A version of Edvard Munch's expressionist masterpiece The Scream is back on public display some four years after it was stolen from a museum in Norway.The version - one of four - it is still showing signs of damage sustained in the daring 2004 heist, despite hours of restoration work.But the Munch Museum says the painting has been rejuvenated by nearly 20 years.Until now, The Scream was thought to have been painted in 1893. The Munch Museum now says that it probably dates from 1910."Written sources, combined with style studies and, to a certain extent, technical observations made during the restoration of the painting point to a more recent dating," museum chief Ingebjoerg Ydstie told AFP."Experts have been squabbling since the early 1970s over the date of 1893. Today the museum is complying with the opinion of the majority."But we're not putting an end to the debate. New technical studies will maybe give us a better answer one day," she added.The Scream depicts an individual on a bridge, hands clasped around the head and mouth wide open in an apparent yell of despair.It along with another Munch masterpiece, Madonna, were damaged in the 2004 heist.Police recovered the works in August 2006 under mysterious circumstances.They were scratched and torn and showed signs of humidity damage.Most visible is a large damp spot in the lower left corner of The Scream that conservationists decided not to repair for fear of damaging the painting further."The stain will remain because we decided that with the current techniques available, it would be stupid to do something that would worsen the damage," Mette Havrevold, the head of Oslo city's art conservation department, said."Maybe more reliable technology will enable us to erase it in the future," she said.　The restoration of the works was a meticulous process. Each torn fibre was glued back individually with precision devices."It was a challenge because we didn't know anything about what these two paintings had been through. There were a lot of unknowns, in particular about where the humidity stain came from," Ms Havrevold said.Painting's historyMs Ydstie says the damage to The Scream does not weaken "the enormous expressive power" of the painting, which the artist himself mishandled."When he wanted to hang it up in his home, since the painting wasn't framed he just struck a nail through the canvas," she said."As spectacular as it was, this episode of the heist and the damage that ensued will fade over time and will, I hope, one day be just one of many incidents in the history of this painting."Three men have been found guilty of the 2004 heist.The museum's security has been beefed up considerably since the theft.