Journal of

Oral Rehabilitation

Journal of Oral Rehabilitation 2014 41; 374--380

Effects of varying fixed lingual apex positions on tongue pressure during straw drinking M. HARA*†, R. ISHIDA*, M. OHKUBO*, T. SUGIYAMA* & S. ABE†

*Department of Dys-

phagia Rehabilitation and Community Dental Care, Tokyo Dental College, Chiba, and †Department of Anatomy, Tokyo Dental College, Tokyo, Japan

We investigated the impact of tonguethrusting on lingual pressure during fluid intake with a straw. In this study, 12 healthy young dentate individuals (two women and 10 men; 19–33 years) were instructed to drink 15 mL of water with a regular drinking straw at 37 °C, when indicated by the investigator. Participants drank after adjusting tongue position to one of the following patterns: (i) Holding the tip of the straw between the lips (Normal Position: NP), (ii) Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth (Tongue-thrusting Position: TP). Five recordings were conducted for each participant in a randomised order. To measure tongue pressure during swallowing, a specially designed 0
1-mm thick sensor sheet (Nitta, Osaka, Japan) with a tactile system for measurement of pressure distribution (I-SCAN; Nitta) was used. Duration, maximal magnitude and integrated value of tongue pressure were analysed based on the wave of tongue pressure recorded while water was SUMMARY

Introduction The tongue plays an important role in respiration, mastication, deglutition and speech (1). In normal deglutition (swallowing), the tongue first collapses along the midline of the dorsum to hold the bolus of food (2). By pressing the dorsum against the palate from the lingual apex position, the bolus is then transported towards the pharynx during which time, the apex rests on the lingual aspect of the dentoalveolar area. However, some disabled children and even © 2014 John Wiley & Sons Ltd

swallowed. Magnitude, duration and integrated value of tongue pressure were significantly lower in TP than in NP at the median line (Ch1–3). Magnitude and integrated value of tongue pressure at the lateral part of the tongue (Ch5) were significantly lower in TP than in NP. When duration, maximal magnitude and integrated values were compared by channel, no significant differences were observed in NP, but a significant difference was found between Ch3 and the lateral areas Ch4/Ch 5 in TP. When the tongue was thrust forward, movement dynamics of the entire tongue changed and influenced contact between the tongue and palate during liquid intake with a straw. The impact was noticeably weaker on the median line than in lateral areas. KEYWORDS: tongue pressure, straw, tongue-thrust, sensor sheet, swallowing Accepted for publication 26 January 2014

healthy adults perform tongue-thrusts instead (3, 4). Tongue-thrust habits during swallowing are often clinically observed by forced opening of the lips for children with cerebral palsy and other neuromuscular difficulties (5). The kinetic analysis of the tongue can be measured by various techniques like videofluorography (6–8) (VF), pressure sensors (9–15), electropalatography (16) and sonography (17, 18). Studies of patients with tongue-thrust habits in particular have employed pressure sensors (14, 15), electropalatography (16) doi: 10.1111/joor.12154

TONGUE PRESSURE DURING STRAW DRINKING and sonography (17, 18) to observe saliva swallowing and instructed swallowing. Tongue movement dynamics during fluid intake with devices such as spoons or straws have yet to be analysed in patients exhibiting tongue-thrust. Feeding devices such as spoons, cups and straws are commonly used for drinking, with straws perhaps the most useful for caregivers of infants. Ishida et al. (19) showed that mothers often gave infants liquid with a spout or straw mug in the early stages of development. It is generally considered appropriate that during fluid intake with a straw, the tip is inserted no further than the front teeth and sealed by the upper and lower lips (5). We previously reported that straws with valves create a valve-opening shape from biting the tip that may hamper lip closure development and affect the development of drinking ability in infants (20). Changes in the lingual apex position are accompanied by changes in the position of the body and the base of the tongue. These changes likely affect the swallowing dynamics of the entire tongue. We hypothesised that inappropriate straw use may influence functional development. Therefore, we investigated the impact of experimental tongue-thrusting on tongue pressure during fluid intake with a straw.

Materials and methods Participants The study population included 12 healthy young dentate individuals (two women and 10 men; mean age: 27
3  3
9 years; range: 19–33 years) with no history of removable prosthodontics, orthodontic treatment, temporomandibular disorder or diseases that cause dysphagia. Written informed consent was obtained from each participant after study aims and methodology were explained. Tongue pressure measurement To measure tongue pressure during swallowing, a specially designed 0
1-mm thick sensor sheet* with a tactile system for measurement of pressure distribution (I-SCAN*) was used(Fig. 1). Based on the

*Nitta, Osaka, Japan. © 2014 John Wiley & Sons Ltd

Fig. 1. The sensor sheet for measuring tongue pressure at five measuring points [Channels (Chs) 1–5]. Three measuring points (Chs. 1–3) were placed along the median line (Ch. 1 was set at the anterior median part, Ch. 2 was set at the mid-median part, Ch. 3 was set at the posterior–median part), and two (Chs. 4 and 5) were in the posterior–lateral part of the hard palate (Ch. 4 was set at the left side, Ch. 5 was set at the right side connected to the cable).

previous studies (9, 10) with an experimental plate, the sheet was T-shaped for easy attachment to the hard palate and used five measuring points [Channels (Chs) 1–5] to record tongue pressure production at different parts of the palate. Three measuring points were placed along the median line (Ch. 1 at the anterior median, Ch. 2 at the mid-median and Ch. 3 at the posterior-median), and two were placed in the posterior-lateral area of the hard palate (Ch. 4 at the left side and Ch. 5 at the right side). Three sizes were available for each participant to choose a sensor sheet that best fit his/her hard palate (11). The sensor sheet was attached using a sheet-type denture adhesive (Touch Correct II†), and measuring points were carefully checked. The system was calibrated by applying negative pressure with a vacuum pump through an air duct in the cable of the sensor sheet. Instructed movement Participants were instructed to drink 15 mL of water at 37 °C with a regular drinking straw, when indicated by the investigator after adjusting to one of the two tongue positions (9, 11, 12). During measurement, each participant was seated in an upright position with feet touching the floor and the head supported by a headrest to avoid retroflexion movement and keep the Frankfurt plane parallel to the floor. Participants drank after adjusting tongue †

Shionogi, Tokyo, Japan.

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376

M . H A R A et al. (a)

(b)

Fig. 2. Tongue position. (a) Normal Position (NP): Holding the tip of the straw between the lips. (b) Tonguethrusting Position (TP): Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth.

position to one of the following patterns (Fig. 2): (i) Holding the tip of the straw between the lips (Normal Position: NP), (ii) Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth (Tongue-thrusting Position: TP). Five recordings were conducted for each participant in a randomised order. Statistical analysis

Ch5 (P = 0
008). Mean maximum tongue pressure in NP was greater than in TP. In NP, tongue pressure magnitude did not differ significantly between measuring points (Table 2). In TP, values for Ch3 were significantly smaller than values for Ch4 (P = 0
004)/Ch5 (P = 0
004). Almost all tongue pressure magnitudes were lower in TP than in NP; however, one participant had considerably higher values in TP at the anterior median (Ch1) and posterior-lateral areas (Ch4, Ch5).

Duration, maximal magnitude and integrated value of tongue pressure were analysed based on the wave of tongue pressure recorded while water was swallowed (Fig. 3). Differences at each measuring point between NP and TP were evaluated by the Mann–Whitney test at a significance level of 0
05. Differences between the five measuring points in NP and TP were analysed using the Kruskal–Wallis test, with the Mann–Whitney test used for post-hoc analyses. P < 0
05 was considered statistically significant. All data are presented as mean  S.D.

Results Duration of tongue pressure. There were significant differences between NP and TP at Ch1 (P = 0
004), Ch2 (P = 0
000) and Ch3 (P = 0
000). Duration of tongue pressure in NP was significantly longer than in TP. In NP, duration of tongue pressure did not differ significantly between measuring points (Table 1). In TP, values for Ch3 were significantly smaller than values for Ch4 (P = 0
000)/Ch5 (P = 0
001). Maximal magnitude of tongue pressure. There were significant differences between NP and TP at Ch1 (P = 0
024), Ch2 (P = 0
004), Ch3 (P = 0
000) and

Fig. 3. Marks for evaluating the state of tongue pressure production during swallowing. The X-axis shows duration of tongue pressure and the Y-axis shows the magnitude of tongue pressure. © 2014 John Wiley & Sons Ltd

TONGUE PRESSURE DURING STRAW DRINKING Table 1. Duration of tongue pressure Normal position

Ch1 Ch2 Ch3 Ch4 Ch5

Table 3. Integrated value of tongue pressure

Tongue-thrusting position

Normal position

Means

SD

Means

SD

P-value

0
50 0
58 0
40 0
58 0
54

0
21 0
21 0
19 0
21 0
28

0
23 0
22 0
11 # 0
45 †† 0
40

0
20 0
19
0
12 †† 0
26 0
27

0
004** 0
000** 0
000** 0
198 0
219

Ch1 Ch2 Ch3 Ch4 Ch5

Tongue-thrusting position

Means

SD

Means

SD

P-value

3
85 4
38 2
84 5
95 4
99

3
13 4
11 2
50 4
61 3
37

2
24 0
90 0
55 # 4
74 †† 1
92

6
16 1
16
1
41 †† 5
85 1
89

0
010* 0
000** 0
000** 0
160 0
017*

**P < 0
01, ††P < 0
01. Normal Position: Holding the tip of the straw between the lips. Tongue-thrusting Position: Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth. Ch, indicates channel.

*P < 0
05, **P < 0
01, ††P < 0
01. Normal Position: Holding the tip of the straw between the lips. Tongue-thrusting Position: Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth. Ch, indicates channel.

Table 2. Maximal magnitude of tongue pressure

X-ray exposure and there is a need for more facilities (6–8). But on the other hand, the sensor sheet used in the present study is non-invasive and can obtain real-time movement information. Other instruments, such as the IOWA Oral Performance Instrument (21) and handy probe (22) are easy to operate and frequently used to measure tongue pressure. However, these probe-type instruments have a fixed volume and must be bitten with the front teeth, which makes measurement of tongue pressure impossible when using feeding devices. In contrast, the cables of the sensor sheets in this study were led outside the oral cavity from behind the maxillary molars through the oral vestibule. Therefore, they did not prevent ingestion of food while using a device or contact of teeth during swallowing. Cayley et al. (16) conducted a study using electropalatography in patients exhibiting tongue-thrust, but a shortcoming was that time-dependent measurements could not be made with a palatogram. Kikyo et al. (17) used an ultrasonographic instrument, which enabled them to measure tongue depression and confirm that the lingual dorsum is in contact with the palate during bolus transport, but not to quantify tongue pressure. Proffit et al. (14) and Kydd et al. (15) performed studies with tongue pressure sensors in patients exhibiting tongue-thrust. Proffit et al. (14) used transducers located just lingual to the maxillary central incisors and bilaterally opposite the second deciduous molars, and Kydd et al. (15) employed transducers as close to the labial and lingual surface of the maxillary central incisor as possible. Although the sensors were arranged at the apex of the tongue

Ch1 Ch2 Ch3 Ch4 Ch5

Normal position

Tongue-thrusting position

Means

SD

Means

SD

P-value

6
88 7
18 6
85 10
02 9
27

5
16 5
38 5
51 5
99 6
06

4
33 2
60 2
35 # 7
47 † 4
42

9
18 2
71
4
70 † 6
93 2
75

0
024* 0
004** 0
000** 0
128 0
008**

*P < 0
05, **P < 0
01, †P < 0
05. Normal Position: Holding the tip of the straw between the lips. Tongue-thrusting Position: Sticking out the tongue to the vermilion zone of the lower lip and inserting the straw 1 cm past the front teeth. Ch, indicates channel.

Integrated value of tongue pressure. There were significant differences between NP and TP at Ch1 (P = 0
010), Ch2 (P = 0
000), Ch3 (P = 0
000) and Ch5 (P = 0
017). Integrated values in NP were greater than in TP. In NP, integrated value did not differ significantly between measuring points (Table 3). In TP, values for Ch3 were significantly smaller than values for Ch4 (P = 0
001)/Ch5 (P = 0
001).

Discussion Research procedures Tongue dynamics during swallowing have been analysed by various methods, and most of them have limitations: VF is complicated for analysis due to © 2014 John Wiley & Sons Ltd

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378

M . H A R A et al. in both configurations, measurements of the posterior region were inadequate. In the present study, the five tongue pressure sensors were arranged at different points of the palate, which made evaluations possible from the apex to the posterior of the tongue. Furthermore, movements from the initiation of liquid intake to swallowing could be measured kinetically. Ono et al. (9) previously stated that 15 mL appropriately quantifies a mouthful of water for experiments with a tongue pressure meter. Other swallow scans were conducted using this amount (11, 12). In studies to date, instructed swallowing was performed after directly injecting water into the oral cavity, and feeding devices were never used. Nilsson et al. (23) and Lawless et al. (24) used mouthful quantities of 25
6 mL and 15–20 mL, respectively, during straw drinking. Considering these together, 15 mL was set as a reasonable quantity in the present study. Temperature was set at 37 °C as in previous studies to avoid any temperature-dependent variables (9, 11, 12). Contact between tongue and palate The tongue-thrust pattern is more common in children younger than 4 years. However, it is difficult to study these children. Tongue-thrust can also be found clinically in children older than 4 and even in adolescent and adult patients. Such tongue-thrust is termed retained infantile swallowing and is considered a tongue dysfunction associated with many dentofacial deformities. For our purposes, the pattern of tongue movement was more important than the age of the patient; therefore, we chose healthy young dentate individuals. Several reports have analysed movement dynamics in patients exhibiting tongue-thrust. Cayley et al. (16) reported that swallow palatograms in tongue-thrusting children showed relatively sparse patterns of contact compared to control participants with a stronger pattern of peripheral contact and a well-defined posterior palatal bolus cavity. Kikyo et al. (17) suggested that children with tongue-thrusting moved the tongue flatly, without pressing its margin onto dental cervices of the upper teeth or the palate well. Peng et al. (18) measured movement at the midline and reported that tongue movement during the entire phase of swallowing showed no significant differences between groups in duration, range, speed and reproducibility. Proffit et al. (14) found that some patients with tongue-thrust

habits exhibited little or no pressure, while others used heavy linguo-palatal pressure. In contrast, Kydd et al. (15) reported that an open-bite patient showed increased tongue pressure during swallowing. None of these studies used feeding devices, while the present study measured tongue pressure during straw drinking in healthy normal adults by changing the fixed lingual apex position. Magnitude, duration and integrated value of tongue pressure were significantly lower in TP than in NP at the median line (Ch1–3), similar to the results of Proffit and Cayley. Magnitude and integrated value of tongue pressure at the lateral part of the tongue (Ch5) were significantly lower in TP than in NP. Study participants ingested liquid normally by holding the tip of the straw between their lips but also drank unnaturally with tongue-thrusting, which is presumably why a left–right difference occurred. These results indicate that when the lingual apex is displaced anteriorly, contact between the tongue and palate weakens, particularly at the median line. The tongue normally pushes boluses of food by a peristalsis-like movement. However, tongue-thrusting causes smaller movement because the tongue is extended anteriorly and becomes restricted in its up–down movements. The genioglossus and styloglossus muscles act antagonistically, which prevents styloglossus contraction during tongue-thrusting when genioglossus contracts and may explain restrictions in the up–down direction. During the developmental stage in infants, the tongue loses the backward–forward movement that predominates in suckling and shifts to an up–down movement (25). When the up–down movement of the tongue becomes restricted as a result of tongue-thrusting, this factor blocks the development of swallowing in adults. For almost all participants, the values in TP were lower than in NP; however, as in the reports of Proffit et al. (14) and Kydd et al. (15), one participant produced substantially higher tongue pressure in TP in the anterior-median and posterior–lateral parts of the tongue. We believe compensatory movements were performed due to the inability of applying sufficient pressure from the central to posterior region of the tongue. It is considered that such unusually high pressures at the lingual apex might have triggered an open bite and misalignment of the teeth. When duration, maximal magnitude and integrated values were compared by channel, no significant differences were observed in NP, but a significant difference was found between Ch3 and the lateral areas © 2014 John Wiley & Sons Ltd

TONGUE PRESSURE DURING STRAW DRINKING Ch4/Ch 5 in TP. These results indicate that the effects of tongue-thrusting in liquid intake with a straw are small laterally, and are particularly large within the posterior area of the median line. This suggests that while a bolus is laterally retained during tonguethrusting, the force that presses it against the palate is small owing to peristalsis-like movement of the tongue; rather than being transported, the bolus may be washed down toward the pharynx with the help of suction force and gravity. Tongue-thrusting likely causes poor retention of boluses in the preparatory and oral cavity phases of swallowing, early inflow into the pharynx and impaired bolus transit. This study was conducted in healthy adults with no abnormalities related to tooth alignment or straw drinking. However, many patients exhibiting tonguethrust have misaligned teeth, such as an open bite. For this reason, clinical cases were unlikely to be reproduced faithfully. Future studies should examine participants who naturally tongue-thrust.

Conclusions When the tongue was thrust forward, movement dynamics of the entire tongue changed and influenced contact between the tongue and palate during liquid intake with a straw. The impact was noticeably weaker on the median line than in lateral areas.

Acknowledgments The Ethics Committee of Tokyo Dental College, Ethical Clearance Number 368, approved the experiment. The study was funded by Tokyo Dental College as part of a PhD. The funders had no role in study design, data collection and analysis decision to publish, or preparation of the manuscript.

Conflict of interest None of the authors have conflict of interests to declare.

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© 2014 John Wiley & Sons Ltd