A different kind of jaws story

A veterinary expert on the temporomandibular joint catches waves and opportunities

November 3, 2023 (published)
Photo by John Doval
An expert in the temporomandibular joint — the hinge of the lower jaw — Dr. Boaz Arzi inspects the skull of an elephant. A professor of dentistry and oral surgery in the University of California's School of Veterinary Medicine, Arzi notes that the TMJ, as it's called for short, is found in most mammal species.

Whether surfing on the way to collecting specimens of arthritic sea lion jaws or being inducted into a professional society normally reserved for physicians, the veterinarian Dr. Boaz Arzi approaches his career and life with equal parts passion and creativity.

A graduate of Haifa University in Israel, Arzi studied veterinary medicine at the University of Szent Istvan in Budapest, Hungary, graduating in 2002. He completed residency training in veterinary dentistry and oral surgery and postdoctoral studies in biomedical engineering at the University of California, Davis, School of Veterinary Medicine, where he's now on faculty.

TMJ disorders, Arzi's field of study, refers to the disorder and dysfunction of the temporomandibular joint. In humans, TMJ problems often manifest as pain, lack of or reduced mobility, and/or clicking in the jaw. As Arzi's work has led him to realize, TMJ disorders occur in most mammals, from cats to elephants.

The VIN News Service recently caught up with Arzi — although sadly, not on the beach — to discuss his recent appointment as the only veterinarian in the American Society of Temporomandibular Joint Surgeons and to talk about translational medicine, advances in veterinary dentistry and oral surgery, and saying yes to opportunities.

The conversation has been edited for clarity and length. For the full interview, listen to the recording.

Can you describe your trajectory? How did you get, first, to the niche of veterinary dentistry and then to focus on the temporomandibular joint and regenerative medicine?

In brief

When I finished vet school, I went into a busy private practice with a blood bank and everything. It was heavy in surgery and trauma. I saw a lot of cases for about six years. Then I wanted to specialize. I found that dentistry and oral-maxillofacial surgery really attracted me. I was accepted for a residency at UC Davis. My mentor, Dr. Frank Verstraete, is double-boarded in surgery and dentistry. I took advantage of this training both in research and in clinics.

An[other] opportunity arose, and I took advantage of a two-year fellowship in biomedical engineering with Dr. Kyriacos Athanasiou, also here at UC Davis, while maintaining about 20% clinical appointments so I could keep my feet wet.

The fellowship was focused on fibrocartilage spectrums, meaning fibrocartilage either in the knee or the TMJ. Much of the work I did was on the TMJ for human application, but I could translate things I learned towards what I'm doing now, and that kind of directed everything toward the TMJ.

Would you say you have always had an engineering or mechanical bent?

I have an affinity for surgery — oral, maxillofacial [jaws and face] — those really attract me.

As for biomedical engineering, I call it divine intervention. When you start working in biomedical engineering and regenerative medicine in general, you see that you are going to do things that you thought were impossible, and they actually work. Because it's a lot of thinking outside the box, and that fits me perfectly.

It sounds like you have made a career out of changing the box into something entirely different. And I know you've recently been appointed as the only veterinarian in the American Society of Temporal Mandibular Joint Surgeons. How did that come about?

When I was a postdoc [in biomechanical engineering], every Friday, we had a lab meeting and I was presenting that I was doing some work on elephant TMJ. I brought some skulls of other animals and talked about them.

In this room were mostly engineers. And then my mentor told me, "Boaz, I think you need to focus on the TMJ. One day, you will be a world expert." I looked at him like, "OK, whatever, I have no idea what you just said."

I'm still part of the research group, and we're doing TMJ research in biomedical engineering towards human application. And we're working a lot with mini pigs. It's a surgical model that I was heavily involved in developing.

One day, I got an email from a group that looks at world experts. I think it's called Expertscape. They said, "Look, in the past 10 years, you're published in the top [percentile]. You are now considered a world expert. Congratulations."

I didn't know if it was real or not. I contacted our media people, and they said, "This is real."

So then it was "world expert," for what it's worth — kind of acknowledging my work throughout the years and publishing so much in the TMJ and being involved in NIH [National Institutes of Health] study sections on the TMJ for people — kind of crossing the veterinary and human worlds on the TMJ.

I also got mentored by David Hatcher in TMJ radiology. He's a TMJ [physician] radiologist in Sacramento and also [works] with us.

So, there is something called the American Society of TMJ Surgeons, and you need to be invited to be part of this closed society of surgeons that have to be active in clinics or in research or both. I was recommended by two colleagues from UCSF [University of California, San Francisco].

Once I was nominated, I had to submit my whole [application] packet. And then I was invited to give the keynote at the [group's annual] meeting in Key West [in March]. That was a first. I see everybody talking about people and all the problems they have, and then I'm going there talking about dogs and cats.

But the way I presented it is at the similar level of human care, and that's what we establish here at Davis. I mean, dogs and cats get TMJ care the same as people, with CT and MRI and PET CT — all the technology is the same.

It captured attention immediately when they saw that the same level of care that they provide to you is what we provide to dogs and cats. It was met with great enthusiasm. It was a very humbling experience.

I think every person in this society came to talk to me and said very nice things, and then they voted. I was obviously not there when they voted. I got accepted as an affiliated member because I don't have clinical responsibility for people.

Did you get to talk to any of your physician colleagues about the wide variety of skull structures of animals, from elephants to hamsters to horses? Are there different types of disease among various species?

Absolutely. What you just mentioned is the biggest item that we are working on, because every group of animals eats differently and uses their jaws differently. And I was fortunate enough to work in research on everything from marine mammals and [land] carnivores like dogs and cats and wolves and tigers and lions, all the way to horses and even to elephants.

They all get their own diseases. There is some overlap, like degenerative joint disease. What I've seen in the literature in people and working towards solutions in people [taught] me how to pursue research in the dog. Sure enough, we find diseases that were not described [in the veterinary literature] before.

Also, we use similar diagnostic imaging modalities. In fact, in our group, there is a human TMJ radiologist that advises how to strategize our imaging for the future and find the diseases that we didn't know existed.

You have animals that have jaws, like carnivores, that can open and close. And then you have those animals that graze, that move their jaws side to side. And then you have those that eat everything, like the omnivores; they also open and close, but they have a little bit of [side-to-side] movement.

And then you have the marine mammals. The best example is the California sea lion. We did a lot of research on California sea lions with Verstraete's lab at the California Academy of Sciences. Then, I got some specimens from the Marine Mammal Center [in Sausalito] to do work on, and we found out that over 60% of California sea lions have arthritis of the TMJ.

The mind-blowing thing is they don't really chew their food. They swallow [their food whole]. So how do you explain this?

[Exploring these mysteries is] a wonderful journey. We learn so much.

Photo by Dr. Boaz Arzi
Catching waves in Pacifica, California, Dr. Boaz Arzi follows the mantra, "Work hard and play hard."

Now I have to ask because I know you're an avid surfer: Did you manage to get the marine mammal exams and some surfing in at the same time?

When I went to the Marine Mammal Center, I went by the beach before [work]. That's for sure. Every opportunity there is to go to the beach, I use it.

That leads me to believe that you're somewhat prone to intense experiences. Surfing? Surgery?

Work hard and play hard.

When I started looking into some of your work, I had to Google "translational medicine" because, as somebody who graduated in the 1990s, that was a new term to me. Can you explain it?

It [applies] in several ways.

One way is that what you invented or discovered in your lab moves from the lab to the clinics: You are translating your research from one place to another.

Another option is moving it from one species to another. My working with the TMJ, it's been largely this [translation] from humans to animals, and that brought up the level of care. But many things, like stem cell therapy, can go exactly the opposite [direction]. We have had opportunities to [use stem cells to] treat diseases in the cat and inspire work in people.

So translating is moving your medicine, moving your discovery, from one species to another and from the lab to the clinics.

I interviewed you and Dr. Verstraete years ago, when you had just pioneered a technique for rebuilding jaws in dogs that had pathologic fractures or severe damage. How has that technique emerged? What other techniques have emerged from that work?

This is ongoing [work]. This is how we practice, not only in jaws but also in long bones. The orthopedic surgery service is using bone morphogenic protein on a regular basis. Between the dentistry, oral surgery service and orthopedic surgery, we have done over 100 cases. We've reconstructed legs, reconstructed jaws. We have fairly good experience now of about 12 years.

In the context of TMJ, we're now [working on] a TMJ replacement — we have a patent pending. This will allow us to reconstruct the entire thing once we find the approach to replace the joint.

Has that work translated to human medicine, as well?

The TMJ replacement actually is translated from people to animals because there are FDA[-approved] devices. This is one of the things I learned in the human world, attending the conferences, being part of the society: how to approach replacement of these joints, the need, when to do it and when not to do it, and what material to use.

With TMJ, do you see more trauma patients or chronic disease, or is it a mix?

Of the two most common things we see with TMJ, the first is TMJ ankylosis, which is basically fusion within the jaw to outside the jaw. The patient cannot open the mouth. The second most common is trauma — fractures.

Then we have degenerative joint disease. And just like in people, it may not manifest with pain and discomfort. Only about a quarter of our patients [in whom] we find arthritic changes in the joint actually have clinical signs.

Is ankylosis overrepresented in certain breeds or skull types, or is it across the board?

Most of the cases we do are cats. Within our practice, cats are overrepresented. There is no breed predilection. I would say that it's most common in younger patients.

Interesting. Congenital component, then?

I'm not sure there's good data. I think it's more of a trauma or infection inflammation. Most of the cats that we see with TMJ ankylosis are one year old [and] younger. Trauma is [the] No. 1 [cause]. And some of the patients may have infection in this area that predisposed [them]; some of them, we just don't know.

People are just not aware of this [possibility]. In one case of a cat with ankylosis, the owner who brought it to our community practice said that the cat may have worms because she is hungry all the time, though she's giving her food. And when they did the oral exam, they [found the cat] simply could not open its mouth. The cat was hungry. That is why it wanted to eat all the time — it was hungry because it couldn't open its mouth.

What happened to the food?

The cat was able to lick food but was skinny. Ankylosis can develop within several weeks and even days.

How do you treat ankylosis?

At this juncture, TMJ ankylosis is repaired with either gap arthroplasty, meaning removal of the fused bones and creating a gap so that fusion does not recur, or, in milder cases, condylectomy can be performed. That's removal of the lower-jaw portion of the ankylosis.

Last question: What drives you? What keeps you going?

First of all, I like working here. I like the people, and I like my team. I like the profession. I like the animals. I like the challenges. And I'm intrigued by my research.

If many friends of mine when I was a child would look at my career, they would probably not really understand what happened. Because I was not like this, growing up. [Being driven] is something that develops throughout the years.

In many ways, the profession also chose me. I wanted to be a veterinarian, and I loved animals. But things that evolved in my career and opportunities that came to my path, they directed me. I just simply took them and pursued this wholeheartedly.

There's a lot to be said for just saying yes when things come up.

Yeah, and to understand that this is an opportunity. This is not something to think, "Maybe should I do it or not do it?" Just go for it and do it. See what happens.

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