14yr old broke another tooth

[bruffin]

DS has had problems shen his back adult teeth come through, which is probably caused by flurosis(sp)

When he went to the dentist in september they found a broken back tooth. He can't remember it happening but I do wonder if it happened when he had a febrile convulsion in May as he bloodied his nose and banged the back of his head at the same time,so obviously hit his head quite hard.

Yesterday he went to school trampoline club, attempted a front flip and landed on his face, grazed head,fat lip and it looks like another broken back tooth.
Surely his teeth shouldn't be breaking this easily? Are there are any other ways of strenghthening them.