Letters From Our Readers

To: Editor, The Angle Orthodontist, Re: Amount and Direction of Temporomandibular Joint Growth Changes in Herbst Treatment: A Cephalometric Long-Term Investigation. Angle Orthod. 2003;73(5):493–501.

There have been several publications examining the long-term effects of functional appliances and specifically the Herbst.1–3 Ruf and Pancherz demonstrated through magnetic resonance imaging the adaptive TMJ changes that could account for increased mandibular prognathism during Herbst treatment.4 They included increased condylar growth, anterior displacement of the glenoid fossa, and anterior positioning of the condyle within the fossa. In the September 2003 issue of The Angle Orthodontist Pancherz et al published an article titled “Amount and Direction of Temporomandibular Joint Growth Changes in Herbst Treatment: A Cephalometric Long-Term Investigation.”5 It concluded: “During Herbst treatment, the amount and direction of TMJ changes (condylar growth, fossa displacement, and effective TMJ changes) were only temporarily affected favorably by Herbst treatment.” Reading the article, I found the conclusion rather misleading.

The glenoid fossa is physiologically displaced inferiorly and posteriorly during normal growth and development.6 Pancherz et al5 demonstrated that during Herbst treatment the glenoid fossa was displaced in an anterior and inferior direction, and these favorable changes were significantly greater that those of the controls. Posttreatment, the fossa on average resumed its inferior and posterior displacement with a net inferior and posterior displacement. However, this doesn't prove that the favorable effects of the Herbst were temporary. In order for them to make that conclusion, they would have had to compare the net change in the position of the fossa (T4-T1) in the experimental group to that of their controls, which is information they simply didn't have. They only took control records at T1 and T2, which defeats the purpose of the title of this study. One could argue that the fossa would have ended up in position even further inferior and posterior at T4 if it weren't for the Herbst. Without T4 controls I don't think they can make any long-term conclusions on the amount of change produced by the Herbst.