A Fused Deposition Modeling Method to 3D Print Gradient Coloured Zirconia

Abstract

<p><strong>Objectives</strong>: Additive manufacturing offers many advantages in dental manufacturing. Whilst 3D printing a single-coloured dental zirconia is possible, direct 3D printing of dental zirconia with gradient colour is still in vain. Fused deposition modeling (FDM) is one of the most popular additive manufacturing (AM) methods for polymeric materials. This feasibility study aimed to investigate a new method to design and develop a low-cost robocasting system that can manufacture gradient-coloured zirconia.<br><strong>Methods</strong>: A commercially available FDM printer with a customized hotend modification was used to print the gradient coloured zirconia. Disc-like samples (12mm diameter, 1.2mm thickness) were prepared by using two coloured zirconia filaments: 1.75mm white zirconia (Zetamix, France) and 1.75mm black zirconia (Zetamix, France). The white: black colour ratio used was from 100%:0% to 0%:100% during the 1.2mm thickness. The sintering process was in a high temperature furnace. The thermal cycle is from 20°C to 1475°C with 50°C/h ramp, in 29 hours and hold 2 hours, then from 1475°C to 20°C with 100°C/h ramp in 15 hours. A ball-on-three-balls (the diameter of the ball is 8mm) test was performed using a universal testing machine at a crosshead speed of 1mm/min, and a four point bending test was performed according to ISO 14577. Then, the maximum load was recorded, and the samples’ fracture strength and Weibull modulus were evaluated. Then we took the SEM of the fracture surface. And we measured the dimension of pre-sintered and post-sintered samples and analyzed the colour of the samples.<br><strong>Results</strong>: Gradient coloured zirconia discs were successfully fabricated. The fracture strength was no significant difference (P>0.05) between white, black, and gradient coloured zirconia. The shrinkage rate of the sample is 21.5%, and there is no significant difference between the three groups. And the gradience of sample colour was successfully controlled.<br><strong>Conclusions</strong>: The gradient coloured zirconia can be additive manufactured by FDM, and this strategy will not affect the strength and the shrinkage rate of zirconia, but there is still room for improvement in this technique.<br></p>