I've never had so many mouth ulcers as I have since these types of tooth-brushes were invented. I've only just realised it.
I'm not joking but I've had a mouth ulcer, on and off, for at least a year. The other day I was thinking to myself: Why the hell have I always got an ulcer in my mouth? I eat plenty of fruit, veg and drink a moderate amount of water.....and then I realised it's because of these tooth brushes. They've got really hard spikey back bits and it's really easy to nick the inside of your lip. But the worst thing is that once you've nicked your lip, then everytime you brush your teeth, it keeps being agitated - that is unless you hold the bottom of your lip whilst brushing your teeth.
Next time I buy a tooth brush, I'm getting a normal one!!