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Theories, Principles & Objectives of impression Making Of Completely Edentulous Patients

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Theories, Principles & Objectives of impression Making Of Completely Edentulous Patients

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Theories, Principles & Objectives of impression Making Of Completely Edentulous Patients

  1. 1. Presented By:- Dr. Soham Prajapati, 1st Year PG, Dept. of Prosthodontics & Maxillofacial Prosthesis Including Oral Implantology 29-05-14 Guided By:- Dr. Dilip Dhamankar Dr. Ravi Kumar C.M. Dr. DRV Kumar Dr. Manish Chadha Dr. Devendra THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING IN COMPLETELY EDENTULOUS PATIENTS THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  2. 2. CONTENTS • Introduction • Definitions • History of Complete Dentures • Theories of Impression Making • Principles of Impression Making • Objectives of Impression Making • Conclusion • References THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  3. 3. Introduction • The beginning of a good denture starts with making of a good impression, so a good impression is a stepping stone. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  4. 4. • Impression: a negative likeness or copy in reverse of the surface of an object. • Dental Impression: a negative imprint of an oral structure used to produce a positive replica of the structure to be used as a permanent record or in the production of a dental restoration or prosthesis. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING Definition Glossary of Prosthodontic terms, 8th edition
  5. 5. • Complete denture is defined as a removable dental prosthesis that replaces the entire dentition and associated structures of the maxillae or mandible THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING Definition Glossary of Prosthodontic terms, 8th edition
  6. 6. History of Complete Dentures • 1711 Matthian G. Purman introduced the use of wax. • 1844 Plaster of paris was first used as an impression material. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  7. 7. • 1845-1899 concepts of atmospheric pressure, maximum extension of denture bearing area, equal distribution of pressure and close adaptation of the denture bearing tissues were stressed. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING History of Complete Dentures
  8. 8. History of Complete Dentures • 1928 Pierre Fauchard made dentures by measuring the mouth with compasses and cutting bone into an approximate shape. • 1896 Green brothers introduced mucocompressive theory. • 1900-1929 Concepts like Rebase impressions, border molding and techniques for flabby tissues were introduced. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  9. 9. History of Complete Dentures • 1930-1940 This era recognized the anatomy of the denture bearing areas, and muscle physiology as related to impression procedures. This is evident by descriptions of border molding of dentures. Several new impression materials were introduced : reversible hydrocolloids, zinc oxide eugenol and zinc oxide and oil of cloves THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  10. 10. History of Complete Dentures • 1950-1964 more emphasis on biologic factor of impression making was given. • 1951 Carl O Boucher introduced selective pressure theory. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  11. 11. History of Complete Dentures 1965-1980 new techniques to manage compromised situations were introduced. New techniques are periodically been formulated to overcome the drawbacks faced. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  12. 12. Theories of Impression Making. • Most of the impressions of the twentieth century are made with a view to functional movement of the musculature. • Theoretically, the impressions are so formed that the complete denture will require no change in contour. This happens often with upper dentures but no so often with lower dentures. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  13. 13. Theories of Impression Making. • Impression are made with – Definitive-pressure impressions – Minimal-pressure impressions – Selective-pressure impressions • COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION – Functional impression technique. – Not discussed about definitive pressure impressions. – DCNA, Volume 40, January 1996. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  14. 14. – Definitive-pressure impressions • Because denture retention is tested most severely during mastication, many dentist formerly considered it essential for the tissue to remain in contact with the denture during chewing. • However, dentures did not fit well at rest, because of » Tissue so distorted, tend to rebound. » Tissues so abused will long maintain the shape that they assumed on the day of impression. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION Theories of Impression Making. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  15. 15. – Definitive-pressure impressions • Many of the proponents of this group advocated the use of closed- mouth techniques (Tryde et al., 1965). • Aside the disadvantages of pressure impression technique mentioned above, the closed mouth technique do not allow adequate muscle trimming of the periphery. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING Theories of Impression Making.
  16. 16. Theories of Impression Making. – Definitive-pressure impressions • Very often dentures made with this technique are over-extended and must be arbitrarily trimmed. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION • Critics of this procedure point out that the dentures are in actual contact for only a relatively short period of time and the constant pressure, even if equal, may overstress the tissue. • Advocates were not always able to actually obtain the desired pressure but tended to creat excessive pressure. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  17. 17. Theories of Impression Making. – Definitive-pressure impressions • Dentures often resulted in good initial retention but eventually bone resorption and loose dentures. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  18. 18. Theories of Impression Making. – Minimal-pressure impressions • The popularization of this techniques in the early forties. • Idea was not new, however for Richardson in 1896 had advocated plaster because it least disturbed the tissues. • Addison (1944) descirbed the so called “muco- static impression” and attributed to Page. This was based on theories and were not applicable in the oral cavity. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  19. 19. Theories of Impression Making. – Minimal-pressure impressions • Main point of the mucostatic principle concerned Pascal’s law, which states that pressure on a confined liquid, will be transmitted throughout the liquid in all directions. • According to this concept, the mucosa, being more than 80 % water, will react like liquid in a closed vessel and thus cannot be compressed. • This is not true, as tissue fluids can easily escape under the border of a denture. Hence mucosa is not a closed vessel. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  20. 20. Theories of Impression Making. – Minimal-pressure impressions • According to principle of mucostatics, impression material should record, without distortion every detail of the mucosa so that complete denture would fit all minute elevations and depressions. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  21. 21. – Minimal-pressure impressions • So much emphasis on recording detail was placed that even seperating medium could not be used at any point in the procedure. • Needless to say, the impression materials and cast exhibited sufficient dimensional change to render worthless the care used to obtain the minute details of the mucosal surface. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION Theories of Impression Making. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  22. 22. – Minimal-pressure impressions • Mucostatics further demanded that a metal base be used rather than the dimensionally unstable acrylic. • Gold, one of the most accurate metals, was by passed in favor of a chrome alloy. Thus another minor inaccuracy was added. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING Theories of Impression Making.
  23. 23. – Minimal-pressure impressions • Most Important of all, the mucosal typography, is not static over a 24-hour period. • There is difference between the mucosal contours just after rising in the morning, and that which exists after 12 hours in the upright position. (Stephens et al, 1966) • So all the infinite details achieved in the impression would be altered by the time the denture is finished. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION Theories of Impression Making. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  24. 24. Theories of Impression Making. – Minimal-pressure impressions • The adherents of the mucostatic principle considered interfacial surface tension as the only important retentive mechanism in complete dentures. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  25. 25. Theories of Impression Making. – Minimal-pressure impressions • Therefore, they did not use conventional flanges. However, Dykins (1947) recommended a short lingual flange in order to resist lateral displacement. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  26. 26. – Minimal-pressure impressions • Mucostatic principle further ignores » The value of dissipating masticatory forces over larger possible basal seat area. » The form of mucostatic denture minimized the retentive role of the musculature. (Fish, 1948) – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING Theories of Impression Making.
  27. 27. Theories of Impression Making. – Minimal-pressure impressions • Reference in literature to negative pressure impressions (Denen, 1944), but one recognize that non pressure or negative pressure impression techniques do not exist. • These are semantic devices to dramatize the minimal amount of forces desirable in making impressions. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  28. 28. Theories of Impression Making. – Minimal-pressure impressions • Thus it attempts to record the oral tissues “at rest”. • Requires a material of high fluidity (low viscosity). • Thus create a denture base that models the unloaded tissues. – DCNA, Volume 40, January 1996. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  29. 29. Theories of Impression Making. – Selective Pressure Technique • This principle is based on the belief that the mucosa over the ridge is best able to withstand pressure, whereas that covering the midline is thin and contains very little submucosal tissues. (Boucher, 1951). – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  30. 30. Theories of Impression Making. – Selective Pressure Technique • Boucher advocated that this technique combines the principles of both pressure and non pressure procedures – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  31. 31. Theories of Impression Making. – Selective Pressure Technique • The technique utilizes a preliminary compound impression that is generously relieved over the midline and incisive papilla areas. • The final impression is taken in plaster, which acts as a wash and also records the relieved areas with minimal pressure while the ridge areas are undergoing considerable pressure. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  32. 32. Theories of Impression Making. – Selective Pressure Technique • Thus, the midline and papilla sections of the denture will not make contact with the mucosa when the denture is not in function, but by the same token, they will not bear heavily when the patient is chewing. – COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  33. 33. Theories of Impression Making. – Selective Pressure Technique • Points to keep in mind:- » Most fine dentures are made with this principle. » This technique demands firm, healthy mucosal covering over the ridge. » If flabby ridge exist, it is preferable to use a minimal pressure impression. • COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD EDITION » This technique optimizes the stability and retention of the prosthesis • DCNA, Volume 40, January 1996. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  34. 34. Theories of Impression Making. – Functional Impression Technique • This technique uses a complete denture that is delivered, relieved on its internal aspects, and filled with a slow setting impression material(tissue conditioning material). • The patient wears the prosthesis for several days, allowing the tissues to be recorded “in function” – DCNA, Volume 40, January 1996. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  35. 35. Theories of Impression Making. – Functional Impression Technique • The completed impression then is converted to and reline material via laboratory processing. • This technique seeks to create a denture base that models the functionally loaded tissues. – DCNA, Volume 40, January 1996. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  36. 36. Principles of Impression Making. • The concepts to be followed to get successful impression are:- – The oral tissues must be healthy. – Impression should include all of the basal seat within the limits of health and function of the supporting and limiting tissues. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  37. 37. Principles of Impression Making. – The borders must be in harmony with the anatomical and physiological limitation of the oral structures. – Physiological type of border moulding should be performed. – Sufficient space should be provided within the impression tray for the selected impression material. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  38. 38. Principles of Impression Making. – Impression must be removed from the mouth without damaging the mucosa. – Selective pressure should be applied on the basal seat during impression making. – A guiding mechanism should be provided for correct positioning of the tray within the mouth. – The tray and impression material should be made of dimensionally stable materials. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  39. 39. Principles of Impression Making. – The external shape of the impression should be similar to the external form of complete denture. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  40. 40. Objectives of Impression Making • In an impression technique for complete dentures, the procedures must strive for five primary objectives. The objectives are:- – Preservation – Support – Stability – Esthetics – Retention THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 40/100
  41. 41. Objectives of Impression Making • Preservation – M. M. De Van’s dictum, “It is more important to preserve what already exists than to replace what is missing” has never been challenged or disapproved. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 41/100
  42. 42. Objectives of Impression Making • Preservation – Preservation of the remaining residual ridges is one objective. – It is physiologically accepted that with the loss of stimulation of the natural teeth the alveolar ridge will atrophy or resorb. This process varies in individual. – Syllabus of Complete denture, Charles M. Heartwell, 4th edition 42/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  43. 43. Objectives of Impression Making • Preservation – This process can be hastened or retarded by local factors. – Pressure in the impression technique is reflected as pressure in the denture base and results in soft tissue damage and bone resorption. – Syllabus of Complete denture, Charles M. Heartwell, 4th edition 43/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  44. 44. Objectives of Impression Making • Preservation – Hence, in impression making, this rule is followed by not using heavy pressure and by not covering as much of the supporting areas as possible to minimize the possibility of the soft tissue abuse and bone resorption. – Bernard Levin, Impressions for Complete Dentures 44/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  45. 45. Objectives of Impression Making • Preservation – Other factors such as • Occlusion • Interocclusal distance • Centric relation in harmony with centric occlusion are of great importance. – Syllabus of Complete denture, Charles M. Heartwell, 4th edition 45/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  46. 46. Objectives of Impression Making • Support – Denture support is the resistance to vertical forces of mastication and to occlusal or other forces applied in a direction towards the basal seat. – Bernard Levin, Impressions for Complete Dentures 46/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  47. 47. Objectives of Impression Making • Support – When the natural teeth are missing, the alveolar ridge and their coverage of mucosal tissues become the supporting elements. – They were never meant to endure the forces of mastication and other constant occlusal pressures that result from swallowing, clenching and bruxing. – Bernard Levin, Impressions for Complete Dentures 47/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  48. 48. Objectives of Impression Making • Support – To make the best of a bad situation, it is necessary to enhance the available support by utilizing maximum coverage of all usable ridge bearing areas. – Must be accomplished without interference of routine movements or function of the stomatognathic system. – Bernard Levin, Impressions for Complete Dentures 48/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  49. 49. Objectives of Impression Making • Support – Maximum coverage provides the “snowshoe” effect, which distributes applied forces over as wide an area as possible. – This helps in preservation, stability and retention. – Syllabus of Complete denture, Charles M. Heartwell, 4th edition 49/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  50. 50. Objectives of Impression Making • Support – Areas of support • Divided into » Primary » Secondary » Slight – Bernard Levin, Impressions for Complete Dentures 50/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  51. 51. Objectives of Impression Making • Support – Primary support • Areas of edentulous ridge that are at right angles to occlusal forces do not resorb easily. • Maxillary:- Posterior ridges and flat areas of the palate. – Bernard Levin, Impressions for Complete Dentures 51/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  52. 52. Objectives of Impression Making • Support – Primary support • Mandibular:- Buccal shelf area, posterior ridges and the pear shaped pad. The pear shaped pad is sometimes soft and can be a poor area of support but must be covered so the important retromylohyoid flange is complete and the buccal shelf is covered. – Bernard Levin, Impressions for Complete Dentures 52/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  53. 53. Objectives of Impression Making • Support – Secondary support • Areas of the edentulous ridge that are greater than at right angles to occlusal forces or are parallel to them; also the areas of the edentulous ridge that are at right angles to occlusal forces tend to resorb under load. • For example, the anterior ridge is known to resorb at a much faster rate than the posterior ridge areas where it is subjected to load. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 53/100
  54. 54. Objectives of Impression Making • Support – Secondary support • Maxillary:- anterior ridge and all ridge slopes • Mandibular:- anterior ridge and all ridge slopes. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 54/100
  55. 55. Objectives of Impression Making • Slight – Areas of very displaceable tissues, i.e, all the vestibular areas that provide very little support but are needed for the the very important peripheral seal. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 55/100
  56. 56. Objectives of Impression Making • Importance of covering the buccal shelf – Buccal shelf is the area of bone between the extraction sites of the molars and the external oblique line. The cortical plate over the site of the extracted teeth is rarely intact and is usually spiculated and rough. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 56/100
  57. 57. Objectives of Impression Making • Importance of covering the buccal shelf – It is intact cortical plate and tends not to resorb due to stimulation of the attachment of the buccinator muscle. – When the ridge is flat, the buccinator is often attached almost to the centre of the ridge. This muscle can be covered by the denture in this area because this muscle is flaccid and inactive, and also its fibers function in a horizontal direction. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 57/100
  58. 58. Objectives of Impression Making • Importance of covering the buccal shelf – Fortunately, in rare old patients, buccinator is tense and active, then it is more difficult to cover buccal shelf area (tend to have flatter ridges). – i.e., thin spiney, or flat, the buccal shelf is usually the only available area of support. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 58/100
  59. 59. Objectives of Impression Making • Importance of covering the retromolar pad – The reason the pear-shaped pads so important for support is that it is an area that rarely resorbs. – Because the very large and active temporalis muscle inserts on the coronoid process and also on the anterior border of the ramus with the tendons ending on the alveolar bone distal to the pad. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 59/100
  60. 60. Objectives of Impression Making • Importance of covering the retromolar pad – Bone responds to tensile stimulation by growth and apposition, which cause areas of muscle attachments not to resorb. E.g genial tuberlce and mylohyoid ridges. – Pad is on an area of bone that is relatively stable. – Important to include the pad in the impression so that it can be used as a landmark for the placement of the occlusal plane. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 60/100
  61. 61. Objectives of Impression Making • Improving Support – There are five basic Methods:- • Surgical removal of pendulous tissue • Use of tissue-conditioning materials • Surgical reduction of sharp or spiney mandibular ridge • Surgical enlargement of ridge. • Implants. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 61/100
  62. 62. Objectives of Impression Making • Retention – Retention of a denture is its resistance to removal in a direction opposite to that of its insertion. – Retention resist the adhesiveness of foods, the force of gravity, and the forces associated with the opening of the jaws. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 62/100
  63. 63. • Retention – FACTORS INVOLVED IN THE RETENTION OF DENTURES • Interfacial force • Adhesion • Cohesion • Oral and facial musculature • Atmospheric pressure • Adhesion, Rotation insertion paths and Parallel walls • Gravity – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. Objectives of Impression Making THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 63/100
  64. 64. Objectives of Impression Making • Interfacial force – “The tension or resistance to separation possed by the film of liquid between two well-adapted surfaces” –GPT – For better understanding, it is divided into:- • Interfacial surface tension • Interfacial viscous tension – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 64/100
  65. 65. Objectives of Impression Making • Interfacial Surface Tension – It results from a thin layer of fluid that is present between two parallel planes of rigid material. – It dependent on the ability of fluid to wet the rigid surrounding material. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 65/100
  66. 66. Objectives of Impression Making • Interfacial Surface Tension – If the surrounding material has a low surface tension, as oral mucosa does, fluid will maximize its contact with the material, thereby wetting it readily and spreading it out in a thin film. – Denture base material vary in their surface tension( termed as wettability), with processed materials displaying greater wettability than autocured resins. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 66/100
  67. 67. Objectives of Impression Making • Interfacial Surface Tension – This factor may not play as important a role in retaining the mandibular denture as it does for the maxillary one. – WHY? • In many patients, there is sufficent saliva to keep the external borders of the mandibular denture awash in saliva, thereby eliminating the effect of interfacial surface tension. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 67/100
  68. 68. Objectives of Impression Making • Interfacial Surface Tension – All the denture base materials have higher surface tension than oral mucosa, but once by salivary pellicle, their surface tension is reduced, which promotes maximizing the surface area between liquid and base. – Thus the thin film furnishes retentive force by virtue of the tendency of the fluid to maximize its contact with both surfaces. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 68/100
  69. 69. Objectives of Impression Making • Interfacial Viscous Tension – It refers to the force holding two parallel plates together that is due to the viscosity of the interposed liquid. – It is explained by Stefan’s Law – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 69/100
  70. 70. Objectives of Impression Making • Interfacial Viscous Tension – F decreases with the increase in (h )width of the space between the denture base and the mucosa. – A slow and steady increase in V (velocity of the displacing force) will have least resistance from interfacial surface tension than a rapid V. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 70/100
  71. 71. Objectives of Impression Making • Interfacial Viscous Tension – To obtain maximum interfacial surface tension:- • Saliva should be thin and even. • Perfect adaptation between the denture base and the tissue should be present. • Denture base should cover a large area. • There should be a good adhesive and cohesive forces, which aid to enhance interfacial surface tension – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 71/100
  72. 72. Objectives of Impression Making • Adhesion – “the physical attraction of unlike molecules to one another” – GPT – Saliva plays an important role in adhesion. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 72/100
  73. 73. Objectives of Impression Making • Adhesion – The amount of adhesion present is directly proportional to the denture base area. – In patients with Xerostomia, adhesion does not play a major role. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 73/100
  74. 74. Objectives of Impression Making • Adhesion and Xerostomia – Denture base seem to stick to the dry oral mucosa – It is not very retentive and predisposes to mucosal abrasion and ulcerations, due to lack of salivary lubrication. – It is annoying for the patients to have stick the denture base to the lips, cheek and tongue. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 74/100
  75. 75. • Adhesion and Xerostomia – Prescription • An ethanol free rinse containing aloe or lanolin, a water soluble lubricating jelly, or a salivary substitute containing carboxymethylcellulose (CMC) or a mammalian mucin can be helpful. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. Objectives of Impression Making THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 75/100
  76. 76. Objectives of Impression Making • Adhesion and Xerostomia – Prescription • In case or irradiation or autoimmune disorder, a prescription of 5 to 10 mg of oral pilocarpine, 3 times a day can be beneficial if a patient can tolerate the likely adverse effects like increased perspiration and occasionally excess lacrimation. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 76/100
  77. 77. Objectives of Impression Making • Cohesion – “the physical attraction of like molecules for each other” – GPT – It acts within the thin film of saliva. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 77/100
  78. 78. Objectives of Impression Making • Cohesion – The effectiveness of these forces increases with increase in denture-bearing area. – Watery serous saliva can form a thinner film and is more cohesive than thick mucous saliva. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 77/100
  79. 79. Objectives of Impression Making • Cohesion – Actually, normal saliva is not very cohesive. – Unless saliva is modifed (as it can be through the use of denture adhesive) – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  80. 80. Objectives of Impression Making • Oral and Facial Musculature – It supply supplementary retentive forces, provided • Teeth being positioned in the neutral zone • Polished surface being properly shaped. This is not to say that patient should hold their prosthetic teeth in place by conscious effort but the shape of the buccal and lingual flanges must make it possible for the musculature to fit automatically against the denture and thereby to reinforce the border seal. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  81. 81. Objectives of Impression Making • Oral and Facial Musculature – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  82. 82. Objectives of Impression Making • Atmospheric Pressure – When displacing forces act on a denture, a partial vacuum is produced between the denture and soft tissues, which aid in retention. – This property is called natural suction of a denture. – Hence atmospheric pressure is referred to as emergency- retentive force or temporary restraining forces. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  83. 83. Objectives of Impression Making • Atmospheric Pressure – Retention produced by an atmospheric pressure is directly proportional to the denture base area. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  84. 84. Objectives of Impression Making • Undercuts, Rotation insertion paths and Parallel walls – The resiliency of the mucosa, submucosa overlying basal bone allows for the existence of the modest undercut that can enhance retention. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  85. 85. Objectives of Impression Making – Less severe undercuts of the lateral tuberosities, maxillary premolar areas, distolingual areas and lingual mandibular midbody areas can be extremely helpful to the retention of the prosthesis. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  86. 86. Objectives of Impression Making • Undercuts, Rotation insertion paths and Parallel walls – Some “undercuts” are only undercut in relationship to a linear path of insertion or presumed vertical path of insertion. – However, if the undercut is seated first and the remainder of the denture base can be brought into proximity with the basal seat on rotation of the prosthesis around the undercut part that is already seated; this rotational path will provide resitance against vertical displacement. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  87. 87. Objectives of Impression Making • Undercuts, Rotation insertion paths and Parallel walls – Prominent alveolar ridge with parallel and buccal walls may provide significant retention by increasing the surface area between denture and mucosa and thereby maximizing interfacial and atmospheric forces. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  88. 88. Objectives of Impression Making • Gravity – When a person is in upright posture, gravity acts as a retentive force for the mandibular denture and a displacive force for the maxillary denture. – Weight of the denture acts as an important factor. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  89. 89. Objectives of Impression Making • Gravity – Curiously, another report focusing on maxillary denture base materials in patients with xerostomia found strong patient preference for metal based prothesis in the maxilla. – Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  90. 90. Objectives of Impression Making • Stability – The stability of a denture is its ability to remain securely in place when it is subjected to horizontal movements. – The latter occurs during the functional forces of chewing, talking, singing, whistling, kissing, etc – all the orofacial activities needed for normal everyday living. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 90/100
  91. 91. Objectives of Impression Making • Stability – To be stable, a denture requires • Good retention • Noninterferening occlusion • Proper tooth arrangement • Proper form and contour of the polished surface • Proper orientation of the occlusal plane • Good control and coordination of the patient’s musculature. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 91/100
  92. 92. Objectives of Impression Making • Stability – Occlusion • No matter how skillfully the impressions were made, the dentures will eventually loosen and cause irritation if there are interfering occlusal contacts. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 92/100
  93. 93. Objectives of Impression Making • Stability • A common occurrence is an interfering contact in the second area that may cause the mandibular denture to rotate upward and forward. – Bernard Levin, Impressions for Complete Dentures THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 93/100
  94. 94. • Stability – Occlussal plane • Ideally the occlusal plane is parallel to and anatomically oriented to the ridges. • If the occlusal plane is tipped, there will be a shunting effect and a loss of stability. – Bernard Levin, Impressions for Complete Dentures Objectives of Impression Making THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 94/100
  95. 95. • Eshetics – The role of esthetics in impression making refers to the development of the labial and buccal borders so that they are not only retentive but also support the lips and cheeks properly. – Bernard Levin, Impressions for Complete Dentures Objectives of Impression Making THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 95/100
  96. 96. Conclusion • Muller De Van stated that the perpetual preservation of what remains is more important than the meticulous replacement of what is lost. THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  97. 97. References • Complete Denture Prosthodontics, John J. Sharry, 3rd edition • Bernard Levin, Impressions for Complete Dentures • Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition. • Syllabus of Complete denture, Charles M. Heartwell, 4th edition • DCNA, Volume 40, January 1996. • Glossary of Prosthodontic terms, 8th edition • M. M. Devan, Basic principles in impression making, JPD 2005, 503-508 THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING
  98. 98. Thank you THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING

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