Management of Loading Forces Distribution in Mandibular Distal-extension Prostheses
Condition: Mandibular Distal-extension Prostheses
Study type: Interventional

Summary: 
      The two structures that support a mandibular distal extension removable partial denture
      differ markedly in their visco-elastic response to loading. The difference between the
      resilience of the residual ridge tissues and the teeth permitted by the periodontal ligament
      presents a disparity of support that is in contrast to the uniform support accorded a
      tooth-supported removable partial denture. Hence the denture tends to rotate about its most
      distal abutments, inducing heavy torsional stresses on alveolar ridges.

      Many methods have been used to control this movement, some of them:

        1. Implant support on distal extension removable.

        2. Stress breakers provide a mean of interposing a flexible connection between the
           tooth-borne retainer portion of removable partial denture and its distally extended
           tissue-borne segment.

        3. Altered-cast technique.

        4. Design development by using mesial indirect retainers rather than distal ones.

      The purpose of this study is: (1) to compare bone absorption around abutment teeth nearby the
      free saddle; (2) denture displacement and pressure on the soft tissue under the denture base
      of distal extension RPD (Removable Partial Denture) (3) cellular changes in the soft tissue
      under the denture base of distal extension RPD.
    

Detailed description: 
      Removable partial dentures (RPD) have an essential role in treating partly edentulous.
      patients with large toothless spaces, or without posterior dental support (Kennedy Class I).

      Rehabilitation with Distal-Extension Removable Partial Denture (DERPD) deserves special
      attention because of the difference in resilience between the remaining mucosa of the
      edentulous area and the periodontal ligament of the abutment tooth. When occlusal forces
      affect the bases, the difference in resilience between the mucosa of the edentulous area and
      the periodontal ligament of the abutment teeth creates a rotating movement whose axis is
      located on the occlusal rests on the abutment teeth. This may induce horizontal forces and
      mainly lateral forces upon them, causing inflammation, gingival retraction, increase in
      dental mobility and distal residual ridge resorption. This movement may cause a reduction in
      function, discomfort and trauma to the RPD supporting tissues.

      MATERIAL AND METHODS:

      Patients will be recruited from the Department of Prosthodontics at the University of
      Damascus Dental School. Thirty patients will be randomly divided into three groups (A, B, and
      C). A mandibular bilateral distal-extension removable partial denture will be used for
      patients in all groups. But every group will have its own specific method of distributing
      loading forces.

      In Group A: A Removable partial dentures will be made by using altered-cast technique for
      free saddle.The investigators will make a primary impression using stock tray. This will be
      followed by a final impression by individual tray. After metal framework try-in, ridge
      regions are removed from uncorrected master cast with saw. Then, corrective impression of
      ridges will be obtained with soft ZOE impression paste. Therefore, a metal framework with
      associated corrective impression will be repositioned on tooth portion of master cast prior
      to altering distal-extension bases.

      In Group B: Removable partial dentures will be made by using precision attachments which will
      be located on the last abutment tooth. At first, crowns will be prepared to receive the
      precision attachment, then these are cemented to their respective abutment teeth. So that a
      mean of interposing a flexible connection between the tooth-borne retainer portion of a
      removable partial denture and its distally extended tissue-borne base will be provided.

      In Group C: Removable partial dentures will be made by using resilient-layer in the distal
      extension of the removable partial denture.
    

Intervention name(s): Altered cast technique; Precision Attachments; Resilient layer
Intervention type(s): Procedure; Device; Procedure
Intervention description(s): This techniques deals with the procedures that are employed when constructing the removable partial denture on working casts.; These are minor attachments used to split the loading forces during appliance wear; This is a layer beneath the appliance which helps in reducing the transmission of loading forces to the underlying soft tissues
Other intervention name(s): Modified case technique; Joint Attachments; Flexible layer
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Loading Forces; Removable partial dentures; Bilateral distal extension