Whats the deal wit saliva/oral drug testing and the science of it?

i use 2 get only urine tests at work and i beat em everytime wit a drink called royal flush by STAT. i followed every instruction now recently i got hit wit a saliva test. i was prepared 4 a urine test not that i herd bout these tests b4 but never really worried but yet w/o any readin on it or into them etc... i still just on a whim i always somewat keep the worst in mind and i would not eat or drink anythin for 4hours prior to test as part the regimen prior to takin the royal flush an i brush my teeth two times wit tootpaste( Crest xtra whitning) i rub the H**L out all corners my mouth wit brush really good & i chew this gum called trident with xylitol but i got hit wit the oral exam one time and i ped it 4 everything. could the gum certain tooth paste the royal flush the no eatin prior etc have anythin to do wit y i ped? or u think it was a fluke test. NEone else have luck pin saliva tests for drugs or marijuana THC