That didn't stop Thomas from scoring a game-high 33 points on 11-of-23 shooting over 38 minutes while helping the Celtics rally from a 17-point deficit for a 123-111 triumph at TD Garden.
Thomas plans to have the tooth professionally reinserted; it came back out after the team repositioned it in the first half.
"It just bothers me to talk. My tongue goes right through my tooth," a lispy Thomas said at his postgame news conference. "I've never had dental problems, so this is new. I've always had teammates that I've always clowned them about the tooth being out, and now I'm one of them. So hopefully we can replace it as soon as possible."
Brad Stevens said Isaiah Thomas will play in Game 2 despite missing practice Monday. "He's finishing up the dental work that he's had," said Stevens. "It's pretty significant as you can imagine. So he's still in a dentist's chair and will hopefully be able to come over later in the afternoon, kinda go through what we did, and go from there."
Midway through the first quarter, Thomas was chasing Otto Porter Jr. as he received a pass while curling at the top of the key. Thomas swiped at the ball and his mouth hit Porter's elbow, knocking out one of his top front teeth.
During the next stoppage, Thomas retrieved the tooth near the 3-point line and delivered it to team trainer Ed Lacerte. Team doctors attempted to reinsert the tooth when Thomas checked out later in the first quarter, but Thomas said it eventually fell out.
Thomas said he hoped to have a dentist reattach the tooth as soon as possible. Teammates told Thomas he should keep the toothless look for the playoffs.
"He looks a little tougher. I like it," joked Celtics guard Avery Bradley. "I was making jokes during the game on the bench, and I got him laughing. It was funny. There's a guy from Seattle named Rodney Stuckey and he plays with a missing tooth and I told Isaiah he should go with that look for the rest of the playoffs. He laughed and said, 'No, I'm getting it fixed tonight.' He played well and definitely got our team going tonight."
Thomas didn't seem overly fazed when the tooth fell out. The Celtics were down 22-5 after Porter made the jumper that Thomas was trying to defend. Thomas responded with a pair of 3-pointers to help ignite Boston's rally.
On the bench during a timeout, cameras caught Thomas, blood around his lips, smiling as team doctors examined the gap in his mouth.
"I wanted him to smile a little bit more. I don't think he cracked a smile," Jae Crowder said. "But it showed a little bit about what he's about. Because he's just going to keep playing no matter what. He's a fighter, man. I'm sure he'll get it fixed, but I just wanted him to smile just to show it off a little bit."
The tooth brought a bit of levity for Thomas, who had flown to Tacoma, Washington, after Boston's Game 6 win over the Chicago Bulls on Friday to attend his sister's funeral on Saturday.
Thomas didn't land in Boston until 4 a.m. Sunday and was at the arena six hours later to go through the team's pregame walk-through.
Celtics coach Brad Stevens marveled at what Thomas has been able to accomplish while grieving the loss of his sister, but the coach had some fun with the lost tooth.
"He and my 7-year-old daughter [Kinsley] just gave each other the open-tooth smile," Stevens deadpanned. "And he just -- he made both 3s right after it fell out. So maybe that tooth was holding him back a little. No, I feel bad for him because he's going to have to have some pretty significant dental work."
Added Stevens: "I think that obviously [losing a tooth] hurts and that's not fun, but in comparison to what he's gone through -- even he was laughing and pseudo-smiling about it there for a while. But I think that what he's been able to do is, I think I've used the word 'unfathomable,' and I'd stick with that. I can't imagine being able to do it myself, if I were in the same situation. He's incredible."