Probably lack of care. The circumstances kind of point that way. They would have been able to tell if the tooth loss was recent, or due to violence, and you'd think they would have mentioned that. Yeah I know. Also, dental care was not nearly as good in the 60s and 70s as we take for granted since then. It was pretty common for people to either not care for their teeth or only see a dentist when they needed to have a tooth pulled. It's still fairly common for people with tooth problems to have them all pulled and get a denture instead (my sister-in-law chose that path) just so they don't have to deal with the pain and problems any more.