July 6, 2020 | David F. Coppedge

Tooth Complexity Bites Darwin

New microscopic techniques are making it harder to be a Darwinian dentist.

Dr Jobe Martin, a dentist, was turned from evolutionist to creationist when he was challenged to explain how biological wonders could have evolved. It was the details in biology that persuaded him some 20 years ago, and it is details once again that have power to change the minds of today’s evolutionists – if they will just pay attention. New methods of microscopy are giving biologists their first looks at tissues like tooth enamel at near-atomic resolution. The stage is set to weigh creation vs evolution!

Complexity of human tooth enamel revealed at atomic level in NIH-funded study (National Institutes of Health). The NIH has no particular inclination to support creationism, but they had to marvel at what they saw using a new technique called Atom Probe Tomography. This takes earlier methods of observation, like STEM (scanning transmission electron microscopy), to whole new levels of resolution. What they observed were “Unprecedented details of enamel structure,” which are helping the next generation of biologists understand how teeth are constructed, and might give dentists new approaches for fighting cavities. Scientists already knew that

Amazing FactsYour teeth are remarkably resilient, despite enduring the stress and strain of biting, chewing, and eating for a lifetime. Enamel — the hardest substance in the human body — is largely responsible for this endurance. Its high mineral content gives it strength. Enamel forms the outer covering of teeth and helps prevent tooth decay, or caries.

Atom probe tomography is bringing scientists closer to the detailed structure of enamel, like seeing individual houses as a pilot flies closer to the ground:

“Earlier studies revealed the bulk composition of enamel, which is like knowing the overall makeup of a city in terms of its population,” said senior author Derk Joester, Ph.D., a professor of materials science and engineering at Northwestern. “But it doesn’t tell you how things operate at the local scale in a city block or a single house. Atom probe tomography gave us that more detailed view.”

What the scientists are finding is the world’s “tiniest sandwich” structure, as a press release from Northwestern University puts it, consisting of hierarchical layers arranged in a complex crystalline order (see animation in PhysOrg‘s copy). The layers are just 6 billionths of a meter across! Additionally, they are finding that tiny defects in the matrix take advantage of stress to make teeth even stronger than if the the matrix was uniform. Who would have thought? It’s like the military proverb, “Whatever doesn’t kill you makes you stronger.”

“Stress may sound bad, but in material science it can be useful, and we think it may make enamel stronger overall,” said co-first author Karen DeRocher, a graduate student in Joester’s lab. “On the other hand, those stresses are predicted to make the core more soluble, which might lead to erosion of enamel.”

A figure caption shows how minerals add to the strength of the enamel matrix. They found that “magnesium is present in two distinct layers in the core, and fluorine and sodium are heavily concentrated in the areas between crystallites, known as the intergranular phase.”

Two views of the “world’s tiniest sandwich” (with scalebar). The left panel shows the magnesium (magenta) sandwich at the enamel crystallite’s core from data acquired by atom probe tomography. The right panel shows an atomic resolution scanning transmission electron microscopy image of an enamel crystallite looking down the long axis of the crystal. The dark areas are distortions in the crystal lattice due to the presence of impurities such as magnesium and sodium, identified by atom probe tomography (left panel). Credit: Northwestern University

The paper in Nature, like many others these days, gives a brief nod to evolution but then hurries along to design evidence:

Dental enamel is a principal component of teeth, and has evolved to bear large chewing forces, resist mechanical fatigue and withstand wear over decades. … Although the past decade has seen progress in our understanding of enamel formation (amelogenesis) and the functional properties of mature enamel, attempts to repair lesions in this material or to synthesize it in vitro have had limited success. This is partly due to the highly hierarchical structure of enamel and additional complexities arising from chemical gradients. Here we show, using atomic-scale quantitative imaging and correlative spectroscopies, that the nanoscale crystallites of hydroxylapatite …, which are the fundamental building blocks of enamel, comprise two nanometric layers enriched in magnesium flanking a core rich in sodium, fluoride and carbonate ions; this sandwich core is surrounded by a shell with lower concentration of substitutional defects. A mechanical model based on density functional theory calculations and X-ray diffraction data predicts that residual stresses arise because of the chemical gradients, in agreement with preferential dissolution of the crystallite core in acidic media. Furthermore, stresses may affect the mechanical resilience of enamel. The two additional layers of hierarchy suggest a possible new model for biological control over crystal growth during amelogenesis, and hint at implications for the preservation of biomarkers during tooth development.

In short, “The researchers found strong evidence that the core-shell architecture and resulting residual stresses impact the dissolution behavior of human enamel crystallites while also providing a plausible avenue for extrinsic toughening of enamel.”

Another proof of design perfection is seen by how long tooth enamel lasts from the the first eruption of permanent teeth in the child’s mouth:

Enamel forms over very specific times during the development of different teeth (in humans it starts as early as the second trimester in utero and continues until the late teens), is not appreciably remodelled, and is very well preserved in remains and fossils.

How could a blind process of evolution create a sandwich structure with minerals arranged in just the right positions to survive strong biting forces for decades, as well as take advantage of stress to become even stronger? Such design requires foresight: the ability to see a need and prepare for it. That was the subject of a book by Brazilian mass spectroscopist Marcos Eberlin, who found evidence of Foresight everywhere in the living world. Tooth enamel is another great example of foresight and of “over-design” for function.

Evolution can only see the immediate. It takes a mind to have the foresight to reach a design goal.

The figure caption in the NIH article contains this “wow” description of what the reader sees in an electron micrograph: “Enamel is made up of tightly bunched, oblong crystals that are about 1,000 times smaller in width than a human hair.

These are some tasty facts to chew on today. Take care of your jewels. Dentists can fill cavities and make repairs, but there’s nothing better than your natural, intact, intelligently-designed teeth. Ever wonder what dental “caries” means? It’s Latin for “rottenness.” Habakkuk knew what that feels like when he worried about the advance of the enemy: “I hear, and my body trembles; my lips quiver at the sound; rottenness enters into my bones; my legs tremble beneath me. Yet I will quietly wait for the day of trouble to come upon people who invade us” (Habakkuk 3:16). Don’t let bacteria win the invasion in your mouth.

 

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