In Conclusion…A guest post by Lysle Johnston
This is a guest blog post by Lysle Johnston one of World’s most respected orthodontists. He addresses some of the issues on Class II correction that have been raised in previous posts.
At the outset, please note that this communication is, to a degree, an apologia for cephalometrics in the 21stCentury. I am willing to acknowledge/admit that much of the past century’s cephalometric “research” has provided useless answers to unasked questions. Perhaps, as a result, it is de rigueurto say that this sort of research is obsolete. Admittedly, cephalometrics can’t answer questions about “satisfaction”: don’t you feel better coming to me knowing that we are going to “work with growth” by treating early and often?
Importantly, the fact that something is easy to do and even easier to sell doesn’t hide the fact that there often is no evidence to characterise what our contemporary “new age” treatments actually can do and how they do it. More? Better? Different? Who cares? As long as nobody dies from anchorage loss, data are beside the point; florid advertising is all that’s necessary. To someone who, since a rural childhood, has taken clocks and cars and all things mechanical apart to understand the underlying mechanics, I would argue that skilled cephalometric analysis (2D or 3D) is at present perhaps the only way to characterize the actual morphological impact of the wares being sold in today’s orthodontic bazaar. So be it. Based on 60 years of cephalometric research, I have reached a number of conclusions about the inner workings of our various treatments. More than a century of “bone growing” with old, new, and re-cycled treatments is a case in point.
How does Class II correction occur?
For both Class I and II malocclusions, it is known (from cephalometrics) that the usual pattern of growth features a mandibular excess. Alas, we also know (again, from cephalometrics) that, in the absence of treatment, this favourable mandibular excess usually has no impact on the molar relationship: maxillary dento-alveolar compensation neutralises the effect of any mandibular excess. Based on data (once more, from cephalometrics) obtained from an analysis of thousands of different Class II treatments, I would argue that all successful modalities (the reader can specify the criteria for “success”) do what they do by controlling the A-P position of the upper dentition.
As a result, “Carriere motion” devices, headgear, TADs, “distal jets,” Class II elastics, and the like all would serve, not only control the maxillary buccal segments as needed but also allow whatever mandibular excess happens to occur to contribute to a molar correction. Appropriate to the present thread, the same argument can be made (based on my cephalometric data) for any treatment that features some sort of bite jumping in the hope of augmenting mandibular growth.
Firstly, it is clear that “functionals” work; however, the bulk of the pertinent evidence (derived from cephalometrics) argues that this outcome depends on the usual pattern of growth, rather than an assumed, but probably imaginary mandibular growth augmentation. Actually, the “Sunday bite” produced by functional appliances serves to keep the mandible forward so that the normal (“usual”; “expected”; average; etc.) mandibular excess can occur without causing maxillary dento-alveolar compensations. Further, it would allow this excess to grow the condyles back into the fossae, thereby helping to hold the forward mandibular occlusal position. Given this analysis, keying a mandibular aligner into a forward position might work; unfortunately, it is probably an unnecessary elaboration.
If the name of the game is to allow the normal mandibular excess to occur without pushing the uppers forward, all that would be needed is to “flat plane” the upper (or lower) aligner. From my cephalometric data, I would argue that, In the absence of occlusal intercuspation, all or part of the Class II correction thus would be achieved “for free.” I suggested this modification to Invisalign years ago, but there was little interest. The future probably will be no kinder to the world of cephalometric inference and its atavistic practitioners. If so, I think we are in danger of throwing out the baby with the bathwater under the assumption that cephalometrics has little place in the world of contemporary craniofacial biology.
If, as seems likely, cephalometric data are to be ignored (rationalised by a self-serving concern for “radiation hygiene”), salability and a practice’s “bottom line” will be the only criteria by which we can guess whether some new appliance actually does what is claimed. That’s the way it is and the way it probably always will be, “World without end.”
I’m glad to be retired.