Mandibular Asymmetries

I was very interested to read the recent Case Report, "Treatment of Adult Midline Deviation by Condylar Repositioning", by Dr. Fred Schudy (JCO, June 1996). I feel compelled to respond for a number of reasons, not the least of which is that I am a co-author in the extensively quoted paper by O'Byrn et al. on mandibular asymmetry and unilateral posterior crossbites in adults.¹

Dr. Schudy's case report appears to offer evidence of "condyle-fossa remodeling in an adult patient"--specifically, in response to "anterior relocation of the condyle" following the extended use of reverse crossbite elastics and Class II elastics for the correction of a Class II subdivision malocclusion in a 42-year-old female. Dr. Schudy obviously supports the idea of TMJ remodeling in response to condylar repositioning. Even though he uses O'Byrn et al. to support his ideas, he takes issue with that paper for not offering condylar remodeling as a consequence of anterior relocation. The O'Byrn study could not determine the site of any TMJ remodeling that may have occurred, which is the reason for constantly referring to the condyles being relatively posterior on the crossbite side.

Furthermore, Dr. Schudy chooses the wrong paper as a reference for his case report. Rose et al.² (with which I was also involved) would have been more appropriate, since it had to do with Class II subdivision in adults and offered data to indicate that mandibular dentoalveolar asymmetry may explain the asymmetry in many of those malocclusions. This paper suggested that in adults, it may be difficult to correct the asymmetry to an ideal occlusion, and questioned the need or desirability of correcting the asymmetry per se, rather than establishing an ideal overjet and overbite as the primary objective and accepting that the posterior occlusion may be less than ideal.

In spite of the apparently successful result reported by Dr. Schudy and his 40 years of similar successful experiences, I take issue with the treatment objectives for this case. Why force a stable, functional mandibular position to change in order to achieve a morphologic occlusion that conforms to an arbitrary ideal? We assume the absence of a functional shift of the mandible from initial contact position to maximum intercuspation (as does Dr. Schudy in this particular case). In an adult, forcing function to adapt so that form (morphology) can be altered may challenge the stomatognathic system unnecessarily, and for what purpose? I also question the indication for treatment and especially the treatment rendered in this case. What was the patient's main complaint? The lower incisor crowding could have been resolved with some reproximation (interproximal stripping) and a spring aligner if the patient so desired. In explaining the treatment outcome, how does Dr. Schudy know that the correction of asymmetry could not be explained by dentoalveolar changes, rather than by "condylar adaptation" as a response to "condylar repositioning"?

As a final point, I also take issue with The Editor's Corner by Dr. Larry White in the same issue, in which he suggests that unilateral extraction in Class II subdivision therapy is a therapy "few patients willingly accept and few orthodontists enthusiastically recommend". If Dr. White is referring to the unilateral extraction of a maxillary premolar on the Class II side, I agree it is an unusual solution--although occasionally appropriate if the maxillary posterior teeth are mesial on the Class II side, usually due to premature loss of primary teeth. I contend, however, that asymmetric extraction (two maxillary premolars and a mandibular premolar on the Class I side) is a very appropriate strategy for these cases when there is crowding and dentoalveolar asymmetry in the mandibular arch. Such treatment results in a symmetrical lower arch, with a Class I molar and canine relationship on the Class I side, a Class II molar and Class I canine relationship on the Class II side, and the midlines coincident. If the Class II subdivision is due to mandibular dentoalveolar asymmetry (in the anteroposterior plane), then any other treatment requires a compromise between a symmetrical maxillary dentition and an asymmetric mandibular dentition. In cases where extractions are not indicated--as with a flat profile, absence of crowding, or absence of dental protrusion--a compromise in the occlusal relationships may be necessary.