Impression Objectives1. Preservation-with the loss of the stimulation of the natural dentition the alveolar ridge will atrophy or resorb, the process can be hastened or retarded by local factors. Pressure in the impression technique is reflected as pressure in the denture base and results in soft tissue damage and bone resorption.2. Support-maximum coverage provides the “snow shoe” effect.3. Stability- close adaptation to the underlying mucosa is most important to reduce the horizontal movement of the denture.4. Esthetics-border thickness should be varied to restore facial contour and proper lip support.5. Retention-atmospheric pressure, adhesion, cohesion (depends on peripheral seal) mechanical locks, muscle control.
Impression Techniques The basic differences in techniques for final impressions can beresolved as those that record the soft tissues in a functionalposition and those that record the soft tissues in the undisplaced orrest position. Soft tissues that are displaced and recorded in this position willattempt to return to the undisplaced position when the forces arereleased. -The dentures will be unseated from their bases by this tissue action. -When tissues are held in a displaced position, the pressure limits the normal blood flow. When normal tissues are deprived of their blood supply, the result is resorption.
Posterior Palatal Seal Posterior palatine glands Maxillary tuberosityWe attempt to record the tissues at rest. Theonly exception is the posterior palatal seal area
Selective Pressure Technique The selective pressure technique is a combination of extension formaximum coverage within tissue tolerance with light pressure orintimate contact with the movable, loosely attached tissues in thevestibules. The impression is refined with minimum pressureutilizing a wash of light body impression material.
Final Impressions Appointment: After establishing the health of the denture bearing areas final impressions are made. Try in custom impression tray and adjust the length of the flanges 2-3 mm short of the vestibule depth. Establish the three dimensional contours of the denture borders by border molding the custom tray utilizing a thermoplastic “compound” material. Final impression with a light body material to achieve a “mucostatic” final impression.
Final Impressions Appointment: Instruct the patient to leave out their dentures for 24 hours prior to the final impression appointment.
Custom Impression TraysDesign Objectives Well adapted to tissues with only slight waxblockout of undercuts to allow for consistent andrepeatable seating and accurate impressions 2-3mm thickness Border extensions should be 2-3mm short of thedepth of the vestibule when the intraoral tissues areat rest Handle design should not impinge on the vestibulenor distort the lips Finger rests in the 1st molar and 2nd premolarregion so the fingers should not distort the vestibulewhen border molding and making the mandibularmaster impression Fabricated utilizing “tray acrylic” which has a Higher % filler material- more accurate, lessshrinkage
Final Impressions-Custom Trays Adjust Tray Extension 2-3 mm short of the depth of the vestibule
Final Maxillary ImpressionsAreas requiring special attention: Posterior palatal seal area Incisive papilla Buccal and labial vestibule
Final Maxillary ImpressionsSpecial considerations: Mobile, hypertrophic tissue Palatal torus
Final Maxillary ImpressionsSpecial considerations: Vibrating line Hamular notch Vibrating line Hamular notch The tray must extend 2-3mm beyond the vibrating line
Custom Tray Check the labial flange extension Check frenum clearance Check extension along the buccal vestibule
Maxillary tray sequence of border molding: The posterior palatal seal area is added last and the tray is tested for peripheral seal.
Border MoldingHeat the modelingcompound over a flame
Border MoldingSlowly soften the very end of the compound
Border Molding Dry the tray, then addthe compound to section A
Border Molding Temper the compound in the water bath. The temperature of thewater bath should be 110 degrees for ISO red compound. Thetemperature varies depending on the type of compound used.
Border Molding Insert the tray with compound being careful to retract the cheekwith a mouth mirror or your index finger. Area “A” is molded by instructing the patient to move themandible laterally and anteriorly, pucker and smile.
Trimming the compound: The compound must be thoroughly cooled before you begintrimming. Otherwise the compound will be easily distorted. Excess compound on the external surfaces is best removedwith the red handled knife with a fresh, sharp scalpel blade.
Trimming the compound: Carefully trim away the compound that has flowed into the inner surface of the tray. Failure to do so will result in an impression that displaces tissues inappropriately. Use a red handled knife orKingsley scraper (arrow) toremove the compound thatflowed into the inside of thetray.
Border Molding- Overextension: A•Area “A” is excessively thick. This is a common area ofoverextension. This area needs to be further remolded.•The compound is reheated with the alcohol torch, retempered inthe water bath and further refined intraorally.
Border Molding AArea “A” has been refined. Note that the denture extensionin this area is thinner and flatter. What structure limits thethickness and length of the denture border in this region? Coronoid Process
Border molding the labial flange-Area “C” The anterior areas are molded by the following: – Massage the upper lip with a lateral motion – Instruct the patient to pucker and smile – Check the flange thickness for proper lip support
Border MoldingDon’t pull down on the lip. This maneuver willforeshorten the denture flange.
Developing the Posterior Palatal Seal- Area “D” Place 2-3 mm of compound on top of the tray in a butterfly configuration to displace the tissues in the posterior palatal seal area.
Developing the Posterior Palatal Seal- Area “D” Seat the tray firmly. After the tray has been in position for 10 seconds ask the patient to swallow. Remove the tray and chill.
Trim compound in posterior palatal seal area This patient presents with a small maxillary torus and the compound has flowed onto the surfaces of the tray that cover it. Remove the compound so as to eliminate heavy contact in this region.
Testing Peripheral Seal Pull on the tray handle to test retention. If retention is lacking check the following: 1) Check buccal pouch, hamular notch and posterior palatal seal area 2) Check the length and thickness of the dentureextensions
Compare the extensions of the border molded tray withthose of the old denture.
Border Molding-Cut BackIf the retention is adequate you are ready to cutback the compound.
Border Molding-Cut Back With the edge of your knife blade scrape away a thin layer of compound from the border molded periphery. This will create space for your impression material and avoid undesirable tissue The areas of the periphery overlyingthe frenums should be relieved moreaggressively.
What is the purpose of the vent hole? Caution: Do not drill the palatal relief hole(s) in the maxillary tray until are borders have been molded and the peripheral seal demonstrated.1) To permit proper seating of the loaded master impression tray while making the final impression.2) To relieve the pressure over the incisive papilla and the rugae.3) To prevent entrapment of air bubbles in the impression.
Apply Tray Adhesive Apply a thin layer of tray adhesive and permit it to dry. Note that adhesive is applied 2-3 mm onto the external border of the tray.
Selection of Impression MaterialsWe recommend an elastic, free flowing, light body polysulfideimpression material for most maxillary impressions.Polyvinylsiloxane impression materials such as Virtual may also beused. The material should have hydrophilic properties andadequate viscocity to reduce the probability of gagging.
Key factors for a successful impression: Measure out equal lengths not equal amounts of polysulfide impression material. Keep the strips of material widely separated so they do not flow into contact and set prematurely. Tape your mixing pad close to the edge of the counter. A stable, immobile mixing pad will make it easier to mix the material. Use the tapered blade spatula as shown.
Key factors for a successful impression (cont’d) Begin mixing with the tip of your spatula. Attempt to confine the impression material to a small area of the pad.
Key factors for a successful impression (cont’d) Finish mixing the polysulfide material with the flat edge of the blade. This technique will minimize the number of air bubbles incorporated into the material. Apply a thin layer of impression material to the tray with a cement spatula.
Key factors for a successful impression (cont’d) The tray is coated as opposed to loaded with a thin layer ofimpression material. Close inspection reveals that there are no bubbles associated withthe impression material and that all surfaces are coated.
Key factors for a successful impression (cont’d) Retract the lips with your index finger or mouth mirror and seat thetray.*Be sure to drape the patient before making the final impression.Polysulfide material cannot be removed and permanently stains clothing.
Key factors for a successful impression (cont’d) We don’t need an impression of the uvula. Raise the lip and line the tray up to the frenum. Firmly seat thetray and allow the impression material to flow. Use the mouth mirrorto remove excess material that may be flowing down the pts. throat.
Key factors for a successful impression (cont’d) Seat the loaded impression tray in pts. mouth and go through the same soft tissue manipulation process as during border molding. massage face pucker lips smile move jaw side to side Instruct the patient to breathdeeply through their nose andtilt their head forward.
Key factors for a successful impression (cont’d) Hold the tray in position until the impression material is set.Light body polysulfide impression material requires 7-8 minutesto polymerize.
Completed Maxillary Impression Remove the impression. Examine it carefully. What factors make for a good impression?1) Smooth well defined peripheries2) Maximum extension3) Even pressure distribution (there should be no areas where the underlying tray or compound shows through)4) There should be intimate tissue contact
Trim and Disinfect the Impression Trim the excess unsupported impression material. Spray the impression with theappropriate disinfectant.
Completed Maxillary Impression Impression is now ready to be boxed. Remember, the impressionmust be poured within 1 hour to avoid distortion.
Final Impressions:Boxing & Pouring Inspect the impression for voids or bubbles Box impression and pour master cast
Window Tray Impression Technique This technique is used to record highly mobile or hypertrophic tissue with minimum displacement.Mobile tissues are most often seen anteriorly and may be particularlyprominent in patients with combination syndrome. It is inadvisable toremove these mobile tissues because the underlying bony ridge isusually knife edged. These tissues act as a cushion and rarely impingeupon the interocclusal space.
Window Tray Impression Technique(cont’d) 1) Outline the mobile tissue on your preliminary cast. 2) Construct the custom tray so that there is a window (open area) over the mobile tissue. 3) The handle should be place in the middle of the palate 4) Border mold and make the polysulfide impression in the usual manner
Window Tray Impression Technique(cont’d) Cut out the polysulfide impression material in the window with a sharp scalpel.
Window Tray Impression Technique(cont’d) The mobile tissue area will be recorded with a zinc oxide impression material (Krex). Seat the impression back into the patient’s mouth. Mix the Zinc Oxide (Krex) impression material and apply it over the mobile tissue with a small brush or syringe.
Window Tray Impression Technique(cont’d) Completed Impression Master cast: Note the detailed recording of the mobile tissues
Master Mandibular ImpressionAreas requiring special attention Retromolar pad Retromylohyoid space Buccal shelf Vestibules
Completed Mandibular Impression Tray Finger rests Note the finger rests and the size and position of the handle.
Fabrication of custom trays from the existing denture Select a container (cup) slightly larger than the denture. Mix sufficient alginate to fill half the cup. Wipe alginate onto the undersurface of the denture taking care not to trap bubbles. Seat the denture into the alginate and cover 2-3 mm of the extension with the material.
Fabrication of custom trays from the existing dentures Inspect the alginate impression. There should be no voids or bubbles and the denture extensions should be defined.
Fabrication of custom trays from existing dentures Apply a thin layer of tray resin polymer to the alginate impression. Wet the tray resin polymer with the tray resin monomer and build up the contour and thickness of the tray so that it is rigid. Finish the tray and smooth the borders as shown.
Mandibular Custom TrayTry in the tray-The extension should be 2-3 mm short of the frenum and the depth
Mandibular Custom Traya) Outline the retromolar pad with an indelible pencil stick.b) Check to ensure that the tray properly extends onto the pad and does not impinge upon the masseter groove.
Note the difference in the denture extensionsOur objective is to maximize the extensions of the new denture.
Mandibular Sequence of Border Molding Dry the tray. Slowly heat the compound and apply to area “A” on one side of the tray.
Border Molding Always temper the compound in the water bath for 5seconds before placing the heated compound in the mouth. Thewater bath should be set at 110 degrees when using low fusingcompound.
Border molding the buccal flange-Area “A” Insert the tray with compound being careful to retract the cheek with a mouth mirror or your index finger. Be careful to seat the tray evenly. Define the tray extension by molding the lateral border “A” by massaging the cheek and having the pt. pucker and smile.
Trimming the labial flange-Area “A” Remove tray from the mouth and chill the compound Trim the excess compound that has flowed onto the tissuesurface or the external surfaces. This is done with care using a red handled knife.
Completed Buccal FlangeSection “A” on one side is complete. This defines theproper tray extension for this area.
Border molding the posterior flange-Area “B” Add compound to area “B” (buccinator insertion, masseter groove region and area defining the posterior border associated with the retromolar pad). Temper, carefully rotate the tray into the mouth, and ask the patient to close while holding the tray in position, resisting the closure with your forefingers on the finger rests.
Border Molding –Completed Areas “A &C” Area “A” and area “B” have been completed and trimmed. Avoid displacing the tissues associated with the retromolar pad.
Border molding the labial flange-Area “C” Apply compound to area “C”. Temper, insert and gently massage the lower lip. Do not pull up the lip for it will foreshorten the labial vestibule.
Border molding the lingual flange-Area “D” Add compound to area “D”.
Border molding the lingual flange-Area “D” Temper, insert and mold area “D” byinstructing the patient to push their tongueagainst your thumb placed in the lowerincisor area. Proper extension into area “D” will createseal for the mandibular denture in selectedpatients with favorable tongue position andfloor of mouth posture.
Border molding the lingual flange-Area “E” Add compound to area “E”. Temper, insert and mold area “E” by instructing the patient to push theirtongue against your thumb placed in the lower incisor area and toswallow. It may take several applications to properly define the lengthand contour of the denture border in this area.
Border Molding Completed Border molding is completed. Inspect carefully to ensure that the extensions are well defined. The borders should be smooth and rounded.Note the varying thickness of thelingual flange. The thinnest borderextends into the retromylohyoidspace.
Border Molding- Cut Back Scrape back the border impression compound .5 mm in width and height to provide space for the impression material.
Apply Tray Adhesive After the compound is cut back apply a thin layer of polysulfidetray adhesive to the surface of the tray. Be sure to apply theadhesive 3-4 mm beyond the border.
Mandibular Impression Mix polysulfide as previously directed and apply a thin layer of impression material to the tray. Do not overload the tray.
Mandibular Impression Instruct the patient to lift their tongue. Insert and seat the tray andbegin border molding. Continue border molding until the materialbegins to polymerize. Do not let go of the tray. Hold the tray in position until the material has polymerized.
Mandibular Impression Following polymerization (7-8 minutes), retract thelip to break the seal and gently remove the tray.
Mandibular Impression Rinse, disinfect, and carefully inspect the impression.Remove flash with a sharp scissors.
What factors make for a good impression?1) Smooth well defined peripheries2) Maximum extension3) Even pressure distribution (there should be no areas where the underlying tray or compound shows through)4) There should be intimate tissue contact
Alternate Technique- Virtual PVS The heavy body and monophase materials are recommended. Paint the tray with a thin layerof adhesive.
Alternate Technique-Virtual PVS Border molding of the tray is accomplished with the heavy body material.
Alternate Technique- Virtual PVS A wash impression is then made with the monophase material. Gently massage the pts lipsand cheeks. After 1 min. have the pt. gentlypucker, smile and move their jawside-to-side, forward and back.
Alternate Technique- Virtual PVS Check the final impression for clinical acceptability. -flange extensions -soft tissue detail -posterior palatal seal -hamular notch
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