The polar bear that mauled a British teenager to death in the Arctic was hungry and had toothache that was likely to have made it more aggressive, an inquest has been told.
A coroner in Salisbury is hearing evidence from a wildlife pathologist about the death of 17-year-old Horatio Chapple.
The inquest was told the bear, estimated to be more than 20 years old, was likely to have been stressed because of pain and therefore acting "unpredictably" when it attacked the camp in Norway's remote Arctic island group of Svalbard.
Wiltshire and Swindon assistant coroner Ian Singleton revealed that a post-mortem examination of the animal found that it had worn-down teeth, with a cavity in one tooth, and swollen and red gums.
The post-mortem report indicated that the pain it was in would have affected its behaviour.
Mr Singleton said: "(It) had badly aligned teeth causing them to wear down more than normal. It's probable it affected the bear's ability to gain food and if the bear is in pain it would have increased levels of stress causing it to behave more aggressively and unpredictably than it would otherwise."
Horatio was part of an adventure holiday in August 2011 organised by the British Schools Exploring Society (BSES) when he died.
The Eton pupil, who was from Salisbury in Wiltshire, was asleep in his tent when the bear crossed trip wire alerts and attacked the group.
He died from fatal injuries to his head and upper body.
Mr Singleton added: "The teeth suggest the bear is very old, more than 20 years based on the appearance of the teeth.
"The fatality rate for bears in Svalbard is high after 15 years, and very high after 20 years, it's rare for a polar bear to reach 25 years."
A total of four other people in the group, known as Chanzin Fire, were hurt in the attack before the bear was shot dead.
Those injured were trip leader Michael "Spike" Reid, from Plymouth, Devon, Andrew Ruck, from Brighton, Patrick Flinders, from Jersey, andScott Bennell-Smith, from Cornawll's St Mellion.
High Court judge Sir David Steel produced an independent report on behalf of the BSES.
He said the animal was seriously underweight at some 39-stone (250kg) - around 40% below normal.