Casts will be ordered whenever the dentist needs to study the size and relationship between the teeth, gums and dental arches. This is the case whenever the dentist is studying a patient’s growth and development, or when significant dental treatment is being contemplated. They are used to make crowns, fixed bridges and dentures. Casts are also made when the patient needs an athletic mouthguard, an orthodontic retainer, or fluoride/ tooth whitening trays. If the dentist wishes to communicate with a laboratory about a patient’s teeth, casts will be made. They are also great for recording treatment progress.
Generally, a dental auxiliary will measure the size of the patient’s mouth to determine how large an impression tray to use. The tray is what holds the impression material in place around the teeth while it is solidifying in the mouth. Lip balm will often be applied to the patient’s lips to keep the sticky impression material from adhering to dry skin surfaces. If you have fixed bridgework in your mouth, it’s a good idea to remind the auxiliary, so that the impression material will not flow under it, set up, and be locked into place in the mouth. Next, the impression material will be mixed and poured into the tray. The tray is inserted into the mouth, and gently pressed over the teeth and gums so that the flowable impression material will extrude into undercuts, pits, and other details of the tooth and gum tissue.
Depending on which type of material is being used to make the impression, the tray will be left in the mouth for one to several minutes. It is then removed in a quick snapping motion. Any residual material that is left in the mouth can be rinsed away. The impression is then taken to the laboratory, where it can be poured with a variety different materials to produce accurate replicas of the patient’s teeth and gums. It can also be silver plated to produce metal-surfaced replicas that are durable.
Advantages and benefits of dental casts
- Accurately reproduce the teeth, gums, and relationships between the upper and lower dental arches.
- Provide an inside-the-mouth view of how the teeth fit together that wouldn’t be achievable without sophisticated computer imaging hardware.
- Allow many different types of dental restorations (e.g. crowns, inlays, etc.), retainers, mouthguards, and trays to be made with great accuracy.
- Establish a point of reference to which future changes can be compared if needed.
Disadvantages and risks of dental casts
A small number of people don’t tolerate impressions very well due to sensitive gag reflex. Your dentist may be able to offer a number of suggestions to overcome a sensitive gag reflex.
Other care that may be needed
Casts of the teeth are part of a suite of diagnostic records which are frequently gathered to develop a complete understanding of a patient’s dental situation. Others include: X-ray images (radiographs); cone beam computed tomography (CBCT); visual / tactile examinations; periodontal probing; oral cancer screening; head and neck assessment (palpation of lymph nodes, thyroid gland, other soft tissue); and laser caries detection. Digital fiber optic transillumination (DIFOTI), infrared caries detection, and other emerging technologies for imaging teeth may be available in the future which can minimize the need to use ionizing radiation for dental diagnoses.
Casts of the teeth are also used to fabricate many types of dental restorations, mouthguards, bleach and fluoride trays, retainers and space maintainers; and other prosthetic appliances and surgical guides.
Other treatment options
For visualizing the teeth three-dimensionally while planning a patient’s treatment, there are currently no options as simple and cost effective as making stone replicas (casts). Digital impressions that scan the teeth with a wand-like handpiece, and create a virtual 3-D computer model are becoming more common for some dental procedures, but they have yet to eliminate the need for traditional impressions and casts.
What if I do nothing?
Casts of the teeth can be a very important diagnostic record, just like X-rays, visual/tactile examination and laser caries detection. If they are not done when recommended, the dentist could overlook important information that may lead to a compromised treatment outcome.
- If diagnostic records are not complete, treatment results can be compromised.
- Indirect restorations (any means of fixing teeth that require lab work) usually require impressions and casts of the teeth to be made. If a patient cannot tolerate impressions for some reason, direct restorations (those performed directly on the teeth) can sometimes be performed. However, this situation is a problem in theory more than in practice, as it would be rare to have a patient who could tolerate direct restorations and not impressions.
- Some offices may use digital impression techniques for certain procedures, which involve scanning the teeth with a probe attached to a computer. Software then creates a virtual model of the teeth, which can be used to generate a physical model, or to build a dental restoration directly from the virtual model. Traditional impressions and casts remain much more common, however, due in part to cost of digital systems and limitations in their use.
Author: Thomas J. Greany, D.D.S.
Editor: Ken Lambrecht
This page was reviewed by members of our review board.
This page was last updated on May 1, 2016.
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Information you may wish to read before making a decision on treatment
A Comparison of Fixed Prostheses Generated from Conventional vs. Digitally Scanned Dental Impressions
Henkel, Gary L., DDS, MAGD
Compendium of Continuing Education in Dentistry
External nasal dilators—A clinical aid for dentists, patients
Moses, Alan J., DDS
The Journal of the American Dental Association
2001 132 (11): 1555-1556