We use intraoral impressions in our practice, but there still are occasions when taking a traditional impression is necessary.
Impressions of your teeth are an important tool in the treatment planning process. We need them to examine and diagnose your orthodontic problems. They help us with the following:
- Analyzing the relationship between your upper and lower jaws.
- Understanding how some tooth movements will affect your bite.
- Making some types of oral appliances.
What’s the difference?
Prior to intraoral impressions, we accomplished the task of creating plaster or gypsum models of the teeth using a material called alginate. Alginate is a powder that we mix with water until it reaches the consistency of cake batter or toothpaste. We place this material in a tray and fit it over your teeth and gums. At this point, its consistency starts to resemble chewing gum. We leave it there to harden for a few minutes and then remove it. This creates a negative imprint of your teeth and gums, which we use to create a cast.
Some patients dislike this impression method, particularly if they salivate a lot or have a sensitive gag reflex. It also can be uncomfortable for patients with small mouths. When doing the upper impression, sometimes patients feel as though the alginate is going down their throats, but don’t worry – that isn’t the case. Conventional impressions can be a bit messy, too. It is common to have a bit of alginate around your mouth after the trays are removed, but it easily is cleaned away.
The process of getting a conventional impression can take three to five days from start to finish. Although it doesn’t happen often, it is possible to get air bubbles in the material while making the impressions and when that happens, you may need to return to the office for a retake.
Intraoral impressions provide all of the information instantly with none of the mess. They are fast, clean and precise digital 3D images that capture the individual characteristics of your teeth surfaces and gums. We just guide a wand with a digital camera in the end across your teeth. Your scanning progress is visible on a computer screen, and computer software translates the information into a 3D image.
The software also allows me to collect important measurements for overjet and overbite, arch length, tooth size and crowding measurements, to name a few examples.
Your appointment goes faster when we use the intraoral scanner, which takes far less time to capture the impression than the conventional method.
Once captured, we can send these digital scans directly to the lab, which improves workflow and gets orthodontic treatment going faster. There’s no need to package and ship stone models.
Although intraoral scans aren’t without errors, the difference is that a scanning error becomes immediately apparent and can be rescanned during the same visit. Our patients appreciate this, because it eliminates the need for extra appointments and more time off work or away from school.
When do you use conventional impressions?
We still use conventional impressions for several appliances that are made in our office:
- Fixed retainers – this is the type of retainer patients commonly get to hold their lower front teeth in place once braces come off. We cement the retainer to the backs of your lower six front teeth to prevent them from becoming crowded or crooked again.
- Essix retainers – This type of retainer is made of transparent plastic and is used to keep your teeth properly spaced and aligned following orthodontic treatment.
- Indirect bonding – This is a method of applying brackets onto the teeth quickly and accurately.
Which impression method is better?
The advent of intraoral scans begs the question: Which is better? I was pleased to read of a recent study that found the results are virtually the same between traditional impressions and those obtained via intraoral scans.
Similar studies have been conducted on this topic for prosthodontics (the branch of dentistry concerned with the design, manufacture, and fitting of artificial replacements for teeth and other parts of the mouth), but not for full-arch results, which we use in orthodontics.
The researchers sought to find out if measurements obtained from a direct, full-arch intraoral scan measured up to those obtained using plaster models. The group reported that they couldn’t identify any significant differences between plaster models and intraoral scans, except for one measurement of lower intermolar width. However, a comparison of all measurements showed that differences between the two models were within the limits of agreement, according to the South Korean researchers who conducted the study, which was published in June in the journal Plos One.
“The results of the present study indicate that the intraoral scans are clinically acceptable for diagnosis and treatment planning in dentistry and can be used in place of plaster models,” wrote Fan Zhang, Kyung-Jin Suh, and Kyung-Min Lee from the orthodontics department at Chonnam National University in Gwangju.
Although we use both types of impressions in our office, there is no question that 3D technology has drastically changed dentistry and orthodontics in the past 20 years. We use 3D technology more often than conventional impressions, and doing this offers a few benefits that as a patient, you may not have realized:
- Digital scans are stored electronically and take up no physical space. Plaster models required significant storage space.
- Moving to digital has environmental benefits, because it greatly reduces the amount of chemicals and materials we must use and later dispose of.
- 3D scanners and their accompanying software make it possible for us to plan, simulate and manage patient care as well as create orthodontic appliances using computer-aided design and manufacturing equipment.
- We can show our patients and their parents on a computer screen not only what their treatment will look like, but also the final result—in 3D color.
Our patients seem to enjoy the intraoral scanners, and they get a charge out of seeing their tooth movements on a computer screen. It’s a great motivator to be able to see their teeth in their current state, and how we will work to improve their smile over the course of their treatment.