The aim of the study was to compare changes occurring within 12 months after orthodontic treatment associated with age. This longitudinal study investigated 30 cast models of subjects previously treated for mild crowding without extractions and having bonded the same flat retainer in the lower arch. The cast models were obtained one day after debonding (T0) and also after one year (T1). Measurements were conducted in lower arch only: Little irregularity index (LII), Arch perimeter (AP), Premolar width (PW) and Inter canine distance (IcD). 15 cast models belonged to growing patients (12-18 years) and 15 to adults (19-25 years). The larger mean increase of LII was registered in patients aged 12-18 years, as 0.26±0.26 for Mann-Whitney U Test: Z=2.074; p=0.038. The AP value was significantly higher in group 12-18yrs, compared to group 19-25yrs for Mann-Whitney U Test: Z=3.837; p=0.0001. The PW value was significantly higher in group 12-18yrs compared to group 19-25yrs for Mann-Whitney U Test: Z=4.106; p=0.0001. No significant difference was found in the IcD value between the 12-18yrs vs. the 19-25yrs one for Mann-Whitney U Test: Z=0.041; p=0.967. Growing subjects showed changes in the lower arch during the first year after orthodontic treatment is finished. Growth factors should be taken into consideration during the post retention stage in growing subjects, in order to better plan retention and avoid relapse.
Keywords:- arch perimeter
- flat retainer
- intercanine distance
- little irregularity index
- premolar width.