Comparison of the effects of modified and full-coverage thermoplastic retainers on occlusal contacts

The purpose of this prospective study was to determine the number of contacts in centric occlusion during retention with modified and full-coverage thermoplastic Essix retainers.

This research was based on 36 patients who were randomly assigned to wear either modified (18 patients) or full-coverage (18 patients) Essix retainers. Silicone-based bite registrations were used to record occlusal contacts at the beginning (T1), end of full-time (6 months; T2), and end of night-time (3 months; T3) wear of retainers. The occlusal contacts determined in treated patients were compared with the values of 18 untreated "normal" Class I subjects. Bonferroni-adjusted Wilcoxon and Kruskal-Wallis tests were used to evaluate intra- and intergroup differences.

Total posterior contacts increased significantly at T3 compared to T1 and T2 only in the modified Essix group. Non-ideal and total contacts on premolars, non- ideal and actual contacts on first molars, and actual contacts on second molars increased significantly at T3 in the modified Essix group. No significant increase was determined in the final total posterior contacts in the full-coverage Essix group. Actual contacts on premolars and first molars and total posterior actual contacts were significantly greater at T3 in the modified Essix group compared to the full-coverage Essix Group. Also the number of final posterior ideal contacts in the modified Essix group was greater than in the normal sample. Total anterior contacts decreased significantly in the modified Essix group, whereas they increased significantly in the full-coverage Essix group.

Increase in posterior contacts was achieved only during night-time wear of modified Essix retainers.