A study of the curves of Spee in healthy individuals with non-abraded teeth

The curves of Spee is an essential component of the sphericity of occlusion and is too often neglected in orthodontic and prostodontic reconstructions. This being said, the different descriptions of the curves of Spee presently available have some clinical shortcomings. First of all using the closest interpolating sphere means that no specific points are utilized and thus precise measurement is made difficult and hazardous. Secondly, using only dental points with no external reference provides no functional considerations. Thirdly, using canines or even the incisors as anterior teeth has provided poor clinical results for the authors and other dental professionals.

The present study analysed the curves of Spee of selected healthy non-abraded dentitions. The posterior extensions of these curves constructed from specifically chosen points were studied as to their proximity to the true hinge axis. The exclusion of the canines in the curves of Spee was investigated.

The radii obtained showed a great degree of individual variability. The Student’s t-test was used for comparison purposes.

The results clearly demonstrate that the canines are not part of the curves of Spee. The true hinge axis does not coincide with the circle formed by the lower cusp tips of the following teeth: canine, mesiobuccal of the first molar and distobuccal of the second molar. It is impossible to conclude that the true hinge axis does not coincide with the circle formed by the lower cusp tips of the first premolar, mesiobuccal of the first molar and distobuccal of the second molar. This conclusion may be influenced by the small size of the sample and also by the possibility that the true hinge axis does coincide with the circle formed by these teeth. The averages and standard deviations of the curves were compared to other similar investigations.