The objective of this study was to develop biologically compatible resins with optimum safety profiles and physical properties that can be used for long periods inside the mouth, and to attempt to use these resins in a 3D printing process to produce direct aligners for use in mouthpiece orthodontics. Low toxicity water-soluble monomers (1M) were used to develop 3D printer-compatible biocompatible resins (polymers) that have no skin reactivity, carcinogenicity, or reproductive toxicity. Cytotoxicity testing (LDH test), proliferation testing (WST1 test), and mechanical testing were also performed. We attempted to use these resins to produce direct aligners. We successfully produced acrylic-epoxy hybrid light-curing resins that have optimal safety profiles composed of water-soluble monomers alone. The results of cytotoxicity testing and proliferation testing showed that all the water-soluble monomers used for 3D printing (3D-1M) exhibited low cytotoxicity, but the cell survival rates suggested that the composition ratio of the raw materials may be an issue. The results of mechanical testing demonstrated that the 3D-1M met the mechanical strength requirements for base polymers used in orthodontics. We successfully produced direct aligners using these biocompatible resins. However, their middle sections were fragile, suggesting that their physical properties must be improved if they are to be used in aligners. We intend to improve the mechanical properties of these monomers, and perform safety testing for approval as Class-II controlled medical devices.
These findings suggested that artificial changes in the mastication do influence the growth of condylar head, condylar bone trabecular structure, and mineralization.
Little is known about the mechanisms of mandibular condylar growth. In this study, gene expression in the mandibular condylar cartilage of young post-natal mice was monitored by means of a cDNA microarray, real-time PCR, and laser microdissection before and after the initiation of mastication (newborn, 7 days, 21 days, initiation of mastication, and 35 days). Insulin-like growth factor-1 (IGF-I), transforming-growth-factor-beta-2 (TGFbeta2), and aggrecan mRNAs were clearly expressed at 21 days, while the expression of osteopontin mRNAs was most clear at 35 days. Parathyroid-hormone-related protein (PTHrP), Indian-hedgehog (Ihh), and insulin-like growth factor-2 (IGF-2) mRNAs were clearly expressed during lactation (newborn and 7 days). Heat-shock-protein 84 (HSP-84) and heat-shock-protein 86 (HSP-86) were clearly expressed at 35 days. These results revealed that gene expression changed during mandibular condylar cartilage growth, and that, interestingly, these changes coincided with the initiation of mastication.
Polymeric dental aligners manufactured by thermoforming are recently used in clinical treatment of misaligned teeth. In this study, a polyester sheet with 0.75 mm thickness was used and the deformability of thermoformed aligner is discussed experimentally with the help of digital image correlation method. The experimental apparatus to apply prescribed displacement to aligners mounted on a teeth model was developed focusing on the situation of treatment for misaligned left canine. The deformation mode was discussed through measured displacement field and maximum principal strain distribution. It was found that mechanical behavior of aligner was influenced more significantly by the shape of teeth, movement vector of left canine and crooked shape of aligner especially at inter-teeth borders than the thickness distribution of thermoformed aligner. The role of deformable edge part of the aligner was also revealed.
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