In a very small percentage (1.
5-3%) of the population post-pubertal growth can cause one jaw to outgrow the other. In a miniscule percent of the population this is indicative of specific syndromes. Althoough your son's abberant groth has taken place at an age when most males have completed growing, it's not unheard of. Please see a dento-facial growth specialist, a fully qualified Orthodontst.