Impression materials and procedures for removable partial denture: Impression materials and procedures for removable partial denture Impression materials: Impression materials Requirements: The material must record accurately the anatomic form of the teeth & surrounding tissues → definite path of insertion & removal, support, stability & retention of the prosthesis will be accurate. The material must not be deformed permanently by removal from the tooth or tissue undercuts. Impression materials: Impression materials Elastic impression materials: Reversible hydrocolloids Irreversible hydrocolloids Mercaptan rubber base impression material Polyether impression material Silicon impression material Removable bounded partial denture: Removable bounded partial denture Select a suitable, sterilized, perforated tray. The tray should provide 4-5 mm border thickness. Build up the palatal portion of maxillary impression tray, lingual flange of mandibular tray & under extended borders of the tray with wax or modeling plastic. Removable bounded partial denture: Removable bounded partial denture Irreversible hydrocolloids are most commonly used. Place the patient in up right position, involved jaw parallel to the floor. Seat the tray first on the side away from you, next on the anterior area, while reflecting the lip, then on the near side, with the mouth mirror or fingers for cheek retraction. Hold the tray immobile for 3 min. with light finger pressure over left & right premolar areas. Do not remove the impression from the mouth until the impression material has completely set. Remove the impression quickly in line with the long axis of the teeth to avoid tearing or other distortion. Rinse the impression, spray it with suitable disinfectant, pour it immediately or place it in saturated atmosphere ( rapping the impression in a damp paper towel or sealing it in a plastic bag). Removable free end partial denture: Removable free end partial denture The distal extension removable partial denture must depend on: the residual ridge for some support, stability, and retention. Indirect retention, to prevent the denture from lifting away from the residual ridge. FACTORS INFLUENCING THE SUPPORT OF A DISTAL EXTENSION BASE 1. Contour and quality of the residual ridge 2. Extent of residual ridge coverage by the denture base 3. Type and accuracy of the impression registration 4. Accuracy of the fit of the denture base 5. Design of the removable partial denture framework 6. Total occlusal load applied Contour and Quality of the Residual Ridge: Contour and Quality of the Residual Ridge The ideal residual ridge to support a denture base would consist of cortical bone that covers relatively dense cancellous bone with a broad rounded crest and high vertical slopes, and covered by firm, dense, fibrous connective tissue. mandible The buccal shelf region (bounded by the external oblique line and crest of alveolar ridge) seems to be better suited for a primary stress-bearing role, because it is covered by relatively firm, dense, fibrous connective tissue supported by cortical bone. Then slopes of the residual ridge also considered primary stress-bearing area. The crest of the mandibular residual ridge considered a secondary stress-bearing area, because the crest of the bony mandibular residual ridge is most often cancellous , and the lining mucosa restricts both the buccal and lingual mucosa adjacent to teeth in the mandible, loss of firm mucosa overlying the residual ridge is common following tooth extraction in the posterior mandible. Pressures placed on tissue overlying the crest of the mandibular residual ridge usually result in irritation of this tissue, accompanied by the sequelae of chronic inflammation. PowerPoint Presentation: Maxilla The crestal area of the residual ridge will become the primary stress-bearing area, consist primarily of cancellous bone, unlike in the mandible, oral tissue that overlies the maxillary residual alveolar bone is usually of a firm, dense nature (similar to the mucosa of the hard palate). Then the immediate buccal and lingual slopes of the ridge also considered primary stress-bearing area. Palatal tissue between the medial palatal raphe and the lingual slope of the posterior edentulous ridge are readily displaceable and cannot be considered as primary stress-bearing sites. Extent of Residual Ridge Coverage by the Denture Base: Extent of Residual Ridge Coverage by the Denture Base The broader the residual ridge coverage the greater the distribution of the load, which results in less load per unit area. A denture base should cover as much of the residual ridge as possible and be extended the maximum amount within the physiological tolerance of the limiting border structures or tissue. Accuracy of the Fit of the Denture Base: Accuracy of the Fit of the Denture Base Support of the distal extension base is enhanced by intimacy of contact of the tissue surface of the base and the tissue that covers the residual ridge. Design of the Removable Partial Denture Framework: Design of the Removable Partial Denture Framework The greatest movement takes place at the most posterior extent of the denture base. The retromolar pad region of the mandibular residual ridge and the tuberosity region of the maxillary residual ridge therefore are subjected to the greatest movement of the denture base Total Occlusal Load Applied: Total Occlusal Load Applied The number of artificial teeth, the width of their occlusal surfaces, and their occlusal efficiency influence the total occlusal load applied to the removable partial denture. The reduction of the size of the occlusal table reduces the vertical and horizontal forces that act on the removable partial dentures and lessens the stress on the abutment teeth and supporting tissue. Type and Accuracy of the Impression Registration: Type and Accuracy of the Impression Registration The residual ridge may be said to have two forms: The anatomic form The anatomic form is the surface contour of the ridge when it is not supporting an occlusal load. The functional form The functional form of the residual ridge is the surface contour of the ridge when it is supporting a functional load. ANATOMIC FORM IMPRESSION: ANATOMIC FORM IMPRESSION The anatomic form impression is a one-stage impression method using an elastic impression material that will produce a cast that does not represent a functional relationship between the various supporting structures of the partially edentulous mouth. It will only represent the hard and soft tissue at rest. A removable partial denture fabricated from a one stage impression, which only records the anatomic form of basal seat tissue, places more of the masticatory load on the abutment teeth and that part of the bone that underlies the distal end of the extension base. The balance of the bony ridge will not function in carrying its share of the load. The result will be a traumatic load to the bone underlying the distal end of the base and to the abutment tooth, which in turn can result in bone loss and loosening of the abutment tooth. METHODS FOR OBTAINING FUNCTIONAL SUPPORT FOR THE DISTAL EXTENSION BASE: METHODS FOR OBTAINING FUNCTIONAL SUPPORT FOR THE DISTAL EXTENSION BASE The objective of any functional impression technique is to provide maximum support for the removable partial denture bases. This allows for the maintenance of occlusal contact between both natural and artificial dentition and, at the same time, minimum movement of the base, which would create leverage on the abutment teeth. Although some tissue ward movement of the distal extension base is unpreventable and dependent on the six factors listed previously, it can be minimized by providing the best possible support for the denture base. Selective Tissue Placement Impression Method: Selective Tissue Placement Impression Method Oral tissues that have been overly displaced or distorted attempt to regain their anatomic form. When they are not permitted to do this by the denture bases, the tissues become inflamed and their physiological functions become impaired, accompanied by bone resorption . Selective Tissue Placement Impression Method use those portions of the residual ridge that can withstand additional stress ( primary stress bearing area ) and at the same time relieve the tissue of the residual ridge that cannot withstand functional loads. Methods : Methods The use of impression compound material for taking an impression for the saddle area in a stock tray, then an impression is taken for the entire arch by using irreversible hydrocolloid impression material. PowerPoint Presentation: The use of a properly prepared, individualized impression tray can be a means to record the primary stress-bearing areas in a functional form and the non stress-bearing areas in an anatomic form, just as is often accomplished in making impressions for complete dentures. PowerPoint Presentation: Ultered cast technique Functional Impression Technique: Functional Impression Technique When the residual ridge mucosa demonstrates a uniformly firm consistency, an impression technique that involves capturing the tissue form while the patient is in occlusion can be considered. Such a technique records the mucosal position and shape under the influence of a static closure force, similar to functional masticatory forces. Where as the functional impression technique has limited application to a uniformly firm ridge consistency.