Photopolymerization Fundamentals and Additive Manufacturing of a Cast Molding Dental Material

Objectives: In recent years, the use of additive manufacturing (AM) and 3D printing has become essential to the dental field and necessary for the advent of digital dentistry. To successfully implement digital dental techniques for AM, materials must be designed and catered to the necessary application. In this work, we developed an improved material for use in 3D printing for molding dental implants, aligners, and other dental devices. The ability to 3D print and cast mold meltable and recyclable materials would greatly enhance the efficiency of the fabrication process, limit waste and facilitate more rapid turnaround. The hypothesis of this work was that the incorporation of appropriate nanoparticles into a 3D printable linear polymer could be used in AM to create custom molds that could be melted, removed, and recycled like wax after use simply by exposing the device to a magnetic (i.e., radiofrequency) field to activate induction heating.
Methods: The material created here was formed by the step growth polymerization of the thiol-ene “click” reaction of diallyl terephthalate (DAT) and hexanedithiol (HDT).
Results: By varying the stoichiometric ratio of thiol:ene from 1:1 to 1.2:1, the molecular weight was changed from 110 kDa to 6 kDa with a corresponding change in Tm and viscosity. With 0.5-2.0wt% CrO₂ nanoparticles, the polymer was accurately 3D printed on a Prusa SL1S 3D printer. The hypothesis was verified in that all these composites melted uniformly and rapidly upon application of a radiofrequency field with the maximum temperature in the AM printed mold reaching 117°C. Mechanical properties and both polymerization and crystallization kinetics were all determined.
Conclusions: Implementing these concepts into the molding process of dental implants or aligners holds great potential for enhancements in digital dentistry associated with cast molding via AM.