Composite 3D printing of biomimetic human teeth

Abstract

Human teeth are mechanically robust through a complex structural composite organisation of materials and morphology. Efforts to replicate mechanical function in artificial teeth (typodont teeth), such as in dental training applications, attempt to replicate the structure and morphology of real teeth but lack tactile similarities during mechanical cutting of the teeth. In this study, biomimetic typodont teeth, with morphology derived from X-ray microtomography scans of extracted teeth, were 3D printed using an approach to develop novel composites. These composites with a range of glass, hydroxyapatite and porcelain reinforcements within a methacrylate-based photopolymer resin were compared to six commercial artificial typodont teeth. Mechanical performance of the extracted human teeth and 3D printed typodont teeth were evaluated using a haptic approach of measuring applied cutting forces. Results indicate 3D printed typodont teeth replicating enamel and dentine can be mechanically comparable to extracted human teeth despite the material compositions differing from the materials found in human teeth. A multiple parameter variable of material elastic modulus and hardness is shown to describe the haptic response when cutting through both human and biomimetic, highlighting a critical dependence between the ratio of material mechanical properties and not absolute material properties in determining tooth mechanical performance under the action of cutting forces.

Figure 1

Reconstructed XMT images of extracted, commercially available typodont teeth and 3D printed typodont teeth, highlighting the differences in material, distribution of particle fillers and structures. (a) Extracted mandibular molar. (b) Commercially available typodont teeth. (c) Reconstructed XMT images of the extracted mandibular molars. (d) Reconstructed XMT image of Acadental, Fabrica de Sorrisos, and Nissin (left to right). (e) Three material groups of 3D printed composites; apatites, dental glass and dental ceramics. (f) Reconstructed XMT images of the 3D printed composites; hydroxyapatite (HAp), carbonated hydroxyapatite (CHAp), bioactive glass (BAG), glass flake (GF), fluormica glass (FM), and dental ceramic (338 N, 347 N, 352 N).

Figure 2

The mean force required to cut extracted and typodont teeth, highlighting the forces required for both enamel and dentine materials. Error bars are presented as the standard deviation of the data. n = 8. Subscript denotes statistical differences between groups, a, b, c.

Figure 3

The mean force required to cut 3D printed teeth, highlighting the forces required for all materials. Error bars are presented as the standard deviation of the individual samples. n = 8. Subscript denotes statistical differences between groups, a, b, c.

Figure 4

Average force required to cut extracted and typodont teeth against $\frac{H^3}{E^2}$. Trendline and R² values refer to typodont teeth, excluding the extracted teeth values. Error bars are presented as the standard deviation of the data. n = 8.

Figure 5

Average force required to cut 3D printed typodont teeth against $\frac{H^3}{E^2}$. Trendline and R² values refer to typodont teeth, excluding the extracted teeth values. Error bars are presented as the standard deviation of the data. n = 8.

Figure 6

Schematic diagram and picture of the automatic force stage set-up. Directions were measured in three, X = Mesiodistal, Y = Buccolingual and Z = Occlusal.

Figure 7

An extracted mandibular molar was imaged at 30 µm resolution using XMT before and after cuts, showing the amount of material removed from each 1 mm deep cut. (a) Before cutting. (b) After cut 1. (c) After cut 2. (d) After cut 3. (e) After cut 4. The force data shows the difference in force required to cut between cuts, with the dotted line in the graphs showing the mean force required. All graphs are set to the same scale.