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What are Dental Impressions?

Mary McMahon
Updated: Mar 03, 2024

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.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By Bakersdozen — On Jul 27, 2011

There was a show on TV a while back about child beauty queens. I saw some of the moms using dental impression kits to get a temporary false tooth made when the kids lost one of their baby teeth.

I'd have thought you needed to be trained to do that properly. but it must work okay if done at home too.

By Penzance356 — On Jul 26, 2011

I've had a few thousand dollars worth of dentistry work done in the last couple of years. I can honestly say that the worst part of the three implants I had was the impression taking process.

Apart from gagging endlessly, (it feels so huge in your mouth), I seem to spend days spitting out pink pieces of plaster!

By sunnySkys — On Jul 25, 2011

@starrynight - My mom was a dental assistant in the '70s, and apparently getting an impression done was quite the ordeal back then. Probably worse than when you were a kid!

Luckily for my moms patients, she had a great bedside manner. Once she helped a patient with a very sensitive gag reflex get through having an impression done without throwing up. Apparently no one had ever been able to do that before!

The lady was extremely grateful to my mom for her help. And, her husband happened to be a jeweler. So my mom ended up getting some free repairs done to her wedding ring out of the deal! I always thought that was a really nice gesture.

By starrynight — On Jul 25, 2011

Dental impressions may be a somewhat quick process now, but they used to be a lot more time consuming. I'm 26, but I remember when I had orthodontic work done, having an impression taken was less than pleasant.

The material used to make the cast tasted horrible and you had to sit there with it in your mouth for at least ten minutes, maybe more. Also, if you jostled the mold too much, they had to take it out and start all over. That actually happened to me once!

On the upside, I have nice, straight teeth now. I also haven't had to have a dental impression done in years!

By bythewell — On Jul 24, 2011

I think my father might have had to do one of these for his trial. Not that he was on trial, he was suing his dentist.

The dentist managed to break off a piece of the drill in my father's teeth and just left it there, covering it with a bit of filler. The bit started moving until it pierced my father's sinus cavity!

So, the dentist was really incompetent, but, unfortunately for dad, he didn't have the best lawyer. I'm not sure if they even managed to get the cost of the surgery dad had to have back. Luckily he had insurance.

Unfortunately, the dental impressions they provided didn't really help because it was mostly on the inside of the teeth that the damage was done.

By croydon — On Jul 24, 2011

I think it was the Ted Bundy case where they managed to bring in some evidence using dental impressions. He had bitten one of his victims and left a clear mark, which they were able to prove came from his teeth.

They made castings of his teeth and used them to show that the bite mark was a definite match. It was one of the things that got him put away, even though he was manipulating the media the whole time and trying his best to get off.

It just shows how every little bit of evidence counts. You'd think with all the things he did it wouldn't be a bite mark that would get him convicted.

By amysamp — On Jul 23, 2011

@bluespirit - No, they did not offer a refund. But I do not blame them, it is a complicated and is seemingly a severely detail oriented thing to make as far as getting the size right no matter how great the impression was.

I did let my former dentist know about the problem, but the dental hygienist is only a part of the impression usually by prepping the dental impression materials for the impression so I didn't really worry about them knowing.

Oh and another thing I learned about dental crowns of importance: although expensive they will only last maybe 5 years (at worst) to 10 years (at best). Here's to hoping my expensive crowns last even longer!

By bluespirit — On Jul 23, 2011

@amysamp - Oh my goodness! Dental crowns are expensive items to be have made wrong! Did you let the dental hygienist or the dentist know what happened? Did they offer you a refund?

By amysamp — On Jul 22, 2011

I had a dental crown and this is just where I think the crown went slightly wrong. That is the thing I have learned since the experience - even only slightly wrong in terms of dental crowns is not good.

My current dentist noticed a *tiny* spot missing on my crown where the crown met the gum line. Seriously tiny spot, I had to squint just to see it.

I didn't think it was a big deal but my dentist said that because it is where my gum line is that germs can get underneath the spot and cause some damage.

So the dental impression procedure, although not painful is quite important!

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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