2. Principles of RPD design 2.pdf

Principles of Removable Partial Denture Design Chapter 10 McCracken’s REMOVABLE PARTIAL PROSTHODONTICS 13th Edition Dr. Maha Suliman Mazyad 1  Difference in prosthesis suppo...

Principles of Removable Partial Denture Design Chapter 10 McCracken’s REMOVABLE PARTIAL PROSTHODONTICS 13th Edition Dr. Maha Suliman Mazyad 1  Difference in prosthesis support and influence on design For a tooth-supported prosthesis: The movement potential is less because resistance to functional loading is provided by the teeth. For a tooth-tissue–supported prosthesis The residual ridge (remaining alveolar bone and overlying connective tissue covered with mucosa) presents with variable potential for support. In general, RPDs opposing natural teeth require greater support and stabilization over time because of the greater functional load demands. Therefore, occlusal relationships at maximum intercuspation should be broadly dissipated to the supporting units. 2  Differentiation between two main types of RPD Designing distally extended RPD cases Designing bounded RPD cases 3  Differentiation between two main types of RPD First consideration: The manner in which each is supported Class I, Class II, Class III ?! 4  Differentiation between two main types of RPD Second consideration: Method of impression registration and the jaw record required for each type will vary 5  Differentiation between two main types of RPD Third considerations: Need for indirect retention exists in the distal extension type of partial denture In tooth-supported (Class III), No extension base is present to lift away from the supporting tissues Tooth-supported partial denture does not rotate about a fulcrum, as does the distal extension partial denture. 6  Differentiation between two main types of RPD Fourth considerations: Manner in which the distal extension type of partial denture is supported often necessitates the use of Base material that can be relined to compensate for tissue changes (Acrylic-resin) Class III - Does not require relining Except: § Eliminate an unhygienic, unesthetic or Uncomfortable condition resulting from loss of tissue contact. So, Metal bases - tooth-supported restorations, as relining is not as likely to be necessary with them 7  Differentiation between two main types of RPD Fifth considerations: Requirements for direct retention A- Tooth-supported :- Clasp at each end of each edentulous space. ü Clasps should flex sufficiently during placement and removal of the denture to pass over the height of contour of the teeth in approaching or escaping from an undercut area. ü Cast retentive arms Circumferential type, approaching the undercut from an occlusal direction Bar type, approaching the undercut area from a gingival direction. 8  Differentiation between two main types of RPD Fifth considerations: Requirements for direct retention Retentive B- In the combination tooth- and tissue-supported RPD: arm made of A retentive clasp arm made of wrought wire wrought (combination clasp)? metal Or Bar type Reciprocation arm made of rigid cast 9 Designing distally extended RPD cases 10  Designing distally extended RPD cases 1- Denture base: A combined metal-acrylic base is used to allow for future relining as bone resorption is usually anticipated. The metal base is designed either in a ladder-like configuration or in the form of a meshwork, to allow for mechanical retention with acrylic resin. 11  Designing distally extended RPD cases 2- Rests: Mesially placed rests are preferably used on abutment teeth. However, absence of a rest adjacent to the edentulous area may permit packing of food. This could be avoided by using properly designed proximal plates. Saucer-shaped rest seats are preferred over box shaped seats to avoid locking of the rest and transmission of torque on abutments. 12  Designing distally extended RPD cases 3- Direct retention: Flexible rather than rigid clasping is preferred to allow slight movement of the base without stressing the abutments. RPI, I-bar, combination clasps, RPA, reverse circlet clasps, back action or reverse back action clasps can be used. 13  Designing distally extended RPD cases 4- Indirect retention: Indirect retention should be designed to counteract displacing rotation forces. Two indirect retainers, one on each side are generally used, they should be located as far anterior to the fulcrum axis as possible. Indirect retainers may be in the form of: 1. Rests 2. Palatal connectors. 14  Designing distally extended RPD cases 5- Major connectors: For maxillary class I: Antero-posterior palatal bars or strap, and palatal plates, are preferred due to: these connectors provide maximum support, direct and indirect retention. For mandibular class I: Lingual bars with terminal rests are preferred due to their simplicity, limited coverage and patient’s tolerance. Mechanically, lingual plates with terminal rests are biologically preferred due to their rigidity, distribution of lateral forces and due to improved indirect retention. 15  Designing distally extended RPD cases 6- Minor connectors: Rigid minor connectors are designed to connect the framework components either to the denture base or to the major connector. Requirements of minor connectors? 1- Sufficient bulk to be rigid WHY? 2- A minor connector that contacts the axial surface of an abutment should not be located on a convex surface INSTEAD should be located in the embrasure space 3- In an embrasure space, the minor connector is tapered to the tooth to avoid bulk and to accommodate the tongue. 4- It should be thickest toward the lingual surface, tapering toward the contact area 5- The deepest part of the interdental embrasure should blocked out WHY? 6- The junctions of these mandibular minor connectors with the major connectors should be strong butt-type joints but without appreciable bulk Angles formed at the junctions of the connectors should not be greater than 90 degrees 16  Designing distally extended RPD cases 7- Guiding plane: Guiding planes are flat axial parallel surfaces in an occluso-gingival direction on the proximal or lingual surfaces of teeth. They are 2-4 mm in height. The bucco-lingual width of the proximal plate is determined by the proximal contour of the tooth. In distal extension base a pronounced guiding plane is not recommended. 17  Designing distally extended RPD cases 8 Artificial teeth: Small teeth that are narrow bucco-lingually are usually preferred to reduce the occlusal load. Teeth should exhibit sharp cutting edges. Lower teeth should be placed over the crest of the ridge to enhance denture stability. Centric occlusion of teeth should coincide with centric relation. When the remaining teeth are weak, periodontally affected, and require splinting and stabilization are usually treated using swing-lock partial dentures 18 Designing bounded RPD cases 19  Designing bounded RPD cases 1-Denture base: The denture base is designed to fit the static rather than the functional form of the ridge because the denture base is adequately supported on both sides by abutment teeth, i.e. tooth supported. Metal plates rather than combined metal-acrylic bases are usually used 20  Designing bounded RPD cases 2- Rests: Are usually placed on the near zone of the abutment teeth to provide adequate support. Rest seat can be prepared in either a box-shaped or saucer-shaped configuration depending on the condition of the abutment teeth. 21  Designing bounded RPD cases Clasps: Rigid clasping is usually required for class III cases bounded by strong abutments. The clasps are located on abutments bounding the edentulous span. A third clasp which may either be an embrasure or a multiple clasp is used on the intact (dentulous) aide. 22  Designing bounded RPD cases 4- Major connectors: Mandibular dentures - A lingual bar Maxillary dentures - A palatal bar or palatal strap 23 THANK YOU 24