EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...

muscular balance. Successful treatment, as evidenced by permanent stability,
must preserve this muscular balance rather than attempt to alter or upset it.
Moss (1969) described a functional matrix theory that suggests that the
form, position, and maintenance of the denture are secondary responses to the
primary demands of the related muscles acting on it. Moss contended that
change or activity in the surrounding muscles would impact the positions and
stability of the teeth and alveolar bone. This accounts for the many changes that
are commonly seen following active orthodontic treatment. The muscles and soft
tissues become the natural retentive forces of the newly acquired position of the
dentition, so aberrant muscle actions present during swallowing, speaking,
chewing, or breathing are likely to manifest themselves on the dentition and
skeletal bases.
Huckaba (1952) referred to the soft tissue environment when he suggested
that the natural forces of retention must be considered when treatment is
planned. If this is not done, the forces of retention may become the forces of
relapse. Moss’s model supports the use of various functional appliances such as
the Fränkel appliance (Fränkel and Fränkel 1989) and the lip bumper. Such
appliances act on the surrounding tissues in an effort to change muscle and
tissue functions to allow for a balance between soft tissues and the newly
acquired position of the dentition.
In an effort to study the effects that muscles can have on the form of
bones, Moyers (1949) used electromyography to study the electrical phenomena
occurring within muscles as a means of analyzing the nature of the muscle
contraction, particularly the role of the temporomandibular musculature in the
etiology of Angle Class II malocclusions. By measuring the electrical impulses, it
became possible to achieve a more accurate understanding of muscular forces
present in the oral environment.
At the University of Washington, Proffit et al. (1964) evaluated 25 young
adult dental students ranging in age from 22 to 32 years old to record tongue and
lip pressures against the dentition in a “normal” sample of people. Three stain
gauge pressure transducers were placed intraorally for each subject so as to
allow simultaneous recording: (1) labial to the maxillary central incisors, (2)
lingual to the maxillary central incisors when the teeth were in occlusion, and (3)
lingual to the maxillary first molar. Intraoral pressures were found to vary
greatly among individuals, but on average were less than had been previously
recorded in the literature (Gould and Picton 1962; Weinstein et al. 1963).
Increasingly higher pressures, as a result of greater tongue and buccinator
muscle involvement were recorded as the transducer was moved farther distally
into the cheek space, which supported similar findings of Weinstein et al. (1963).
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