Changes in sagittal molar relationship during and after fixed appliance extraction treatment

To determine the effectiveness of fixed appliance treatment in achieving planned sagittal molar positions, and to assess the stability of the resulting changes.

Cohort study.

District General Hospital Orthodontic Department, UK.

Patients undergoing fixed appliance treatment involving extractions (n = 250).

Consecutive patients completing treatment who fulfilled the specific inclusion criteria were invited to participate. In addition to the normal start and finish study models, additional models were obtained at three further stages following treatment, corresponding to cessation of full-time and commencement of nights-only retention, at the end of planned retention, and finally 12 months after the end of retention. Sagittal molar relationships were assessed for each case at each stage by matching them to diagrams representing ideal intercuspations, and deviations either side of these positions. The actual changes that occurred were compared to the planned molar positions which should have been achieved for an ideal result; post-treatment changes were also determined.

In only a minority of cases was the precise pre-planned sagittal molar position achieved at treatment completion. However, this did not appear to have any significant effect on the subsequent stability of the molar relationships, as changes were recorded both for those cases that completed active treatment having achieved such positions (i.e. definite class I, II or III) as well as those that finished with imprecise intercuspations. Nevertheless, the changes were normally of small magnitude and in the majority of cases no post-treatment change whatsoever was detected.

Achievement of an ideal post-treatment sagittal molar intercuspation appears to be an elusive goal, but the clinical significance of this is questionable, particularly as realisation of an ideal outcome did not appear to guarantee post-treatment stability.