Impression And Mouth Preparation Long Essays

Impression And Mouth Preparation Long Essays

Question 1. Define impression. Discuss in detail the most widely accepted technique of making an impression in complete dentures.
Answer:

Impression:

A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.

Impression Techniques:

1. Mucostatic
2. Mucocompressive
3. Selective pressure technique
   • It is the most widely accepted impression technique
   • In this technique, forces are confined to stress-bearing areas whereas non-stress-bearing areas are relived

Technique:

• Primary impression is made with overextended borders Primary cast is prepared from it
• Undercuts are blocked with wax on cast Relief wax is adapted over relief areas on cast
• A spacer is adapted throughout the extent of the special tray
• Separating media like cold mold seal or tin foil is applied over cast
• Special tray with a handle is fabricated
• It should be 2 mm short of sulcus
• Materials used for it are: Shellac, cold cure acrylic, Type II impression compound
• Wax spacer is then scraped off
• Border moulding is done using greenstick compound
• Relief wax is removed
• Escape holes are made over the tray
• Secondary impression material is loaded over the tray
• It is then seated in the patient’s mouth and the secondary impression is made.

Materials Used:

Question 2. Define impression.
Or
Discuss various impression procedures in the complete denture.
Or
Add a note on selection of impression materials.
Answer:

Impression:

A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.

Impression Procedures:

1. Custom Tray Impression:
   • Design a custom tray with a spacer
   • It should be 2 mm short of sulcus
   • Border molding is done
   • It results in recording the sulcus in dynamic function
   • Spacer is scraped
   • The impression is recorded by ZOE
   • It results in recording the stress-bearing areas un- der pressure & non stress-bearing ares are relieved.
2. Tray Compound:
   • The impression made using tray impression compound
   • The impression is refined & trimmed
   • The metal wire is attached to tray compound to act as a handle
   • Treat it as a custom tray
   • Border molding done
   • Wash impression is made over it

Read And Learn More: Prosthodontics Question And Answers

Selection Of Materials:

• They should be fluid enough to adapt to oral tissues
• Should be viscous enough to be contained in the tray that is seated in the mouth
• While in the mouth, they should set into a rubbery or rigid solid in a reasonable amount of time
• The set impression should not tear or distort when removed
• The impression made should be dimensionally stable
• Stability should be maintained after the removal of a cast so that a second or third cast can be made
• The material should be biocompatible
• It should be cost-effective
• Should be nontoxic
• Should be acceptable to patients with pleasant odor and color
• Should have adequate shelf life Easy to use with minimum equipment Should have adequate strength

Question 3. Define retention, stability, and support in the complete denture. Discuss various factors affecting retention.
Or 
Define complete denture retention. Enumerate various factors of retention.
Or
Write in detail about retention in complete dentures.

Answer:

• Retention: 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
• Stability: The quality of the denture to be firm, steady & constant, to resist displacement by functional stresses & not to be subject to change of position when forces are applied
• Support: Resistance to vertical forces of mastication, occlusal forces & other forces applied in a direction toward the denture-bearing area

Factors Affecting Retention:

1. Anatomical factors:

• Size of denture bearing area:
  • The retention increases with an increase in the size of the denture-bearing area
  • Maxillary dentures are more retentive than mandibular as it has 24 cm² compared to that 14 cm²

• Quality of denture bearing area:
  • Displaceability of the tissues influences the retention of denture
  • Displacement of tissues during impression making
  • Result in tissue rebounding
  • Leads to loss of retention of dentures

2. Physiological factors:

• Saliva:
  • Thick & ropy saliva-loss of retention
  • Thin & watery saliva- compromised retention
  • Ptyalism- gagging
  • Xerostomia-Soreness & irritation

3. Physical factors:

• Adhesion:
  • The physical attraction of unlike molecules to one another
  • The amount of adhesion present is proportional to the denture base area
  • In xerostomia there is no adhesion

• Cohesion:
  • The physical attraction of like molecules for each other
  • Act within the film of saliva
  • Watery serous saliva- more retentive

• Interfacial surface tension:
  • The tension or resistance to separation possessed by the film of liquid between two well-adapted surfaces
  • Present within film of thin saliva
  • Useful in retention of the maxillary denture
  • Depends on the presence of air at the margins of liquid & solid contact

• • To attain maximum interfacial tension
  • Saliva should be thin
  • Perfect adaptation
  • Covering large denture area
  • Presence of good cohesive & adhesive forces

• Capillarity attraction:
  • That quality or state, because of surface tension causes elevation or depression of the surface of a liquid that is in contact with a solid
  • Presence of close adaptation between denture & the mucosa increases surface contact
  • Results in an increase in retention
  • Factors:
    1. Close adaptation
    2. Greater surface area
    3. A thin film of saliva
• Atmospheric pressure & peripheral seal:
  • It prevents air entry between the denture & soft tissue
  • To obtain it denture borders should rest on soft & resilient tissues
  • On application of forces, a vacuum has created that aid in retention
  • This is a natural suction of denture
  • It is directly proportional to the denture base area

4. Mechanical factors:

• Undercuts
• Retentive springs
• Magnetic forces
•  Denture adhesives
• Suction chambers & suction discs

5. Muscular factors:

• The balance should be between the forces acting from the buccal musculature & tongue

Question 4. Define complete denture impression. Discuss impression theories & techniques in treating complete denture patients.
Answer:

Complete Denture Impression:

A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.

Impression Theories:

1. Mucostatic Impression:

• By Richardson:
  • The impression is made with the oral mucous meme- brane & the jaws in a normal relaxed condition
  • The material of choice is impression plaster

2. Mucocompressive Impression:

• By Carole Jones:
  • Records oral tissues in a functional & displaced form
  • Dentures made by this technique tend to get displaced due to the tissue rebound at rest
  • This leads to residual ridge resorption

3. Selective Pressure Theory:

• By Boucher:
  • The impression is made to extend over as much denture-bearing area as possible without interfering with the limiting structures at function & rest
  • Forces are confined to the stress-bearing areas
  • Non-stress-bearing areas are relieved

Techniques of Impression:

1. Custom Tray Impression:

• Design a custom tray with a spacer
• It should be 2 mm short of the sulcus
• Border molding is done
• It results in recording the sulcus in dynamic function
• Spacer is scraped
• The impression is recorded by ZOE
• It results in recording the stress-bearing areas un- der pressure & non stress-bearing ares are relieved

2. Tray Compound:

• The impression made using tray impression compound •
• The impression is refined & trimmed
• The metal wire is attached to the tray compound to act as a handle
• Treat it as a custom tray
• Border moulding done
• Wash impression made over it

Question 5. Define impression. Discuss biological considerations for a maxillary impression.
Answer:

Complete Denture Impression:

A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.

Biological Considerations:

• The anatomy of the edentulous ridge in the maxilla is important in designing of complete denture
• Some parts of the ridge are capable of withstanding forces compared to others
• Thus it is considered before impression making

Limiting Structures:

• Labial frenum:
  • It is limiting structure of the Maxilla & Mandible
  • It is a fibrous band
  • Covered by mucous membrane
    • Extention: Labial aspect of residual ridge to lip
    • Maxillary: Passive due to absence of muscle fibres

Recorded In Impression:

Recorded in impression as a V shaped notch

• Requirement: Notch should be narrow & deep

• Labial vestibule:
  • That portion of the oral cavity which is bounded on one side by the teeth, gingival & alveolar ridge & on the other side by the lips & cheeks
  • Presence of orbicularis oris
  • It has an indirect displacing effect on the denture
•  Buccal frenum:
  • It separates the labial & buccal vestibule
  • Muscles attachments present: Levator anguli oris, orbicularis oris & buccinator
  • It needs greater clearance on the buccal flange of the denture

• Buccal vestibule:
  • It extends from buccal frenum to the hamular notch
  • Its size varies with: contraction of muscle, the position of mandible & amount of bone loss in maxilla
• Hamular notch:
  • Depression present between maxillary tuberosity & hamulus of medial pterygoid plate
  • Can be easily displaced to achieve posterior pala tal seal

Supporting Structures:

1. Primary Stress Bearing Areas:

•  Hard palate:
  • Trabeculae pattern of it perpendicular to direction of forces acting on it
  • Thus it acts as primary stress-bearing area

• Postero-lateral slopes of residual ridge:
  • Ridge rapidly resorbs following extraction of teeth
  • Resilient submucosa over it provides support to the denture

2. Secondary Stress Bearing Areas:

1. Rugae:
   • It is a secondary support area in maxilla
   • It is covered by thin mucosa

1. • Location:
     1. In the anterior region of the palatal mucosa
     2. At the angle of occlusal plane of the residual ridge
   • Significance: Important in speech
   • Precautions During Fabrication:
     1. Should not distort this area while impression making
     2. Metal denture should reproduce this area to make it comfortable
2. Maxillary tuberosity:
   1. Bulbous extension of residual alveolar ridge in 2nd 3rd molar region
   2. It is least likely to resorb

Relief Areas:

• Incisive papilla
• Location:
  • Midline behind central incisors
• Reason for Relieving:
  • It is exit point of nasopalatine nerves & vessels
  • If it is not relieved it compresses vessels & nerves
• Results:
  • Necrosis of the area
  • Paraesthesia of the anterior palate

1. Cuspid eminence:

• Bony elevation on residual alveolar ridge
• Location: between canine & 1st premolar

2. Mid-palatine raphe:

• Median suture area
• As it is covered by thin mucosa, it should be relieved

3. Fovea palatine:

• Coalescence of ducts of mucous glands
• Determines position of the posterior border of denture
• Relieved because of presence of ducts

Question 6. Describe mandibular anatomical structures.
Answer:

Limiting Structures:

• Labial frenum:
  • Active due to the presence of muscle incisive & orbicularis oris
  • It is fibrous band
  • Covered by mucous membrane
  • Extention: labial aspect of the residual ridge to lip
  • Recorded In Impression: Recorded in impression as a V-shaped notch
  • Requirement: Notch should be narrow & deep
    
• Labial vestibule:
  • That portion of oral cavity which is bounded on one side by the teeth, gingiva & alveolar ridge & on the other side by the lips & cheeks
  • Influences retention of dentures
• Buccal frenum:
  • Contains fibres of the buccinator
  • Prevent displacement of denture

Buccal vestibule:

• • Extends from buccal frenum to retromolar region
  • Bound by alveolar ridge & buccinator
  • Influenced by masseter
  • Notch is produced in denture flange called masseteric notch
• Lingual frenum:
  • Effects stability of denture high frenal attachment is called tongue tie

Alveololingual sulcus:

• Has 3 regions:

1. 1. Anterior region
      • From lingual frenum to pre-mylohyoid fossa
   2. Middle region
      • From pre-mylohyoid fossa to the distal part of mylohyoid ridge
   3. Posterior region
      • In the region of retro mylohyoid fossa
      • Determines lateral throat form

• Retromolar pad:
  • Forms posterior seal of denture
  • Location: Distal to the third molar
  • Consists of: Loose connective tissues, mucosal glands
  • Boundaries:
    1. Posteriorly: temporalis
    2. Lateral: buccinator
    3. Medial: Pterygomandibular raphe & superior constrictor

• Pterygomandibular raphe:
  • Extend: Hamular process to mylohyoid ridge
  • Muscles attached:
    • Postero- medially- superior constrictor
    • Antero-laterally-buccinator

Supporting Structures:

1. Buccal shelf area:

• Between buccal frenum & anterior border of the masseter
• Boundaries:
  • Medial: crest of the ridge
  • Distal: retromolar pad
  • Lateral: external oblique ridge
• Significance: Width increases with resorption of ridge
• Serves as primary stress bearing area

2. Residual alveolar ridge:

• Flat with concave denture-bearing surface
• On resorption inclines outward

Relief Areas:

 Mylohyoid ridge:

• Lies close to the inferior border of the mandible
• Covered with mucosa so should be relieved

3. Mental foramen:

• Location: Between 1st & 2nd premolar region
• Relieved as it may lead to paraesthesia

4. Genial tubercle:

• Location: anterior on the lingual side of body of the mandible
• Increases due to resorption

5. Torus mandibularis:

• Location: on lingual side near premolar region (b)
• Covered by a thin mucosa
• Relieved or surgically removed

Question 7. Discuss principles & objectives of making impressions for completely edentulous patients.
Or
What are the objectives of impression making
Answer:

Principles Of Impression Making:

1. Presence of healthy oral tissues
2. Inclusion of all supporting & limiting tissues
3. Borders within anatomical and physiological limitations
4. Border molding – physiological type
5. Space between material & tray
6. Not damaging the tissues
7. Application of selective pressure technique
8. Use of guiding mechanism
9. Use of dimensionally stable materials
10. Similarity to the form of dentures

Objectives Of Impression Making:

1. Retention:

“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”.

• Factors:

1. 1. Anatomical factors:
      • Size of denture-bearing area
      • Quality of denture-bearing area
   2.  Physiological factors:
      • Saliva
   3.  Physical factors:
      • Adhesion
      • Cohesion
      • Interfacial surface tension
      • Capillary attraction
      • Atmospheric pressure
   4. Mechanical factors:
      • Undercuts
      • Retentive springs
      • Magnetic forces
      • Denture adhesives
      • Suction chambers & suction discs
   5. Muscular factors:

• • • The balance should be between the forces acting from the buccal musculature and tounge

2. Stability:

• The quality of the denture to be firm, steady & constant, to resist displacement by functional stresses & not to be subject to change of position when forces are applied
• It withstands horizontal forces
  • Factors:
    1. The vertical height of the residual ridge
    2. Quality of soft tissue
    3. Quality of impression
    4. Occlusal rims
    5. Teeth arrangement
    6. Shape of denture

3. Support:

• Resistance to vertical forces of mastication, occlusal forces & other forces applied in a direction toward the denture-bearing area
• The denture base should cover as much denture-bearing area as possible
• Results in the distribution of forces over wider area
• This leads to a reduction of force per unit area

Called Snow Shoe Effect:

4. Aesthetics:

• Thicker flange leads to fullness of the mouth

5. Preservation of Remaining Structures:

• Muller stated that the preservation of what remains is more important rather than to replace what is lost.
• Stress is provided over the stress-bearing area.
• Relief is provided over non-stress-bearing areas.
• Prevent damage to oral structures.
• Avoid overextension of dentures.

Question 8. Define stability & discuss factors affecting it.
Answer:

Stability:

• “The quality of denture to be firm, steady & constant, to resist displacement by functional stresses & not to be subject to change of position when forces are applied”.
• It withstands horizontal forces

Factors:

1. Vertical height of residual ridge:

• A ridge with an adequate height of ridge provides sufficient support
• Resorbed ridge causes loss of stability or reduced stability of the denture

2. Quality of soft tissue:

• Adequate submucosa is required for good stability
• Excessive submucosa results in poor stability

3. Quality of impression:

• The impression should be:
  • Accurate
  • Smooth surface
  • Devoid of voids
  • Not wrap on removal Dimensional stable

4. Occlusal plane:

• Should be parallel to ridge
• Should divide interarch space equally

5. Teeth arrangement:

• Teeth are arranged in a neutral zone
• That is balance is achieved in between tongue & buccal musculature

6. Shape of denture:

• Polished surface should resemble oral structures
• Should not interfere with the functioning of oral structures