Explain the RPI clasp system in RPD construction.

Explain the RPI clasp system in RPD construction.

1. In 1973 Krol made developments to the I-bar retainer system and devised the 'RPI' system in an attempt to reduce excessive loading to the edentulous ridge area.

   • The advantage of adopting this design is the minimal tooth contact and gingival coverage.

2. Mesial Rest

   • Function of rests are to provide vertical support against occlusal forces and control the relationship of the prosthesis to supporting structures.
   • Mesial rest modification:
     • The mesial rest extends only into the triangular fossa even in molar preparations.
     • The canine rests are limited to triangular fossa circular, concave depressions prepared on the mesial marginal ridge.
     • It does not cover the entire marginal ridge.

3. Proximal plate

   • Provides horizontal stability. Reunites & stabilizes the arch. Increases retention because of parallelism and because dislodgement is limited to the path of insertion. Protects the tooth-tissue junction by preventing food impaction and because of mental coverage in the area. Provides good reciprocation. Distributes occlusal force throughout the arch.
   • Proximal plate modification:
     • One of the major disadvantages of the I-bar denture was the excessive tooth contact produced by the extra-long proximal plate. Krol introduces 3 modifications to the proximal plate.
       • Proximal plate modification I - the proximal plate is designed to extend from the marginal ridge to the junction between the middle & cervical third of tooth
       • Proximal plate modification II - the proximal plate is designed to extend along the entire length of the proximal surface of the abutment with a minimum tissue relief. A relief is provided near the gingival margin at tooth tissue junction. This allows the proximal plate to disengage into proximal undercut during occlusal overloading.
       • Proximal plate modification III - the proximal plate is designed to contact just about 1 mm 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.

4. I-Bar.

   • I-bar provides retention against vertical displacement
   • 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 embrasure 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 & mesial rest.