Posterior palatal seal (post damming)

1. Posterior palatal seal (post damming) Dr. Waseem Bahjat Mushtaha Specialized in prosthodontics

2. Posterior palatal seal (post damming) 1- The posterior palatal seal (post dam) of the upper denture should be placed on non-movable tissue of the soft palate just behind the hard palate. 2- The vibrating line of the soft palate , normally used as a guide to the ideal posterior border of the denture, is usually located slightly posterior to the foveae palatine. 3- The posterior palatal seal is formed through both humular (pterygomaxillary) notch and across the palate over the vibrating line. 4- The vibrating line is observed in patient's mouth as the patient says a series of short "ah" and the hamular notches are palpated.

3. Techniques of post-damming There are several established for the placement of the posterior palatal seal: 1- Conventional method 2- Scraping of master cast 3- Post damming during try-in stage

4. 1- Conventional method A strip of low fusing compound is traced on the impression over the vibrating line and through the hamular notches. The compound is heated with alcohol torch, tempered and seated in the mouth under pressure. The added material will spread out on both sides of the vibrating line and form a raised strip across the distal end of the impression. The final impression with the posterior border seal is carefully boxed and poured in stone.

5. 2- Scraping of master cast A –this technique is the least accurate and leaves the most to chance of tissue compressibility of the insertion of the denture. B – This technique is almost as unphysiologically correct as the technician's attempt to place the posterior palatal seal. So post damming must be done at the impression stage rather than by attempting the scrap the cast.

6. 3- Post damming during try-in stage The trial denture base is inserted so the indelible pencil line marked on vibrating line of the soft palate will be transferred from the soft palate to the trial denture base. And the excess base plate is reduced to this line. The trial denture base is placed on the cast and a knife or pencil is used to mark a line following the posterior limits of the base plate.

8. Dimensions of the post dam 1- The post dam extends from the humular notch on one side to the other humular notch of the other side. It should be wide enough to avoid cutting or irritating the soft tissues, but not so wide to compress too large an area and thus prevent the denture from sealing properly.

9. 2- The post dam is usually narrow in it's central part, wider as it extends laterally on each side, and narrow again as it approaches the hamular notch to fade out behind the tuberosity. It is sometimes called butterfly (Cupid's bow) post dam 3- The post dam should be about 3-4mm wide in its widest part. The depth or thickness of the post dam should vary in different individuals, according to compressibility and softness of the tissue. Its depth should also vary in different parts of the same mouth in exactly the same manner as its width. The average thickness is 1mm.

11. Function of post damming 1- during impression making: The rational for the placement of a post dam in the impression tray is: A – To establish contact posteriorly to prevent the final impression material from sliding down in to the pharynx. B – To serve a guide for positioning the impression tray, especially if a shim has been used within the tray to establish the borders.

12. 2- during jaw relationship: 1- Posterior palatal seal is incorporated into the trial denture base for added retention. 2- To determine if adequate retention and seal of the potential denture border is present.

13. 3-Post dam with finished denture: 1-it slightly displaced the soft tissue of the distal end of the denture to inhance the posterior border seal: A- Increase retention of the denture by atmospheric pressure. B –it prevents air and food from getting under the denture. 2- it makes the thickness of the base less conspicuous to the tongue and diminishes reflex irritation.

14. Boxing-in the impressions and making the casts Def: Boxing in an impression is the process of building up of vertical walls, usually in wax developing around the final impression for complete dentures to produce the desired size and form of the base of the cast, and to preserve certain landmarks of the impressions.

15. Technique 1- A strip of boxing wax is attached all the way around the outside of the impression approximately 1 to 2mm below the border and seated to it with a spatula. 2- The strip must be at its full width, particularly at the distal ends of the impression, to hold the vertical wall of the boxing away from the impressions and provide space for adequate thickness of the cast in these regions.

16. 3-the vertical walls of the boxing are made of sheets of beeswax. 4- The tongue space in the lower impression is with a sheet of beeswax or plasticine that is fitted and attached on the superior surface of the boxing wax. The beeswax tongue space filler is seated to the boxing wax. And located just below the lingual border.

17. 5- A thin sheet of wax is used for making the vertical walls of the boxing. This may be special boxing wax. Or half sheet of beeswax may be cut lengthwise and used as a boxing wax. It is attached around the outside of the boxing strip so as not to alter the borders of the impression. It should extend 9 to 15mm above the impression so the base of the cast at its narrowest point will be of this thickness. 6- The sheet of boxing wax should extend completely around the impression and be seated to the boxing wax strip to prevent the escape of stone when this is poured in to the impression. Sufficient space must be available posteriorly between the impression and boxing to provide for adequate thickness of casts distal to the impression.

18. 7- A stone is mixed carefully and vibrated, and then sufficient stone is poured in to the boxed impression that the base of the cast will be 9 to 15mm thick. The stone is allowed to harden for at least 30 minutes before impression. After the final impression is separated from the cast, the borders of the cast are trimmed to leave a ledge of about 3mm posteriorly and little anteriorly. The cast must be shaped to maintain the form of the borders of the impression and yet be easily accessible for adaptation of the materials used in making the record blockes.

23. Advantages of boxing –in 1- The correct width of the periphery of the impression is preserved. 2-the mixed stone can be vibrated, the cast will not contain air bubbles and a stronger cast will be produced. 3- The thickness of the cast may be more accurately judged. 4- boxing-in is time saving, because trimming may be not be required. 5- Material is economized.

24. Recording bases and occlusion rim Def: the recording base (trial denture base) is a temporary form that closely resembles the final base of the denture under construction. It is used for recording maxillo-mandibular jaw relationships and for setting the artificial teeth.

25. Function of recording base 1- Establishment of the rest and occlusal vertical dimensions. 2- Determination and recording of centric relation 3- The transfer of the accurate jaw relationships to an articulator 4- Enabling the setting of artificial teeth for the trial denture.

26. Requirements for recording base 1- Well adapted and accurately formed to the final cast. 2- Stable, both on the cast and in the mouth. 3- Rigid and strong. 4- Smooth and rounded to be comfortable to the patient. 5- Easily contoured and polished. 6- Fabricated from materials that are dimensionally stable. 7-the materials used should be easy to manipulate. 8- Base plate materials should be non-irritant to the mouth tissues.

27. Materials for recording bases I-Temporary recording bases: the materials that are most frequently used are: 1- Shellac base plate wax. 2- cold-curing acrylic resin. 3-vacuum formed vinyl or polystyrene. 4-base plate wax. 5-swaged tin base plate. N.b these materials are used during the various technical procedures, but discarded at the time the denture is processed in to its permanent form. II-permanent denture bases: Is one, which eventually becomes the base of the finished denture: 1- Processed (heat-cured) acrylic resin. 2-cold 3-chromium – cobalt alloys. 4-chromium – nickel alloys.

28. The material used should meet the following criteria as much as possible 1- Readily adapted to the required shape and contours with minimum of time, expense and technical skill. 2-rigid and strong in relatively thin sections. 3-not exhibit flow at mouth temperature. 4-not warp or distort appreciably during the procedures required for denture fabrication. 5-exhibit a color that will not distract from viewing the arrangement of the teeth of the trial denture, as they will appear in the complete denture.

29. I-Temporary recording bases 1- Shellac recording base material: 1- Shellac is commonly used material for recording base. 2-it is supplied in forms shaped to correspond to the general shapes of the maxillary and mandibular arches.

30. 3-if adapted accurately strengthened and handled carefully, it can be effectively utilized both for maxillary and mandibular recording base. If not adequately strengthened, shellac tends to warp when subjected to repeated changes in temperature. Wires should be used to increase strength rigidity and thus reduce distortion of shellac base. For the maxillary cast, the wire is placed across the posterior palatal seal area, while for the mandibular cast it is adapted within the lingual flange.

31. Fabrication of shellac recording base 1- The proper shellac form, corresponding to either the maxillary or the mandibular arch, is selected for the final cast. 2-all undercut must be blocked out prior to adapting the base.

32. 3-to prevent the base material from sticking to the cast, A- It is first dusted with talcum powder B-soaked in water for a short period of time until the surface of the cast is moist: immersion of the cast in water for a prolonged period of time many damage the surface of the cast. C-tin foil (0.001 inch) can be adapted to the cast. 4-soften the shellac until it appears shiny and applied with wet fingers to accurately adapted the shellac to the palatal portion of the maxillary cast or to the lingual surface of mandibular cast.

33. 5-the material is then reheated and adapted over the crest of the ridge and into the reflections. Care must be taken to avoid trapping air between the shellac form and cast surface. 6-while the material is still warm and soft; it is removed from the cast and trimmed with scissors, leaving approximately 5mm beyond the edge of the cast. 7-the shellac is repositioned and reheated, and then carefully readapted. The trimmed edges are heated, elevated from the cast, and folded onto themselves and burnished with wax spatula to form a smooth rounded border. 8-care must be taken not to overheat, the shellac overheating will cause the molten shellac to adhere to the surface of the cast on cooling attempt to remove the shellac base can result in a fracture of the cast surface.

34. Advantages of shellac recording base: 1- It can be easily and quickly adapted 2-inexpensive Disadvantages: Shellac being a brittle material, it is subjected to breakage.

35. 2- autopolymerizing resin recording base materials Fabrication of autopolymerizing resin recording base: three basic techniques are used to fabricate recording base utilizing chemically activated resins: A-no-flasking method: 1-a layer of tin foil (o.oo1 inch) or a thin layer of petrolatum is applied to the prepared final cast. 2-all undercuts are blocked out with wax or and the suitable plastic material.

36. 3-The autopolymerizing resin is mixed, when it reaches the doughy stage, it is rolled to the desired thickness 2 to 3mm. 4-a thin film of petrolatum must be applied to prevent the resin from adhering. A thin application of petrolatum to the fingers will prevent the resin from sticking to the hands. Keeping the fingers wet with water during handling will also prevent this difficulty. 5-the resin sheet is transferred to the cast, adapted to the hard plate area first or to the lingual surface of the mandibular cast and then onto the crest of the ridge and into the reflection area.

37. 6-a sharp instrument is used to trim the excess resin while it is in the soft, moldable state. 7-after polymerization has been completed; the resin base is removed and trimmed. Soaking the cast in water will help removable of the base if difficulty is encounted. 8-the borders are further adjusted with burs, and the external surface can be polished with wet pumic. The thickness on the facial slope of the ridge and extending over the crest of the ridge is reduced to approximately 1mm.

38. B- Alternating application of cold-curing powder (sprinkle-on technique). 1-well-adapted bases can be formed using this technique. 2-undercuts are blocked out and tin foil or petrolatum is applied to the cast.

39. 3-polymerization shrinkage is kept to a minimum. A thin layer of powder (polymer) is dusted over a small surface area of the cast and sufficiently wetted with liquid (monomer) to produce a slight flow. 4-alternative applications of powder and liquid are made until a thickness of 2 to 3mm has been developed 5-the complete base is then removed, trimmed and polished. The polymerization reaction takes approximately 20 to 30 minutes; the bases should not be removed during this period in order to prevent distortion.

40. C-flasking method 1-recording bases produced from this method are accurate and stable. Thy do, however, require considerable time for fabrication and therefore are most costly them bases formed using shellac or autopolymerizing resin.

41. 2-since breakage of the master cast is possible with this technique, it is advisable to duplicate the cast and to construct the recording base on the duplicated model. 3-An autopolymerizing resin is mixed in glass jar and then covered .when the resin reaches the doughy stage ,its placed into the model , the flask is closed, and the resin is allowed to polymerize for 20 to 30 minutes . The base is removed from the flask, trimmed, and polished. If there are a number of undercuts present that will, interfere with seating the base on the master cast, they must be relieved before seating is attempted

42. Advantage of resin recording base: 1-acrylic resin base plates are excellent for making maxillo-mandibular relation records. 2-They fit accurately and are not easily distorted 3-any type of occlusal rims can be mounted on it Disadvantages: 1- They may take up space needed for setting the teeth, necessitating some grinding of the resin base in required areas. 2-they may be loose because of the necessary block out of undercuts in the cast

43. 3-vacuum-formed bases 1-the vacuum method provides a fast and efficient means of forming rigid, accurate fitting recording base. Depending on the material used, temporary or permanent bases can be formed. Permanent bases formed using this method have not gained wide acceptaptance. 2-the cast is prepared by blocking out the existing undercuts with a suitable material (wax or any other material that melts during heating should no be used

44. 3-a sheet of base plate resin is inserted in the frame located below the electric heater coil, and the heater is activated. Heating is contained until the resin sheet begins to sag approximately 1\2 inch. At this time, the sagging sheet of softened resin is lowerd onto the cast by means of the supporting farm and vacuum is turned on. 4-the sheet of soften resin is drawn in to close adaptation to the cast. The heater is then turned off and the base allowed to cool for one minute. After removal from the cast the base is trimmed and finished.

45. Other recording base materials 1-base plate wax: This type of base plate is used in conjunction with wax rim so forming the all wax-recording blocks. Talcum powder is applied to the cast .an alternative the cast may be immersed in water for a short period of the time until moist. The wax is then softened and adapted. Excess wax is removed with a sharp instrument and the borders rounded and smooth.

46. Advantages: Base plate wax recording bases are inexpensive, easily formed and esthetic. Disadvantages: 1-base plate wax recording base softens readily at body temperature that leads to distortion during the maxillo-mandibular jaw relations recording 2-it does not withstand the pressure to witch it is subjected during jaw relationship recording.

47. 2-swaged tin base plate Three pieces of 5-gauge tin are swaged down on top of other, on to a model die made from the master cast and trimmed similar in out line to a cast or swaged metal base. The layers of tin may be cemented together with a thin film of hard wax and the complete until re-swaged for final adaptation to the cast.

48. Advantage: 1- it does not soften at mouth temperature 2-it has a reasonable accurate fit 3-it gives a uniform thickness for the palate of the finished denture. 4-it reproduces the rugae to some extend. Disadvantage: 1-time consuming 2-expensive

49. II-Permanent denture base A-processed resin (heat-curing acrylic resin): 1-fabrication of heat-processed resin recording bases result in the destruction of the final casts. The recording bases that are formed are permanent and become part of the final denture.

50. 2-undercuts are not blocked out. A wax form of the desired shape and dimensions is adapted onto the cast. The wax pattern is invested in applied, and a denture resin is mixed and packed into the model.The resin is processed according to the manufacture's instruction.The processed base is recovered and finished. Undercuts on the tissue side of processed base are blocked out with a plastic material, and dental plaster or stone is poured in to the base to provide mounting casts for the transfer of jaw records to the articulator. 3-the artificial teeth are set in wax, which is attached to the processed base, to provide the trial denture. When satisfactory, the trial denture is flasked, processed and finished. Either cold-cured resin or heat-cured resin may be used to attach the teeth to the processed base.