The teeth of captive orca, or killer whales, are in a sorry and painful state, an international research team has found.
The study by the team, which includes New Zealand-based scientists Dr Carolina Loch and Dr Ingrid Visser, has raised concerns over the overall health and welfare of orca in captivity.
The researchers looked at 29 orca owned by one company and held in the United States and Spain, and they found that every one of them had damaged teeth.
Two-thirds had moderate to extreme tooth wear in the lower jaw, mostly from chewing concrete and steel tank surfaces.
Six in 10 had teeth that were so worn they had to be drilled to extract the soft pulp inside, according to the study published in the journal Archives of Oral Biology.
Dr Loch, from Otago University's dentistry faculty, says that, unlike with humans, the resultant hole is not filled or capped.
Instead, it is left open, requiring daily flushing with chemicals to keep the teeth empty of food and bacteria.
Dr Loch added that a drilled tooth was severely weakened and, if any other trauma occurred, fractures would happen.
Dr Visser, who has studied orca in the wild for more than three decades, said the research offered hard numbers to show how health and welfare were compromised by being confined in tanks.
"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," she said.
"Compared to free-ranging orca, the teeth of captive orca are incredibly compromised and you just don't see this type or level of damage in the wild."