Use of Interarch Width Ratio to measure Transverse Relationship: A New Method to measure and assess Interarch...

The purpose of this study was to assess the arch width, transverse discrepancy, and transverse interarch ratio for class I malocclusion sample, with and without crossbite, in permanent dentition stage.

Records of class I malocclusion patients with minimal crowding and spacing with and without posterior crossbite were selected. Each group consisted of 40 pairs of dental casts (20 males and 20 females). Arch widths were measured for the canine, first, and second premolars, and first permanent molars using the buccal approach. Means and standard deviations (SDs) of dental arch widths were measured for the maxillary and mandibular arches, and the interarch width ratio was calculated.

There was a highly significant difference between the noncrossbite and crossbite groups regarding the maxillary width, p < 0.001. However, no differences were found between groups for the mandibular widths, p > 0.01. There were also significant differences between both groups for the intercanine, first and second premolars, and first molar ratios, p < 0.001.

This new simple method showed that a transverse maxillary-mandibular ratio of 1:1.1 is ideal. A ratio less than 1:0.9 will indicate the presence of crossbite.

The interarch ratio significantly aids in orthodontic treatment planning in patients requiring maxillary expansion and/or surgical cases.