The aim of this study was to determine if a difference existed between arch forms created from tooth surfaces and arch forms created from alveolar bone.
CBCT images were collected using the PaX-Zenith3D imaging system. The study included 35 individuals of an Asian population, who required orthodontic treatment and demonstrated Class I molar relationship. The Facial-axis point (FA point) was chosen to create the arch form from teeth, and a new point, the Bowman-Kau point (BK point), was used to establish arch form from the alveolar bone. The BK point was defined as the point located at the buccal extent of the alveolar ridge in the axial cross-section taken at the level of the estimated center of resistance of the tooth with the axes defined by the patient’s natural head position. The FA point and the BK point were plotted on every tooth. A predetermined algorithm was used to create 4 separate arch forms per patient. The arch form from FA points was superimposed on the arch form from BK points within an arch and the 2D distance between the FA point and the BK point of each tooth was then calculated (FA-BK distance).
The mean FA-BK distance in females was 1.93mm (SD 0.65) and 2.83mm (SD 0.49) for the parameters in the maxilla and mandible respectively. In males, it was 1.98mm (SD 0.84) and 2.73mm (SD 0.58) in the maxilla and mandible respectively. In females, the difference between the FA-BK distance in the maxilla as compared to the mandible was statistically significant in the central incisors, canines, first premolars, and right second molars. In males, this difference was statistically significant in canines, first premolars, and left first molars.
The arch form defined by the FA points emphatically differs from that defined by the BK points.