The variability of the curve of Spee : An analysis of multiple setups of the same Angle Class I patient case

The aim of this study was to examine possible parameters correlating to the shape of the curve of Spee (COS) by analyzing multiple setups of the same Angle class I patient case.

In all, 65 setups of the same Angle class I patient case were constructed. We measured the depth of the COS, length and width of the dental arch, steps, rotations, spaces and symmetry of the constructed setups. With a correlation analysis, possible relationships between the depth of the COS and measured parameters were evaluated.

The COS in the constructed setups was more exaggerated than in the reference case but none of the measured parameters correlated to the depth of the COS. The largest deviation was found on the mesiobuccal cusp tip of the first molar (-0.5 ± 0.4 mm left side; -0.8 ± 0.5 mm right side). This study found a negative correlation between the length and width of the lower dental arch (r = -0.61). While maintaining Angle class I, a large spread width of the depth of the COS, the dental arch width and length was shown.

The different manifestations of the COS in this study show the freedom of arrangement of the individual tooth morphology without exhibiting a correlation to parameters of the dental arch.