Distal extension removable partial dentures /certified fixed orthodontic courses by Indian dental academy


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Distal extension removable partial dentures /certified fixed orthodontic courses by Indian dental academy

  1. 1. DISTAL EXTENSION REMOVABLE PARTIAL DENTURE PROSTHESIS. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. CONTENTS: Introduction Movements of a distal extension Rpd Nature of load acting in distal extension partial denture Treatment of distal extension partial denture Altered cast impression procedure Review of literature Summary and Conclusion References www.indiandentalacademy.com
  3. 3. INTRODUCTION A removable partial denture prosthesis as its name implies is a prosthodontic restoration that supplies teeth and its associated structures to a partial edentulous arch and can be removed and inserted by the patient. Removable partial dentures can be classified according to the support they derive from the remaining dentition and associated soft tissues. www.indiandentalacademy.com
  4. 4. Many RPD’s derive all their support from the remaining natural teeth and are referred to as toothborne RPD’s. RPD’s that derive their support from both the teeth and associated residual ridge tissues are termed as tooth-tissue borne RPD’s or distal extension RPD’ www.indiandentalacademy.com
  5. 5. Movements of a Distal Extension RPD Rotation of the prosthesis around a fulcrum line passing through the two principal occlusal rests of the direct retainer or through the points where the minor connectors adjacent to the edentulous area break contact with the tooth surface. Rotation of the prosthesis around the longitudinal axis formed along the crest of the residual ridge. Rotation of the prosthesis around an imaginary perpendicular axis located along the center of the dental www.indiandentalacademy.com arch.
  6. 6. FORCES AROUND THE FULCRUM LINE www.indiandentalacademy.com
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  8. 8. FORCES AROUND THE LONGITUDINAL AXIS www.indiandentalacademy.com
  9. 9. FORCES AROUND THE PERPENDICULAR AXIS www.indiandentalacademy.com
  11. 11. THE BILATERAL DISTAL EXTENSION PARTIAL DENTURES The bilateral distal extension partial denture is the most common design of partial denture and occurs more often in the mandible than the maxilla. Before considering the design of such a denture it is necessary to understand what happens to it during function and in particular under the vertical, lateral and anterior-posterior loads to which it is subjected. www.indiandentalacademy.com
  12. 12. VERTICAL LOAD The vertical load that may be exerted on a partial denture can be divided into parafunctional load and functional load. In additional an uncomplicated vertical load is likely to be applied intermittently throughout the day in empty swallowing function. It has been demonstrated that the degree of displacement of the tissues under the saddle of the denture is greater than that of the tooth within its socket, and that the displacement increases towards the retromolar area. www.indiandentalacademy.com
  13. 13. When vertical load is applied to the saddle both the abutment teeth and the soft tissue covering the saddle area are displaced with the alveolar tissues being displaced to a greater content than the tooth. The result of this is rotation of the free end saddle being displaced into the soft tissue posteriorly and the clasp arm exerting leverage on the abutment tooth in a distal direction. www.indiandentalacademy.com
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  15. 15. With a rigid connector present between the saddle, the same effect will occur on the opposite side of the arch. This is such a design that application of the vertical load will cause rotation of the free end saddles into the tissues overlying the residual ridges and the line joining the occlusal rest can be considered as the axis of rotation. At the same time as rotation of the saddles into the supporting tissues occurs, so also is three rotation in the opposite direction of the lingual bar connecting the saddles. www.indiandentalacademy.com
  16. 16. The amount of displacement of both the saddle and the connector is however dependent upon the nature and amount of the fibrous submucosa that covers that covers the residual alveolar ridge and this can be assessed by palpation. Since increased vertical load causes increased bony resorption it is wise to make the saddle cover as large an area as possible in order to reduce the load per unit area and ensure that the residual ridge is subjected to minimal stress. www.indiandentalacademy.com
  17. 17. It has been generally accepted that when the saddle of a Kennedy class I denture with occlusal rest placed distally on the abutment teeth is loaded vertically, there is tendency to distal displacement of the abutment tooth. This is not a bodily movement but rather one of the tilting due to the arch of rotation of the saddle, which in the gingival area of the abutment tooth is almost parallel to the mucosa, resulting in minimal or no support from the mucosa near the tooth. www.indiandentalacademy.com
  18. 18. This will result in distal bone loss, eventual tooth mobility and of course denture movement, dependent upon the state of the inter dental marginal ligament and its regenerative capacity. It has been shown that bilateral loading of the denture saddles is more favorable to the abutment teeth than unilateral loading and that loads applied to the saddles are transmitted to the abutment teeth primarly through the occlusal rests www.indiandentalacademy.com
  19. 19. The potential mobility of the abutment tooth will depend upon Magnitude of the vertical load. The physical characteristic of the overlying mucosa. Angulation of the residual ridge to the horizontal plane. The periodontal status of the tooth itself. www.indiandentalacademy.com
  20. 20. The effects of clasping are that The more rigid the clasp, the greater the leverage on the tooth and the less the load on the alveolar ridge. The more flexible the clasp arms the less leverage on the tooth and more load on the ridge. www.indiandentalacademy.com
  21. 21. THE LATERAL COMPONENT Lower distal extension saddles may be displaced laterally as a result of the inclined plan action of the cusps of the posterior teeth and the steeper the cusp inclines the greater will be the load which acts laterally. Lateral load may also act on the saddle during these tooth contacts that may take place at times other than during mastication and like the vertical forces will be greater in magnitude. www.indiandentalacademy.com
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  23. 23. The efficiency depends up on the anatomy of the residual ridge and the condition of the soft tissue of the working saddle. Flat ridge with a marked fibrosis of the submucosa offers comparatively little resistances, but if the ridge is well formed and shows a thinner submucosa, resistance is increased. Lateral displacement have an adverse effect on the residual alveolar ridge and in this respect the lateral component of load is probably a major factors is ridge resorption than the vertical component. www.indiandentalacademy.com
  24. 24. Stress Communicated by Resisting structure Working side saddle. Buccal ridge plate on working side. Abutment tooth on working side. Buccal arm of clasp on working side. Balancing side saddle. Lingual arm of claps on balancing side. Continuous clasp (if included in design). Lingual plate (if included in design. Lingual ridge plate on balancing side. Abutment tooth on balancing side. Teeth on balancing side. Lingual plate of ridge supporting teeth, and teeth themselves, on balancing side. www.indiandentalacademy.com
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  26. 26. Lateral loads will also be exerted on the denture by the adjacent facial and lingual musculature particularly during swallowing. These loads, which act through out the day may total twice the load resulting from masticatory function and their effects can be minimized by using marrow posterior teeth and shaping the flanges so that they do not extend beyond the zone of minimal conflict. In addition the flanges should be kept thin in order to give steam lined appearance to the denture. www.indiandentalacademy.com
  27. 27. ANTERO - POSTERIOR COMPONENT. Posterior displacement of the mandible from the inter cuspal position takes place only during the first power strokes which are used when a hard or tough bolus is being masticated. Although the magnitude of the load involved in considerable and an anterior displacing load on the lower denture results, it is generally well resulted by the abutment teeth and those anterior in the arch. www.indiandentalacademy.com
  28. 28. Although a masticatory performance a true protrusive movement of the mandible is only used in incision, there is often a protrusive element in grinding. The cusp of the lower teeth, instead of being accommodated in the fossae of the upper teeth, make a contact on the slopes of the upper cusps. This results in a inclined plane action which produces a distal force on the lower denture, the magnitude of which will depend on the musculature and the steepness of the cusp angles. This backward force is in part resisted by the ridge when it slopes upwards into the ascending ramus of the mandible, but the greater part of the resistance comes from the clasped abutment tooth. www.indiandentalacademy.com
  29. 29. The arms of the three arm clasp encompass the tooth almost completely on its buccal and lingual surfaces, and the tips of the arm lie on the mesial of the crown. Consequently the abutment tooth tends to be pulled in a distal direction. The magnitude of the force applied will be greater if the clasp arm are cast alloy than if they are wrought wire. A greater problem arises if the abutment tooth is a canine. Due to the crown morphology of this tooth it is difficult to design a claps that will encompass the tooth and also be an aesthetically acceptable. In such a situations the clasped tooth is unable to offer resistance to the distal displacement of the saddle, which is borne entirely by the residual ridge. www.indiandentalacademy.com
  30. 30. TREATMENT OF DISTAL EXTENSION PARTIAL DENTURE www.indiandentalacademy.com
  31. 31. KENNEDY CLASS I The suggested methods of restoring the bilateral free end saddle may be achieved by 1.Reducing the load 2.Distributing the load between teeth and residual ridges. i) By varying the connector between clasp and saddle. a) Stress breaking. b) Combining rigid connection and gingivally approaching clasp. c) Combining rigid connection and occlusal approaching clasp www.indiandentalacademy.com
  32. 32. ii) By anterior placement of the occlusal rest : a) The RPI system. b) The balance of force system. iii) By mucocompression 3. Distributing the load widely i) Over more than one abutment tooth on each side. ii) Over the maximal area of edentulous ridge. www.indiandentalacademy.com
  33. 33. Reducing the load The vertical load on the saddle in mastication may be reduced by decreasing the size of the occlusal table and also by ensuring as wide a coverage of the residual ridge area by the base of the saddle as is compatible with function. Using canines and premolars instead of premolars and Molars. Using narrow teeth or reducing the width of selected teeth by removing the lingual cusp (s). www.indiandentalacademy.com Leaving a tooth off a saddle.
  34. 34. DISTRIBUTION OF THE LOAD BETWEEN TEETH AND RIDGES i) By varying the connection between clasp and saddle. a. Stress breaking The principle of stress breaking in partial denture design is the provision of some degree of movement or flexibility between the clasp unit and the distal extension saddle. The stress transmitted by the denture to the tissues is distributed differently therefore and also reduced by the energy absorbed in deformation than if the connection had been rigid. Any device which allows movement between the saddle unit and the retaining unit is known as a stress breaker. www.indiandentalacademy.com
  35. 35. Stress Breakers can be divided into two groups.  Those having a movable joint between the direct retainer and the saddle.  Those having a flexible connection between the direct retainer and the saddle. The first group is necessary when a precision attachment is used, but can also be used when a claps is preferred. They vary in their range of movement, some allowing only up and down and side to side movements, whereas others also permit a vertical hinge action. www.indiandentalacademy.com
  36. 36. Construction of a flexible or semi-flexible connector between the direct retainer and tooth supported part of the denture and the mucosally supported saddle is achieved with a distally extended flexible bar connected to the rigid connector. The degree of flexibility will depend upon in its length and cross sectional form. Where a lingual bar connector has been used to join the two saddles it should be distally extended on each side and then re-curved along the residual ridge to allow attachment into the matrix resin of the saddle. www.indiandentalacademy.com
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  38. 38. Alternatively if a lingual plate connector is used a split of an appropriate length can be made at its inferior border. The saddle is attached to the more flexible bar while the clasp units are attached to the rigid part of the framework. The use of such designs allows the mucosa supported saddle a degree of movement which is independent of the rigid tooth supported part of the denture and therefore lessens the stress of the abutment teeth. www.indiandentalacademy.com
  39. 39. When a vertical load is applied the saddle is displaced downward into the soft tissue covering the ridge to a greater extend than where the retainer and occlusal rest have direct connection with a saddle. This means that the ridge bone has to withstand an increased vertical load which is more evenly spread over the whole ridge rather than concentrated at the free end of the saddle. Although not quite accurate it may be assumed that the centre of saddle rotation is at the portion of the connector lying anterior to it. www.indiandentalacademy.com
  40. 40. The net result of the stress breaking action as far as the vertical component is concerned is a greater assignment of load to the edentulous ridge and less to the abutment tooth. The torque on the abutment is reduced markedly in magnitude and is favorable in direction. www.indiandentalacademy.com
  41. 41. When a lateral component acts on the stress broken saddle a greatly increased lateral stress is placed on the alveolar bone. Less of the load falls on the abutment teeth and consequently the magnitude of the damaging lateral torque is reduced. If a continuous clasp or lingual plate is included in the design it is incorporated in the retainer unit and thus plays less part in the distribution of lateral load. www.indiandentalacademy.com
  42. 42. Stress breaking has little effect on the anterior component of force acting on the denture saddle during the power strokes ; uninterrupted contact between tooth and retainer and retainer and saddle ensures no saddle movement in an anterior direction and load distribution is accordingly not altered. The dangerous horizontal torques acting on the abutment teeth are reduced by stress breaking and that, in consequence, their supporting structures are less liable to break down. However, the edentulous ridge is called upon to accept more vertical and horizontal stress and as a result tends to resorb more quickly. www.indiandentalacademy.com
  43. 43. B. COMBINING RIGID CONNECTION AND GINGIVALLY APPRAOCHING CLASPING When rigid connection between retainers and saddles is used, with gingivally approaching clasps, a condition may exist which is similar in principle to stress breaking. The portion of this type of claps that is in contact with the abutment tooth is at the end of a bar that is resilient to a degree which depends upon its length and cross section and the alloy used. www.indiandentalacademy.com
  44. 44. If the occlusal rest is allowed to move over the occlusal surfaces of the tooth to a small degree in lateral and antero-posterior directions (and this may occur when saucer-shaped rest seat preparation are used), the action of the clasp bar resembles a stress breaker, since its resilience reduces the horizontal forces on the abutment tooth. The effectiveness of the stress breaking actions of these clasps may be increased by increasing the resilience of the bar. www.indiandentalacademy.com
  45. 45. C. COMBINING RIGID CONNECTION AND OCCLUSALLY APPROAHING CLASPING. A combination of rigid connection and occlusally approaching clasps is the opposite extreme to stress breaking. In this condition more load is placed on the abutment tooth and ridge is capable of variation and depends on the ridge. When the arm is resilient, a certain amount of movement of the clasp over the surface of the tooth is permitted. At one extreme a wrought gold wire clasp allows most movement of the clasp over the enamel. Whereas a cast cobalt chromium clasp permits least movement. www.indiandentalacademy.com
  46. 46. The extent of these clasp movements is small but they may, however, be sufficient to reduce the torque acting on the abutment and keep them within the physiologic limit. If the mucosal tissues covering the ridge areas are highly displaceable and mobile, then there may be an indication for some type of movable or flexible connection between the saddles and the retainer units. www.indiandentalacademy.com
  47. 47. d. THE DISJUNCT DENTURE In the older patient it is not uncommon to find a situation, particularly in the lower jaw, where the few remaining teeth are anterior teeth with considerable gingival recession and a generally poor periodontal condition. It has been suggested that such a problems may be overcome by the construction of a two part denture, composed separately of tooth borne and mucosa borne sections each acting independently of each other on its supporting tissues. www.indiandentalacademy.com
  48. 48. The tooth borne part comprises a lingual plate which acts to protect the teeth and the gingivae from the connector of the mucosa borne part, and which also carries retention elements. In addition, it is constructed with distally extending buccal bars which are designed to engage a slot in the saddle of the mucosa borne part. These are known as disjunct bars as they are not attached directly and rigidly to the mucosa borne saddle but allow some movement. They are however, necessary for its retention. www.indiandentalacademy.com
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  50. 50. The mucosa borne section of the denture are essentially separate, there is no transfer of the vertical masticatory load from the mucosa borne saddle to the tooth borne section. In addition because of the absence of a rigid connection between the two separate parts there is little transfer of load by means of the disjunct bars. The mucosa borne part can therefore move independently according to the compressibility of the mucosa. www.indiandentalacademy.com
  51. 51. This technique has been suggested as particularly useful in the treatment of the bilateral free end saddle, where the support contribution of the remaining standing teeth is poor and their periodontal health also might be further compromised by a totally mucosally borne designed denture. The disadvantage of the denture is that is technically difficult to construct and also that patients occasionally complain it ‘rattling’ during function which is of course due to the principles inherent in its design. www.indiandentalacademy.com
  52. 52. II. BY ANTERIOR PLACEMENT OF THE OCCLUSAL REST The distribution of load between the abutment teeth and residual ridge can sometimes be altered favorably by anterior placement of the occlusal rest. This has the effect of altering stresses on the saddle from a Class I lever situation where the resistance to the applied load lies on the opposite side of the fulcrum, to a Class II lever where the resistance lies between the applied load and the fulcrum. This permits more even distribution of load and less stress on the abutment teeth www.indiandentalacademy.com
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  54. 54. a. THE RPI SYSTEM This system of partial denture design involving a clasp unit comprised of a rest, proximal plate and “I” bar retainer An important consideration of this system is the positioning of the occlusal rest to provide the element of tooth support. If the rest is placed distally on the abutment tooth and applied to the saddle, it has been demonstrated that the arc of movement of the denture base tends to the mainly perpendicular to the residual ridge in the posterior region. www.indiandentalacademy.com
  55. 55. On moving anteriorly, however, the region near the abutment tooth the saddle movement is almost parallel to the ridge in an anterior direction. It is clear that in this situations the mucosa adjacent to the tooth can offer little resistance to the applied load, it and the gingival margin being likely to be traumatized by the horizontal movement of the denture against the abutment tooth. This area, where tooth support ends and mucosa support begins, should therefore be protected. www.indiandentalacademy.com
  56. 56. If the occlusal rest is placed mesially on the abutment teeth, it has been shown that the arc of movement of the saddle under applied load will alter and be more perpendicular to the mucosa throughout its length, due to the presence of a mesial rather than a distal fulcrum. This will increase the support provided by the mucosa whilst reducing the anterior movement of the saddle under applied www.indiandentalacademy.com load.
  57. 57. If the rest is placed distally then the tooth will tend to tilt distally, where it has little support. If it is placed mesially however, although there will be a tendency of mesial tilting of the abutment tooth, this will be resisted by other teeth in the arch anterior to it. Potential damage to the gingival tissues distal to the abutment tooth can be lessened if the distal surface of the tooth is covered by a thin plate of cast metal (the proximal plate) which extends on to the soft tissues. This is relieved at the gingival margin. www.indiandentalacademy.com
  58. 58. Wear and damage will also be limited and the metal will maintain a close adaptation so protecting the tissues from food packing and preventing gingival hypertrophy. In addition the plate should extend lingually on the proximal surfaces of the tooth in order to provide some reciprocation for the “I” bar clasp. It has been argued that by constructing a conventional occlusally approaching clasp the external contour of the tooth is altered adversely, particularly in relation to natural stimulation of the gingivae and in food shedding. www.indiandentalacademy.com
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  60. 60. If its tip is placed towards the mesial portion of the tooth it also serves to bring the proximal plate into tight contact with the distal surface. As the denture is depressed on to its basal seat the clasp will move towards and downwards and out of contact with the tooth so removing any possibility of leverage. The mesial rest is linked to a minor connector which also provides some reciprocation and is placed in the mesio lingual embrasure but free of the adjacent tooth anterior to it. With applied load to the saddle the rest acts as a fulcrum point, ensuring mesial rather than distal loading of the abutment tooth. www.indiandentalacademy.com
  61. 61. Under load it will be depressed tissue wards further into the undercut area without exerting torque or leverage on the abutment tooth. The “I” bar crosses the gingival margin at right angles and contacts the tooth in its gingival third and at the greatest mesiodistal prominence of the tooth, its precise position of contact immediately below and above the survey line. Besides being retentive, it will move mesio gingivally away from the tooth under applied load. www.indiandentalacademy.com
  62. 62. The RPI system will result in a denture with  Enhanced mucosal support due to loading. perpendicular Reinforcement against mesial tilting of the abutment tooth. Adequate retention with minimal effect on natural tooth contour. No adverse stress on the abutment tooth during masticatory loading. Protection of the transitional region between the tooth and the mucosal areawww.indiandentalacademy.com saddle. of the edentulous
  63. 63. b. Balance of force system The balance of force system, canbe considered as a further refinement of the RPI system being based on the mechanical principles of a class II lever. As the magnitude of masticatory loads on the abutment teeth are much greater than those of the forces of displacement and as the tooth is less able to withstand this, the design has been developed to ensure that loads during masticatory performance are directed vertically along the long axis of the tooth so avoiding torque and leverage. www.indiandentalacademy.com
  64. 64. A rest seat must be provided on the part of the occlusal surface of the abutment tooth that is distant from the saddle. This will act as the fulcrum point and ensure vertical loading on the tooth during function. In distal extension partial dentures this would be a mesially placed support unit. In addition to rest seat preparation an interproximal access area of about 1 mm must be created between the abutment tooth and the anterior tooth adjacent. It is in this area that reciprocation for the clasp arm will be positioned together with the minor connector. www.indiandentalacademy.com
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  66. 66. The clasp unit is designed so that retentive tip of the claps arm is positioned on the interproximal surface of the abutment tooth adjacent to the edentulous saddle. It should lie below the maximum convexity of this surface engaging a degree of undercut according to the physical properties of the material. The reciprocation for the retentive force of the clasp arm in resisting displacement is provided by a vertical plate in the prepared access area on the abutment tooth above its maximum convexity. The vertical plate is joined to the major connector. www.indiandentalacademy.com
  67. 67. The unit should be so designed that the flexible tip of the clasp arm, the occlusal rest and the contact surface of the vertical reciprocating plate are in line with the crest of the edentulous ridge. Retention is therefore achieved mesiodistally as opposed to bucco-lingually and the design ensures that the greatest loads on the tooth are applied mesio-distally where it is well supported. www.indiandentalacademy.com
  68. 68. When masticatory load is applied to the distal extension saddle its downward movement towards the underlying tissue is accompanied by a similar movement of the retentive tip of the clasp arm. This allows the clasp to disengage the tooth as it moves into an area of increased undercut, this eliminating horizontal tooth loading. The mesial occlusal rests will direct loads vertically along the long axis of the tooth hence it is better able to withstand them. www.indiandentalacademy.com
  69. 69. If a displacing force is applied to the denture, the saddle and clasp tip once again move in the same direction occlusally. The clasp tip will now engage the proximal surface of the tooth below its maximum convexity thus providing resistance to further displacement. Reciprocation during this action is provided by the vertical interproximal plate on the opposite side of the tooth. www.indiandentalacademy.com
  70. 70. III. BY MUCOCOMPRESSION Mucostasis Mucocompression. The greater the amount of displacement the less is the magnitude of the torque and load on the abutment, when a vertical load is placed on the saddle. Different impression materials give varying degrees of mucosal displacement The saddle base fitted accurately against the mucosa from which tissue fluid has already been displaced sinks less under the masticatory load than if fitted against an undisturbed mucosa. www.indiandentalacademy.com
  71. 71. The amount of displacement affects the distribution of load between abutment and ridge bone. The greater the displacement the more evenly is the stress distributed between the abutment and the edentulous ridge. However, the mucosa cannot be continuously subjected to such heavy pressure since this will result in decreased blood supply to, and drainage from, the soft tissues. Coupled with the fact that the tissue fluid is also reduced, this may result in a tropic disturbance www.indiandentalacademy.com
  72. 72. The natural tendency of the displaced tissue is to recoil in a visco-elastic manner. In assuming that the saddle is maintained in the closest approximation with the displaced mucosa, the presence of some force to hold it in this position is also assumed. This force can only come from rigid clasping of the abutment tooth and results in a continuous force acting on the abutment. It is thus seen that the use of rigid connection and clasping together with mixture displacement leads to an unacceptable situation in respect of potential damage to the abutment and covering mucosa. www.indiandentalacademy.com
  73. 73. If maximum displacement is to be used, arrangement must be made to allow some recoil of the mucosal tissues. This can be achieved either by very light clasping, generally wrought gold wires of thin gauge, or by a stress breaker giving flexible connection between the saddles and retainer units. www.indiandentalacademy.com
  74. 74. The method of maximum displacement coupled with light clasping directly attached to the saddles is not used  Retention of such a denture is inadequate because of the light clasping and poor adhesion, the latter being due to the uneven thickness of saliva film between the mucosa and the fitting surface of the denture after recoil of the tissues.  Lateral stresses are resisted largely by the edentulous ridge, which is, therefore, liable to resorb. www.indiandentalacademy.com
  75. 75. With mucostasis, even when cast clasps are directly attached to the saddles, no forces act either on the ridge or abutment when the saddle is not under load. In the resting stage, too, adhesion is maximal. With this type of impression too, the bone is not evently stressed, the areas underlying thinner mucosa receiving an increased share of the load. With such a technique and where rigid clasping directly attached to the saddle is used, maximal leverage and torque is placed on the abutment teeth, which are, therefore, predisposed to periodontal breakdown. www.indiandentalacademy.com
  76. 76. With this type of impression too, the bone is not evenly stressed, the areas underlying thinner mucosa receiving an increased share of the load. There is however, a condition intermediate between maximum displacement and mucostasis that has considerable advantages Thus a compromise between stasis and maximum displacement seems to give a result with the advantages of each present to some degree. www.indiandentalacademy.com
  77. 77. 3. WIDE DISTRIBUTION OF LOAD I)WIDE DISTRIBUTION OF LOAD OVER THE TEETH When clinically circumstances permit, the procedure is to move the occlusal rest anteriorly so that it lies not on the tooth that immediately bound the saddle, but on the occlusal surface of the tooth that lies immediately anterior. If a rest is placed on this tooth some of the vertical load is placed upon it and its marginal ridge becomes the fulcrum point. www.indiandentalacademy.com
  78. 78. If two flexible arms now arise from this and its encompass the buccal and lingual surfaces of the posterior tooth and if these arms lie above the survey lines then some of the vertical load is dispersed. Part is dissipated in opening the clasp arms and part is directed down the long axis of the tooth. The retaining clasp is on the rested tooth. Which accepts vertical load through the occlusal rest. Lateral www.indiandentalacademy.com load is distributed to the two teeth by the clasp arms.
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  80. 80. II.) WIDE DISTRIBUTION OF LOAD OVER THE RIDGE The saddles of the denture should always cover the largest possible area, so that the pressure falling on any unit area of the edentulous ridge is reduced under vertical and horizontal loading. While full coverage over the retromolar area and the buttress bone both buccally and lingually is desirable for load distribution it may not www.indiandentalacademy.com always be acceptable to the patient.
  81. 81. Modification of the bilateral free end saddle lower denture www.indiandentalacademy.com
  82. 82. Modification of the bilateral free end saddle lower denture 1) An anterior saddle present in addition to 2 free end saddle 2) Long free end saddle interrupted by a single standing www.indiandentalacademy.com
  83. 83. An anterior saddle present in addition to 2 free end saddle The stress on the abutment tooth depends on • saddle length and shape •Displaceability of mucosa A rigid construction is advisable By clasping the 4 abutment teeth , vertical and horizontal forces are resisted by 2 teeth on each side . This facilitates wide distribution of load www.indiandentalacademy.com
  84. 84. a)If only 2 premolars remain bilaterally • Lingual bars and continuous clasps The clasps are constructed in wrought wire but if ridges are well formed they may be constructed in cast metal b)if premolars are severely inclined lingually • Buccal bar • Back action clasp c)Only 2 canine remain •Simple acrylic resin mucosa supported denture www.indiandentalacademy.com
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  88. 88. 2)Long free end saddle interrupted by a single standing a) Extract b)Retain if healthy . This reduces length of saddle thereby reduces leverage Wide distribution of load since clasping on 2 teeth c)when molar is single long standing tooth it is sensible to dispense with the small free end saddle www.indiandentalacademy.com
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  91. 91. Bilateral free end saddle upper denture The basic problem encountered with Bilateral free end saddle upper denture is similar to those found with lower denture Indirect retention is more necessary with the upper than with the lower Indirect retention is obtainable in these cases by. • Continuous clasp •Cummer arms •Anterior extension of palatal bar www.indiandentalacademy.com •Extension of any palatal plate to cover the rugae
  92. 92. Modifications of the Bilateral free end saddle upper denture a)Long free end saddle interrupted by a single standing b)Anterior natural teeth missing c)Series of single tooth saddles separated by single teeth standing If no teeth are to be extracted a horse shaped metal base covering hard palate is often the treatment of choice www.indiandentalacademy.com
  93. 93. ALTERED CAST PROCEDURE The purpose of altered cast procedure is to obtain the maximum support from the edentulous area of the extension partial denture. This procedure applies the principal of recording the edentulous tissue in a form that provides the proper denture base extension without distortion or displacement of the tissues. The objective is to ensure the best possible relationship between the casting framework, properly fitted on the teeth and the denture base thereby deriving the greatest support potential from both teeth and edentulous www.indiandentalacademy.com areas.
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  99. 99. Impression procedure www.indiandentalacademy.com
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  101. 101. Cast alteration www.indiandentalacademy.com
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  104. 104. THE LOADED IMPRESSION TECHNIQUE FOR THE DISTAL EXTENSION REMOVABLE PARTIAL DENTURE In order to obtain an optimum impression of an arch that will receive a Kennedy class I or II RPD, a dual impression technique must be employed. The final impression combine an elastomer to register the anatomic form of the teeth and surface detail of the residual ridge and a more viscous material to load the residual ridge. www.indiandentalacademy.com
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  109. 109. Review of Literature www.indiandentalacademy.com
  110. 110. Stress analysis is distal extension partial dentures. George W. Hindels J. Prosthet Dent. 7; 197 – 205, 1952. He described the load distribution in extension saddle partial dentures. He said that the method used to make impression of the supporting and retaining anatomic status of the mouth is of basic importance for obtaining optimum distribution of the masticatory load in the construction of remarkable partial denture, especially those of the lower extension saddle type. His opinion is that there are three definite requirement that must be fulfilled to assure proper load distribution in extension saddle partial denture. www.indiandentalacademy.com
  111. 111. They are The tissue surface of the saddle should be negative reproduction of the anatomic, undisturbed surface of the alveolar mucosa. The masticatory load should be distributed between the ridge and the abutment teeth during function and cannot be left to be carried by alveolar ridge alone. The denture saddle should be related to the metal frame work in such a way as to be similar to the relationship existing between the supporting teeth and the supporting mucosa when latter is a masticatory load. www.indiandentalacademy.com
  112. 112. The Bilateral free end saddle lower denture. Lamme G.A. and John Osborne J. Prosthet Dent 4 : 640 – 652, 1954. They stated that the bilateral free end saddle lower denture (class I lower denture of the kennedy’s classification) always presents a treatment problem. A free end saddle can have tooth support at only one extremity and this at least part of lead falling upon it must be resisted by the edentulous alveolar bone. This is in contra distinction to the bounded saddle, which has anteriorly and posteriorly placed abutment teeth. in this he given following methods for the treatment of the free and saddle. The following method of attempting to control the vertical load are designed to give the optimal reaction in both www.indiandentalacademy.com
  113. 113. 1.Reducing the load directly. 2.Distributing the load between teeth and alveolar i) By varying the nature of the connection between clasp and saddle. a)Stress breaking b)Combining rigid connection and gingivally approaching clasping. c)Combining rigid connection and occlusal approaching clasping. ii) By anterior placement of the occlusal rest. iii) By mucocompression. 3. Distributing the load widely i) Over more than one abutment tooth on each side. www.indiandentalacademy.com ii) Over the maximal area of edentulous alveolar
  114. 114. Stress analysis is distal extension partial dentures. George W. Hindels J. Prosthet Dent. 7; 197 – 205, 1957. He did a stress analysis in distal extension partial dentures, he said that masticatory stresses exerted on the base of a distal extension partial denture are transmitted to the supporting anatomic structures through contacting parts of the appliance. If the parts are incorrectly designed or constructed, they will alter the direction and force of these masticatory stresses and may create stresses which are not within the physiologic limits of tissue tolerance. The partial denture should be constructed. www.indiandentalacademy.com So this movement is vertical is relation to the supporting bone.
  115. 115. Clasp and rest should be designed to allow for this vertical movement of the denture base. Stress other than those vertical to the abutment teeth should be reciprocated. Reciprocation is best obtained by contact of rigid parts of the partial denture with modified axial surface of the abutment teeth which are made parallel to each other and the path of insertion www.indiandentalacademy.com
  116. 116. A study of partial denture design and masticatory pressure in the mandibular bilateral distal extension case. Anthony K. Karies : J. Prosthet dent. 8: 340-350, 1958 In a study of masticatory performance, he found out that the followings;  The reduction of the size of the occlusal table reduces the forces acting on the partial denture and lessens the stresses on the abutment teeth and supporting tissues.  The effect of the partial denture on masticatory performance did not reveal any significant relationship.  The rigid design of the partial denture were more desirable than the flexible are specifically the rigid lingual bar is more desirable than a flexible bar in withstanding horizontal stresses. www.indiandentalacademy.com
  117. 117. Preparation of abutment teeth for removable partial dentures. Holmes J.B. J. Prosthet Dent. 20: 396 – 406, 1968. He mentioned about the preparation of abutment teeth for dentures, he says that the preparation of spoon shaped or rounded rest seat areas that direct forces towards the long axes at abutment teeth provides positive support for the partial denture. The location of rest areas affects the movements of abutment teeth by changing the direction of force applied to the www.indiandentalacademy.com teeth and to the denture base.
  118. 118. Metal guiding planes that contact the proximal surface of the abutment teeth and extend 1 to 2 mm onto the residual ridge lessen the possibility that debris will collected around the denture the residual ridge and the abutment. The development of adequate support for partial denture without applying under torquing force to the abutment and the maintenance of the health of the periodontal supporting structure pre vital to the success of partial denture treatment. www.indiandentalacademy.com
  119. 119. Clasp design for extension base removable partial dentures. Arthur J. Krol J. Prosthet Dent. 29:408-416, 1973. He mentioned that clasp design for extension base partial dentures is one of the more fascinating and thought provoking subject in dentistry. Many types of clasp for unilateral and bilateral distal extension base partial dentures are consult being and by dentist and dental laboratories throughout the work in an attempt to prolong the life of the remaining teeth. The clasp returd to as an R.P.I. clasp is introduced which minimizes tooth coverage and reduces stress on the abutment www.indiandentalacademy.com
  120. 120. RICHARD P. FRANK in 1986 in his clinical observation indicated that the wrought wire clasp assembly. The I-bar clasp assembly and the L-bar clasp assembly yield similar results. Several thousand observations have been made by the faculty and no special trend of problems has been noted that would cause one clasp assembly to be favoured over another. These three types of clasp assemblies work satisfactorily when properly chosen and carefully applied. www.indiandentalacademy.com
  121. 121. RONALD E. MYERS in 1986 in his photoelastic study of rests found out that with a distal extension removable partial denture, maximum use of existing oral structure can aid in the total support of the prostheses and reduce the force on the solitary abutment. Four rests with relieved and unrelieved guide plates were evaluated for optimum stress distribution around the root of a solitary premolar abutment. The rest were the mesial, the distal. The mesial and distal and the continuous rest. www.indiandentalacademy.com
  122. 122. The findings demonstrated that : 1.The continuous rest had the most favourable stress concentrations. 2.All other rest design demonstrated more lateral stress than the continuous rest. 3.Relieved guide planes demonstrated 58% less maximum shear stress in the apical portion than unrelieved guide planes. www.indiandentalacademy.com
  123. 123. An analysis of rotational movements of asymmetrical destal extension removable partial dentures. Aviv I. Et al J. Prosthet Dent 61; 211 - 214, 1989. He states that an axis of rotation is created through the most distally placed occlusal rest. When a distal extension removable partial denture is loaded. If the residual ridges are of unequal length, the axis of rotation may not be perpendicular to the residual ridge. Movements of I bar retainers loaded on the mesiobuccal aspect of asymmetrical abutment teeth may torque the abutment teeth as the denture base moves tissues wards. Use of L shaped direct retainer on the distobuccal surveyed undercut will create a more favourable class II lesser effect on the abutment tooth www.indiandentalacademy.com
  124. 124. Comparison of vertical movements occurring during loading of distal extension RPD bases made by three impression techniques. Richard J Leupold, Robert J Flinton, David L Pfiefer JPD 1992;68:290-293 The study clinically compared the vertical displacement of the distal extension RPD made from altered cast impression, an impression from border molded custom tray. Stock tray irreversible hydrocolloid was used as a control. Although statistically significant 0.19mm difference between impression techniques may or may www.indiandentalacademy.com not be clinically significant.
  125. 125. Sectional impression for mandibular distal extension RPD Hanaa Al Shiekh, Adel M Abdul Hakim JPD1998;80:216-219 The final impressions made in border molded full arch custom tray clinically comparable to sectional impression for distal extension mandibular RPD. Sectional impressions demonstrated significant reduction in vertical movement when analyzed statistically. However this finding maybe clinically insignificant. www.indiandentalacademy.com
  126. 126. Clinical outcome of altered cast impression procedures compared with the use of a one piece cast. Richard P Frank , James S Brudvik, Karleen G Noonan JPD 2004;91:468-476 The altered cast impression procedure does not have significant advantages over the one piece cast provided standards in this study are met. These include completely extended impression, use of a magnification to ensure complete seating of the frame work and coverage of the retromolar pad and buccal shelf by the base. www.indiandentalacademy.com
  127. 127. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com