Here’s my face.

I went to the dentists’ office recently for a regular checkup and cleaning, and when my dentist learned that I taught human anatomy, he volunteered to send me a high-res copy of my panoramic x-ray. I couldn’t think of any plausible scenario wherein someone could use it for evil, and it has lots of cool stuff in it besides teeth, so decided to post it so I could yakk about it.

First things first: my teeth are in pretty good shape. I had to have my wisdom teeth (3rd molars) pulled back in 2009, and my upper 1st molar on the left has a root canal and a porcelain crown, which stands out bright white on the radiograph. Everyone else is present and looking good. If it’s been a while since you’ve covered this, the full human dentition consists of 2 incisors, 1 canine, 2 premolars, and 3 molars on each side, top and bottom, for a total of 32 teeth. Because I’ve had all four 3rd molars removed, I’m down to 28.

I could go on and on about the cool stuff in this image. Here are 12 things that stand out:

  1. The mandibular condyle, which is the articular end of the mandible that fits into the mandibular fossa, a shallow socket on the inferior surface of the temporal bone, to form the temporomandibular joint (TMJ). There’s an articular disk made of fibrocartilage inside the joint, which separates it into two fluid-filled spaces, one against the condyle and one against the fossa. This allows us to do all kinds of wacky stuff with our lower jaws besides simply opening and closing them, such as slide the jaw fore and aft or side to side. This is a strong contrast to most carnivores, which bite down hard and therefore need a jaw joint that works as a pure hinge. See this post for pictures and discussion of the jaw joint in a bear skull.
  2. The coronoid process of the mandible, which is a muscle attachment site. A few fibers of the masseter and buccinator muscles can encroach onto the coronoid process, but mostly it is buried in the temporalis, one of the primary jaw-closing muscles. Put your fingers on the side of your head a little above and in front of your ear and bite down. That muscle you feel bulging outward is the temporalis. Back in the 1960s, Melvin Moss (1968) discovered that if he removed the temporalis muscles from newborn rats, the coronoid processes would fail to develop. Moss’s ambition was to discover the quanta of anatomy, which in his view were “functional matrices” – finite sets of soft tissues related by development and function, which might contain “skeletal units” that grew because of the morphogenetic demands of the functional matrices. His tagline was, “Functional matrices evolve, skeletal units respond”. Not all of Moss’s ideas have aged well in light of what we now know about the genetic underpinnings of skeletal development, but he wasn’t completely wrong, either, and functional matrix theory is still an interesting and frequently productive way to think about the interrelationships of bones and soft tissues. For more horrifying/enlightening Moss experiments on baby rats, see this post.
  3. The mandibular angle, which is another muscle attachment. The medial pterygoid muscle attaches to the medial surface, and the masseter attaches laterally. You can feel this, too, by putting your fingers over your mandibular angle and biting down – that’s the masseter you feel bulging outward. Note that the angle flares downward and outward on either side of my jaw. This flaring of the angle tends to be more pronounced in males than in females, and it is one of many features that forensic anthropologists (like the one I belong to) take into account when attempting to determine biological sex from human skeletal remains. Like most sexually dimorphic features of the skeleton, this is a tendency along a spectrum of variation rather than a binary yes/no thing. There are women with flared jaw angles (Courtney Thorne-Smith, probably) and men with slender mandibles, so you wouldn’t want to sex a skeleton by that feature alone.
  4. The mandibular canal, a tubular channel through the mandible that houses the inferior alveolar artery, vein, and nerve. This neurovascular bundle provides innervation and blood supply to the tooth-bearing part of the mandible and to the teeth themselves, and emerges through the mental foramen to provide sensory innervation and blood supply to the chin.
  5. The upper surface of the hard palate, formed by the palatine process of the maxilla anteriorly and by the palatine bones posteriorly. The palate is the roof of the mouth and the floor of the nasal airways.
  6. The median septum of the nasal cavity, formed by cartilage anteriorly, the perpendicular plate of the ethmoid bone superiorly, and the vomer posteriorly and inferiorly.
  7. The blue lines are the inferior margins of my maxillary sinuses – air-filled spaces created when pneumatic diverticula of the nasal cavity hollow out the maxillae. You have these, too, as well as air spaces in your frontal, ethmoid, sphenoid, and temporal bones. It looks like many of the roots of my upper molars stick up into my maxillary sinuses. This is not an illusion, as shown below.
  8. When I had the root canal on my left upper 2nd molar, the endodontist filled the pulp cavities of the tooth roots with gutta-percha, a rigid natural latex made from the sap of the tree Palaquium gutta. Gutta-percha is bioinert, so it makes a good filling material (it was also used to insulate transoceanic telegraph cables), and it’s radiopaque, which allows endodontists to confirm that the cavities have been filled completely. The other teeth show the typical structure of a dense enamel crown, less dense dentine forming the bulk of the tooth, and radiolucent pulp cavities containing blood vessels and nerves.
  9. This is the rubber bit I gripped with my incisors to keep my teeth apart and my head motionless while the CT machine rotated around me to make the scan. Not that cool in a science sense, but I figured it deserved a label.
  10. Note that the roots of the canines go farther into the jaws than those of the other teeth. This is true for all four canines, it’s just easiest to see with this one. This is a pretty standard mammalian thing, for taxa that still have canines – they tend to be big and mechanically important, so they have deep roots. Even though our canines are absolutely and proportionally much smaller than those in the other great apes, we can still see traces of their earlier importance, like these deep roots.
  11. In places you can see the trabecular internal structure of my mandible clearly. As someone who geeks out pretty much anytime I get a look inside a bone, this tickled me.
  12. The remains of an alveolus or tooth socket. I had my 3rd molars out almost a decade ago, and by now the sockets will have mostly filled in with new trabecular bone. But you can still see the ghostly outline of at least this one – a sort of morphogenetic trace fossil buried inside my mandible. I assume that in another decade or two this will have disappeared through regular bone remodeling.

Here’s a closeup of my left upper 2nd premolar and first two (and only remaining) molars. The gutta-percha filling the pulp cavities of the three roots of the 1st molar is obvious. The disparity in root length is mostly illusory – this was an oblique shot and the two ‘short’ roots are foreshortened.

Here’s the same image with the roots of the 2nd molar traced in pink, and the inferior margin of the maxillary sinus traced in blue. It’s not that uncommon for upper molar roots to stick up into the maxillary sinuses. That was true of my 3rd molars as well, and when I had them taken out, the endodontist had to put stitches into my gums to close the holes. Otherwise I would have had open connections between my oral cavity and maxillary sinuses, which would have sucked and been dangerous. Nasal mucus in the maxillary sinuses could have drained into my mouth, and food I was chewing could have been forced up into the sinuses, where it would have decomposed and caused a truly vile sinus infection.

In a developmental sense, it’s not that the roots of the teeth grow upward into the sinuses, it’s that the sinuses grow downward, eroding the bone around the roots of the teeth. This happens well after the teeth are done forming – the sinuses continue to expand as long as the skull is growing, and they retain the potential to remodel the surrounding bone for as long as we live. Even in cases like mine where the roots of the molars stick up into the sinuses, the tooth roots are still covered by soft tissue, including branches of the superior alveolar artery, vein, and nerve that enter the pulp cavities of the tooth roots through foramina at their tips.

If you ask your dentist for copies of your own dental x-rays, you’ll probably get them. If you do, have fun exploring the weird territory inside your head.

Reference

  • Moss, M. L. (1968). A theoretical analysis of the functional matrix. Acta Biotheoretica, 18(1), 195-202.
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Upcoming book signings

April 19, 2017

Come gawk at this weirdo in public!

I’ll be signing copies of The Sauropod Dinosaurs: Life in the Age of Giants at regional events the next two weekends.

This this coming Saturday, April 22, I’ll be at the Inland Empire Science Festival, which will run from 10 AM to 4 PM at the Western Science Center in Hemet, California. There will be a ton of other special exhibits and activities, too. I don’t know all of them off the top of my head, but I know that Brian Engh will have the table next to mine, so come by and get two doses of awesome paleo art.

The following Friday, April 28, I’ll be at Beer N’ Bones 2017, which runs from 7-11 PM at the Arizona Museum of Natural History in Mesa, Arizona. In addition to signing books, I’ll also be in the “Speed Dating a Scientist” thing, where small groups of people get five minutes each at a table with a researcher, to ask whatever they want. Not just paleontologists, but scientists of all stripes. That said, I know of a couple of other local paleontologists who will also be there as guests – Andy Farke and Thierra Nalley. I was at Beer N’ Bones last year and it was a blast. As you might suspect from the name, it is 21-and-over only.

I’ll have books for sale – at a healthy discount – at both events. Hopefully I’ll see you out there.

This is very belated, but back in the summer of 2014 I was approached to write a bunch of sections — all of them to do with dinosaurs, naturally — in the book Evolution: The Whole Story. I did seven group overviews (Dinosauria overview, prosauropods, sauropods, stegosaurs, ankylosaurs, marginocephalians, and hadrosaurs), having managed to hand the theropod work over to Darren.

My author copy arrived in February 2016 (which, yes, is over a year ago. Your point?) It’s really nice:

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And at 576 heavy, glossy pages, it’s a hefty tome.

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My contribution was fairly minimal, really: I provided about 35 pages. Darren wrote a lot more of it. Still, I’m pleased to have been involved. It’s nicely produced.

Here a sample spread — the first two of a four-page overview of sauropods, showing some nice illustrations and a typical timeline across the bottom of the page.

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And here’s one of the ten “highlights” sections I did, mostly on individual dinosaurs. This is the best one, of course, based on sheer taxon awesomeness, since it deals with Giraffatitan:

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Unfortunately, not all of the artwork is of this quality. For example, the life restoration that graces my spread on Argentinosaurus makes me want to stab my own eyes out:

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Still, putting it all together, this is an excellent book, providing a really helpful overview of the whole tree of life, each section written by experts. It’s selling for a frankly ludicrous £16.55 in the UK — it’s easily worth two or three times that; and $30.24 in the US is also excellent value.

Highly recommended, if I do say it myself.

In the summer of 2015, Brian Engh and I stopped at the Copper Ridge dinosaur trackway on our way back from the field. The Copper Ridge site is 23 miles north of Moab, off US Highway 191. You can find a map, directions, and some basic information about the site in this brochure. The BLM has done a great job of making this and other Moab-area dinosaur trackways accessible to the public, with well-tended trails and nice interpretive signage. Brian has gotten to do the art for interp signs at several sites now, including Copper Ridge, and he put together this video to explain a bit about the site, what we know about the trackmaker, and the lines of evidence he used in making his life restoration. I’m in there, too, yammering a bit about which sauropod might have been responsible. We weren’t sure what, if anything, we would end up doing with the footage at the time, so I’m basically thinking out loud. But that’s mostly what I do here anyway, so I reckon you’ll live.

Stay tuned (to Brian’s paleoart channel) for Part 2, which will be about the Copper Ridge theropod trackway. And the next time you’re in the Moab area, go see some dinosaur tracks. This is our heritage, and it’s cool.

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Not much to say this time – the pictures tell the story for now.

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It was a pretty transcendental experience, as I imagine it must be for anyone who loves dinosaurs, or has a pulse.

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A huge thank-you to Dan Chure, the Park Paleontologist for the Monument, who conveyed us safely up and down the Wall, taught us about the prehistory of the site and the human history of its excavation and conservation, held scale bars, moved backpacks, took photos, and generally seemed to be having just as much fun as we were. This has been a common theme on the trip – every single person we’ve interacted with at a museum or fossil site has been unfailingly welcoming and generous with their time and knowledge. Whatever challenges vert paleo faces, a lack of wonderful people is not one of them.

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I was up there, too, for the second time in my life – that will be a post for another day. For now, just bask in the glory of Mike basking in the glory of a literally mind-numbing array of amazing fossils.

Wedel 2016 OMNH lecture flyer

Just a quick heads up for any SV-POW! readers within convenient striking distance of Norman, Oklahoma, this Wednesday, March 16. Like all of the lectures in the “Dinosaurs Past & Present” series at OMNH, this one is free to the public. I hope to see some of you there!

My last post (Unhappy thoughts on student projects at SVPCA 2015) was stupid and ill-judged. As a result of very helpful conversations with a senior palaeontologist (who was much more courteous about it that he or she needed to be), I have decided to retract that article rather than editing it further to clarify. I deeply wish I’d never posted it, and I offer my apologies to everyone I insulted.

First, and most importantly, to people presenting projects under the influence of nerves, which I misinterpreted as a lack of interest in their own projects. Nervousness particularly affects people giving their first talks — an effect I should have allowed for. It’s awful to think that what I wrote may have been discouraging to people taking first steps into palaeo.

Second, to supervisors who felt that the “roll four dice” section in the middle of the post was aimed at them. All I can say is that it wasn’t. I had no-one in mind when I wrote that: I was just so seduced by the comical imagery of generating a project by rolling dice that I wrote it down without thinking through how it would be interpreted.

Did I have good intentions? I honestly did. Did I have legitimate concerns about the ubiquitous application of techniques that are not always appropriate, and whose results are not always interpreted with a suitable degree of scepticism? I think so. But clearly I should have discussed those concerns privately with more involved people, rather than spilling my brains all over the blog. I welcome the increasing availability of techniques that allow us to bring numerical rigour to our palaeobiological speculations. (I could discuss in more detail when and how I think those techniques should be used, but that’s for another day. My purpose here is to apologise, not to justify myself.)

In short, I had a very bad day at the office on Friday, and I hate the idea that in my carelessness I could have hurt anyone other than myself. To those in that category, I can only ask your forgiveness; and promise to think more before blogging in future.