Comparison of dental arch forms created from assessment of teeth, alveolar bone, and the overlying soft tissue

The objective of this study was to determine whether there are differences among the arch forms created from assessments of tooth surfaces, alveolar bone, and overlying soft tissue.

This study included 18 individuals who presented with a class I malocclusion, mild crowding, and a cone beam computed tomography (CBCT) image of good diagnostic quality. The facial axis point was chosen to create the arch form from teeth, the Bowman-Kau (BK) point was used to establish the arch form from alveolar bone, and the WALA ridge was used to calculate the soft tissue arch form. A predetermined algorithm was then used to create five separate arch forms per patient. These arch forms were categorized according to shape and were superimposed. The distances between the tooth-, bone-, and soft tissue-derived arch forms were calculated.

The calculated distances between all arch forms were significantly different. The distances between the tooth- and bone-derived arch forms were larger for the mandible compared to the maxilla (mean 3.30 vs. 2.48 mm, respectively). The larger distances seemed to be located more posteriorly in the arch than anteriorly. The distance between tooth- and soft tissue-derived arch forms was largest for the second premolar (2.35 ± 1.59 mm), first molar (2.86 ± 0.63 mm), and second molar (3.25 ± 0.87 mm). There were no significant differences in the distance between the tooth- and either bone- or soft tissue-derived arch forms with regard to sex.

The arch form shapes obtained from the teeth, alveolar bone, and soft tissue are correlated and show the same general shape. Although future large-scale studies are needed for confirmation, our results suggest that evaluating the easily visualized external features, including the WALA ridge, can adequately predict the underlying bone shape, and thus the desired arch form. Nevertheless, the shapes vary significantly between patients, so the final treatment plan should be individualized rather than relying on over-simplified general wire shapes.