Potential impact of lingual retainers on oral health: comparison between conventional twistflex retainers and CAD/CAM fabricated nitinol retainers : A clinical in vitro and in vivo investigation.

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.