Tongue dysfunction screening: assessment protocol for prescribers

The tongue rehabilitation technique developed by the physiotherapist Maryvonne Fournier may be prescribed in several medical disciplines: dentistry, orthodontics, oral and maxillofacial surgery, ENT, pulmonology, pediatrics, neurology and geriatrics. Other health care providers, such as speech therapists and dental hygienists, have also taken an interest in the technique. The aim of this article is to present a simplified non-operator-dependent version of the tongue dysfunction assessment protocol implemented in maxillofacial physiotherapy, that can be used by practitioners in all fields.


INTRODUCTION
for tongue posture and function maturity. According to Fournier 9 , it would be 2 years (establishment of deciduous dentition); according to Chateau 8 , 3 years (stable deciduous dentition); according to Woda and Fontennelle 39 , primary tongue posture and function is dysfunctional if it persists after 10 years (transition from stable mixed dentition to adolescent dentition: a period of occlusal instability with lateral sector (teeth 3, 4 and 5) change). These differences in prevalence and age-threshold for dysfunction may be related to patient recruitment, treatment practices and requirements, and/ or care providers: physiotherapists, speech H. GIL, N. FOUGERONT therapists, orthodontists, pediatric dentists; they may also, however, be due to non-standardization of diagnostic criteria.
The aim of the present article is to specify diagnostic criteria. Persistent primary lingual function does not in itself spell disorder; when, however, the impact of the dyspraxia is patho-genic, detection is vital and urgent, to allow early correction. The present assessment protocol is intended for dentists, orthodontists, maxillofacial surgeons, ENT specialists, pulmonologists, pediatricians, neurologists and geriatricians. In all these specialties, complete maxillofacial rehabilitation can enhance treatment efficacy.
Maxillofacial rehabilitation is not taught in all physiotherapy schools, and practitioners able to assess and rehabilitate the tongue are not always easy to find. The present protocol was therefore designed with prescribers in view, to detect tongue dysfunction and associated disorders. "Difficult" patients, with iterative consultation, are not rare; they may present orthodontic and/ or surgical recurrence 30 , temporomandibular disorder (TMD) pain (Table I) 18,19,20,29,31 (frequently associated with migraine or tension headache) 15 , respiratory disorder (oral respiration, rhonchopathy, obstructive sleep apnea syndrome (OSAS) 24,36 , and/or hearing loss due to Eustachian tube dysfunction 37 .
All these pathologies have one thing in common: tongue dysfunction. Most of these so-called "difficult" patients have another thing in common: they have already tried many other treatments and consulted many other therapists. To resolve the problem of this medical market-place which reduces the quality of health care and increases public health costs, prescribers need a means of knowing whether lingual rehabilitation should be undertaken or not, so as to avoid the many cases of recurrence. In terms of means, certain tongue dysfunctions can be treated simply by counseling, or by neuromuscular training using devices such as Bonnet's nocturnal lingual envelope 5,6,23 . Not all cases require specialized physiotherapy. The tongue body occupiesthe oral cavity and, behind the lingual V, the tongue base occupies the oropharynx down to the hyoid bone. The tongue comprises two muscle groups 3 , all innervated by the hypoglossal nerve (XII), the motor nucleus of which is organized somatotopically between protrusion and retrusion muscles 24,25 . The extrinsic muscles have bone insertions, and comprise: styloglossus, hyoglossus (retrusion) and genioglossus (protrusion). The intrinsic muscles (vertical, transverse, superior longitudinal and inferior longitudinal) have no bone insertion. The palatoglossus muscle of the anterior pillar of the soft palate (innervated by vagus nerve X) is considered rather to be a soft palate muscle like its counterpart, the palatopharyngeal muscle (posterior soft-palate pillar). Finally, the geniohyoid and mylohyoid muscles (innervated by the trigeminal nerve V) belong to the floor of the mouth, and contribute to tongue mobilization.

INTEREST OF AN ASSESSMENT PROTOCOL FOR NON-PHYSIOTHERAPISTS
The tongue is mainly active in respiration, swallowing, mastication and phonation 25 . Lingual muscle action is also interrelated with mandibular motility and posture 24,25 , which normally involves intersegmental coordination between the motor nuclei of V, VII (facial nerve) and XII; this may be why, according to Fournier 9 ,lingual rehabilitation contributes to recovering mandibular mobility. The pressure exerted by the tongue during swallowing is 75 g/cm 2 in the anterior palate and 140 g/cm 2 in the lateral sectors 25 , making the tongue essential in dento-dental and dento-maxillary balance and facial morphogenesis 5,6,10,23 . Over and above function, however, the habitual posture of the tongue has a continuous impact on morphogenesis 23,30 . When the tongue is dysfunctional, it is defective in all three functions (Chateau's "triptych" principle): position at rest, swallowing and phonation. When any one of these is impaired, the others are sure to be also.

Tongue posture
Tongue posture changes with age 9 , but there is no consensus on maturation age. At birth, all babies have a protruding, outspread tongue. Between 4 and 6 months, the tongue begins to withdraw, behind the dental arcades. At 6-8 months, it begins to become more vertical. Between 15 and 18 months, muscle development increases mobility within the oral cavity in all directions. according to Fournier 9 , by 2 years the tongue should have acquired a position with the tip on the palate, thanks to increasingly precise somesthetic contact. The age of 2 years also is that of pyramidal system motor maturity, with control of postural tonus and the beginnings of precise "idiokinetic" motricity (fine distal idiokinetic motricity is an essential element, under pyramidal system control, in contrast to the more proximal and approximate "holokinetic" motricity, which is basically under extrapyramidal control), independent movement of each limb, and inhibition of primary reflexes 1 . The functional tongue shows balance between agonist and antagonist muscles, retracting and curving the H. GIL, N. FOUGERONT tongue, and protruding and spreading it, respectively. This balance ensures the resting position of the tongue: -position in which tongue-base tonus is lowest; -with apex in contact with the retroincisor buds ("contact" here meaning just touching or next to, and certainly not pushing against); -tip of the tongue on the palate, at a postero-inferior angle toward the pharynx, thus dilating the fauces isthmus; -when the patient's lips are gently opened and the mouth is not in maximal intercuspal occlusion, the ventral side of the tongue is visible, with a space between it and the dental arcades.
tion in fish, and is thus older than air respiration, which appeared only with terrestrial vertebrates (tetrapods) 2 . At birth, babies show the primary, immature swallowing known as suction-swallowing. According to Fournier 9 , at the age of 2 years suction-swallowing should give way to secondary, mature swallowing, and if the resting position of the tongue is not established by then, it never will be spontaneously.
Swallowing has 3 stages: oral, pharyngeal and esophageal; it finishes at the cardia when the bolus passes into the stomach. The oral and pharyngeal stages overlap (isthmic stage, crossing the fauces isthmus formed by the anterior pillars of the velar palate and palatoglossus muscle), which is why the term "oropharyngeal stage" is often used; this lasts about 1 second, whereas the esophageal stage may last more than 8 seconds. The tongue is involved in the oral and pharyngeal stages 25 .
Neurophysiologically, swallowing is a reflex governed by a segmental central pattern generator in the reticular formation of the spinal bulb. It can be triggered reflexively, by stimulation of Wassilieff's reflexogenic zone (tongue base and oropharynx posterior to the anterior pillars of the velar palate), or voluntarily, by the cortical masticatory area in the M1 motor cortex, although only the oral stage is influenced by M1; this cortical regulation explains why rehabilitation of the oral stage is clinically possible. In primary, immature lingual motricity, the platysma muscles (VII) predominate over the masticatory muscles (V), whereas in secondary motricity it is the converse 39 ( fig. 1).

Swallowing 2,11,12,39
Swallowing is a sequential reflex of the oral, lingual, pharyngeal, laryngeal muscles and esophagus, enabling active oral-aboral transport of solid and liquid food and saliva (upper digestive tract lubrication) to the stomach. It requires motor coordination between swallowing and respiration, and transient mechanical airway closure to prevent foreign-body inhalation. Concomitantly, soft-palate tension allows middle ear ventilation by dilating the Eustachian tube, balancing the pressures on either side of the tympanum, between middle and outer ear.
Ontogenetically, swallowing appears at the 12 th week in the fetus, whereas suction does not appear until the 24 th week. This is phylogenetically understandable, as swallowing is an ancestral function ensuring food ingestion and branchial respira-5 TONGUE DYSFUNCTION SCREENING: ASSESSMENT PROTOCOL FOR PRESCRIBERS In swallowing solid food or saliva, which happens about 1,200 times per 24-hour cycle, the mandible is blocked in maximal intercuspal occlusion, with an occlusion force of about one-tenth of maximal bite strength, while during the swallowing pause in maximal intercuspal occlusion it is about one-third. In contrast, the pause is longer (400-600 ms) in swallowing than in mastication (200 ms) (reference in ref. 12), while in swallowing liquid, the blockage in maximal intercuspal occlusion is unnecessary, and swallowing is similar to the immature function.

Phonation 4
Palatal consonants (L, N, D and T): assessment criteria and thus procedures differ from therapist to therapist, due to differences in definition of palatal consonants. In French speech therapy, D and T are called "apicodental occlusive" as occlusion is achieved by applying the apex of the tongue against the superior incisors. The L is an "apicodigital lateral constrictive" , as the tip of the tongue may touch the superior incisors or their alveolae. In physiotherapy, palatal consonants should be produced by the tip of the tongue in contact with the retro-incisor bud without spreading the tongue.
Sibilants (S and Z): in French speech therapy, these are known as "apicodental constrictive" , being produced by approaching the tip of the tongue to the incisors. In physiotherapy, the tongue is withdrawn and should not touch either the inferior or superior incisors.
Palato-alveolar fricatives: SH and ZH: the tongue does not go along the sides.
Fricatives (F and V): the inferior side of the tongue should not be bitten or go under the superior incisors.
Labial consonants (M): the superior side of the tongue descends to touch the lower lip, and both lips move simultaneously.

Respiration
The genioglossus muscle (prime tongue protruder) is essential to maintaining airway permeability, and is activated in time with the in-breath 24,25 . Moreover, in oral breathing, tongue posture is low and anterior 36 . In OSAS, tongue volume, activity and posture are also to be taken into account 24 . The Mallampati (tongue in protrusion) and Friedman (tongue at rest) classifications allow clinical assessment of OSAS severity ( fig. 2). A meta-analysis 16 demonstrat-  The tongue is involved in facial growth and morphogenesis: if it fails to achieve its normal functional position, it may induce dental-maxillary dysmorphism 8 . The pressure of the tongue on the dental arcades may jeopardize orthodontic treatment. In some cases, it may even detach the contention mechanism. The tongue plays an essential part in dento-dental and dento-maxillary balance 8,23 and may induce dysmorphism or, conversely, its behavior may result from adaptation to dysmorphism. The tongue reaches almost its definitive size around the age of 8 years, but in some cases continues to grow in adulthood 32 .
for masticatory impotence and reduced bite force) and weak antagonist activity on opening (accounting for reduced oral opening). In TMD pain, the prevalence of tongue dysfunction is elevated 18,19,31 (Table I). The weak activity of the masticatory muscles (V), due to persistent or chronic musculoskeletal pain, may also induce primary lingual motricity whereby platysma muscle activity (VII) compensates masticatory muscle (V) antagonist hypoactivity 13 . Conversely, immature tongue posture and function may be one of the risk factors for masticator dysfunction. The hypotheses require investigation.
Masticatory apparatus pain according to Lund's pain-adaptation model 13,26,27 , involves paradoxical masticatory muscle activity: antagonist hypoactivity on closure (accounting A badly positioned tongue can form an obstacle to naso-nasal breathing (in and out both through the nose), inducing oral breathing -unless, conversely, oral breathing leads to tongue malpositioning. This may correlate with reduced oral cavity and sinus permeability, stagnation of secretion, iterative ENT infection (rhinopharyngitis, otitis, etc.), or impaired middleear ventilation due to Eustachian tube dysfunction, inducing hearing loss. Lund 27 distinguished 3 categories of patient: (i) bruxism with TMD, (ii) bruxism without TMD, and (iii) TMD without bruxism. In TMD, however, the prevalence of bruxism is greater than in patients without TMD. According to Lund, the higher prevalence of bruxism (muscle hyperactivity) in TMD has led to confusion between the two, with muscle pain being attributed to hyperactivity (on Travell's 38 old vicious-circle theory). However, the two are not to be confused, even if bruxism is doubtless a risk factor for pain in TMD, although we do not really know why or how bruxism causes or maintains TMD in some patients but not others 33 . Normal sleep shows rhythmic masticatory muscle activity (RMMA), which is 3-fold more frequent in sleep bruxism: moreover, H. GIL, N. FOUGERONT RMMA displays elevator/depressor co-contraction, enhancing airway permeability 22 .
In OSAS, sleep bruxism may be a compensatory phenomenon in respiration, explaining their frequent association 28 . It was also recently sug-gested that there are interrelations between bruxism and lingual dysfunction 21 , unless indeed respiratory disorder is the common denominator of bruxism and lingual dysfunctionbut these hypotheses remain to be explored.
There are basically 3 professions practicing tongue rehabilitation: speech therapists, hygienists (dental assistants, in the US and Canada), and physiotherapists. It is interesting to compare their respective approaches, with their differences and common points.  The clinical assessment follows detailed history-taking ( fig. 3).

Tongue
• Resting position -Good position: apex in contact with retro-incisor buds. -Bad positions: between teeth or lips (vertical gap, fig. 4), against palatal side of maxillary incisors (class II1 malocclusion), tip against lingual side of mandibular incisors with back on palate (class II2 malocclusion), low (class III malocclusion, fig. 5), or laterally interposed. In class II1 with severe overhang or class II2 with overlap, tongue position is not visible, and phonetic tests are necessary to assess lingual dyspraxia.
• Frenum -Length normal if interincisor distance on maximal opening is at -Is the tongue still in the same position after treatment? -Is the tongue bent (tooth pressure)? -Particular oral habits (thumb/finger sucking, nail biting)? -Does the tongue touch the teeth in pronouncing "S"? -Does the tongue pass between the teeth on swallowing? -If the patient is an oral breather, is there gingivitis? -Does the patient grit his/her teeth? -Does the patient show chronic stomach pain, eructation, drooling, hiccough? -Does the patient have the head leaning forward? least 3 finger-widths, with apex on palate. -The frenum is too short if the tongue cannot touch the palate in maximum oral opening. In open mouth, the maximum inter-incisor distance at which the tip of the tongue remains in contact with the palate is measured (fig. 7). If the frenum is too short, the tongue may fork.

DIAGNOSTIC CRITERIA FOR DYSFUNCTIONS AND PARAFUNCTIONS
Resting position of tongue

Swallowing
Open the patient's lips slightly, after warning.
-Patients tend to show labial interocclusion. the tongue is visible between teeth/lips. Anterior or lateral dental gap with the tongue in the gap (see fig. 3

Respiration Phonation Parafunctions
It is not just because the patient has the mouth closed and breathes nasally during the day that the same is true at night. Ask: "In the morning, when you wake up, is your mouth dry; do you have a drink during the night; do you have chapped lips?" If the answer is "yes" , there is nocturnal oral respiration and a problem that needs correcting. If the disorder is severe, there may be pinching of the nasal alae on the inbreath. If there is ENT pathology, the tongue must be malpositioned, with oral respiration.
The "DINETTE / TARTINE" palatal test optimally diagnoses lingual dyspraxia, with larger opening and better tongue visibility. When there is no dysfunction, the apex touches the retro-incisor buds on pronouncing L, N, D and T. In dyspraxia, the tongue protrudes. The test also contributes to the patient's awareness, encouraging rehabilitation.
For bad habits, it is useful to ask the same questions at the next appointment. Patients are not immediately aware of their habits, and assessment can enable the practitioner to: -detect lingual dyspraxia; -advise about treatment; -suggest neuromuscular rehabilitation with prostheses; -prescribe maxillofacial rehabilitation.

CONCLUSION
It seems that the greater the number of disorders detected on assessment, the more important it is to initiate rehabilitation early. This is especially true when disorder is associated with parafunction. However, rehabilitation is always difficult when the patient is bearing orthodontic apparatuses (palatal plate, screw-jack plate, quadhelix, etc.). Apart from At the end of maxillofacial rehabilitation, Chateau triptych (resting position, swallowing and phonation) corrections should become reflex: otherwise, there is risk of recurrence. Likewise, all associated problems have to be solved: lip tonus, naso-nasal respiration at rest and under effort, relaxation of tense muscles, bruxism, and posture.
Alongside relaxation, the clinical effects of maxillofacial and lingual rehabilitation are many: masticatory and cervical muscle pain relief, reduced incidence of bruxism and, with associated orthodontic treatment, correction of dentomaxillary dysmorphism due to poor tongue posture. Bruxism may recur, but the patient no longer tolerates it and now has the means to stop it completely.
Recent clinical studies demonstrated the biological effects of physiotherapy in musculoskeletal disorders (non-specific low back and neck pain) and suggested hypotheses 14 . Likewise, pioneering studies showed that tongue exercises crowding, tongue/palate exteroception is vitiated, preventing correction becoming reflex. For some prescribers, the problem is finding a nearby rehabilitation practitioner, and motivating the patient: not all cases require such active rehabilitation: some will respond to a nocturnal lingual envelope, functional rehabilitation, etc. induced neuroplastic modifications in the primary motor cortex (M1) of the lingual muscles, increasing corticobulbar motor neuron excitation and the size of the lingual muscle motor area ( fig. 9) 7,34,35 . (The corticobulbar motor neurons of the cranial nerve motor system constitute the corticobulbar bundle, previously known as the geniculate bundle, which is the counterpart of the pyramidal bundle of the spinal motor system. The corticobulbar motor neurons connect to the cranial nerve motor neurons, and the corticospinal motor neurons to the ventral (motor) horn of the spinal cord. Both ventral spinal horn and cranial motor nuclei form the origin of the α motor neurons commanding the muscle fibers 11 .) Thus, better knowledge of these biological effects should help rationalize maxillofacial rehabilitation as a whole and lingual rehabilitation in particular.