A lioness has undergone a three-hour dental appointment and root canal treatment to save two canine teeth.
Mo, an 18-year-old from Africa Alive zoo at Kessingland in Suffolk, was anaesthetised earlier under the care of a specialist vet.
It is not always easy to tell if a lion has toothache, staff at the zoo said, but the operation went well and she was recovering.
"It's like human dentistry - just on a larger scale," the zoo said.
"Animals mask pain very well, and there was nothing to indicate that Mo was having toothache," said Haylee Parker, from the zoo's animal management team.
"But there were little things that staff noticed, as they're with her all the time.
"We could see that one canine was damaged and the other canine had some damage."
A root canal procedure was decided upon and Miss Parker fired the tranquiliser dart into the lioness.
"We left it for about 30 minutes until we knew it had taken," she said.
"Everything has been drilled out right down into the root and it's then packed out to make sure everything's going to be hygienic and sterile.
"It's like human dentistry - just on a larger scale."
The zoo's own vet was there, as well as specialist dental vet Gerhard Putter and his own veterinary nurse.
"The procedure went well," Mr Putter said.
"It's always a long procedure because there's a lot of work to be done in really large root canals."
The root of one tooth was 60mm (2.3in) long, he said.
"An alternative would have been extracting the tooth - which would have been far more invasive and traumatic... and you have a wild patient... that has to be monitored", he said.
"We've removed the source of the bacterial infection which is the important part."
Mo, one of six lions at the park, took a couple of hours to begin to come round from the anaesthetic, Miss Parker said.
"She's up on her feet, but a bit wobbly."
Mo will be left in the enclosure on her own overnight so she can get a bit of much-needed rest and recuperation.