The polar bear which mauled a 17-year-old schoolboy from Wiltshire to death was elderly and had been suffering from worn-down teeth which would have led to it becoming stressed and behaving more "aggressively and unpredictably", an inquest has heard.
Horatio Chapple was on an adventure holiday to the remote Svalbard islands in August 2011 with the British Schools Exploring Society (BSES) when he died.
The Eton pupil was sleeping in his tent when the bear went on the rampage, inflicting fatal injuries to his head and upper body.
Four others were hurt before the bear was shot dead at the camp site, where the group, known as Chanzin Fire, had been staying.
Also injured during the incident were trip leader Michael "Spike" Reid, from Plymouth, Devon, Andrew Ruck, from Brighton, Patrick Flinders, from Jersey, and Scott Bennell-Smith, from St Mellion in Cornwall.
Assistant coroner for Wiltshire and Swindon Ian Singleton said that a post mortem examination of the bear's mouth found that it suffered from worn-down teeth, a cavity in one, swollen and red gums and peritonitis in several teeth.
He said that the report stated that the pain suffered by the bear would have influenced its behaviour.
Mr Singleton said: "(The bear) 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."
Mr Singleton said that an examination of the teeth showed that the bear was estimated to be 24 years old.
He continued: "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."
An independent report produced by High Court judge Sir David Steel on behalf of BSES also said the bear was seriously underweight at about 250kg rather than the typical 400kg and the maximum age of a polar bear was normally 25.