Potential impact of lingual retainers on oral health: comparison between conventional twistflex retainers and CAD/CAM fabricated nitinol retainers.

Purpose: To evaluate the impact of a novel computer-fabricated lingual nitinol retainer compared to a conventional lingual flexible spiral wire twistflex retainer on oral health.Methods: The study was based on a retrospective controlled clinical study with pilot character, an in vitro investigation of material-dependent biofilm formation and an analysis of biofilm formation after intraoral incubation. Sixty-one patients with completed fixed orthodontic treatment and retention phase for at least 6 months with twistflex retainers (group 1, n = 31) or computer-aided design/computer-aided manufacturing (CAD/CAM) nitinol retainers (group 2, n = 30) were included and examined regarding plaque index (PI), gingival index (GI), probing depths, bleeding on probing (BOP) and marginal recessions (MR). Material-dependent biofilm formation of twistflex, untreated nitinol and electropolished nitinol wire samples were assessed (1) in vitro: using optical density (OD) measurement of 10 samples of each and (2) in vivo: using histomorphometric analysis of 18 samples of each.Results: Patients treated with nitinol retainers had significant better oral health indices (PI₁ = 1.29 ± 0.06, PI₂ = 0.94 ± 0.06; GI₁ = 0.71 ± 0.05, GI₂ = 0.56 ± 0.04; BOP₁ = 0.11 ± 0.01, BOP₂ = 0.08 ± 0.01; PD₁ = 1.79 ± 0.03 mm, PD₂ = 1.59 ± 0.04 mm) except for MR (0.08 ± 0.03 mm versus 0.08 ± 0.02 mm) compared to twistflex retainers. After 24 h intraoral incubation nitinol retainers demonstrated significant less biofilm formation compared to twistflex retainers. In the in vitro investigation the temporary significant differences between the groups were compensated in the end.Conclusions: Based on the results it can be assumed that nitinol-made CAD/CAM developed lingual retainers have a positive effect on oral health. [ABSTRACT FROM AUTHOR]