Incline and length of guiding elements in untreated naturally grown dentition

The incline and length of guiding elements, i.e. marginal ridges and lingua l surfaces of front teeth, marginal ridges and internal cusp slopes of prem olars and molars, play an important role in dentistry. Since the so far rep orted values differ considerably, it was the purpose of the present investi gation to replicate the measurements, including all the occlusal landmarks proposed and defined by previous investigators. The measurements were perfo rmed on 34 pairs of mounted casts from a selected group of untreated, natur ally grown dentitions from adolescents of mean age 14 years. The upper cast s were mounted with a face bow, the kinematic hinge axis and the left incis ura infraorbitalis representing the posterior and anterior reference points . The lower pinned casts were mounted joint related. All measurements were carried out with a computer-aided, three-dimensional digitizer. The incline s were expressed as angles related to the axis-orbital-plane. Taking the pr oposed occlusal landmarks as a basis, the inclines of guiding elements were found to be in agreement with previously reported values, despite ethnic a nd racial differences of the various study-populations, The values, however , differed markedly when measurements based on individual, functional relev ant landmarks were compared to measurements based on anatomical, easy ident ifiable or mathematically constructed landmarks. The successive decrease of the inclines of the guiding elements from the central incisors to the seco nd molars could be confirmed, the molars displaying very flat inclines. Int erestingly, 9% of the first molars and 21% of the second molars showed nega tive values, pointing to a functional arrangement characterized by a buccal ly oriented occlusal surface of those teeth. Combined with the finding that the length of the guiding elements of the anterior teeth was almost twice as long as that of the posterior teeth, the results corroborate the occlusa l concept of an anterior-posterior sequence of the guiding elements, or a s o-called sequential guidance with front-canine-dominance.