DIRECT RETAINERS.pptx

DIRECT RETAINERS- Dr.Shajahan P A

1. DIRECT RETAINERS Dr Shajahan P A Professor Department of Prosthodontics

2. DEFINITION The component of a partial removable dental prosthesis used to retain and prevent dislodgment ,consisting of a clasp assembly or precision attachment DIRECT RETENTION Retention obtained in a partial removable dental prosthesis by the use of clasps or attachments that resist removal from the abutment teeth

3. CLASSIFICATION

4. INTRACORONAL DIRECT RETAINER DEFINITION A retainer consisting of a metal receptacle (matrix) and a closely fitting part( patrix ) the matrix is usually contained within the normal or expanded contours of the crown on the abutment tooth\dental implant and the patrix is attached to a pontic or the removable dental prosthesis framework, precision attachment or internal attachment

5. INTRACORONAL ATTACHMENTS Theses are prefabricated attachments positioned within the normal contour of the abutment tooth Also called ‘internal attachments’ or ‘precision attachment ‘ These were developed by Dr herman E S Chayes in 1906

6. It consist of male and female components .The female part called matrix is a receptacle placed in the abutment tooth .Male part ( patrix ) is an insert which is processed into the denture .

7. ADVANTAGES Elimination of visible retentive component Elimination of visible support Provide some horizontal stabilization ,but additional stabilization is desirable Greater stimulation to underlying tissue because of intermittent vertical massage

8. DISADVANTAGE Require preparation of abutment tooth and casting . Complicated clinical and lab procedures. Loss of retention due to wear. Repair and replacement is difficult. Difficult to place completely within the tooth cost

9. CONTRAINDICATIONS Presence of large pulp –related to age, placement may cause pulp exposure. Short or abraded teeth – as they are prefabricated , length may be insufficient. Distal extension base –do not permit horizontal movement ,all the tipping and rotational forces are trasmitted directly to abutment teeth .

10. EXTRACORONAL DIRECT RETAINERS These provide retention through components placed outside the normal contour of the abutment tooth. They are classified as: Prefabricated attachment Clasp

11. CLASP – Most commonly used extracoronal direct retainer CLASP ASSEMBLY :The part of a removable dental prosthesis that act as a direct retainer and \or stabilizer for a prosthesis by partially encompassing or contacting an abutment tooth –usage. CLASP: The component of the clasp assembly that engages a portion of the tooth surface and either enters an undercut for retention or remains entirely above the height of contour to act as a reciprocating element.

12. UNDERCUT :Portion of the surface of an object that is below the height of contour in relationship to the path of placement. HEIGHT OF CONTOUR :A line encircling a tooth and designating its greater circumference at a selected axial position determined by a dental surveyor ;a line encircling a body designated its greatest circumference in a specified plane.

13. Clasp can be 2 type : Circumferential or Akers clasp –approaches an undercut occlusally Cast circumferential clasp Combination clasp Vertical projection or bar or roach clasps-approach the undercut gingivally

14. Components part of a clasp assembly : Rest Retentive arm Retentive terminal Body Shoulder Reciprocal arm Minor connector

15. REST: Provide vertical support or prevents tissue ward movement of the prosthesis . Retentive arm : Three parts are there Terminal third –is flexible and engage the undercut area Middle third –has limited flexibility and may engage minimal undercut Proximal third or body-not flexible and is placed above the height of the contour

16. RECIPROCAL ARM Clasp arm is placed above the height of the contour on the surface of the opposing the retentive arm .It resist lateral force extended by retentive terminal as it passes over the height of the contour during removal and insertion of the partial denture . FUNCTIONS: Reciprocations against action of retentive terminal Stabilization against horizontal forces Contributes also to vertical suppoet and indirect retention

17. Retentive terminal Distal third of the retentive arm .It is the only component that is placed below the height of the contour ,hence it is the only flexiblr component . Body The body connects the rest and shoulder to the minor connector Shoulder It connect the body to the clasp terminal .Also provide some stabilization against horizontal forces. MINOR CONNECTOR It joins the body to the remaining part of the framework.in gingiv ally approaching clasp it is called ‘approach arm ‘

18. REQUIREMENTS OF CLASP Retention Stabilty Support Reciprocation Encirclement Passivity

19. RETENTION It is the quality inherent in denture that resists the vertical forces of dislodgement. Eg.force of gravity,adhesiveness of foods or the force associated with the opening of the jaw. Factors affecting retention Dimension of retentive undercut Buccolingual depth –it is measured by the undercut gauge of surveyor and is called ‘angle of gingival convergence’ Distance between survey line –it affect the clasp arm length which in turn affects flexibility Mesiodisltal length-longer is mesiodistal length more flexibility will be clasp .

20. Flexibility of clasp arm Length of clasp –greater the length of clasp greater is the flexibility . Diameter of clasp –flexibility is inversely proportional to diameter Cross section form-clasp that is round in cross section has greater flexibility. Clasp material –chrome alloys have a higher modulus of elasticity . Type of clasp

21. STABILITY The quality of the prosthesis to be firm ,stable or constant and to resist displacement by functional ,horizontal or rotational stresses. SUPPORT The resistance to displacement of the prosthesis towards the basal tissue or underlying structures.provided by occlusal ,lingual or incisal rests

22. RECIPROCATION The mechanical by which lateral force are generated by a retentive arm passing over a height of contourb are counterbalanced by a reciprocal arm passing along a reciprocal guiding plane . ENCIRCLEMENT Property of the clasp assembly to encompass more than 180 degree of the abutment tooth either by continuous or broken contact to prevent dislodgement during function .

23. PASSIVITY The quality or condition of inactivity or rest assumed by the teeth , tissue and denture when a removable dental prosthesis is in place but not under masticatory pressure.

24. CIRCUMFERENTIAL CLASP DEFINITION A retainer that encircles a tooth by more than 180 degree ,including opposite angles,and which generally contacts the tooth throughout the extent of the clasp ,with at least one terminal located in an undercut .

25. CAST CIRCUMFERENTIAL CLASP It is also called AKERS clasp All components of the clasp assembly are made of cast alloy Retentive terminal should orginate above height of contour and terminate below it Retentive terminal should point towards the occlusal surface ,never towards gingival The retentive tip should only terminate in mesial or distal line angle of the tooth ,never in the middle of facial or lingual surface Clasp arm should be kept as low as possible to gain mechanical advantage against any lever action on tooth

26. ADVANTAGES Easiest to design ,construct and repair Excellent support ,bracing and retentive qualities Most logical choice for tooth supported removable partial dentures Cause less food retention Many types available so can be used in most situations

27. DISADVANTAGES More coverage of tooth surface which may lead to dacalcification and \or caries of enamel Alter the morphology of abutment which may affect normal food flow pattern and can lead to damage of gingival tissues due to lack of physiologic stimulation If positioned high on abutment ,they can increase the width of occlusal table which can cause greater occlusal forces to be exerted on tooth Difficult to adjust with pliers as with all cast clasps as they can be adjusted only in one plane

28. TYPES OF CAST CIRCUMFERENTIAL CLASPS SIMPLE CIRCLE CLASP Most versatile and widely used Approaches the tooth undercut from the edentulous area and engage the undercut remote from the edentulous space Clasp of choice for tooth supported removable partial denture Contraindicated for distal extension partial dentures as it can only engage mesiobuccal undercut

29. REVERSE CIRCLET CLASP Engages the undercut adjacent to edentulous space by approaching from mesio-occlusal rest Indicated for distal extension situations when bar clasp is contraindicated DISADVANTAGES Poor aesthetics as clasp runs from mesial to distal side of facial surface hence not in choic ein premolars Obtaing sufficient clearance for the rest to be placed between teeth is difficult

30. To protect the marginal ridge ,an additional rest must be placed adjacent to edentulous space Wedging may occur between the abutment and adjacent tooth ,if occlusal rest is not well prepared

31. MULTIPLE CIRCLET CLASP This is a combination of two opposing simple circlet clasps joined at terminal end of reciprocal arms When principle abutment has lost some of its periodontal support,this clasp is used to share retention responsibilities among other teeth It is used in periodontally compromised abutment teeth in distal extension situations

32. EMBRASURE CLASP OR MODIFIED CRIB CLASP Two simple circlet clasps joined at the body Used on the side of the arch where thereis no edentulous space It is indicated in kennedys class 2 and class 3 with out any modifications It crosses both marginal ridges and engages undercut on opposing line angle If tooth preparation is insufficient ,breakage of clasp is common

33. RING CLASP It start on the opposite side of the undercut adjacent to edentulous space and engages the undercut by encircling the entire tooth almost from its origin . Indicated on tipping molars where undercut is present adjacent to edentulous space . Mandibular molars tip mesiolingually and maxillary molars tip mesiobuccally Because of great length of the clasp,it is usually supported by an auxiliary bracing arm from the minor connector of the denture base to the centre reciprocal arm

34. CONTRAINDICATION buccinator attachment lies close to mandibular molar such that auxiliary bracing arm encroaches on it

35. BACK ACTION CLASP It is the modification of ring clasp Minor connector attached to the clasp arm on the lingual surface unlike others clasp where the minor connector are attached to the occlusal rest Indicated in kennedy class 1 and class 2 where only mesiobuccal undercut is present Its use is not justified as lack of support to occlusal rest can make it ineffective

36. FISH HOOK OR HAIRPIN CLASP ‘C’ clasp is essentially a simple circlet clasp where the retentive arm after crossing the facial surface ,loops back in a hairpin turn to engage the proximal undercut below its point of origin Upper retentive arm is rigid while the lower part is flexible and tapered because it engages the undercut The abutment should have sufficient crown height to accommodate the two arms It is indicated in distal extension base abutment where distobuccal undercut is present

37. DISADVANTAGE can trap foodb and cause tooth decay Poor aesthetic

38. ONLAY CLASP It is an extension of occlusal rest with buccal and lingual arms Indicated when occlusal surface of abutment is below occlusal plane and the only will restore the same As it cover a large amount of tooth ,it may lead to enamel break down .hence used only in caries mouth and alloy of choice is gold alloy Metal occlusal surface can be lined with tooth coloured acrylic resin to reduce the wear of opposing teeth

39. HALF AND HALF CLASP Consist of a circumferetial retentive arm arising from one direction and reciprocal arm arising from others

40. COMBINATION CLASP DEFINITION A circumferential retainer for a removable dental prosthesis thwt has a cast reciprocal arm and a wrought wire retentive clasp It consist of wrought wire retentive arm and a cast reciprocal arm

41. ADVANTAGES Good flexibility –help dissipate stresses on abutment Easy to adjust the clasp as it can flex in all planes More aesthetically acceptable as it can be used in premolar and canine Makes only a line contact with tooth surface and hence collect less food and is easy to maintain

42. DISADVANTAGE Extra lab procedure Can be easily distorted by careless handling Poor resistance to horizontal stabilization