Polymerization kinetics of 3D-printed orthodontic aligners under different UV post-curing conditions

• Published in: Progress in orthodontics 2024-10, Vol.25 (1), p.42-9, Article 42
• Main Authors: Manoukakis, Thomas, Nikolaidis, Alexandros K., Koulaouzidou, Elisabeth A.
• Format: Article
• Language: English
• Subjects: 3D-printing; Aligners; Atmosphere; Curing; Dentistry; FTIR; Humans; Infrared spectroscopy; Kinetics; Materials Testing; Medicine; Nitrogen; Nitrogen - chemistry; Orthodontic; Orthodontics; Polymerization; Polymerization kinetics; Post-curing; Printing, Three-Dimensional; Spectroscopy, Fourier Transform Infrared; Spectrum analysis; Statistical analysis; Ultraviolet Rays
• ISSN: 2196-1042; 1723-7785; 2196-1042
• DOI: 10.1186/s40510-024-00540-4

Background The purpose of the study was to measure the degree of conversion (DC) of direct-printed aligners (DPA) that were post-cured under ambient and nitrogen atmosphere at specific time intervals and investigate the kinetics of polymerization reaction of this material. Methods A total of 48 aligners were produced in 4 printing series by a 3D printer with TC-85DAC resin (Graphy Inc). From each series of printing, 12 aligners were included. The aligners were divided into two groups according to their post-curing conditions. One group was post-cured under ambient air with the presence of oxygen and the other under a nitrogen atmosphere, both using the same UV post-curing unit recommended by the company. The aligners were post-cured at six different time intervals: 1, 2, 3, 5, 10, and 20 min. Each time interval included 8 aligners, with 2 aligners from each series. The DC of the cured aligners was measured by means of attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) through acquisition of the respective spectra for each UV-curing condition. Statistical analysis was performed to compare the results and differences within each atmosphere post-curing protocol, as well as between the different selected atmosphere conditions. Statistical significance level was set at p-value ≤ 0.05. Results Pairwise analysis between post-curing protocols showed statistically significant differences only at the first minute of polymerization. Post-curing with nitrogen did not yield statistically significant results across different time intervals. Post-curing in ambient air showed some significant differences on the 1st and 2nd minute of the post-curing process. Conclusions Almost complete double bond conversion was observed. Significant differences were observed only during the first minute of polymerization under the nitrogen atmosphere.