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Questions and Answers
What is the purpose of border molding in making a preliminary impression?
To mold the borders of the impression to accurately capture anatomical landmarks and create rounded peripheries.
Which of the following is a cause of inaccurate impressions?
Gagging can complicate impression making by forming voids in the impression.
True
What method is the most reliable to locate the anterior limit of the proposed posterior palatal seal area?
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What is the purpose of mandibular border molding using green stick compound?
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Phonation of 'ah' sound in short bursts is effective in locating the ______ vibrating line.
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What is the definition of an impression in Removable Prosthodontics?
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What are the objectives of an impression in prosthodontics?
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Retention is the resistance to removal in a direction same as that of its insertion.
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Stability is the quality of the denture to be firm, steady, and constant in position when forces are applied to it, especially in hard bony areas and those ______ located and freely movable.
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Match the impression material characteristics with their advantages:
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What should be done to interfere with the insertion and removal of the tray in the presence of undercut areas?
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Which of the following are techniques for upper and lower definitive impressions?
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Border molding ensures an optimal peripheral seal and maximum coverage within the physiological _______ movement of the patient.
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Active border molding involves functionally trimming the borders of the impression by patient movements.
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What is the purpose of the posterior palatal seal in dentures?
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What is the working time of the admix for making impressions?
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Which material may be used for localized areas of poor functional adaptation in dentures?
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Using boxing methods is important to preserve the details of the final impression. Is this statement true?
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______ and pumice boxing method is suitable for boxing alginate, rubber base, and silicon impressions.
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Study Notes
Impression Making in Completely Edentulous Cases
- Impression is a negative representation of an object from which a positive likeness can be made.
- In Removable Prosthodontics, an impression is a negative reproduction of the entire denture-bearing area and the border limiting structures.
Objectives of an Impression
- To provide retention, support, and stability for the denture.
- To act as a foundation for improved lip esthetics and to maintain the health of the oral tissues.
Retention
- Resistance to removal in a direction opposite to that of its insertion.
- Can be achieved by:
- Maximum coverage of the denture-bearing area within physiologic movement of the border limiting structures.
- Perfect peripheral seal.
- Intimate tissue contact and close adaptation of the denture base to the underlying tissues.
Stability
- Quality of the denture to be firm, steady, and constant in position when forces are applied to it.
- Can be achieved by:
- An impression that equalizes the pressure distribution.
- Hard bony areas, especially those centrally located and freely movable.
Support
- Resistance of a denture to the vertical component of mastication and other forces applied in the direction of the basal seat.
- Can be achieved by:
- Wide tissue coverage.
- An impression technique that directs most occlusal forces to the primary stress-bearing areas.
- Selective placement of pressure that is in harmony with the resiliency of the tissues that make up the basal seat.
Providing Improved Lip Support
- In patients with severely resorbed maxillary ridges, the flanges and borders of the denture should have sufficient thickness to provide proper lip support and proper arrangement of artificial teeth.
Maintaining the Health of the Oral Tissues
- Inflammation of the denture-bearing area can be prevented by avoiding excessive pressure and over-displacement of the tissues by pressure from the impression.
Types of Impressions
- Primary impressions
- Made using readymade stock trays of different sizes.
- Definitive impressions
- Conventional techniques
- Selective pressure techniques
- Functional techniques
- Reline and rebase techniques (including secondary template impressions)
Primary Impression for Completely Edentulous Arch
- Definition: A negative registration of the entire denture-bearing area and border seal area by using an impression material.
- Techniques:
- Conventional technique
- Template technique
Impression Material for Preliminary Impression
- Alginate impression material
- Advantages:
- Simple manipulation
- Fast setting time
- Pleasant for the patient
- Does not distort the tissues
- Precautions:
- Should not be exposed to air to avoid dehydration
- Should not be immersed in water to avoid imbibition
- Should be protected from dehydration by placing it in a humid atmosphere
Impression Techniques
- Conventional technique: Made using readymade stock trays of different sizes.
- Template technique: Used to replicate the form of the polished surfaces of the dentures.
Maxillary Preliminary Impression Procedure
- Steps:
- Examine the shape, size, and form of the residual ridge and palate.
- Select a suitable sized perforated stock tray.
- Load the tray with alginate impression material.
- Position the tray in the mouth.
- Border molding:
- Cheeks are pulled upward and downward to release the lip and cheeks.
- The patient is asked to:
- Purse his lips, retract them, and move them downward.
- Suck the operator's finger.
- Move his jaws laterally to functionally mold the width of the impression.
- Bend his head forward, move the head to the right and left sides, and swallow.
Mandibular Preliminary Impression Procedure
- Steps:
- Examine the shape, size, and form of the residual ridge and the width and depth of the vestibule.
- Select a suitable sized perforated stock tray.
- Load the tray with alginate impression material.
- Position the tray in the mouth.
- Border molding:
- Labially:
- The fingers are used to gently mold the labial and buccal borders.
- The lower lip is lifted downward, outward, and upward.
- Posteriorly:
- The buccal flange is border molded when the cheek is moved downward, outward, and upward.
- The distobuccal border is extended into the functioning area of the masseter muscle.
- Lingually:
- The lingual borders are functionally trimmed by active movement of the tongue.
- The patient is instructed to protrude his tongue, move it from side to side, and push it forcefully against the anterior part of the palate.
- Labially:
Causes of Inaccurate Impressions
- Impression made on inflamed tissues
- Improper selection of the tray:
- Short tray
- Large tray
- Small tray### Factors Affecting Impressions
- Lesions of extra pressure can dislodge the denture and impair tissue health
- Long trays can cause excessive displacement of resilient tissues and interfere with surrounding muscle action
- Improper tray positioning can result in:
- Thick borders on one side and thin borders on the other
- Excessive labial border thickness or showing through the impression
- Insufficient vestibule depth and width recording
- Pressure spots on the anterior lingual flange
- Insufficient or excessive seating pressure can cause:
- Lack of tissue detail
- Excessive impression material on the flange
- Presence of pressure spots
Voids in the Impression
- Voids on the border may be due to:
- Soft impression mix
- Labial and buccal tissues trapped between the impression
- Insufficient seating pressure
- Voids on the tissue surface may be due to:
- Soft mix
- Excessive space between the tray and oral tissues causing sagging
- High palatal vault
Factors that Complicate Impression Making
- Excessive salivation and thick ropy saliva can cause voids and gagging
- Muscle tone:
- Tense muscles can interfere with proper border extension
- Weak muscles can result in insufficient peripheral seal
- Muscular control:
- Good coordination is essential for effective border molding
- Tongue movements are important for lingual flange recording
- Gagging:
- Active gag reflex can be triggered by:
- Long trays
- Distal portion of the lingual tray
- Upper tray that is too short or too long
- Treatment involves gentle manipulation, use of minimal impression material, and local anesthesia if necessary
- Active gag reflex can be triggered by:
Definitive Impressions
- Purpose:
- Record entire functional denture-bearing area
- Ensure maximum support, retention, and stability
- Techniques:
- Conventional
- Selective pressure
- Functional
Final Impression Trays
- Checking the tray:
- Length and form of the flanges
- Harmony with limiting anatomic structures
- Labial, buccal, and lingual borders
- Border molding:
- Classified into:
- Sectional border molding
- One step border molding
- Border molding techniques:
- Active border molding
- Passive border molding
- Materials:
- Green stick compound
- Elastomeric impression material
- Classified into:
Posterior Palatal Seal
- Located between the anterior and posterior vibrating lines
- Techniques for determining the location:
- Phonation of the "ah" sound
- Swallowing method
- Nose-blowing method (Valsalva maneuver)
- Intraoral palpation with a blunt instrument is the most reliable method for locating the anterior limit of the proposed posterior palatal seal area### Impression Making
- The mixed polyether material is positioned on the borders of the tray, and the tray is positioned in the mouth by a rotating motion, while the lip is retracted sufficiently to avoid scraping the polyether material from the borders.
- The patient is instructed to elevate their tongue as the tray is seated.
Labial and Buccal Border Molding
- Labial and buccal border molding are performed by manipulating the lower lip and cheeks outward, downward, and upward.
- The patient is instructed to protrude the tongue to regulate the length of the anterior lingual flange and to activate the superior constrictor muscle to limit the posterior extension of the impression.
Functional Border Molding
- The patient is instructed to push the tongue against the anterior part of the palate to regulate the thickness of the anterior lingual flange and to move the tongue from side to side to determine the length of the borders in the molar region.
- The patient is instructed to swallow to activate the posterior fibers of the mylohyoid muscle.
- The patient is instructed to close their jaw against resistance to activate the masseter muscle to functionally mold the distobuccal area.
Removing the Tray
- The tray is removed after the material has set, and examined for correct extension.
Maxillary Final Impression
- Check the fit and extension of the special trays.
- Place Vaseline over and around the patient's mouth and lips.
- Dry the palate and basal seat tissues with gauze.
- Dry the tray and mix the impression material according to the manufacturer's instructions.
Distribution of Impression Material
- The final impression material is distributed uniformly in the tray using a small cement spatula.
- Cover the borders 2-3 mm onto the labial and buccal surface of the tray.
- Load the tray with impression material and position it in the mouth by alternate pressure on each side of the tray.
Molding and Inspection
- Molding is performed in the usual manner.
- The completed impression is then removed from the mouth and inspected for acceptability.
- If pressure spots are detected, the area should be reduced with a carbide bur, and an overall impression is made.
Disinfecting the Impression
- Disinfect the impression by rinsing excess saliva with water.
- Place the impression in a ziplock bag and spray with the current approved disinfectant.
- Wait 10 minutes before unsealing the bag and pouring the impression.
Selective Pressure Impression Technique
- This technique combines considerable pressure on certain areas and minimal pressure on others.
- The place that has less space between the tray and the tissues to be recorded will transmit more pressure from the denture during function.
Modified Impression Techniques
- Displaceable upper anterior (flabby) ridge: Use zinc-oxide-eugenol (ZOE) or a medium-bodied polyvinyl siloxane (PVS) impression material.
- Fibrous (unemployed) posterior mandibular ridge: Use a customized tray with tracing compound (greenstick) and a light-bodied PVS.
- Flat (atrophic) mandibular ridge covered with atrophic mucosa: Use a viscous admix of impression compound and tracing compound.
Functional Impressions
- Two variations are commonly used for functional impressions:
- Local areas of modification
- Problems associated with denture space/neutral zone
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Description
Learn about impression making in completely edentulous cases, including the definition and importance of impression in removable prosthodontics.
