Biodegradable artificial teeth based on 3D Printing

Source: Materials Science and Engineering

The basic function of human teeth is to mechanically cut and grind up food to break it down and facilitate further swallowing and digestion.
The second function of the teeth is to achieve aesthetic maxillofacial appearance.
For patients with edentulous jaws, tooth loss not only affects chewing and reduces the quality of life, but also leads to the collapse of the maxillofacial area, making people look particularly old and affecting appearance.

Tooth structure
The teeth are composed of the crown (the part above the gum line) and some of the roots (the part just below the gum line).
The outer layer of the crown is enamel and the outer layer of the root is bone.
Both sections have a continuous inner dentin surrounding the pulp cavity (see Figure 1).
Bones and most teeth are made of the same basic materials.
Just the hard, thin outer layer of tooth enamel is completely different.
The materials that make up bones are also referred to collectively as “bones,” and the teeth (other than enamel) are referred to collectively as “dentin.”

Tooth root material selection
Once the treatment is established and the tooth structure is clear, the next step is to consider the choice of implant material.
Since the teeth are made up of two parts, they need to be considered separately.
Materials used as roots should meet certain requirements.
They should be designed to diffuse nutrients into transplanted cells and guide their tissue, attachment and migration.

Cellular components, extracellular matrix and scaffold, and growth and differentiation factors are necessary for bone tissue engineering.
Scaffolds are needed for cell attachment, proliferation and differentiation.
In addition, growth and differentiation factors must induce cell proliferation.
In the past, metals, ceramics and polymers have not been widely used due to low cell viability and slow vascularization.
Appropriate mechanical properties and degradation behaviors are also essential to achieve the cellular tissue, adhesion and migration of these materials.
Therefore, it is necessary to choose biodegradable materials as the base part and non-biodegradable materials as the top part in the project.

Characteristics and attributes of PHA:

Polyhydroxyalkanate is a biodegradable polymer which can be used in tissue engineering.
The polyhydroxyalkyl Group has a variety of materials, including hard brittle materials and soft elastomer materials.
In recent years, people have been exploring and studying the properties of polyhydroxyalcanates to develop their applications in biomedical fields, such as suture, cardiovascular patch, wound dressing, guided tissue repair/regeneration device, tissue engineering scaffold, etc.

Characteristics and properties of PHB
P(3HB) is the simplest and most common PHA group, and is also the first PHA polymer to be applied in the biomedical field.
Due to good economic applicability, mechanical, chemical and degradation properties.
With the development of polyhydroxyalkanic acid, researchers began to study the possibility of designing composite materials that are combined with inorganic materials to further improve mechanical properties, degradation rates, and give biological activity.
In order to meet the needs of teeth (figure 3, transparent part), PHB is an ideal material for repairing and filling alveolar bone defects.
PHB is the basis of teeth mainly because PHB is a biodegradable and biocompatible material.

Dental crown material selection
ABS is a kind of engineering plastic, butadiene is distributed uniformly on acrylonitrile-styrene matrix.
ABS polymers have high toughness (even at low temperatures), sufficient rigidity, good thermal stability, resistance to chemical erosion and environmental stress cracking.
In addition, PHB also has low cost, durability, thermal expansion coefficient low significant performance.
Easy forming, ABS parts size stability, good surface quality.
In conclusion, ABS is biocompatible and non-degradable, and can be used as a part of dental implant.
In addition to alveolar bone, some implant materials should be non-biodegradable. ABS is preferred due to its strength, flexibility, manufactability and high temperature resistance. However, harmful smoke will be generated in 3D printing and disappear after drying.

Application of 3D printing tissue engineering
3D printing is an advanced technology defined as a rapid method of adding material layer by layer to make it a target.
In fact, it has become a rapid manufacturing process that can be applied to different fields such as manufacturing, building maintenance, automobile manufacturing, medical applications and so on.
In the field of medical and health, three-dimensional applications can be summarized into four different levels.

First of all, 3D printed models can show the position of the body that needs surgery more three-dimensional on a two-dimensional basis, thus reducing the risk of surgery.
Secondly, 3D printing is regarded as a tool for surgeons.
For example, 3D printing can assist in the construction of personalized tooth models (figure 4 is the 3D printed tooth root model), and doctors can make plans more professionally based on individual models.
The third is a 3D-printed implant, which is actually used to create a replacement scaffold for dead bone tissue.
Finally, in terms of tissue regeneration, 3D printing could also create substitutes that are closer to human organs, reducing rejection.

(Article: Zhang Zixuan)
Reference:
[1] r.s. Weiner, “Insights into whole bone and tooth function usingoptical metrology,” j. Mater. Sci., vol. 42, no. 21, pp. 8919 — 8933,2007.
[2] R. Shado-Zadeh, A. Farsaii, A. Goodarzi, and E. L. Davis, “Loss of Tooth Structusociated with Preparation for Two monolithic CAD-CAM Complete Coveragerestorations,” J. Prosthet. Dent.
Vol. 120, No. 3, PP. 403 — 408, 2018.

Zixuan Zhang, Postgraduate student of Roy Ipsita Laboratory, University of Sheffield, UK.