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← First Teeth Grew on Outside of Body

First Teeth Grew on Outside of Body - Comments

Agrajag's Avatar Comment 1 by Agrajag

As a dentist, I always like to see articles like this. Embryology of our current dental structures is fascinating in its own right, but their evolutionary history makes them even more interesting.

Of course, my irony meter was pegged when I saw one of the ads alongside the article:

  • Holistic Dentist in Miami Bio-Friendly, Mercury & Metal-FreeInvisalign® & Ceramic Braces
  • Steve

    Fri, 18 Nov 2011 04:49:05 UTC | #891251

    alaskansee's Avatar Comment 2 by alaskansee

    Wouldn't that make flossing easy!

    Fri, 18 Nov 2011 06:40:41 UTC | #891270

    adamaba's Avatar Comment 3 by adamaba

    Certainly gives a new meaning to having your teeth out... gets coat and leaves quietly

    Fri, 18 Nov 2011 09:48:50 UTC | #891297

    justinesaracen's Avatar Comment 4 by justinesaracen

    Wouldn't that make flossing easy!<

    Yeah, but it would be hell for romance.

    Fri, 18 Nov 2011 12:28:57 UTC | #891328

    MilitantApatheist's Avatar Comment 5 by MilitantApatheist

    I love this article. It is something you can really sink your teeth into.

    Fri, 18 Nov 2011 12:36:04 UTC | #891331

    DavidMcC's Avatar Comment 6 by DavidMcC

    Actually, the title should read "The first ORAL teeth grew on the outside", because before the sharks, the agnathans had teeth of sorts, but they were on the pharynx (then at the front of the mouth), but our pharynx is at the back of the throat, so we would have to ram our food down our throats before we could chew it! :)

    Pubmed paper

    Abstract Vertebrate dentitions originated in the posterior pharynx of jawless fishes more than half a billion years ago.

    Fortunately, natural selection managed to juggle the genes so, that the same tooth genes owned by agnathans were expressed in a different place in sharks.

    Fri, 18 Nov 2011 12:52:57 UTC | #891337

    PCIRL2011's Avatar Comment 7 by PCIRL2011

    This is a class article. It goes to show that with an open human mind, you can learn new unexpected and amazing things everyday that may surprise you!

    Fri, 18 Nov 2011 14:21:38 UTC | #891352

    rod-the-farmer's Avatar Comment 8 by rod-the-farmer

    Cheeky devils....

    Fri, 18 Nov 2011 14:22:21 UTC | #891353

    KenChimp's Avatar Comment 9 by KenChimp

    Oooh no! The puns in this thread are quite "long in the tooth"

    evil grin

    Sorry. I had to.

    As to agnathans, I'm extremely glad for natural selection. I'd rather chew my food as it enters my gob, not as it enters my throat. :-P

    Fri, 18 Nov 2011 15:43:31 UTC | #891377

    Agrajag's Avatar Comment 10 by Agrajag

    @ Comment 6 by DavidMcC:
    Some modern fish have Pharyngeal Teeth.
    I found one of these pharyngeal bones on a beach years ago and showed it to one of my oral anatomy professors who explained it to me. :-)
    Steve

    Fri, 18 Nov 2011 16:13:44 UTC | #891383

    aquilacane's Avatar Comment 11 by aquilacane

    The fictional Cheshire cat's smile seemed to have a life of its own, outside of the cat's body, and now new research suggests the world's first teeth grew outside of the mouth before later moving into the oral cavity.

    Someone was tokin' while writing this

    Fri, 18 Nov 2011 18:10:23 UTC | #891406

    ganggan's Avatar Comment 12 by ganggan

    It has long been known (well, better use suggested) that teeth evolved from external sensory organs (modified scales). That’s why we have toothache. We don’t need to feel the pressure on teeth when we chow, but we still have nerves to teeth, which often give us trouble. Too bad, evolution is not perfect.

    I don’t think the statement that the teeth found in these specimens are the first teeth is accurate. The first teeth may be the ones in conodonts, which lived in the Cambrian period (500 million years ago).

    “Blais said jaws, which must have evolved earlier,…” This is not true. Teeth came earlier than jaws. Hagfish and lamprey have no jaws but teeth.

    Fri, 18 Nov 2011 19:23:00 UTC | #891417

    Southpaw's Avatar Comment 13 by Southpaw

    Hagfish and lamprey have no jaws but teeth.

    So what? Hagfish and Lamprey are modern animals.

    Sat, 19 Nov 2011 00:12:18 UTC | #891486

    steve oberski's Avatar Comment 14 by steve oberski

    Could this be the origin of the Vagina dentata folk tale ?

    Sat, 19 Nov 2011 00:13:13 UTC | #891487

    Agrajag's Avatar Comment 15 by Agrajag

    Comment 12 by ganggan

    It has long been known (well, better use suggested) that teeth evolved from external sensory organs (modified scales). That’s why we have toothache.

    That is one of the better non-sequiturs I have heard, and that's not why we have toothache. We have toothache mainly when the sensory nerves in the pulp (loose connective tissue inside the tooth) are stimulated by an irritant. Common irritants are the inflammatory mediators released when decay (caries) extends deep into the tooth and approaches the pulp. There are other causes of toothache, of course, but tooth decay is the most prevalent. There are also structures that are not derived from the outermost germ layer which also are capable of producing pain (think "internal organs").

    We don’t need to feel the pressure on teeth when we chow, but we still have nerves to teeth, which often give us trouble. Too bad, evolution is not perfect.

    We are usually not aware of pressure on our teeth when we chew. Each tooth root is surrounded by a thin ligament (the periodontal ligament), which contains a lot of sensory nerves. These nerves effectively "hard wire" our teeth to our brainstem. This is part of a very complex system which basically monitors the position of the jaws, cheeks and tongue during mastication. Have you ever wondered why you so rarely bite your lips, cheeks or tongue while chewing? Even if you are drinking a glass of wine and carrying on a conversation, and your tongue is flipping food around just millimeters away from your gnashing teeth, you rarely injure yourself. The masticatory system is fascinating, and of course it has evolved to keep us alive with the least amount of self-injury.

    When I was in dental school, I wondered why teeth evolved to contain sensory nerves in their pulps anyway. Dentistry is a relatively recent development (in the last few thousand years), and mammalian teeth have been around in their present form for much longer than that. What is now known is that the nerves, while transmitting sensory impulses to the brain, also release transmitter substances which affect the performance of the cells (odontoblasts) which produce one of the hard tissues (dentin) that form the substance of the tooth (the other is enamel, produced by ameloblasts). This allows the pulp to thicken and reinforce the dentin as caries approaches. This has an obvious survival advantage: delaying the onset of pulpal pain, and possible subsequent dental infections, past the age of reproduction. Of course, with our modern diet, decay progresses faster than the odontoblasts can keep up, and teeth can reach the stage of needing root canal treatment or extraction fairly soon after they erupt. At my dental school we regularly see children under the age of 10 with teeth in this condition.

    Remember, you don't have to floss all your teeth...
    ... just the ones you want to keep. ;-)
    Steve (see my avatar)

    Sat, 19 Nov 2011 04:22:32 UTC | #891506

    Greyman's Avatar Comment 16 by Greyman

    Comment 13 by Southpaw :

    Hagfish and lamprey have no jaws but teeth.

    So what? Hagfish and Lamprey are modern animals.

    Uhm, not so much.  The Agnathans (jawless vertebrates) appeared during the Cambrian period, and the first Gnathostomes (jawed vertebrates) arose from them during the Ordovician period—a few hundred million years earlier than the Devonian period.

    Sat, 19 Nov 2011 04:55:22 UTC | #891508

    S. Gudmundsson's Avatar Comment 17 by S. Gudmundsson

    I wonder how Conservapedia is going to spin this one. Perhaps it'll make the "Biblical Foreknowledge" section?

    Sat, 19 Nov 2011 10:03:36 UTC | #891523

    Metamag's Avatar Comment 18 by Metamag

    Can this site post this talk please?

    Sat, 19 Nov 2011 10:04:59 UTC | #891524

    Stafford Gordon's Avatar Comment 19 by Stafford Gordon

    Comment 1: Agrajag.

    I'm wearing Invisalign as I write; I'm on the eighteenth set of - FORTY EIGHT - so you'll understand just how English my gnashers are/were. I hope to end up with there being something distinctly American about me.

    Sat, 19 Nov 2011 10:41:25 UTC | #891529

    hellosnackbar's Avatar Comment 20 by hellosnackbar

    The term holistic is to the dentist in Miami is innapropriate since he is restrictive in his practice. It makes me cringe when I see some dentist who believes in the toxicity of amalgam or indulges in homeopathy. He might use ceramic brackets but he's forced to use metal wires as the activation force. The banality of marketing oneself.

    Sat, 19 Nov 2011 10:52:07 UTC | #891531

    DavidMcC's Avatar Comment 21 by DavidMcC

    Comment 10 by Agrajag Some modern fish havePharyngeal Teeth.

    I didn't know that! It's interesting, because it shows that goldfish, etc didn't lose their agnathan inheritance completely. Indeed, we didn't completely lose the genes involved either, only those involved in putting them in the pharynx, I guess. EDIT: On second thoughts, it might just be the control segment of a gene that has changed to alter their location. In other words, what turns them on has changed.

    Comment 15 by Agrajag

    We are usually not aware of pressure on our teeth when we chew.

    But we are if we have to bite hard enough! I can feel my teeth when they strike each other. Indeed, I would have thought that that was another reason (beyond the neurotransmitter function you mention) why we have sensory nerves in our teeth - to monitor our bite force. If we were completely numb there, we might bite too hard and either break our teeth, or at least make them point too far outwards over time (something my own dentist warned me about some time ago, because mine are leaning outwards a bit).

    Sat, 19 Nov 2011 11:27:06 UTC | #891534

    Agrajag's Avatar Comment 22 by Agrajag

    Comment 21 by DavidMcC

    I can feel my teeth when they strike each other. Indeed, I would have thought that that was another reason (beyond the neurotransmitter function you mention) why we have sensory nerves in our teeth - to monitor our bite force. If we were completely numb there, we might bite too hard and either break our teeth, or at least make them point too far outwards over time (something my own dentist warned me about some time ago, because mine are leaning outwards a bit).

    The sensory nerves in the periodontal ligament (PDL) are the ones you feel when you bite. The pulpal nerves are not involved unless there is a crack in the tooth, or a loose filling or decay allows pressure to reach the pulp.
    The neuromuscular control of chewing (mastication) is pretty complicated. Think about biting on a carrot... it takes a lot of pressure to break one ot those, and once it yields, you have your opposing teeth hurtling towards each other... and the intervening distance is not great. When the teeth biting the carrot are suddenly unloaded as the carrot splits, the jaw-closing muscles are (almost) instantly inhibited, saving the teeth from potentially damaging impact. A similar process occurs when a bit of your lip or cheek gets between your teeth. It's not a perfectly infallable system, but it works quite well. Have a look at the JAW JERK REFLEX.
    Teeth can be persuaded to move by continuous light pressure (Hi, Stafford!). This involves the PDL and a remodelling process in the bone of the tooth socket (alveolar bone) and does not normally involve pulpal nerves. There can be pain involved, though. Also, extended clenching or grinding of the teeth may cause PDL pain as well as damage to the teeth (wear, fracture) and the jaw joints (Temporo-Mandibular Joint). Muscle pain can also result, and can recruit neighboring muscles and... you have a mess!
    Steve

    Sat, 19 Nov 2011 14:58:18 UTC | #891566

    DavidMcC's Avatar Comment 23 by DavidMcC

    I can't argue with that, Steve! Thanks. :)

    Sat, 19 Nov 2011 15:06:27 UTC | #891571

    DavidMcC's Avatar Comment 24 by DavidMcC

    Going back to the pharyngeal teeth, these would have been on the outside as the lamprey's pharynx is right at the front of its body, and the pharyngeal teeth are used only to hook on to the prey. It's bone-like tongue is used to rasp away the skin and causen bleeding, so the predatory lamprey's tongue is used more like a jawed vertebrates's teeth, in a way.

    (Footnote,many people refer to predatory lampreys as "parasitic". This is dubious, because the prey usually ends up bleeding to death, unless it is a very large fish.

    Mon, 21 Nov 2011 10:24:12 UTC | #891932

    DavidMcC's Avatar Comment 25 by DavidMcC

    This may interest you, Steve: Soft food may lead to a mouth with too many teeth

    ... Or, rather, a smaller mouth with the same number of teeth. If that went on too long, we might have ended up with teeth on the outside again! :)

    "The work demonstrates it is possible for diet to affect facial shape."

    Another example of how it isn't genes alone that determine our exact morphology.

    Wed, 23 Nov 2011 08:58:50 UTC | #892526