I've seen teeth out for all manner of reasons, its not likely, but if he was being restrained and was fighting free, its possible his head came into contact with a table edge, or similar surface, at a specific angle it can take teeth out.
Doesn't happen often, but teeth do get knocked out, and more commonly it isn't a fist has taken them.
Also the guy is non-Caucasian, so he has a higher likelihood of gum disease, he is also fundamentality Islamic, so he might directly follow the Holy Book, which had writing involving cleaning ones teeth with 'a stick', which if the only form of cleaning might lead to rapid deterioration.
There could exist reasons why his teeth might not be able to withstand much of a knock, but its simply a case of 'perhaps' and 'maybes', and frankly I don't care. I just don't want my taxpaying money paying for an investigation, or worse, compensation for this murderer.
Well it sounds like there were five officers involved you only need 3 to deploy c&r one should have been in charge of the head to prevent injuries to it the other two the arms and a fourth for the legs if required. That is how prison service control and restraint in done! In 10 years I've never heard of anyone getting their teeth smashed! Yeah sure lots if arm injuries but the head is the number one priority to protect in these incidents!
I hope they hang these officers out to dry! I've met many prison officers mostly ex-military who go out of their way to provoke prisoners and use it as an excuse to dive in on a prisoner. After what this guy has done I'm betting a bunch of ex-army screws got one in on him