Dental Impression Techniques and Viscosity

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Questions and Answers

What is the purpose of the occlusion rim in denture fabrication?

To establish accurate maxillomandibular jaw relations (correct)

To eliminate wax from the denture formation

To smoothen plaster on the cast

To create a base for the denture

Which materials are mentioned for use in the fabrication of denture bases?

Silicone and Gel

Shellac and self cure acrylic (correct)

Glass and Additive materials

Polyurethane and Composite resin

What process is described as being used to prepare the mold space in denture creation?

Applying wax over a baseplate

Using thermal expansion to adjust fit

Cooling wax to solidify

Smoothing plaster to eliminate undercuts (correct)

Which type of alloy is not mentioned as a material in denture fabrication?

Titanium alloy Signup and view all the answers

What happens to the temporary baseplate during the processing phase?

It is removed but not discarded. Signup and view all the answers

Which classification of soft palate provides the most favorable denture retention?

Class I palate Signup and view all the answers

How does a Class II palate compare to Class I and Class III palates?

It has a palatal contour that is intermediate between Class I and Class III. Signup and view all the answers

What does the term 'capillary attraction' refer to in the context of denture retention?

The force causing liquid to rise or fall in relation to a solid. Signup and view all the answers

Why does saliva have a different role in the retention of maxillary and mandibular dentures?

Saliva aids retention on both sides for maxillary dentures but not mandibular ones. Signup and view all the answers

What is the purpose of recessing the denture border in the posterior area?

To minimize the end of the denture base for better retention. Signup and view all the answers

What is the primary advantage of using a high viscosity impression material when making preliminary impressions?

It compensates for deficiencies in the tray. Signup and view all the answers

Which material is commonly used for border molding in mandibular impressions?

Modeling compound stick type Signup and view all the answers

During the labial border molding process for mandibular impressions, which patient movement indicates the proper engagement of the lip?

The patient puckers and sneers. Signup and view all the answers

What indicates a need to adjust the surface of modeling compound during the impression process?

There is a deficiency in capturing anatomical landmarks. Signup and view all the answers

Which anatomical landmark is assessed when a patient is instructed to close against the clinician's hand on the chin?

Retromolar pad Signup and view all the answers

What action should the patient take to properly mold the retromylohyoid sulcus?

Lick the lower lip and cheeks. Signup and view all the answers

What movement of the tongue is important for capturing the lingual border during an impression?

The tongue should push against the handle of the tray. Signup and view all the answers

During the impression taking process, what should be noted when observing the prominence of the frenum?

It should be duplicated in the impression. Signup and view all the answers

What is the purpose of setting the base of a complete denture on the master cast?

To ensure proper adaptation and stability Signup and view all the answers

What should be avoided when soaking the cast in water?

Soaking for too long causing etching Signup and view all the answers

What is required to properly invest the wax pattern in the flask?

Applying a separating medium to the cast Signup and view all the answers

What aspect is critical about the surface that contacts the oral mucosa?

It must be free of voids or projections Signup and view all the answers

During the processing of the denture base, which of the following steps is essential?

Pressing the cast at the center of the flask Signup and view all the answers

Which step follows soaking the cast in water?

Applying separating medium to the base Signup and view all the answers

How should the dimension adjustment on a cast trimmer be handled?

With extreme caution to avoid over-trimming Signup and view all the answers

Which characteristic defines a stable denture base in relation to a master cast?

It needs to be well adapted and accurately formed Signup and view all the answers

What is the primary function of the peripheral seal in dentures?

To create a border seal that reduces dislodgement Signup and view all the answers

Which factor contributes to the retention of prostheses through the physical attraction of molecules?

Adhesion Signup and view all the answers

What role does oral and facial musculature play in denture retention?

It enhances retentive forces when positioned correctly. Signup and view all the answers

What must be achieved for atmospheric pressure to be an effective retentive force for dentures?

Perfect peripheral seal on the denture Signup and view all the answers

How does gravity affect the retention of maxillary and mandibular dentures?

It may act as a retentive force for the mandibular denture but a displacing force for the maxillary one. Signup and view all the answers

What is the main function of the posterior palatal seal (PPS) in maxillary dentures?

To maintain contact with the anterior portion of the soft palate Signup and view all the answers

What is meant by 'undercuts' in the context of denture retention?

Modest undercuts that work with mucosal resiliency Signup and view all the answers

What occurs due to polymerization shrinkage in denture processing?

The processed base is pulled away from the cast Signup and view all the answers

Study Notes

Impression Material Viscosity

High viscosity impression material is recommended when using a tray, as it helps compensate for tray deficiencies.

Border Molding

Mandibular:
- Labial: Note prominent frenum, observe during aggressive lip movements (puckering, sneering, wide opening, grimacing, smiling).
- Buccal Shelf: Observe during wide opening, grimacing, and puckering.
- Masseteric Notch: Patient closes against hand on chin.
- Retromolar Pad: Patient opens wide and closes against hand on chin.
- Retromylohyoid Sulcus: Push compound into fossa area, patient licks lower lip and right and left cheeks, and lastly swallows.
- Lingual Border and Lingual Anterior Border: Patient licks lower and upper lip and right and left cheeks and pushes tongue against tray handle or clinician's thumb. Border should gently curve under the tongue at midbody.
Maxillary:
- Labial: Note prominent frenum, observe during aggressive lip movements (puckering, sneering, wide opening, grimacing, smiling).
- Soft Palate: House described 3 classifications:
  - Class I: Most favorable for denture retention, horizontal soft palate with minimal muscular activity.
  - Class II: Palatal contour lies between Class I and Class III.
  - Class III: High V-shaped palatal vault with high muscular activity.

Factors Affecting Denture Retention

Adhesion: Attraction of unlike molecules, occurs in thin film of saliva between denture base and mucosa.
Cohesion: Attractive force between like molecules, similar to adhesion.
Capillary Attraction: Force developed due to surface tension causing liquid elevation or depression when in contact with a solid. Thin film of saliva between denture base and mucosa acts like a capillary tube.
Atmospheric Pressure: Resistance to denture removal from basal seat; no suction or negative pressure except when another force is applied. Requires a perfect peripheral seal for effectiveness.
Oral and Facial Musculature: Supplementary retention provided by musculature when teeth are in the neutral zone between cheeks and tongue, and denture surfaces are properly shaped.
Undercuts, Rotational Insertion Paths, and Parallel Walls: Modest undercuts combined with mucosal and submucosal resiliency can enhance retention.
Gravity: Acts as retentive force for mandibular dentures in upright position, but as a displacing force for maxillary dentures.

Purpose of Pressure Pouring System (PPS)

Recess denture border posteriorly: Minimizes contact with tongue during swallowing and speaking.
Create a border seal: Reduces denture dislodgement during speaking and mastication.
Counter polymerization shrinkage: Prevents processed denture base from pulling away from the cast along the palate.

Functions of PPS

Stability: Maintain contact with anterior portion of soft palate during functional movements of the stomatognathic system (mastication, deglutition, phonation).
Retention: Primary purpose of PPS for maxillary dentures.

Baseplate

Criteria:
- Well-adapted and accurately formed to the master cast.
- Stable on the cast and in the mouth.
- Free of voids or projections on the surface contacting the oral mucosa.
Materials:
- Shellac
- Self-cure
- Permanent base (processed acrylic resin, gold, chromium cobalt alloy, chromium nickel alloy)

Processing of Denture Base

Investing:
- Prepare flasks by applying separating medium to the inside of the upper and lower halves, knock-out plate, and cover.
- Wet cast thoroughly but don't oversoak.
- Apply separating medium to the base.
- Fill the sides of the lower flask half with POP, leaving enough space in the center for the cast.
- Press the cast at the center of the lower flask, ensuring the base of the cast touches the flask base.
- Contour plaster to the cast, smoothing it to remove undercuts.
Wax Elimination and Mold Space Preparation:
- This step results in a laboratory sample, a mold space prepared for the denture base.
Occlusion Rim: Wax form used to establish accurate maxillomandibular jaw relations and to arrange artificial teeth in a trial denture.

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Description

This quiz covers key concepts in dental impressions, focusing on the viscosity of impression materials and the techniques for effective border molding. Learn how to optimize tray usage and the specific steps for both mandibular and maxillary molding. Test your knowledge and understanding of these critical aspects of dental practice.