Master of Engineering Science
Musculoskeletal Health Research
The use of additive manufacturing (AM) in dentistry has gained momentum in recent years. However, high initial costs and uncertainty surrounding the quality of AM products are considered barriers to their use. This research compared dental substructures fabricated by AM versus conventional casting and milling.
Cobalt-chromium alloy rectangular bars and three-unit bridge substructures were fabricated by AM, casting or milling. Bars manufactured by AM exhibited superior flexural strength, shear bond strength of porcelain coating, and Vickers hardness. Bridge substructures fabricated by AM showed similar flexural stiffness to cast, similar flexural loads at failure to milled and cast, and overall accuracy of fabrication within 12 micrometers. Cast substructures showed the greatest internal porosity, while samples fabricated by AM exhibited pores primarily within the abutment region.
Overall, bars and three-unit bridges manufactured by AM exhibited equal or better mechanical properties than those fabricated by conventional techniques.
Summary for Lay Audience
Additive manufacturing (AM) is a computerized process of depositing materials layer by layer to produce three dimensional objects. The use of AM in dentistry has gained momentum over the last 30 years, with computer-aided design and manufacturing (CAD/CAM) being used for production of dental restorations. Despite the potential benefits of AM, dental labs are hesitant to adopt its use due to high costs for initial production, as well as uncertainty about the quality of the AM products compared to those fabricated using conventional methods. The objective of this research was to compare dental restorations made by AM versus the conventional methods of casting and milling.
Metal (cobalt-chromium) alloy bar samples and three-unit bridge substructures were fabricated by AM and conventional casting and milling methods. Bar samples were designed to conform to testing standards, and geometrically uniform three-unit bridge substructures were custom designed for standardized testing. 3D X-ray images were obtained for a subset of the three-unit-bridge substructures before testing. Bar samples were mechanically tested to assess bending, hardness, and porcelain coating properties. Three-unit bridge substructures were mechanically tested to compare the bending properties of clinically relevant geometries. As well, X-ray images of fabricated three-unit bridges were used to generate 3D models for investigation of internal porosity and surface geometry related to the accuracy of fabrication.
Bar samples manufactured by AM exhibited superior bending strength, hardness, and porcelain coating bond strength compared to cast or milled samples. Three-unit bridges fabricated by AM and casting showed superior bending stiffness compared to milling, while no differences were found in bending loads at failure among milled, cast, and AM samples. Accuracy of fabrication for three-unit bridges were all within 12 micrometers from the ideal model, with no significant difference among the three groups.
Overall, alloy bar samples and three-unit bridges fabricated by AM showed equivalent or superior performance to those produced by milling or casting. Results from this thesis provide information to the dental manufacturing industry regarding the mechanical performance, internal structure, and accuracy of fabrication of dental restorations manufactured by AM compared to the conventional methods of milling and casting.
EL Najjar, Mai, "Metal Additive Manufacturing for Fixed Dental Prostheses" (2020). Electronic Thesis and Dissertation Repository. 7123.
Available for download on Saturday, June 26, 2021