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principles and objectives in impression making.docx

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Principles and objectives of
impression making
Principles of impression making
Concepts to be followed to get a successful...
2
10. Impression should include all of the basal seat within the
limits of health and function of the supporting and limit...
3
Factors that affect retention-
o Anatomical factors
o Physiological factors
o Physical factors
o Mechanical factors
o Mu...
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principles and objectives in impression making.docx

  1. 1. Principles and objectives of impression making Principles of impression making Concepts to be followed to get a successful impression are : 1. The oral tissue must be healthy 2. The tray and impression material should be made of dimensionally stable material 3. A guiding mechanism should be provided for correct positioning of the tray within the mouth 4. Sufficient space should be provided within the impression tray for the selected impression material 5. The borders must be in harmony with the anatomical and physiological limitations of the oral structure 6. Physiological type of border molding should be performed 7. Selective pressure should be applied on the basal seat during impression making 8. Impression must be removed from the mouth without damaging the mucosa 9. The external shape of the impression should be similar to the external form of complete denture
  2. 2. 2 10. Impression should include all of the basal seat within the limits of health and function of the supporting and limiting tissue Objectives of impression making in complete denture An impression should be made with purpose of obtaining the following characteristics in the denture to be fabricated.  Retention  Stability  Support  Aesthetics  Preservation of remaining structures Retention It is defined as, “That quality inherent in the prosthesis which resists the force of gravity, adhesiveness of foods, and the forces associated with the opening of the jaws.” _ GPT Retention is the ability of the denture to withstand displacement against its path of insertion.
  3. 3. 3 Factors that affect retention- o Anatomical factors o Physiological factors o Physical factors o Mechanical factors o Muscular factors Anatomical factors Size of the denture bearing area: Retention increases with increase in size of the denture bearing area. The size of the maxillary denture bearing area is about 24 cm^2 and that of mandibular is about 14 cm^2. Hence the maxillary denture have more retention than mandibular denture.
  4. 4. 4 Quality of the denture bearing area: The displaceability of the tissue influence the retention of the denture. Tissue displaced during impression making will lead to tissue rebound during denture use, leading to loss of retention. Physiological factors Saliva : The viscosity of saliva determines retention. Thick and ropy saliva gets accumulated between the tissue surface of the denture and the palate leading to loss of retention. Thin and watery saliva can also lead to loss of retention. Thin and watery saliva can also lead to compromised retention. Cases with ptyalism can lead to gagging and in patients with xerostomia, denture can produce soreness and irrigation. Physical factors o Adhesion o Cohesion o Interfacial surface tension o Capillary attraction o Atmospheric pressure 24cm 14cm
  5. 5. 5 Adhesion Adhesion is defined as, “The physical attraction of unlike molecules to one another.” The role of saliva is very important for adhesion. Saliva wets the tissue surface of the denture and the mucosa. A thin film of saliva is formed between the denture and the tissue surface. This thin film help to hold the denture to the mucosa. The amount of adhesion present is proportional to the denture base area. Cohesion Cohesion is defined as l, “The physical attraction of like molecules to each other.” The cohesive forces act within the thin film of saliva. 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 mucus saliva. Interfacial surface tension Interfacial surface tension is defined as, “The tension or resistance to separation possessed by the film of liquid between two well adapted surfaces.”
  6. 6. 6 It play a major role in the retention of a maxillary denture. It is totally dependent on the presence of air at the margin of liquid and solid contact. In mandibular denture there is excess saliva along the borders of a mandibular denture there is minimal interfacial surface tension. Capillary attraction Capillary attraction is defined as, “that quality of surface tension that is elevation or depression of the surface of a liquid that is in contact with a solid.” Atmospheric pressure Retention produced by atmospheric pressure is directly proportional to the denture base area
  7. 7. 7 Mechanical factors o Undercuts o Retentive springs o Magnetic forces o Denture adhesives o Suction chambers and suction disks Muscular factors There is balance between force acting from buccal musculature and tongue. This balance is obtained in neutral zone.
  8. 8. 8 Stability Stability is defined as, “The quality of a denture to be firm, steady, or constant, to resist displacement by functional stresses and not to be subject to change of position when forces are applied.” _ GTP THE VARIOUS FACTOR AFFECTING STABILITY ARE: o VERTICAL HEIGHT OF RESIDUAL RIDGE o QUALITY OF SOFT TISSUE COVERING THE RIDGE o QUALITY OF THE IMPRESSION o OCCLUSAL RIMS o ARRANGEMENT OF TEETH o COUNTER OF THE POLISHED SURFACE VERTICAL HEIGHT OF RESIDUAL RIDGE The residual is should have sufficient vertical height to obtain good stability. Highly resorbed ridges often is stability.
  9. 9. 9 QUALITY OF SOFT TISSUE COVERING THE RIDGE The ridge provide a firm soft tissue base with adequate submucosa to offer goods ability. Flabby tissues with excessive submucosa offer poor stability. QUALITY OF THE IMPRESSION  An impression should be as accurate as possible.  The impression surface should be smooth and duplicate all the details accurately.  It should be devoid of voids and any rough surfaces.  The impression should not warp on removal.  The impression should be dimensionally stable and the cast should be poured as soon as possible. OCCLUSAL RIMS The occlusion plane should be oriented parallel to the ridge. If the occlusal plane is inclined, then the sliding forces may act on the denture, reduce its stability. The occlusal plane should divide the interarch space equally.
  10. 10. 10 ARRANGEMENT OF TEETH The teeth in the denture should be arranged in neutral zone. The neutral zone is defined as, “The potential space between lip and cheeks on one side and the tongue on other. Natural or artificial teeth in this zone are subject to equal and opposite forces from this surrounding musculature.”_GTP COUNTER OF THE POLISHED SURFACE The polished surface of the denture should be harmonious with the oral structure. They should not interfere with the action of the musculature.
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