Residual ridge resorption

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1. Residual Ridge Resorption

2. Definitions Pathology classification Pathogenesis Epidemiology Etiology P revention Treatment Summary and conclusion Contents :

3. DEFINITIONS : “ Bone - a highly vascularised , living, constantly changing, mineralized connective tissue”. [Gray’s Anatomy-40 th edition] “ Alveolar process -- that part of the maxilla and mandible that forms and supports the sockets of the teeth”. [ Orban’s ]

4. “ Alveolar bone is the bony portion of the maxilla and the mandible in which roots of the teeth are held by fibers of periodontal ligament”. [GPT-8]

5. “ Residual alveolar ridge is the portion of the alveolar ridge and its soft tissue covering which remains following the removal of or loss of teeth. [GPT-8]

6. The residual bony architecture of the maxilla and mandible undergoes a life-long catabolic remodelling. The rate of reduction in size of the residual ridge is maximum in the first 3-6 months and then gradually tapers off. However, bone resorption activity continues throughout life at a slower rate, resulting in loss of varying amount of jaw structure, ultimately leaving the patient a ‘ dental cripple ’.

7. According to Atwood’s : (JPD 1971 Vol.26) Order 1 : Pre-extraction Order 2 : Post-extraction Order 3 : High, well rounded Order 4 : Knife-edge Order 5 : Low, well rounded Order 6 : Depressed Pre extraction Post ext High well rounded Knife edge Low well rounded Depressed

8. Atwood’s classification

9. Immediately following the extraction (Order II), any sharp edges remaining are rounded off by external osteoclastic resorption leaving a high well rounded ridge (Order III). As resorption continues from the labial and lingual aspects ,the crest of the ridge becomes increasingly narrow, ultimately becoming knife edged (Order IV). As the process continues, the knife-edge becomes shorter and eventually disappears leaving a low well-rounded or flat ridge (Order V). Eventually this too resorbs , leaving a depressed ridge (Order VI). Pathogenesis

10. Class I : Upto one third of the original vertical height lost. Class II : From one third to two thirds of the vertical height lost. Class III : Two third or more of the mandibular height lost. Classification by WICAL AND SWOOPE :

11. Based on Bone Height (Mandible only) Type I : Residual bone height of 21 mm or greater measured at the least vertical height of the mandible. Type II : Residual bone height of 16 - 20 mm measured at least vertical height of the mandible. Type III : Residual alveolar bone height of 11 - 15 mm measured at the least vertical height of the mandible. Type IV : Residual vertical bone height of 10 mm or less measured at the least vertical height of the mandible. According to the American college of prosthodontists : McGarry et al, J Prosthodont 8(1):27-39, 1999

12. Some clinicians feel that RRR is not a disease but a normal physiological process. However there is wide variation in the rate of RRR in different individuals- depending on multiple factors. The need to elucidate these major differences warrants labeling this process a “ disease ” or “ pathology ” Physiology v/s Pathology ???

13. “Until a process is recognized as a disease entity, little progress is made in understanding its etiology and in developing adequate treatment and prevention.” - Douglas Allen Atwood

14. Based on the clinical fact that : RRR is not inevitable Its rate varies The rate of resorption is greater that the rate of formation in some patients , ….RRR should be considered a pathologic process.

15. Residual ridge remodelling

16. Changes in the Residual Ridge after tooth extraction

17. Pattern of bone formation in extraction socket

18. Epithelial tissues begin its proliferation and migration within the first week and the disrupted tissue integrity is quickly restored. Histologic evidence of active bone formation is seen as early as 2 weeks after the extraction and the socket is progressively filled with newly formed bone in about 6 months. . The most striking feature of the extraction wound healing is that even after the healing of wounds, the residual ridge undergoes a lifelong catabolic remodeling .

19. This unique phenomenon has been described as RESIDUAL RIDGE RESORPTION (RRR). The rate of RRR is different among persons and even at different sites in the same person.

20. Coupled process between: Bone deposition by osteoblasts Bone resorption by osteoclasts 5-7% of bone mass recycled weekly All spongy bone replaced every 3-4 years. All compact bone replaced every 10 years . Bone is Dynamic! Bone is constantly remodeling and recycling Prevents mineral salts from crystallizing; protecting against brittle bones and fractures

21. Pathology of RRR Gross Microscopic

22. Gross pathology Patient has an expression “ My gums have shrunken” RRR Is primarily a localized loss of bone structure. In some cases it may leave excessive and redundant overlying mucoperiosteum and in some cases it may not .

23. The careful superimposition of portions of tracings of lateral cephalograms clearly shows the gross reduction of bone in size and shape that occurs on the labial, crestal , and lingual aspects of the residual ridge.

24. In dry specimens * External cortical surface of maxilla and mandible are uniformly smooth & crestal area of residual ridge shows porosities and imperfections. *Bones with more severe RRR display gross porosities of medullary bone on the crest of ridge.

25. Panoramic radiograph showing severe RRR in both maxilla and mandible in contrast to dentulous area that support three mandibular teeth.

26. Osteoclastic activity occurs on the external surface of crest of ridges . Scalloped margins of Howships lacunae sometimes contain visible osteoclasts . Frequently the scalloped external surface seems inactive without bone resorbing cells. Microscopic pathology

27. T he sequence of resorptive events is considered to be Attachment of osteoclasts to mineralized surface of bone Creation of a ruffled border and a sealed acidic environment through action of the proton pump Dissolution of the Hydroxyapatite Fall in pH to 2.5-3 in the osteoclast resorption space Digestion of the organic components of the matrix by proteolytic enzymes

28. 1. Serial Examination of diagnostic casts. 2. Lateral cephalometric radiographs Most accurate Measures RRR over a period of time. Measurement of RRR

29. 3.Panoramic radiograph ( Wical and Swoope ). -simplest method- Original Bone height = Three times the distance from inferior border of mandible to the lower edge of mental foramen . {Kenneth E. Wical and Charles C. Swoope . Studies of residual ridge resorption . Uses panaromic radiographs for evaluation and classification of mandibular resorption . JPD;1974;32;7}

30. EPIDEMIOLOGY OF RRR: To date, it appears that RRR world-wide , occurs in males and females, young and old, sickness and in health, with and without dentures and is unrelated to the primary reason for the extraction of the teeth (Caries / periodontal disease). Rate of RRR is variable -between persons. -within the same person at different times. -within the same person at different sites.

31. According to Boucher, During the first year after tooth extraction, the reduction in residual ridge height in the midsagittal plane is 2-3 mm for maxilla 4-5 mm for mandible Annual rate of reduction in height 0.1-0.2 mm for mandible 4 times less in the maxilla Amount and rate of bone Resorption

32. Maxilla resorbs upward and inward to become progressively smaller because of the direction and inclination of the roots of the teeth and the alveolar process. The opposite is true of the mandible, which inclines outward and becomes progressively wider . This progressive change of the edentulous mandible and maxilla makes many patients appear prognathic . direction of bone resorption

33. Thus, RRR is centripetal in maxilla and centrifugal in mandible.

34. In the Mandible , large proportions of bone loss occurs in the labial side of anterior residual ridge, equally on the buccal and lingual side in premolar region and lingually in the posterior or molar region.  In the Maxilla bone loss primarily occurs on the labial or buccal aspect. Patterns of bone resorption

35. While teeth arrangement we should try to restore the natural position of the teeth before they were lost, Hence teeth in the maxillary arch are arranged slightly labially and buccally . While in the mandible, teeth in the anterior region are arranged labially , on the centre of the ridge in the premolar region and slightly lingually in the molar region. Therefore ,

36. It is a clinically acknowledged fact that the anterior mandible resorbs 4 times faster than the anterior maxilla. Woelfel et al have cited the projected maxillary denture area to be 4.2 sq in and 2.3 sq in for the mandible ; which is in the ratio of 1.8:1. If a patient bites with a pressure of 50 lbs, this is calculated to be 12 lbs/sq in under the maxillary denture and 21 lbs/sq under the mandibular denture . The significant difference in the two forces may be a causative factor to cause a difference in the rates of resorption . Maxilla V/s Mandible

37. Cancellous bone is ideally designed to absorb and dissipate the forces it is subjected to. The maxillary residual ridge is often broader, flatter, and more cancellous than the mandibular ridge. Trabeculae in maxilla are oriented parallel to the direction of compression deformation, allowing for maximal resistance to deformation. The stronger these trabeculae are, the greater is the resistance. Also,

38. Generally more in mandible than in maxilla but the reverse may also occur…. So one must treat every patient as a “PARTICULAR PATIENT, NOT THE AVERAGE PATIENT!”! RRR is chronic, progressive, irreversible, and cumulative. Autonomous regrowth has not been reported.

39. Acc. To Atwood… {Some clinical factors related to rate of resorption of residual ridges JPD Vol 12,issue 3, pages 441-450 . RRR is a multifactorial biomechanical disease caused by a combination of ANATOMIC FACTORS MECHANICAL FACTORS METABOLIC FACTORS Etiology of RRR :

40. It is postulated that RRR varies with the quantity and quality of the bone of residual ridges.. ie , the more bone there is, the more RRR will ultimately be. But this cannot be considered a good prognostic factor, because in some cases large ridges resorb rapidly and some knife-edge ridges may remain with little change for long periods of time. ANATOMIC FACTORS RRR α Anatomic factors

41. We should always try to evaluate the present status of the residual ridge to determine what has gone on before. If a ridge has existed as high and well rounded (order III) for several years, it will likely to continue to do so. But if a ridge has gone from an order II to order IV in just two years it will probably continue to resorb rapidly.

42. RRR varies directly with certain systemic or localized bone resorptive factors and inversely with certain bone formation factors. METABOLIC FACTORS RRR  BONE RESORPTION FACTORS BONE FORMATION FACTORS

43. BONE RESORPTION FACTORS LOCAL SYSTEMIC - Endotoxins from dental plaque - Osteoclast activating factor(OAF) - Prostaglandins -Human gingival bone resorption factor -Trauma due to ill fitting dentures which leads to increased or decreased vascularity and changes in oxygen tension. Correct amount of circulating estrogen, thyroxine , growth hormone, calcium, phosphorus, vitamin D , -Osteoporosis - Hypophosphetemia Parathormone Calcitonin

44. Osteoporosis is defined by the WHO as bone mineral density (BMD) greater than 2.5 standard deviations below that of the young adult BMD. Osteoporosis is common in aging individuals, especially post menopausal women when the estrogenic blood level is low. In elderly men and women, osteoporosis is caused by a variety of factors such as calcium loss, calcium deficiency, hormonal deficiency, change in protein nutrition and decreased physical activity. Osteoporosis

45. Normal Bone Osteoporosis

46. Residual ridge resorption of the jaws is also more rapid in increasing age group, depleted bone being prone to the injurious impact of mechanical forces.

47. The most popular theory of how osteoporosis occur in females is based on the central role of oestrogen in bone remodelling . P athophysiology

48. Prosthodontic implications

49. Mandibular and maxillary radiographs are suggested in screening patients for osteoporosis for two reasons potential frequency of dental radiographs compared to the rest of the body the prosthodontic implications of osteoporosis . Bone density may be assessed by a prosthodontist using linear measurements ( morphometric analysis ) or by measuring optical density of bone ( densitometric analysis ). Dental screening for osteoporosis

50. Bone that is used by regular physical activity will tend to strengthen within certain limits, than the bone that is in “ disuse atrophy ”, while others postulated that due to denture wearing RRR is caused due to an “abuse” bone resorption. Perhaps there is truth in both the hypotheses. The fact is that with or without dentures some patients have little or no RRR and some have severe RRR. Mechanical /prosthetic factors Disuse V/S Abuse

51. When force is considered one must be concerned not only about the amount of force but also with the frequency of force, the duration, the area over which the force is distributed and the damping effect of underlying tissue.   The amount of force applied to the bone may be affected inversely by the damping effect or energy absorption. RRR α Force 1 RRR α ———————- Damping effect

52. The damping effect is due to the viscoelastic property of the mucoperiosteum and may vary from patient to patient and also from maxilla to mandible. Cancellous bone helps in the absorption and dissipation of forces and is more in maxilla than mandible, which could be a reason in the difference in RRR between them.

53. Excessive stress resulting from artificial environment. Abuse of tissues from lack of rest- Bone is moldable. It can tolerate masticatory forces within the limits of physiologic tolerance. But exceeding that it causes damaging forces which will result in resorption of the alveolar bone. PROSTHETIC FACTORS

54. Long continued use of ill fitting dentures: may be due to : Long use, Loss of bone, Incorrect occlusion, Incorrect jaw relation Lack of freeway space due to increased vertical dimension of occlusion : Freeway space is present in the teeth in the physiologic rest position. It is normally around 2mm . At times, due to lack of freeway space the bone resorbs because of increased vertical height in an attempt to create the space.

55. Incorrect Centric relation record: If the Centric relation is not recorded properly, the mandibular teeth will not occlude properly with those on the maxillary arch. This proper occlusion is essential to the health of bony support. Otherwise , during eccentric movement, it causes pressure on bone due to failure of denture stability. Hence resorption of base occurs.

56. If occlusal corrections are not done: These errors which may be caused due to processing techniques if not corrected causes premature contacts resulting in increased stress. Selective grinding should be done to minimize lateral stress and resulting tissue trauma.

57. Kelly first described the “ combination syndrome ” wherein patients with remaining mandibular natural teeth against a maxillary complete denture were shown to have an exaggerated loss of anterior segment of maxillary residual ridge. Localised mechanical stress from removable prostheses {J Prosthet Dent 1972; 27:140-150} .

58. In addition to the 3 major categories of factors (anatomic, metabolic and mechanical) the importance of time since extraction is also important. This can be added to the formula by an inverse relation. Bone resorption factors Force factors RRR α anatomic factors + ———————————— + ——————— + Bone formation factors Damping effect 1 —— Time

59. Apparent loss of sulcus width and depth. Displacement of muscle attachment close to the ridge. Loss of vertical dimension of occlusion. Reduction of the lower face height. Increase in relative prognathia Consequences of RRR :

60. Changes in inter alveolar relationship. Morphological changes of the alveolar bone such as sharp, spiny uneven residual ridges. Location of mental formina close to the ridge crest.

61. “ Treatment of RRR is ideally by preventing it.” a. Prevention of loss of natural teeth: Alveolar bone supporting natural teeth receives tensile loads through a large area of periodontal ligament. While the edentulous residual ridge receives vertical, diagonal and horizontal loads applied by a denture with a surface area much smaller than the total area of the periodontal ligament of all the natural teeth that had been present. Treatment and prevention

62. Optimal tissue health prior to making impression. Impression procedures Minimal pressure impression technique. Selective pressure impression technique: places stress on those areas that best resist functional forces Adequate relief of non stress bearing areas eg. Crest of mandibular ridge. Broad area of coverage helps in reducing the force /unit area( Snow Shoe Effect ) : b.Proper design of dentures and maintenance

63. Avoidance of inclined planes to minimize dislodgment of dentures and shear forces. Centralization of occlusal contacts to increase stability and maximize compressive forces. Provision of adequate tongue room to improve stability of denture in speech and mastication. Adequate interocclusal distance during jaw rest to decrease the frequency and duration of tooth contact. Occlusal table should be narrow The concept and arrangement of teeth in neutral zone helps the teeth to occupy a space determined by the functional balance of the oro- facial and tongue musculature.

64. It has been seen that one of the cofactor in RRR is low calcium and vitamin D metabolism. Diet counseling for prosthodontic patients is necessary to correct imbalances in nutrient intake. Denture patients with excessive RRR report lower calcium intake and poorer calcium phosphorus ratio, along with less vitamin D. c. Nutrition:

65. Excessive RRR leads to loss of sulcus width and depth with displacement of muscle attachment more to the crest of residual ridge. Osseous reconstruction surgeries, removal of high frenal attachments, augmentation procedures, vestibuloplasties etc may be required to correct these conditions.   d. Preprosthetic surgery :

66. Inferior Border Augmentation Superior Border Augmentation Interpositional Grafts Ridge augmentation procedures

67. e. Immediate dentures: Some authors claim that extraction followed by immediate dentures reduces the ridge resorption .  

68. f. Overdentures Tooth supported over dentures help in improved stress distribution there by maintaining the integrity of residual ridge. The occlusal and parafunctional stresses are distributed through the abutment teeth . A study was conducted with overdentures supported by canines and it was seen that, the bone loss was 0.6mm where as 5mm in conventional complete dentures.

69. 1 . The denture bearing mucosa of the residual ridges are spared abuse. 2 . Maintenance of the alveolar bone. 3. Sensory feedback . 4 . Tactile sensitivity discrimination. 5 . Masticatory performance. 6 . Reduction of Psychological trauma. The advantages of the overdenture over the conventional denture are :

70.   The introduction of osseointegrated implants has eclipsed traditional preprosthetic surgical techniques. The use of implant-supported overdentures resembles the same clinical situation of teeth supported overdentures . g. Osseointegration and implant supported overdentures :

71. Metal based denture with soft liner is advocated in patients with severely atrophic residual ridges. Metal base provides- Weight necessary to facilitate retention Maintain Adequate strength with modest extensions The soft liner accomodates ridge irregularities and changes. Metal based dentures {JPD 1987 ;57:6 }

72. Precautions during extraction to reduce RRR When a tooth is removed the labial plate should be preserved. The labial periosteal covering should remain intact as its inner layer is responsible for remodeling of bone. If a bone has to be removed it must be the palatal plate.

73. The ultimate aim of a successful prosthesis is stability in function and excellent esthetics . The expectations of edentulous patients are highly variable therefore the outcome of patient treatment varies significantly. Patients should be educated regarding the type and extent of treatment that is ideal for them, the prognosis of the treatment outcomes with various types of removable or fixed prostheses and the alternatives that are available. Summary and Conlusion