Hi Everyone

I am using dental floss thread to sew the elevator to my combat wing. Do I need to fuelproof the dental floss thread?

Agree with Paul. Dental floss is not particularly strong and waxed to boot,  so it is hard to glue.  I've seen it break in flight, and in moderate crashes.
Use some kind of braided fishing line for sewn hinges.  30 lb Dacron, or 40-50lb. Spectra line is much stronger.

_Unwaxed_ dental floss is as good as it gets, although harder to find.  Kevlar fishing line is the next best, with dacron flying line coming in next.  These three threads are fuel proof, oil proof, sunlight resistant enough for years, and abrasive resistant to hangar rash

Waxed dental floss causes bonding problems.

These three are a plastic fiber and does not require fuelproofing.  However the holes through the wood require protection from oil more than fuel.  If you drill the holes then dope them, or push a fuel proof glue like Testors cement through the holes, and redrill after the glue dries you will be in excellent shape.  With film covered wings consider treating the edges before covering.  If the parts ard sprayed with enamel paint like rustoleum the paint will be fine, although brushing in paint to fill the holes becomes an option.

I have used common poly-cotton thread for a field repair.  It lasted only a couple outings and needed redone.

I have small spools of Kevlar thread that I use for sewn hinges.