Is wear time of Hawley retainers measured with microsensors related to mandibular arch stability?

Abstract

The aim of this study was to show apossible correlation between the mean wear time of Hawley retainers and long-term mandibular arch stability as assessed via wear time analysis with microsensors. This longitudinal retrospective study comprised 47subjects (mean age 16.30 ± 1.06years) having been treated with anonextraction protocol and presenting moderate crowding at pretreatment. For retention, all patients were instructed to use amandibular Hawley retainer for 12months, and wear time was documented every 3months during aposttreatment period of 6months using TheraMon software. These individuals were divided into two groups. Those who adhered to awear time equal to or more than 12 h/day (group1A; N = 17) and those who complied for less than 12 h/day (group2A; N = 30) were compared with respect to changes of the mandibular arch during the first 6months of retention. Furthermore, asubgroup of 28patients who completed a12-month follow-up period were again divided into two groups: the individuals in group1B (N = 12) adhered to awear time equal to or more than 8 h/day, while those in group2B (N = 16) complied for less than 8 h/day. Little's Irregularity Index, intercanine and intermolar widths, arch length, overjet, and overbite were measured on mandibular models taken at pretreatment (T0) and posttreatment (T1), as well as 6months (T2) and 12months (T3) after debonding. Pearson correlation test, independent samples t‑test, and Mann-WhitneyU test were used for statistical evaluation. From T1to T2, group1A and group2A showed asignificant relapse in intermolar width with adifference in the median value of 0.38 mm (p = 0.019). At the complete 12-month follow-up, the increase in Little's irregularity score was significantly greater in group2B (2.54 ± 1.29 mm) than in group1B (1.32 ± 1.03 mm; p = 0.012). The established wear time measurements showed significant negative correlations with the Little's irregularity score and overjet changes between T1 and T3 (p < 0.05). The results emphasized that the use of aretainer should not fall below alevel of at least 8 h/day.