Stability in complete dentures

HELPFUL FOR PGS IN PROSTHODONTICS

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2. Stability in complete dentures Dr. Fateema Priyam 2 nd year P G Student Dept of Prosthodontics 2

3. Contents Introduction and definitions Factors influencing denture stability The relationship of denture base to the underlying tissues The relationship of the external surface and border to the surrounding orofacial musculature The relationship of the opposing occlusal surfaces 3

4. Patient education Checking of stability of dentures Discussion Summary References 4

5. Introduction 5

6. Success of complete denture 6

7. STABILITY :- The quality of a removable prosthesis to be firm, steady or constant to resist displacement by functional horizontal or rotational stresses. Resistance to horizontal displacement of prosthesis.GPT-9 7

8. FISH (1948) described three denture surfaces. Tissue surface. Polished surface. Occlusal surface . All the three surfaces helps in determining stability of the complete denture. 8

9. The factors that contribute to stability include ridge height and conformation, base adaptation, residual ridge relationships, occlusal harmony, and neuromuscular control. 9

10. 1. The relationship of the denture base to the underlying tissues 2. The relationship of the external surface and border to the surrounding orofacial musculature 3. The relationship of the opposing occlusal surfaces 10

11. The relationship of the denture base to the underlying tissues 11

12. Denture base adaptation Residual ridge anatomy Mandibular flange area Sublingual crest region 12

13. Denture base adaptation Maximum coverage without undue displacement of tissue not only allows the development of a good border seal but also provides close adaptation of denture base with facial and lingual slopes -improving stability. 13

14. Boucher stipulated the following objectives of complete denture impression Retention Stability Support Esthetic values Preservation of alveolar ridge 14

15. He notes that stability is obtained by incorporating the surfaces of the maxillary and mandibular ridges, which are at right angles to the occlusal plane. He further states “ maximum use of all bony foundations where the tissues are firmly and closely attached to the bone” 15

16. R esidual ridge anatomy The development of stability is limited by the anatomic variations of the patient that determines the residual ridge height and conformation 16

17. Large, square, broad ridges offers a greater resistance to lateral forces than do ovoid , narrowed tapered ridges. 17

18. The contacting of the labial and buccal flanges with labial and buccal ridge slopes is one of the critical factors contributing stability.-Friedman Small and rounded irregularities present on the vertical walls of the ridges also contribute. So alveoloplasty should be limited only to removal of bone that would prevent fabrication of successful prosthesis. 18

19. The arch form – square arches tends to resist rotation of the prosthesis better than the ovoid OR tapered arches. Shape of palatal vault – stability is limited by the length and angulations of the palatal ridge slopes. A steep or high arched palate enhances the stability by providing greater area of contact and long inclines approaching at right angle to the direction of force. 19

20. Mandibular lingual flange Most desirable feature of lingual slopes is that it approaches 90 to the occlusal plane. Effectively resist horizontal forces . Although the posterior fibres of the mylohyoid muscle attach more superiorly than anterior, they descend nearly vertically to attach hyoid bone 20

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22. The posterior lingual flange is usually able to be extended inferiorly more than the anterior lingual flange. 22 Anteriorly, the mylohyoid muscle fibers are directed more horizontally to communicate with fibers of the opposite side along a midline tendinous raphe.

23. Musculature of the floor of the mouth may also influence the degree of intimate contact allowed. Any flange extension below the mylohyoid ridge must incline medially away from the mandible to allow for the mylohyoid muscle contraction. 23

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25. Sublingual crescent area The crescent shaped area on the anterior floor of the mouth formed by the lingual wall of the mandible and the adjacent sublingual fold. It the area of the anterior alveolingual sulcus.(GPT-9) 25

26. Its coverage by denture results in 1)Increased stability by allowing the tongue to aid in holding the denture in place. 2) Increased retention of the denture. 26

27. Making the impressions with minimal pressure on the floor of the mouth while tongue is at rest position allows greater mobility of the underlying muscles without denture dislodgement and without occlusion of the sublingual gland duct. 27

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29. Relationship of the external surface and periphery to surrounding orofacial musculature 29

30. Orofacial musculature Both stability and retention depend upon the relationship of polished surface and surrounding orofacial musculature . The musculature can facilitate stability in two ways???? 30

31. First, the action of certain muscle groups must be permitted to occur without interference by the denture base -will not dislodge the prosthesis during function or compromise stability. Second, the dentist must recognize that normal functioning of some muscle groups can be used to enhance stability. 31

32. The action of the levator anguli oris , depressor anguli oris ( triangularis ), mentalis , mylohyoid and genioglossus muscles can dislodge the denture if the denture base does not provide freedom for these muscle action. 32

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34. Fish believed that the contours of the polished surface provided the principal factor governing complete denture stability. Robert P R (1960) stated that “The form and contour of the polished surface of the denture base is an important factor in the denture function and plays a significant role in the complete denture stability” 34

35. Strain C J (1969) stated that “The polished surface of the lower denture greatly influences the stability due to the proper adaptation of its surface to the tongue, lips and cheeks.” The basic geometric design of denture bases should be triangular . In the frontal cross section, the maxillary and mandibular dentures should appear as two triangles whose apexes correspond to the occlusal surface. 35

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37. The buccal and labial flanges of the maxillary and mandibular dentures should be concave to permit positive seating by the cheeks and the lips. 37

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39. The primary muscles of cheeks and lips are orbicularis oris and buccinator . These muscles are active in mastication, deglutition and speech. The proper contour of the denture flanges permits the horizontally directed forces , that occur during contraction of these muscles, to be transmitted as vertical forces tending to seat prosthesis . 39

40. To direct a seating action on the mandibular denture, the tongue should rest against a lingual flange inclined medially away from the mandible and somewhat concave . The degree of inclination depends on the balance of the muscular forces of the tongue. 40

41. Modiolus (hub of a wheel) The musculi cruculi modioli or modiolus and their associated musculatures has various actions on the denture. An anatomical landmark near the corner of the mouth that is formed by the intersection of several muscles of the cheeks and lips . 41

42. These muscles are:- Orbicularis oris . Buccinator . Caninus ( levator anguli oris ). Triangularis (depressor anguli oris ). Zygomaticus major. Risorius . Quadratus labii superioris . Depressor labii inferioris . 42

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44. Because none of these muscles contains fibres that have more than one bony attachment, they depend on fixation of the modiolus to allow isometric contraction . E.g.-contraction of the triangularis, caninus , and zygomaticus muscles fixes the modiolus, allowing the buccinator muscle to contract isometrically. 44

45. This allows the buccinator muscle to tense , allowing it to control the food bolus on the occlusal table. 45

46. Isotonic contraction of the buccinator muscle in the absence of modiolus fixation would pull the corner of the mouth posteriorly . It can be fixed more anteriorly as when the word “Hoe” is pronounced or posteriorly as in case of “He”. The denture base must be contoured to permit the modiolus to function freely . 46

47. In the premolar region the mandibular denture should exhibit both a shortened and narrowed flange to permit the action that draws the vestibule superiorly and the modiolus medially against the dentures. The buccinator muscle may be divided into superior, middle, and inferior divisions. 47

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49. According to Fish, Superior fibers acts to seat the maxillary denture. Middle fibres controls the bolus of food. The inferior fibres contributes to mandibular denture stability . 49

50. Neutral zone concept Harmony between the polished surface of the denture and associated musculature. Neutral zone is the area of potential denture space where the forces of tongue pressing outward are neutralized by the forces of the cheek and lips pressing inward 50

51. 51 The Potential ‘Denture Space’ Mandible

52. Importance of neutral zone: As the area of the impression surface decreases (alveolar ridge resorption ) less influence it has on the denture retention and stability. Consequently retention and stability become more dependent on the correct positioning of the teeth and the contours of the external surface of the dentures. 52

53. 53 1. Those muscles which primarily dislocate the dentur e during activity ( Dislocating muscles ), 2. Those muscles that fix the denture by muscular pressure on the polished surfaces ( Fixing muscles ).

54. 54 Dislocating muscles Vestibular: Masseter Mentalis Incisive Labii Infer. Lingual: Medial Pterygoid Palatoglossus Styloglossus Mylohyoid Fixing muscles Vestibular: Buccinator Orbicularis oris Lingual: Genioglossus Lingual longitudinal Lingual vertical Lingual transverse

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57. Tongue It completely fills the floor of the mouth The lateral borders rest over the ridge which would normally represent the occlusal surfaces of the teeth. The tip or apex of the tongue rests on or just to the lingual side of the lower anterior ridge. 57

58. As the patient becomes edentulous, the continuous destruction of residual ridges occurs. Because of these changes the tongue will expand in the space formerly occupied by the teeth. The position of the tongue will become retracted. 58

59. (1) The tongue is pulled back into mouth and the floor of the mouth is exposed. (2) The lateral borders are either inside or posterior to the ridge. (3) The tip of the apex of the tongue sometimes lies in the posterior part of the floor of the mouth or may be withdrawn into the body of the tongue. 59

60. When natural teeth are present retracted tongue position has little effect on the ordinary function of the mouth. It is only when a person becomes edentulous that a retracted tongue position becomes a problem. 60

61. Some authors recommend posterior extension of the lingual flange to fill the retromylohyoid space to permit the base of the tongue to contribute to the neuromuscular control of the prosthesis.“’ 61

62. Inclination of the lingual flange must be designed to guide the tongue to rest over the flange and permit any horizontal forces generated against the denture base to be transmitted as seating forces. 62

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64. Relationship of opposing occlusal surfaces 64

65. The dentures must be free of interferences within the functional range of movements of the patient. During both functional and parafunctional movements the occlusal surfaces should not strike prematurely in localized areas????? 65

66. Anatomic occlusal scheme In maximum intercuspation, surface contact between posterior anatomic teeth consists of multidirectional but equalized, forces. 66

67. But the directional forces change in eccentric position, and there is a significant lateral force component exerted on the denture bases 67

68. Balanced occlusion The bilateral, simultaneous , anterior and posterior occlusal contact of teeth in centric and eccentric positions. (GPT-9) 68

69. Patients with balanced occlusion do not upset the normal static, stable and retentive position. Absence of occlusal balance will result in leverage of the denture during mandibular movement, compromising stability. 69

70. Various philosophies have been proposed either to provide for a fully balanced occlusion throughout lateral and protrusive excursive movements or to control the direction of forces experienced during localized occlusal contact. 70

71. Setting of anatomic or semianatomic artificial teeth to provide excursive balance is thought to minimize localized stress concentration and lateral dislodging forces by ensuring multiple points of contact to distribute functional occlusal forces. 71

72. To minimize dislodging forces the occlusion must be balanced throughout the functional range of movement of the patient. A balanced occlusion is limited by the buccolingual and mesiodistal width of the anatomic cuspal inclines. 72

73. Some authors recommend occlusal schemes that direct forces to minimize the unseating of the denture during unilateral excursive tooth contacts. 73

74. Zero degree teeth Two dimensional/ monoplane occlusion . Non-anatomic teeth. Eliminating cusps will reduce the lateral forces. Balanced occlusion in eccentric relation is not a part of the occlusal scheme 74

75. A monoplane scheme reduces the horizontal force components because direction of forces between zero degree teeth in centric and eccentric position is essentially vertical. 75

76. LINGUALIZED OCCLUSION Anatomic (30/33 ) teeth are used for the maxillary denture . Tooth form with prominent lingual cusps are helpful. Nonanatomic or semianatomic teeth are used for the mandibular denture . Either a shallow or flat cusp form is used. 76

77. Maxillary lingual cusps should contact mandibular teeth BUT the mandibular buccal cusps should not contact the upper teeth in centric occlusion. 77

78. The theories of lingualized occlusion provide both a limited range of excursive balance and a directing of forces to the lingual side of the lower ridge during working-side contacts 78

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80. Balancing and working contacts should occur only on the maxillary lingual cusps. Protrusive balancing contacts should occur only between the maxillary lingual cusps and the lower teeth. Since in lingualized occlusion, vertical forces are centralized on the mandibular teeth, it is proposed to aid in stability. 80

81. Maxillary and mandibular tooth position The arch curvature should correspond to curvature of alveolar ridge, facial contour and maxillary lip position. Anterior and posterior teeth should be arranged as close as possible to the position once occupied by the natural teeth, with only slight modifications made to improve leverages and esthetics 81

82. Mandibular anterior teeth should be in harmony with the maxillary anterior tooth position. Errors in maxillary tooth position will be transferred to the mandibular arch. 82

83. OCCLUSAL PLANE A mandibular occlusal plane that is too high can result in reduced stability. 1. Lateral tilting forces directed against the teeth are magnified as the plane is raised. 2.The mandibular denture needs to be controlled by the musculature of the tongue, lips, and cheeks. 83

84. An elevated occlusal table prevents the tongue from reaching over the food table into the buccal vestibule. A raised mandibular occlusal plane is usually present when the vertical dimension of occlusion is increased excessively. 84

85. The best stability is obtained when the occlusal plane is parallel to and evenly divided between the ridges. 85

86. If the occlusal plane is tipped??? If the occlusal plane is lower in molar area, there will be a tendency for upper denture to be displaced posteriorly and lower denture anteriorly . 86

87. Patient education Patients must be advised that chewing is not random but an intentional and selective activity . The eating skills must be slowly developed and refined 87

88. How to eat with dentures is a skill that has to be learned Basically chewing with dentures is more methodical than with natural teeth. Patients must be instructed to divide the normal spoonful of food into half and place each half posteriorly and bilaterally 88

89. Checking stability of the denture Pressure is applied with the ball of the finger in the premolar-molar regions of each side alternatively. This pressure must be at right angle to the occlusal surface. If pressure on one side causes the denture to tilt and raise on the other side, it indicates that the teeth on the side on which the pressure was applied are outside the ridge. 89

90. Improving denture stability Over dentures Dentures get more ridge support, this enhances the retention of the denture and ultimately stability gets improved. Rate of resorption of residual ridge decreases. tooth supported Implant supported 90

91. Prospective clinical evaluation of mandubular implant overdentures part-I -retention stability and tissue responses . David R.Burns,et al J Prosthet Dent 1995;73(4): 354-63 91

92. 17 subjects with preexisting conventional complete dentures were evaluated. Two implants were placed bilaterally in the anterior mandible. The conventional dentures were modified, and the retention stability, and tissue response for conventional dentures were compared (cross over experimental study) 92

93. The study showed superior statistics of implants as an treatment alternative to increase stability than ridge augmentation or vestibular extension procedures. 93

94. Discussion 94

95. Summary Stability prevents anterio -posterior shunting of the denture base . It has been cited as the most significant property in providing physiology comfort to the patient. Denture instability adversely affect retention & support and results in deleterious forces on the edentulous ridge during function and parafunction . 95

96. References Journal references: T.E.Jacobson , A.J Krol “ A contemporary review of the factors involved in complete dentures part II: stability” J Prosthet Dent 1983;49:165-172. Corwin R. Wright , “Evaluation of the factors necessary to develop stability in complete dentures” J Prosthet Dent 1966;16:414-30. reprint J Prosthet Dent 2004;92:509-18 96

97. Brill N , Tryde G, Cantor R, The dynamic nature of the lower denture. J Prosthet Dent 1956, 15:401-417 Ross L Taylor, The stability of complete dentures . Aust Dent Journal 1962; 7(2): 145-154. Becker C M, Swoope C C , Gucker A D, Lingualized occlusion for removable prosthodontics J prosthet Dent 1973;38: 601-608 97

98. Krishna Prasad D, B Rajendra prasad , Enhancing stability: A review of various occlusal schemes in complete denture prosthesis. NUJHS 2013; 3(2):105-112. C H Jooste , C J Thomas, The influence of retromylohyoid extension on mandibular complete denture stability . Int J Prosthodont 1992; 5 : 34-38. 98

99. Textbook reference: Zarb Bolender , Prosthodontic Treatment for Edentulous Patients ,2004,12 Ed,Mosby Inc Winkler ,Essentials of Complete Denture Prosthodontics 1996,2 nd Ed,AITBS Publishers. Heartwell,Syllabus of Complete Dentures,1992,4 th Ed,Varghese Publishing House. Glossory of prosthodontics -9 99

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