Journal of Dental Medicine

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Mohsenpour M, Arianian S, GhorbanipouR R, Sheykhzadeh S, Arash V, Gholinia Ahangar H. Evaluation of the effect of vacuum-formed retainers (Essix) thicknesses on occlusal characteristics in patients undergoing fixed orthodontic treatment. J Dent Med-tums 2026; 39 : 24
URL: http://jdm.tums.ac.ir/article-1-6402-en.html

Background and Aims: Post-treatment relapse is one of the common challenges in maintaining orthodontic results, and the selection of the type and characteristics of retainers plays a crucial role in treatment stability. Vacuum-formed retainers (Essix) are widely used due to their ease of fabrication, esthetics, and high patient acceptance. However, the effect of different thicknesses of these retainers on the preservation of occlusal characteristics has not been fully elucidated. The aim of this study was to evaluate the impact of Essix retainer thickness on maintaining occlusal characteristics.
Materials and Methods: This prospective cohort study was conducted in 2025 on 30 patients (23 females and 7 males) who had completed fixed orthodontic treatment at the Department of Orthodontics, Babol University of Medical Sciences, Iran. Patients were randomly assigned to two groups receiving Essix retainers of different thicknesses (1.5 mm and 1 mm) under similar retention protocols. The variables of overjet, overbite, inter-canine width, inter-molar width, upper arch length, and the dental irregularity index were measured immediately after debonding at 6 and 9 months of the retention phase. Data were analyzed using repeated measures ANOVA, and comparisons were made between the two groups.
Results: The results demonstrated that the use of 1.5 mm thickness of Essix retainers led to a significant increase in overjet over time (p=0.04), whereas the 1 mm thickness showed no significant change (p=0.22). Changes in overbite were not significant in either group (p=0.60) and the difference between the two groups at 9 months was also not significant (p=0.23). Inter-canine width (p=0.38) and inter-molar width (p=0.13) did not change significantly over time and the difference between groups at 9 months was not significant (p>0.05). Regarding the arch length, the 1.5 mm thickness showed significant changes (p=0.04), whereas the 1 mm  thickness  did not (p=0.16). However, the difference between groups at 9 months was not significant (p=0.44). The dental irregularity index decreased significantly in both groups (p≤0.001), but the degree of change between groups was not significant (p=0.35).
Conclusion: Based on the findings of this study, clinically, the thinner Essix retainers did not result in greater relapse compared to the thicker Essix retainers. Therefore, the selection of Essix retainer thickness can be based on the patient preference and clinician judgment, without a need to recommend a specific thickness definitively. However, further studies with longer follow-up periods are suggested to evaluate the long-term stability of treatment outcomes.