Occlusal interferences entail painful muscular changes from the static as well as dynamic viewpoint. On the basis of this hypothesis, the causes for occlusal interferences were to be detected by means of clinical findings and model findings. In accordance with an earlier study by the author, the following main causes were found in 212 juveniles (98 without and 114 with orthodontic treatment) in the age of 12 to 15 years: occlusal interferences are dut to premature contacts and lacking disclusion. The juveniles were classified according to the type, causes, and consequences of their occlusal interferences. 178 juveniles had occlusal interferences and 34 had physiological occlusions.