Evaluation of mechanical changes to clear aligners caused by exposure to different liquids

Abstract

Introduction The purpose of this study was to compare the mechanical changes of clear aligners manufactured using either the direct method (Graphy Tc-85) or the indirect method (CA Pro or Invisalign) following an exposure to different liquids.Material and Method The clear aligners were produced using a single patient's digital maxillary model. CA Pro aligners were produced indirectly using the Ministar S device, while Graphy Tc-85 resin aligners were produced directly using a three-dimensional printer (Ackuretta, Taipei, Taiwan). Invisalign appliances were produced by Align Technology, Inc. The appliances were randomly divided into seven groups: a control group and six experimental groups. The control group appliances were not immersed in any liquid. The appliances in the experimental groups were immersed in six different liquids (orange juice, soy sauce, cola, red wine, tea, and coffee) for 24 hr at 37 degrees C. Following immersion, the upper right first molar section of each appliance was separated using an abrasive disc and embedded in a 2 mm thick acrylic layer. A cyclic loading test was conducted using a specialised mechanism (a combination of a dynamometer and a deformation depth measuring instrument) and each sample was subjected to varying cyclical forces until a deformation depth of 1 mm was reached. The force magnitude required to achieve the 1 mm material deformation at the 1st, 5th, 10th, and 50th cycles of loading was recorded for each sample.Results As a result of repeated loads, the indenting force values decreased in the three sample groups, regardless of the liquid in which the appliances had been stored. However, soy sauce and orange juice had a greater detrimental effect on the mechanical properties of the aligners compared to the other liquids. On comparing the force values required for the material to reach a 1 mm depth during the 1st and 50th loadings, the decreases were recorded as 0.4% for Graphy Tc-85, 26.3% for CA Pro, and 42.1% for Invisalign.Conclusions Of the tested aligners, Graphy Tc-85 was the most resistant to repetitive loads, while Invisalign was the least resistant. It is inherently difficult to predict how different liquids will affect aligners made of different materials.