Stability /certified fixed orthodontic courses by Indian dental academy


Published on

The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit ,or call

  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Stability /certified fixed orthodontic courses by Indian dental academy

  2. 2. CONTENTS Introduction. Factors involved in complete denture stability. Dynamic impression technique. Muscles influencing the denture space. Neutral zone. Lingualised occlusion. Review of literature. Conclusion.
  3. 3. INTRODUCTION Optimum outcome of prosthetic treatment depends on the successful integration of the prosthesis with the patients oral function and the psychological acceptance of the prosthesis by the patients. The recognition, understanding and incorporation of certain mechanical, biological and physical factors are necessary to ensure optimum prosthetic treatment. These factors are the determinants that promote the properties of retention, stability and support in the finished prosthesis through their influence on the relationship between the fitting/ tissue surface of the prosthesis and the tooth/ tissue surface of the basal seat.
  4. 4. Biological factors Physical factors Mechanical factors RETENTION STABILITY SUPPORT Psychological comfort Physiologic comfort Longevity PROSTHETIC SUCESS
  5. 5. STABILTY The quality of a prosthesis to be firm, steady, or constant, to resist displacement horizontal or rotational stresses. by functional (GPT 7) It differs from retention in that stability resists forces in the horizontal planes where as retention is the resistance to the vertical dislodging forces. The lack of stability often makes ineffective the factors involved in retention and support.
  6. 6. A denture that shift easily in response to laterally applied forces can cause a disruption in the border seal or prevent the denture base from correctly relating to the supporting tissues. The factors that contribute to stability include ridge height and conformation, base adaptation, residual ridge relationships, occlusal harmony and neuromuscular control.
  7. 7. Factors involved in complete denture stability 1.The relationship of the denture base to the underlying tissues 2.The relationship of the external surface and border to the surrounding orofacial musculature. 3.The relationship surfaces. of the opposing occlusal
  8. 8. The relationship of the denture base to the underlying tissues Residual ridge anatomy The development of stability is limited by the anatomic variations of the patient that determine the residual ridge height and conformation. Large, square, broad ridge offer resistance to lateral forces than do small, narrow, tapered ridges.Small rounded irregularities of the residual ridge also contribute favorably to stability.
  10. 10. Shape of the hard palate Flat- Resist vertical displacement but is easily displaced by lateral forces Rounded and u shaped- best resistance to vertical and lateral forces V shaped- poor retention and stability
  11. 11. Quality of soft tissue covering the ridge Adequate extension of the denture border as limited by movable tissue allows the establishment of border seal and coverage of maximum supporting area and also provide maximum contact of the denture base with the facial and lingual ridge slopes. The nature of the overlying soft tissues determines the potential of a given area in tolerating stress. Maxillary palatine inclines- resist forces of denture base
  12. 12. Maxillary facial and mandibular lingual incline- less effective due to the thin alveolar mucosal covering Optimum denture stability requires that those tissues that provide resistance to horizontal forces be properly recorded and related to denture base. The ridge should provide a firm soft tissue base with adequate sub-mucosa to offer good stability. Flabby tissue with excessive sub-mucosa offer poor stability.
  13. 13. DYNAMIC IMPRESSION TECHNIQUE In extreme resorption of the mandibular residual ridge, the shape of the osseous structures offers little possibility of retention and stability of complete dentures. Muscle attachments are located near the crest of the residual ridge and, consequently, the dislocating effect of the muscles on the denture is great. For these reasons, the range of muscle action, as well as spaces into which the denture can be extended without dislocation, must be accurately recorded in the impression.
  14. 14. The advantages of dynamic impressions are: (I) Avoidance of the dislocating effect of the muscles on improperly formed denture borders, (2) Complete utilization of the possibilities of active and passive tissue fixation of the denture
  15. 15. Impression trays The impression tray has three functions 1) The tray must not interfere with active muscle movements (2) The tray must permit a proper thickness of impression material, and (3) The tray should stabilize the mandible in a correct position in relation to the maxillae.
  17. 17. Impression material Alginate It is mixed with 50 per cent extra water to get the desired viscosity. After spatulation sufficient amount of material is placed directly into the mouth to cover all tissues to be included in the impression. The tray is pressed through the irreversible hydrocolloid in the mouth by digital force. The patient is asked to close his mouth slowly until the mandibular rests have obtained firm contact with the maxillae and simultaneously keeps the tip of his tongue in contact with the tongue rest on the tray
  18. 18. The patient is advised to swallow, forcefully protrude the lips and vigorously contract the buccinator muscles in between swallowing. An old lower denture can be used as an individual tray for a dynamic impression when opposing natural or artificial teeth are present. The denture is first processed on the basis of a conventional impression and then a correcting dynamic impression is made in the denture base to reshape and complete the final design and the denture is relined.
  19. 19. Master cast from a conventional impression and by dynamic impression of the same patient.
  20. 20. Dentures fabricated by dynamic impressions
  21. 21. Anatomic prognosis for a mandibular complete denture, stability criteria Factors Best prognosis Worst prognosis Buccal shelf supporting area Flat and broad Sloping, narrow Tongue position Normal Retracted Tissue tonicity Cheek and lip tissue full and resilient Cheek and lip tissue tense and taut Denture-bearing tissue Firm, connective tissue support Movable tissue or thin, inelastic mucosa
  22. 22. Anatomic prognosis for a maxillary complete denture stability criteria Factors Best prognosis Worst prognosis Ridge form Broad, U-shaped or flat Deep, V-shaped vault Vestibular extensions Resilient, displaceable mucosa with depth Taut, tense, shallow vestibule Denture-bearing Firm, definite tissues cushion of submucosa Thin, inelastic mucosa
  23. 23. The relationship of the external surface and border to the surrounding orofacial musculature. Various structures of the oral cavity change considerably when a patient becomes edentulous. The lips and cheeks are no longer supported by the teeth and bone, and therefore show a tendency to "fall" into the oral cavity. At the same time, the tongue will expand into the space formerly occupied by the teeth. In this way, characteristic spaces develop in the oral cavity of the edentulous patient forming the so called DENTURE SPACE.
  24. 24.
  25. 25. The musculature of the denture space is divided into two groups: (1) those muscles which primarily dislocate the denture during activity (2) those muscles that fix the denture by muscular pressure on its secondary supporting surfaces
  26. 26. DISLOCATING MUSCLES FIXING MUSCLES VESTIBULAR  Masseter Buccinator  Mentalis Orbicularis oris  Depressor labii inferioris LINGUAL  Internal pterygoid  Palatoglossus  Mylohyoid Muscles of tongue
  27. 27. VESTIBULAR DISLOCATING MUSCLES MASSETER MUSCLE The posterior extension of the inferior buccal part of the denture space is determined by the action of the masseter muscle. If an impression is made of this region while the masseter muscle is relaxed, a denture constructed from such an impression will tend to be displaced when this muscle contracts as the tissues covering the masseter muscle are displaced anteriorly.
  28. 28. Straight - Moderate activity Concave - Active Convex - Inactive
  29. 29. MENTALIS MUSCLE This muscle originates from the frontal surface of the mandible between alveolar bone of the lateral incisor and the canine eminence. The origin of the mentalis muscle is located closer to the crest of the residual ridge. The bottom of the sulcus is lifted when the mentalis muscle contracts; and thereby, the depth and space of the oral vestibule can be decreased considerably.
  30. 30. DEPRESSOR LABII INFERIORIS This muscle originates from the lower canine region and runs laterally to the origin of the mentalis muscle and extends anteriorly and laterally toward the oral angle. It originates from very near the crest of the residual ridge and extends down and beneath the alveololabial sulcus. Therefore, during contraction this muscle contributes to the reduction of the denture space by raising the bottom of the sulcus.
  31. 31. LINGUAL DISLOCATING MUSCLES INTERNAL PTERYGOID MUSCLE The internal Pterygoid muscle originates in the pterygoid fossa, and the fiber bundles take a nearly parallel course posteriorly, inferiorly, and laterally. Internal pterygoid muscle determines the extension of a denture in the lower posterior lingual part of the denture space.
  32. 32. PALATOGLOSSUS MUSCLE The posterior lingual part of the denture space is further influenced by the palatoglossus muscle. The muscle descends from the soft palate in the arch to enter into the lateral margin of the tongue. The mucosa covering the lower part of the muscle is lifted superiorly, anteriorly, and medially.
  33. 33. MYLOHYOID MUSCLE The mylohyoid muscles form the floor of the oral cavity. The bilateral muscle originates from the mylohyoid line. The anterior fibers of the mylohyoid muscle run horizontally, whereas, the more posterior fibers are placed in a vertical direction. when both the mylohyoid muscles contract, the floor of the oral cavity is lifted and the tongue is pressed against the palate, decisively changing the denture space.
  34. 34. PTERYGOMANDIBULAR RAPHE The tendinous Pterygomandibular raphe extends inferiorly from pterygoid hamulus into the retromolar region. When the mouth is opened widely, Pterygomandibular raphe is stretched causing it to stand like a string between the pterygoid hamulus and the retromolar pad. A denture that is overextended onto this structure may be dislodged during an energetic opening of the mandible
  35. 35. GENIOGLOSSUS MUSCLE Powerful muscle that arises from genial spine and inserted into the tongue. When the apex of the tongue is lifted, the tendinous origin of the genioglossus muscle as well as the lingual frenum will be stretched and lifted causing a dislocating effect on the lower denture.
  36. 36. VESTIBULAR FIXING MUSCLES BUCCINATOR Horse shaped origin.It originates from the molar region at the base of the alveolar process in maxilla,mandible and pterygomandibular raphe. Fibers extend horizontally towards the modiolus, located laterally to the angle of the mandible and the upper and lower lip. The cheeks are pressed against the dental arches when the buccinator muscle is contracted. During chewing and swallowing, the muscle coordinates with the muscles of mastication.The buccinator muscle assists in positioning food between the teeth and returning food that has escaped into the Vestibular sulcus to the occlusal table.
  37. 37.
  38. 38. Modiolus is formed by the intersection of several muscles of the cheek and lips. These include orbicularis oris, buccinator, caninus, triangularis and zygomaticus muscle. Because none of these muscle contain fibers that have more than one bony attachment, they depend on the fixation of the modiolus to allow contraction. The denture base must be contoured to permit the modiolus to function freely. In the premolar region the mandibular denture should exhibit both a shortened and narrowed flange to permit the action that draws the vestibule superiorly and the modiolus medially against the denture.
  39. 39. ORBICULARIS ORIS MUSCLE Anterior sphincter of the oral cavity. The muscle is active when the lips are pressed against the teeth and the alveolar processes. As with the buccinator muscle, the orbicularis oris muscle is rhythmically active during chewing and swallowing.
  40. 40. LINGUAL FIXING MUSCLES Tongue They consist of the extrinsic and intrinsic groups of muscles. The extrinsic muscles have their origin external to the tongue, but their course terminates within it. Their contraction causes the tongue to move in relation to other oral structures. The intrinsic muscles lie completely within the tongue, and their activities sustain or alter tongue form.
  41. 41. Wright classification on tongue position Class I Class II Class III
  42. 42. To determine whether the patient has proper tongue position Ask the patient to open just wide enough to accept food. Only the dorsal surface of the tongue and the occlusal surfaces of teeth should be seen. In this position, the tongue is in intimate contact with the lingual surface of denture and the floor of mouth is at a normal level. At this position mandibular denture will be stable. If the occlusal surface of teeth, lingual surface of the denture, and the anterior floor of the mouth is seen, the tongue is in a retracted position. The denture will be unstable, have no retention and will be easily be dislodged.
  43. 43. ACTIVE MUSCULAR FIXATION When forces of the tongue are directed against a lower denture, the denture will be easily dislocated if the forces are not counteracted by equal forces exerted by the musculature of the cheeks and lower lip. Their antagonistic activity can be used to stabilize dentures. Similar action of antagonistic muscle groups between the functioning genioglossus and orbicularis oris muscles will fix a lower denture by opposing forces on its anterior section
  44. 44. PASSIVE MUSCULAR FIXATION It is possible to fix a lower denture even if all the muscles of the cheeks, lower lip, and tongue are quite passive. The denture is fixed by the mass and weight of these structures and through the pressure exerted by muscle tonus. Two factors that help in this are 1. The inclination of the polished surfaces. 2. The position of the polished surfaces of the denture between the cheeks and the lower lip on the one side and the tongue on the other side.
  45. 45. INCLINATION OF POLISHED SURFACES The basic geometric design of denture base should be triangular with the apexes corresponding to the occlusal surface. The maxillary buccal flange should incline laterally and superiorly. The buccal flanges of the lower denture must slope inferiorly and laterally, and the borders must be extended out beneath a fold of the buccinator muscle in the molar region.
  46. 46. The lingual flanges must also definitely extend inferiorly and medially below the anterior and lateral parts of the tongue, and as far posteriorly as permitted by the range of action of the tongue and the internal pterygoid muscle. Such inclination will provide a favorable vertical component to any horizontally directed forces.
  47. 47. Narrow artificial teeth permit the polished surfaces to be automatically formed with favorable inclined planes that can be wedged below the tongue, lower lip, and cheeks. In this way, these structures are brought to rest on the polished surfaces, and their weight will force the denture to remain on its foundation.
  48. 48. POSITION OF POLISHED SURFACES When a denture is held in place by the cheeks and lips, the tongue should be displaced with a pressure equal to the one with which the cheeks and lips are displaced. The denture must be placed in the denture space so that there is an equilibrium between the inward pressure exerted by the lips and the cheeks and the outward pressure exerted by the tongue. The denture space has been given different names because of this possible equilibrium. Some of these are: the dead space, the stable zone, the neutral zone, and the zone of minimal conflict.
  49. 49. The neutral zone is that area in the mouth where, during function, the forces of the tongue pressing outward are neutralized by the forces of the cheeks and lips pressing inward. The of theory neutralization of forces that stabilize dentures was made by Dr. Russell Tench
  50. 50. CLINICAL PROCEDURES IN LOCATING THE NEUTRAL ZONE Manipulation of the compound A water bath, preheated to the proper temperature, is used to soften the material, which is then kneaded and worked until it is uniformly soft.
  51. 51. Adapting compound on to the tray
  52. 52. LOCATING THE NEUTRAL ZONE FOR THE LOWER ARCH To locate the neutral zone for the lower arch the patient's lips are lubricated with petrolatum jelly. The tray with the softened modeling compound is rotated into the mouth and carefully seated. The patient is instructed to swallow and then purse the lips as in sucking.
  53. 53. Molded compound rim
  54. 54. ESTABLISHING THE OCCLUSAL PLANE To locate the occlusal plane, place the rim back into the mouth and use a sharp pointed pencil to mark the commissures of the lip and the height of the lower lip at rest. These three points are connected by a line that is continued on each side to a point one half to two-thirds the height of the retromolar pad
  55. 55. TESTING THE STABILITY OF THE LOWER OCCLUSION RIM The lower occlusion rim is placed back into the patient's mouth and checked for stability by having the patient open wide, wet the lips with the tongue, count from one to ten, and say exaggerated "ohs," "ahs," and "ees." If these movements raise the rim, the lack of stability must be caused by an improper molding of the compound.
  56. 56. LOCATING THE NEUTRAL ZONE FOR THE UPPER ARCH The modeling compound is attached to the upper tray. It is flamed, tempered and molded into the shape of an rim.
  57. 57. The upper rim is placed back into mouth and usually excess compound will seen extending below the relaxed upper. A line is scribed about 2 mm below the upper lip at rest and the compound is trimmed to this line.
  58. 58. REGISTERING VERTICAL DIMENSION BY SWALLOWING The lower occlusal rim is lubricated and inserted into the mouth. The upper rim after being softened by flaming and tempering, is inserted into the mouth and the mandible is guided into centric relation.
  59. 59. REGISTERING CENTRIC RELATION Two or four V shaped notches, approximately 3mm deep and 5mm wide are cut into the upper rim in the bicuspid and molar area. The lower rim from the first bicuspid back is reduced approximately 1mm.
  60. 60. The notched upper rim is now lubricated with petroleum jelly and placed in the mouth. The pyramid on the lower rim should fit into the notches on the upper rim without any movement.
  61. 61. FABRICATION OF A TONGUE, LIP, AND CHEEK MATRICES The compound rim thus formed indicate within a given range where teeth should be placed so that the denture will not be displaced during functional movement. To make sure that the teeth have been set with in the neutral zone, matrices are made of plaster.
  62. 62. The cast must be indexed so that the matrices will fit back into the proper position. Several circular holes are made on the labial and buccal surfaces of the cast and a cross is made in the tongue area of the lower model.
  63. 63.
  64. 64. Occlusal rims removed, and matrices repositioned to indicate the neutral zone.
  65. 65. Matrices used to check the position of teeth
  66. 66. RELATIONSHIP OF OPPOSING OCCLUSAL SURFACES Regardless of the type of posterior tooth form or occlusal scheme used, the dentures must be free of interferences within the functional range of movement of the patient. Such contacts cause uneven stresses to be transmitted to the dentures during function.This results in lateral and torquing forces that adversely affect stability. Bilateral, simultaneous, posterior tooth contact in centric relation is essential.
  67. 67. Occlusal forms of teeth are classified as follows Anatomic- 300 cusp Semi anatomic- 200 cusp Non anatomic- 00 cusp
  68. 68. Cusp form Advantage Anatomic occlusion Penetrate food more easily. Resist rotation of denture bases through cusp interdigitation. Provide better esthetics. Act as a guide for proper jaw closure. Non anatomic occlusion Does not lock the mandible in one position. Less time consuming procedure. Minimises horizontal stress . Easier to arrange in cross bite
  69. 69. Cusp form Disadvantage Anatomic occlusion Precise jaw closure and base stability required for interdigitation. Increased horizontal forces. Non anatomic occlusion Poor esthetics. Decreased masticatory efficiency. More difficult to get balanced occlusion.
  70. 70. Complete denture occlusion can be classified into three types. Balanced occlusion. Monoplane occlusion. Lingualized occlusion.
  71. 71. LINGUALIZED OCCLUSION In 1927 Dr. Alfred Gysi of switzerland introduced the concept of lingualized occlusion. In 1941 payne reported the use of 300 cusp teeth modified by selective occlusal reshaping and articulated against mandibular teeth with reduced facial and lingual cusps and widened central fossa.
  72. 72. This scheme of occlusion maintain the esthetic and food penetration advantages of the anatomic form while maintaining the mechanical freedom of the non anatomic form. The lingualized concept utilizes anatomic teeth for maxillary denture and modified non anatomic or semi anatomic teeth for the mandibular denture.
  73. 73. Balanced occlusion Monoplane occlusion
  74. 74. Lingualised occlusion
  75. 75. The lingual cusp of maxillary posterior teeth in a lingualized occlusion operates on a bolus in a holding and grinding fashion similar to the action of a mortar and pestle.
  76. 76. PRINCIPALS OF LINGUALIZED OCCLUSION 1. Anatomic posterior teeth are used for maxillary denture. Tooth form with prominent lingual form are used. 2. For a balanced occlusal scheme mandibular teeth with shallow inclines are used and for a non- balanced occlusion a monoplane mandibular denture tooth is selected. A narrow occlusal table is preferred when severe resorption has occurred.
  77. 77. 3. Selective grinding smoothens the central fossa of the mandibular teeth, lower marginal ridge and forms slight buccal and lingual inclines. This creates a slight concavity in the occlusal surface.
  78. 78. 4. Maxillary mandibular lingual teeth in cusps should contact centric occlusion. The mandibular buccal cusp should not contact the upper teeth in centric occlusion. 5. Balancing and working contacts should occur only on the maxillary lingual cusp. The posterior teeth are arranged and adjusted to establish bilateral balanced occlusion in lateral mandibular excursion for a range of 2 to 3 mm around centric relation.
  79. 79. 6. The teeth are set in a cross bite set-up if mandibular posterior ridge is wider than the maxillary ridge. In this case maxillary buccal cusp are arranged in the mandibular fossae. The maxillary lingual cusp are set, off the occlusal plane and are shortened to avoid interference with the tongue during speech.
  80. 80. Advantage of lingualized occlusion Most of the advantage attributed to both the anatomic and non anatomic forms are retained. Cusp forms are natural in appearance compared to non anatomic tooth form. Good penetration of the food bolus is possible. Bilateral balanced occlusion. Vertical forces are centralized on the mandibular teeth.
  81. 81. KELLY’S COMBINATION SYNDROME Complication seen in patients wearing a maxillary complete denture opposing a mandibular distal extension prosthesis. Combination progresses in a sequential manner. The group of complications are interlinked to one another. The progress of the disease can occur in any one of the following sequences. syndrome
  82. 82.
  83. 83. Lineal occlusal concept in complete denture In this concept a straight line of knife edge contact on artificial teeth in one arch occluding with flat non anatomic teeth in the opposing arch suggested as a means of reducing unfavorable occlusal forces and simplifying occlusal adjustment in complete denture. This has the potential of creating the smallest lateral component of force against the denture bases.
  84. 84. Since the area of contact is minimal, the frictional resistance is reduced. In the dental arch with the line of occlusal contact, there is no change in the location of contact during lateral movement. Therefore the direction of force in the dental arch remains fairly constant. The lineal ridge of occlusal contacts may be located in either dental arch. The decision depends on factors of denture stability and esthetics.
  85. 85.
  86. 86. Since the mandibular dentures are almost always less stable than maxillary dentures, the line of occlusal contacts is usually placed on the lower denture. With the ridge of occlusal contacts located in the mandibular arch, occlusal forces in any jaw position will be applied to the mandibular dentures at the same point. Tooth positioning for lineal occlusion The anterior teeth are arranged with no vertical overlap to prevent interference in lateral and protrusive mandibular movements. The occlusal plane should be kept as high posteriorly as practical to aid in developing protrusive balancing contacts with a flat plane of occlusion.
  87. 87. The lower posterior teeth are set first and centered over the crest of the ridge. The buccal line of contact should be set in a straight line anterior posteriorly. A clearance greater than 1.0mm between the non-contacting cusp decreases the crushing efficiency of the teeth. The maxillary posterior teeth are arranged against the mandibular posterior teeth so that the line of contact of the teeth is centered bucco-lingually.
  88. 88. INFLUENCE OF INCLINED PLANE The inclined plane deflects forces and thus produces instability. when the direction of force is at a right angle to the support, there is no inclined plane action to destroy stability.To accomplish this, the dentist should consider the following points Direction of Closing Force Since the effect of the inclined plane is dependent on the direction of force as related to the supporting surface, direction of the mandible's closing force is important. Closing force should be directed at right angle to surfaces that would otherwise act as inclined planes.
  89. 89. The closing force from eccentric relations to centric relation tend to unstabilize artificial dentures, not only because of nonvertical muscle pull, but also because of the inclined plane influence exerted by tooth cusps if they are present and the inclined articular surfaces of one or both glenoid fossae. So instruct the patient to avoid protrusive and lateral chewing and to confine the action more or less to up and downward movements.
  90. 90. Articular surface of glenoid fossa The backward facing articular surface of the glenoid fossa presents an inclined plane along which the mandibular condyle glide posteriorly under the upward muscle pull on the mandible.
  91. 91. The inclined articular surface of the glenoid fossa produces a thrust that is to be avoided. Such a backward shift of the mandible under biting force can be avoided if both the condyle lie against their stops at the time biting force is exerted. The patient should be advised to chew in centric relation.
  92. 92. Angle of opposing area of support When the vertical closing force is directed at right angle to the area that support denture, no horizontal force results.
  93. 93. Tooth position and occlusal plane Anterior and posterior teeth should be arranged as close as possible to the position once occupied by the natural teeth, with only slight modifications made to improve leverages and esthetics. The superiorinferior position of the occlusal plane is also a factor to be recognized.
  94. 94. A mandibular occlusal plane that is too high can result in reduced stability. Lateral tilting forces directed against the teeth are magnified as the plane is raised. An elevated occlusal plane prevents the tongue from reaching over the food table into the buccal vestibule. This compromises stability and makes control of the food bolus and denture more difficult.
  96. 96. An electromyographic analysis of the function of the buccinator muscle as an aid to denture retention and stability JPD 9:44, 1959 Donald Q lundquist Electromyographic analysis of the buccinator during function was analyzed. The muscles on the working side of unilateral chewers contract more vigorously than those on the balancing side and exert pressure on the buccal flange. Action of the muscle was not felt on the balancing side. The results shows that buccinator muscle is effective bilaterally as an aid in denture retention and stabilization only if the patient is a bilateral chewer
  97. 97. Complete denture stability related to tooth position. 9 JPD 11:1032, 1961 Aruther R Freehette The most outstanding observation from the recordings from both maxillary dentures was that denture stability and force distribution were more favorable during bilateral chewing than during unilateral chewing on either side. It was found that pressure at the ridge crest of the working side increased 3080% during unilateral chewing. There was an accompanying decrease in the number of positive pressure stroke on the balancing side during unilateral chewing on either side. This emphasizes again the importance of bilateral chewing as a means of augmenting the stability of complete denture.
  98. 98. Stabilizing lower denture on unfavorable ridge.10 JPD 12: 420, 1962 Thomas E J, Shanahan Patients with advanced resorption of mandibular ridge need denture made from dynamic impression because they provide more comfort and stability than denture made from a static impression. Dynamic impression are made by physiologically extending the denture base into prescribed areas of extension for retention and then making an impression of the denture supporting tissues while the various function of the mouth are performed.
  99. 99. However, before a dynamic impression is made, a receding tongue must be trained by means of certain exercises to occupy a favorable position irritated tissue must be treated. Finally the occlusion is physiologically conformed to the horizontal and vertical movement of the mandible to free the residual ridge from harmful lateral stress.
  100. 100. A comparison of lingualized occlusion and monoplane occlusion in complete dentures. J Prosthet Dent. 1983 Aug;50(2):176-9. Clough HE, Knodle JM, Leeper SH, Pudwill ML, Taylor . Two sets of dentures, one with lingualized occlusion and the other with monoplane occlusion, were made for each of 30 edentulous patients. Sixty-seven percent of those people preferred the lingualized occlusal scheme because of improved masticatory ability, comfort, and esthetics
  101. 101. Complete mandibular denture stability when posterior teeth are placed over a basal tissue incline. 11 Oral Rehabil. 1992 Sep;19(5):441-8. Lott etal Six patients with previous denture experience were provided with new dentures. Metal indicators were placed on either side of the mandibular denture and a cobalt-chromium alloy marker was inserted in the left bucco-posterior area of the mandible in each case. In the new dentures posterior teeth were positioned up to the retro-molar pad, over the basal tissue slope of the posterior mandibular alveolar ridge. After habituation had taken place, a cineradiographic recording was made of chewing.
  102. 102. Prior to the second recording the mandibular teeth were removed to a point where the remaining teeth were not over inclined residual alveolar ridges. Denture movement was observed by measuring the distances between the markers on an analytical projector. The results show a significant difference between the cranial values of the two chewing experiences. Values for all denture movements were less after removal of the teeth over an incline. These results support the clinical observation that teeth placed over a basal tissue incline have a destabilizing effect during complete mandibular denture function.
  103. 103. Influence of the buccolingual position of artificial posterior teeth on the pressure distribution on the supporting tissue under a complete denture. 12 J Oral Rehabil. 1996 Jul;23(7):456-63 Roberts etal The buccolingual position of artificial teeth is one of the important factors affecting denture stability, chewing efficiency, and pressure distribution on the supporting tissue under a denture. This study compared the pressure values on the supporting tissue under a denture during chewing in denture wearers, each of whom tried three different setting positions of artificial posterior teeth..
  104. 104. The pressure on supporting tissue was greater on the working side that on the non-working side during chewing. The difference in mean pressure was found among the buccolingual positions of artificial posterior teeth. When the posterior teeth were set on the crest, the total pressure was the smallest. This strongly suggests that the setting position of artificial teeth should be considered not only for denture stability but also for the avoidance of high pressure on the supporting structures.
  105. 105. A simplified approach to optimizing denture stability with lingualized occlusion.13 Compend Contin Educ Dent. 2000 Jul;21(7):555-8, 560, 562 Occlusal Edward LF etal prematurities are destructive and destabilizing influences in complete dentures. Unless denture bases are adequately and evenly stabilized, it is virtually impossible to properly equilibrate the occlusion. One reason is that all artificial teeth in a denture unit are physically bound into a single denture base and literally act as a single tooth.
  106. 106. Therefore, a single point of occlusal prematurity disrupts the entire denture occlusion and negatively affects the denture base stability and retention, preventing proper equilibration. This article describes a step-by-step approach using an intraoral central bearing point tracing device and lingualized occlusion to achieve an effective and simplified equilibration.
  107. 107. Finite element analysis of the effect of the bucco-lingual position of artificial posterior teeth under occlusal force on the denture supporting bone of the edentulous patient.14 J Oral Rehabil. 2003 Jun;30(6):646-52. Kelsy etal To improve the quality of the complete denture prosthesis, the bucco-lingual position of the artificial posterior teeth must be determined with consideration of the shape of the maxillary and mandibular residual ridge and the relationship between them.
  108. 108. The arrangement of posterior artificial teeth should be considered not only for the denture stability but also for the avoidance of high pressure on the supporting structures. A two-dimensional finite element method program to investigate the statics for the contour of the complete denture and the residual ridge was developed. With this program, the effect of the bucco-lingual position of the artificial posterior teeth under occlusal force on the denture supporting bone could be investigated.
  109. 109. Effect of denture adhesive on stability of complete dentures and the masticatory function.15 J Med Dent Sci. 2003 Dec;50(4):239-47. Johnson etal Did a study to examine the effects of denture adhesive on the retention and stability of complete dentures and the masticatory function. a The stability of complete dentures was estimated from 3-dimensional (3-D) denture movement and rotational denture movement and additionally the masticatory function from cycle time and chewing time. Denture movement was recorded using a 3-D motion capture system while chewing 3 kinds of food (peanuts, fish paste, rice).
  110. 110. Both the new and old dentures showed that using a denture adhesive contributes to reducing 3-D denture movement, rotational denture movement and chewing time during chewing the various foods.. The results of this study suggest that denture adhesive contributes to reducing denture movement and so improves chewing function.
  111. 111. Maximizing mandibular prosthesis stability utilizing linear occlusion, occlusal plane selection, and centric recording.16 J Prosthodont. 2004 Mar;13(1):55-61 Becker etal. The stability of mandibular complete dentures may be improved by reducing the transverse forces on the denture base through noninterceptive occlusion, selecting an occlusal plane that reduces horizontal vectors of force at occlusal contact, and utilizing a central bearing intraoral gothic arch tracing to record jaw relations.
  112. 112. CONCLUSION Both complete denture stability and retention are essential in providing successful prosthetic treatment. The factors that contribute to these properties are highly interrelated, and the constant interrelation between stability and retention often makes them indistinguishable. Care must be taken in the development of the denture surfaces to ensure optimum denture stability of the final prosthesis.
  113. 113. 1. The neutral zone in complete and partial dentures – Victor E. Seresin, FRANK J SCHIESSER 2. Complete denture prosthesis – HALPERIN 3. Complete denture prosthesis – NAGIL, SEARS 4. Text book of Prosthodontics – DEEPAK NALLASWAMY 5. Dental clinics of north America – V 40 N 1 January 1996 6. Lingualized occlusion for removable prosthodontics JPD 30: 601-8, 1977 7. Dynamic impression methods JPD 20: 1023-34, 1965 8. An electromyographic analysis of the function of the buccinator muscle as an aid to denture retention and stability JPD 9:44, 1959
  114. 114. 9. Complete denture stability related to tooth position. JPD 11:1032, 1961 10. Stabilizing lower denture on unfavorable ridge. JPD 12: 420, 1962 11. Complete mandibular denture stability when posterior teeth are placed over a basal tissue incline. Oral Rehabil. 1992 Sep;19(5):441-8. 12. Influence of the buccolingual position of artificial posterior teeth on the pressure distribution on the supporting tissue under a complete denture. J Oral Rehabil. 1996 Jul;23(7):456-63 13. A simplified approach to optimizing denture stability with lingualized occlusion. Compend Contin Educ Dent. 2000 Jul;21(7):555-8, 560, 562
  115. 115. 14. Finite element analysis of the effect of the buccolingual position of artificial posterior teeth under occlusal force on the denture supporting bone of the edentulous patient. J Oral Rehabil. 2003 Jun;30(6):64652. Kelsy etal 15. Effect of denture adhesive on stability of complete dentures and the masticatory function. J Med Dent Sci. 2003 Dec;50(4):239-47. Johnson etal 16. Maximizing mandibular prosthesis stability utilizing linear occlusion, occlusal plane selection, and centric recording. J Prosthodont. 2004 Mar;13(1):55-61 Becker etal.
  116. 116. 17. A contemporary review of the factors involved in complete denture. Part II stability. JPD 49: 165-72, 1983 18. Dynamic nature of the lower denture space. JPD 15: 401-18, 1965
  117. 117.