Rpd designing /certified fixed orthodontic courses by Indian dental academy


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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 www.indiandentalacademy.com ,or call

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Rpd designing /certified fixed orthodontic courses by Indian dental academy

  1. 1. REMOVABLE PARTIAL DENTURE DESIGNING INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Philosophy of design. There are three basic, underlying approaches to distributing the forces acting on a partial denture between the soft tissue and the teeth. 1.Stress equalization 2.Physiologic basing. 3.Broad stress distribution www.indiandentalacademy.com
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  4. 4. Disadvantages The stress director is comparatively fragile, and its construction is complex and costly. It requires constant maintenance and may be difficult or impossible to repair. Although attempts are usually made to strengthen the hinge to prevent lateral movement of the denture base, its lack of ability to prevent damaging lateral stresses from occurring on the edentulous ridge can result in rapid resorption of bone. www.indiandentalacademy.com
  5. 5. Stress Equalization The resiliency of the tooth secured by the periodontal ligament in an apical direction is not comparable to the greater resiliency and displaceability of the mucosa covering the edentulous ridge. Because of this great disparity, forces are transmitted to the abutment teeth as the denture bases are displaced in function. A rigid connection between the denture bases and the direct retainer on the abutment teeth is damaging and that some type of stress director or stress equalizer is essential to protect the vulnerable abutment teeth. www.indiandentalacademy.com
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  7. 7. The treatment of the partially edentulous patient requires the knowledge and the skill of the dentist in almost every phase of dental practice. Decisions relative to teeth to be retained, surgical procedures to be employed, and types of restorations to be placed must be made with the ultimate design of the prosthesis in mind. www.indiandentalacademy.com
  8. 8. Advantages The stress director design usually calls for minimal direct retention, because the denture base operates more independently than in a conventional denture. Theoretically, at least, the stress director eliminates the tipping strain on the tooth, thus preventing bone resorption about the tooth. Sum of its resiliency and that of the periodontal ligament is equal to the resiliency of the mucosa. Thus forces are distributed equally between the teeth and the soft tissue. Intermittent pressure against the mucosa caused by the movement of the bases has a massaging or stimulating effect www.indiandentalacademy.com on the underlying bone and soft tissue.
  9. 9. Disadvantages The stress director is comparatively fragile, and its construction is complex and costly. It requires constant maintenance and may be difficult or impossible to repair. Although attempts are usually made to strengthen the hinge to prevent lateral movement of the denture base, its lack of ability to prevent damaging lateral stresses from occurring on the edentulous ridge can result in rapid resorption of bone. www.indiandentalacademy.com
  10. 10. Philosophy of design. There are three basic, underlying approaches to distributing the forces acting on a partial denture between the soft tissue and the teeth. 1.Stress equalization 2.Physiologic basing. 3.Broad stress distribution www.indiandentalacademy.com
  11. 11. Principles of Design by A.H. Schmidt in 1956. 1. The dentist must have a thorough knowledge of both the mechanical and biologic factors involved in removable partial denture design. 2. The treatment plan must be based on a complete examination and diagnosis of the individual patient 3. The dentist must correlate the pertinent factors and determine a proper plan of treatment 4. A removable partial denture should restore form and function without injury to the remaining oral structure. 5. A removable partial denture is a form of treatment and not a cure www.indiandentalacademy.com
  12. 12. Physiologic Basing This philosophy of design denies the necessity of using stress directors to equalize the disparity of vertical movement between the tooth and mucosa. The belief is that the equalization can best and most simply be accomplished by some form of physiologic basing, or lining, of the denture base. The physiologic basing is produced either by displacing or depressing the ridge mucosa during the impression making procedure or by relining the denture base after it has been constructed www.indiandentalacademy.com
  13. 13. It seems obvious that the artificial teeth of a removable partial denture constructed from a tissue displacing impression will be positioned above the plane of occlusion when the denture is in the mouth and not in function. To permit vertical movement of the partial denture from the rest position to the functioning position, the direct retainers or retentive clasps must be designed with minimal retention and the number of direct retainers must be limited. The occlusal rests and direct retainers will also be slightly unseated at rest. www.indiandentalacademy.com
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  15. 15. Advantages The intermittent base movement that occurs as occlusal loads are applied and removed has a physiologically stimulating effect on the underlying bone and soft tissue, which is said to reduce the frequency of the need to reline or rebase the prosthesis to correct for tissue change cause by resorption. www.indiandentalacademy.com
  16. 16. Disadvantages Because of the artificial teeth are always slightly above the occlusal plane when the denture is not in function, there will always be slightly premature contacts between the opposing teeth and the denture teeth when the mouth is closed. By the time the indirect retainer engages a rest seat to prevent the denture base from being dislodged, the direct retainer will have lost contact with the abutment tooth. www.indiandentalacademy.com
  17. 17. Broad stress distribution Advocates of this school of partial denture design believe that excessive trauma to the remaining teeth and residual ridge can be prevented by distributing the forces of occlusion over as many teeth and as much of the available soft tissue area as possible. This is accomplished by the use of additional rests, indirect retainers, clasps, and broad coverage denture bases. www.indiandentalacademy.com
  18. 18. Advantages Lateral forces may be distributed over as many teeth as possible. Clasps may be used on some teeth not for retention but to aid in lateral stability. Because of the increased stability and decreased movement, the broad stress distribution partial denture does not require relining as frequently as the other types because the residual ridge does not bear as much of the occlusal plane. www.indiandentalacademy.com
  19. 19. Disadvantages An increased amount of tooth surface coverage philosophy. is associated with this design Preventive dental programs to monitor caries must be instituted and carefully followed for each patient. www.indiandentalacademy.com
  20. 20. DESIGN PROCEDURE Color-coding A color coding system for the various parts of the removable partial denture as well as for other items of information that should be included on the diagnostic casts helps prevent confusion on the part of a dental laboratory technician or anyone trying to understand the design being proposed. Red, blue, and brown crayon pencils and a black lead pencil, two H or three H hardness, are used. www.indiandentalacademy.com
  21. 21. The brown crayon pencil is used to outline the metallic portion of the partial denture; the blue crayon pencil, to outline the acrylic resin portion of the prosthesis. Rest seats are drawn in solid red. The black pencil and the carbon marker in the surveyor are used to denote survey lines, tripod marks, soft tissue undercuts, and other information that must be included such as the type of tooth replacement or the use of wrought wire for retentive clasps. www.indiandentalacademy.com
  22. 22. Step-by-Step Procedure 1. Examine the occluded diagnostic casts. 2. Indicate with a pencil using the following symbols, the type of tooth replacement desired. Denture teeth on a denture base - no symbol Tube tooth - T Facing - F Metal pontic - M Reinforced acrylic pontic - RAP www.indiandentalacademy.com
  23. 23. 3. Place the cast on the cast holder at a horizontal tilt. Examine the teeth to be clasped for favorable retentive undercuts examine anterior edentulous area for esthetic considerations. Examine proximal and lingual tooth surfaces for guiding planes. Outline in red-pencil those surfaces that will require re-contouring or reshaping to produce the desired result. 4. Tripod the cast www.indiandentalacademy.com
  24. 24. 5. Place a carbon marker in the vertical arm of the surveyor and scribe the survey line on the teeth that will be contacted by the partial denture. 6. with a red pencil draw in the extent of rest areas to be prepared in the mouth. 7. Outline the exact position and extent of the denture base area. Blue pencil indicates acrylic resin denture base; brown indicates a metal denture base. www.indiandentalacademy.com
  25. 25. 8. With a brown pencil, outline the framework design to harmonize and join the major connectors, rest areas, indirect retainers, minor connectors, denture bases, and replacement teeth. Use the carbon marker to outline soft tissue undercuts that will influence the design www.indiandentalacademy.com
  26. 26. 9. Replace the carbon marker with the appropriate undercut gauge. (For most clasps of chrome, cobalt alloy a O.OIO-inch undercut is adequate. For wrought wire retentive clasps, 0.020 inch is usually indicated). 10. With the brown pencil, draw the clasp arms to the actual shape size and location desired. If wrought wire clasps are to be used, place the symbol WW on the soft tissue below the tooth. 11. Re-examine the design for accuracy and clarity. www.indiandentalacademy.com
  27. 27. The Various Principles Involved in the Functioning of a Removable Partial Denture  Different forces acting on a denture in the mouth. The response of the denture to the forces acting on it. Design methods, which help to limit the effects of these harmful forces www.indiandentalacademy.com
  28. 28. Different Forces Acting on the Denture Inside the Oral Cavity Occlusal force - It acts on the occlusal surface of the denture. It is of very high magnitude. This force pushes the denture on to the tissues on the edentulous ridge. Excessive occlusal forces can produce residual ridge resorption. Forces from the tongue - The tongue tends to push the denture buccally and labially. Excessive force from the tongue can displace the denture frequently during function. www.indiandentalacademy.com
  29. 29. Forces from the surrounding musculature (lip and cheek muscles)- These forces compensate the forces of the tongue. Excessive forces tend to displace the denture .A balance is usually maintained between the buccinator and the tongue. This balance results in a 'dead zone of nil force'. This zone is called neutral zone or zone of minimal conflict or zone of equilibrium .Artificial teeth on the denture should be placed on this zone to achieve good stability for the denture. www.indiandentalacademy.com
  30. 30. Response of the Denture to Various Forces Acting on it Generally tissue supported partial dentures respond like a lever or like an inclined plane when a force is applied on them. Tooth supported partial dentures (Kennedy's Class III) are not supported by resilient structures, and they transmit all the forces acting on the prosthesis along the long axis of the abutment tooth. www.indiandentalacademy.com
  31. 31. A tooth supported partial denture is rarely subjected to induced stresses because Leverage type of forces are not involved. There is no fulcrum line around which the partial denture can rotate. www.indiandentalacademy.com
  32. 32. Lever- "A lever is a long bar with a single support around which it rotates when a load is applied to any one of its ends." The support around which the lever rotates is called as the fulcrum. Levers can be of three types namely: 1st - order levers IInd - order levers IIIrd - order levers Each lever modifies the intensity of the force acting on the denture to a different degree. www.indiandentalacademy.com
  33. 33. Ist order lever: In this lever the fulcrum is in the center, resistance is at one end and effort (force) is at the other .These levers are more efficient and easily controlled. This type of lever can occur in patients with distal extension partial dentures. The direct retainer will be the fulcrum, effort end lies on the point where the denture takes up the occlusal load (area where the artificial teeth are located) the load is the region of the anterior end of the major connector . www.indiandentalacademy.com
  34. 34. IInd order lever: In this lever, the fulcrum is at one end, effort is at the opposite end and resis-tance or load is the center. This type of lever action occurs in indirect retention of a removable partial denture. When a displacing force tends to lift a denture from one end (effort), the anterior most point of the major connector will act as the axis of rotation (fulcrum), the intermediate zone of the denture, which is lifted by the force, will form the resistance (load) of the lever. www.indiandentalacademy.com
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  37. 37. IIIrd order lever: In this lever, the fulcrum is at one end, resistance is at the opposite end and effort is at the center e.g. tweezers. This type of lever action does not occur in partial dentures. www.indiandentalacademy.com
  38. 38. Lever action prosthesis: in a Kennedy's Class I In a distal extension partial denture rotation occurs around 3 principal fulcrums. They are: •Horizontal fulcrum line passing between two principal abutment teeth: It acts along the x-axis of the denture. This controls the rotational motion of the denture towards or away from the supporting soft tissues. Forces across this lever produce the most deleterious effect on the supporting tissues and the abutment teeth . www.indiandentalacademy.com
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  40. 40. Second rotational fulcrum line (Sagittal): It extends posteriorly from the occlusal rest of the terminal abutment. It passes along the alveolar crest till the posterior extent of the residual ridge on the same side. It acts along the z-axis of the denture. This fulcrum controls rocking or side-toside movement of the denture that takes place over the crest of the residual ridge . In a Class I condition, there are two such fulcrums extending posteriorly from each primary abutment to the respective retromolar pads. These forces also have severe effects on the soft tissues. www.indiandentalacademy.com
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  42. 42. Third fulcrum line (Vertical): It is vertical and is located on the midline, lingual to the anterior teeth. It acts along the y-axis of the denture. It controls the movement of the denture around the y-axis). www.indiandentalacademy.com
  43. 43. Inclined plane Inclined plane is nothing but two inclined surfaces in close alignment to one another. The direct retainers and the minor connectors slide along the guide planes of the teeth and can act as inclined planes if not prepared correctly. When a force is applied against an inclined plane it may produce two actions: • Deflection of object, which is applying the force (Denture). • Movement of the inclined plane itself (tooth). These results should be prevented to avoid www.indiandentalacademy.com damage to the abutment teeth.
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  45. 45. Designing an RPD to Limit the Effects of Harmful Forces Factors influencing magnitude transmitted to abutment teeth of stresses The various factors that control the amount of stress transmitted to the abutment are: 1. Length of edentulous span. 2. Quality of support of ridge. 3. Response of oral structures to previous stress. www.indiandentalacademy.com
  46. 46. 4. Occlusal relationship of the remaining teeth and orientation of the occlusal plane. 5. Qualities of a clasp. 6. Clasp design. 7. Length of clasp. 8. Material used in clasp construction 9. Abutment tooth surface www.indiandentalacademy.com
  47. 47. Length of edentulous span: The longer the edentulous span, the longer will be the denture base and the greater will be the force transmitted to the abutment tooth. Posterior teeth should be preserved as far as possible to reduce the length. Quality of support of ridge : Large, well-formed" ridges are capable of absorbing greater amounts of stresses than small, thin, or knife edged ridges. Broad ridges with parallel sides permit the use of longer flanges on the denture base, which helps to stabilize the denture against lateral forces. A mucoperiosteum, which is approximately 1 mm thick, gives good support compared to a thin atrophic mucosa. www.indiandentalacademy.com
  48. 48. 3. Response of oral structures to previous stress. The periodontal condition of the remaining teeth, need for splinting and the amount of abutment support remaining, are all a result of the previous stress subjected on the oral tissues. These factors affect the prognosis of the new prosthesis too. 4. Occlusal relationship of the remaining teeth and orientation of the occlusal plane. Improper occlusal relationship and a steep occlusal plane tend to increase the amount of force acting on the denture. www.indiandentalacademy.com
  49. 49. The force applied on natural teeth is 300 pounds and the force acting on artificial teeth is about 30 pounds. Poor occlusal relationship can lead to supra-eruption of the opposing natural teeth. The denture base area against which the occlusal load is applied determines the amount of stress transmitted to the abutment and the edentulous ridge. The occlusal load should be applied on the center of the denture bearing area both anteroposteriorly and buccolingually (the second premolar and first molar region). Artificial teeth should be arranged so that the bulk of themasticatory forces are concentrated here. www.indiandentalacademy.com
  50. 50. 5. Qualities of a clasp A flexible retentive clasp arm decreases the stress that will be transmitted to the abutment tooth. Example: A wrought wire clasp is more flexible than a vertical projection clasp, hence, it decreases the forces acting on the abutment tooth and increases the forces transferred to the edentulous ridge. But it provides less horizontal stability. www.indiandentalacademy.com
  51. 51. 6. Clasp design A clasp should be passive when it is completely seated on an abutment tooth. The passive clasps will exert less stress on the teeth. If a clasp is active throughout the period of denture wear, it will produce injury to the abutment. When the framework is completely seated, the retentive clasp arms should become passive. Disclosing wax can be used to test the proper placement of a framework. A clasp should be designed so that the reci-procal arm contacts the tooth before the retentive tip passes over the greatest bulge of the tooth during insertion and it should be the last compo-nent to lose tooth contact during removal of the prosthesis. www.indiandentalacademy.com
  52. 52. 7. Length of clasp The flexibility of a clasp depends on its length. Doubling the length incre-ases the flexibility by five times. This decreases the stress on the abutment tooth. Using a curved rather than a straight clasp on an abutment tooth will aid to increase the clasp length www.indiandentalacademy.com
  53. 53. 8. Material used in clasp construction A clasp I constructed of chrome alloy will exert more stress on the abutment tooth than a gold clasp because of its greater rigidity. To decrease the stress, the chrome alloy clasps are constructed with smaller diameter. 9. Abutment tooth surface The surface of a gold crown or restoration will offer more functional resistance to the movement a clasp arm than enamel. Therefore, more stress is exerted on the tooth restored with gold than on the tooth with intact enamel. www.indiandentalacademy.com
  54. 54. Controlling stress by design consideration A removable partial denture will always have a destructive effect within the oral cavity. The following factors can be modified to reduce the stresses developed within a denture. 1. Direct retention – the retentive clasp arm is responsible for transmitting the destructive forces to the abutment teeth. A removable partial denture should be designed in such a way that the retention obtained from the clasp is just enough to provide adequate retention to prevent dislodgement of the denture. It should also be remembered that the retentive clasp should be designed such that it is active only during insertion and removal. www.indiandentalacademy.com
  55. 55. 2. Forces of adhesion and cohesion Adhesion is defined as "The physical attraction of unlike molecules for one another" - GPT. Here, Adhesion refers to the attraction of saliva to the denture and the tissues. Cohesion is defined as "The physical attraction of like molecules for one another" - GPT. Here, Cohesion refers to the internal attraction of the molecules of saliva for each other. Forces of adhesion and cohesion can be increased by: Recording an accurate impression so that the denture base fits accurately to the supporting tissues. Increasing the denture bearing area. Atmospheric pressure may also contribute to retention. Generally, major connectors are beaded at their margins so that a tight valve seal is obtained. www.indiandentalacademy.com
  56. 56. 3. Frictional control: Partial dentures should be designed to have maximum number of guide planes. Guide planes are flat surfaces on the teeth that are created such that they are parallel to one another and also to the path of insertion. As the name suggests, guide planes help to guide the denture during insertion. www.indiandentalacademy.com
  57. 57. Preparation of guide planes on the proximal surfaces of the teeth adjacent to edentulous spaces will increase the retention by frictional contact. These planes may be created on the enamel surfaces of the restorations placed on the teeth. During displacement, the components of the denture produce frictional retention along the surface of the guide planes. www.indiandentalacademy.com
  58. 58. Kratochvil (1963) advocated an extension guide surface preparation to eliminate space between the guide plate and the abutment. Maximum contact of the guide surface and the guide plate was desired. A 2-3mm of metal foot extended from the base of the guide plate onto the mucosa of the residual ridge. Binding of the guide plate against the abutment during function (movement of the extension base toward the tissue when biting force is applied over the base) was prevented by physiologic relief of the metal at the framework try-in stage www.indiandentalacademy.com
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  60. 60. Ten years later, Krol (1973) modified Kratochvil's design and created the term RPI clasp (restproximal plate-I-bar). He recommended a much smaller guide surface preparation (2 to 3 mm in height; located in the occlusal third of the proximal surface) and a guide plate that contacted only the bottom 1 mm of the guide surface. Binding or torquing of the abutment was prevented by retaining a small space below the guide surface (into which the guide plate could move during function). The portion of the guide plate in contact with the gingival tissue was relieved. www.indiandentalacademy.com
  61. 61. Demer (1976) proposed another alteration in the design. He concurred with Krol that a slight undercut should be retained below the guide surface. However, he felt that the more gingival location of the guide plate would create the potential for food entrapment between the occlusal aspects of the abutment and the artificial tooth. He recommended that the guide plate contact the proximal surface of the abutment only at the top of the guide surface. Demer also extended the guide plate lingually far enough so that, in combination with the minor connector of the mesial rest, it would provide reciprocation and prevent lingual migration of the abutment. www.indiandentalacademy.com
  62. 62. Research comparing the concepts noted has been inconclusive. Excellent clinical success can be expected using any of the three designs if certain conditions are ensured. First either by initial design or by way of physiologic relief the guide plate must be prevented from binding against the abutment Second the mesial minor connector must have freedom to move between the abutment and the adjacent tooth during function www.indiandentalacademy.com
  63. 63. Third. metal (e.g.. guide plate. plating) located distal to the terminal rest must not be allowed to extend above the height of contour . Fourth, the mesial rest-I-bar-guide plate design should be avoided on mesially inclined terminal abutments because it is extremely difficult to achieve any "releasing" capacity for the guide plate .During function the guide plate will contact the tooth and act as a rest on an inclined plane. Efforts to prevent contact with physiologic relief would create a significant space between the abutment and the prosthesis. www.indiandentalacademy.com
  64. 64. 4. Neuromuscular control The action of lips, cheeks and tongue can be a major factor in the of the denture. A properly contoured denture base can. aid to improve the patient's neuromuscular control of the prosthesis. An overextended denture will 'get constantly dis-placed due to the neuromuscular action. Frequent displacement of these denture~ will lead to excessive stress on the abutment. 5. Clasp position. Position of the retentive clasp in relation to the height of contour is more important in retention and in controlling stresses than the number of clasps present in the entire prosthesis. 'Consider the following example: It is easier to pullout a pole immersed in sand from its tip than at a point just above the level of the sand. Similarly, a clasp located deep in the undercut will be more difficult www.indiandentalacademy.com to remove.
  65. 65. 6. Number and placement of clasps The number of clasps used and their placement determine the type of stress developed within a denture" Removable partial dentures with four clasps are described to have a quadrilateral configuration. Similarly removable partial dentures with three and two clasps are described to have a tripod and bilateral configuration respectively. Quadrilateral configuration is the most efficient in controlling the stresses developed within a denture. Additional clasps are usually added to increase the stability and force distribution of the partial dentures with few clasps www.indiandentalacademy.com
  66. 66. Quadrilateral configuration This design involves the use of four clasps. It is used commonly for Kennedy's class III arches particularly when there is a modification space on the opposite side of the arch. A retentive clasp should be positioned on each abutment tooth adjacent to the edentulous spaces. In a Kennedy's class III arch with no modification, one clasp is placed as far posterior on the dentulous side as possible and the other is I placed as far anterior as possible depending on the availability of space and aesthetics. This retains the quadrilateral concept and is effective in controlling the stress. www.indiandentalacademy.com
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  68. 68. Tripod configuration This design involves the use of three clasps. It is used for Kennedy's class II arches. In class II cases, rotational forces act on the prosthesis producing stress over the terminal abutment tooth. Adding two abutments on the opposite side helps to stabilize and distribute the forces. One clasp is placed on the posterior most abutment of the edentulous space, and the other two are placed on the anterior and posterior ends of the dentulous quadrant. If a modification space is present, the anterior and posterior teeth adjacent to the modification space are clasped. If a modification space is not present, the posterior clasp is placed as posterior as possible. The placement of the anterior clasp is determined by the availability of interocclusal space and aesthetics. www.indiandentalacademy.com
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  70. 70. Bilateral configuration: This design is used for a Kennedy's class I partially edentulous arch. The terminal abutment teeth are clasped. The clasps have a very minimal neutralizing effect on the stresses developed by leverage-induced forces on the denture base. These stresses should be controlled using other methods. Additional clasps can be used at the anterior end to convert the design into a quadrilateral configuration. www.indiandentalacademy.com
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  72. 72. 7.Clasp Design Circumferential cast clasp The movement circumferential cast clasp originating from a distal occlusal rest on the terminal abutment tooth and engaging a mesiobuccal retentive undercut should not be used on a distal extension removable partial denture. The terminal of this clasp reacts to movement of denture base toward the tissue by placing a distal tipping, or torquing, force on the abutment tooth. This particular force is the most destructive force a retentive clasp can exert. This clasping concept must be avoided at all costs. www.indiandentalacademy.com
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  74. 74. The reverse circlet, a cast circumferential clasp that approaches a distobuccal undercut from the mesial surface of a terminal abutment tooth, , is acceptable. The effect on the abutment tooth is reversed from that of the conventional circumferential clasp. www.indiandentalacademy.com
  75. 75. Vertical Projection, or Bar, Clasp. The vertical projection, or bar, clasp is used on the terminal abutment tooth on a distal extension partial denture when the retentive undercut is located on the distobuccal surface. It is never indicated when the tooth has a mesiobuccal undercut. The bar clasp functions in a manner similar to the reverse circumferential clasp. As the denture base is loaded toward the tissue, the retentive tip of the T clasp rotates gingivally to release the stress being transmitted to the abutment tooth. The bar clasp does not produce the wedging force sometimes produced by the reverse circumferential www.indiandentalacademy.com clasp
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  77. 77. One school of thought on the philosophy of removable partial denture design has advocated omitting the distal occlusal rest from the terminal abutment in favor of a mesial rest when a bar clasp is used. The belief is that a distal rest would cause the fulcrum line around which the denture tends to rotate to be distal to the retentive clasp terminal. Theoretically the retentive tip could not release if the denture base were to move toward the tissue. Another advantage claimed for moving the occlusal rest more anteriorly is that the lever arm (the distance from the rest to the denture base) is increased, which causes the force direct toward the residual ridge to be more vertical and thus better tolerated by the ridge. www.indiandentalacademy.com
  78. 78. If the distal rest, or a rest adjacent to any edentulous space, is omitted, a space is left between the framework and tooth surface in which food debris will collect and be trapped against the most critical and sensitive area of the tooth, the gingival crevice. www.indiandentalacademy.com
  79. 79. Combination clasp When a mesiobuccal undercut exists on an abutment tooth adjacent to a distal extension edentulous ridge, the combination clasp can be employed to reduce the stress transmitted to the abutment tooth. Wrought alloy wire, by virtue of its internal structure is more flexible than a cast clasp. It can flex in nay spatial plane, whereas a cast clasp flexes in the horizontal plane only. The wrought wire retentive arm has a stress breaking action that can absorb torsional stress in both the vertical and horizontal planes. A cast circumferential clasp under the same circumstances would transmit most of the leverage www.indiandentalacademy.com induced stress to the abutment tooth.
  80. 80. Splinting of Abutment Teeth Adjacent teeth may be splinted by means of crowns to control stress transmitted to a weak abutment tooth. Splinting two or more teeth actually increase the periodontal ligament attachment area and distributes the stress over a larger area of support. Splinting is also indicated when the proposed abutment tooth has either a tapered root or short roots such that there is not an acceptable amount of periodontal ligament attachment present. www.indiandentalacademy.com
  81. 81. One of the most important and frequently indicated needs for splinting is when the terminal abutment tooth on the distal extension side of the arch stands alone, that is, an edentulous space exists both anterior and posterior to it. This situation is most often seen in second premolars, both maxillary and mandibular. Such a premolar is potentially a weak abutment because of the rotational forces it must withstand. Splinting of this tooth to the tooth anterior to it, usually the canine, should be accomplished with a fixed partial denture. www.indiandentalacademy.com
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  83. 83. Splinting by means of clasps on the removable partial denture is possible under some conditions. This should not be attempted if fixed splinting is possible because it is considered a compromise form of treatment. It is indicated when no other approach is feasible. The splinting consists of clasping more than one tooth on each side of the arch, using a number of rests for additional support and stabilization, and preparing guiding planes on as many teeth as possible to contribute to horizontal stabilization of the teeth and the prosthesis. The multiple clasps should not all be retentive. www.indiandentalacademy.com
  84. 84. A principal advantage of splinting with a removable prosthesis is cross arch stabilization. The teeth on both sides of the arch, supported by lingual plating, can be held together rigidly to prevent damage from horizontal forces. Other forms of removable prosthesis such as the swing-lock partial denture can be used to splint teeth effectively. www.indiandentalacademy.com
  85. 85. Indirect retention An indirect retainer is a part of the removable partial denture that helps the direct retainer prevent displacement of the distal extension denture by resisting the rotational movement of the denture around the fulcrum line established by the occlusal rests. The indirect retainer is located on the opposite side of the fulcrum line from the denture base. www.indiandentalacademy.com
  86. 86. The indirect retainer is essential in the design of Classes I and II partial dentures. By using the mechanical advantage of leverage, it counteracts the forces attempting to move the denture base away from the residual ridge by moving the fulcrum farther from the force. In a Class I prosthesis the fulcrum line would be moved from the tips of the retentive clasp to the most anteriorly located component, the indirect retainer www.indiandentalacademy.com
  87. 87. Because the indirect retainer resists lifting forces at the end of a long lever arm, it must be positioned in a definite rest seat so that the transmitted forces are diverted apically through the long axis of the abutment tooth. The indirect retainer also contributes, to a lesser degree, to the support and stability of the denture. The need for indirect retainers varies with the type of removable partial denture. In a class I arch indirect retention must always be used. The indirect retainer or retainers must be positioned as far anterior to the fulcrum line as possible. www.indiandentalacademy.com
  88. 88. Although indirect retention is not as critical in a Class II arch as in a Class I arch, it is still required. If a modification space exists on the tooth supported side, abutment teeth on both sides of the space should be selected. The fulcrum line will run through the most posterior abutment on the tooth supported side and the terminal abutment on the distal extension side. The most anterior abutment on the tooth supported side, with its rest and clasp assembly, may be located far enough anterior to the fulcrum line to serve as the indirect retainer. However, a definite rest seat positioned even farther anterior, if possible, may increase the effectiveness of the indirect retention. www.indiandentalacademy.com
  89. 89. If there is no modification space in the tooth supported side of the arch, the most posterior tooth on that side with favorable contours for clasping should be used as one abutment. This design places the fulcrum line in a posterior position, allowing the indirect retainer to be placed farther from the fulcrum line. To develop a good triangular configuration of clasping, an additional abutment tooth with suitable contours for clasping should be selected as far anterior on the tooth supported side as possible. this abutment tooth, with its rest and clasp assembly, may serve as the indirect retainer if it is located far enough anterior to the fulcrum line. www.indiandentalacademy.com
  90. 90. For the class III arch, indirect retention is not ordinarily required because there is no distal extension denture base to create a lever arm. However, auxiliary rests may be needed to provide additional vertical support for a long lingual bar major connector or an extensive palatal major connector. Auxiliary rests are always indicated for support of a lingual plate major connector. www.indiandentalacademy.com
  91. 91. There are times when the contours of the posterior abutment teeth of a Class II or III partial denture are not suitable for retention and the prognosis for the teeth may be such as not to warrant construction of cast gold restorations. These teeth, even with reduced periodontal support, can usually provide support and stability for the prosthesis. An occlusal rest and non retentive stabilizing clasp should be designed for them. Under these circumstances the clasp design for the anterior abutment teeth need not be the same as for the terminal abutments on a class I or II partial denture, but indirect retention is required. www.indiandentalacademy.com
  92. 92. The consideration for the Class IV arch is the reverse of that for class I and Class II arches, and the design of the partial denture, in order to resist the rotational forces in the opposite direction, must also be reversed. The lever arm is anterior to the fulcrum line, so that indirect retainer must be located as far posterior as possible. Occlusal rests and clasp assembles are placed on the most posterior teeth with favorable contours for both direct retention and support. www.indiandentalacademy.com
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  94. 94. Essential of Design A. Classes I and II Direct retention a. Retention should not be considered the prime objective of design 1. The main objectives should be the restoration of function and appearance and the maintenance of comfort, with great emphasis on preservation of the health and integrity of all the oral structures that remain. b. Close adaptation and proper contour of an adequately extended denture base and accurate fit of the framework against multiple, properly prepared guide planes should be used to help the retentive clasp arms retain www.indiandentalacademy.com the prosthesis.
  95. 95. Clasps a. The simplest type of clasp that will accomplish the design objectives should be employed. b. The clasp should have good stabilizing qualities, remain passive until activated by functional stress, and accommodate a minor amount of movement of the base without transmitting a torque to the abutment tooth. www.indiandentalacademy.com
  96. 96. c. Clasps should be strategically positioned in the arch to achieve the greatest possible control of stress. 1. A class I prosthesis usually requires only two retentive clasp arms; one on each terminal tooth. a) If a distobuccal undercut is present, the vertical projection retentive clasp is preferred. www.indiandentalacademy.com
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  98. 98. b) If a mesiobuccal undercut is present, a wrought wire clasp is indicated. A cast of circumferential type clasp should not be used. c)The reciprocal or bracing arm must be rigid. This component of the clasp system can be www.indiandentalacademy.com replaced by lingual plating.
  99. 99. 2. A class II Prosthesis should usually have three retentive clasp arms. www.indiandentalacademy.com
  100. 100. a. The distal extension side should be designed with the same consideration as for as Class I prosthesis. b. The tooth supported, or modification, side should usually have two retentive clasp arms; one as far posterior and one as far anterior as tooth contours and esthetics permit. It a modification space is present, it is usually most convenient to clasp a tooth anterior and a tooth posterior to the edentulous space. 1. The type of clasp and position of the retentive undercut can be selected for convenience. 2. Rigidity is required for all bracing arms. Lingual plating may be substituted. www.indiandentalacademy.com
  101. 101. 3. Rests a)Teeth should be selected for rest preparation to provide maximum possible support for the prosthesis. b)Rest seats should be prepared so that stress will be direct along the long axis of the teeth. c) Rests should be placed next to the edentulous space with few exceptions. www.indiandentalacademy.com
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  103. 103. 4. Indirect Retention a)Indirect retention should be employed to neutralize unseating forces. 1. The indirect retainer should be located as far anterior to the fulcrum line as possible. www.indiandentalacademy.com
  104. 104. 2. Two indirect retainers should generally be used in a Class I design, whereas one placed on the side opposite the distal extension base may be adequate in a Class II design. www.indiandentalacademy.com
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  107. 107. 3.The indirect retainers should be positioned in teeth prepared with positive rest seats that will direct forces along the long axis of the tooth. b) Lingual plating can be used to extend the effectiveness of indirect retention to several teeth. It must always be supported by positive rest seats. www.indiandentalacademy.com
  108. 108. 5. Major Connector a. The simplest connector that will accomplish the objectives should be selected. 1. The major connector must be rigid. 2. It must not impinge on gingival tissue. b. Support from the hard palate should be used in the design of the maxillary major connector when it would be beneficial. www.indiandentalacademy.com
  109. 109. c. Extension of the major connector onto the lingual surfaces of the teeth may be employed to increase rigidity, distribute lateral stresses, improve indirect retention, or eliminate potential food impaction areas. Lingual plating should always be supported by adequate rest seats. www.indiandentalacademy.com
  110. 110. 6. Minor Connectors a)Minor connectors must be rigid. b)Minor connectors should be positioned to enhance comfort, cleanliness, and the placement of artificial teeth. www.indiandentalacademy.com
  111. 111. 7. Occlusion a.Centric occlusion and centric relation should coincide. b. A harmonious occlusion should be established with no interceptive contacts and with all eccentric movements dictated by or in harmony with, the remaining natural teeth. www.indiandentalacademy.com
  112. 112. c. Artificial teeth should be selected and positioned to minimize stresses produced by the prosthesis. 1.Smaller and / or fewer teeth, and teeth that are narrower buccolingually maybe selected. 2. For mechanical advantage teeth should be positioned over the crest of the mandibular ridge when possible. 3. Teeth should be modified if necessary to produce sharp cutting edges and ample escape ways. www.indiandentalacademy.com
  113. 113. 8. Denture base a. The base should be designed with broad coverage so that the occlusal stresses can be distributed over as wide an area of support as possible. 1.The extension of the borders must not interfere with functional movement of the surrounding tissues. b. A selective pressure impression should record the residual ridge in a functional form. c. The polished surfaces should be contoured to enable the patient to exercise maximum neuromuscular control. www.indiandentalacademy.com
  114. 114. B. Class III 1. Direct retention a. Retention can be achieved with much less potential harmful effect on the abutment teeth than with the Class I or II arch. b. The position of the retentive undercut on abutment teeth is not critical. www.indiandentalacademy.com
  115. 115. 2. Clasps a. The quadrilateral positioning of direct retainers is ideal. b. The type of clasp selected is not critical 1. Tooth and tissue contours and esthetics should be considered, and the simplest clasp possible selected. 2. If restorations are required to correct tooth contours, the wax patterns must be shaped with the surveyor. c. Bracing arms must be rigid. www.indiandentalacademy.com
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  117. 117. 3. Rests a. Rest seats should be prepared next to the edentulous space when possible. b. Rests should be used to support the major connector and lingual plating. 4. Indirect retention a. Indirect retention is usually not required b. If one or both of the posterior abutment teeth are used for vertical support alone without retentive clasp arms, the entire design must be follow the requirements of a Class II or II design. www.indiandentalacademy.com
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  119. 119. 5. Major and minor connectors a. They must be rigid and meet the requirements as for a Class I or II design. same 6. Occlusion a.The requirements for occlusion are the same as for a Class I or II design 7. Denture base a. A functional type impression is not required. b. The extent of coverage of the residual ridge areas should be determined by appearance, comfort and the avoidance of food impaction areas. www.indiandentalacademy.com
  120. 120. C. Class IV 1. The movements of this type of removable partial denture and the resulting stresses transmitted to the abutment teeth are unlike the pattern seen in any other type of prosthesis. 2. The esthetic replacement arrangement teeth may of the anterior necessitate their placement anterior to the crest of the residual ridge, resulting in potential tilting leverage. www.indiandentalacademy.com
  121. 121. a.Every effort should be made to minimize these stresses. Some possibilities follow : b. As much of the labial alveolar process should be preserved as possible. c. A central incisor or other tooth should be retained to serve as an intermediate abutment or as an over denture abutment. 1. A critical evaluation of each remaining tooth in the arch should be made with the intent of retaining as many teeth as possible. The shorter the edentulous area, the less will be the harmful tilting leverage. www.indiandentalacademy.com
  122. 122. 3. Strategic clasp position should be used. The quadrilateral configuration, with the anterior clasps placed as far anterior and the posterior clasps placed as far posterior as possible, would be the idea. 4. The major connector should be rigid, and broad palatal coverage should be used in the maxillary arch. 5. Indirect retention should be used as far posterior to the fulcrum line as possible. a. An ideal quadrilateral configuration of clasping may preclude the need for an additional indirect retainer. 6. A functional type of impression may be indicated www.indiandentalacademy.com if the edentulous area is extensive.
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  124. 124. Denture Base The denture base should be designed to cover the maximum amount of soft tissue available. The denture base should have long flanges in order to stabilize the denture against horizontal movements. Distal extension denture bases must always extend into the retromolar pad area in the mandible and cover the entire tuberosity in the maxilla. The denture base will displace the soft tissues on the ridge during functional occlusal load. Hence, a functional impression should be recorded to fabricate the denture in order to improve its adaptation and avoid excessive tissue displacement. www.indiandentalacademy.com
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  126. 126. Major connector The major connector of choice in the maxillary arch is the broad palatal major connector because it can distribute stresses over a large area. In the mandibular arch, a lingual plate with rests can aid to distribute functional stresses to the remaining teeth. Functions of the major connector include rigidity, retention, and stability. Major connectors should be selected to best suit the patient. It should distribute the occlusal load over a wide area at the same time produce the least amount of stress. www.indiandentalacademy.com
  127. 127. There are three important principles for design exclusively used for a major connector. They are L-bar or L-beam principle. Circular configuration Strut configuration www.indiandentalacademy.com
  128. 128. L-bar or L-beam principle The L-beam or L-bar or linear beam theory states that the flexibility of a bar is directly proportional to the length of the bar and inversely proportional to its thickness. When a load is placed on the bar or beam supported at its ends, maximum stress is present in the centre and zero stress at the supported ends. A bar supported at both its ends can be divided into two parts namely the parabolic and quartic parts. The parabolic part forms the middle 2/4th of the distance between the supports and the remaining 1/4th on the either sides of the bar form the quartic part. The parabolic part shows maximum stress concentration and the quartic part shows minimum or zero stress concentration. www.indiandentalacademy.com
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  130. 130. Hence, if we design a bar such that it has a smaller parabolic part and a larger quartic part it will be less flexible. The material becomes more rigid (less flexible) without adding bulk to the bar. If we bend the bar on either side, the length of the bar lying in the quartic part will increase. Now apply this concept in the design of a major connector. The palate has a flat vault and two lateral slopes. If the slopes are shallow, the quartic part of the major connector also decreases leading to increased flexibility of the prosthesis under occusal load. The major connector should be located and designed such that it lies over the steeper slopes in the plate www.indiandentalacademy.com
  131. 131. Hence, broad palatal major connectors, palatal strap major connectors can be fabricated with lesser bulk of material (but with adequate rigidity) because it extends in three planes (one central vault and two lateral slopes) with the length of the quartic part (the two lateral slopes) being greater than the parabolic part. www.indiandentalacademy.com
  132. 132. Circular configuration The advantages of a circle is that is a continuous unit without an end. Any force acting on a circular bar can be easily distributed all along the circumference. Hence, a circular bar is more rigid than linear bar with the same area of cross section. This concept can be used to reduce the bulk of the major connector with a circular configuration (anteroposterior double palatal bar and close horse shoe). www.indiandentalacademy.com
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  134. 134. Strut Configuration According to this configuration, a straight bar bent at its ends near the support is more rigid because, the bent slopes of the bar aid to transfer the load acting on the horizontal portion. This is similar to the linear bar theory (L-beam discusses stress concentration but struts discuss stress distribution). The major connector on a narrow vault is more rigid than a major connector extending over a shallow vault. In other words, the major connector extending in two different planes has more rigidity. This concept is seen in the anterior plate of the double palatal bar, where, the slope of the rugae area acts as an additional strut. www.indiandentalacademy.com
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  136. 136. Minor connector The minor connector joins the major connector to the clasp assembly and the guidance planes located on the abutment tooth surface. The minor connector should be designed such that it does not interfere with the placement of the artificial teeth, tongue etc. The minor connectors used for auxiliary rest aid in indirect retention. It has the following functions; It provides horizontal stability to the partial denture against lateral forces on the prosthesis. The abutment tooth receives stabilization against lateral forces by the contact of the minor connector. www.indiandentalacademy.com
  137. 137. Rests Rests help control stresses by directing the forces acting on the denture to the long axis of the abutment teeth. The floor of the rest seat should be less than 90o to a tangent line drawn parallel to the long axis of the tooth. In class I and Class II partial dentures, the rest seat preparation must be saucer shaped. Adding rests on additional teeth decreases the amount of occlusal load on each tooth and helps to distribute the occlusal load equally to all the abutment teeth. www.indiandentalacademy.com
  138. 138. I-BAR REMOVABLE PARTIAL DENTURES The i -bar removable partial denture, a subject of discussion since Kratochvil introduced a design in 1963. Has achieved considerable status as a treatment modality in recent years. Mesial rest, i-bar, and guide plane Kratochivil addressed his attention to the tooth mucosa junction and developed a system that includes a mesial rest, i-bar retainer, and long guide planes that extend onto the tooth tissue junction. The i-bar retainer is one element in the design equation www.indiandentalacademy.com and as such has been overemphasized
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  140. 140. Rests The function of rests is to provide vertical support against occlusal forces and control and relationship of the prosthesis to supporting structures The ideal anterior rest is the crescent shaped cingulum rest, which places vertical force low on the tooth and provides maximum stabilization. The cingulum rest can be prepared directly in enamel on bulky canines and maxillary central incisors or can be implemented with a cast restoration. The incisal is used on mandibular anterior teeth when esthetics allows. www.indiandentalacademy.com
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  143. 143. Premolar rests are prepared in the marginal and the triangular ridges and molar rests extent into the central fossa. In distal extention cases the most distal rests are placed on the mesial aspect of the abutment teeth for the following two reasons (kratochvil, 1963 ). I. Anterior placement of the rest (fulcrum) helps verticalize the forces occlusion on bearing mucosa under the denture base extension. II. The mesial rest directs tipping forces on the abutment mesially and tends to move the abutment tooth into firm contact with the support www.indiandentalacademy.com of the anterior teeth
  144. 144. Proximal plates Parallel guide planes are prepared on all proximal tooth surfaces adjacent to edentulous spaces. The proximal plate covers the guide plane from marginal ridge to the tooth tissue junction and extends onto the attached gingiva for 2 mm. This configuration serves many functions 1. Provides horizontal stability 2. Reunites and stabilizes the arch 3. Increases retention because of parallelism and because dislodgement is limited to the part of insertion. 4. Protects the tooth tissue junction by preventing food impaction and because of metal coverage in this area. 5. Provides reciprocation. www.indiandentalacademy.com 6. Distributes occlusal force throughout the arch
  145. 145. Major connector Major connectors are designed for maximum rigidity and gingival health. The combination anteroposterior strap is preferred for maxillary partial dentures, and lingual bar is preferred for mandibular partial dentures. Maxillary major connectors are placed 5 to 6 mm away from tooth tissue junctions, and mandibular major connectors are placed on attached mucosa or at least 4 mm away from the gingival crest. www.indiandentalacademy.com
  146. 146. Minor connectors Minor connectors connect rest, proximal plates, and retainers to the major connector. They also help provide horizontal stability. Denture base connectors One-millimeter relief is provided for retention, and the retentive meshwork is placed on the lingual aspect of the ridge and extends only to the crest of the ridge to avoid interference with tooth placement on the facial side of the ridge. www.indiandentalacademy.com
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  148. 148. Direct retention The i bar provides retention against vertical displacement, but this retention is augmented considerably by the parallelism of guide planes that. In most situations limit displacement to the path of insertion. The i-bar is an infrabulge retainer with a configuration designed to minimize the deleterious effect that over contoured retainers have on the health of both tooth and gingiva. The arm is long and tapering with a half round cross section. The tip, which flexes, engages an undercut at the height of mesiodistal contour or mesial to it. The position of the i -bar in relation to the height of contour is essential to this design because proper positioning allows the tip to move passively into the mesial embrasure space when the extension base receives occlusal loading. The retainer engages the undercut www.indiandentalacademy.com vertical displacement. area and resists
  149. 149. The following important advantages are gained with the i-bar configuration: 1 . Because tooth contour is not altered, food accumulation against the tooth surface is minimized 2. The i -bar is passive in its relationship to the abutment tooth except against vertical displacing forces www.indiandentalacademy.com
  150. 150. The disadvantages of the i-bar are of consequences only if the design concept is not fully deployed I. Less horizontal stability than other retentive elements. 2. Less retention. When used in the tooth-borne situation, the i-bar retainers can be placed for convenience relative to retentive undercuts and esthetics. In extension situations, the retentive i-bars are placed with respect to the axis of rotation. www.indiandentalacademy.com
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  152. 152. Indirect retention Indirect retention is provided by rests placed on secondary abutments as far from the axis of rotation and the edentulous area as possible to stabilize the major connector. Although recent studies have cast doubt on the effectiveness of indirect retention against displacing force (frank and nicholls, 1977), the indirect retainer has been shown to be effective in redistributing occlusal force more evenly throughout the entire dent alveolar structure (mcdoweii, 1978 www.indiandentalacademy.com
  153. 153. Design variations Physical considerations and alternate components Most problems in design application are related to tipped abutment teeth, soft tissue contours or frenum attachments. Tipping of abutment teeth affects retention in several ways. Buccolingual tipping frequently eliminates the necessary retention in undercut or creates an excessive undercut when tilting creates an excessive undercut, the solutions include enameloplasty to reduce the undercut or a cast restoration to provide ideal contours. When lack of retention exists, the solutions are preparation of an undercut or the use of a lingual undercut for retention. Severe tipping is most effectively controlled www.indiandentalacademy.com with a cast restoration.
  154. 154. The attachment of the buccinator muscle adjacent to mandibular molars will occasionally obliterate the vestibule in this area. Lack of attached gingiva further aggravates the problem of i-bar placement. An alternative to placement of an i-bar in an inadequate vestibule is again the use of a lingual i-bar for retention and a buccal rest extension for reciprocation www.indiandentalacademy.com
  155. 155. RPI Rest, proximal plate, and i-bar In agreement with kratochvil’s basic design but unable philosophically to accept the amount of tooth preparation that is sometimes necessary to execute it, krol developed a modification that studiously avoids tooth preparation the stated emphasis in krol's system is stress control with minimal tooth coverage and minimal gingival coverage the clasp system includes the three elements of kratochvil's system: mesial rest, proximal plate, and i -bar. Each element however has undergone significant change to meet krol's criteria. Rest preparations are less extensive in the rpi system. The mesial rest extends only into the triangular fossa, even in molar preparations, and canine rests are often circular concave depressions prepared in the mesial www.indiandentalacademy.com marginal ridge.
  156. 156. The prepared guide plane is 2 to 3 mm high occlusogingivally and the proximal plate contacts only 1 mm of the gingival portion of guide plane. The i-bar terminus is pod shaped to allow more tooth contact and placement tends towards the mesial embrasures space to achieve more efficiency reciprocation from the diminutive proximal plate. www.indiandentalacademy.com
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  158. 158. Swing lock removable partial dentures In the swing lock removable partial dentures first described by Dr Joe .J. Simmons in the Texas dental journal in February 1963, all or several of the remaining teeth are used to retain and stabilize the prosthesis against vertical displacement. The prosthesis consists of a hinged buccal or labial bar attached to a conventional major connector. Retention and stabilization are provided by the bar. The labial bar is generally designed with small vertical projection arms that contact the labial or buccal surfaces of the teeth gingival to the height of contour. These vertical arms look like an i or t bar and provide both retention and stabilization for the www.indiandentalacademy.com prosthesis.
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  161. 161. Advantages The primary advantages of the swing lock concept of treatment is that it provides a relatively inexpensive method of using all or most of the remaining teeth for the retention and stabilization of a prosthesis because the construction of a swing lock removable partial denture is relatively simple and inexpensive, it can be used in situations for which more conventional types of treatment may appear hopeless. www.indiandentalacademy.com
  162. 162. Disadvantages A swing lock prosthesis can produce a relatively poor esthetic result for patients with short of extremely mobile lips. A long distal extension base is likely to move toward the tissue under the forces of occlusion. This movement can tip the teeth grasped by the prosthesis www.indiandentalacademy.com
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  164. 164. Indications. 1. Too few remaining natural teeth for a removable partial denture of conventional design 2. Remaining teeth too mobile to serve as abutment teeth for remaining teeth for conventional design. 3. Position of remaining teeth too mobile not favorable for a conventional design. 4. To retain a prosthesis for patients who have lost large segments of teeth and alveolar ridge through traumatic injury www.indiandentalacademy.com
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  168. 168. Selection of metal for swing lock framework Chrome alloy is the material of choice for the metallic framework of a swing lock removable partial denture. Gold is contraindicated because the hinge and lock mechanisms show noticeable wear in a relatively short time when gold is used and gold component must be made fairly bulky compared with chrome components to provide the necessary rigidity and strength. www.indiandentalacademy.com
  169. 169. Design The swing lock removable partial denture consists of a labial or buccal bar which is fastened to the partial denture by a hinge at one end and a latch at the other end. Reciprocation is achieved through a lingual plate. The basic swing lock design incorporates a lingual path of insertion. a hinge connection of the labial bar to the framework with a locking mechanism on the opposite end of the bar, and a labial opening arch of the retentive bar with struts and / or veneers contacting the infrabulge area of the labial surface of the teeth. www.indiandentalacademy.com
  170. 170. It braces and supports a natural tooth that is being occlusally loaded by the contact of the retentive labial struts and the lingual plate loaded by the contact of the retentive labial struts and the lingual plate on opposite sides of the tooth. Since a rigid major connector is essential, a continuous lingual plate or bar contacting the suprabulge region of remaining anterior teeth and the height of contour of the posterior teeth used for stabilization in both the mandible and maxillae. In the maxillae the connectional designs are used i.e. anterior- posterior bar, or complete metal palate. www.indiandentalacademy.com
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  172. 172. Controlled direct retention and stabilization on all or part of the remaining teeth resists dislodgement of the swing lock removable partial denture. This is accomplished by a labial bar, with one end extending from the framework by a hinge, and the other end of the bar terminating with a latch attached to the framework. From the labial or buccolabial bar, vertical struts similar to I-bar clasp arms traverse the free margins o the gingivae (with proper relief) and passively contact the teeth in the gingival third. www.indiandentalacademy.com
  173. 173. These struts are rigid since they swing into any undercut by the hinged bar and act as both the retentive and stabilizing elements To avoid torquing forces on the anterior teeth in distal extension situations, these struts are adjusted to incorporate some freedom and allow for movement of the denture base in friction. If exposure of the roots of anterior teeth due to gingival recession or periodontal surgery is an esthetic problem, a gingiva colored acrylic resin veneer can be processed to the labial bar with proper relief for the marginal gingiva. Occlusal rest can be used to direct forces to the abutment teeth if desired but they are not indicated in most distal extension situations. www.indiandentalacademy.com
  174. 174. CONCLUSION A properly designed RPD in combination with a well planned comprehensive treatment will contribute to the preservation of the remaining teeth, bone and gingiva by maintaining the gingiva, tooth position and occlusion. It will also improve mastication and speech and enhance appearance. The emphasis is on design as it is one of the major weak link in the process of total care. The results of a detailed clinical and radiographic examination should dictate the ultimate design of the prosthesis. www.indiandentalacademy.com
  175. 175. REFERENCES :1.An Atlas of Removable Partial Denture Design Russell J. Stratton Frank J. Wieblt 2.Partial Dentures John Osborne George Alexander Lammie 3. Clinical Removable Partial Prosthodontics Stewart Rudd Kuebker 4.Textbook of Prosthodontics Deepak Nallaswamy www.indiandentalacademy.com
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