Assessment of posterior tongue mobility using lingual‐palatal suction: Progress towards a functional definition of ankyloglossia

Abstract Background A functional definition of ankyloglossia has been based on assessment of tongue mobility using the tongue range of motion ratio (TRMR) with the tongue tip extended towards the incisive papilla (TIP). Whereas this measurement has been helpful in assessing for variations in the mobility of the anterior one‐third of the tongue (tongue tip and apex), it may be insufficient to adequately assess the mobility of the posterior two‐thirds body of the tongue. A commonly used modification is to assess TRMR while the tongue is held in suction against the roof of the mouth in lingual‐palatal suction (LPS). Objective This study aims to explore the utility and normative values of TRMR‐LPS as an adjunct to functional assessment of tongue mobility using TRMR‐TIP. Study Design Cross‐sectional cohort study of 611 subjects (ages: 3‐83 years) from the general population. Methods Measurements of tongue mobility using TRMR were performed with TIP and LPS functional movements. Objective TRMR measurements were compared with subjective self‐assessment of resting tongue position, ease or difficulty elevating the tongue tip to the palate, and ease or difficulty elevating the tongue body to the palate. Results There was a statistically significant association between the objective measures of TRMR‐TIP and TRMR‐LPS and subjective reports of tongue mobility. LPS measurements were much more highly correlated with differences in elevating the posterior body of the tongue as compared to TIP measurements (R2 0.31 vs 0.05, P < .0001). Conclusions This study validates the TRMR‐LPS as a useful functional metric for assessment of posterior tongue mobility.


| INTRODUC TI ON
Restricted tongue mobility has long been appreciated to impact speech, 1,2 feeding 3,4 and oral hygiene 5 and more recently has also been potentially implicated in maxillofacial development, 6,7 mouth breathing, 8 myofascial tension 9 and even sleep-disordered breathing. 10,11 Whereas ankyloglossia (tongue-tie) has been described as a condition of restricted tongue mobility caused by a restrictive lingual frenulum, 12 there are many other causes for impaired tongue mobility (such as airway obstruction and lack of generalised practice, as well as inadequate tongue space and extraoral fascial restrictions, among other factors) that are often underappreciated. 9 The term 'functional ankyloglossia' is used to characterise limitations of tongue mobility that may or may not be directly attributable to a structural restriction in the lingual frenulum. 13 The lingual frenulum is a dynamic three-dimensional structure formed by a central fold in a layer of fascia that extends across the floor of the mouth with high degree of morphologic variability between different individuals. 14 The presence or absence of a short or tight lingual frenulum alone may or may not be directly associated with impairments of tongue mobility. 15 Many patients with restrictive lingual frenulum may have only minor difficulties and may compensate for limitations in tongue movement. 16 Patients may compensate for tongue movement, for example by lifting the mandible and/or the floor of the mouth. 9 The compensations, in some cases, may not be benign and can be the genesis of future oro-facial myofunctional or temporomandibular disorders. 33 The word 'ankyloglossia' (ie tongue-tie) is etymologically derived from ancient Greek by the words 'ankúlos' which means 'to bend' or 'crooked, curved, rounded' and 'glôssa', which refers to the 'tongue'; as such ankyloglossia most appropriately refers to alterations in the mobility of the tongue that may sometimes be attributable to a tight or short lingual frenulum. According to a recent clinical consensus statement among otolaryngologists on ankyloglossia, 12 however, there appears to be a bias towards considering restrictions of the lingual frenulum as the primary or sole determinant of tongue mobility. One of the biggest limiting factors for clinical research on the topic of 'functional ankyloglossia' is the paucity of objective measurements to define the presence or absence of the condition. Most definitions of the condition are based on structural characterisations of the lingual frenulum 15,[17][18][19] or subjective descriptions of mobility, [20][21][22][23][24] as there are limited objective tools to actually quantify functional variations in tongue mobility on a continuous numeric scale. 25 Recently, our group demonstrated the need for moving towards a functional definition of ankyloglossia based on assessment of tongue mobility. 9,13 The tongue range of motion ratio (TRMR) based on work by Irene Marchesan 25 was validated as a useful tool for the assessment of tongue mobility in children, adolescents and adults. 13 The tool is based on a ratio of vertical extension of the tongue to the incisive papilla (TIP) in comparison with the maximal interincisal mouth opening. Whereas this measurement has been helpful in serving as an initial screening tool to assess for variations in the mobility of the anterior one-third of the tongue (tongue tip and apex), we hypothesise that the measurement may be insufficient to adequately assess the mobility of the posterior two-thirds (or body) of the tongue. A commonly used modification is to assess the tongue range of motion while the tongue is held in suction against the roof of the mouth in lingual-palatal suction (LPS). Tongue strength can also be assessed by measuring the endurance with which the patients are able to sustain this posture. This manuscript aims to explore the utility and normative values of LPS as an objective tool for assessing the mobility and endurance of the posterior two-thirds body of the tongue.

| Objective assessment of tongue mobility
Step 1: Measurement of maximum interincisal mouth opening with the mouth opened as wide as possible without pain or discomfort, that is comfortable mouth opening (CMO).
Step 2: Measurement of the maximum interincisal mouth opening while the tongue tip is extended to the incisive papilla (TIP).
Step 3: Measurement of the maximum interincisal mouth opening while the tongue body is held against the palate in lingual-palatal suction (LPS).
Step 4: TRMR-TIP is calculated as a percentage of TIP divided by CMO.
Step 5: TRMR-LPS is calculated as a percentage of LPS divided by CMO.
All measurements were obtained using a tongue range of motion instrument (Great Lakes Orthodontics) with the subjects sitting upright in a natural head position with a horizontal visual axis. F I G U R E 1 For assessment of anterior tongue mobility, maximum interincisal mouth opening with the tongue tip to the incisive papilla (TIP) is compared with the maximum interincisal mouth opening with the mouth opened as wide as possible without pain or discomfort (comfortable mouth opening, CMO); the percentage of TIP divided by CMO is defined as the TRMR-TIP. For assessment of posterior tongue mobility, maximum interincisal mouth opening with the tongue in lingual-palatal suction (LPS) is compared with CMO; the percentage of LPS divided by CMO is defined as the TRMR-LPS. Note: Lingual-palatal suction (LPS) is also described as 'tongue suction', 'suction hold', 'tongue click and hold' or 'cave' among the myofunctional therapy community [Colour figure can be viewed at wileyonlinelibrary.com]

| Subjective assessments
Other assessments included in the analysis for this manuscript from the FAIREST dataset included the following self-assessment items rated subjectively on a 4-point Likert scale: resting tongue position, ease or difficulty elevating the tongue tip to the palate, ease or difficulty elevating the tongue body to the palate; mouth breathing, slouching posture and positional sleep.

| Clinical history
Measurements of mouth opening and tongue mobility were stratified based on the presence or absence of the following clinical history items: orthodontic treatment, myofunctional therapy, lingual frenectomy, tonsillectomy and temporomandibular joint disorder.

| RE SULTS
There were 611 subjects who participated in the tongue mobility revealed that the tongue mobility and comfortable mouth opening measurements were modestly reduced in the child age cohort (P < .0001) but not significantly affected by gender (P = .1500), see Table 1.
There was a statistically significant association between the objective measures of tongue mobility (TRMR-TIP  Other clinical history including whether the patient had a prior lingual frenectomy or tonsillectomy did not significantly impact TRMR measurements, see Table 2.

| D ISCUSS I ON
The present study demonstrates normative values for anterior and posterior tongue mobility using TIP and LPS functional movements. The results in this study build on the work by Yoon et al 13

and
Marchesan. 25 The prior studies helped establish and validate a functional approach to the assessment of ankyloglossia based on vertical extension of tongue mobility compared with mouth opening (described in this manuscript as the TRMR-TIP assessment). TRMR-TIP was found to be a more reliable tool for the functional assessment of tongue mobility in comparison with the traditional assessment of ankyloglossia which was based on the structural free-tongue 17 or frenulum length. 15 Since that time, the TRMR-TIP measurement has been used to demonstrate an association of restricted tongue mobility to development of the maxillary arch and elongation of the soft palate, 6 as well as case selection in lingual frenuloplasty and myofunctional therapy for the treatment of mouth breathing, snoring, clenching and myofascial tension in appropriately selected patient candidates. 9 In the present study, a cross-sectional analysis was performed to take measurements of tongue mobility using TIP as well as LPS among subjects in the general population. This study validates TIP measurements as an effective assessment of anterior tongue mobility and LPS measurements as an effective assessment of posterior tongue mobility. The advantage of the LPS measurement is that it best describes one of the main functional outcome goals of myofunctional therapy: achieving tongue body to palate contact requisite for establishing ideal resting oral posture and swallow mechanics.
LPS measurements have been used to track progress with tongue strengthening and rehabilitation in myofunctional, speech and swallow therapy protocols. 9 Measurements for this study were taken at The present work identifies TIP-TRMR of <50% and LPS-TRMR of <30% to be considered as representative of moderately restricted anterior and posterior tongue mobility, respectively, among subjects ages 12-65 + years. The results in this manuscript demonstrate that TRMR measurements may be unreliable in pre-school and gradeschool children (ages 3-11 years), see Table 3. In the prior work by Marchesan, 25 LPS measurements were described, but abandoned because TIP measurements were found to be more highly associated with structurally apparent alterations of the lingual frenulum.  among other devices, 30,31 but are only reliable if performed in combination with electromyography of the neck and jaw to control the involvement of cervical and facial muscles that may confound intra-oral tongue pressure measurements. 32 The endurance in seconds with which the subjects can maintain lingual-palatal suction may be a useful metric for investigation in future studies. Tables S1 and S2 are provided as potential resources for future research and clinical validation.

| CON CLUS ION
This study validates the TRMR in lingual-palatal suction as a useful functional metric for assessment of posterior tongue mobility. We <5% or unable to sustain.

TA B L E 3
Clinical grading scale for assessment of anterior and posterior tongue mobility using the tongue range of motion ratio (TRMR)