The Effects of Tongue Position on Mandibular Muscle Activity Charles R. Carlson, PhD The purpose of this study was to determine the relationship Jeffrey J. Sherman, MA between tongue position and mandibular muscle activity. Thirty- three subjects (28 tvomen) between the ages of 18 and 34 years Jamie L. Studts, MS (mean = 22.1 years) with no prior injury to or pain in the jaw, Department of Psychology and mouth, or tongue participated in the study. Subjects were asked to Orofaeial Pain Center rest quietly while baseline electromyographic recordings were University of Kentucky made from the temporaiis, masseter, and suprahyoid muscle Lexington. Kentucky regions. Afterwards, subjects were randomly assigned to condi- tions requiring them to position the tongue either "against the Peter M. Bertrand, DDS anterior palate " or "on the floor of the mouth, making sure the tip National Navai Medical Center Bethesda, Maryland does not press against any part of the mouth." The results indi- cated that right temporaiis activity was higher when the tongue Correspondence to: was positioned against the roof of the mouth than when it was Dr Charles R. Carlson, PhD either at baseline or resting on the floor of the mouth (P < .03). A Department of Psychology similar pattern of results was observed for the suprahyoid muscle 112 Kastle Hall group (P < .01). There were no significant differences in masseter University of Kentucky muscle activity as a function of tongue position (Ps > .20). These Lexington, Kentucky 40506-0044 findings suggest caution in labeling the "rest" position of the Fax: (606)323-1979 tongue and indicate that further study of the relationship between tongue position and orofacial pains is needed. I OROFACIAL PAIN l997;ll:291-297. key words: muscle activity, electromyogram, tongue position ver the past 10 years, experimental data in the fieid of temporomandibular disorders (TMD) are forcing health Opractitioners to revise their understanding of the etiology and maintenance of these phenomena. Issues such as the reiation- ship between occlusion and TMD pain, the so-called vicious cycle of muscle tension and pain, and the effectiveness of occlusal splint therapy have been examined under more stringently controlled sci- entific conditions.''- With the efforts of many clinical researchers, well-designed research studies have hegun to establish a founda- tion of knowledge upon which to develop treatment options. It is from within that tradition that the current study was conceived. It is common for dental and physical therapy practitioners to instruct patients on the correct "rest" position for the tongue.^"-^ Rocahado's 6X6 program^ for treatment of craniocervical and craniomandibular system disorders emphasizes that the dentist must teach the patient the correct "rest" position of the tongue. Specifically, he recommends that the tip of the tongue should be maintained against the palate with slight pressure. Rocabado fur- ther states that in this position, masticatory muscle activity is at a Journal of Orofacial Pain 291 Carlson et al minitnum. No scientific data in the lirerature, from instructions that the usual and customary rest either in the form of electromyography (EMG) or position of the tongue is on the roof of the inunrh. self-report findings, were found to substantiate this The present investigation was conducted tn IIIL:;I- claim. Therefore, this recommendation concerning sure the activity in masticatory muscle grmiRS the "rest" position of the tongue currently may be wben the tongue is placed either on the palate or hased more on clinical lore than on data derived on the floor of the mouth. It was predicted that from careful scientific study. positions of the tongue requiring even slight pres- sure or overcoming gravitational forces (ie, tongue Both the degree of muscle activity associated on the palate) would involve greater muscle activ- with tongue positioning and the association be- ity in the orofacial region than would positioning tween tongue position and the development or the tongue without pressure and resting it on the maintenance of TMD are unclear at this point. bottom of the mouth. Intuitively, this resting posi- However, there are some reasons for concern with tion would not involve muscle activity or energy labeling rhe tongue placement on the roof of the expenditure to oppose the force of gravity, unless mouth as a "rest position." First, maintaining pres- the weight of the mandible and tongue would sure agaitist rhe palate would require recruitrnent require an increase in elevator muscle activity to of some muselé fibers, and such muscle activity maintain the position. Scientific studies of tem- would be tnconsistcnt with the term "rest." Sec- poromandibular functioning are important in iden- ond, if the person were upright, muscle activity tifytng those factors contributing to the develop- and energy would need to be expended to over- ment and maintenance of dysfunction from those come the force of gravity. Goodheart' describes that anecdotally appear to play a role. the difference hetween what a dentist might call a "physiologic rest position of the mandible" and what a physiologist might tertn the "postural posi- tion of the mandible." He states that the term Materials and Methods "physiologic rest" is inappropriate because the postural position of the mandible requires the mus- Subjects cles innervated by the fifth nerve to contract iust enough to hold the mandible in a balanced state of Thirty-three subjects (28 women) ranging in age equilibrium against gravity. It is difficult to know from 18 to 34 years were recruited from a univer- where this balance lies for the tongue and its sup- sity community to participate in this study. Sub- porting muscles. Third, the constant maintenance jects were screened prior to participation and were of the tongue in this position, if it is not the "nor- excluded if they had any current or prior injury to mal" position, has the potential to produce muselé or pain in the jaw, mouth, or tongue. All subjects fatigue and discomfort because of the effort re- gave informed consent after the procedures and quired to maintain a "relaxed" position.^ hi sum- the voluntary nature of the experiment had been mary, "resting" the tongue against the roof of the explained. While gender representation is obvi- oral cavity with slight pressure very likely involves ously imbalanced, this proportion (85% female) is the use of muscle activity. Without controlled lab- representative of the patients seen for treatment of oratory experiments, however, tbis proposition facial pain complaints.'' Twenty-nine (93.5%) cannot be evaluated. subjects described themselves as Caucasian, two In some cases, there may be a reasonable clinical (6.5%) described themselves as African American, rationale for placing the tongue on the roof of the and two declined to answer. The average height mouth. For example, some patients have excessive for participants was 5 ft 6 in (SD - 29 in). Average translation of the mandible during rotational move- weight was 137 Ih (SD = 29 Ib), and average age ments. With such persons, it is conceivable that was 22.1 years (SD = 3.4 years). This research was correct ¡aw alignment may be obtained by placing approved by the institutional Review Board for the the tip of the tongue on the roof of the tnouth dur- Protection of Human Subjects at the University of ing mandibular rotation.^ Further, to restore ap- Kentucky. propriate mobility and to strengthen the mastica- tory muscles after soft tissue injury or surgery, opening and closing the mouth with the tip of the Experimental Setting tongue on the palate enables the patient to exercise Ail procedures were conducted in a sound-attenu- the muscles within a conrroMed range while re- ated room at tbe Orofacial Pain Genter of the training tbem in proper rotational movement.^ University of Kentucky. Participants were seated However, such instructions are distinctly different upright in a cushioned chair with head support. 292 Volume 1 1. Number 4, 1997 Carlson et al Electromyograph Recordings tongue positions. The order of tongue placement Physiologic measures were recorded using a J&J was randomly assigned. Seventeen subjects began 1-330 compnterized physiograph (J&J Enterprises, with instructions to place the tongue on the roof Poulsbo, WA), which integrated data over l-sec- of the mouth. ond intervals during the data collection trials. During all trial periods, suhjects were asked to Electromyograph sites were monirored using 0.5 keep their lips and teeth slightly apart to control cm- silver/silver chloride surface electrodes. The for facial positioning and to minimize extraneous surface of the skin was cleaned and abraded with movements. While this is also a modification of Rocabado's original instructions, this position has an alcohol swab, and elecrrolyte paste was applied been identified by Rugh and Drago'^ as the posi- to the EMG electtodes before they were attached tion of the mandible at which activity of the mas- to the sktn surface with adhesive collars. The ticatory muscles is minimal. These instructions EMG electrodes were then placed hilaterally on were also included in order to reduce the error the masseter muscles and on the right temporalis variance associated with the multiple positions of muscle according to procedures descrihed by the mandible that subjects might assume. Carlson et al.'"'" Electromyograph electrodes Complete instruction sets are given in Appendix were also placed on the suprahyoid muscle region 1. For each position of the tongue, the full instruc- as descrihed by Lemke and Van Sickels.'- The tions were given at the beginning of the first two monitoring was restricted to these four sites trials and then abbreviated for the last trial, either because a maximum of four EMG channels could as, "up on the roof of your mouth" or as "down be monitored with the available equipment. on the floor of your mouth." All subjects alter- nated positions until three trials were recorded in both positions.