Captive orca are suffering serious tooth damage from biting steel bars and concrete, new research involving New Zealand scientists has found.
The study, published in the journal Archives of Oral Biology, found all 29 orca owned by one company in the United States and Spain had some form of dental damage, with more than 65 percent suffering moderate to extreme tooth wear.
Carolina Loch from Otago University's Faculty of Dentistry, who co-authored the study, said more than 60 percent of the orca had "been to the dentist", which led to more problems.
"Once the tooth gets worn to the point where the pulp is exposed this opens up a channel for disease and infection, so the staff then drill the teeth," she said.
The resulting hole was not filled or capped, but left open, requiring daily flushing with chemicals in an attempt to manage infection.
Drilled teeth were also severely weakened and easily broken, Dr Loch said.
"We have documented more than 60 percent of the second and third teeth of the lower jaws were broken and this high number is likely linked to the drilling."
Co-author Professor John Jett of Florida's Stetson University, an ex-orca trainer, said the team found tooth damage started at a very early age in captivity.
"Teeth are incredibly important to the overall health of an animal, and the results of our study should raise serious concerns for the health and welfare of captive orca," he said.
Four of the five orca with the worst tooth damage were born in captivity.
Another researcher, New Zealand-based scientist Ingrid Visser, who has studied orca in the wild for more than three decades, said damage of this type or level was never seen among free-ranging orca.
"We know that confining them in tanks is bad for the animals and this research now gives us some hard numbers to illustrate just how their health and welfare is compromised," said Dr Visser, a long-time campaigner against keeping orca in captivity.
"Given how big the root of an orca's tooth is and that orca have a nervous system similar to ours, these injuries must be extremely painful."
Another of the study's authors, Jeff Ventre, who once drilled orca teeth in his former role as an orca trainer, said he witnessed "whales breaking their teeth on steel gates while jaw popping. Small tooth fragments were then collected below the gate while diving the pool".
Due to their damaged teeth, these orca would be unlikely to survive a transition to the wild, should the companies ever consider releasing them, said Dr Ventre, who's now a medical doctor.