Impression And Mouth Preparation Question and Answers

Impression And Mouth Preparation Definitions

  1. Impression: A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.
  2. 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
  3. Stability: The quality of the denture to be firm, steady & constant, to resist displacement by functional stresses & not to be sub-subject to change of position when forces are applied
  4. Support: Resistance to vertical forces of mastication, occlusal forces & other forces applied in a direction toward the denture-bearing area
  5. Posterior palatal seal: The soft tissues at or along the junction of the hard & soft palates on which pressure within the physiological limits of the tissues can be applied by a denture to aid in the retention of the denture
  6. Anterior vibrating line: It is an imaginary line lying at the junction between the immovable tissues over the hard palate & the slightly movable tissues of the soft palate.
  7. Posterior vibrating line: It is an imaginary line located at the junction of the soft palate that shows limited movement & the soft palate that shows marked movement

Impression And Mouth Preparation Important Notes

1. Types of impression:

  1. Muco compressive – records tissue in functional and displaced form
  2. Mucostatic records tissue in a relaxed form
  3. Selective pressure – records tissue without interfering with the limiting structures at function and rest

2. Objectives of impression:

  • Retention: It is the resistance to displacement away from the tissue surface. It is a mucosa-borne phenomenon.
  • Support: It is the resistance to the occlusal forces in the vertical direction. It is a bone borne phenomenon.
  • Stability: It is resistant to lateral shifting.
  • Preservation of remaining structures.

3. Factors affecting retention:

  • Anatomical factors- Size of denture bearing area, quality of denture bearing area
  • Physiological factor – Saliva Physical factor-adhesion, cohesion, capillary attraction, interfacial surface tension, atmospheric pressure
  • Mechanical factors- Undercuts, retentive springs, magnetic forces, denture adhesives
  • Muscular factors

4. Primary stress-bearing areas:

Impression And Mouth Preparation Primary Stress Bearing Areas

5. Secondary stress-bearing areas:

Impression And Mouth Preparation Secondary Stress Bearing Areas


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6. Relief areas:

Impression And Mouth Preparation Relief Areas
7. Anterior vibrating line:

  • It is an imaginary line at the junction of the attached tissues overlying the hard palate and movable tissues of the soft palate
  • It is always on soft palatal tissue
  • It is visualized by asking the patient to say “ah” with a short vigorous burst

8. Posterior vibrating line:

  • It is an imaginary line at the junction of the aponeurosis of the tensor veli palatine and muscular portion of the soft palate
  • It represents the demarcation between the parts of the soft palate showing limited movements and those with marked movements
  • It is the most distal extension of the denture

9. Alveolar lingual sulcus:

  • Extends from the lingual frenum to the retro mylohyoid curtain
  • It is divided into three partsImpression And Mouth Preparation Alveolar Lingunal Sulcus

10. Posterior palatal seal:

  • Lies between anterior and posterior vibrating line
  • Functions
    • Retention of the maxillary denture
    • Maintain contact with the anterior portion of the soft palate during functional movements
    • Slightly displaces the soft tissue at the distal end of denture to ensure a complete seal that helps in retention of denture.
    • Prevents ingress of food and saliva beneath denture base.
    • Prevents excess impression material from running down the patient’s throat.

11. Buccal frenum:

  • The buccal frenum of maxilla contains Caninus or levator anguli oris.
  • The buccal frenum of mandible contains Triangularis or depressor anguli oris.

12. Pterygomandibular raphe:

  • It is the tendinous insertion of superior constrictors and buccinators
  • It arises from the hamular process of the medial pterygoid
  • Gets attached to the mylohyoid ridge

13. Fovea palatine:

  • The fovea palatine are indentations near the midline of the palate formed by the coalescence of several mucous gland ducts.
  • They are always on the soft palate 2mm behind the vibrating line.

14. Retromylohyoid fossa is bounded by:

  • Anterior – Retro mylohyoid curtain
  • Posterolateral – Superior constrictor of the pharynx
  • Posteromedial – Palatoglossus and lateral surface of the tongue
  • Inferior- Submandibular gland

15. Buccal frenum has the following muscle attachments:

  • Levator anguli oris
  • Orbicularis oris
  • Buccinator

16. Buccal shelf area is bounded by:

  • Medially crest of the ridge
  • Distally-retromolar pad
  • Laterally external oblique ridge

17. Retromolar pad:

  • Contains glandular tissue and fibers of temporalis, buccinators, superior constrictor, and pterygomandibular raphe
  • All these prevent the placement of extra pressure
  • Functions
    • Provides peripheral seal to mandibular denture
    • Marks distal extension
    • Provides retention, stability, and support to the denture

18. Frena present:

Impression And Mouth Preparation Frena Present

19. Border molding:

  • It is the procedure by which the entire periphery of the tray is refined
  • Polyether impression material is the material of choice
  • Ideal requisites
    • Should have sufficient viscosity
    • Should not be sticky
    • Should have setting time 3-5 min
    • Should not displace tissues
    • Should be easily trimmed
    • Should retain its flow properties

20. Advantages of ZOE paste include:

  • Accurate borders are formed since the material is more plastic in nature.
  • Does not absorb the mucous secretion produced in the palate and thus accurately records the palatal part of the impression.
  • Does not require a separating medium.

21. Modiolus is a point where eight muscles meet at the Angle Mouth:

  • Depressor anguli oris (or) tringularis
  • Levator anguli oris or canines
  • Risorius
  • Orbicularis oris
  • Buccinators
  • Zygomaticus major
  • Quadratus labii superioris
  • Quadratus labii inferioris

22. Snow shoe effect:

  • The denture base should cover as much denture-bearing area as possible
  • It results in the distribution of forces over a wider area
  • Leading to the reduction of force per unit area
  • Called snowshoe effect

Impression And Mouth Preparation Short Essays

Question 1. Pre-prosthetic surgical management in complete denture
Pre-prosthetic surgery

1. Bony Surgeries:

  1. Excision of the torus:
    • Tori are small bony projections of unknown etiology
    • They gradually increase in size
    • It should be excised because mucosa over tori is more prone to irritation
  2. Alveoloplasty:
    • It is done to reduce severe undercuts or bilat- eral moderate undercuts
  3. Reduction of genial tubercle or Reduction of mylohyoid ridge:
    • Sometimes these become very prominent due to ridge resorption
    • They should be removed if there occurs re- peated ulceration, loss of peripheral seal
  4. Maxillary tuberosity reduction:
    • It is easy to correct wide tuberosity compared to the large tuberosity
    • It should be evaluated radiographically before surgical correction

2. Soft Tissue Surgeries:

  1. Removal of redundant crystal soft tissue:
    • Crystal soft tissue may interfere with the stability of the denture so it should be removed
  2. Frenectomy
    • It is indicated in case of
      • High frenal attachment which cannot be relived by large labial notch
      • Hypertrophic lingual frenum
  3. Excision of epulis
    • Epulis is the hyperplastic reaction of the mucosa occurring along the borders of the denture
    • Treated with excision of the tissues and shortening and smoothening of dentures

Question 2. Mucostatic impression.

Mucostatic Impression:

  • It is an impression technique used in complete denture patients based on theory of impression-making.
  • By Richardson
  • The impression is made with the oral mucous membrane & the jaws in a normal relaxed condition
  • The material Of Choice is impression plaster
  • Border moulding is not done here
  •  Tray Used: Oversized tray
  •  Retention: Due to interfacial surface tension

Significance of Mucostatic impression:

  • Closely adapted denture
  • Good stability of the denture

Disadvantages of Mucostatic impression:

  • Poor peripheral seal
  • Poor retention
    • Synonym: Passive impression as the impression is made in rest position of oral tissues

Question 3. Posterior palatal seal area
Definition & functions of the posterior palatal seal.

Posterior palatal seal Definition:

The soft tissues at or along the junction of the hard & soft palates on which pressure within the physiological limits of the tissues can be applied by a denture to aid in retention of the denture

Impression And Mouth Preparation Posterior palatal Seal Area

  • Functions of Posterior Palatal Seal:
    • Aids in retention
    • Maintain constant contact with soft palate during functions
    • Reduces gag reflex
    • Prevents formation of gap between denture & pal- ate during function
    • Prevents food accumulation
    • Compensate for polymerization shrinkage
  • Parts of Posterior Palatal Seal:
    • Pterygomaxillary seal
    • Postpalatal seal

Methods To Record It:

  • Conventional approach
  • Fluid wax technique
  • Arbitrary scraping of the master cast
  • Extended palatal technique

Question 4. Methods of recording posterior palatal seal

1. Conventional method

Fabricate trial base using shellac base plate or self-cure resin

  • The posterior palatal area is wiped with gauze
  • T burnisher is used to locate the hamular notch by palpating posteriorly to the maxillary tuberosity on both sides
  • The full extent of the hamular notch is marked with in- delible pencil
  • The posterior vibrating line is marked
  • Line marked in the hamular notch is connected with a posterior vibrating line
  • The trial base is inserted into the patient’s mouth
  • Markings are transferred to the trial base is seated on the master cast
  • This transfers the markings to cast
  • The trial base is trimmed to the posterior border Anterior vibrating line is marked in the patient’s mouth
  • These markings are transferred to the cast The area between the anterior and posterior vibrating line is scrapped

2. Fluid wax technique:

  • Wash impression is made
  • Anterior and posterior vibratory lines are marked in the patient’s mouth
  • The impression is re-inserted in the patient’s mouth
  • Markings are transferred into impression The impression is painted with wax in the area of markings
  • The impression tray is inserted in the patient’s mouth and the patient is asked to make rotational movements
  • The impression is removed after 4-6 minutes and examined
  • In contrast to green stick compound, glossy areas show tissue contact
  • The procedure is repeated till even tissue contact is achieved
  • Wax in the region of the anterior vibrating line should have a knife-edge margin

3. Arbitrary scrapping of master cast:

  • In this technique, anterior and posterior vibratory lines are visualized in patient’s mouth and ap- proximately marked overcast
  • Technician scrapes 0.5-1 mm of stone in posterior palatal seal area and fabricates the denture

Impression And Mouth Preparation Viva Voce

  1. The anterior portion of the lingual flange is called Dublin- goal crescent area
  2. The hamular notch determines the distolateral termination of the denture base
  3. Posterior vibrating line marks most distal extension of the denture
  4. The mid-palatine raphe is the most sensitive part of the palate
  5. Retromolar pad aids in the stability of the denture
  6. The mandibular denture border should not interfere with the opening of Wharton’s duct
  7. The anterior lingual border is the secondary peripheral seal area for the mandibular denture
  8. Primary impression can be made using impression compound, impression plaster, or alginate
  9. Secondary impression can be made using ZOE im- impression paste, medium-bodied elastomeric impression material
  10. Underextension of the peripheral border of mandible- lar denture affects the stability
  11. Flabby tissue will interfere with the stability of the denture
  12. Passive impression or mucositis or pressure-less impression technique records the tissues with minimal distortion and causes the least possible displacement of tissues.
  13. Silicone or metallic oxide paste or rubber base materials are used in a custom tray during the final impression.
  14. A wax spacer is used to provide space in the tray for the final impression material
  15. The selective pressure technique is the most widely respected and accepted theory by transferring load to acceptable areas.

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