The Primate Team keepers have to train orangutans to open their mouths wide so they can check their 32 teeth - the same number as humans.
Part of the training means giving injections but just using water.
Charlie has been trained to present his shoulder and have it injected, which meant that yesterday morning he was not stressed when water was replaced with anaesthetic.
The dose was enough for the hour-long operation expected - a root canal on a worn central incisor tooth.
However, when Dr Tucker checked his other teeth he found a fracture of the upper canine tooth.
"It's a huge tooth which is like that of a large dog," said Dr Tucker.
"He needed another root canal and he had a lot of leaves and vegetable matter packed up into the root and we had to clean it out."
Doing two root canals took an exhausting three hours.
"I was going as fast as I can to keep him from being under anaesthesia too long but he seemed to handle it well."
Once during that time, Charlie regurgitated and partially sat up and tried to roll over.
"They rushed us out of the room for safety reasons."
Dr Tucker said he did a successful root canal for Charlie two years ago and had also worked on a tiger, which had an 80mm root canal compared with Charlie's 59mm.
Charlie woke up back in his house and he made a nest for himself and slept all afternoon.
He lives with three other orangutans - Melur, aged 26, who is the mother of his son Madju, who also lives with him, and a female, Wanita, 36.
5 five facts about orangutans
1 Genes
They are 97 per cent genetically the same as humans.
2 Breeding
Orangutans have the longest birth interval of any mammal - in Sumatra (Indonesia), some females may give birth only once every 10 years and not until they are 17.
3 Extinction
The Bornean orangutan is listed as endangered and the Sumatran orangutan as critically endangered.
4 Population
Only 6600 Sumatran orangutans remain in the wild - in patches of rainforest.
Threat
Deforestation of the rainforest (mostly to make way for palm oil plantations) remains the greatest threat to survival.
- source Auckland Zoo
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