The polar bear which mauled a 17-year-old schoolboy 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 from Salisbury, Wiltshire, 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.
Lieutenant General Peter Pearson, from Earlswood, Chepstow, Monmouthshire, who is executive director of BSES, said the organisation had adopted all of the recommendations made by Sir David in his report.
He explained that the specific recommendations relating to polar bears were not implemented because BSES have not returned to areas where polar bears lived since the incident three years ago.
In his conclusion, Sir David criticised the reliance on a tripwire system to alert the group to the presence of polar bears and said that a bear watch should be used instead and also called for an overhaul of rifle training.
Sir David concluded: "In future a bear watch must become the norm for expeditions to Svalbard.
"There needs to be complete review of available tripwire systems but they should be treated only as a secondary protection device. There needs to be a rigorous upgrade of rifle training."
Mr Pearson defended the two leaders of the expedition, Mr Ruck and Mr Reid, and said: "These two leaders were perfectly competent, if we were to select them today we still would."
He said he was not aware at the time that there were parts of the tripwire system missing .
He added that he had accepted the equipment, which was modified by the expedition group with paperclips, was unsatisfactory and explained that the BSES was working with a company to build a new system which was being trialled in Greenland.
Lizanne Gumbel QC, representing the Chapple family, criticised the system, saying it was designed to protect chickens from foxes and asked Mr Pearson: "When safety equipment is modified, it needs to be tried and tested by the manufacturer, not by children of 16 who had their physics GCSE?"
Mr Pearson said the tripwire did not fire because the bear hit a post rather than the wire, and added: "However much equipment we had around that camp, if the bear had hit a post it would not have gone bang.
"We have accepted what Sir David Steel said is the way we should go and we have actively sought to develop another system which will be more effective but I can never guarantee any system.
"In principle, we have accepted in the future it will be safer if there is a wire and a bear watch.
"This is not a fly-by-night organisation, we tasked a High Court judge to carry out an independent inquiry ... we are absolutely an open book."
Saying that the rifle training will be improved, Mr Pearson, who was formerly commandant of the Royal Military Academy at Sandhurst, said: "What we are putting in place is more training which may reflect better the situation they may find themselves in by getting people tired, by getting their heart rate moving faster and providing distraction and getting them to fire the appropriate distance.
"But it's going to be down to the individual and how they respond to stress and some are better than others."
He said that Mr Reid, who had difficulty firing a rifle at the bear before finally being able to shoot it dead, had a background in using firearms and he would have chosen him to handle the rifle.
He added: "On the occasion he didn't get it right but he did have the absolute courage after he had been badly injured to come back, find a round and shoot the bear."