Efficacy of thermoplastic retainers on maintaining the stability of transversal dimensions

Objective: This study aimed to evaluate the stability of transversal arch widths of upper and lower dental arches following retention with thermoplastic retainers applied after non-extraction fixed orthodontic treatment. Materials and Method: The material consisted of the pre-treatment (T1), post-treatment (T2) and post-retention (T3) cephalometric data and the dental models of 21 patients (16 female, 5 male; average age 17.5 ± 1.2 years), who presented skeletal Class 1 and dental Angle class I relationship with an optimal vertical facial pattern, and small amount of crowding in both jaws. The patients had been treated by non-extraction fixed orthodontic treatment followed by the application of thermoplastic retainer with a mean retention period of 1 year. The dental models were scanned and transferred to digital environment to measure inter-canine, inter-premolar and inter-molar widths for both dental arches. Repeated Measures ANOVA and Wilcoxon Signed-Rank tests were used for the statistical analysis of the data having normal and non-normal distribution, respectively (α=0.05). Results: Statistically significant differences were found in the upper inter-premolar width between the T1-T2 periods (p<0.001), and between the T1-T3 periods (p<0.001), and in the lower inter-premolar width, between the T1-T2 periods only (p<0.001). In none of the arches and for none of the parameters a statistically significant difference was found between the T2-T3 periods (p>0.05). Conclusion: Retention with thermoplastic retainers was found to be effective in maintaining transversal arch width in both arches after non-extraction fixed orthodontic treatment