BDS8230 Clinical Partial Prosthodontics: Final Impression 2023 PDF

NEWGIZA UNIVERSITY BDS8230 Clinical partial prosthodontics: Final impression 2023 NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Objectives: On completion of this lecture, the student should have: - An understanding of how to choose the appropriate impression material and tray - An understanding of to...

NEWGIZA UNIVERSITY BDS8230 Clinical partial prosthodontics: Final impression 2023 NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Objectives: On completion of this lecture, the student should have: - An understanding of how to choose the appropriate impression material and tray - An understanding of to make an accurate impression NEWGIZA UNIVERSITY Types of RPD according to support • Tooth Support • tissue support • Tooth-tissue support NEWGIZA UNIVERSITY Types of RPDs (Support) TissueBorne Distal extension base Free end saddle ToothBorne Bounded saddles Tooth-supported NEWGIZA UNIVERSITY Functional Impression Anatomic Impression NEWGIZA UNIVERSITY Anatomical Impressions • An impression which records the anatomical form of the ridge. Which is the surface contour of the ridge when it is not under occlusal load. • Single Impression recording both teeth and tissues at the same time. • Stock tray / custom tray Stock Tray NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Primary Impression NEWGIZA UNIVERSITY Acrylic resin Custom Tray • Block undercuts •Wax spacer 4 mm for Alginate 2-4 mm for rubber base • Stoppers NEWGIZA UNIVERSITY •2 layers of base plate wax •Short of the vestibule NEWGIZA UNIVERSITY Stoppers Perforations NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Functional Impressions Disparity of support Mucosa is 8 times more compressible than periodontal ligament Impression must record teeth in their ANATOMICAL form and the tissues in their FUNCTIONAL form Impression of distal extension bases must NEWGIZA UNIVERSITY 1. Record supporting structure under some loading. 2. Maximum coverage of the base, to distribute the load over largest possible area. 3. Direct forces to the 1ry stress bearing area. 4. Equalize support derived from edentulous ridges and abutment teeth. 5. Minimize movement of the base. Maximum support Less harm to the teeth and the ridge NEWGIZA UNIVERSITY Types of Functional Impressions 1. At the framework stage • Altered Cast Technique 2. At the finished denture stage • Functional relining techniques NEWGIZA UNIVERSITY Selective pressure impression Techniques • A thorough understanding of the characteristics of impression materials and techniques leads to the conclusion that no single material can record both the anatomic form of teeth and the functional form of the ridge at the same time. • Based on the concept that specially designed trays will develop denture bases that will use those portions of the residual ridge that can withstand stresses and at the same time relieve the tissues that cannot withstand functional loading and maintain their health. NEWGIZA UNIVERSITY Steps of altered cast impression technique Primary impression Secondary anatomical impression Framework construction Framework trying in and fitting NEWGIZA UNIVERSITY Try-in of the framework NEWGIZA UNIVERSITY • Base plate wax is adapted over the cast, 2 mm short of the vestibule. • Framework is warmed and placed over the wax. NEWGIZA UNIVERSITY • A.R. is constructed over the wax with the same extension • Perforations should be made opposing the residual ridge and RMP to allow escape of material  relief • Spacer is removed NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY • Framework and tray are tried in the patient’s mouth, checked for extension and proper seating • Border molding is done NEWGIZA UNIVERSITY Fingers are placed on the 2 main occlusal rests and one on the indirect retainer (tripod) during molding and complete setting of the impression material NEWGIZA UNIVERSITY Preparation of the cast • Edentulous areas are sawed off the cast • Fix framework to cast with sticky wax NEWGIZA UNIVERSITY Preparation of the cast NEWGIZA UNIVERSITY What about this impression in maxillary cases???? NEWGIZA UNIVERSITY Not often used: -In the maxilla, because the maxillary distal extension is usually covered by a firm well attached mucosa, and the primary stress bearing area includes the crest and the buccal slope of the ridge. single anatomical impression. NEWGIZA UNIVERSITY 2. At the finished denture stage Functional relining techniques The Functional Relining Impression Technique 1- For New denture: constructed from single anatomic impression to avoid movement on the edentulous area after application of masticatory load. 2- After denture use for many years , a combination of occlusal wear and sinking of the denture following alveolar resorption occurs. So functional impression is required to correct this situation NEWGIZA UNIVERSITY The functional relining impression technique Done after denture construction, (open mouth procedure ) 1- Borders are shortened and denture base is relieved ( to create space for impression material ). 2- Border molding using Green Stick Compound impression. 3- Zinc Oxide impression is done under tripod pressure 4- Overall alginate impression is made . 5- Cast is poured , relining , adjust occlusal errors . NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY The functional impression techniques can be performed with different impression materials • Rubber base impression material • Zinc oxide and eugenol paste or • Fluid wax. NEWGIZA UNIVERSITY NEWGIZA UNIVERSITY Objectives: On completion of this lecture, the student should have: - An understanding of how to choose the appropriate impression material and tray - An understanding of to make an accurate impression NEWGIZA UNIVERSITY Thank You