Direct retainers prevent RPD movement away from the hard and soft tissues. They can be intra-coronal (precision attachments, semi-precision attachments) or extra-coronal, which are generally clasp assemblies. Only the terminal part of the retentive arm sits below the contour line of the tooth and engages the undercut. 

Intra-coronal attachments derive their function from closely fitting, coupling parts. One component is attached to the removable partial denture and the connecting component is traditionally incorporated into a cast crown or a fixed partial denture, sometimes referred to as patrix and matrix. Intracoronal attachments allow for the placement of torquing forces close to the long access of the tooth and eliminates the need for visible external clasps. They are generally more hygienic. However, more tooth reduction is required, they are more expensive and technically difficult to fabricate, and more difficult to repair. Intra-coronal attachments are fine for tooth-borne dentures but not appropriate in patients with distal extension bases since the functional movement will result in abutment tooth torquing. 

Precision attachments are prefabricated and incorporated in a denture design. Semi-precision attachments show a similar design but are made of wax, and replaced by metal during the casting process. 

Indirect retention counters the lifting of the denture base away from the soft tissue during function. Indirect retainers take the form of rests and are placed on the opposite side of the fulcrum line from the denture base, as anteriorly as possible. Common locations include the lingual surface of the canines or mesial surfaces of lower premolars. They provide retention, but also protect soft tissues from impingement by the major connector. Indirect retainers may not be included in some designs (e.g. tooth borne Kennedy Class III appliances). 

Reciprocation is included in denture design to counter the effects created by another part of the prosthesis. In an RPI design, reciprocation is achieved by rigid plating, minor connectors and guide planes. A minimum of 180° encirclement is recommended for adequate reciprocation.

A reciprocal clasp/stabilizing clasp is usually positioned on the lingual side of the assembly. Originating from the minor connector, the reciprocal clasp should contact the tooth above the height of contour. During insertion the reciprocal arm should engage the tooth at the same time as the retentive clasp arm to counter any unwanted lateral forces on the tooth. 

Minor connectors link components of the removable partial denture to the major connector. They must be rigid to transmit functional stresses evenly throughout the mouth.

Stress-breakers can be incorporated to relieve abutment teeth of excessive forces during function. When a stress-breaker is used next to a free-end distal extension RPD, the majority of the functional stress is directed onto the residual ridge with only minimal force transfer to the abutment tooth. This protects the tooth and supporting structures, but will likely result in increased ridge resorption, requiring more frequent relines. Types of stress breakers include:

• Wrought-wire clasps – the simplest form of stress relief, providing a flexible connection between the direct retainer and the denture base. Compared to cast clasp arms, wrought-wire clasps exhibit greater flexibility, adjustability, ductility, toughness, and tensile strength. But the yield strength can be negatively impacted by excessive heat or long term cyclic loading. The terminal end of the wrought-wire clasp is usually placed in the middle of the gingival third of the clinical crown, but positioning is dictated by the location of the undercuts. When seated the arm should be passive. 20-gauge wire is twice as flexible as thicker 18-gauge. 

• Split-bar major connectors – flexible connections between the direct retainer and the denture base.

• Stress-breaker with a moveable joint – connecting the direct retainer and denture base. Examples include Distal Extension Hinge (DE hinge), Crismani attachment, ASC-52 attachment, and Dalbo attachment. 

Bracing occurs when rigid components are placed on the RPD to sit against non-undercut areas. A bracing component resists horizontal forces. 

Guidance is obtained by incorporating rigid components that brace against teeth during insertion and removal. Guiding surfaces are parallel to the path of insertion.

Beading is the procedure of scribing a rounded trench 0.05 mm deep following the anterior and posterior borders of a maxillary major connector. Beading an RDP adds strength (volume) to the major connector and ensures proper tissue contact to prevent food impaction.

The dental surveyor is an instrument used to determine the relative parallelism of oral anatomy. With a dental surveyor a clinician can determine the path of insertion, position of guide planes, and the location of undercuts. Areas used for support cannot be determined by surveying. Tilting the cast will change the path of insertion, position of survey lines, and the location of undercuts and non-undercut areas. When surveying casts the dentist/technician places tripod marks on the cast to record and reproduce the cast’s orientation on the surveyor.