Component Parts of A Partial Denture

Component Parts of A Partial Denture
Copyright by Prosthodontic Department, UDM

1. Component Parts of a Partial Denture Dr. Khin Than Kyi Associate Professor Dept. of Prosthodontics

2. saddles Connectors Direct Retainers (clasps) Indirect retainers Occlusal and incisa rests

3. Saddles Part of a denture which carries the artificial teeth Tooth borne or mucosa-borne and different saddles may occur in the same denture Tooth borne saddles are made in metallic alloy Mucosa-bone saddles constructed metal or acrylic, for reason of economy The periphery of the denture in the saddle region should always reach to the functional depth of the sulcus

4. Connectors A major connector is part of a denture which joins one saddle to another, a minor connector joins a clasp, rest or indirect retainer to a saddle Major connector Palatal plates and bars Lingual plates and bars Labial plates and bar

5. Palatal plates Should be as thin as possible with the required strength and should be dammed along free anterior and posterior borders in order that the tongue may pass from mucosa to denture without encountering an edge Food particles may not collect under the denture This damming must not be too deep or too broad because mucosa covering the bone is rather thin

6. Advantages wider and thinner in section than bars transfer some of the occlusal load to the palate nonmetallic denture base material is used in economic point do not worry the tongue if thicker

7. Disadvantages it covers more tissue than a bar

8. Palatal bars Always made of alloy and should be as thin as possible commensurate with strength They must fit the palatal tissue accurately In mucosa-bone dentures if may be necessary to form a relief on the cast The position of a palatal bar will very according to the position of the saddle areas to be connected and will be in the posterior third of the palate, middle third or the anterior third

9. A posterior palatal bar is the most suitable is less conspicuous to the tongue Fulfils the function of an indirect retainer Areas less frequently associated with bony prominences or with thin mucosa A middle palatal bar can seldom act as an indirect retainer

10. An anterior palatal bar can be used in conjunction with a posterior bar to increase the rigidity and strength of the denture It can also act as an indirect retainer and as link to an anterior saddle from posterior saddles

11. Lingual plates may be made of acrylic or alloy cast alloy plates should copy the anatomical form of the lingual surface of the teeth and mucosa and if made thin, are delightfully smooth to the tongue act as indirect retainers and provide good bracing against lateral load

12. Lingual bars usually made of metal and are used to connect two lower saddles or one lower saddle with a clasp on the opposite side should be placed midway between the gingival margins of the teeth and the highest functional position of the floor of the mouth Cast lingual bar is the most satisfactory type

13. Tissue relief is provided during construction of the bar by swaging metal foil over the surface of the cast

14. Contraindication Lack of space between the functional position of the floor of mouth and gingival margins Undercut lingual alveolar process Lingually inclined teeth A continuous clasp also known as a continuous bar, positioned on the cingulae of the incisor teeth to act as an indirect retainer or supplementary rest

15. Advantage avoiding coverage of gingival margins but not well tolerated by the tongue

16. Sublingular bar is an improvement on the lingual bar - lies in the anterior lingual sulcus , but more difficult to make - act as rigid major connector

17. Sublingular bar Con- - kidney shaped in section - the lingual sulcus is relieved with 0.06 mm metal foil to avoid any trauma against the lingual tissues

18. Labial bars and plates always made of cast alloy but are not use as they tend to worry the patient's lips used when lingual inclination of the standing teeth, presence of excessive lingual under cuts or problems such as torus mandibularis made as broad and as thin as the sulcus depth and strength

19. Indirect retainers a  component  of a removable partial denture that assists the direct retainers in preventing  displacement  of the  distal extension  bases by functioning through  lever action on the opposite side of the fulcrum  line when the denture base attempts to move an occlusal direction or in a rotational path about the fulcrum line”( GPT 9)

20. Indirect retainers So called because it retains in position some part of a denture remote from itself It works on the principle of the counter balance This principle can be employed in partial dentures whenever a free end saddle is present and cannot be retained adequately by the clasp fitted to the abutment tooth

21. It shifts the fulcrum line away from the point of application of the force, there by counteracting the lifting force and stabilizing the denture

22. Reduces the antero -posterior twisting leverage Helps stabilization Acts as a guiding plane May act as auxiliary rest to support major connector It counteracts horizontal force by providing support and stability to the denture

23. Indirect retainers are best made of cast alloy as part of a major connector so that they fit the teeth accurately and appear as unobtrusive as possible An occlusal or incisal rest or various parts of a denture may act as an indirect retainer

24. The important points are : - They should be used only in periodontally sound teeth - The should contact as many teeth as possible to reduce the possiblity of moving teeth by the application of excessive forces - Extension of the denture base on mucosa are effective provided the mucosa is firm - The can only function in conjunction with direct retainers (clasps)

25. Occlusal rests The forces acting on the occlusal surface of a partial denture must be absorbed by the alveolar bone If the area of mucosa covered by the denture is sufficiently large, forces will be absorbed by the soft tissue and transmitted to the bone If the area of a partial denture is small, the force applied to unit area of the soft tissue will be above its tolerance and pain and ulceration will ensue with destruction of hard and soft tissue

26. Transferring the occlusal loads to the bone are required The parts of the denture which transmit the loads to the teeth are called supporting elements or rests The main function of rest is to transfer some or all of the c lenched and masticatory loads to the natural teeth

27. Other 4 important functions are - act as contact points and prevent food packing between the denture and the natural tooth - maintain clasps in their correct position and prevent them sinking and pressing into the gingival tissues - act as indirect retainers - assist in bracing against lateral movement

28. Occlusal rest These are made to fit into a mesial or distal fossa on the occlusal surface of a tooth They must fit the tooth accurately in order to minimize the collection of food debris beneath them and also to locate them correctly in relation to the tooth They must be strong enough to bear all normal masticatory and clenched loads without deformation

29. They must not interfere with the occlusion They must transmit the stress down the long axis of the tooth without damage to the periodontal membrane They must be at right angles or less to the long axis of the tooth

30. Cingulum rest Lie on the palatal or lingual surface of anterior teeth They are often unsatisfactory because the shape of the palatal surfaces of most teeth is not suitable to carry a rest Rest seats must be prepared in most anterior teeth The rest must not interfere with the occlusion, particularly in lateral and protrusive positions Cingulum rest can be used on maxillary canines or central incisors and mandibular canines

31. Incisal rests Rest seats on anterior teeth may be cut on the incisal edges, in the semilunar shape occurpying only the lingual part of the incisal edge On maxillary laterals and mandibular incisors, where the incisal edges are thin, effective support is gained by notching the mesial or distal corner to create a rest seat about 1 mm wide and 1mm deep The rest must not interfere with occlusion

32. Surveying A partially edentulous mouth has undercut areas which result from The naturally bulbous shape of the crowns of the teeth The long axes of the teeth are inclined at an angle to a vertical taken from the occlusal plane The soft tissue and underlying bone being inclined at an angle to a vertical taken from the occlusal plane

33. Rigid denture bases and the rigid parts of clasps will not pass into undercuts An undercut - an area which is out of contact with any vertical dropped from a given horizontal Surveying is the determination of the undercut areas on the cast by using surveyors Such undercut areas are found in the maxillary labial and tuberosity region, lingual alveolar region of the mandible

34. The reasons for surveying a cast It enables undercuts to be accurately blocked out on the cast to the acrylic procession or alloy casting of the denture, so that of the base not fill the undercuts and prevent the denture from being inserted It marks the most bulbous part of a tooth which is to carry a clasp This enables to place the rigid part of the clasp above the undercut area and the flexible arm which retains the denture into the undercut

35. It will demonstrate undercut areas which can be used for the retention of the denture It enables these parts of the denture base which fit against the crown of the teeth to be placed above the survey line, that the denture fits snugly against the tooth and prevent food stagnation It permits the dentist and technician to design a denture with one path of insertion, so that all saddles and clasps are related to this predetermined path, and not as individual units

36. It will demonstrate undercut areas which can be used for the retention of the denture It enables these parts of the denture base which fit against the crown of the teeth to be placed above the survey line, that the denture fits snugly against the tooth and prevent food stagnation It permits the dentist and technician to design a denture with one path of insertion, so that all saddles and clasps are related to this predetermined path, and not as individual units

37. It enable the dentist and technician to measure, with undercut guages , the horizontal depth of an undercut below the survey line marked on a tooth and determine the type of clasp to be used and the material of which it is constructed

38. Direct retainers (Clasps) Partial dentures obtain their retention mainly from clasp (direct retainers) attached to the denture which embrace natural teeth and hold the denture in place A clasp consists of a resilient metal projection from the denture which grips the natural tooth and retains that part of the denture, to which it is attached, in its functional position

39. 2 main types Encircling or occlusally approaching clasps Projection or gingivally approaching clasps

40. Encircling clasps These consists of two arms which encircle the tooth on opposite side and are in contact with it along their whole length, gripping it at their extremities.

41. Projection clasps These differ from the encircling type by not being in contact with the tooth along their whole length and by approaching the undercut area from the gingival aspect

42. The encircling clasp is superior to the projection type They are The rigid part of the clasp which is in contact with the tooth provides valuable bracing for the denture against lateral movement It holds the minimum of food debris in contact with the teeth

43. The value of projection clasp is They can be used in situations unfavourable to the use of encircling clasps Any degree of flexibility can be obtained by lengthening the arm They are often less conspicuous They can be placed in the area of the greatest undercut They can be used as stress breakers

44. Factors in the selection of a clasp The selection of the clasp mainly depends on the type of survey line Other factors are The position of the tooth The occlusion of the teeth The appearance

45. Types of Clasps Encircling clasps Two-arm encircling clasp The normal arm can be employed whenever the tooth to be clasped is adjacent to an edentulous space and the survey line on that part of the tooth nearest to the space allows rooms for the rigid part of the clasp The flexible terminals of the clasp travel for as long a distance as possible in the undercut area

46. Two-arm encircling clasp from the buccal and occlusal view

47. Two-arm encircling clasp. The tip should travel in the undercut area for as long a distance as possible.

48. The recurve arm clasp the length of the arm is increased by curving in on itself The length of the retentive terminal to be increases and brings it nearer to the denture so providing superior retention The length of the rigid part is also increased and provides excellent bracing

49. Recurved arm encircling clasp

50. One arm form Only one arm is flexible, the other arm or reciprocal, being formed by an extension of the denture The formed of the single arm may be normal or recurved

51. One-arm clasps reciprocated by mucosaborne denture base

52. Circumferential from (Ring clasp) employed on isolated teeth it provides excellent bracing

53. Ring clasp

54. Back action arm This is similar to the ring clasp except that it is attached to the denture by a mean of strut placed anterior or posterior to the saddle on the lingual or palatal side

55. Back action clasp with occlusal rest. Clasp is attached to denture at A

56. Jackson crib This clasp is a completely encircling clasp with no free flexible terminal It provides retention by gripping the undercut areas in proximal embrasures of tooth

57. Diagram of Jackson crib clasp reciprocated by denture base

58. Interdental clasps This clasp has two forms The first consists of a round wire which has been fused at the end to form a ball The second is a small triangular wedges or two clasp arms This clasp are employed when no edentulous gaps exists between the teeth

59. Ball-ended interdental clasp, usually made of wrought alloy

60. Interdental clasps, usually cast, either ending in a wedge or spreading into two buccal arms

61. Projection clasps T-shaped clasp It is used when the survey line indicates that no room exists for the rigid part of an encircling clasp and yet there is a large undercut area On canine and incisor

62. T-shaped projection clasps on anterior teeth (diagrammatic).

63. T-shaped projection ( gingivally -approaching) clasps

64. U-Shaped clasp This clasp is useful when the survey line dips to the gingival margin on the buccal aspect of the totoh of molars

65. U-shaped projection clasp

66. L-Shaped clasp This clasp is usually employed on premolar or canine when the survey line is extremely small

67. L-shaped projection clasp

68. C- Shaped clasp This clasp is used when a tooth exhibits only a small undercut area mesially or distally

69. C-shaped projection clasp

70. Ball and socket This clasp is used when the slope of the tooth surface is no undercut area exists This clasp gives a very positive retention and need not be restricted to teeth which exhibit no survey line Tooth bone denture require clasps at the ends of all saddles

71. When only two clasps are used, a straight line joining them should bisect the denture as nearly as possible If a denture would tend to rock about two clasps, then a third clasp should be added and the father it is away from the other two the better

72. Ball and socket projection clasp

73. Which teeth to clasp? Molars Premolars Canines Incisors

74. Location of clasps

75. Location of clasps: Kennedy class upper

76. The principles of clasp design The rigid portion must be on the occlusal side of the survey line At least part of the flexible portion must rest in an undercut area The flexible portion must not fit more deeply into an undercut area than its elastic or proportional limit will permit

77. The tip of the clasp must remain in contact with tooth Any pressure must be opposed by equal ie , a clasp must never press on one side only of an unsupported tooth The clasp together with its rigid opponent or reciprocal, must embrace more than half the circumference of the tooth Unless fitted with an occlusal rest the clasp must not rest too near the gingival margin

78. Wrought wire Clean Minimum friction Highly flexible Easily constructed Suitable for cases requiring several clasps Do not transmit every movement of the pressure to the tooth

79. Cast alloy Accurate fitting Easily varied in thickness Easily formed to act as a rigid bracing or reciprocal Easily include an occlusal rest Can be cast as part of denture base

80. Thank You