Changes in facial dimensions associated with the use of forces to retract the maxilla

Abstract

Legitimate questions exist concerning the degree to which routine orthodontic treatment alters face form. To the extent that such alterations do occur, the delivery of different vectors should result in different sorts of skeletal change. In this study, we have attempted to discern and quantify differences in the rates of change of nine linear measures of mandibular and facial proportions during the course of Phase 1 treatment for the correction of Class II mixed-dentition malocclusion. The analysis took the form of a series of computer-conducted tests performed upon a previously reported tape-stored numerical data base which had been constructed earlier by digitizing pre- and posttreatment lateral cephalograms for a large group of Class II subjects. Rates of change for the nine linear measures were computed separately for samples of subjects treated with cervical face-bow, high-pull face-bow, and activator type intraoral appliances as well as for a control group of untreated Class II subjects. Statistically significant between-treatment differences which we believe are large enough to be of clinical importance were detected for several measures. As compared to the control group, a statistically significant rate of increase in condyle-pogonion distance was found in the intraoral group. Such an observation is consistent with the hypothesis of treatment-associated alteration of growth pattern in the region of the condyle. To our considerable surprise, the cervical group exhibited a similar statistically significant rate of increase in condyle-pogonion distance which is as yet unexplained. In general, rates of increase in measures of anterior face height had higher values in the cervical group than in the control group, implying that consideration should be given to avoiding the use of this treatment modality in patients for whom facial elongation during treatment would be undesirable. The cervical group also exhibited a statistically significant rate of increase in ramus height. Such an effect would tend to keep mandibular plane orientation relatively unchanged in the presence of increase in anterior face height, helping to explain our previously reported findings as to the relative constancy of mandibular plane angle. In the high-pull-treatment group, rates of increase in ramus height and condyle-pogonion distance were significantly lower than those in the control group and rates of increase in lower face height and anterior face height were significantly lower than those in the cervical group. In all three treatment groups, the rate of increase in mandibular body length was less than in the untreated control group, though only in the cervical group was this effect large enough to be statistically significant.