Underbites are usually caused by a lower jaw that is disproportionately larger than the upper jaw. This can be seen clinically, by assessing the patient's profile. A lateral cephalogram (an xray of the skull in profile) will confirm this.
Underbites can also be caused by a bite interference when the teeth try to meet together, and this can cause the lower jaw to deviate from a straight path of closure to avoid the interference. Resolving the interference by aligning the teeth can eliminate the jaw shift.
An uncorrected underbite will tend to worsen during the pubertal growth spurt. The wisdom teeth may appear to be the cause of the underbite, because the eruption tends to coincide with skeletal maturation that happens after the pubertal growth spurt.