Prosthesis II lesson 6 part I and II

• RPD Retainers


  Any type of device used for the stabilisation or retention of a prosthesis
• RPD Retainers


  • Elements that keep the RPD in place at rest and during function
  • Primary retention provided by direct retainers
  • Secondary retention by major connectors and bases
  • Need in tooth-tissue supported: Adhesion, Cohesion, Border seal
• 90% of the primary retention is provided by direct retainers
• Indirect retainers don’t provide direct retention
• Objectives of RPD Retainers

  • Retention: opposing vertical forces
  • Horizontal stabilization: Stability in antero-posteriorly with proximal plates and laterally with Reciprocal arm
  • Support: preventing the impact of the bases, maintaining relationships between prostheses, abutments, and soft tissue with Occlusal rest
  • Reciprocation: counterbalance of lateral forces during insertion-placement with Reciprocal arm
• Thanks to classification
• Classification of RPD Retainers

  • Direct retainers retain at the very place where they are, oppose all movements, and have two types of retention mechanisms: Clasp (extracoronal retainer) and Frictional (precision attachments)
  • Indirect retainers are passive, oppose rotation around the fulcrum line, and are at a distance from where they are
• Types of direct retainers

  • Clasp assemblies: Cast retainers like Circumferential retainers, Bar or contact point retainers, and Wrought wire retainers
  • Friction retainers like Buch & Carmona, Single-continuous arm clasp, Nally-Martinet, Posterior action, and Multiple clasp
• Components of Direct Retainers

  • Retentive arm that surrounds the tooth, part of the framework, and fix part cemented over the teeth
• Tooth-tissue and tooth-supported RPDs provide retention and stability to RPDs
• Circumferential retainers consist of minor connector (rigid) and a retentive system
• Types of RPD Retainers

  • Circumferential Retainers
  • Bars
• Indirect retainer
• Circumferential retainers consist of

  1. Minor connector (rigid)

  2. Retentive system: Occlusal rest, Body, Reciprocal arm, Retentive arm
• Body of the retainer

  • Guides the path of insertion, Stabilisation, Connection, Extension of the minor connector
• Guiding planes on the interproximal surface of the abutment teeth determine the path of insertion
• To have one single path of insertion, the guiding planes need to be parallel
• In the surveyor, the insertion path is decided and the body of the direct retainer guides the RPD to always have the same insertion
• The guiding plates provide stability (anteroposterior)
• For bar/contact point retainers

  • The proximal plate acts as reciprocal arm and body of the retainer at the same time: Limits and guides the insertion and removal path of the denture, Improves stability (antero-posteriorly), Friction retention, Reciprocation (RPI), Reduces embrasures
• Occlusal rest


  • Located at the occlusal surface of the tooth, Functions: Support, Prevents the denture from embedding in the soft tissues
• Occlusal rest functions


  1. Support

  2. Prevents the denture from embedding in the soft tissues

  3. Prevents tooth movements (rotations, migrations, and inclinations)

  4. Maintains vertical dimension and occlusion by preventing denture teeth from impacting during function

  5. Keeps retainer arms in position during function to prevent disinsertion of the retention system

  6. Distributes and transfers occlusal loads received by artificial teeth
• We need occlusal rest to provide support. During eating, the support prevents intrusion of the removable denture and maintains the vertical dimension by opposing occlusal forces and transferring the load applied to the remaining teeth
• Occlusal rest design
• Occlusal rest design


  • Rounded and slightly triangular
  • Spoon shape
  • Adequate thickness to be rigid and fulfill functions
  • Same width and length
  • Width of ½ to 1/3 of the distance between cusps
• Occlusal rest design


  • Angle between body-minor connector and occlusal rest must be less than 90º towards the center of the tooth to stabilize the occlusion, transmit axial forces, and keep the retention elements in position
  • Vertex directed to the center of the tooth so that forces generated are directed to the center of the tooth
• Sometimes an occlusal seat needs to be prepared by removing enamel to make space for the occlusal opposite cusp. Assessment can be done in the articulator with the diagnostic cast. This preparation is not making a hole or cavity, but rather preparing a spoon shape
• Occlusal rest design


  • Angle less than 90° to transfer the load following the axis of the tooth
• Occlusal rest design at anterior teeth

  • Better at canines than incisors due to greater root support. If no canines, multiple supports on incisors will be used. Resting over the cingulum is better than the incisal edge because it is closer
• Occlusal rest


  • If made at anterior teeth, better at canines than at incisors due to greater root support
  • Resting over the cingulum is better than the incisal edge for better biomechanics and aesthetics
• If the seat is not in the occlusal rest, it can be called Cingular rest
• Clasp arms encircle the tooth and provide retentive, reciprocating, and stabilizing properties
• Clasp arms provide


  1. Retention

  2. Reciprocation

  3. Stabilisation
• Retentive clasp arms determine the amount of retention based on cervical convergence angle, depth below the undercut area, and flexibility
• Retentive arms provide retention, reciprocal arms provide reciprocation, both surround the tooth, known as encironment
• The retentive arm must be placed in the right position to determine the amount of retention
• Cervical convergence angle determines the amount of retention for retentive clasp arms
• The greater the cervical convergence angle, the less the retainer will extend towards the gingival
• Undercut gauges measure the horizontal depth of the undercut and are influenced by the cervical convergence angle
• Undercut gauges


  1. Measure the horizontal depth of the undercut

  2. Rest over the survey line and at a point below it