DIRECT RETAINERS DR MUHAMMAD RIZWAN MEMON F C

DIRECT RETAINERS DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Role of Direct Retainers in Prosthesis Movement Control l Primary retention: Direct Retainers l Secondary retention: Minor connector, Denture bases, Major connectors DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Types of Direct Retainers l l Intra coronal retainers: Precision attachment Extra coronal retainers: Clasp type DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Precision attachment Dr Herman E. S Chayes (1906) l An interlocking device, one component of which is fixed to an abutment and the other is integrated into a removable dental prosthesis in order to stabilize and/or retain it. DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

l Advantages: l Elimination of visible retentive and support components l Better vertical support l Disadvantages: l Require preparation of abutments l Complicated clinical & lab procedures l Eventually wear l Difficult to repair & replace l Least effective on short teeth l Difficult to place in tooth with large pulp chamber l More costly DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

l Clasp Assembly: The part of a removable dental prosthesis that acts as a direct retainer and/or stabilizer for a prosthesis by partially encompassing or contacting an abutment tooth. Components of the clasp assembly: Clasp ( Stabilization & Retention) Rest (Support) Minor connector (Stabilization) DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

l 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. Generally it is used to stabilize and retain a removable dental prosthesis DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Amount of Retention l Tooth Factors: l Depth l of undercut Prosthesis factors l Flexibility of clasp arm l Clasp length (Longer clasp arm more flexible it will be) l Clasp diameter (Greater the diameter of clasp arm the less flexible it will be) l Clasp cross sectional form (round form of clasp is more flexible) l Material used ( Type IV gold more flexible than Chromium cobalt) DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Basic principles of Clasp design l l l Encirclement more than 180 degrees (Basic principle). Occlusal rest must be designed. Retentive terminal should be opposed by a reciprocal component. Clasp retainers on abutment adjacent to distal extension bases should be designed to avoid direct transmission of tipping & rotational forces to the abutment. Amount of retention should always be minimal DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

Types of Clasp Assemblies DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

A-Clasp designed to accommodate functional movement 1. RPI, RPA and Bar Clasp l l l R = Rest P = Plate I = I bar A = Ackers I Bar: l l Located in gingival third 0. 01 inch undercut DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

l Class I lever l Two strategies adopted l l Change fulcrum location Minimize the effect of lever by use of flexible arm DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

l Indication of using I bar l Small degree of under cut (0. 01 inch) l Distal extension partial dentures l Tooth supported partial dentures l In situation where esthetic considerations must be accommodated l Contraindications: l Deep cervical undercut exists l Severe tooth or tissue undercut exists l Shallow vestibule l Excessive buccal/lingual tilt of abutment DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

2. Combination Clasp Another strategy to reduce effect of the class I lever is to use flexible component in resistance arm. Wrought wire retentive clasp arm + cast reciprocal claps arm. DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

B-Clasp designed without movement 1. Circumferential Clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

2. Ring Clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

3. Embrasure Clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

4. Back action clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

5. Multiple Clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

6. Reverse action Clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

7. Inter-dental clasp DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)

DR MUHAMMAD RIZWAN MEMON F. C. P. S (T) (Prosthodontics)