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Arch Development Under developed arches are a very common skeletal problem. They are primarily the result of incorrection tongue function and the lack of nasal respiration. When this problem exists in the upper arch the entire maxilla is underdeveloped. In the lower arch, it is only the dental alveolar base, as opposed to the corpus (body) of the mandible.
The maxilla is usually developed in the primary and mixed dentition with Schwarz type of appliances. This allows the functional force to be placed directly on the bone, and not on the deciduous teeth. In the permanent dentition, the arch developing appliances are most often Light Wire appliances such as the ALF, and the RN-Sagittal.
When the patient has an underdeveloped maxilla, there is usually not arch length loss unless deciduous teeth have been lost prematurely. This is not true in the lower arch. Active “mesial drift” can cause arch length loss if the cuspids lose their key stoning effect in the narrow arch.
Appliances like Schwarz work well to develop the transverse width of the arch, but they do not recover lost arch length. When the lower arch is narrow with arch length loss in the mixed dentition the Williams is the appliance of choice. The same situation in the permanent dentition is usually treated with an A.L.F. appliance.