[Preprosthetic orthodontics: technical aspects of mechanotherapy]

This paper describes the rationale as well as some of the therapeutic tools which may be used during simple preprosthetic orthodontic movements. First a typical bracket is examined: the overall design, the base, the slot and the tie-wings. All those components allow mechanical force transmission from the archwire to the tooth in all three orders of movement. In the classic "edgewise" form of treatment, final placement of the teeth is determined by the bends incorporated into the archwire. Conversely, in the more recent "straight-wire" approach, the angulation of the slot relative to the bracket base provides for an optimal positioning of each individual tooth on the dental arch. Mesio-distal angulation of the roots being referred to as "tip" and bucco-lingual angulation as "torque". The bracket also allows bodily bucco-lingual tooth placement relative to the dental arch as a whole (in-out). Prior to a comprehensive treatment, brackets are placed on teeth according to a standard set of criteria. They must be located midway mesio-distally on the buccal aspect in accordance with the true anatomic longitudinal axis of the root. Its occluso-gingival position however can be slightly adjusted according to the individual needs of the case. In more limited situations, where only a few teeth are moved, those rules have to be adapted since the anchorage teeth are kept stable. Examples are presented which illustrate the key features of limited orthodontic movements. Archwires present themselves in various sections and alloys. The most commonly used metals are stainless steels and the more recently introduced nickel-titanium superelastic alloys.(ABSTRACT TRUNCATED AT 250 WORDS)