Devin Haney's shining in both the boxing ring AND the dentist chair these days ... TMZ Sports has learned that after beating Vasiliy Lomachenko last month, the star-fighter copped some crazy diamonds for his teeth!!
We're told the undisputed lightweight champ reached out to famous jeweler JimmyBoi ahead of the May 20 Loma fight to have a grill made for him ... win, lose or draw.
Turns out, Haney was able to beat the Ukrainian fighter -- and then he was happily rewarded with the bling!!
The mouthpiece is fully iced-out ... we're told the set is filled with 17 carats of princess cut flawless clarity D color diamonds -- and also features 18k rose gold.
The 24-year-old was clearly pumped for it all -- showing it off in a recent selfie.
It hasn't all been super fun for Haney following the big tilt vs. Loma -- a lot of boxing fans have been upset with him over the controversial decision -- but seems he's going to smile through all the hate ... with some serious pizzazz now!