These ill fitting mouthguards cannot deal with idiosyncrasies athletes and children may have. If everyone had the same dentition; were of the same gender; played the same sport under the same conditions; had the same experience and played the same position at the same level of competition, and were the same age and same size mouth, with the same number and shape of teeth, prescribing a standard mouthguard would be simple. This is the precise reason why mouthguards bought at sporting good stores, without the recommendation of a qualified dentist, should not be worn.