I am in the US. Here typically oral surgeons and dentists just do the dental work, then tell you to see a physician to handle medical issues.

"It's just the way he determined which type/brand of supplement which suit my body that concerned me."

You can analyze your diet and see what is missing, or you can have blood tests to check your levels of vitamins and minerals.
Most vitamins usually don't have to be tested for, as taking a reasonable amount of supplements won't hurt you. Imo many doctors do too much unnexessary testing.