and the reciprocal arm is

continuous connecting the two restscontinuous connecting the two rests . .

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