What causes mouth ulcers?: Dr Ian Kelly, Dentist
Typically mouth ulcers are caused by trauma. This can be mechanical – knocking your gum with your toothbrush, or it can be thermal - the Sunday hot potato or the slice of pizza. The mouth ulcer is caused by damage to the surface gum, which breaks down and that exposes the sensitive surface below.
A mouth ulcer will last, on average, seven to ten days, becoming more sore in the middle period before it improves.