Abstract
Objective:
To investigate the effect of different durations of post-curing ultraviolet (UV) light exposure on the compressive strength, amount of displacement and water absorbed by direct-printed aligners.
Design:
An in-vitro randomised control trial.
Setting:
Orthodontics laboratory in Maulana Azad Institute of Dental Sciences, New Delhi, India.
Methods:
Dental LT V2 resin was used to print 30 aligners, which were divided into three groups and subjected to different post-print UV light exposures. Each group was subjected to compression loading of 1000 N to evaluate their load vs. displacement behaviour. The amount of water absorbed by aligners in each group was also evaluated. Data were analysed using one-way analysis of variance (ANOVA) and repeated measures ANOVA.
Results:
The ‘60-min cure’ group bore the maximum mean compressive load (1016.03 ± 37.27 N) and had the least mean displacement (2.87 ± 0.52 mm) and water absorption (0.18 g).The ‘40-min cure’ group did not show significant results for any of the tests carried out.
Conclusion:
Aligners subjected to 60 min of post-print UV light exposure were the most rigid and had highest compressive strength. Increasing the duration of post-UV light curing reduced the amount of water absorbed by the aligners. Since the ‘60-min cure’ group was excessively rigid, a post-curing duration of 40 min is recommended to provide sufficient flexibility for comfortable daily use and wear.
Plain language summary
This study reports about the effect of different ultraviolet (UV) light cure durations for postprocessing of direct printed aligners on the mechanical properties of aligners.
The increased use of aligners in orthodontic practice has led to 3D printing being used in orthodontics. At first, it was used to print models upon which aligners were made. New materials have been introduced to allow direct printing of aligners. This makes the workflow easier by decreasing time, cost and waste. Any direct 3-D printed object needs to be exposed to UV light after it has been made (cured). This hardens the final product. This in vitro study was carried out to assess the ideal length of time for the UV exposure after curing. We also wanted to find our whether different UV exposure times affected the physical properties of the aligner which may affect how the aligner moved the teeth.
The researchers did a study in the lab using an ideal model of the upper teeth. They printed 30 aligners. After they had been cured, they were exposed to different lengths of UV light. After this, they were texted in the lab to see how much force they would withstand, how much their shape changed and how much water they soaked-up.
The researchers found that 40 and 60 minutes of post cure UV light exposure gave similar results. However, after 60 minutes of UV light exposure, the aligners became too stiff, which might make it difficult for patients to wear or remove them.
This study suggests that 40 minutes exposure to UV light, after the first cure, may be the best for orthodontic aligners.
Keywords
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