Life Cycle Assessment, Optical 3D printing of dental models using acrylic resin based on soybean oils

Abstract

To facilitate the current transition toward a circular economy, the availability of renewable materials for additive manufacturing also becomes increasingly important. Additive manufacturing started in the 1980s with the development of the stereolithography apparatus (SLA) by Hull at 3D Systems (Hull 1984, Gross 2014). SLA printing is the layer-by-layer curing of liquid photopolymer resins using a focused laser beam. When a light projector is applied instead, exposing the entire layer to UV light simultaneously, the process is named digital light processing (DLP). Additive manufacturing via SLA or DLP process is applicable for high-resolution prototyping and fabrication of biomedical devices, for example, dental implants (l’Alzit 2022). The commercialized photopolymer resins used in SLA/DLP process are expensive and fossil fuel-based (Gross 2014, Voet 2021).

The increased interest in bio-based products lead to active research and development that resulted in the development of vegetable oil-based 3D printable resin formulations. It is important to ensure that the new bio-based resin formulations do not have unintended environmental or health impacts from emissions during the production of novel ingredients, during the product use phase and during end-of-life disposal. Therefore, it is necessary to apply a holistic assessment tool to measure the sustainability of the resin formulation and the product made of it on a life cycle basis.

Life Cycle Assessment (LCA) is a tool to assess the potential environmental impacts and resources used throughout a product’s life cycle, considering all potentially hazardous emissions and multiple categories of health and environmental impacts that result from those emissions (International Organization for Standartisation 2006). LCA can be used to investigate the most important contributors to environmental impacts by identifying the processes or materials in product life. Thus, it will provide data for designers to guide material selection, assist in supply chain management efforts, compare alternate designs or formulations, and provide product-level assessments that can be used for technology development and marketing (Montazeri 2018).

The advancement in digital technology has increased the options available for dental treatment. To produce solid casts from digital data, there are two types of 3D manufacturing processes. Subtractive manufacturing is one of the processes that can produce 3D models (Kafle 2021). The other fabrication method being used is additive manufacturing such as 3D printing. This method of fabrication includes many advantages such as a minimum material usage with diminished waste accumulation during the production and the ability to create multiple products at a time (Kafle 2021).

Dental model printing generally requires exceptional surface quality and very high accuracy as these models are used by dental technicians and dentists not only for a visual purpose but for the planning of dental treatment as well. Optical 3D printing here is also very beneficial as most of these prints are personalized, unique and applied to a specific customer only. Currently, the dental models are made from petroleum-based acrylic resins. Cradle-to-gate LCA results are compared across multiple impact categories to highlight potential environmental benefits or impacts of printing a batch of dental models from soybean oil-based resin formulation and provide recommendations for further improvements applicable to different life cycle phases of the product.