Dental impressions are molds taken of the teeth for use in diagnosis and treatment of dental conditions. They are also used in forensics. Impressions are also known as dental or teeth molds. Typically, impressions are made in a dentist's office although a dentist can also travel to a patient or subject under special conditions, as the necessary equipment is relatively portable.
To make a dental impression, a viscous substance that is designed to harden is mixed and poured into a tray. The tray is inserted into the patient's mouth and the patient is directed to bite down. After a set period of time, the patient is asked to release the jaw, and the tray is removed from the mouth. Some dental impressions are made with very quick setting cements, allowing the patient to bite into a rubbery substance and then immediately release. This reduces discomfort and irritation for the patient.
The finished dental impression is a negative mold, showing the teeth in reverse. The mold can be filled with plaster or another material that is then allowed to set to produce a positive cast of the teeth. Impressions and casts can be used in the design of dental appliances like retainers and crowns. They can also be used in diagnosis, providing a model of the teeth that can be inspected at leisure without patient discomfort, and casts can also be sent out to consultants for evaluations.
Taking dental impressions requires some skills. It is important that the impressions are not jostled or compressed while they set, because otherwise the mold of the teeth could be disrupted. This may lead to creating a dental appliance that does not fit the patient. Dentists may keep molds and casts on file for future reference. Dental schools also keep molds of unusual examples of dentition as well as disease processes so that dental students can learn to recognize dental problems.
In forensics, dental impressions can be used to match up or rule out people who are suspected of having left evidence of a dental nature at a crime scene. Some unwary criminals have left evidence like partially-eaten food behind and this evidence has later been linked to suspects in a lab setting and used to support a case for conviction. Dental impressions can also sometimes be useful for forensic identification of unknown human remains; dental records can be matched with information collected from human remains for a positive identification.