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 Jimmy Boiahead 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!