Introduction
It has previously been shown that patients with different vertical facial patterns present with different natural arch-forms. In general, greater changes in arch-form have been associated with long-term instability of orthodontic treatment. The use of various standard sized and shaped finishing arch-wires is common place in contemporary practice. With all this in mind, this study was designed to examine arch dimensional changes occurring in patients with different vertical facial patterns when a final arch-wire of particular size and shape has been used.

Methods
The retrospective records of 70 patients treated by one private specialist orthodontist were obtained for this study. All patients had been treated with fixed appliances in the early permanent dentition without premolar extractions and were selected according to either a high or low mandibular plane angle. Pre- and post-treatment maxillary and mandibular study casts were analyzed and the measurements were then correlated with various pre-treatment cephalometric variables.

Results
Despite the use of finishing arch-wires of the same size, shape and dimensions there was considerable variation in dimensional changes occurring during treatment and indeed the final arch-forms and sizes.

Conclusions
A large amount of individual variation was found for changes in inter-canine, premolar and molar widths. Given that the same size and shape final arch wires resulted in different final arch dimensions in different patients, this highlights the importance of the neuro-muscular envelope in which the dentition exists and functions. Perhaps these different responses to treatment have potential implications for long term stability. It also emphasizes that careful consideration of each patient's individual vertical facial pattern is essential.