Residual ridge resorption

RRR

1. residual RIDGE RESORPTION Della s indran ii nd MDS

2. CONTENTS INTRODUCTION DEFINITIONS BASIC CONCEPT OF BONE MECHANISM OF BONE RESORPTION CLASSIFICATION OF RRR ETIOLOGY OF RRR PATHOLOGY OF RRR PATHOPHYSIOLOGY OF RRR PATHOGENESIS OF RRR CHANGES IN MAXILLA AND MANDIBLE EPIDEMIOLOGY OF RRR DIAGNOSTIC AIDS TO DETECT RRR CONSEQUENCES OF RRR PROSTAGLANDINS AS MEDIATORS OF RRR CALCIUM HOMEOSTASIS AND RRR OSTEOPOROSIS AND RRR MANAGEMENT OF RRR REVIEW OF LITERATURE CONCLUSION REFERENCES

3. INTRODUCTION Residual ridge resorption (RRR) is a major disease that results in functional impairment of stomatognathic system. Treatment of edentulous patients requires maintenance of this phase that must be carried out throughout the patient’s lifetime.

4. DEFINITIONS Residual bone – “That component of maxillary or mandibular bone, once used to support the roots of the teeth, that remains after the teeth are lost.” Residual ridge – “The portion of the residual bone and its soft tissue covering that remains after the removal of teeth.” Residual ridge crest – “The most coronal portion of the residual ridge.” RESIDUAL RIDGE RESORPTION – “A term used for the diminishing quantity and quality of the residual ridge after teeth are removed - GPT 9

5. BASIC CONCEPT OF BONE The structural elements of bone are: Osteocytes found in bone lacunae. The intercellular substance or bone matrix consisting of fibrils and calcified cementing substance. Osteoblasts. Osteoclasts Osteoprogenitor cells

6. INTERCELLULAR SUBSTANCE ORGANIC PART – 33% - 35% Collagen – 88% - 90% Non-collagen – 10% - 11%. Mono-, Di-, Poly- and Oligosaccharides – 6% -9% Proteoglycans – 0.8% ( sulphated and n on- sulphated ) Sialoproteins , Glycoproteins – 0.35% Lipids – 0.4%

7. INORGANIC PART – 65% - 67% Calcium & Phosphates – 95% Hydroxyapatite Crystals – Ca 10 (PO 4 ) 6 OH 2 Magnesium Trace elements – Nickel, Iron, Fluoride, Cadmium, Magnesium, Zinc and Molybdenum .

8. TYPES OF BONE According to bone density: Compact bone Trabecular bone Microscopically: Woven bone Lamellar bone Bundle bone Composite bone

9. MECHANISM OF BONE RESORPTION Attachment of osteoclasts to mineralised surface of bone Creation of a ruffled border and an acidic environment through action of the proton pump Dissolution of the Hydroxyapatite Fall in pH to 2.5-3 in the osteoclast resorption space

10. The organic components of the intercellular substance are removed by proteolytic action of the osteoclasts. The Ca salts (inorganic) are dissolved by a chelating action of the osteoclasts. As resorption takes place, the osteocytes released may revert to osteoblasts or become osteoclasts, depending on the physiologic and pathologic demands. Histologically, bone apposition and resorption take place in close approximation, making it possible to balance the shape and size of bone.

11. CLASSIFICATION OF RRR According to Branemark et al in 1985, ridges were classified on the basis of bone quantity and quality by radiographic means. BONE QUANTITY : ( Branemark ) Class A : Most of the alveolar bone is present Class B : Moderate residual ridge resorption occurs Class C : Advanced residual ridge resorption occurs Class D : Moderate resorption of the basal bone Class E : Extreme resorption of the basal bone

12. BONE QUALITY : Class 1 : Almost the entire jaw is composed of homogenous compact bone. Class 2 : A thick layer of compact bone surrounds a core of dense trabecular bone. Class 3 : A thin layer of cortical bone surrounds a core of dense trabecular bone. Class 4 : A thin layer of cortical bone surrounds a core of low-density trabecular bone.

13. BY WICAL AND SWOOPE : Class I : Up to 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.

14. NIEL’S CLASSIFICATION : Class 1 : Approximately 0.5 inch of space exists between mylohyoid ridge and floor of mouth. Class 2 : Less than 0.5 inch of space exists between mylohyoid ridge and floor of mouth. Class 3 : The mylohyoid muscle is at the same level as the mylohyoid ridge.

15. ATWOOD’S CLASSIFICATION : Order 1 : Pre-extraction Order 2 : Post-extraction Order 3 : High, well rounded Order 4 : Knife-edge Order 5 : Low, well round Order 6 : Depressed

16. ATWOOD’S CLASSIFICATION ORDER I : PRE EXTRACTION : The tooth held in its socket with very thin labial and lingual cortical plates. ORDER II : POST EXTRACTION : The healing period includes clot formation, clot organisation , filling of the socket to the height of the cortical plates with new trabecular bone, & epithelialisation over the socket site. The edge of the RR are still sharp.

17. ORDER III : HIGH , WELL –ROUNDED RESIDUAL RIDGE :The cortical plates are rounded off , narrowing of the crest of the ridge has begun, & remodeling of the internal trabecular structure has taken place. ORDER IV : KNIFE-EDGE RESIDUAL RIDGE - There is marked narrowing of the labiolingual diameter of the crest of the ridge with a compensatory internal remodeling which sometimes leads to incredibly sharp crest of the ridge.

18. ORDER V : LOW WELL-ROUNDED - The end results of progressive labiolingual narrowing of a knife-edge ridge is the disappearance of the knife-edge portion. A more widely rounded, but considerably lower RR remains ORDER VI : DEPRESSED RR - Resorption has continued below the level of the genial tubercle.

19. SIEBERT’S CLASSIFICATION Class I: Buccolingual loss of tissue with normal ridge height in apicocoronal dimension Class II: Apicocoronal loss of tissue with normal ridge width in a Buccolingual dimension Class III: Combination Bucco - lingual and apico -coronal loss of tissue resulting in loss of normal height and width

20. MERCIER’S CLASSIFICATION : Group 1 : No atrophy Group 2 : Minimal atrophy Group 3 : Moderate atrophy Group 4 : Severe atrophy Group 5 : Extremely severe atrophy ZELSTER’S CLASSIFICATION : Group 1 : High muscle attachment & minimal RRR. Group 2 : Severe residual ridge resorption with pain. Group 3 : Absence of residual ridge. Group 4 : Severe resorption of basal bone. Mercier, P., & Lafontant , R. (1979).  Residual alveolar ridge atrophy: Classification and influence of facial morphology. The Journal of Prosthetic Dentistry, 41(1),

21. American college of prosthodontists : Based on Bone Height (Mandible only) Type I : Residual bone height of 21 mm or greater . Type II : Residual bone height of 16 - 20 mm. Type III : Residual alveolar bone height of 11 - 15 mm. Type IV : Residual vertical bone height of 10 mm. McGarry TJ, Nimmo A, Skiba JF, Ahlstrom RH, Smith CR, Koumjian JH. Classification system for complete edentulism . Journal of Prosthodontics. 1999 Mar;8(1):27-39.

22. MISCH’S CLASSIFICATION D1 -Dense cortical bone. D2 -Thick dense to porous cortical bone on crest and cortical trabecular bone within. D3 - Thin porous cortical bone on crest and fine trabecular bone within D4 - Fine trabecular bone

23. ETIOLOGY OF RRR It is postulated that RRR is a multifactorial, biomechanical disease that results from a combination of the following factors: Anatomic Mechanical Metabolic Functional Prosthetic

24. ANATOMIC FACTORS It is postulated that RRR varies with the quantity and quality of the bone of the residual ridges: RRR α anatomic factors Size of ridge Type of bone removed Amount of bone Quality of bone

25. Quantity of bone : It is not a good prognostic factor for the rate of RRR, because it has been seen that some large ridges resorb rapidly and some knife edge ridges may remain with little changes for long periods of time. Quality of bone: On theoretic grounds, the denser the bone, the slower the rate of resorption because there is more bone to be resorbed per unit time .

26. MECHANICAL FACTORS RRR α FORCE DAMPING EFFECT

27. Damping effect takes place in the mucoperiosteum, which has a viscoelastic property Maxillary bone (RR) is frequently broader, flatter and more cancellous than its mandibular counterpart. So it is ideally constructed for the absorption and dissipation of energy. Frost pointed out that the trabaculae in cancellous bone are arranged parallel to direction of compression deformation.

28. METABOLIC FACTORS Generally, body metabolism is the net sum of all the building up (anabolism) and the tearing down (catabolism) going on it the body. RRR α bone resorption factors bone formation factors

29. The thyroid hormone affects the rate of metabolism of cells in general and hence the activity of both, the osteoblasts and osteoclasts. Parathyroid hormone influences the excretion of phosphorous in the kidney and also directly influences osteoclasts. Vit C aids in bone matrix formation. Vit D acts through its influence on the rate of absorption of calcium in the intestines Various members of Vit B complex are necessary for bone cell metabolism.

30. According to Reifenstein , in the young person, there is a relative predominance of anabolic hormones (estrogen and testosterone) over the anti anabolic hormones( cortisone and hydrocortisone) resulting in continued growth of skeleton. He further states that, as people get older, the anabolic hormones are so reduced that the anti-anabolic hormones are in relative excess with the result that bone resorption may take place faster than bone formation and that bone mass may be reduced. Reifenstein , E. C., Jr.: The Relationship of Steroid Hormones to the Development and Management of Osteoporosis in Aging People, Clin . Orthop . 10:206-253, 1957.

31. BONE RESORPTION FACTORS

32. PROSTAGLANDINS – MEDIATORS OF RRR Prostaglandins (PG) has been demonstrated to mediate bone resorption . PG is not stored in cells in their final form but is quickly released in response to mechanical, physiologic and pathologic stimuli. It is hypothesised that osteoblasts are involved in bone resorption by coupling with osteoclasts, because the cellular receptor against various bone resorbing hormones (including PG) have been found in osteoblasts but not in osteoclasts.

33. PG’s are released from many kinds of cells including inflammatory cells such as neutrophilic granulocytes and macrophages as well as local mesenchymal cells such as osteoblasts and cells of the periodontal ligament . Mechanical stimulation of osteoblastic cells causes a significant elevation in cAMP and PG synthesis.

34. CALCIUM HOMEOSTASIS AND RRR The only sources of Ca for the body are Diet Bone reservoir. Ca homeostasis is maintained by controlling Ca obtained from these 2 sources. This can occur by altering internal absorption mechanisms (income) or tubular reabsorption (recycling) or by liberation of Ca from the skeleton via resorption (savings). There is a reciprocal relationship between Ca concentration and bone resorption to maintain Ca homeostasis. As the level of serum calcium drops, resorption is stimulated.

35. Skeletal depletion of calcium occurs as a result of stimulation of parathyroid gland and the alveolar bone is the first to be affected. This is due to the function of parathyroid hormone in maintaining the blood calcium level by mobilizing it from bones by osteoclastic activity. Simultaneously , there is an increased renal excretion of phosphate, which disturbs the blood calcium:phosphorous ratio by raising the blood calcium level. This results in mobilization of phosphates from bones by osteoclastic activity. Under these conditions , alveolar bone becomes susceptible to diseases like osteoporosis.

36. OSTEOPOROSIS AND RRR Osteoporosis is characterized by low bone mass and micro architectural deterioration of the bone, which leads to increased bone fragility and risk of fracture. It has two forms. The more prevalent Type I (post menopausal) affects women for a decade or so after menopause. The Type II (senile or idiopathic) attacks males and females at any age for no obvious reason. RRR maybe a manifestation of Type I osteoporosis . Both cortical and trabecular bone are affected.

37. Treatment for osteoporosis Estrogen replacement therapy Ca supplement Good nutrition and regular exercise New drugs for systemic osteoporosis are under evaluation, including biophosphonates to inhibit osteoclasts Calcitonin to reduce resorption .

38. FUNCTIONAL FACTORS Forces within the physiological limits are beneficial in their massaging effect. On the other hand, increased or sustained pressure produces bone resorption . Bone that is used as by regular physical activity will tend to strengthen within certain limits , while bone that is in disuse will tend to atrophy. Disuse atrophy - It is directly proportional to the extent of disuse. After the loss of natural teeth, bone cannot be stimulated by a denture base as the teeth did internally. The lack of internal stimuli contributes to the disuse atrophy.

39. PROSTHETIC FACTORS Long continued use of ill fitting dentures: Loss of bone Incorrect occlusion Incorrect jaw relation Under-extended dentures: Lead to less retentive dentures and increased load per unit area. Common sites are: Lingual flange Buccal shelf area Retromylohyoid area and Retromolar pad

40. Excessive stress resulting from artificial environment: Human tissues have not evolved in nature to accept ranges of artificial things and the denture acts as an artificial entity. 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 and alteration in tissue form .

41. Faulty improper impression procedures : Before impression procedures, care has to be taken on selection of trays. If the tray selected is too large, it will distort the tissues around the borders of the impression. If it is too small, the border tissues will collapse inward onto the residual ridge. This will reduce the support by the denture flange. The use of minimal and selective pressure impression techniques should be implicated in order to avoid distortion of the mucosa and ridge area which may be under considerable pressure.

42. Error in relating maxilla to the cranial landmarks (orientation relation): The plane of the maxilla should be oriented to the facial reference line (Camper’s plane or ala tragus line). If not, may cause instability of denture leading to resorption . Lack of freeway space due to increased vertical dimension of occlusion: Freeway space is present in the teeth in the physiologic rest position. At times, due to lack of freeway space the bone resorbs because of increased vertical height in an attempt to create the space.

43. 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, it causes pressure on bone due to failure of denture stability. Hence resorption of base occurs Faults in selection and placement of posterior teeth When the ridge is weak, resorbed and covered by only lining mucosa, then the use of the posterior teeth should be smaller. This will limit the occlusal surface, which in turn will minimise the forces directed to such a ridge.

44. Overclosure The loss of proper vertical dimension after the insertion of complete dentures results in the triggering of a cyclic series of events detrimental to the health of the residual alveolar ridge. Overclosure causes the mandible to be moved or rotated in an upward and forward direction causing occlusal disharmony and excessive trauma to anterior region .

45. PATHOLOGY OF RRR Gross pathology: The basic structural change in RRR is a reduction in the size of the bony ridge under the mucoperiosteum. It is primarily a localised loss of bone structure. In some situations, this loss of bone may leave the overlying mucoperiosteum excessive and redundant. Gross reduction of the bone in size and shape that occurs on the external surface on the labial, crestal and lingual aspects of the residual ridge. Bones with the most severe RRR may display the gross porosity of medullary bone on the crest of the ridge

46. RRR does not stop with the residual ridge, but may well go below where the apices of the teeth were, sometimes leaving only a thin cortical plate on the inferior border of the mandible or virtually no maxillary alveolar process on the upper jaw. Sometimes a knife edge ridge maybe masked by a redundant or inflamed soft tissue, which can be detected by palpation or by Lateral cephalometric radiographs.

47. Microscopic pathology: Studies have revealed evidence of osteoclastic activity on the external surface of the crest of the residual ridges. The scalloped margins of Howship’s Lacunae sometimes contain visible osteoclasts . Studies have shown total absence of periosteal lamellar bone on the crest of the residual ridge, and a presence of cortical layer consisting of an endosteal type of bone, or no cortical layer but simply a medullary type of trabecular bone. Varying degrees of inflammatory cells, including lymphocytes and plasma cells , have also been seen.

48. PATHOPHYSIOLOGY Bone Remodelling

49. RRR is a localised pathologic loss of bone that is not built back by simply removing the causative factors. Yet, the physiologic process of internal bone remodeling goes on even in the presence of this pathologic external osteoclastic activity that is responsible for the loss of so much of bone substance. Even if a great deal of RR is removed in total, there is often a cortical layer of bone over the crest of the ridge. This means that new bone has been laid down inside the RR in advance of the external osteoclastic removal of bone. The mechanism of the reduction of the mandibular residual ridge actually represents a modified version of the Enlow’s “V” principle, showing external resorption accompanied by endosteal deposition.

50. PATHOGENESIS OF RRR RRR is a chronic progressive irreversible disease which proceeds slowly over a long period of time from one stage to next Autonomous regrowth has not been reported. Tallgren , Atwood & Coy studied rate of residual ridge resorption for 25 years Mean ratio of anterior maxillary RRR to anterior mandibular RRR was 1:4 RRR is more in mandible than in maxilla and reverse can also occur.

51. WHY THERE IS MORE RESORPTION SEEN IN MANDIBLE THAN MAXILLA ? 1. Mandible provides a smaller surface area of support for the dentures 2. Amount of cancellous bone is lesser as compared to maxilla Dentures help to preserve the horizontal dimensions of residual ridge to some extent & vertical dimensions undergo resorption especially in mandible (4 times )

52. CHANGES IN the MAXILLA AND the MANDIBLE

53. CHANGES IN MAXILLA Maxillary teeth are generally directed downward and outward, so bone reduction generally is upward and inward. Since the outer cortical plate is thinner than the inner cortical plate, resorption from the outer cortex tends to be greater and more rapid. As the maxilla becomes smaller in all dimensions, the denture bearing area (basal seat) decreases. The bone of the maxillae resorb primarily from the occlusal surface and from the buccal and labial surfaces. Thus the maxillary residual ridge loses height and maxillary arch becomes narrower from side to side and shorter anteroposteriorly .

54. CHANGES IN MANDIBLE The anterior mandibular teeth generally incline upward and forward to the occlusal plane, whereas the posterior teeth are either vertical or incline slightly lingually . The mandibular ridge resorbs primarily from the occlusal surface. Because the mandible is wider at its inferior border than at the residual alveolar ridge in the posterior part of the mouth, resorption , in effect, moves the left and right ridges progressively farther apart

55. CHANGES IN MAXILLA AND MANDIBLE The mandibular arch appears to become wider, while the maxillary arch becomes narrower. Thus, RRR is centripetal in maxilla and centrifugal in mandible .

56. EPIDEMIOLOGY OF RRR To date, it would appear that RRR is 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.

57. There have been no large scale studies of RRR Longitudinal cephalometric studies of few subjects have been done Studies also suggest that knife edge tendency (KET ) in mandibular residual ridge in women is more compared to men. KET = Change in area / Change in height

58. DIAGNOSTIC AIDS TO DETECT RRR Serial examinations of diagnostic casts Radiographs : - Cephalometrics - Panoramic. Tetracycline labelling Mercury porosimetry

59. CONSEQUENCES OF RRR Apparent loss of sulcus width and depth. Displacement of muscle attachment close to the ridge. Loss of vertical dimension of occlusion. Increase in relative prognathia Changes in inter alveolar relationship following RRR Morphological changes of the alveolar bone such as sharp, spiny uneven residual ridges. Location of mental formina close to the ridge crest .

60. MANAGEMENT OF RRR Systemic evaluation Diet Tissue treatment therapy Pre prosthetic surgery Prosthetic management Impression techniques Teeth selection and arrangement Overdenture Implant supported prosthesis

61. SYSTEMIC EVALUATION Any systemic condition that can contribute to the degeneration of the bone condition should be corrected and stabilized, for e.g.: osteoporosis, hyperparathyroidism, diabetes mellitus. Any dental treatment should follow only after the condition is under control and the patient is fit for treatment.

62. DIET Patients with bone disease need a diet high in proteins, vitamins and mineral content. Should reduce alcohol and caffeine intake.

63. TISSUE TREATMENT THERAPY Soft conditioning materials can be used to rejuvenate the tissue-bearing area. Hypertrophied tissues, previously treated by surgery, can be reconditioned by using this material.

64. STIMULATION OF EDENTULOUS AREAS Exercise stimulation is a practical & desirable part of complete denture therapy. Exercise stimulation for a period of 12 weeks is usually adequate in most severe cases. Intermittent use of exogenous pulsed electromagnetic fields has demonstrated the effectiveness in decrease in the rate of residual ridge resorption

65. PRE – PROSTHETIC SURGERIES It includes the following surgical procedures: Ridge correction. Ridge extension/ vestibuloplasty . Ridge augmentation

66. RIDGE CORRECTIVE SURGERIES Soft tissue deformities Labial frenectomy . Lingual frenectomy . High buccal frenal attachments. Hyperplasia of soft tissues .

67. Bony deformities Sharp irregular ridge. Alveoloplasty . Alveolectomy . Excision of tori and genial tubercles Ridge extension surgery/ vestibuloplasty Labial. Lingual. Tuberoplasty .

68. Ridge augmentation Increase in the ridge height and width providing a large denture bearing area Protection of neuro vascular bundles Restoration of proper maxillomandibular arch relationship. Ridge augmentation has been tried with: Bone transplants Autogenous cartilage Hydroxyapatite

69. PROSTHODONTIC MANAGEMENT Impression techniques Teeth selection and arrangement Overdentures Implant supported prosthesis

70. IMPRESSION TECHNIQUES In patients with severely resorbed ridges, lack of ideal amount of supporting structures decreases support. T he encroachment of the surrounding mobile tissues onto the denture border reduces both stability and retention. Thus the main aim of the impression procedure is to gain maximum area of coverage . Selection of proper trays and the correct impression procedure is very essential for an accurate impression.

71. Selective pressure technique - This technique is most widely advocated to manage RRR. - It makes it possible to confine the forces acting on the denture to the stress bearing areas . -This helps in better withstanding the mechanical forces induced by denture wearing . - Adequate relief of non stress bearing areas .

72. - Winkler describes a technique which uses tissue conditioners. An over extended primary impression of alginate is made. Denture bases with occlusal rim were fabricated on primary cast. Jaw relations were done to record appropriate horizontal and vertical dimensions. Tissue conditioning material was applied on the tissue surface of mandibular denture base patient was asked to close the mouth in the prerecorded vertical dimension and do various functional movements.

73. 3 applications of conditioning material are used – each application approximately 8-10 minutes . The third and final wash is made with a light bodied material . This technique results in the impression that has tissue placing effect with relatively thick, buccal , lingual and sublingual crescent area borders.

74. McCord & Tyson (BDJ 1997) - Use of admixed technique for impressions : Impression compound and green tracing stick compound in the ratio of 3 : 7 parts by weight placed in a bowl of water at 60 °C and kneaded to a homogenous mass provides a working time of about 90 seconds patient is made to do various tongue movements.

75. All Green Technique : Mandibular impression was made using all green technique. Green stick compound was kneaded to a homogenous mass and was loaded on the special tray and border movements were done. Final impression was made using zinc oxide eugenol .

76. Elastomeric technique : A putty material is loaded along the borders of special tray. The special tray is placed in the mouth and is border molded; the patient is asked to move the tongue according to standard impression procedures . The tray is removed from the mouth, and the impression is examined . Light-body impression material is loaded in the impression and inserted in the mouth . The patient is instructed to repeat the tongue movements, light-body impression material is border molded along the buccal and labial flange areas.

77. Cocktail technique Praveen G., Gupta, S., Agarwal, S., & Agarwal, S. K. (2011).  Cocktail Impression Technique: A New Approach to Atwood’s Order VI Mandibular Ridge Deformity. The Journal of Indian Prosthodontic Society, 11(1), 32–35.

78. TEETH SELECTION AND ARRANGEMENT The selection and arrangement of posterior teeth plays a significant part in the retention and stability of dentures and the conditions of supporting tissues. Buccolingually narrow teeth are used to reduce the masticatory forces per unit area of the ridge. The width of the artificial teeth should be half of the natural teeth. (3) Non anatomic or zero degree posterior teeth should be used to eliminate the horizontal forces and thus provide increased stability to the denture.

79. (4) Acrylic teeth are used in preference to porcelain teeth as acrylic teeth are easy to adjust and transmit less forces to the supporting structures. (5) Arrange the teeth to get a bilateral occlusion in the neutral zone.

80. PROPER DESIGN OF DENTURES AND MAINTENANCE Optimal tissue health prior to making impression. Broad area of coverage helps in reducing force per unit area. Decreased buccolingual width of teeth will decrease the amount of force required to penetrate a bolus of food. Avoidance of inclined planes to minimise dislodgment of dentures and shear forces. Centralisation of occlusal contacts to increase stability and maximize compressive forces.

81. Adequate inter- occlusal distance during jaw rest to decrease the frequency and duration of tooth contact. Resilient denture lining materials helps in transmission of less force/unit area. A number of problems can results from errors in the occlusion. Soreness may develop on the crest of the residual ridges from the pressures created by heavy contacts of opposing teeth in the same region. Correction of occlusion is necessary in this case .

82. OVERDENTURES Teeth supported over dentures helps in improved stress distribution thereby 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 5 mm in conventional complete dentures.

83. IMPLANT SUPPORTED PROSTHESIS According to Morris et al, residual ridge resorption in implant supported prosthesis on the mandibular ridge was less compared to the conventional denture for over a period of 5 years The use of implant-supported overdentures resembles the same clinical situation of teeth supported overdentures .

84. Review of literature

85. Effect of mucostatic and selective pressure impression techniques on residual ridge resorption in individuals with different bone mineral densities: A prospective clinical pilot study Tripathi et al. J.Prosth.Dent.2018 Purpose. The purpose of this prospective clinical pilot study was to objectively evaluate the effect of complete dentures fabricated by different impression techniques on mandibular residual ridge resorption in individuals with different bone mineral density . Material and methods. Ninety-six participants with edentulism , underwent bone mineral density assessment and were divided into normal, osteopenic , and osteoporotic groups . Half of the participants in each group were provided with dentures fabricated by selective pressure impression technique (subgroup SIT), and the other half were provided with dentures fabricated by mucostatic impression technique (subgroup MIT).

86. Computed tomographic scans of the mandible were made at denture delivery and 1 year after prosthesis use to assess alveolar bone height and width difference at marked locations at and after denture delivery. RESULTS No statistically significant differences (P>.05) in mandibular residual ridge height or width were found between subgroups .

87. CONCLUSION RRR is reduced for dentures fabricated using mucostatic impression technique compared with the selective pressure impression technique in patients with diminished bone density.

88. Association between occlusal force distribution in implant overdenture prostheses and residual ridge resorption . Khuder T ,. Journal of Oral Rehabilitation. 2017 May;44(5):398-404. AIM This study aimed to compare residual ridge resorption (RRR) of anterior and posterior maxillary and mandibular edentulous ridges, in patients treated with mandibular implant overdentures (IOD) and compare with conventional complete dentures (CD ). METHOD The anterior and posterior RRR of IOD (6 males, 17 females) and CD (12 males, 11 females) were determined using baseline and follow-up dental panaromic radiographs ( DPT. The bone ratios were calculated using proportional area; anatomic to fixed reference areas, and mean difference of ratios between the intervals determined RRR . The ridge locations included anterior and posterior maxillary and posterior mandibular arches. The T-Scan III digital occlusal system, was used to record anterior and posterior percentage occlusal force (%OF) distributions.

89. RESULT A total of 46 edentulous individuals (23 in each group) participated in this study; and the results showed no significant differences in patients’ demographic variables between IOD and CD.

90. Residual Ridge Resorption in Complete Denture Wearers Samyukta et al , J. Pharm. Sci. & Res. Vol. 8(6), 2016, 565-569 AIM To find out the rate of ridge resorption by w ical and swoop method

91. Materials and Methods 60 completely edentulous subjects with age between 50 – 85 years, completely edentulous for more than 6 months were selected for the study. A standardized panoramic radiograph was made for all patients. Measurements were made digitally and the amount of resorption was calculated using the Wical and Swoope method .

92. CONCLUSION With an increase in age, there is an increase in the amount of resorption . For a particular period of edentulousness, as age is increased, there is an increase in the amount of resorption . The amount of resorption in females is found to be more than that of male. In males and females, as duration of edentulousness increases, there is an increase in the amount of resorption . Duration of edentulousness has the most significant impact on resorption followed by age and then gender.

93. The effects of fixed and removable implant- stabilised prostheses on posterior mandibular residual ridge resorption .   Clinical Oral Implants Research. 2002 Apr;13(2):169-74 AIM This study investigated the change over time in the area of the posterior mandibular residual ridge in patients wearing either i ) mandibular overdentures ii ) mandibular fixed cantilever prostheses stabilised on five or six implants .

94. CONCLUSION In conclusion, this study has demonstrated low rates of posterior mandibular resorption rates in patients with advanced posterior resorption who were stabilised with implant retained overdentures .

95. Effect of serum vitamin D, calcium, and phosphorus on mandibular residual ridge resorption in completely edentulous participants: A clinical study Kalavathy et al.J.Prosth.Dent . 2020 AIM The purpose of this clinical study was to evaluate the degree of mandibular residual ridge resorption in completely edentulous participants and to investigate the role of dietary nutrients in the resorption process . MATERIAL AND METHODS Three hundred (55% men and 45% women; aged between 35 and 85 years) completely edentulous participants. A standardized panoramic radiograph was made, measurements were made digitally, and the amount of resorption was calculated using the Wical and Swoope method.

96. The blood plasma levels of vitamin D3 were analyzed by using the direct competitive chemiluminescence immunoassay (CLIA) method, The total calcium and phosphorus were determined by using spectrophotometer method . RESULTS

97. CONCLUSIONS 1. A strong influence of serum vitamin D3, calcium, and phosphorus levels was found on mandibular residual ridge resorption . 2. Mandibular residual ridge resorption increased as the level of serum vitamin D3, calcium, and phosphorus decreased . 3. No association was found between age and serum vitamin D3, calcium, and phosphorus levels . 4. No association was found between sex and serum vitamin D3, calcium, and phosphorus levels . 5. Age and sex were found to be least associated with mandibular residual ridge resorption .

98. PROSTHODONTIC MANAGEMENT OF RESIDUAL RIDGE RESORPTION BY CONVENTIONAL METHODOLOGIES INCLUDING NEUTRAL ZONE AND LINGUALIZED OCCLUSION SCHEMES: REPORT OF TWO CASES Sonali et al.Journel of critical reviews.2020 AIM This paper presents report of two cases wherein prosthodontic management of residual ridge resorption has been attempted by neutral zone technique and lingualized occlusion scheme. CASE REPORT (NEUTRAL ZONE) A 48-year-old female patient with complaint of difficulty in chewing for the past 6 years .

99. Plaster index placed to conform the neutral zone

100. CASE REPORT [LINGUALIZED OCCLUSION ] A 64 year old male patient with highly resorbed lower anterior ridge Atwood’s class V (Low Well Rounded) reported to the department of prosthodontics of the institution. Patient was an old denture wearer.

101. CONCLUSION R ecording the neutral zone is a quick, reliable, non-invasive and economic technique that greatly improves denture stability . The benefit of neutral zone technique for denture fabrication is that, it stabilizes the denture with the surrounding tissues, instead of dislodging it . Lingualised occlusion redirects vertical forces more centrally on the mandibular alveolar ridge, resulting in enhanced stability of the lower denture.

102. PATTERN OF POSTERIOR RESIDUAL RIDGE RESORPTION UNDER MANDIBULAR IMPLANT HINGING OVERDENTURES: A 5 –YEAR RETROSPECTIVE STUDY Elsayed et al.Egyptian Dental Journel.2017 Purpose: This 5-year retrospective study aimed to investigate and compare the effect of bar designs of two-implant-retained overdentures (2-IRO) on pattern of the residual ridge resorption (RRR) of the posterior mandibles using 3-D Cone Beam Computed Tomography (CBCT) imaging. Materials and Methods : Forty five edentulous patients treated with mandibular 2-IRO opposing maxillary complete denture were selected for the study . According to bar designs; the enrolled patients were divided into three groups: Group BC (n=19) patients treated with two implant overdentures retained by a bar joint with a plastic retentive clip.

103. Group BL (n=14) patients treated with two-implant overdentures retained by locator attachments on the top of milled bar. Group BD (n=12) patients treated with two-implant overdentures retained by a straight bar with a plastic retentive clip & distally cantilevered ball attachments. The pattern of posterior RRR was evaluated by using CBCT imaging after 5 years post-treatment . RESULT For group BL, no significant differences were revealed in height and width (for both buccal and lingual sides) of alveolar bone when comparing molar and premolar areas . For group BD, the reduction in RRR recorded highly significant differences

104. CONCLUSION Mandibular posterior residual ridge resorption occurs irrespective of 2-IRO design. The impact of bar design on the rate of residual ridge resorption is a matter of controversy.

105. CONCLUSION As prosthodontists, we need to perform the most meticulous prosthodontic care of edentulous patients. More research is needed on RRR to find better methods of prevention or control of the disease to provide best possible oral health care.

106. REFERENCES Essentials of complete denture-Winkler Syllabus of Complete Denture- Heartwell Prosthodontic treatment for edentulous patient-Boucher Clinical Dental Prosthetics- Fenn Levin B: impressions for complete dentures. Ortman HR: Factors of bone resorption of the residual ridge. J Prosthet Dent 1962;12,3:429-440. Atwood DA: Reduction of residual ridges: A major oral disease entity. J Prosthet Dent 1971;26:266-279. Atwood DA : Post extraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and serial cephalometric roentgenograms. J Prosthetic Dent 1963;13:810-824

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