Final determination of the dental arch form depends on:

 # Final determination of the dental arch form depends on:

A. Angle’s classification

B. Growth pattern

C. Facial type

D. Balance between extraoral and intraoral muscle forces

The correct answer is D. Balance between extraoral and intraoral muscle forces.

Although negative pressure is created within the mouth during sucking, there is no reason to believe that this is responsible for the constriction of the maxillary arch that usually accompanies sucking habits. Instead, arch form is affected by an alteration in the balance between cheek and tongue pressures. If the thumb is placed between the teeth, the tongue must be lowered, which decreases pressure by the tongue against the lingual of upper posterior teeth. At the same time, cheek pressure against these teeth is increased as the buccinator muscle contracts during sucking. Cheek pressures are greatest at the corners of the mouth, and this probably explains why the maxillary arch tends to become V -shaped with more constriction across the canines than the molars. A child who sucks vigorously is more likely to have a narrow upper arch than one who just places the thumb between the teeth.

Reference: Contemporary Orthodontics, 4th Edition, Proffit, Page NO. 152

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