Tongue pressure on loop of transpalatal arch during deglutition☆☆☆★★★♢

Material and methods 

The sample consisted of 4 male volunteers (mean age, 27.5 years; range, 23 to 30 years) with normal occlusion, not undergoing orthodontic treatment, with normal oral behavior, and without restorations covering the tips of cusps. This study was performed with their consent.

The TPA can be either fixed or removable, depending on the preference of the clinician.5, 12 In this study, removable TPAs in the form of the 3-dimensional multiaction palatal appliance of Wilson and Wilson13, 14 (Rocky Mountain Orthodontics, Denver, Colo) were selected.

Three-dimensional lingual tubes were welded to the lingual surface of the band. The TPA was made with 0.9-mm stainless steel wire and a 3-dimensional transfer insert. To minimize disturbance of the oral muscles, the 0.9-mm stainless steel wire was welded to the buccal surface of the band of the right first molar, carrying the connecting wires of the pressure sensor out of the oral cavity. The loop of each TPA was designed to measure the tongue pressure at the surface of the loop (Fig 1).

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Fig. 1. Design of TPA. Loops of TPA were designed to measure tongue pressure at surface of TPA loop in practice. When sensor was affixed, TPA loop, surface of TPA loop, and surface of sensor were at same level. TPAs were welded to 3-dimensional transfer inserts.

The loop of the TPA was positioned at the middle of the second premolars (P), the first molars (M1), or the second molars (M2) (Fig 2).

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Fig. 2. Position of pressure sensor (occlusal view).

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Fig. 3. Distance from palatal mucous membrane to pressure sensor (lateral view). A, 2 mm; B, 4 mm; C, 6 mm.

To minimize the influence of temperature, each TPA was soaked in 36°C water for 5 minutes and left in the mouth for 5 minutes before measurements were taken. Measurements were taken with the subjects seated upright in a firm chair with their heads unsupported in a natural position. A dynamic strain amplifier (DPM-600; KYOWA Electronic Instruments Co, Ltd, Tokyo, Japan) was calibrated to 0 when the tongue was not touching the pressure sensors. At each TPA position, pressure measurements were recorded 10 times. Subjects swallowed 5 mL of 36°C water at each measurement, according to the method of Kydd.15 The tongue pressure exerted on the TPA during deglutition was recorded with PS subminiature pressure transducers (pressure detecting devices; KYOWA Electronic Instruments Co, Ltd). In this study, we ignored strain in the palatal arch bar and measured only tongue pressure. During data collection, 512 points were collected every 2.56 seconds. The signal from the pressure sensor was amplified and converted from analog data to digital data by the data analyzer (DDA-110B, KYOWA Electronic Instruments Co, Ltd), which was connected to the dynamic strain amplifier.

The means and SDs of maximum recorded points (Fig 4) were calculated for each subject, and the data were analyzed with multiple comparisons (Scheffe test) on the basis of analysis of variance.

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Fig. 4. Wave of tongue pressure. Wave shows transition of tongue pressure during 1 deglutition for 2.56 seconds. Maximum point of wave was used for statistical analysis.

Results 

All measurements of tongue pressure are shown in Table I.

Table I. Mean and SD of 10 measurements of each subject (N/cm2)

			Second premolar		First molar		Second molar
	Distance (mm)	Subject	X̄	SD	X̄	SD	X̄	SD
	2	1	0.76	0.07	1.31	0.24	2.27	0.30
		2	0.84	0.21	1.48	0.20	1.52	0.23
		3	1.00	0.10	0.53	0.08	1.36	0.46
		4	1.29	0.18	1.70	0.17	1.99	0.20
	4	1	0.91	0.07	0.83	0.13	2.38	0.30
		2	2.08	0.42	1.85	0.38	1.66	0.30
		3	1.14	0.23	1.98	0.14	2.08	0.22
		4	1.46	0.21	2.18	0.27	1.73	0.18
	6	1	2.02	0.27	1.88	0.16	2.26	0.31
		2	0.78	0.12	1.10	0.38	2.26	0.25
		3	1.88	0.21	2.23	0.47	2.61	0.44
		4	1.38	0.14	1.08	0.26	1.78	0.22

There were no intrasubject differences (Scheffe test). X̄, mean.

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Fig. 5. Comparison of positions of pressure sensor at each distance from palatal mucosa. Maximum pressure was obtained at M2, and minimum pressure was obtained at P, irrespective of distance. I, standard deviation.

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Fig. 6. Comparison of distances from palatal mucosa at each position of pressure sensor. Maximum pressure was obtained at 6 mm, followed in order by 4 and 2 mm, irrespective of position. I, standard deviation.

Table II. Mean and SD of measurements of tongue pressure (N/cm2)

		Second premolar		First molar		Second molar
	Distance (mm)	X̄	SD	X̄	SD	X̄	SD
	2	0.97	0.14	1.25	0.17	1.78	0.30
	4	1.40	0.23	1.71	0.23	1.96	0.25
	6	1.52	0.18	1.57	0.32	2.23	0.30

X̄, mean.

Table III. Multiple comparison (Scheffe test)

	*Significance less than 0.01. †Significance less than 0.001.

NS, no significance.

There were no intrasubject differences (Scheffe test).

When the position was P and the distance was 2 mm, the minimum value of 0.97 N/cm2 was observed. When the position was M2 and the distance was 6 mm, the maximum value of 2.23 N/cm2 was detected.

When we compared P, M1, and M2, we obtained maximum pressure at M2 and minimum pressure at P, irrespective of the distance (Fig 5). There were significant differences between P and M1, M1 and M2, and P and M2 (Table III).

When we compared distances of 2, 4, and 6 mm, we obtained maximum pressure at 6 mm, followed in order by 4 mm and 2 mm, irrespective of the position (Fig 6). There were significant differences between 2 and 4 mm, and 2 and 6 mm. There was no significant difference between 4 and 6 mm (Table III).

Discussion 

The tongue works during mastication and deglutition, and also at rest. The tongue always influences the dentofacial morphology.16, 17 Tongue habits often cause malocclusion, open bite, and stomatognathic dysfunction.15, 18, 19 According to Winders,20 tongue pressure during deglutition ranges from 41 to 709 g/cm2 (0.40-6.95 N/cm2); Kydd and Toda21 reported that tongue pressure has a range of 37 to 240 g/cm2 (0.36-2.35 N/cm2) and 112 g/cm2 (1.10 N/cm2) on average. The results of this study were consistent with these reports.

In this study, the measurements of tongue pressure showed a tendency to increase when the loop was positioned more distally (Table II). Considering the position of the loop, significant differences were observed in comparisons between P and M1, M1 and M2, and P and M2 (Table III). Maximum pressure was obtained when the loop of the TPA was placed at the middle of the palatal mucous membrane between the right and left second molars (Fig 6).

Before deglutition, the food bolus is sucked into the mouth by withdrawing the tongue from front to back. Deglutition begins by increasing the palatal contact of the tongue from front to back as the back of the tongue is lowered in the same sequence. When the bolus has passed the back of the mouth, the jaw opening is restricted by contraction of the palatoglossus muscles. The upward and backward movement of tongue base closes off what remains of the opening. The tongue activity largely consists of a wave along its dorsum; this sweeps the fluid backward down the pharynx.22, 23

As stated above, because the base of the tongue is moved forcibly upward and backward toward the hard palate, it could be inferred that tongue pressure should be highest at the area of M2. This result implies interference with tongue motion by the TPA.

The tongue pressure was increased when the distance from the palatal mucosa was greater at P and M2. However, the results at position M1 did not show a fixed tendency. This could be related to the wide variation in values among the subjects. When the position was M2 and the distance was 6 mm, the maximum tongue pressure was seen in all subjects (Table II). There were significant differences between 2 and 4 mm, and 2 and 6 mm. There was no significant difference between 4 and 6 mm (Table III). Considering these findings and patients' disturbances, the best distance for practical applications appears to be 4 mm.

The tongue affects the dentition and the alveolar bone during mastication, deglutition, speech, and at rest.16, 19, 21 Kincaid24 reported that the average frequency of deglutition was 1600 times a day, and Staub18 stated that it was about 2400 times a day. Therefore, one could conclude that the tongue can deliver orthodontic forces with considerable frequency. The TPA is a useful clinical appliance, capable of aiding treatment in ways other than anchorage modification. More precise use of the TPA will allow us to achieve various treatment goals.

Conclusions 

This study examined tongue pressure changes in 4 adults who used a 3-dimensional TPA with a pressure sensor. Statistical analysis of the data collected in our study supported the following conclusions: