In the last couple of Newsletters, we have been talking about when is the best time to start orthodontic treatment for a child. There are so many factors to consider, like the eruption of permanent teeth, the adolescent growth spurt, the age of the child, and none of those coincide with each other very well. In this article, we will look at HOW an orthodontist can predict the onset of an adolescent growth spurt. Warning: sciency stuff ahead!
We have already established that the adolescent growth spurt is one of the most important factors to consider when choosing a time to start orthodontic treatment. Usually, you want to start treatment before, but sometimes after is better. The distinction is more for your orthodontist to decide based on the biomechanics involved. Nonetheless, we need to know when that growth spurt will occur!
In 1982, Leonard Fishman published Radiographic Evaluation of Skeletal Maturation: A Clinically-Oriented Method Based on Hand-Wrist Films, which was one of the more profound articles published in the orthodontic literature. Basically, he evaluated x-rays of hands, and noticed the way that the bones of the hand and wrist change shape as a child matures. Mostly, he was looking at the epiphysis of the hand bones, which is the bulbous part of the bone on the end of it. In a child, the epiphysis is separate from the rest of the bone, and then it begins to change shape and eventually fuse. This is what Fishman was looking at, and he developed a system of 11 stages from childhood to maturity. He was then able to correlate those stages with the change in height as a child grew. As a result, we can very accurately determine where a child is on their growth curve based on Fishman’s system. The adolescent growth spurt usually begins around stage 4-5 and lasts for a year to a year-and-a-half.
The major problem with this technique is that orthodontists take x-rays of the head, not the hands! It is also a fairly cumbersome technique for less experienced orthodontists. Thus it is not frequently used and there was demand for a more convenient technique. A technique published in 1975 by Don Lamparski, which evaluated the shape of the neck bones visible in an x-ray of the skull, was refined and simplified in 2002 by Tiziano Baccetti, Lorenzo Franchi, and James McNamara.
The Baccetti, et al technique is the most commonly used technique in orthodontics today. In this technique, we can see the change in shape of the vertebral bones from wedge-shaped to tall rectangles with a concave bottom surface, and correlate that to where a child is on their growth curve. Although it is not as accurate as Fishman’s method, it can give an idea of when growth changes will occur. In this picture, the graph roughly indicates how rapidly a child is growing in correlation with the shape of the neck bones.
Orthodontists use this information to determine when to start the bite correction portion of treatment. Understanding how the lower jaw will typically grow more than the upper jaw, we can use this knowledge to use growth to carry the teeth to their proper position relative to each other, aka “the bite.” But why the complex method rather than relying on the age of a child? Because the age of a child is unreliable. The “average” girl hits their growth spurt between 11 and 12 years old, and the “average” boy hits it between 13 and 14.5 years old, but the variation from “average” is so much that we just can’t rely on a child’s age to determine how they will grow.
So, we have talked about how the permanent teeth erupt, how to predict and use the adolescent growth spurt, and how those events are totally unrelated to each other and also do not correlate well with the age of a child. This is one of the fun parts for an orthodontist. We have to figure out how to make all of these unrelated pieces fit together to create a smooth and elegant treatment plan.
I hope that it has been interesting to see how orthodontists evaluate growth! There is, of course, much more to it than just this though. We need to know whether the jaws will grow more horizontally, more vertically, whether the lower jaw will ever “catch up” with the upper, or whether the lower jaw will outgrow the upper jaw by too much and create an underbite. I will spare you those details, it gets pretty technical.
Next time I will talk about one of the biggest issues around timing treatment, that many parents are faced with and many of you have already been faced with. We will talk about starting treatment early and doing a two-phase treatment (Phase 1 followed by Phase 2) versus waiting until the child is a bit older and treating the case whole case all at once. There is a right and a wrong time for each of those approaches, which I will hopefully be able to clarify for you.