Concepts of rpi/ dentistry dental implants


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  • Direct retainers
  • Concepts of rpi/ dentistry dental implants

    1. 1. CONCEPTS OF RPICONCEPTS OF RPI INDIAN DENTAL ACADEMY Leader in continuing dental education
    3. 3.  RPI is a modified I-bar retainer system.  It was devised by Krol in 1973.  All the components of the I-bar assembly were modified significantly to fulfill Krol’s design.
    4. 4.  Principle of Krol’s design was  “stress control with minimal tooth and gingival coverage” His concept is intended to minimize plaque accumulations that may endanger the health of teeth and their vesting structures.
    6. 6. MODIFICATION OF EACH COMPONENT OF THE I-BAR RETAINER REQUIRED TO FORM A RPI SYSTEM †Mesial rest modification †Proximal plate modification - Modification I - Modification II - Modification II †I-bar modification
    7. 7. Mesial rest preparationMesial rest preparation: In molars the mesial rest extends only into triangular fossa. The canine rests are circular, concave depressions prepared on the mesial marginal ridge. It does not cover the entire marginal ridge.
    8. 8. Proximal plate modifications:Proximal plate modifications:  One of the major disadvantages of the I-bar denture was the excessive tooth contact produced by the extra long proximal plate.  Krol introduced three modifications to the proximal plate. They are - Design modification I - Design modification II - Design modification III
    9. 9.  Design modification I :: The proximal plate is designed to extend along the entire length of the proximal surface of the abutment with a minimum tissue relief.
    10. 10.  Bar clasp assembly in which guiding plane (GP) and proximal plate (PP) extend entire length of proximal tooth surface.  Physiologic relief is required to prevent impingement of gingival tissues during function.  Extending proximal plate to contact greater surface area of guide plane direct functional forces in horizontal direction, thus tooth (teeth) are loaded more than edentulous ridge
    11. 11.  Design modification II :Design modification II :  The proximal plate is designed to extend from the marginal ridge to the junction between the middle and cervical third of the tooth.  Where as in I-bar retainer the proximal plate extends about 2mm across the tooth tissue junction.
    12. 12.  Bar clasp assembly in which guiding plane (GP) and proximal plate (PP) Extends from marginal ridge to junction of middle and gingival thirds of proximal tooth surface.  The decrease in amount of surface area contact of proximal plate on guiding plane more evenly distributes functional force between tooth and edentulous ridge.
    13. 13.  Design modificationDesign modification III :III :  † The proximal plate is designed to contact just about 1mm of the gingival third of the guiding plane of the abutment tooth.  † The purpose of reducing the length of the proximal plate is to improve the gingival health.
    14. 14.  Bar clasp assembly in which proximal plate (PP) contacts approximately 1 mm of gingival portion of guiding plane (GP).  During function, proximal plate and I – bar clasp arm are designed to move in mesiogingival direction, disengaging tooth. Lack of sustained contact between proximal plate and guiding plane distributes more functional force to edentulous ridge
    15. 15. I-bar modification:I-bar modification: † The tip of the I-bar is modified to have a pod shape in order to allow more tooth contact. † It is placed more mesially so that it shifts towards the mesial embrassure space under occlusal load and increases reciprocation. † The I-bar is designed to compensate for the decreased encirclement, {tooth contact}, provided by the proximal plate and mesial rest.
    16. 16. ADVANTAGES :  Minimal tooth coverage.  Hence these dentures are easy to maintain
    17. 17. RPARPA System R - Rest P - Proximal Plate A -Aker’s clasp
    18. 18. R P AR P A  This is a modification of the RPI retainer, again devised by Krol in 1976.  The I-bar in the RPI system could not be used for patients with soft tissue undercuts and high frenal attachments.  In such cases the I-bar of the RPI retainer is replaced with an Aker’s {circumferential} clasp to form the RPA retainer. Frontal view Occlusal
    19. 19. Advantages :  Easier to grasp for removal of prosthesis .  It can be used in case of large tissue undercuts, high frenum etc.  Indicated when bar clasp is contraindicated and desirable undercuts is located in gingival 3rd of tooth away from distal extension area.
    20. 20.  Successful use of the system requires careful analysis of each component for the function that it provides and thoughtful execution of the system in the abutment preparation.
    21. 21.  Mc Cracken’s Removable partial denture prosthodontics. 11th edition, 2004.  Stewart, Rudd and Kuebker – Clinical Removable partial prosthodontics- third edition  Stewart, Rudd and Kuebker: Clinical Removable denture prosthodontics. 2nd edition, 2001.  Davenport, Basker and Heath :A color atlas of removable partial dentures, 1st edition, 1980.  McCrackens ,Removable partial prosthodontics, 8th edition.
    22. 22. THANK YOUTHANK YOU For more details please visit