Which sign characterizes the functional form of Angle Class III malocclusion?

Which sign characterizes the functional form of Angle Class III malocclusion?

• A. Overgrowth of the mandible
• B. Overgrowth of the maxilla
• C. Underdevelopment of the lower jaw
• D. Displacement of the mandible anteriorly

Answer: (D)

The key idea is that a functional Class III is not caused by a fixed skeletal discrepancy, but by an anterior shift of the mandible during function. In this pattern, the jaw moves forward to achieve contact because of occlusal interferences or a crossbite, so the bite appears Class III only in the acting position. At rest, the skeletal relationship may be relatively normal or less pronounced, but when seated into the bite, the mandible slides forward. So the defining sign is displacement of the mandible anteriorly during closure—a forward functional shift. This distinguishes it from skeletal Class III issues, where the forward position is present even at rest (due to mandibular prognathism) or maxillary deficiency, rather than a reversible functional shift.

The key idea is that a functional Class III is not caused by a fixed skeletal discrepancy, but by an anterior shift of the mandible during function. In this pattern, the jaw moves forward to achieve contact because of occlusal interferences or a crossbite, so the bite appears Class III only in the acting position. At rest, the skeletal relationship may be relatively normal or less pronounced, but when seated into the bite, the mandible slides forward.

So the defining sign is displacement of the mandible anteriorly during closure—a forward functional shift. This distinguishes it from skeletal Class III issues, where the forward position is present even at rest (due to mandibular prognathism) or maxillary deficiency, rather than a reversible functional shift.