I'm a Dentist & I used 1 Rx of Adipex in 2009 to control a "patient's HEAVY salavating" problem for dental work to be done that month. Adipex for a weight loss medication was secondary. Would this be considered "Legal" by most Dental Boards???
Two reasons why a dentist may ask about this particular combination of drugs:
First reason is the U.S. Food and Drug Administration states that as many as 32 percent of users of Fen-Phen may have developed cardiac valve damage, placing them at risk for bactermia-induced infective endocarditis. Endocarditis is an inflammation that occurs when bacteria carried in the blood lodges on the damaged valves or in the lining of the heart. Some dental procedures can allow the entrance of bacteria in the bloodstream. Simple dental procedures like cleaning, placing orthodontic bands and scaling as well as more invasive procedures like root canals, and extractions may require antibiotic treatment before the dental procedure. This may be why they're asking new patients about their drug history. If they know you've taken it in the past they'll make sure they prescribe the correct course of antibiotics before certain dental procedures are undertaken, just to make absolutely sure there's no risk to you.
Second reason they may be wanting to know is regarding the condition called Xerostomia, also known as "dry mouth", which is a contributing factor to gum disease, rapidly progressing cavities, and bad breath. Below is a partial list of medications which have been known to cause dry mouth. You'll see it contains the drugs you mentioned in your query:
Adipex-P, Fastin, Ionamin, Zantryl .............phentermine
Anorex SR, Adipost, Bontril PDM ................phendimetrazine
Mazanor, Sanorex ...................................mazindol
Pondimin, Fen-Phen ................................fenfluramine
Tenuate, Tepanil, Ten-Tab .......................diethylpropion
Could be for either one of these reasons that the dentist wants to know if you've ever taken the drug. Hope this was helpful.