Thank you for your question. I have never heard of braces treatment causing teeth to crack.
It is important to note that before braces treatment begins, your dentist should check that your teeth and gums are healthy, free of decay and damage, free of any pre-existing cracks and any other pathology.
You braces dentist will see you regularly during your braces journey to check that your teeth are moving according to plan and that your teeth and gums remain healthy throughout your braces journey.
I hope my answer helps!
Kind Regards,
Dr Gerald Tan