An orthodontic patient who was wearing twin block braces recently asked me how long it would be before they could move on to fixed orthodontic appliances (aka “train track braces”). I decided to put together a series of articles about the things that orthodontists consider when they change a patient over from to train tracks. (Or “functionals to fixed”, as we’d call it).
Twin block changeover and overjet
People often come in to see their orthodontist saying “my front teeth stick out”, but after a few quick checks of “landmarks” on the face (during an exam of the face and jaws), and maybe an X-Ray picture too, it usually turns out that it’s the lower jaw that’s really the problem.
In many cases, patients start off wearing twin blocks because they have a small lower jaw, or the lower jaw is sitting too far back compared to their upper jaw. This usually shows up as a big difference between the prominence of the upper and lower front teeth. (This is what we’d usually call an Overjet, but people on TV call an Overbite).
Sometimes this prominence is made worse by a “lip trap”, where the patient’s lower lip has a resting position between the upper and lower front teeth. The blocks help stop this habit. This lip trap can also be a problem if it reduces the natural protection that the lips would provide for the teeth against physical damage (“dental trauma”).
In this case the blocks would usually keep going until the front teeth meet edge-to-edge. (This would be an overjet of 0mm). Sometimes patients think this is the way that their teeth are meant to meet, but actually the orthodontist is carrying out a bit too much correction on purpose. A lot of orthodontists like to “overcorrect” certain problems to allow for a bit of relapse. This is particularly true for moving on to fixed braces, as it usually slips back a couple of millimetres while the patients moves from one brace to the other. (This is what we’d call “the transition”). A normal overjet would be 2-4mm.
So one thing to look out for if you’re wondering if you’re ready to finish with your twin blocks is the relation between your upper and lower teeth. It’s not always the case, but the orthodontist will often keep the blocks going until the front teeth can bite together. If in doubt, ask your own orthodontist to give you an idea of your progress through the treatment plan.
Source by S D Murray