Ace the Smile Squad Challenge 2026 – Orthodontic Assistant Exam to Brighten Your Future!

An underbite is characterized by the lower teeth being positioned ahead of the upper teeth when the jaws are closed. This malocclusion occurs when the mandible is protruded relative to the maxilla, leading to a misalignment where the lower teeth extend beyond the upper teeth. This condition can result in various dental and orthodontic issues, such as difficulty in chewing, increased wear on teeth, and jaw pain.

The other options describe different dental conditions. For instance, significant crowding pertains to a situation where there is insufficient space for teeth to align properly, resulting in overlapping or misplaced teeth. The alignment of teeth in a straight line refers to normal occlusion where teeth are properly aligned, while the overlap of upper teeth on lower teeth describes an overbite, which is the opposite of an underbite. Thus, the defining characteristic of an underbite is the positioning of the lower teeth relative to the upper teeth.