Has he weighed this much for a while or has he suddenly lost lots?
With his tooth problems, it is possible that he's stopped eating, therefore loosing weight. When he's ill you should weigh him quite often to make sure he's not loosing weight. Even when he seems healthy, they should still be weighed weekly because weight is a good indicator of whether they are poorly or not.
My guinea pigs, who are both about 2 years old have weighed from 900g - 1300g in the time that they've been with me. When they were 11 months old, I would say they were around 1050g. However, it also depends on the size of the pig - some are just generally smaller, therefore they'll weight less, whilst others are bigger, so ofcourse they weigh more.