Dental Impressions and Casts

Questions and Answers

What is the purpose of making an impression?

To produce a cast of the teeth

To examine the patient's oral hygiene

To produce a positive replica over which a dental restoration can be constructed (correct)

To construct a dental restoration directly

Why is it necessary to examine old dentures before making impressions?

To determine the patient's oral hygiene

To examine the denture's material

To evaluate the fit and occlusion of the denture (correct)

To determine the patient's age

What should be done to the dentures before making impressions?

Soak them in a disinfectant

Remove them from the patient's mouth for 24-48 hours (correct)

Clean them with soap and water

Leave them in the patient's mouth

What is the final step in tissue preparation for impressions?

Tissue massage and rinse with warm water and salt Signup and view all the answers

What is a cast?

A positive replica of the form of the tissues or teeth Signup and view all the answers

Why is tissue preparation necessary?

To ensure the supporting tissues are in an acceptable condition Signup and view all the answers

What is the primary purpose of a primary impression?

To record the overall shape and size of the patients mouth Signup and view all the answers

What is the advantage of using a stock tray?

They are inexpensive Signup and view all the answers

What is the purpose of the floor of a stock tray?

To guide the tray into position in the mouth Signup and view all the answers

Why is it important to block out undercuts in the mouth before making an impression?

To avoid distorting the impression material during removal Signup and view all the answers

What is the purpose of a custom tray?

To accurately record the details of the mouth Signup and view all the answers

What material is often used to line a custom tray?

Impression compound Signup and view all the answers

What type of flanges are characterized by less modifications?

Non-Metal Signup and view all the answers

What is the significance of recording anatomical landmarks in mandible?

To identify the labial frenum Signup and view all the answers

What is the purpose of pouring primary impressions?

All of the above Signup and view all the answers

What are the characteristics of an acceptable impression material mix?

It is properly mixed according to the manufacturer's instructions Signup and view all the answers

What is the significance of borders in impression taking?

They should be 2mm short, except in certain cases Signup and view all the answers

What type of trays is used to record the impression of a full arch?

Full arch trays Signup and view all the answers

What is the purpose of identifying supporting structures in impression taking?

To identify areas of support Signup and view all the answers

What type of resin is commonly used in denture construction?

Acrylic resin Signup and view all the answers

Study Notes

Mouth Preparation and Primary Impression

An impression is a negative reproduction of teeth and/or adjacent structures from which a positive replica (cast) can be made.
The purpose of an impression is to produce a cast over which a dental restoration can be constructed.

Patient Preparation

A denture should not be constructed unless the supporting tissues are in an acceptable condition.
Existing dentures should be examined for fit and occlusion, and corrected temporarily with tissue conditioning material if necessary.
Dentures should be removed from the patient's mouth for 24-48 hours before making impressions.
Tissue preparation/conditioning involves clinical examination, correction of denture, application of tissue conditioning material, oral hygiene instructions, tissue massage, and rinse with warm water and salt.

Impressions for Complete Dentures

Primary impressions are made using a stock tray, which is then used to construct a custom tray.
Secondary impressions are made using the custom tray to produce a master cast.

Stock Trays

Stock trays are ready-made, come in different sizes and forms, and can be adapted to fit the patient's mouth.
They allow addition or removal of material and can be bent to fit the patient's mouth.
The tray should be checked for size and adjusted by adding wax or trimming the border.

Tray Components

A tray consists of a floor, body, flanges, and handle.
The floor and flanges make up the body of the tray.

Tray Types

Trays can be metal (aluminum or stainless steel) or non-metal (plastic).
Perforated trays are used for alginate impressions, while non-perforated trays are used for impression compound.

Anatomical Landmarks

Anatomical landmarks include peripheral, supporting, and relief areas.
Examples of anatomical landmarks in the mandible include the labial frenum, labial vestibule, lingual frenum, buccal frenum, and buccal vestibule.

Primary Cast

A primary cast is used to study the ridge shape, palatal vault shape, denture bearing areas, areas of undercut, relief areas, posterior palatal seal area, sharp bony edges, depth of the sulcus, inter-ridge space, and inter-ridge relations.
It is constructed for each patient and provides more accurate information due to its customized nature.
Types of primary cast materials include acrylic resin and shellac.