The piece costs ??16,800 and is designed by Dr Lee Gause, a New York dentist who often flies to Las Vegas to fit the American???s mouthguard before fights.
Dr Gause??inserts a portion of the $100 note into the plastic.
Mayweather, who will clash with the Flipino on May 2 in Las Vegas, also has a female chef who is being paid $1,000 for each meal she prepares during his training camp.
The unbeaten fighter has had an unorthodox training regime in the build up to the fight and was filmed last month chopping wood.
He is expected to earn around $120???million for the fight, which is live on Sky Sports Box Office, while Pacquiao will take home an estimated $80???million.