I was told its best to spay before the first heat as the chance of cancers is far far less. Like you said the chances of teeth being pulled at 6 months could be unlikely so its a lose lose situation. In Tias case she was spayed before her first heat at 6 months and therefore no teeth needed extracting. Now at 15 months she still has one baby tooth left , a canine ,but had it checked today (at her first annual booster) and the vet said it looks ok and to keep brushing it should come out on its own.
So he decision is yours but I would spay before the first heat.
