Impression And Mouth Preparation Definitions
- Impression: A complete denture impression is a negative registration of the entire denture bearing, stabilizing & border seal areas present in the edentulous mouth.
- 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 sub-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
- 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
- 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.
- 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:
- Muco compressive – records tissue in functional and displaced form
- Mucostatic records tissue in a relaxed form
- 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:
5. Secondary stress-bearing areas:
Read And Learn More: Prosthodontics Question And Answers
6. 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 parts
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:
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
(or)
Pre-prosthetic surgery
Answer:
1. Bony Surgeries:
- 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
- Alveoloplasty:
- It is done to reduce severe undercuts or bilat- eral moderate undercuts
- 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
- 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:
- Removal of redundant crystal soft tissue:
- Crystal soft tissue may interfere with the stability of the denture so it should be removed
- Frenectomy
- It is indicated in case of
- High frenal attachment which cannot be relived by large labial notch
- Hypertrophic lingual frenum
- It is indicated in case of
- 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.
Answer:
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
Or
Definition & functions of the posterior palatal seal.
Answer:
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
- 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
Answer:
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
- The anterior portion of the lingual flange is called Dublin- goal crescent area
- The hamular notch determines the distolateral termination of the denture base
- Posterior vibrating line marks most distal extension of the denture
- The mid-palatine raphe is the most sensitive part of the palate
- Retromolar pad aids in the stability of the denture
- The mandibular denture border should not interfere with the opening of Wharton’s duct
- The anterior lingual border is the secondary peripheral seal area for the mandibular denture
- Primary impression can be made using impression compound, impression plaster, or alginate
- Secondary impression can be made using ZOE im- impression paste, medium-bodied elastomeric impression material
- Underextension of the peripheral border of mandible- lar denture affects the stability
- Flabby tissue will interfere with the stability of the denture
- Passive impression or mucositis or pressure-less impression technique records the tissues with minimal distortion and causes the least possible displacement of tissues.
- Silicone or metallic oxide paste or rubber base materials are used in a custom tray during the final impression.
- A wax spacer is used to provide space in the tray for the final impression material
- The selective pressure technique is the most widely respected and accepted theory by transferring load to acceptable areas.