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.

Novel lingual retainer created using CAD/CAM technology: evaluation of its positioning accuracy.

OBJECTIVES: Permanent retention is currently the method of choice to stabilize orthodontic treatment results. Frequently, permanent retention schemes are adopted to prevent posttreatment changes in the esthetic zone of the anterior teeth. With increasingly prolonged times of intraoral device use, and retention to be provided in the maxilla despite limited space, the demands placed on well-planned and precise retainer positioning are becoming more exacting. The aim of the present study was to analyze the intraoral precision of lingual retainers made using computer-aided design and machining (CAD/CAM). MATERIALS AND METHODS: A custom manufacturer (Retaintechnology; Cologne, Germany) employing innovative CAD/CAM technology was commissioned to fabricate 16 lingual retainers. Following intraoral insertion using the manufacturer's recommended transfer system, impressions of the intraoral situations were taken and scanned for digitization. On this basis, the intraoral retainer positions were compared to the preceding virtual setups by superimposition with the manufacturer's datasets. Three-dimensional processing software (Geomagic Qualify 2012; Geomagic) was used to analyze the retainers, based on a total of 80 interproximal sites, for deviations from their planned positions along the horizontal (x-), sagittal (y-), and vertical (z-) axes. These deviations of the achieved from the intended positions were considered clinically relevant if ≥ 0.5 mm and, based on this premise, were subjected to a t-test with statistical software (Prism; GraphPad). RESULTS: The intraoral retainer positions were found to correlate closely with the preceding virtual setups (i.e., the positions as they had been planned by the custom manufacturer). Positional deviations were significantly less than 0.5 mm. They were very small in the horizontal and sagittal planes and moderately larger in the vertical plane. CONCLUSION: Highly precise intraoral results may be achieved by transferring three-dimensional virtual setups for lingual retainers to the actual patients. This CAD/CAM strategy of making retainers can offer high predictability even in anatomically demanding regions and in the presence of limited space.