On the subject of tooth damage, many of my teeth have gum-line grooves. A friend who is a retired dental technician insisted that gum-line grooves are a result of brushing horizontally and using an excessively hard toothbrush.

Looking closely at an object and noticing its features and details is a good way to increase our creative powers. Following up on our curiosity is a good way to build a solid foundation of knowledge. Studying natural objects in this way is an excellent entrance to the world of scientific facts.

After the X-ray seen in Figure 1 (see part 1), they put a little optical camera (pediatric size, for which I was grateful) in my mouth to obtain a 3-D digital model of the remaining tooth shape.

Last month, my right rear-lower molar broke. As shown in Figure 1, the fracture event resulted in a chipped condition. The red arrows show the boundary (edge) of the missing piece.

Maybe a half a dozen times in my life I have learned something that, in a minute, totally transformed and rearranged everything I thought I knew about a subject that I thought I had previously understood.

On a trip with so many highlights, it’s hard to pick only a few. But if pressured, I would give first prize to the A.E. Seaman Mineral Museum, which is part of Michigan Tech. I literally had to pry my feet from the floor and force myself to move on to the next exhibit. After three hours, I had only seen half of the items. We went back on the same $8 ticket the next day it was open. My colleague was very patient and enjoyed the benches, while I barely noticed my aching feet.

Last month, my right rear-lower molar broke. As shown in Figure 1, the fracture event resulted in a chipped condition.

One of my colleagues graduated from Michigan Technological University (MTU) in 1986 and had not been back since. He’s a mechanical engineer but has worked his entire career in the foundry industry. As an MTU alum, he gets invited to the school’s events, and that included a geology tour.

Let’s wrap up our discussion on fatigue cracks.

How can we tell if it is a fatigue crack if the most well-known feature of a fatigue crack is not present? Figure 2 shows a tie rod from an injection-molding press. While there are a few faint and indistinct beach marks, we have another indicator: ratchet marks.