Posterior palatal seal /certified fixed orthodontic courses by Indian dental academy


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Posterior palatal seal /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. POSTERIOR PALATAL SEAL Introduction Complete dentures may suffer from a lack of proper border extension, but none are more important than the posterior limit and the posterior palatal seal on maxillary completedentures. The posterior border is terminated on a surface that continues and is movable in varying degrees and not at a turn of tissue as are the other denture borders.
  3. 3. The Glossary of Prosthodontic Terms defines posterior palatal seal as “ the soft tissue along the junction of the hard and soft palate on which pressure within physiologic limits of the tissues can be applied by a denture to aid in the retention of the denture.”
  4. 4. The proper placement of the posterior palatal seal begins with the initial oral examination. The morphologic contours of the hard and soft palates, hamular notch regions, and the integrity and displaceability of the mucosa and the underlying tissues should be evaluated and noted. Observation and palpation are essential elements in formulating the proper diagnosis and treatment plan. Hardy and Kapur stated that retention and stability that is achieved from adhesion, cohesion, and intersurface tension are able to resist only dislodging forces that act perpendicular to the denture base. Horizontal forces and lateral torquing forces of the maxillary denture can be resisted only by adequate border seal. Terminating the denture borders on soft resilient tissues will allow the mucosa to move with the denture base during function and thereby, maintain the denture seal.
  5. 5. Historical review • 1883: Ames and the Greene brothers introduced atmospheric pressure as a means of denture retention and recommended the use of functional denture borders as opposed to passive borders in the fabrication of complete dentures. • 1886: Wilson described adhesion as the primary determinant in denture retention • 1907: Green brothers " Modeling compound" • 1920: Hall revived interest in the use of atmospheric pressure as a retentive factor by interpreting and demonstrating the functional denture borders.
  6. 6. •1948: Stanitz used a lab model to suggest that atmospheric pressure is in equilibrium with fluid pressure exerted on molecules within a capillary tube with a liquid level in a container as well as the attraction of two glass slabs. These models explained how fluid film contributed to denture retention. •1951: Craddock described the gripping action of the buccinator muscle on the buccal flange of the mandibular denture and also coined the term "pear shaped pad". • 1962: Stamoulis believed that atmospheric pressure combined with intimate tissue contact and peripheral seal comprise the most critical retentive forces. • 1964: Fish discussed determinants of retention and differentiated between tissue, polished, and occlusal surfaces and how each permits the dentist to incorporate mechanical, biologic, and physical factors of the denture retention.
  7. 7. Functions performed by the posterior palatal seal The seal prevents the passage of air between the denture and the tissues. The seal depends on the proper extension if the denture borders, both in width and height so that they fill the mucobuccal space and contact the cheek tissues laterally. At the posterior aspect of the denture, in the area of the soft palate there are no cheek tissues to seal the denture border. Therefore, the proper placement of the posterior palatal seal commands a definite clinical procedural protocol if one is to create an optimally retentive complete maxillary prosthesis.
  8. 8. The function of the posterior palatal seal is also to maintain contact with the anterior portion of the soft palate during functional movements of the stomatognathic system. Therefore the primary purpose is retention of the maxillary denture. The reduction in gag reflex can also be achieved since there should be no separation of the denture base and soft palate during “normal” functional movements; reduction in food accumulation beneath the posterior aspect of the denture, owing to proper utilization of tissue compressibility, reduction in patient discomfort when contact occurs between the dorsum of the tongue and the posterior end of the denture base, as the posterior denture border will closely approximate the soft palatal tissues; and compensate for the volumetric shrinkage that occurs during the polymerization of methyl methacrylate resin. The correctly placed posterior palatal seal will not impinge upon the non displaceable tissues of the hard palate, nor will it limit the
  9. 9. muscular movements of the soft palate. It will however create a partial vacuum beneath the maxillary denture. This partial vacuum is activated only when horizontal or tipping forces are directed against the denture base. The duration of time that the partial vacuum acts on the tissues is extremely small, and consequently little or no irreversible alterations to the underlying mucosa will take place. Millsap and Ettinger summarized functions of the posterior palatal seal as • To make the sunken distal border less noticeable to the tongue • Aids in compensating for dimensional changes in curing • The proximity of the tissue contact prevents food from getting under the denture base • Firm contact with the tissue of the soft palate reduces the tendency to gag • The thickened area provides added strength across the denture and to provide retention
  10. 10. Anatomic and Physiologic Considerations The posterior palatal seal is divided into two separate but confluent areas based upon anatomic boundaries. The post palatal seal extends medially from one tuberosity to the other. Laterally, the pterygomaxillary seal extends through the pterygomaxillary notch continuing for 3 to 4 mm anterolaterally approximating the mucogingival junction.
  11. 11. The notch is covered by the pterygomandibular fold, which extends from the posterior aspects of the tuberosity posterior – inferiorly to insert into the retro molar pad. This fold of tissue can influence the posterior border seal if mouth in a wide-open position during the final impression procedure. Since this will affect the length and direction of the pterygomaxillary seal. The hamular processes are covered by a thin layer of mucous membrane. One has only to palate the processes in the course of outlining the posterior palatal seal area to realize the painful episode that the patient would experience if the hard denture base were to cover them. Therefore, the hamular processes should never be covered by the denture. There are two glandular openings within the tissues of the posterior portion of the hard palate, usually lying on either side of the midline. The fovea palatini, as they are known, are not constant findings in every individual; however, they are unique to humans.
  12. 12. The fovea are ductal openings into which the ducts of other palatal mucous glands drain. They serve no other function. According to Lye, the fovea palatini are located, on average, 1.31 mm anterior to the anterior vibrating line. Chen, however, found that a majority of the subjects in his investigation had fovea that was located either on or behind the anterior vibrating line. Therefore, the position of the fovea does not represent the junction of the hard and soft palates. The fovea palatini should be used only as guidelines to the placement of the posterior palatal seal. The dentist who observes the fovea and utilizes these anatomic landmarks as the posterior extent of the denture base can deprive his patients of from several millimeters up to a centimeter or more of tissue coverage. This, in turn will have direct effect upon the retentive potential of the denture base.
  13. 13. The median palatal raphe, which overlies the medial palatal suture, contains little or no sub-mucosa and will tolerate little compression. Placement of the posterior palatal seal across the midpalatal suture in the region of the posterior nasal spine demands careful attention. When a prominent midpalatal fissure is present on the hard palate, it often extends onto the soft palate. When this fissure is present, on the hard palate, it often extends onto the soft palate. When this fissure is present on the hard palate, it should be carefully reproduced in the master cast. The posterior seal should be extended into this fissure to ensure proper peripheral seal. The practitioner must visually discern the approximation of the torus to the posterior palatal seal area. If the torus extends to the bony limit of the palate, leaving little or no room to place the posterior border seal, then its removal is indicated. This evaluation should be made at the initial diagnostic session.
  14. 14. The presence of thick, ropy saliva may create a problem for maxillary complete denture retention. Thick saliva can create hydrostatic pressure in the area anterior to the posterior palatal seal, resulting in a downward dislodging force exerted upon the denture base. In an effort to alleviate this potential problem, a fine line or Cupid’s bow can be scribed on the master cast, anterior to the cluster of palatal mucous glands. Watt and Macgregor feel that this extension of the posterior palatal seal line will contain the thick mucus in the posterior part of the denture to provide a seal even if the posterior portion of the denture base is slightly out of contact with palatal tissues.
  15. 15.
  16. 16. Anterior and posterior vibrating lines The posterior palatal seal area lies between the anterior and posterior vibrating lines. In order to correctly locate these lines, careful observation and palpation of the tissue is necessary, as their locations vary with the contour of the soft palate. The anterior vibrating line is an imaginary line located at the junction of the attached tissues overlying the hard palate and the moveable tissues of the immediately adjacent soft palate. This should not be confused with the anatomic junction of the hard and soft palate
  17. 17. One way to locate the anterior vibrating line is to have the patient perform the Valsalva maneuver, which requires that both nostrils be held firmly while the patient blows gently through the nose. This will position the soft palate inferiorly at its junction with the hard palate. The anterior vibrating line can also be approximated by visualizing the area while instructing the patient to say “ah” with short vigorous bursts. Due to the projection of the posterior nasal spine, the anterior vibrating line is not a straight line between both hamular processes. The anterior vibrating line is always on soft palatal tissues. As the soft palate extends further posteriorly, the actions of the palatal muscles become more exaggerated. The posterior vibrating line is an imaginary line at the junction of the aponeurosis of the tensor veli palatini muscle and the muscular portion of the soft palate. It represents the demarcation between that part of the soft palate that has limited or shallow movement
  18. 18. during function and the remainder of the soft palate that is markedly displaced during functional movements. The posterior vibrating line is visualized by instructing the patient to say “ah” in short bursts in a normal, unexaggerated fashion. The posterior vibrating line marks the most distal extension of the denture base.
  19. 19. Classification of Soft Palate There are three classes of soft palate. They are based upon the angle that the soft palate makes within the hard palate. The more acute the angle of the soft palate in relation to the hard palate, the more muscle activity that will be necessary to establish velopharyngeal closure (closing off of the nasopharynx). Consequently, the more the soft palate is markedly displaced in function, the less that can be covered by the denture base. The more resorbed the edentulous ridges, the more difficult is the determination of the soft palatal configuration.
  20. 20. Therefore, careful visualization during functional movements of the soft palate is necessary .
  21. 21. Class I: indicates a soft palate that is rather horizontal as it extends posteriorly, with minimal muscular activity. When this classification is visualized, by going through the procedures, a considerable number of millimeters separate the anterior and posterior vibrating lines. This will allow for a wide posterior palatal seal, but one that is not very deep. Class I palates are considered the most favourable configuration, since more tissue surface can be covered, yielding a potentially more retentive denture base. Class III: indicates the most acute contour in relation to the hard palate, necessitating marked elevation of the musculature to create velopharyngeal closure. It is usually seen in conjunction with a high V – shaped palatal vault. As there is a greater elevation of the soft palatal musculature in function, fewer millimeters separate the anterior and posterior vibrating lines. This results in a smaller area for the posterior palatal seal than for a class I configuration. In addition to being smaller, it is usually deeper than with the class I palate.
  22. 22. Class II: designates those palatal contours that lie somewhere between class I and class III House’s Classification of the palatal form •Class I: 5-13mm distal (more than 5mm of movable tissue available) Ideal for retention •Class II: 3-5mm distal (1-5mm of movable tissue available) Good retention Class III: 3-5mm anterior (less than 1mm of movable tissue available) Poor retention •Class III difficulties are in tissue movement, typically present in high vaulted patients, and because of the small area for the posterior palatal seal.
  23. 23. Designs of the posterior palatal seal The six most common Posterior palatal seal configuration described by Winland and Young are 1. A bead posterior palatal seal 2. A double bead posterior palatal seal 3. A butterfly posterior palatal seal 4. A butterfly posterior palatal seal with a bead on the posterior limit 5. A butterfly posterior palatal seal with the hamular notch area cut to half the depth of a #9 bur 6. A posterior palatal seal constructed in reference to House’s classification of palatal forms.
  24. 24. Placement of the Posterior palatal seal The purpose of the posterior palatal seal is to ensure that the saliva film is as thin as possible at the posterior edge of the maxillary denture so that retention is maximal. Post dam should be a zone at distal edge where soft tissues are compressed. The ideal site is a matter of debate. All agree that line of compressed tissue should pass thru hamular notches but authorities vary as to the site of intermediate part and can achieve good retention when placing the post dam at either of the two defined sites.
  25. 25. Some advise that it be placed over the hard palate at a point where the underlying bone has sufficient soft tissue over it to allow compression without ulceration of mucosa. Others advise that the line of the post dam should be sited at the vibrating line which marks the junction between mobile and immobile areas of functioning soft palate. Only recently has it been shown by an ultrasound investigation that the two sites rarely coincide and that the vibrating line is approximately 3 mm distal to bony margin of hard palate in the midline. The investigation also confirmed that a certain amount of latitude exists in the determination of the most effective post dam site.
  26. 26. Recording of posterior Palatal seal Prior to the corrective wash impression procedure, the posterior denture border must be fully extended, which means that all of the soft palate that is to be covered by the denture has been captured in the border molded custom tray. In fact tissue that is 1 to 2 mm distal to the expected denture border should also be present in the impression tray to protect against any over-trimming of the processed denture base. The practitioner should at this time, if he has not yet done so during the initial examination determine the classification of the soft palate.
  27. 27. The laboratory technician cannot visualize the movements of the soft palate in the laboratory. Only the dentist can create the proper posterior palatal seal. If compound is used to capture the seal area, usually two applications are necessary to ensure adequate tissue contact, since the heaviest areas of compound will slump and the thickest areas will contract upon cooling. The rationale for the placement of a seal in the impression tray is as follows: To establish positive contact posteriorly to prevent the final impression materials from sliding down the pharynx. To serve as a guide for positioning the impression tray, especially if a shim has been used within the tray to establish the borders. To create slight displacement of the soft palate. To determine if adequate retention and seal of the potential denture border is present.
  28. 28. Conventional method After an accurate and fully extended final impression has been made, boxed, and poured, well – adapted resin or shellac tray is fabricated on the stone cast. The patient is seated in an upright position. It has been suggested that, prior to marking the posterior palatal seal area, the patient should be instructed to rinse with an astringent mouthwash to remove stringy saliva that might prevent clear transfer markings.
  29. 29. The posterior palatal area is then dried with gauze; a “T” burnisher or a mouth mirror is used to palate for the hamular processes. Once located, they should be marked with an indelible pencil or noted visually to ensure that they are not covered by the denture. The instrument (“T” burnisher or mouth mirror) is then placed along the posterior angle of the tuberosity until it drops into the pterygomaxillary notch. Locating the notch with an instrument is necessary, as there are times when small depressions in the residual alveolar ridge may resemble the pterygomaxillary notch. The tissue covering the alveolar ridge is unyielding, and the peripheral seal on many dentures has been lost because of improper location of the notch. A line is placed with an indelible pencil (or Dr. Thomson’s Sanitary Color Transfer Applicators) through the notch and extended 3 to 4 mm anterolateral to the tuberosity, approximating the
  30. 30. mucogingival junction. The same procedure is then performed on the opposite side. This will complete the outlining of the pterygomaxillary seal. The patient is asked to say “ah” in short bursts in an unexaggerated fashion. While observing the movement of the soft palate (noting the area between shallow displacement or quivering and marked muscular activity), the posterior vibrating line is marked with an indelible pencil. By connecting the line through the pterygomaxillary seal with the line just drawn demarcating the “post palatal” seal (posterior vibrating line), the posterior denture extension is delineated. The patient is instructed to keep the mouth open to prevent smudging of the markings. The resin or shellac tray is then inserted into the mouth and seated firmly to place. Upon removal from the mouth, the indelible lines should have been transferred to the tray.
  31. 31. The tray is then returned to the master cast to complete the transfer of the posterior border. The resin tray is trimmed with a carbide bur, while a shellac tray may be trimmed with a hot knife to approximate the posterior denture border. The palatal tissues anterior to the posterior border are palpated with the “T” burnisher or mouth mirror to determine their compressibility in width and depth. The termination of the glandular tissues usually coincides with the anterior vibrating line. The use of the Valsalva maneuver or visualizing the area while the patient says “ah” with short vigorous bursts may also be used. This line is marked with an indelible pencil and transferred to the master cast in a manner similar to that used with the posterior vibrating line. The visual outline is in the shape of Cupid’s bow.
  32. 32. The area between the anterior and posterior vibrating lines is usually narrowest in the midpalatal region because of the projection of the posterior nasal spine. It should be noted that in the region of the pterygomaxillary seal, the anterior and posterior vibrating lines are confluent. A Kingsley scraper is then used to score the cast. The deepest areas of the seal are located on either side of the midline, on third the distance anteriorly from the posterior vibrating line. It is usually scraped to a depth of approximately 1 to 1.5mm high and 1.5mm broad at its base. A greater width creates an area of tissue placement that will have a tendency to push the denture downward gradually and to defeat the purpose of the posterior palatal seal. In other words the seal should not be too wide.
  33. 33. Placement of tissues should be such that when the dentures move in function the placed tissue will move with the dentures and not break the seal. The tissue covering the median palatal raphe has little submucosa and cannot withstand the same compressive force as the tissues lateral to it. This area is scraped to a depth of approximately 0.5 to 1.0mm. Within the outline of Cupid’s bow, the cast is scraped to a depth of about one half the amount to which the palatal tissues in that area can be compressed, being tapered progressively shallower anteriorly until it feathers out in the area of the anterior vibrating line. In other words, as the seal approaches the anterior vibrating line there is just a slight scraping of the cast. Just posterior to the deepest portion of the seal, it is also tapered to the posterior vibrating line. Failure to taper the seal posteriorly may lead to tissue irritation.
  34. 34.
  35. 35. If a shellac tray is used, it can now be replaced on the remoistened master cast, reheated, and readapted to conform to the scored palatal seal area. After it is cool, it is tried in the mouth to evaluate the retentive qualities of the trail base, which will be a good indication of the retention to be expected in the completed prosthesis. A mouth mirror can then be placed into the mouth so that the posterior border can be observed. The patient is again instructed to say “ah” in a short, unexaggerated manner. If no space is noted between the trial base and the soft palate when this procedure is performed, then an adequate posterior seal has been created. If the soft palatal tissues separate from the trial base, further scraping of the cast is indicated. This usually increases the depth of that area located one-third the distance anterior to the posterior vibrating line.
  36. 36. The shellac tray is then reheated and readapted, and then reinserted into the mouth. The position of the base in relation to the soft palate during function is once again observed. This procedure is repeated until no separation of the base and tissue is noted. If a resin tray has been used, small amounts of auto polymerizing resin can be added to the tray after the master cast has been scraped and a proper separating medium applied.
  37. 37. Advantages of placing the seal in the trail base: The trail base will be more retentive; this can produce more accurate maxillomandibular records. Patients will be able to experience the retentive qualities of the trial base, giving them the psychologic security of knowing that retention will not be a problem in the completed prosthesis. The practitioner will be able to determine the retentive qualities of the finished denture, leaving nothing to chance at the insertion appointment. The new denture wearer will be able to realize the posterior extent of the denture, which may ease the adjustment period. Disadvantages of the conventional method  It is not a physiologic technique and therefore depends upon accurate transfer of the vibrating lines and careful scraping of the cast. The potential for over compression of the tissues is great.
  38. 38. Fluid wax technique All of the procedures regarding the location and transfer marking of the anterior and posterior vibrating lines delineated under the conventional approach are performed for the fluid wax technique. However, the indelible transfer markings are recorded on the final wash impression. Zinc oxide and eugenol or plaster are preferred over the elastic impression materials as they set rigid.
  39. 39. Impressions made with elastic materials are slightly resilient, and when reseated in the mouth under pressure may distort the relationship between wax added to the posterior border and the rest of the denture bearing surface. Furthermore, wax will not readily adhere to elastic materials. Either the material in the seal area must be removed prior to the wax application or laboratory varnish must be applied to the elastic material in the seal area before the wax is placed. Any one of four types of wax can be used for this technique Iowa wax, white, developed by Dr. Earl S. Smith; Korecta wax No. 4, orange, developed by Dr. O. C. Applegate H–L physiologic paste, yellow–white, developed by Dr. C. S. Harkins; Adaptol, green, developed by Nathan G Kaye. These waxes are designed to flow at mouth temperature
  40. 40. The melted wax is painted onto the impression surface within the outline of the seal area. The wax is applied slightly in excess of the stimulated depth and allowed to cool to below mouth temperature to increase its consistency and make it more resistant to flow. The impression is carried to the mouth and held in place under gentle pressure for four to six minutes to allow time for the material to flow. The position of the head and tongue during the fluid wax procedure is of particular importance. Nelson feels that if an effective posterior seal is to be established without inducing tissue irritation, the soft palate should be impressioned in its most functionally depressed position. The maximum depression (downward and forward position) of the soft palate will be recorded when the Frankfort plane (portion – orbitale) is 30° below the horizontal and the tongue is firmly positioned against the mandibular anterior teeth.
  41. 41. A properly positioned maxillary tray handle can serve as a substitute for missing incisors. At no time should the patient protrude the tongue beyond the approximated position of the incisal edges, as this will foreshorten the posterior border of the final impression. The head and tongue position translate the mandible anteriorly. The soft palate will then be passively brought downward and forward due to the indirect attachment of the soft palatal tissues to the body of the mandible and the insertion of the palatoglossus muscle into the side of the tongue. Flexion of the head also contributes to moving excess impression material and saliva out of the mouth, rather than progressing down the pharynx. While maintaining the 30° flexion of the head and the anterior tongue position, the patient is asked to periodically rotate the head so that all functional positions of the soft palate are recorded.
  42. 42. After four to six minutes, the impression tray is removed from the mouth and the wax examined for uniform contact throughout the posterior palatal seal area.
  43. 43. If the tissue has been contacted, the wax will have a glossy appearance. Where the wax appears dull, more wax should be applied and the procedure repeated. If, on the other hand, excess wax protrudes from the end of the tray, it should be removed with a hot scalpel. While the impression is out of the mouth, the patient should be cautioned against rinsing with cold water, as this will cause contraction of the tissues and act to reduce the flow properties of the wax upon insertion. The secondary impression is reinserted and held for three to five minutes under gentle pressure, followed by two to three minutes of firm pressure applied to the midpalatal area of the impression tray. During the period that the wax material is in the mouth, the head and tongue positions must be maintained to prevent over placement of the palatal seal area.
  44. 44. Upon removal of the tray from the mouth it is carefully examined to see if the wax terminates in a featheredge near the anterior vibrating line. If a butt joint is present instead of the featheredge, then the proper flow has not taken place and the impression tray should be reinserted. If wax extends beyond the outline of the posterior palatal seal area, it should be carefully trimmed with a sharp scalpel. The advantages of this technique are as follows: It is a physiologic technique displacing tissues within their physiologically acceptable limits. Over compression of tissues is avoided. Posterior palatal seal is incorporated into the trial denture base for added retention. Mechanical scraping of the cast is avoided.
  45. 45. The disadvantages of this technique are as follows:  More time is necessary during the impression appointment. Difficulty in handling the materials, and added care during the boxing procedure. There is some controversy regarding the appropriate sequencing for the placement of the posterior palatal seal. Some believe that the posterior seal should not be placed until after the try – in of the trail base has been completed and the final maxillomandibular records made. Their reasoning includes the possible mechanical displacement of the trial base by the tissues, which would result in an inferior placement of the posterior segment of the denture base. The proponents of this theory argue that unless the base is seated under pressure for at least five minutes each time that it is inserted into the mouth, errors in record making, such as maturities in the second molar region, will result.
  46. 46. Arbitrary Scraping of Master Cast This technique is the least accurate and leaves the most to chance at the insertion appointment. It relies upon the dentist’s recollection of the palatal configuration and tissue compressibility in order to “guesstimate” the anterior and posterior vibrating lines and the depth to which the cast should be scraped. This technique is almost as unphysiologically correct as the technicians attempt to place the posterior palatal seal at the dentist’s request.
  47. 47. Significance of posterior palatal seal After packing a flask the acrylic dough is heated during polymerization and arising from the polymerization, volumetric shrinkage of resin takes place. Shrinkage is not uniform but takes place where exotherm of reaction raises the temperature and initiates more rapid reaction, namely thicker parts of the base over the crest of alveolus. Contraction of dough takes place towards the sites of initial polymerization and because the shape of space containing the dough provides a physical constraint, a space is created between polymerizing dough and the palate. In the midline the gap of 0.5 mm wide is seen, tapering as it passes laterally. On this basis it has been suggested to compensate for the shrinkage and re establish contact between denture and the palate,
  48. 48. Failures in recording the Posterior Palatal Seal Under extension The most common cause for failure of the seal in the posterior palatal area is the under-extended distal denture border. Commonly, this is a result of the practitioner’s use of the fovea palatini as the landmark for terminating the denture base. By so doing, he may be depriving the patient of as much as 4 to 12 mm of tissue coverage, which can significantly improve the retentive qualities of the denture.
  49. 49. There are patients who inform the dentist on the very first visit for complete denture therapy that they are gaggers. These individuals make the practitioner very aware that they cannot tolerate any material far back against their palates. Under this type of pressure, the practitioner who is unsure of his technique, or lacks the understanding of a properly extended posterior palatal seal, may comply with the patient’s wishes. Obviously, the retentive qualities of the denture are compromised. There are many methods that can be employed to overcome this voluntary reflex. One such method is to ask the patient to concentrate upon a point on the wall while taking even and equal breaths through the nose. This is especially helpful during the impressioning procedures. For individuals who require more conditioning, it may be necessary to construct a highly polished auto polymerized resin tray on the master cast that is extended to the posterior vibrating line.
  50. 50. The patient is instructed to wear this appliance in the comfort of his or her home. When the patient can demonstrate that he or she can successfully maintain this base in the mouth, the fabrication of the denture can be completed. Clinically, another obvious but common reason for under extended maxillary dentures is the failure of the dentist to carefully examine the hard and soft palates, making note of the palatal configuration. Without careful visualization, palpation, and marking of the vibrating lines, it is easy to misinterpret the proper posterior border extension. Under extended posterior borders frequently result when the laboratory technician is asked to trim and polish the processed denture borders. He will trim the posterior border to the scribe line that he arbitrarily placed initially, which could be several millimeters short of the proper posterior extension.
  51. 51. Under post damming Whether one employs the conventional approach or the fluid wax technique to establish posterior palatal seal, it is possible for there to be insufficient placement of the tissues at some points along the terminal border of the denture. It may be the result of recording the tissues when the mouth was wide open during the final impression. When the mouth is in the wide-open position, the pterygomandibular fold becomes taut. When the patient assumes any position other than a wide-open position, a space will be present between the denture base and the tissue, since the fold is no longer activated. The diagnosis of this condition consists of placing the wet denture base into the mouth and slowly pressing in the midpalate region until it is firmly seated, all the while observing the distal denture border. If air bubbles can be seen escaping from beneath the distal border, then at that point the denture base is underpostdammed.
  52. 52. The correction can easily be made by further scraping the cast and readapting the trial base if the conventional approach is used, or by adding more wax and reminding the patient to refrain from opening the mouth so wide if the fluid wax technique is employed.
  53. 53. Over post damming It is not uncommon that the master cast was scraped too aggressively and the posterior palatal seal displaces too much tissue. If significant overpostdamming has taken place, especially in the pterygomaxillary seal area, then upon insertion of the denture the posterior border will be displaced inferiorly. If it is moderately overpostdammed, then at the first or second post insertion appointment, tissue irritation will be discernible across the posterior palatal region. Selective reduction of the denture border with a carbide bur, followed by lightly pumicing the area while maintaining its convexity will remedy the problem.
  54. 54. Over extension In the practitioner’s attempt to maximize the retentive qualities of the denture, he may inadvertently violate the physiology of the soft palatal musculature and place the posterior denture border too far distally. Usually, it is not the entire border that is overextended, but rather small areas. When this occurs, the active portion of the soft palate drapes against the hard, unyielding denture base. The most frequent complaint from the patient will be that swallowing is painful and difficult. Small-ulcerated areas in the region of the soft palate will be evident. By marking the lesion with an indelible pencil and transferring it to the denture base, the precise position of the overextension can be removed with a bur and then carefully repolished. If the hamuli are covered by the denture base, the patient will experience sharp pain, especially during function. The pterygoid hamuli must never be covered by the denture base.
  55. 55. Adding a Posterior Palatal Seal to an Existing Denture There are times when a completed denture is deficient in the posterior palatal seal area. The deficiency may be either in depth or in length of the denture base, or in both. However, prior to taking any corrective measures, the dentist should evaluate the entire prosthesis. If the correct aesthetic and phonetic requirements have been fulfilled, the proper vertical dimension and centric relation positions established, and the remaining denture borders correctly extended, then one should undertake the correction of the posterior seal area.
  56. 56. There are many techniques to improve the posterior palatal seal in an existing denture Moghadam and Scandrett suggest a procedure that utilizes the fluid wax technique. All of the steps outlined for locating, marking, and placing the wax in the seal area are followed, except that this time the wax is placed on the processed denture base. After the wax has had an adequate chance to flow, the denture is removed from the mouth. An indelible pencil is used to outline the anterior extent of the seal on the denture. Utility wax is placed vertically across the plate, separating the posterior two thirds from the anterior region, and extended around the posterior portion of the denture. Stone is vibrated into the denture wax surface outlined by the utility wax. After the stone has set, the wax is eliminated and the denture cleaned. The denture base is ground distal to the anterior vibrating line that has been delineated by the indelible pencil.
  57. 57. Care should be exercised not to perforate the polished side of the denture. Lubricant is then applied to the unground areas, including the polished surface, and a separating medium is applied to the stone cast. The denture is then replaced on the stone cast and held firmly with rubber bands. Auto polymerizing acrylic powder is sprinkled between the denture base and the cast while held on a vibrator. Monomer is then added dropwise. This is continued until the void has been completely filled. The cast and denture are placed in an upright position until the initial set has taken place. They are then placed in a pressure pot with water (140°F) for 20 minutes under 30-psi pressure. After the cast and denture are separated, the excess acrylic is trimmed and the border polished lightly. If there is any question concerning the presence of free monomer that might irritate the tissues, the denture should be stored in water for 24 to 36 hours.
  58. 58. A similar technique using softened green stick modeling compound has been suggested by Carroll and Shaffer. Lauciello and Conte incorporate both green stick modeling compound and fluid wax. Since auto-polymerizing acrylic sets with an exothermic reaction and residual free monomer can irritate the oral mucosa, extreme caution should be exercised if an addition to the denture base is to be performed intraorally. Light cured resin can be utilized for the intraoral correction of the posterior palatal seal. This material allows for accurate placement of the seal by adding material selectively, similar to the fluid wax technique, curing it in stages. The curing procedure requires the use of a high intensity white light.
  59. 59. Review of literature 1. Carl O Boucher (1951) did a critical analysis of impression technique for full denture. The vibrating line is the imaginary line which marks the beginning of the motion in the palate. It also plans the end of the denture in a position for post damming. An acceptable practice in final impression is a small groove 1mm deep and 1mm wide carved on thecast about 2mm in front of the vibrating line.
  60. 60. 2 Millsap C . (1964) Reviewed the anatomy and the physiology to accurately determine the posterior limit for the palatal seal. The purpose was to allow movement against the yielding tissue and maintain a posterior border seal as the denture moves with torque producing forces.Other purposes include: compensates for dimensional changes, prevents food from getting beneath the denture, reduces gagging, adds strength, and less noticeable to the tongue. 3 Boucher (1964) reported that arbitary scraping of the cast for Incorporating the posterior palatal seal carved a single hand design on the master cast . A Vshaped groove 1.0 –1.5mm deep and 1.5mm wide at its base was carved 2mm anterior to the vibrating line.
  61. 61.          4      Laney W. and Gonzalez J. (1969) examined the need for palatal relief in maxillary denture and examined the fabrication of the posterior palatal seal The relief of the palate and the posterior palatal seal should be evaluated by the dentist and should not be left up to the laboratory technician. According to the authors, most maxillary dentures do not  require relief. The posterior palatal seal must be properly placed and designed to enhance border seal and increase stability. This phase of denture fabrication is extremely important to the success of the denture and the health of the patient. Li limited elasticity over the anterior part of the hard palate and in the area of the anterior palatine foramen may contribute to the denture producing paresthesia, pain, or a burning sensation. If palatal relief is desired, It should be kept to a minimum.       A technique of scribing the master cast by transferring the posterior border the denture is described. The use of tin foil to provide relief is described.
  62. 62. 5 Blahoua Z. and Neuman M. (1971) presented a model of mechanisms involved in denture retention. None of the physical factors for retention can be totally explained. H However, they all commonly and intricately participate at the moment of dislodgment. Retention is enhanced by the elasticity of the mucous membranes of the basal seat area and by a good border seal which keeps space between denture and mucosa as small as possible.      1. 6 Silverman and Sidney I (1971) documented the hypothesis that retention and stability of a complete maxillary denture will be increased by extending the posterior denture border beyond the vibrating line. 1. 7 Winland, RD and Young JM (1973) reviewed the various types of posterior palatal seals and their construction
  63. 63. 8 Avant W.E (1973) did a study to determine if a posterior palatal seal is necessary for complete denture retention and if altering the type and location of that seal affects retention.
  64. 64. Thank you For more details please visit