Secondary Impression Techniques PDF

Secondary Impression Definitive (Secondary) impressions 'should record the entire functional denture-bearing area to ensure maximum support, retention and stability for the denture during use'. Definitive impression is to record accurately the tissues of the denture-bearing areas, in a...

Secondary Impression Definitive (Secondary) impressions 'should record the entire functional denture-bearing area to ensure maximum support, retention and stability for the denture during use'. Definitive impression is to record accurately the tissues of the denture-bearing areas, in addition to recording the functional width and depth of the sulci. Objectives of an impression ▪Retention. ▪Stability. ▪Support. ▪Providing impression lip support. ▪maintaining the health the oral tissue.  The final impression (Secondary impression) Types of Secondary Impression techniques: 1. Minimal pressure impression technique (impression theory) 2. Definitive Pressure (functional) impression technique (impression theory) 3. Selective pressure techniques (impression theory) 4. Reline and rebase techniques 5. Conventional techniques Impression philosophies 1-Mucostatic impression technique or minimal pressure impression technique: (Open Mouth) It is made by providing holes and large amount of space between the tray and the soft tissues of the basal seat and the use of an impression material with high flow and low viscosity. Tray used: Impression material: Plaster of Paris Denture base: Metallic denture base. This technique considers interfacial surface tension as the denture retentive force.  Advantages 1. As it is an open mouth technique, the operator inspects the borders and insures proper border molding. 2. There is less distortion to the mucosa and accordingly the tissues do not exert a displacing force on the denture, this results in a more stable denture during rest 3. It is the technique of choice for flabby and thin wiry ridges where minimal pressure is essential. 4. The tissues beneath the denture are not subjected to a continuous pressure which often results in bone resorption. 5. Minimal interference with the blood supply. Disadvantages: 1. The mucosal topography (contour) is not static over the day. 2. This technique causes un-even loading of the denture bearing. 3. Peripheral seal neglected in retaining the denture. 4. Intimate contact between the finished denture and the oral is impossible. (due to dimensional changes of the impression material, the cast material or during denture processing) 5. The denture is not stable during function. 6. It neglects the principle of distributing masticatory forces over the largest possible basal seat area.  Definitive pressure impression technique (impression theory) It is also called muco-compressive or functional or Closed mouth impression technique) It is the negative representation of the denture bearing tissues at function, under the patient’s biting force. Impression material: viscous impression material to allow transmission of pressure to the mucosa. The material used is zinc oxide and eugenol paste or medium body rubber base (Zinc oxide eugenol material is a viscous material, have a long setting time to allow functional movement and border molding.) Impression tray: special tray without spacer with occlusion rims set at the proper vertical dimension.  Advantages: The patient can exert his own masticatory force on the impression material. It permits adequate trimming of the lingual borders of the lower impression. This is because tongue movement required to trim the lingual border are more forceful when the mouth is closed than when the mouth is opened and the tongue is protruded. Disadvantages: Dentures constructed from such an impression do not fit well at rest, as the compressed tissues tend to rebound and regain their form when pressure is released. An overextended denture may result due to improper border molding. Prolonged pressure exerted on tissues may interfere with blood supply and accelerates ridge resorption. Wax Rim on impression tray  -Functional Impression Technique is a type of Definitive pressure impression technique Functional Impression poor muscle adaptation problems of available denture space. patients who have recently suffered from a stroke. presence denture instability problem. When the patient suffers from denture looseness due to the presence of localized areas of poor functional adaptation.  Functional Impression In some cases of denture loosening , the application of a thin mix of a chairside resilient lining material may be beneficial (e.g Visco-Gel) Procedures: The chair side relining material is mixed according to the manufacturer instructions. The material is added to the fitting surface of the denture & the patient is instructed to wear the denture for one hour. After one hour of functional molding; the denture is removed from the patient mouth & the conventional relining process completed. Selective pressure impression technique. This technique combines considerable pressure on certain areas and minimal pressure transmits more pressure from the denture on favorable parts of the bone transmit less pressure on unfavorable parts, incisive papilla area. The tray is constructed with relief over areas of least pressure and closely adapted over other areas (stress bearing areas). The selective pressure impression technique is used when the flabby tissue is in the anterior part of the mouth (localized tissues and not expected to interfere with the stability of the denture) If the flabby tissues are generalized (cover the whole denture bearing area which may interfere with denture stability) , surgical removal may be done or minimal pressure impression technique is used when surgery cannot be performed.  This impression technique fulfils all the requirement Maximum extension of the denture. Adequate peripheral seal and Selective placement of the occlusal pressure. 1.Displaceable (Flabby) Anterior Maxillary Ridge  Impression of the whole maxilla is taken using either zinc-oxide- eugenol (ZOE) or a medium-bodied polyvinyl siloxane (PVS) impression material. The extent of the displaceable tissue is drawn on the impression surface. This area, and the equivalent area of the tray, is then removed, using a scalpel and acrylic bur Displaceable area removed from special tray. In this case, a medium- bonded PVS impression was used. b) Completed impression. Here a light bodied PVS impression material was syringed or painted onto the displaceable tissue 2. Fibrous (Unemployed) Posterior Mandibular Ridge  Fibrous posterior mandibular ridge. This ridge as such is not useful for support This condition may be recognized by the presence of a thin, mobile thread-like ridge which is essentially fibrous in nature  a-c Staged sequence of techniques: a) An impression of the denture-bearing area recorded using tracing compound. b) Crestal area cleared of tracing compound - tray perforated on crestal area;  Inject some light-bodied PVS onto the buccal and lingual shelves of the greenstick and gently insert the impression. Excess material will be extruded through the perforations, and the fibrous ridge will assume a resting central position, having been subjected to even buccal and lingual pressures. c) Definitive impression using light- bodied polyvinyl siloxane Secondary impression for flabby ridge. Secondary impression for flabby ridge. Secondary impression for flabby ridge Secondry impression for flabby ridge. Secondary impression for flabby ridge  Digital pressure - Digital pressure technique. Reline & Rebase Impression Techniques: These impression techniques are performed in an old denture. The denture to be relined should be border molded to ensure adequate peripheral seal. Undercuts in the fitting surface of the denture are blocked-out to facilitate removal of the master cast. Zinc oxide& Eugenol, poly-sulphide or polyvinyl siloxane impression materials may be used. The maxillary denture should be perforated in area of midline of the palate & rugae area to allow for excess relining material to escape. Conventional technique Border molding the special tray: Border molding is the process by which the shape of the borders of the impression are in harmony to the physiologic action of the limiting anatomic structures.  This essential functional refinement of the impression borders ensures an optimal peripheral seal, and maximum coverage within the physiological muscaular movement of the patient.  Material that can be used for simultaneous molding should: 1-Have sufficient body. 2-Retain adequate flow in the mouth. 3-Does not cause excessive displacement of the border limiting tissues. 4-Allow some finger reshaping of the borders and 5-Have sufficient setting time of 3-5 minutes. The final impression tray The final impression tray Over extended lower tray. Border molding the special tray: Border molding is the process by which the shape of the borders of the tray is made in harmony with the physiologic action of the limiting anatomic structures.  Active border molding: patient himself performs functional muscle movements Passive border molding: the operator applies them to the patient  Border molding is classified Sectional border molding One step border molding Sectional border molding One step border molding Border molding the final maxillary impression tray Border molding the final maxillary impression tray Posterior Border molding the final maxillary impression tray Posterior Border molding the final maxillary impression tray  the Posterior Palatal Border( Post-Damming) In the region of compressible tissue just distal to the hard palate and anterior to the vibrating line. (On the immovable part of soft palate) Functions of posterior palatal seal: 1. It increases retention of the denture by offering negative atmospheric pressure. 2. It prevents air and food from getting under the denture. 3. It reduces reflex irritation and gag by: a) Reducing patient awareness of this area, no separation of the denture base and soft palate. b) Making the thickness of the base less conspicuous to the tongue. 4. It compensates for dimensional changes that are inherent in the laboratory procedures Scraping the Border molding. Buccal vestibular area The final upper impression The final upper impression The final upper impression  Border molding the final mandibular impression tray.  Border molding the final mandibular impression tray. Border molding the final mandibular impression tray. The final mandibular impression.  Errors in Secondary impression 1-A thick buccal border on one side with a thin buccal border on the opposite side. (poorly centralized tray----- as the tray was out of position in the direction of the thick border). 2-A thin labial border with the tray showing on the inside surface of the labial flange. This indicates that the tray was placed too far posteriorly and not centered correctly over the anterior ridge. 3-A thick lingual border on one side with a thin lingual border on the opposite side. This indicates that the lower tray was out of position in the direction of the thin border. 4-A thin anterior lingual border with the tray showing on the inside surface of the lingual flange. This suggests that the lower tray was too far forward in relation to the residual ridge. It will be accompanied by a thick labial border. In a similar manner, a thick labial border in the upper arch with the tray showing through over the anterior slope of the palate. This indicates that the tray was too far forward in relation to the residual ridge. 5. Excess thickness of impression material over the fitting surface of the tray and material unsupported by the borders of the tray. This indicates that the tray was not seated down sufficiently on the residual ridge (insufficient pressure). -The correct thickness of material over the fitting surface of the tray, but material extending beyond the border of the tray so that it is unsupported by the tray, suggests that the tray is under extended in that area. 6. tray showing through the impression material over the fitting surface of the tray and the borders showing through the final impression material. This indicates that the tray has been seated on the residual ridge with too much pressure. The correct thickness of material over the fitting surface of the tray, but with the border showing through the final impression material, suggests that the tray is overextended in that area. 7. Voids or discrepancies that are too large to be corrected accurately 8. Incorrect consistency of the final impression material (granular impression with poor tissue details). 9. Movement of the tray while the final impression material was setting 10. Incorrect border molding procedures. (For example, unsupported impression material by the tray) 11- using either too much or too little impression material. 6- Sticking the impression material to the teeth. 12-Pulling the impression material away from any area of the tray. 8- Layered impression. 13- Trapping lip, cheek, tongue or floor of the mouth. 14- Tearing of important area of impression. Thank you