Stability in complete dentures

1. STABILITY IN COMPLETE DENTURES

2. Contents Definitions Factors effecting stability Methods to check stability Methods to improve stability Residual ridge anatomy Quality of soft tissue covering the ridge Quality of the impression Occlusal planes Arrangement of teeth Contour of polished surface

3. What is stability???

4. Retention Stability Support Psychologic Physiologic Longevity Comfort Comfort Prosthesis Success

5. STABILITY DEFINITIONS – GPT 8 That quality of maintaining a constant character or position in the presence of forces that threaten to disturb it; the quality of being stable; to stand or endure The quality of a removable dental prosthesis to be firm, steady, or constant, to resist displacement by functional horizontal or rotational stresses Resistance to horizontal displacement of a prosthesis

6. Fish 1948 3 surfaces: Polished surface Occlusal surface Tissue surface STABILITY

7. 1. Relationship of denture base to underlying tissues

8. Maximum coverage without undue displacement of the tissues Development of good border seal Close adaptation of denture base Denture base adaptation

9. Impression should be as accurate as possible The impression surface should be smooth & duplicate all the details accurately The impression should not warp on removal The impression should be dimensionally stable & the cast should be poured as soon as possible Quality of the impression

10. Friedman: Contacting of labial and buccal flanges with labial and buccal ridge slopes increases stability.

11. Boucher Incorporating the surfaces of maxilla and mandible which are at 90 degree to occlusal plane improve stability. Maximum use of all bony foundations where tissues are firmly and closely attached to bone”

12. The residual ridge should have sufficient vertical height to obtain good stability Highly resorbed ridges offer the least stability Vertical Height of residual Ridges

13. Shape of palatal vault A steep or high arched palate enhances the stability : providing greater area of contact long inclines approaching at right angles to the direction of force.

14. Arch form Square arches tend to resist rotation of the prosthesis better than the other arch forms.

15. The ridge should provide a firm soft tissue base with adequate mucosa to offer good stability Flabby tissues with excessive submucosa offer poor stability

16. Mandibular lingual flange Lingual slopes approach 90 degree to occlusal plane Effectivley resists horizontal forces The posterior lingual flanges extends more inferiorly than anterior lingual flange

17. Musculature of the floor may allow influence the degree of intimate contact allowed. Presence of any thin mucousa overlying the bony ridge slopes that may require relief make close contact impossible.

18. 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 is the area of the anterior alveolingual sulcus (GPT-8) Extension of the denture over the resting tissues of the sublingual crescent area completes the border seal Its coverage by denture results in : Increased stability by allowing the tongue to aid in holding the denture in place

19. Making the impression with minimal pressure on the floor of the mouth while the tongue is at rest position allows: -Greater mobility of the underlying muscles without denture dislodgement. -Without occlusion of the sublingual gland duct

20. 2.Relationship of external surface and periphery to surrounding orofacial musculature.

21. Polished surface should allow muscle to function individually without any interference which may dislodge the denture Some normally functioning muscles can aid to stabilize the denture

22. Dislodging muscles Levator anguli oris Depressor anguli oris Incisivus Mentalis Genioglossus Mylohyoid

23. Fish 1933 “It is not so widely understood that the actual shape of the whole buccal,labial and lingual surfaces can wreck the stability of a denture as bad as a wrong impression”

24. Frontal cross section of denture Maxillary buccal flange: Superior and lateral Mandibular buccal flange: Inferior and lateral Mandibular lingual flange: Inferior and medial Provide vertical component to horizontal forces

25. The buccal and labial flanges of the maxillary and mandibular dentures  concave Lingual flange  inclined and concave

26. Primary muscles of lips and cheeks: - Orbicularis oris - Buccinator

27. Modiolus ( Musculi cruculi modioli )

28. Various actions on the denture None of these fibres have more than one bony attachement Depend on the modiolus to allow isometric contraction

29. The denture base must be contoured to allow the modiolus to function freely In the premolar region the mandibular denture: -Shortened flange -Narrow flange This permits action which: -draws vestibule superiorly - modiolus medially against the denture

30. Buccinator muscle

31. Seat maxillary denture Control food bolus Denture stability

32. Medial roll of buccinators Function of the medial roll: -Forms the buccal wall of food trough -Retrieve food that is forced into the buccal pouch. This mechanism is known as "shunting effect".

33. Middle fibers: -contract and controlling food bolus Inferior fibres : -Relax to form pouch to store food until needed to form another bolus

34. Clinical significance Extension of concave denture base into this pouch allows cheek to lie over flange Electromyography: - Buccinator muscle contraction cannot adapt to changes in contour of denture base -Denture contours should be designed to harmonize with existing buccinator muscle function

35. Neutral zone The potential space between the lips and cheeks on one side and the tongue on the other; that area or position where the forces between the tongue and cheeks or lips are equal

36. Tongue As the patient becomes edentulous,the continous destruction of residual ridges occurs . Because of these changes the tounge will expand in spaces formerly occupied by the teeth This occurs partially due to growth of tounge known as Proptosis lingualis

37. A small narrow tongue contributes to the ease of impression making but jeopardized the lingual seal for mandibluar dentures An extremely large tounge poses additional problems during impression making and impairs denture stability

38. 3.Relationship to opposing occlusal surfaces.

39. Balanced occlusion The bilateral simultaneous,anterior and posterior occlusal contacts of teeth in centric and eccentric positions.-GPT 8

40. Establishing a balanced occlusion is key to maintaining stability and in turn the border seal. Lower dentures are particularly vulnerable to instability as a result of poor retention. Here the occlusal table should be designed to provide optimum load distribution in order to seat the denture

41. The 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.

42. Lingualized occlusion Balancing and working contacts should occur only on maxillary lingual cusps. In lingualized occlusion,the vertical forces are centralized on the mandibular teeth,it is proposed to aid in stability.

43. Tooth position Anterior and posterior teeth should be arranged as close as possible to the position once occupied by the natural teeth Modifications can be made to improve aesthetics and leverage

44. Maxillary anterior tooth position The arch curvature should correspond to: curvature of alveolar ridge facial contour Maxillary lip position

45. Arranging the teeth in to a square arch form on a tapering ovoid residual ridge causes canines to be labial to crest of the maxillary ridge than the incisors

46. This results in bicuspids being more buccal to the ridge than they should be. Working side occlusal pressure produces a diplacing tendency , the ridge crest acting as a fulcrum

47. The labial axial inclination of the natural anterior tooth places the incisal edge labial to the centre of rotation of the tooth . If prosthetic tooth is placed exactly in the same position as the natural crown it will be labial to the ridge support Incisal pressure causes a displacing torque.

48. Mandibular anterior tooth position It should be in harmony with the maxillary anterior tooth Errors in maxillary tooth position will be transferred to the mandibular arch For maximum stability overbite should be as minimum as possible

49. Maxillary posterior tooth position Natural posterior maxillary teeth have a buccal inclination and the mandibular teeth have a normal lingual axis inclination

50. The normal residual ridge resorption pattern leads to an increase crossbite relation ship Tendency to avoid cross bite arrangement results in placing the maxillary teeth in buccal position or mandibular teeth in lingual to desired position Results in impaired stability

51. In such cases the working side occlusal pressure causes a displacing tendency because the line of force is buccal to the fulcrum

52. Mandibular posterior teeth The buccal cusps and fossae of the mandibular posterior teeth should lie directly over crest of the ridge

53. If placed more buccally , the working side occlusal pressure causes a displacing tendency because the line of force is buccal to the fulcrum If placed lingually tongue will displace the denture

54. Occlusal plane The occlusal plane should be oriented parallel to the ridge If the occlusal plane is inclined , then the sliding forces may act on the denture & reduce its stability The occlusal plane should divide the interarch space equally

55. Patient education Eating : Eating skill must be slowly developed and refined Initially patient should have soft diet Patient should be instructed to divide normal spoonful of food into half and place each half posterioirly and bilaterally.

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

57. Maximizing stability Maximum coverage of denture bearing area within physiological limits Understanding muscle actions Neutral zone Correct occlusal plane and teeth position Patient education Denture modifications Denture adhesives

58. P reprosthetic surgeries Over dentures Soft liners

59. CONCLUSION Stability is cited as the most significant property in providing physioloical comfort to the patient. It is important to know the factors affecting stability The main factors cited were the occlusal tissue and polished surfaces

60. Though to fabricate perfectly stable denture may not be truly possible we should still try to achieve the maximum stability as possible

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