Researchers in Germany have reported that mesenchymal stem cells from horses’ teeth are providing insight into how equine teeth develop, grow, and maintain a healthy and sealed pulp.

While complicated to isolate, the MSCs in equine dental soft tissues could possibly improve regeneration in periodontal lesions, periodontal reattachment after dental implantation, and other dental therapies that rely on soft tissue healing. But, just as importantly, investigating these MSCs will probably shed light on the mechanisms behind the “lifelong eruption” of equine teeth, said Laura Beate Heilen, of the Faculty of Veterinary Medicine at the Institute of Veterinary-Anatomy, -Histology, and -Embryology at Justus-Liebig-University, in Giessen.

MSC Extraction from Equine Teeth

Heilen and her colleagues have been studying equine teeth for many years and have always found their regenerative capacity “striking,” she said.

Unlike human teeth, horses’ teeth never stop erupting. Such never-ending eruption calls for a healthy, constantly renewing periodontal ligament (PDL, which anchors teeth into the jaws). At the same time, equine teeth experience lifelong occlusal wear, so that there is always a risk of opening the dental pulp (which is located inside the tooth). In order to avoid occlusal pulp exposure, a constant, high level of dentin production is absolutely necessary.

Curious about the MSCs that must be playing a role in this processes, Heilen’s group set out to discover where MSCs are located in the PDL and within the dental pulp, and whether it’s possible to isolate them to investigate their qualities. This new retrieval technique allows researchers to directly compare cell populations after extraction.

They collected the heads of four horses aged 2.5 to 24 years old that had recently died for reasons unrelated to the study. Through a slow, multistep process of cutting, cleaning, dissection, fixation, extraction, and suspension, the researchers isolated MSCs from the dental pulp and PDL of the horses’ incisors as well as from retrobulbar fat tissue for comparison reasons.

The team then compared microscopic characteristics of these MSCs and found their specific locations within these dental tissues.

They found that while the process was complex, all the MSCs they isolated were viable, Heilen said. Furthermore, they saw that the cells bore “important characteristics” of MSCs, such as being spindle-shaped and having several significant proteins in their cell membranes—especially two, known as CD90 and CD44—which serve as biomarkers for MSCs.

In fact, the cells in certain tissue layers seemed to, somewhat surprisingly, continuously express CD90 on their surfaces, she added. That’s important because researchers had already identified CD90 in previous studies on rat teeth—but only when the teeth were regenerating following experimental cavity preparation in the laboratory. “This supports the hypothesis that the equine dental pulp remains in a very productive and regenerative status for life,” she said.  

Future Therapeutic Opportunities with Equine Dental MSCs

These findings open the door for future research that explores the roles of MSCs in horses’ dental structures, said Heilen. “We think that MSCs obtained from dental pulp are especially useful to understand more about regeneration and remodeling in equine teeth,” she said.

Additionally, though, isolating MSCs from equine teeth might help researchers test the effects of various therapies on the regenerative capacities of horse teeth. “For example, it might be useful to know how pulpal MSCs react to the application of different substances used as cleaning and filling materials for endodontic treatments,” Heilen said. “Are there substances which stimulate the regeneration, proliferation, or differentiation of cells (towards odontoblast-like cells, which can be damaged by inflammation) inside dental soft tissue? Or are there substances in use which might be harmful for the cells?”

As a stem cell therapy, however, the dental MSCs are less promising, she added. “The procedure to isolate viable cells from equine teeth is very complicated,” Heilen said. “Furthermore, it is doubtful whether an application of MSCs gained from dental pulp is reasonable, because there are a lot of regions (of the body) that contain MSCs, which are easier to reach.”

It also seems impossible to harvest MSCs from the teeth of live horses—except perhaps in the case of tooth extraction, she added. In order to extract suitable MSCs, the tooth being removed must be healthy, which can cause ethical concerns in live horses.

“When the principles about how MSCs become activated to support pulpal and periodontal healing are understood, it might be possible to recruit inherent and/or surviving MSCs—instead of injecting foreign ones.” Dental tissue injuries are often triggered by bacteria or mechanical stimuli. This causes inflammation which motivates the tooth to separate the affected part by producing more odontoblasts; therefore, MSCs are needed to reduce inflammation and possibly replace damaged odontoblasts. The researchers encourage further studies in hopes they will lead to concrete therapeutic recommendations, Heilen said.

The study, “Isolation and cultivation as well as in situ identification of MSCs from equine dental pulp and periodontal ligament,” appeared in Frontiers in Veterinary Science in March 2023.