This study used an experimental dental arch model to examine the orthodontic forces generated by a quadhelix appliance in terms of parallel expansion, fan expansion, or a combination of the two. Strain gauges were attached to experimental brass rods that represented the teeth arranged in the shape of an average dental arch to detect forces in the buccal, lingual, mesial, and distal directions. Orthodontic forces generated by different types of activation were compared by Scheffe’s multiple test.

The largest orthodontic force generated during parallel expansion was observed at the first molar in the buccal direction. When fan expansion was applied, significant orthodontic force was observed at the canine in the mesial and labial directions, whereas force in the mesial and lingual directions was noted at the first molar. When a combination of 3 mm parallel and 5 mm fan expansion was used, the forces generated at the canine and first and second premolar, and first molar were nearly equivalent. Depending on the type of malocclusion, the most appropriate expansion technique may be parallel or fan expansion or a combination of the two. When expanding the entire dental arch simultaneously, a combination of 3 mm parallel and 5 mm fan expansion may be the most suitable.