Tongue Thrust

Robert M. Mason

In clinical examinations in dentistry and speech pathology, many clinicians have observed that some patients with malocclusion exhibit a protrusive tongue tip pattern against or between the anterior teeth during swallowing or speaking. This observation has led some clinicians to assign a causal relationship between thrusting of the tongue tip and the open bite or excessive incisor protrusion noted during examination.

There is a natural tendency for a clinician to presume a cause and effect relationship from two observations noted in examination. With regard to the mutual occurrence of tongue protrusion and anterior dental malocclusion, it is understandable for a dentist or speech pathologist to wonder about a causal link for these conditions.

Some clinicians have become strong advocates for the notion that teeth are pushed into a new, abnormal position by thrusting (and abnormal) activities of the tongue in swallowing, and to some extent, in speaking. Such advocates recommend a therapy regimen to retrain tongue activity in swallowing that is referred to as "myofunctional therapy" (Garliner, 1971).

Tongue thrusting in children or adults has produced a great deal of speculation and controversy as to the effects of this behavior on tooth position. Such a controversy is appropriate, as the remediation processes of myofunctional therapy for tongue thrusting involve a considerable investment of time, money, and patient motivation. While some dentists and speech pathologists feel strongly that tongue thrusting has a deleterious effect on tooth position (Garliner, 1971; Pierce, 1978), other clinicians contend that tongue thrusting is a normal transitional behavior and does not merit any therapy before puberty or, in most cases, ever (Mason and Proffit, 1974).

The controversy about the possible effects of tongue behavior during swallowing on tooth position prompted the American Speech and Hearing Association (ASHA) to request a position statement from the Joint Committee on Dentistry and Speech Pathology. This committee was supported by the National Institute for Dental Research and is comprised of selected members of the American Speech and Hearing Association and the American Association of Dental Schools. The Joint Committee's Policy Statement on tongue thrust was adopted by the ASHA Legislative Council in 1975, and by the House of Delegates of the American Association of Orthodontists in 1977. The policy statement is:

Review of data from studies published to date

has convinced the Committee that neither the validity of

the diagnostic label tongue thrust nor the contention
that myofunctional therapy produces significant consis-
tent changes in oral form or function has been documen-
ted adequately. There is insufficient scientific
evidence to permit differentiation between normal and
abnormal or deviant patterns of deglutition, particularly
as such patterns might relate to occlusion and speech.
There is unsatisfactory evidence to support the belief
that any patterns of movements defined as tongue thrust
by any criteria suggested to date should be considered
abnormal, detrimental, or representative of a syndrome.

In view of the above considerations and despite our recognition that some dentists call upon speech pathologists to provide myofunctional therapy, at this time, there is no acceptable evidence to support claims of significant, stable, long term changes in the functional patterns of deglutition and significant, consistent alterations in oral form. Consequently, the Committee urges increased research efforts, but cannot recommend that speech pathologists engage in clinical management procedures with the intent of altering functional patterns of deglutition. (1974)

While the position statements of the American Speech and Hearing Association and American Association of Orthodontists relegates the tongue thrust controversy to a moot level, there are, nonetheless, no established guidelines to date for increased research efforts.

The purpose of this report is to recast the tongue thrust issue in a palatable form, and to provide a perspective about myofunctional therapy for tongue thrusting that will not be such a bitter medicine for some to swallow.

What Is Tongue Thrust?

It

At present, tongue thrust has no single title or definition. is variously referred to in the literature as tongue thrust (Hanson, 1967), tongue thrust swallow (Fletcher, Casteel, and Bradley, 1961), visceral swallow (Ward, Malone, Jann, and Jann, 1961), infantile swallow (Leighton, 1960), reverse swallow (Barrett, 1961), deviant swallow (Garliner, 1964), tongue thrust syndrome (Palmer, 1962; Jann, Ward, and Jann, 1964), and most recently, orofacial muscle imbalance (Garliner, 1971).

The most frequently cited signs of tongue thrust include protrusion of the tongue against or between the anterior teeth and excessive circumoral muscle activity during swallowing (Weinberg, 1970). These behaviors,

however, have been reported to occur variously in normal subjects (Rosenblum, 1963; Ardran and Kemp, 1955; Cleall, 1965). The confusion evident in defining tongue thrust as a condition outside the range of normal raises obvious difficulties in studying tongue thrusting in clinical samples. Many of the pertinent issues associated with tongue thrust have been reviewed in papers by Weinberg (1970), Moorrees, Burstone, Christiansen, Hixon, and Weinstein (1975).

The common denominators of tongue thrust appear to involve one or a combination of three conditions: (1) during the initiation phase of a swallow, a forward gesture of the tongue between the anterior teeth so that the tongue tip contacts the lower lip; (2) during speech activity, fronting of the tongue between or against the anterior teeth with mandible hinged open (in phonetic contexts not intended for such placements); and (3) at rest, the tongue carried forward in the oral cavity with mandible hinged slightly open and tongue tip against or between the anterior teeth. All of these conditions are also found in individuals who have no speech or dental problems.

What Problems Are Associated With Tongue Thrust

Advocates of myofunctional therapy for tongue thrust contend that uncorrected tongue thrusting during swallowing or speech can produce or maintain dental malocclusion in children and adults. Specifically, they consider it a primary etiologic factor in open bite and incisor protrusion (Straub, 1951; Garliner, 1964; Pierce, 1978). Others doubt that tongue thrusting is anything more than a normal developmental stage (Ward et al., 1961; Shelton, 1963; Bell and Hale, 1963; Hoffman and Hoffman, 1965; Mason and Proffit, 1974). The Position Statement by the Joint Committee on Dentistry and Speech Pathology supports the normal developmental nature of tongue thrusting.

A perspective about the possible relationships between tongue thrusting and incisor protrusion and anterior open bite can be appreciated by examining the incidence figures for these conditions. It is generally accepted that all infants exhibit tongue thrusting during deglutition, and that about 50% of children at age 6 are tongue thrusting. By age 15, the percentage has decreased to about 25% (Fletcher, Casteel and Bradley, 1961; Hanson and Cohen, 1973). In a U. S. Public Health Service sample of some 8,000 children, 5.6% of children between the ages of 6 and 11 years had an anterior open bite, while about 17% had excessive incisor protrusion (Kelly, Sanchez, and Van Kirk, 1973). These data indicate that tongue thrusting occurs much more frequently than the dental conditions linked etiologically to the behavior.

To date, no research has reported the relative occurrence of an anterior resting tongue posture in tongue thrusters. Research pertaining to tongue thrust has focused on the characteristics of the tongue thrust swallow rather than the resting posture of the tongue. The emphasis on

the swallow behavior in tongue thrust with the omission of data
on resting tongue position is an unfortunate exclusion of important
data, as it appears that the teeth are relatively insensitive to
pressures from the tongue in function (Proffit, 1972).

What Have Pressure Transducer Studies Revealed About Tongue Thrust?

Proffit and coworkers have done much to provide a reasonable perspective about the relative importance of functional activities of the tongue and the resting posture of the tongue. Using miniature pressure transducers mounted in acrylic appliances in various locations in the oral cavity, Proffit and coworkers have found that tongue pressures in speech and swallow are not significantly different in tongue thrusters and nonthrusters (Proffit, Chastain, and Norton, 1969; Proffit, 1972; McGlone and Proffit, 1973; Proffit, 1973; Wallen, 1974). When tongue functions are catalogued in patients with incisor protrusion, the data reveal a pattern of anteriorly directed pressure inverse to the degree of protrusion (Proffit, 1978). That is, the greater the incisor protrusion, the less are horizontally directed tongue pressures in swallow. In the vertical plane of space, Wallen (1974) found that patients with open bite malocclusion exhibited an inverse relationship between degree of anterior open bite and vertically directed tongue pressures in deglutition. Swallow pressures in the horizontal plane of space, however, were normal in the open bite sample.

Intraoral pressure transducer studies do not support the empirical observations of myofunctional therapy advocates regarding the causeeffect relationships presumed between tongue thrusting and anterior tooth position.

Oral pressure transducers have been used to study speaking and swallowing activities and associated orofacial muscle functions in normal individuals and in patients with lisping, tongue thrusting, and surgical repositioning of the jaws (orthognathic surgery). many insights that have been revealed from these studies by Proffit and associates can be summarized as follows: (1) the swallows of children are characterized by variability, one swallow from another in serial repetition and over time; (2) there are many transitional swallow patterns (from 3 to 10) that a child passes through on the road to an adult swallow pattern; (3) the swallows of adults are stable and highly predictable as per pressure pattern and contact site with the maxillary apparatus; (4) tongue pressures directed horizontally against the teeth by tongue thrusters are not sufficient in force or duration to push teeth into a new position; (5) tongue pressures directed vertically against the teeth in swallowing and speaking are less for open bite patients than in non-tongue thrusters with normal anterior dentition; (6) orthognathic surgery patients adapt tongue pressure and contact patterns to the environment created, usually within a one-year span;

(7) tongue and lip pressures never balance during swallowing, and tongue pressures are always several times higher (corroboration of earlier research by Lear and Moorrees, 1969); (8) tongue and lip pressures during swallowing do not correlate well with tooth position (supportive of previous work by Lear and Moorrees, 1969); (9) the duration of tongue and lip pressures over time do not balance out to create an equilibrium (original work by Lear and Moorrees, 1969); and (10) resting tongue and lip pressures do not balance out over time (Gorbach, 1972). Altogether, the findings and impressions gleaned from oral pressure transducer studies indicate that functional activities of the tongue (speaking and swallowing) are not important determinants of tooth position, but an anterior resting tongue position and associated continuous vertical pressure against the anterior teeth can contribute to or maintain an anterior open bite malocclusion (Proffit, 1972; Mason and Proffit, 1974; Proffit and Mason, 1975; Proffit, 1978). Excessive incisor protrusion is not apparently linked to the

tongue in creating or maintaining the problem.

Why Does Tongue Thrusting Usually Self Correct At Puberty?

It is a common observation that the child who is a tongue thruster and has an anterior open bite at age 6 does not have a tongue thrust and open bite at age 12 years. While the spontaneous remission of open bite and tongue thrusting does not occur in every patient, a significant number of patients experience this. There are no good longitudinal data for the mutual and coincident self-remission of tongue thrusting and open bite malocclusion with maturation and dental eruption. It is a common clinical observation that tongue thrusting will persist as long as the open bite is present.

Worms, Meskin and Isaacson (1971) found that 80% of anterior, simple open bites spontaneously corrected in a cross-sectional sample of 1408 Navajo boys between the ages of 7 and 9 years. While some researchers may argue against the 80% figure as an inference from cross-sectional data collected, it should be accepted that a significant number of open bites spontaneously correct as children pass through puberty.

The opportunity to catalogue lingual pressure patterns on a longitudinal and cross-sectional basis has permitted the correlation of such data with other clinical records. The comparison of pressuretransducer records with lateral cephalometric x-ray films and dental study models suggests several morphologic reasons as to why tongue thrusting spontaneously remits in most patients at puberty (Proffit and Mason, unpublished studies). The contingent variables are associated with the posterior airway dimensions.

We have observed clinically that tongue thrusters with anterior open bite tend to possess the following constellation of morphologic characteristics: 1) a short mandibular ramus; 2) a small oral isthmus, both horizontally and vertically (the horizontal diameter is reduced.