The appliances originally developed by George B. Crozat are a special form of orthodontic treatment appliance. The basic device, comprising lingually or palatally attached brackets made of heat-treatable 1.3-mm steel wire, can be extended with springs and hooks for elastics. The Crozat appliance controls growth forces during natural development of individual supportive tissues that are in the transitional stage during child facial development. The normal existing forces are directed into the "correct" path by gentle mechanical effects with a Crozat appliance; external forces applied are below-threshold stimuli and hence act through continuity.
The treatment is performed with extended appliances over prolonged periods of time and can last until the end of normal dentition growth. Treatment breaks are observed to allow growth reactions and analyze the state of the dentition for the next treatment phase. Alveolar bone growth is stimulated so that occlusal leveling can be performed and deep bites can be remedied. An es-thetically and functionally satisfactory outcome is achieved, and neither tissue damage nor tooth loosening results from bone and root resorption.
The advantages of a Crozat appliance include the following:
- Moderate forces cause no tissue damage.
- Its slender frame facilitates self-cleaning.
- The appliance is esthetically acceptable.
- It has good wearing characteristics due to its slender frame.
- It causes virtually no speech restriction.
- It is easy to fabricate and handle.
The disadvantages of a Crozat appliance include the following:
- Late cases cannot be treated successfully.
- It requires a very long treatment period.
- The appliance is very susceptible to distortion.
- The patient's cooperation is required over long periods of time.
The practicability of Crozat appliances lies mainly in the support of sagittal and transverse den-
tal arch development. Single-tooth movement in a lingual or vestibular, mesial or distal direction as well as correction of tipping and rotation are possible with these appliances. It is even possible to eliminate occlusal discrepancies by means of maxillomandibular bracing with elastics.
Throughout the treatment period, the patient is always able to wear the same appliance because the appliance is a basic device that is extended or reduced in response to treatment progress. Furthermore, the appliance can be adapted to the enlarged, grown state of the dentition on a later model as it is bent to fit the new situation. Subsequent heat treatment removes stresses and strain hardening of the material so that the appliance regains adequate mechanical properties.
The basic appliance comprises the body wire and the retentive components in the posterior region; from there in a lingual direction lie two activatable wire arms directed mesially and in the maxilla two short bars directed buccally to the retentive components. These lingually and buccally placed extensions are attachment points for extending the appliance with bars, springs, and hooks. The lingual extensions can be activated and used for tooth movement. The individual components must be bent separately, then soldered together.
The body wire is formed by the transverse palatal bar in the maxilla (Fig 10-61) and by the lingual bar in the mandible (Fig 10-62). The body wire is shaped from 1.3-mm wire and runs from one retentive component (usually at the first molar) to the other half of the jaw. The wire must not touch the mucosa. The body wire is shaped to follow the normal course of a sublingual bar, which creates a 4-mm gap from the cervical margins without interfering with the floor of the mouth. It is soldered to the distolingual portions of the retentive components and can be activated for dental arch expansion by being bent open in the anterior curvature area. In the maxilla, the body wire runs transversally over the palatal vault and is fitted with an omega-shaped middle loop for activation. The middle loop is shaped to be large or small, depending on the degree of arch expansion. If the loop is bent open, spring force for lateral arch expansion arises. The maxillary wire also does not lie against the mucosa and is soldered distolin-gually with the retentive components.
Springs can be attached to the Crozat appliance to move the incisors (Figs 10-63 and 10-64).
The retentive components of the Crozat appliance are the Jackson clasps on the first molars (see Fig 10-61). This clasp is a closed wire loop made of 0.8-mm material that fits closely to the tooth on all sides (Fig 10-65). The Jackson clasp encircles the tooth bodily without itself having a clamping effect. Instead, four vertical clasp parts roughly parallel to each other lie in the mesial and distal interdental spaces and provide excellent control of the clasp. The clasp parts running vestibularly and lingually fit closely to the tooth horizontally. In the approximal area, the transverse parts of the clasp running from the lingual in a vestibular direction are fitted to the tooth without rest contact.
The functional supports of the clasp are the vertical wires at the four corners of the molars, which are known as uprights and fit as firmly as possible in the interdental spaces. The clasp has an occlusal rest to prevent it from slipping off in a cervical direction. This rest runs from the lingual in the central groove between the lingual cusps occlusally and is bent out of 1.0-mm wire profile and soldered.
The clasp effect of the Jackson clasp is produced with an additional crescent archwire. This crescent runs below the buccal part of the clasp and projects beyond the vertical part deep into the interdental spaces. The archwires are soldered to the buccal part in the middle.