Clear aligner retention revisited: Three-year mandibular alignment with annually renewed removable polyurethane and fixed lingual retention protocols

Title (English)

Clear aligner retention revisited: Three-year mandibular alignment with annually renewed removable polyurethane and fixed lingual retention protocols

Thong tin bai bao / Article info

• Tac gia / Authors: Kamy Malekian, Eva Maria Rosa, Jose Maria Alamán, Elena Figuero, Tommaso Castroflorio, Conchita Martín, Ricardo Ortega
• Tap chi / Journal: The Angle Orthodontist
• Ngay xuat ban / Published: 2026-10-14
• DOI: 10.2319/051526-483.1
• Nguon / Source: OpenAlex

Abstract (English)

Abstract Objectives To compare 3-year mandibular alignment after clear aligner therapy between an annually renewed nighttime removable polyurethane retention protocol and fixed canine-to-canine lingual retention. Materials and Methods Patient-level data were reanalyzed from a retrospective private-practice cohort. Here, 87 adult nonextraction patients with end-of-treatment (T0) and 3-year (T4) numeric mandibular Little’s irregularity index values and complete covariates were included. Allocation was clinical, not randomized. The fixed protocol used a mandibular canine-to-canine multistrand wire; the removable protocol used maxillary and mandibular polyurethane retainers prescribed for approximately 8 hours nightly at least 5 nights per week, renewed annually. The primary analysis used baseline-adjusted analysis of covariance with heteroscedasticity-consistent robust standard errors. Results Eighty-seven patients were analyzed (48 fixed, 39 removable). In the primary adjusted model, the removable protocol was associated with lower T4 mandibular Little’s irregularity index (adjusted difference = −0.81 mm; 95% confidence interval [CI] = −1.37, −0.26; P = .004). Median regression was consistent (−0.73 mm; 95% CI = −1.22, −0.25; P = .003). The mixed-effects time × group interaction favored the removable protocol but was not statistically significant. Conclusions The annually renewed nighttime removable polyurethane protocol was associated with better mandibular anterior alignment at 3 years than fixed canine-to-canine retention. The 0.81-mm adjusted difference (approximately 24% lower residual irregularity) was consistent across robust and distribution-resistant analyses, supporting this protocol as a clinically credible retention option while prospective confirmation remains warranted.

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