Assertion: simple canker sore | /r/CreatedBy | sharp tooth surface
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Source sentences:
text: A simple canker sore is thought to be caused by any number of things: stress, tissue injury (such as a sharp tooth surface rubbing on the inside of the cheek or an oral appliance rubbing on the gums/tongue) or acidic foods (such as lemons, oranges, pineapple and tomatoes).