Quite normal to need to throw the rule book out the window when child is poorly, hurt (or when older, scared).
There'll be these times for many, many years to come. My 12 year old dd visited our bed not long ago when she was nervous about going to secondary school. Our 7 year old pops in if he's poorly. My 2 year old had a bout of norovirus last week and needed extra mummy and daddy cuddles.
So frankly, ignore this idea:
I don't want to get into that habit with him.
I assume this is the first time his sleep has been disturbed enough to need you? It'll happen for years to come. Of course he'll have times when he's poorly or in pain. He just needs extra care and compassion while he's not well, that's all. You can go back to normal once he's better and the tooth has cut through.
If you're happy and getting enough sleep on the mattress in his room, great do that and don't stress it. If you might get more sleep with him in your bed, do that.
Hands-off parenting and independant sleeping just doesn't work for those times baby just needs extra cuddles.
The good news is, cutting a tooth takes about 3 days or so. So soon he'll be back to himself and so will his sleep.