The underbite that had been explained away for years

Before treatment — in their own words

She was seventeen, near the end of secondary school. Her mother had brought her in partly because the university years were approaching and she wanted the opportunity settled before then. The mother was direct: she had an underbite herself, had always been told nothing could be done without surgery, had never had surgery, and now had a daughter with the same problem. She was not asking whether anything could be done. She was asking what specifically could be done, and on what timeline.

The daughter added one detail her mother had not mentioned: she found chewing on the left side more comfortable than the right, and had been doing this for so long it felt normal. She had not thought it was relevant until she mentioned it.

The clinical picture

Examination confirmed a Class III malocclusion. On habitual closure, the lower incisors were anterior to the upper. However — critically — when asked to close from rest position with the lips apart and no muscular guidance, the relationship improved substantially. This was the functional shift her chewing preference had been compensating for. The mandible was deflecting forward on closure due to premature occlusal contact at the canine region, which was then triggering an anterior slide. The underlying skeletal discrepancy, while present, was mild. This was a pseudo-underbite with a significant functional component — treatable with orthodontics alone.

The plan

Invisalign Teen Comprehensive with Class III elastics and upper arch proclination to create positive overjet and eliminate the functional shift. Once the premature contact was removed and the upper anterior teeth proclined past the lower incisors, the mandible would no longer deflect forward on closure. The true skeletal discrepancy — mild Class III — could then be camouflaged with dental positioning alone. The mother, who had been told surgery was her own only option twenty years earlier, sat quietly through the explanation and then asked why no one had ever assessed her bite this way. There was no good answer.

The outcome

After twenty months, the functional shift had been eliminated. Positive overjet was established. The molar and canine relationships were Class I. The lower incisors no longer protruded in front of the upper on closure from any position. Her chewing preference had normalised by around month fourteen, which is often the clearest functional indicator that the shift has resolved. She began university in the autumn after debond. Her mother came to the debond appointment. She spent most of it looking at the before photos.