Indirect Retainers for Removable Partial Dentures PDF

3rd year prosthesis 9. Indirect Retainers for Removable Partial Dentures INTRODUCTION: A component of RPD that assists the direct retainer in preventing displacement of the distal extension denture base >> by functioning through lever action on the opposite side of the fulcrum line wh...

3rd year prosthesis 9. Indirect Retainers for Removable Partial Dentures INTRODUCTION: A component of RPD that assists the direct retainer in preventing displacement of the distal extension denture base >> by functioning through lever action on the opposite side of the fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line. indirect Retention: The effect achieved by one or more indirect retainer that reduces the tendency for a denture base to rotate about the fulcrum line. Movements of RPD Movement of Distal Extension RPD Movement of Tooth-borne RPD 1. Movement of Distal Extension RPD Bodily vertical movements in 2 directions − Toward the ridge tissues >> Support − Away from the ridge tissues >> Direct retention Rotational movement about an axis (fulcrum line) − Horizontal axis (IR) − Sagittal axis (rigidty of major conector) − Vertical axis (extention of flanges , recprocal element) 1. Rotation about Horizontal axis (away VS toward) indirect retainers do not prevent displacement towards the ridge. This movement is resisted by Gaining maximum support from residual ridge “functional impression”.  Impression of functional ridge form = capturing surface contour of the ridge when it’s supporting a functional load Indirect Retainer: A component of RPD that assists the direct retainer in preventing displacement of the distal extension denture base ➔ by functioning through lever action on the opposite side of the fulcrum line when the denture base moves away from the tissues in pure rotation around the fulcrum line. The indirect retainer is located on the opposite side of the retentive fulcrum line from the mucosa supported base Movement of tooth-borne RPD: Usually do not exhibit rotational movements, due to their extensive tooth support. However, any tooth borne RPD that has mobile or disengaged abutments may exhibit rotational movements >> Fulcrum line A fulcrum line is an imaginary line around which an RPD will tend to rotate. Indirect retainers provide resistance to rotational movement of a distal extension RPD away from the denture bearing tissues around the retentive fulcrum line (vs supportive fulcrum = toward) Retentive fulcrum line an imaginary line connecting retentive tips of the abutment teeth adjacent ''near" to the distal extension base Class II modification 1 Class 1 Most posterior 2 Page 2  Class IV (Most Class II (Most anterior) posterior) Class III Class III modification I modification I Most anterior Indirect retention in RPD >> Indications 1. On all extension-base partial dentures retained by clasps. 2. When the tooth at one end of a denture base is clasped for retention but the tooth at the other end is not suitable for retention. Factors for effectiveness of indirect retainers (IR): 1) Distance from fulcrum line 2) Effectiveness of tooth support 3) Effectiveness of direct retainer 4) Rigidity of indirect retainers 5) Rigidity of the connectors supporting IR 1) Distance from fulcrum line The greater the distance >> more effective IR. Placed on a tooth with good periodontal support. Perpendicular to the fulcrum line. Bilateral rests on the first premolars "better PDL support than central incisors" are quite effective, even though they are located closer to the axis of rotation. 3 Page 3  The IR are inefficient because If the clasp is moved closer to they are placed too close to the saddle, the effectiveness of clasp axis If the clasp axis the IR is improved. 2) Effectiveness of tooth support IR must be placed on a definite rest seat. Weak teeth shouldn't be used to support IR. 3) Effectiveness of direct retainer If the denture base and rests lift bodily away from tissues >> action of IR is lost. 4) Rigidity of indirect retainers If the arm of the IR were to flex IR will not be effective. 5) Rigidity of the connectors supporting IR All connectors must be rigid if the indirect retainer is to function as intended. Forms of indirect retainers IR supported by teeth 1. Auxiliary Occlusal Rest 2. Canine rest 4 Page 4  3. Canine Extensions 4.Cingulum Bars (Continuous From Occlusal Rests Bars) and Lingual plates IR supported by palate: 1. Palatal arm 2. Anterior Palatal bar 4. posterior Palatal bar 3. Horse shoe Palate >> Examples of RPD designs which include indirect retention: 5 Page 5