ABSTRACT: Orofacial myofunctional disorders include specific conditions or behaviors that can have a negative impact on oral postures and functions. Historically, interest has focused on behaviors in the horizontal plane, highlighted by tongue thrusting. Currently, the scope of practice also includes tongue forward posturing, lip incompetence, open mouth rest posture, thumb and finger sucking, bruxism, and biting habits involving lips, fingers, tongue and cheeks.

The common denominator for myofunctional conditions is a change in the inter-dental arch vertical rest posture dimension, the dental freeway space. The purposes of myofunctional therapy include normalizing the freeway space dimension by eliminating noxious habits or postures related to freeway space change. Improving cosmesis with a lips-together rest posture is also an important treatment goal.

The clinical significance of the freeway space is explained in terms of the dental consequences of differential eruption patterns that can develop from postural modification of the freeway space. When the freeway space is opened for extended periods beyond the normal range, the tongue can act as a functional appliance and contribute to the development of anterior open bite for a Class II malocclusion.

A clinical procedure is proposed for evaluating the freeway space dimension and incorporating the information into treatment planning and evaluation of treatment success. While dentistry/orthodontics has a primary focus on dental occlusion, or teeth-together relationships, orofacial myologists focus on teeth-apart behaviors and postures that can lead to, or have already resulted in malocclusion.

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Key Words: Freeway space, myofunctional disorders, scope of practice, functional appliance, clinical assessment.