Not a dentist talking.    Could your friend possibly get a prescription for
Valium or Ativan,1 mg.  and take one before going to dentist.   That wlll
alleviate the anxiety of dental work.   Eventually he will need to go to a
dentist and the sooner he can get started, the better condition he will be
able to keep his teeth.    Fear  and anxiety might cause a flareup of the
arthritis?   Perhaps that is true of many conditions.   so for all of what
may need attention in the future, fear should be dealt with.
There is a saying,  All healing is essentially the release of  fear"    If a
prescription for a few Ativan or Valium cannot be gotten, a herb Valerian is
sold in drug stores and health stores.   Nature's Resource is a good brand.
The effects only last a couple of hours compared to eight for Ativan.
In the meantime, home remedies like good nutrition, vitamins, brushing and
flossing can help     Why would he need an antibiotic if there is no known
infection, unless there is a heart condition.  If he has not been to the
dentist in years, he many need restorations, etc. but have the dentist point
out that there are such problems for certain.     There are no absolute
guarantees and the more knowledgeable a person is about anything, the less
there is to be anxious about.
Just my opinion formed through years of hit and miss.     Maybe a dentist
could elaborate.
Gail