Still Trying to Promote an Understanding!
Orthodontic literature reveals that most contributors do not seem to understand the function of the jaws. There is frequent reference to the thought that when lower face height is increased, that the mandible hinges down and back. This is only true when the condyles fail to grow vertically an equal amount.
When the condyles grow vertically as much as the Ans/menton distance increases, then there is no "hinging down" of the mandible and the mandibular plane remains parallel to its original inclination. There seems to be constant fear that there will be created too much vertical growth; but for many patients vertical growth of the lower face is needed for aesthetics and stable overbite correction. Also it is often expressed that when we have avoided stimulating lower face height, we have performed superior treatment, but this is not necessarily true.
Most studies of overbite fail to report the relationship between condylar growth and vertical molar growth. Unless this relationship is closely monitored, the study is of little value. That is why the myriad of such studies shed such little light on the problem of overbite correction. Evidently it is because there is limited understanding of the effects of causative growth increments and how they relate to one another.
In a recent article I was misquoted in an article published in 1968. The author of this recent article states, "The intrusion of maxillary incisors was stable, since only 0.15 mm of post treatment extrusion occurred. This contradicts Schudy, who in 1968, suggested that incisor intrusion was not stable."
What I really said was, quote, "When mandibular incisors and cuspids are intruded, they have a strong tendency to extrude in the post treatment period."
There is an important distinction between lower incisor intrusion and upper incisor intrusion. The author, just quoted, lumps them together as "incisor intrusion." Upper incisor intrusion is quite stable, while lower incisor intrusion is usually not stable. This has been stated many times through the years.
Another quotation from the same article: "Overbite relapse during the post treatment period was positively correlated with incisor intrusion and molar changes. Overbite relapse, however, did not correlate with the amount of molar extrusion during treatment." (Emphasis added).
This confirms what we have been preaching for many years, that intruded lower incisors have a strong tendency to extrude post treatment and close the bite. Also, we have been preaching that when molars have been moved occlusally, they remain at this level for life, even if there has been much published to the contrary. We challenge colleagues to show us evidence of where molars have been intruded by normal muscle functions!!
Again this is another effort to try to promote sound precepts and principles.
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