On Tuesday, LIL WAYNE underwent the oral surgery that got his sentencing on felony gun charges postponed earlier this month . . . and it was a MAJOR operation.

–According to TMZ, the procedure took EIGHT hours . . . yes, for dental surgery . . . and it featured EIGHT root canals. He also had several tooth implants redone, had a few new implants added, and also had some of his real teeth repaired. (!!!)

–Oh, and he also had some work on his grill done.

(–Unfortunately, there’s no word on how his teeth got that bad. Lil Wayne is 27 years old . . . and it’s debatable whether COMPLETE NEGLECT could even cause that much damage.)

(–Regardless, it’s safe to say that Wayne’s dental hygiene habits are lacking.)

–The judge previously rescheduled the sentencing for March 2nd, and warned him that there would be no further delays.

(–Wayne is expected to begin serving a year in the clink immediately after his sentencing. He could end up serving just 10 months for good behavior.)