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Nov 14, 2016 | By Alec

Tooth-like structures can be found in vertebrates throughout the history of the world, and the ancestors of sharks and related fish species might even be the first to develop them from rough shapes on the jaw that could grind down food. Exactly because they are so common in so many species, teeth and jaws are a very important target for evolutionary biologists – as they can aid researchers in tracking the evolutionary process of various animals.

The only problem is that fossil evidence is almost never suitable for testing biological functions, and testing the effectiveness of various teeth structures (and effectiveness is always a driver of evolution) can therefore be quite difficult. But 3D printing is coming to the rescue. Researchers from the University of Massachusetts Amherst have developed a set of 3D printed teeth that were used to test the damaging ability jaws of the earliest mammals. Through this approach, they found evidence for the theory that the ability for teeth to damage prey is a much more significant reason for evolutionary success than bite force or the animal's energy expenditure.

In a nutshell, this 3D printing approach thus created a new analysis for evolutionary biomechanics studies. The 3D printed teeth themselves were based on the teeth of 200-million-year-old insect eating mammals, and could change the way natural selection is studied through dental morphology. Tooth shape is, after all, linked to diet and feeding and a lot of knowledge of early mammal evolution is already derived from dental studies. The Amherst findings are published in the latest edition of the British Royal Society journal.

This breakthrough was realized by evolutionary biology doctoral student Andrew John Conith and his supervisor Elizabeth Dumont, with help from polymer scientists Alfred Crosby and graduate student Michael Imburgia. Dumont and Crosby are members of the Center for Evolutionary Materials at UMass Amherst, a center at which researchers can bring together biological thinking and engineering.

To actually build the 3D printable teeth models, the Amherst team relied on tooth data from two of the earliest mammal species: the primitive Morganucodon and more advanced Kuehneotherium. Both of these shrew-like creatures are considered exemplar species in early mammal evolution, and existed alongside the dinosaurs during the Triassic Period 200 million years ago.

The issue they were facing has been a key question in evolutionary biology. “The big question here is why teeth look the way they do. Most of the work on early mammalian tooth evolution has been descriptions of what they look like and how they could potentially work as tools for biting and crushing insects,” Conith explained. “We took it one step further, to make these tools and test them. We merged two modern technologies and used 3D prints of teeth to ‘bite’ into polymer gels with a exoskeleton-like crust that accurately mimicked insects.”

As these experiments showed, actually breaking food up is crucial. “we think the factor that natural selection worked on was the ability to break apart food, and that selection for maximum damage is the primary determinant of tooth shape,” Conith says.

While it sounds logical most research so far focused on force and energy use during hunting, with the assumption being that evolution favored efficient users of those two. “But I think people will need to reconsider these typical parameters and now think more critically about damage. It's an important consideration. We haven't rewritten the book, but we have added a new chapter,” he added.

To actually reach this conclusion, the researchers constructed gel-filled rectangles coated with a polymer shell that mimic an insect’s exoskeleton. Through pre-determined factors, they constructed two of these fake insects: one with a harder and one with a softer shell, running ten experiments on both using the Morganucodon and Kuehneotherium molar shapes. The 3D printed teeth were attached to a force-testing machine, and the researchers measured the force and energy used (and damage done) on the ‘insects’. Damage was measured by analyzing cracks in the exoskeleton.

As it turned out, the more primitive Morganucodon model used less force and energy to fracture hard shells – while the Kuehneotherium teeth was more efficient on the softer shells. “More importantly, Kuehneotherium also inflicted more damage to both the hard and the soft gels. These results suggest that changes in tooth shape in some early mammals was driven primarily by selection for maximizing damage, and secondarily for maximizing biomechanical parameters such as force or energy,” Conith explained. “It wasn't until we actually saw the destruction Kuehneotherium could inflict on our model insects that we thought it would be interesting to measure. In science your general ideas may be correct, but the details can be so much more complex.” Another fantastic example of how 3D printing can add a whole new dimension to laboratory studies.

 

 

Posted in 3D Printing Application

 

 

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