St George Illawarra tough guy Neville Costigan's fear of the dentist almost cost him a start in the Dragons' 13-12 NRL preliminary final victory over the Wests Tigers on Saturday night.

Costigan broke a tooth three weeks ago but didn't get it checked out, only for it to blow up at the worst possible time - on match eve.

He made it to ANZ Stadium and went on to play a major role in his side reaching next week's grand final, still with swelling and after finally getting to bed at 4.30am.

Dragons coach Wayne Bennett said he'd been alerted to the problem at 11.30pm on Friday night.

"I thought it was one of my former players on the drink somewhere ringing me up to tell me the Dragons can't play," Bennett joked.

"So I ignored it and about 10 minutes later the door bell started ringing and I checked my phone ... it was from one of the staff.

"I realised we had a problem.

"His face was out here somewhere looking like elephant man and in a fair bit of pain and discomfort.

"As tough as Neville is, he hates needles so he didn't go and tell anyone about it ... it became infected.

"They were at the St George hospital about 12.30 (Friday) night, didn't leave there 'til about 4am (Saturday morning), he was on drips and other stuff.

"Nev got to bed about 4.30 this morning and we managed to get him on the field tonight so we count ourselves pretty lucky."

Costigan finally got his dentist's appointment on match day.

"We got a dentist here before the game but everything checked out OK," Bennett said.

"He's still swollen but it certainly came down a lot, he was in a lot less pain."

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