The diversity of embryologic origins of the different parts making up the face; the racial variations in facial morphology; the functional differences observable from one individual to the other; all these are conductive to individual adaptations of the alveolodental system. Although they are devoid of any muscular insertions, teeth are subjected to a sum of physiological forces which determine their position. The mastering of mechanical technics allows to correct, remarkably well, all malpositions; the stability of the resulting effect can be but obtained by respecting fundamental physiological rules. Physiological control tests should, therefore, be included when establishing either the indications or the contraindications for mechanotherapy, the latter representing an outstandingly precise and effective element of treatment.