I often hear from patients that their teeth moved after their braces came off and they want to know why. There are basically 3 reasons for a failed case (that was treated well.)
1. The patient did not wear their retainers properly. This is patient error.
2. The patient did not eliminate mouth habits, and did not wear appliances to protect them from their mouth habits. This is a combination of patient and dentist error (if the dentist did not make the patient aware of their habits, and/or did not make appliances that could protect the patient from these habits.)
3. The patient grew unfavorably. No one had control over this one.
4. If the teeth were not aligned in the middle of the bone ridge, they will relapse to be centered in the ridge again. The treating dentist had control over this reason.
The next few blogs will address these errors. Today we will address #1: the patient did not wear his retainers properly.
In order for teeth to move with orthodontic treatment, the bone around the teeth has to remodel. The bone on the pressure side (the side to which we are moving the teeth) resorbs, and bone on the tension side (the side from which we are moving the teeth) rebuilds. Over time, the teeth are surrounded by new bone. This new bone is immature and weaker than mature bone.
Imagine that you broke a bone and went to the orthopedist to reset the bone. After aligning the bones to the best position, the orthopedist would put on a cast to hold the bones still, in that new position, until the bone fills into the break, and matures in that position. The retainer is like the cast. The teeth are slightly mobile when the orthodontic treatment is completed and the teeth need to be held in their final positions while the bone holding them matures.
A good retainer is rigid, like the cast for a broken bone is rigid. It should hold the teeth still even if the patient leans his tongue on the retainer, or if the patient clenches or grinds his teeth. Rigid retainers are make of hard acrylic, and have wires that hold them and the teeth in place.
It has become common for orthodontists to use other forms of retention. Essex and aligner retainers are non- rigid vacuum formed retainers which are less expensive to make, and are less effective because they flex when forces are applied to them. These plastic retainers also stretch out over time and need to be replaced frequently. If the treating orthodontist does not intend to provide long term retention care he may choose to use this style retainer.
It is also common for the orthodontist to "glue" the front teeth together, often with a wire or fiberglass thread that is bonded to the tongue surface of the teeth. Bonded retainers will hold the front teeth straight with respect to each other, but the bonded can move as a unit with respect to the back teeth. The bonded retainers offer no retention to the back teeth, and if the patient has mouth habits (like grinding the teeth) the retainer will break as the back teeth move vertically. Bonded retainers are difficult to keep clean, and often have issues with developing cavities and gum disease.
A removable retainer has to be worn "fully seated." If the patient lifts the retainers with his tongue, or floats it above his teeth, it cannot do it's job. If the patient repeatedly moves it in and out with his tongue he may actually make the teeth looser, rather than letting the teeth "tighten up." If the retainer is "floating" it is not contacting the teeth, and therefore cannot hold them in place. If the patient is holding the retainer in his hand, instead of wearing it in his mouth, the retainer can also not do it's job.
Retainers should be worn full time until the teeth "tighten up". This takes between two and six months. Then the wear-time should be decreased, and the mobility of the teeth should be evaluated by the orthodontist. If the retainer always feels the same when it is replaced after a period of time, as when it is replaced immediately after removing it, it means that the teeth have not moved when the retainer was out of the mouth. If the retainer feels different after it has been left out for a period of time, it means that the teeth had a chance to move somewhere, and the retainer had to push the teeth straight again. The goal is to eliminate the habits that are causing the teeth to move, in order that the teeth stay in place when the retainer is removed. Over the course of the first year the patient should be able to decrease wear-time to be only when sleeping. The orthodontist needs to evaluate whether it is necessary to continue retainers at night indefinitely, or whether the patient can discontinue night time wear of the retainers when his face finishes growing.
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