Artificial enamel: tougher & more durable than natural enamel

Enamel, the hardest tissue in the human body, is tough enough to resist dents yet elastic enough not to crack during heavy masticatory forces.

Researchers have long been interested in generating artificial enamel because our bodies cannot regenerate it. The cells that create our enamel die as soon as the teeth emerge from the gums.

Creating a substitute for enamel has remained one of the biggest challenges—until now. Now, researchers have designed an artificial enamel that happens to be tougher and more durable than natural enamel.

The research team feels this artificial enamel may have uses beyond repairing teeth, ranging from creating body armor to strengthening or hardening surfaces for floors or cars.

Mimicking enamel structure is tricky because of its nested modes, similar to wool fibers spun into yarn and then knitted into a cable-knit sweater. To mimic enamel - calcium, phosphorus, and oxygen atoms must come together to form crystalline wires in a complex, repeating pattern, which later receives a magnesium-rich coating around those wires and undergoes further weaving.

Earlier attempts to create artificial enamels have struggled to achieve the multiple levels of its complex structural organization. Previous experiments tried using peptides to build proteins to create crystalline wires. However, they could not go beyond this. They fell short of arranging the wires to design the complex structures required to create enamel’s elasticity and hardness.

In the newer studies, instead of peptides and other biological tools, researchers have used extreme temperatures to coax the wires into an orderly formation. Like the previous studies, even the newer experiments have used hydroxyapatite wires— the same mineral that makes up natural enamel. However, there is a difference this time - the newer wires are encased in a malleable metal-based coating.

This malleable coating on the crystalline wires is the critical modification that has given resilience to this artificial enamel. The coating can absorb pressures and shocks, making the wires less likely to snap.

Another modification that the researchers have introduced is substituting magnesium-rich coating, seen in natural enamel, to zirconium oxide, known to be strong yet nontoxic.

What about the 3D structure? Even the newer wires do not weave into the complex 3D architecture of natural enamel. Nevertheless, the parallel structure of wires is closer to natural enamel than previous attempts.

When they compared the elasticity, toughness, and fracture resistance, the artificial enamel outperformed natural enamel in six different areas, including its elasticity and ability to absorb vibrations.

Clinical dentistry application is still far away. We need studies on how this artificial enamel bonds to natural enamel - a crucial requirement for tooth repair. Furthermore, one needs to heat the raw materials to 300˚C, then freeze them carefully before cutting them into shape with a diamond saw - nearly impossible to accomplish in most dentist offices.

However, exciting applications are possible outside the mouth - from daily protection of delicate electronic chips in laptops to large-scale applications like designing building materials that could resist earthquake damage.

Artificial enamel opens up opportunities for all sorts of applications beyond medicine.

Ref: Graycen Wheeler. New artificial enamel is harder and more durable than the real thing. DOI: 10.1126/science.ada0937

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