Yesterday the topic of the ninth district dental society meeting was digital scanning and CAD/CAM technology. A digital scan in dentistry is the substitution of a digital 3D image for a dental impression.  It involves taking pictures with a mini- camera which uses either a blue LED ( light emitting diode) or laser light to make a three dimensional model of the teeth. This model can be used to make a digital restoration (like a crown, inlay, or onlay) which can be digitally printed for use in the mouth (i.e. CAD/CAM technology). This can replace, in some situations, the use of gooey impression material in a tray to make a negative image of the teeth. The “footprint” is either used to make a stone model of the teeth, or is scanned to make a digital model. Scanners have come a long way.  Intraoral scanners can very accurately reproduce the shape of one to three teeth in the arch to be able to make a single tooth restoration (crown, inlay or onlay), or even a three unit bridge.  The problem with intraoral scans is that they take tiny images which are “stitched together”.  If a larger area is scanned there is more distortion from the multiple sites of “stitching,” i.e. the bigger the scan, the greater the distortion.  The intra-oral scanning technology is not advanced enough to make a full mouth model which is as accurate as the model which can be made from a dental impression. If the scan is made outside the mouth, i.e. an impression is taken and then scanned, the model is very accurate and can be used to make a “printed” dental restoration which is bigger than three teeth, such as the framework for a partial denture. The technology is very expensive, and is outdated every three to four years.

What does this mean for the patient? If you want a crown made by your dentist and don’t like the feeling of gooey impression material in your mouth, you can find a dentist who has a digital scanner, and a digital printer to make the crown out of a block of “ceramic” material. If he has enough staff the can even prepare the tooth and restore it the same day.  If you want aligner treatment and can’t tolerate impression material in the tray, you can find a large, high volume, orthodontic practice which has a digital scanner, and they can take a digital scan of the full arch to send electronically to the aligner company.  There is enough flexibility of the aligner material to counteract the inaccuracies in the scan. If however, you like a small dental office with the personal touch, you may have to forgo the digital scan.  The technology is too expensive to be supported in a small, low volume, office, and also keep fees reasonable.

What does this mean for the dentist?  If you are competent in taking impressions it is fine to stick with taking impressions.  They are more accurate, and they can be scanned accurately by a digital lab.  There are dental labs that scan impressions, there are dental labs that print the models, and there are dental labs that print the restorations. Therefore your patients can still benefit from the accuracy of digital restorations.  If you are a new dentist who has not been trained in impressions taking because your school has “gone digital”, you are in trouble.  The scanning technology is great for single tooth restorations, but you still need impressions to make full arch restorations (crown and bridge or denture type restorations) accurately.

Bonded (Permanent) Retainers- Pros and Cons

I was asked to weigh in on a facebook discussion about bonded retainers.  The opinions ranged from “why would you want to attach something to your teeth forever,” “They are hard to clean because you have to floss under them (or waterpik around them), ” “they promote tooth decay and periodontal disease because of plaque build- up (i.e  it is difficult cleaning around them) “ to “at least you can’t lose them” and “they keep the front teeth looking straight so you haven’t thrown your money out for the braces when everything moves.”

I loved this opinion:

“If it helps to hear a positive old-school retainer story: my kids have managed to not only NOT lose, but use their retainers for five years now. They can keep track of keys and wallets too. It's not a bad skill to develop and less risky than the permanent option.”

I also enjoyed reading this one:

“I sometimes wonder when orthodontists recommendations cross the line between good dental health and strictly cosmetics reasons. I probably could have used a permanent retainer, but the slight crookedness of my lower teeth has never had a bad impact on my dental health. I would want a second opinion and a very detailed explanation why a permanent retainer was necessary.”

Here is how I responded:

Teeth will move your whole life- from any force that is put on them. This includes over-bulked fillings that make the contact too tight, mouth habits (such as pencil biting, improper tongue posture, clenching your teeth), and aging (which causes the lower jaw to rotate forward "throwing" the lower front teeth against the upper front teeth.) Some orthodontists choose to "guarantee" the lower front teeth stay straight with respect to "each other" by bonding them together. This does not stop them from moving as a unit! It can also have other undesirable side effects (such as creating space between the upper front teeth, or pushing the lower jaw backwards causing clicking in the temperomandibular joints) in patients who clench their teeth. It is necessary to floss or waterpik the bonded retainer daily to prevent gum problems, and to have it checked every year to make sure that it is still bonded securely- otherwise you can get decay under it.

 "Invisalign" or "Essex" vaccuum formed retainers stretch-out over time so that they become less effective, and they prevent posterior teeth from settling fully into occlusion (i.e. they prevent your bite from working properly) when used long term.

 I still prefer removable hawley style retainers (with a shelf on the front of the top one for vertical control)- worn full time when the braces come off, and then just “at night” after the first year- at least til the patient stops growing. (I switch to an occlusal guard if the patient is a clencher.) If the braces were worn as an adult it is likely retainers will be needed at night forever.

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