Introduction: Human teeth are made up of complex tissues and are mechanically very strong. In real life, people need to "replicate teeth", for example in dental training applications, where they try to replicate the structure and form of real teeth, but their mechanical properties are not consistent with those of real teeth. So how can the mechanical properties of real teeth be replicated? This has been the focus of research by researchers.
In May 2022, researchers from Queen Mary University of London created biomimetic teeth, whose morphology was derived from X-ray microtomography scans of extracted teeth, and they 3D printed them using a new composite material that has mechanical properties comparable to those of real teeth. The researchers have published their research in Scientific Reports under the title 'Composite 3D printing of biomimetic human teeth', and here's a look at what they've come up with, along with Antarctic Bear!
Development challenges and issues to be addressed
The development of biomimetic teeth requires an understanding of the complex interactions between materials in an established manufacturing process to provide appropriate mechanical properties comparable to those of human teeth. There is a wide range of dental materials, but poly (methyl methacrylate) (PMMA) resins remain the leading candidate for dentistry due to their high availability, low cost, biocompatibility and acceptable aesthetics. PMMA materials have relatively high properties, can be processed in a range of manufacturing processes, are biocompatible and are therefore often used in denture production.
However, PMMA can easily fail due to fatigue or over-chewing, making PMMA dentures difficult to restore. Research has shown that adding fillers to PMMA to produce composites can improve the impact strength of dentures, but preparation is difficult because the fillers increase the viscosity of PMMA, thereby reducing its ability to flow to the desired shape. The production of composites from relatively hard and soft materials is therefore advantageous in terms of mimicking the different material compositions of the hard enamel of human teeth and the hydroxyapatite within the softer dentin region. Despite the large amount of research into improving dentures, there is little research into creating bionic types of teeth with mechanical properties that provide realistic tactile responses, such as the 'feel' when cutting teeth, in dental education applications.
Research process
The aim of this study was to 3D print dentures from materials that mimic the morphology and mechanical response of natural teeth. The researchers used X-ray microtomography (XMT) to image natural teeth at high resolution in order to accurately map the geometry of the samples. XMT was chosen as the imaging technique because of its non-destructive nature and ability to easily segment data between structures, and the imaging data could be processed and converted into a format suitable for 3D printing. xMT allowed a full description of the morphology of the teeth and produced high-contrast images that highlighted structural differences between teeth. The high contrast scan clearly shows the difference between highly mineralised enamel and low mineralised dentin (shown as bright areas in the image). One commercial type tooth (Frasaco) has no bright areas, indicating that one material was used for both enamel and dentin, or that both materials have the same X-ray opacity. The rest of the type teeth were distinguished by the use of different materials for enamel and dentin, resulting in XMT images with different contrasts. Figure f shows the reconstructed XMT images of the 3D printed materials. All images show uniformity in geometry and size, with varying degrees of grey due to the additional filler particles. The reconstructed XMT images show the distribution of the filler particles (25 wt.%) in the 3D printed structure.
ΔXMT images
A force measurement system was further developed in this study to enable mechanical evaluation of the cut teeth as an indicator of the performance of the 3D printed bionic type teeth compared to other teeth. The composite used by the researchers incorporated a range of glass, hydroxyapatite and porcelain reinforcements in a methacrylate-based photopolymer resin, which was compared to six commercially available artificial teeth. The mechanical properties of extracted human teeth and 3D printed type teeth were assessed using a tactile method of measuring applied cutting forces.
△Experimental setup
ΔAverage force required to cut extracted and orthodontic teeth
The range of materials evaluated in this study and the different weight percentages of reinforcement used to create the 3D printed teeth are presented in the article. Based on the results it can be seen that in all samples the cutting force decreased as the weight percentage of the reinforcements increased. Of the 40 different compositions, three closely matched (±0.02N) the force required to cut the extracted enamel (0.31N), specifically 25% HAp (0.31N ±0.06), 20% CHAp (0.32N ±0.06) and 25% CHAp (0.31N ±0.03).
The results show that the 3D printed teeth can be mechanically equivalent to human teeth, despite the fact that the composition of the materials used for printing is different from those found in human teeth. Multi-parametric variables of the material's modulus of elasticity and hardness were shown to describe the haptic response during human and bionic teeth, demonstrating that the ratio of the material's mechanical properties is a key factor in determining aspects of the mechanical properties of teeth under cutting forces.
