PINNIPED DENTISTRY
Tavishi
Happy October! I'm kind of a white girl about fall, and so October is a national holiday for me...
Anyways! Also, today is my FDOC, so that's fun. I am officially starting my second year of college. That's kind of insane. I started this blog when I was like fifteen.
I like teeth as a concept. In practice, I am immensely grossed out by human saliva and mouths. I don't mind animal saliva and mouths, but I have a visceral reaction to other people's saliva, or my own (sometimes the dentist is a nightmare).
Anyways, dentistry is pretty cool.
Teeth can be classified in two main ways: homodont/heterodont and hypsodont/brachydont.
Animals with homodonty have only one shape of tooth, whereas animals with heterodonty have variation in the structure of their teeth to adapt to their diet. For example, humans and pinnipeds are heterodonts, as they have different types of teeth, including incisors, canines, and premolars. Most dolphins, on the other hand, have conical teeth all shaped the same.
Animals can also be hypsodonts or brachydonts. Whereas hypsodonts have their teeth erupt throughout life, brachydonts have their teeth reach a fixed size. Hypsodonts are typically grazing herbivores like horses, whereas brachydonts tend to be more omnivorous or carnivorous, like pinnipeds. Structurally, a tooth has two parts: the crown and the root. The crown is the visible part that is above the gumline, whereas the root is, well, below the gumline (kinda like a plant root).
The crown is encased in a protective layer of enamel. The bulk of a tooth, just below the enamel layer, is composed of dentin, which is continously produced throughout life by odontoblasts. Enamel, on the other hand, is produced only before a tooth erupts. The enamel you have on a tooth is what you're stuck with for the rest of your life.
Finally, pulp is the innermost layer of the tooth. The pulp is the squishy part that makes a tooth alive- within the pulp, you can find nerves, blood vessels, and the odontoblasts that synthesize dentin.
Whereas the crown is protected by enamel, the root of the tooth is encased in cementum, which is produced by cementoblasts. These cells ultimately will end up entrapped in the cementum, and are then called cementocytes.
Fun fact: teeth are very good at getting dirty. This is why it's important to brush your teeth! Something I learned at the Aquarium of Niagara is that some pinnipeds know how to brush their teeth, like Isabel, who gets her teeth brushed every day.
Pinnipeds do not, notably, have the same teeth as people. They are very similar in structure and function, but have a few key differences and adaptations.
For one, some pinnipeds have differently specialized teeth. The walrus, most notably, has tusks! Walrus tusks are actually just longer canine teeth that continue to grow throughout life; in fact, walruses are typically born without teeth. They have gummy mouths like human babies. However, when their teeth grow in, those teeth are their adult teeth. Pinnipeds do have baby teeth; they just lose them during utero.
There's a new walrus calf at the Alaska SeaLife Centre right now, and he's adorable, and he's their twelfth walrus calf ever rescued.
On the topic of specialized teeth, there's also the crabeater seal and the lobodontine seals. The lobodontine seals are all members of the tribe Lobodontini, translating roughly to "lobed teeth". All four of thse seal species have uniquely shaped teeth..
Among these, the most well known and most specialized are the teeth of the crabeater seal.
Something really cool about RVC is that it actually has the skulls of two lobodontine seals in its incredible anatomy museum- the leopard seal and the crabeater seal! Anyways, despite the name, the crabeater seal eats no crabs. In fact, its diet consists almost entirely of Antarctic krill, despite being the weight of a small tractor (I did google this to fact check before I claimed it!). While all four of the species have lobed teeth, the crabeater seal makes the most use of these teeth, as it uses these teeth to filter feed:
Note how the canines and incisors are normal and still allow for tearing of flesh. In stark contrast to the krill-itarian diet of the crabeater seal, the leopard seal is a devout carnivore. Regardless, the leopard seal still has filter feeding molars and carnivorous canines and incisors. In contrast to the crabeater seal, the leopard seal has larger front teeth.
The Weddell seal also has larger front teeth than the crabeater seal, but tends to stick to eating fish rather than mammals and birds like leopard seals.
The Ross seal has the smallest canines and incisors of all four species of lobodontine seals.
Going back to walruses. Walruses are the species of pinniped with the most tooth resorption. Because they are suction feeders, a lot of their teeth prove useless- when it comes to feeding, their tongue is much more useful. These teeth are typically resorbed within the first year of life, and include the upper second incisor and the molars.
A common dental pathology in pinnipeds is very similar to that seen in dogs- dental fractures! My puppy managed to crack her molars when chewing on a toy bone (no more bone for puppy baby doggy, unfortunately), which meant she had to get those teeth extracted.
Anyways, dental extractions are harder in pinnipeds than in dogs. For one, because they are diving mammals, anesthesia is a lot more dangerous. Pinnipeds under anesthesia are remarkably good at uh. not breathing. Which is not ideal for survival of animal! I did write a whole post about pinniped anesthesia. I don't remember how well I talked about ensuring the animal Stays Alive (bee gees reference..)
Dental fractures can be graded based on how deep they are. An enamel infraction is just a crack in the enamel without a loss of the actual toothy bits, whereas a complicated crown fracture results in exposed pulp, which is where all the nerves are. An uncomplicated fracture leaves the pulp unexposed, and is less severe than a complicated fracture.
To deal with a tooth extraction, there are Many Fun and Joyous tools!
Before you do any tooth yanking, you have to sever the gingival ligament, for which you commonly use an elevator. Then you grab some extraction forceps, and some yanking occurs (i'm a yanker [get it because i'm an american! haha yankee?])
After that, you suture the gums up. This is a very crass way to describe a dental extraction, as there are a lot of factors you have to attend to, but I think it's kinda an apt depiction!
Teef moment. Crabeater teeth are so mesmerising.