Evaluation of a Newly Developed Device for Resonance Disorders: A Clinical Pilot Study

Abstract

This clinical pilot study aimed to assess the clinical effectiveness of a newly developed device, Smart Naso^TM, for resonance disorders and compare its performance with that of the Nasometer II 6450. A group of 18 total participants (nine each in normal and hypernasality groups) were examined using the VIP inspection and K SNAP Test while wearing Nasometer II 6450 or Smart Naso^TM, and the reliability of the new device and similarity of both devices were evaluated. When the newly developed Smart Naso™ and Nasometer II 6450 were applied to the hypernasality group, similarity was observed (Smart Naso^TM: 0.776–0.989, Nasometer II: 0.922–0.996). In the test–retest reliability evaluation, both devices were found to be highly effective and reliable in the hypernasality group (Smart Naso^TM: 0.948, Nasometer II: 0.953); the Smart Naso^TM was found to be similarly effective and reliable for clinical applications. Smart Naso™ exhibited comparable effectiveness to that of Nasometer II 6450 and exhibits clinical utility for patients with hypernasality and those diagnosed with cleft lip and palate, cleft palate, and submucosal cleft palate.

1. Introduction

In speech production, the glottic tone originates in the lungs and is generated in the vocal tract through the vocal organ. This glottic tone resonates through selective amplification and filtration based on the characteristic shape of the vocal tract and is released through the oral and nasal cavities, which are the articulatory organs. When the velopharyngeal valve exhibits velopharyngeal incompetence owing to anatomical defects, neurological damage, or functional causes during speech sound generation, resonance disorders may occur [1,2].

Resonance disorders typically encompass the cleft lip and palate and the submucosal cleft palate, which are also associated with dental malocclusion, upper airway obstruction, and hearing impairment [3,4,5]. Kummer [4] categorized resonance disorders into hypernasality, hyponasality, mixed nasality, and cul-de-sac resonance. Hypernasality is characterized by nasalance that produces excessive nasal resonance during the production of glides, liquid sounds, and oral consonants. Notably, high nasalance is more pronounced in high vowels (i, ɯ, u) than in low vowels (e, a).

When evaluating nasalance in normal adults, it is essential to consider sex, age, and geographical dialect as well as segmental and suprasegmental factors and inspection word length. Consequently, establishing normal reference values presents considerable challenges [6]. A nasometer, which is non-invasive and exhibits the highest correlation with auditory perceptual investigation outcomes, is a widely used computer-based system [7] that quantitatively measures sound between the nasal and pharyngeal cavities [8,9,10]. The device captures oral and nasal consonants through a microphone, divides the nasal acoustic energy into the sum of the oral and nasal acoustic energy, multiplies this value by 100, and displays it as a percentage, thereby facilitating the assessment of nasal resonance for analyzing nasalance. Nasometers are utilized globally for nasalance research and inspection [11,12,13,14,15,16]. Despite the numerous advantages, the clinical application of nasometers is limited owing to the following factors: non-differentiation of headgear sizes for adults and children; risk of cutaneous irritation when tightened; cumbersome and heavy design resulting in discomfort during prolonged use; significant transportation requirements of all associated programs; and high costs owing to international import [17,18].

Recently, Smart Naso™ was developed for patients with resonance disorders to address the aforementioned limitations [17,19]. This study aimed to assess the clinical effectiveness of this device, verifying its efficacy and reliability compared to the existing device, Nasometer II 6450, by measuring the nasalance of patients with resonance disorders. We hypothesized that Smart Naso™ would be non-inferior to Nasometer II 6450 in terms of the reliability and similarity of nasalization measurements of participants in the normal and hypernasality groups.

2. Materials and Methods

2.1. Study Design

This study was approved by the Institutional Review Board (IRB) of Jeonbuk National University Hospital (IRB No.:2022-05-055, CRIS No: KCT0008727). The study cohort comprised nine patients in the normal group (mean age: 13.56 ± 5.88 years) and nine patients in the hypernasality group (mean age: 14.44 ± 7.00 years) who presented at the outpatient departments of Rehabilitation and Oral Maxillofacial Surgery at the Jeonbuk National University Hospital Dental Center at 20, Geonjiro Deokjin-gu, Jeonju-si, Jeollabuk-do from February 2023 to April 2023 (

Table 1. Participant characteristics.

	Normal Group (n = 9)	Hypernasality Group (n = 9)
Age, years	13.56 (±5.88)	14.44 (±7.00)
Sex (male/female)	2:7	4:5

).

A randomized order table was created using a computer program to generate a series of random numbers. This table was used for screening through block random assignment: each measurement session for each participant was divided into blocks, and Smart Naso and Nasometer devices were assigned 1:1 using www.randomization.com.

2.2. Enrollment Procedures

(1) Prior to assessment, the therapist thoroughly disinfected two nasometers (Nasometer II 6450, KayPENTAX, Lincoln Park, NJ and Smart Naso™, Humanopia, Co., Ltd., Pohang, Republic of Korea) with ethanol. The therapist turned on the PC and calibrated the Nasometer II 6450 device using the associated program according to the manufacturer’s instructions. Additionally, the therapist activated the power of Smart Naso™, connected it to a laptop (LG Electronics Gram 15-inch, 15Z95N-GA56K) via Bluetooth, and subsequently checked Smart Naso™.

(2) On the day of the participant’s visit, the velopharyngeal insufficiency (VPI) screening test was performed to evaluate nasalance while conducting an auditory perceptual evaluation using the VPI articulation differential inspection scale (Table 1) [17].

The VPI articulation differential inspection scale ranged from 0 to 4 points (0 points: normal, 1 point: minimal, 2 points: mild, 3 points: moderate, and 4 points: severe). Patients scoring 0 points were placed in the normal group, and those scoring ≥1 point were placed in the hypernasality group.

(3) After the screening test, participant nasalance was measured using the newly developed Smart Naso™ or Nasometer II 6450 according to a randomized order table. Following a 5 min interval, nasalance was reassessed using Smart Naso™ or Nasometer II 6450, following the same procedure.

The inspection words were derived from the K SNAP Test, which was developed by the Dental Treatment Center at Jeonbuk National University Hospital through translation of the SNAP Test-R [5,20].

2.3. VPI Articulation Differential Inspection

To differentiate between the hypernasality and normal groups, this study conducted an auditory perceptual evaluation, specifically the VPI articulation differential inspection [21].

The evaluation sentences included 2-syllable words comprising mid and low vowels at the vowel level; 1-, 2-, and 3-syllable words consisting of stop sounds; 2- and 3-syllable words consisting of affricate sounds; 1- and 2-syllable words consisting of sibilant sounds; 3-syllable words consisting of lateral sounds; 2-syllable words consisting of glottal sounds; and 2-syllable words consisting of nasal consonants at the consonant level (

Table 2. Example of VPI articulation differential inspection sheet.

Inspection Levels	Inspection
Word	Vowels	Middle vowel	‘Cucumber’ /o i/
		Low vowel	‘Crocodile’ /ɑ ɡ ʌ/
	Consonants	Stop sound	‘Frog’ /k ɛ ɡ u ɾ i/
			‘Elephant’ /kh o k* i ɾ i/
			‘Magpie’ /k* ɑ tɕh i/
			‘Cabbage’ /p ɛ tɕh u/
			‘Grape’ /ph o d o/
			‘Horn’ /p* u l/
			‘Pig’ /t wɛ dʑ i/
			‘Ostrich’ /th ɑ dʑ o/
			‘Strawberry’ /t* ɑ l ɡ i/
		Affricate sound	‘Swallow’ /tɕ ɛ b I/
			‘Toothbrush’ /tɕh i t s* o l/
			‘Mismatch’ /tɕ* ɑ k tɕ* ɑ ɡ i/
		Sibilant sound	‘Apple’ /s ɑ ɡ wa/
			‘Clock’ /s i ɡ jɛ/
			‘Rice’ /s* ɑ l/
		Lateral sound	‘Slipper’ /s ɯ l l i ph ʌ/
		Glottal sound	‘Pumpkin’ /h o b ɑ k/
		Nasal consonants	‘Garlic’ /m ɑ n ɯ l/
			‘Butterfly’ /n ɑ b i/
			‘Peacock’ /k o ŋ dʑ ɑ k/

).

2.4. K SNAP Test

In this investigation, the inspection word patterns utilized were based on the K SNAP Test (

Table 3. K SNAP Test sentences.

Inspection Levels	Articulatory Form		Evaluation Items	Composition
Vowel	Monophthong		A, /a/ I, /i/	Low vowel, /a/ High vowel, /i/
Syllable repetition	Nasal sound	Bilabial nasal	Mommy, /mami/	Low vowel, /a/ High vowel, /i/ 6 syllables for each (2 syllables, 3 repetitions)
		Alveolar nasal	Nani /nani/
		Velar nasal	Anging /aŋiŋ/.
				Low vowel	Middle vowel	High vowel	Diphthongs
Simple sentences	1. Spread butter on the pie: /phaiɛ pʌthʌrɯl parɯs’io/			2	2	5	-
	2. Look at Sook-hee’s dress: /sukhiɰ dɯrɛsɯl posip˺			-	2	7	2
	3. My mom makes lemon juice: /ʌmmanɯn remontɕusɯrɯl mandɯrʌjo/			2	4	5	1

), which was developed for clinical use by the Department of Oral Maxillofacial Surgery at the Jeonbuk National University Hospital Dental Center based on the SNAP Test, a test for cleft palate and speech disorders published by Kay PENTAX in the United States. The inspection sentence patterns were as follows: at the vowel level, low vowel /a/ and high vowel /i/ are at the syllable repetition level; meaningless 2-syllable repetition consists of bilabial nasal, alveolar nasal, and velar nasal. Furthermore, the patterns at the sentence level were as follows: a simple sentence with 10 syllables (2 low vowels, 2 middle vowels, and 5 high vowels) for 1 person; a simple sentence with 11 syllables (2 middle vowels, 7 high vowels, and 2 diphthongs) for 2 persons; and a simple sentence with 12 syllables (2 low vowels, 4 middle vowels, 5 high vowels, and 1 diphthong) for 3 persons.

2.5. Device Preparation

Smart Naso™ was designed to enhance the ease and comfort of measuring nasalance by connecting to the application site (software program used by connecting to an Internet address) through Bluetooth pairing, utilizing a PC with Internet access without the need to install specific software [17].

The hardware comprises a speech input/output device designed to calculate nasalance by connecting to a PC application via Bluetooth and capturing nasal sound energy with a microphone. The helmet-shaped headgear is adjustable to accommodate various head sizes, and the philtrum separator features an adjustable wire that enables adjustment to fit the face size (Figure 1).

2.6. Statistical Analysis

After randomly testing and retesting the newly developed Smart Naso™ and the existing Nasometer II 6450 in any order on patients with a diagnosed cleft palate in the hypernasality group with the normal group as a control, the newly developed Smart Naso™ and the existing Nasometer II 6450 were tested and retested in the same way after a 5 min interval. The results were statistically analyzed to determine the effectiveness and reliability of the newly developed Smart Naso™ as a clinical nasometer compared to the existing Nasometer II 6450 [22] as follows:

• Cosine similarity was employed to evaluate the effectiveness of both devices for nasalance measurements in the normal and hypernasality groups.
• To examine the consistency of inspection results without measurement errors when Smart Naso^TM and the Nasometer II 6450 were applied to measure and re-measure nasalance in the normal and hypernasality groups. The test–retest reliability of the devices was analyzed using the intraclass correlation coefficient (ICC).

ICC refers to the degree to which the scores allocated to the same subject are similar. The reliability judgment criteria range from 0 (not at all consistent) to 1 (perfectly consistent), with values closer to 1 indicating stronger reliability [23].

In this study, the ICC was categorized into four levels based on the 95% confidence interval: low (0.50 < ICC), moderate (0.50 ≦ ICC < 0.75), high (0.75 ≦ ICC < 0.90), and very high (0.90 ≦ ICC).

All statistical analyses were performed using SPSS 24.0 (IBM SPSS Statistics for Windows Version 24.0, Armonk, NY, USA: IBM Corp) with a statistical significance level of 0.05.

3. Results

3.1. Similarity Evaluation

To assess the effectiveness of the newly developed Smart Naso™ and existing Nasometer II 6450, we initially measured nasal sound and subsequently examined the consistency of the mean nasalance values of the normal and hypernasality groups using the cosine similarity technique.

Cosine similarity values range between 0 and 1, with values closer to 1 signifying higher similarity, whereas those closer to 0 indicate low similarity.

In the normal group, nasalance measurements of the two devices demonstrated similarity >90% for the sentence patterns /i/, /papi papi papi/, /mami mami mami/, /nani nani nani/, /aŋiŋ aŋiŋ aŋiŋ/, and /ʌmmanɯn remontɕusɯl mandɯrʌjo/. For the sentence patterns /p^hap^hi p^hap^hi p^hap^hi/, /p’ap’i p’ap’i p’ap’i/, /p^haiɛ pʌt^hʌrɯl parɯsio/, and /suk^hiɰ tɯresɯrɯl posip˺s’io/, the devices exhibited > 80% similarity, whereas the sentence pattern of /a/ demonstrated > 70% similarity. In the hypernasality group, all sentence patterns exhibited >90% similarity (

Table 4. Similarity of measured nasalance values by both devices in normal and hypernasality groups.

	Similarity of Nasalance Values by Both Devices in the Normal Group			Similarity of Nasalance Values by Both Devices in the Hypernasality Group
Sentence Pattern	Smart Naso™ Nasalance Value	Nasometer II 6450 Nasalance Value	Similarity	Smart Naso™ Nasalance Value	Nasometer II 6450 Nasalance Value	Similarity
/a/	39.67 ± 13.73	31.67 ± 24.78	0.776	29.78 ± 9.77	23.44 ± 9.58	0.922
/i/	47.89 ± 23.01	37.22 ± 21.62	0.942	49.78 ± 20.86	48.56 ± 24.49	0.958
/papi papi papi/	35.11 ± 14.53	21 ± 11.73	0.915	35.67 ± 17.44	25.67 ± 12.30	0.996
/phaphi phaphi phaphi/	25.11 ± 8.05	18.44 ± 11.70	0.872	32.00 ± 20.35	22.00 ± 14.29	0.988
/p’ap’i p’ap’i p’ap’i/	33.22 ± 10.41	18.89 ± 12.12	0.868	36.78 ± 24.36	22.67 ± 13.34	0.958
/mami mami mami/	72.56 ± 9.46	66 ± 12.7	0.983	60.22 ± 8.91	59.56 ± 6.67	0.982
/nani nani nani/	71.22 ± 10.56	67.33 ± 9.95	0.982	63.11 ± 8.65	60.44 ± 7.16	0.983
/aŋiŋ aŋiŋ aŋiŋ/	79.86 ± 11.02	76.33 ± 9.17	0.989	68.56 ± 13.48	73.33 ± 6.18	0.984
/phaiɛ pʌthʌrɯl parɯsio/	25.78 ± 6.82	17.56 ± 9.55	0.889	30.33 ± 13.40	22.67 ± 10.39	0.958
/sukhiɰ tɯresɯrɯl posip˺s’io/	19.67 ± 6.93	16.67 ± 10.46	0.848	25.11 ± 11.90	21.89 ± 14.13	0.963
/ʌmmanɯn remontɕusɯl mandɯrʌjo/	54.22 ± 7.12	49.56 ± 10.99	0.974	49.44 ± 12.47	41.44 ± 13.64	0.982

).

3.2. Reliability Evaluation

The test–retest reliability of nasalance measurement using the ICC was analyzed. In this study, the ICC was categorized as low (0.50 < ICC), moderate (0.50 ≦ ICC < 0.75), high (0.75 ≦ ICC < 0.90), and very high (0.90 ≦ ICC) based on the 95% confidence interval.

3.2.1. Evaluation of Test–Retest Reliability of Both Devices in the Normal Group

In the normal group, the test–retest reliability of Smart Naso^TM for nasal sounds was very high (≥0.90) for the sentence patterns /p’ap’i p’ap’i p’ap’i/ and /ʌmmanɯn remontɕusɯl mandɯrʌjo/, while demonstrating high reliability (≥0.75) for the sentence patterns /a/, /i/, /papi papi papi/, /p^hap^hi p^hap^hi p^hap^hi/, /mami mami mami/, /p^haiɛ pʌt^hʌrɯl parɯsio/, and /suk^hiɰ tɯresɯrɯl posip˺s’io/, and moderate reliability (≥0.50) for the sentence patterns /nani nani nani/ and /aŋiŋ aŋiŋ aŋiŋ/ (

Table 5. Evaluation of the Smart Naso™ test–retest reliability in the normal group.

	Test–Retest Reliability in the Normal Group
Sentence Pattern	Reliability of Smart Naso™ Results			Reliability of Nasometer II 6450 Results
	Session 1	Session 2	ICC (2,1)	Session 1	Session 2	ICC (2,1)
/a/	39.67 ±13.73	37.44 ±10.45	0.859	31.67 ±24.78	23.78 ±16.87	0.861
/i/	47.89 ±23.01	38.22 ±19.89	0.810	37.22 ±21.62	31.00 ±20.96	0.896
/papi papi papi/	35.11 ±14.53	28.44 ±8.56	0.780	21.00 ±11.73	23.11 ±16.97	0.751
/phaphi phaphi phaphi/	25.11 ±8.05	22.67 ±11.40	0.858	18.44 ±11.70	15.67 ±12.43	0.019
/p’ap’i p’ap’i p’ap’i/	33.22 ±10.41	27.33 ±8.50	0.929	18.89 ±12.12	12.56 ±4.77	0.597
/mami mami mami/	72.56 ±9.46	66.89 ±8.45	0.765	66.00 ±12.70	60.56 ±10.42	0.910
/nani nani nani/	71.23 ±10.66	68.22 ±9.09	0.594	67.33 ±9.95	64.44 ±8.76	0.751
/aŋiŋ aŋiŋ aŋiŋ/	79.89 ±11.02	76.89 ±10.53	0.615	76.33 ±9.17	75.00 ±8.51	0.858
/phaiɛ pʌthʌrɯl parɯsio/	25.78 ±6.82	23.89 ±8.75	0.832	17.56 ±9.55	12.22 ±7.03	0.689
/sukhiɰ tɯresɯrɯl posip˺s’io/	19.67 ±6.96	17.44 ±4.30	0.863	16.67 ±10.46	12.00 ±5.20	0.760
/ʌmmanɯn remontɕusɯl mandɯrʌjo/	54.22 ±7.12	50.11 ±7.85	0.920	49.56 ±10.99	43.22 ±7.03	0.802

).

In the normal group, the test–retest reliability of the Nasometer II 6450 for nasal sound was very high (≥0.90) for the sentence pattern /mami mami mami/, while showing high reliability (≥0.75) for the sentence patterns /a/, /i/, /papi papi papi/, /nani nani nani/, /aŋiŋ aŋiŋ aŋiŋ/, /suk^hiɰ tɯresɯrɯl posip˺s’io/, and /ʌmmanɯn remontɕusɯl mandɯrʌjo/, moderate reliability (≥0.50) for the sentence patterns /p’ap’i p’ap’i p’ap’i/ and /p^haiɛ pʌt^hʌrɯl parɯsio/, and low reliability (<0.50) for the sentence pattern /p^hap^hi p^hap^hi p^hap^hi/.

3.2.2. Evaluation of Test–Retest Reliability of Both Devices in the Hypernasality Group

In the hypernasality group, the test–retest reliability of Smart Naso^TM for nasal sound was very high (0.90 or higher) in the sentence patterns of /a/, /i/, /papi papi papi/, /p^hap^hi p^hap^hi p^hap^hi/, /mami mami mami/, /p^haiɛ pʌt^hʌrɯl parɯsio/, /suk^hiɰ tɯresɯrɯl posip˺s’io/, and /ʌmmanɯn remontɕusɯl mandɯrʌjo/ and high (0.75 or higher) in the sentence patterns of /p’ap’i p’ap’i p’ap’i/ of /i/, /nani nani nani/, and /aŋiŋ aŋiŋ aŋiŋ/.

The test–retest reliability of the Nasometer II 6450 in the same group was very high (≥0.90) for the sentence patterns /a/, /i/, /p^hap^hi p^hap^hi p^hap^hi/, /p’ ap’i p’ap’i p’ap’i/, and /p^haiɛ pʌt^hʌrɯl parɯsio/, while demonstrating high reliability (≥0.75) for the sentence patterns /papi papi papi/, /mami mami mami/, /nani nani nani/, /aŋiŋ aŋiŋ aŋiŋ/, and /suk^hiɰ tɯresɯrɯl posip˺s’io/, and low reliability (<0.50) for the sentence pattern /ʌmmanɯn remontɕusɯl mandɯrʌjo/ (

Table 6. Evaluation of the Smart Naso™ test–retest reliability in the hypernasality group.

	Test–Retest Reliability in the Hypernasality Group
Sentence Pattern	Reliability of Smart Naso™ Results			Reliability of Nasometer II 6450 Results
	Session 1	Session 2	ICC (2,1)	Session 1	Session 2	ICC (2,1)
/a/	29.78 ±9.77	29.11 ±10.78	0.948	24.78 ±10.89	23.44 ±9.58	0.935
/i/	49.78 ±20.56	51.33 ±23.30	0.948	45.67 ±28.24	48.56 ±24.49	0.953
/papi papi papi/	35.67 ±17.44	35.33 ±15.28	0.988	24.78 ±13.74	25.67 ±12.30	0.857
/phaphi phaphi phaphi/	32.00 ±20.35	30.44 ±19.38	0.977	20.89 ±13.23	22.00 ±14.29	0.946
/p’ap’i p’ap’i p’ap’i/	36.78 ±24.36	35.56 ±19.35	0.889	22.78 ±11.85	22.67 ±13.34	0.962
/mami mami mami/	60.22 ±8.91	59.78 ±9.52	0.902	58.89 ±9.53	59.56 ±6.67	0.886
/nani nani nani/	63.11 ±8.65	62.33 ±11.99	0.895	57.89 ±8.67	60.44 ±7.16	0.836
/aŋiŋ aŋiŋ aŋiŋ/	68.56 ±13.48	70.00 ±9.89	0.793	69.89 ±9.60	73.33 ±6.18	0.856
/phaiɛ pʌthʌrɯl parɯsio/	30.33 ±13.40	31.56 ±12.97	0.976	22.89 ±10.01	22.67 ±10.39	0.951
/sukhiɰ tɯresɯrɯl posip˺s’io/	25.11 ±11.90	27.56 ±11.38	0.958	24.33 ±10.72	21.89 ±14.13	0.864
/ʌmmanɯn remontɕusɯl mandɯrʌjo/	49.44 ±12.47	51.11 ±8.43	0.932	44.33 ±7.81	41.44 ±13.64	0.190

).

4. Discussion

When the newly developed Smart Naso™ and existing Nasometer II 6450 were used in the hypernasality group, more than 90% similarity was observed; when both devices were applied to the normal group, a high similarity of 70–80% was observed. In a comparison of the two devices in the two groups, Smart Naso™ and Nasometer II 6450 exhibited comparable similarity. However, the newly developed Smart Naso™ demonstrated more than 90% similarity in patients with resonance disorders, indicating its clinical effectiveness. This difference can be induced owing to the system of nasalance calculations between the two devices, given that variations in nasalance can occur in different experimental environments and conditions among individuals [10,14,23].

In the reliability evaluation, ICC was utilized to verify the test–retest reliability for nasalance. During this process, low (0.50 < ICC), moderate (0.50 ≦ ICC < 0.75), high (0.75 ≦ ICC < 0.90), and very high (0.90 ≦ ICC) categories were designated based on the 95% confidence interval. Smart Naso™ test–retest was conducted on the normal group to determine if consistent results were obtained for the same subject. The results revealed that the inspection words /nani nani nani/ and /aŋiŋ aŋiŋ aŋiŋ/ demonstrated a reliability of 0.594 and 0.615, respectively, indicating a moderate level of reliability, while exhibiting high reliability for the sentence patterns /a/, /i/, /papi papi papi/, /p^hap^hi p^hap^hi p^hap^hi/, /p’ap’i p’ap’i p’ap’i/, /mami mami mami/, /p^haiɛ pʌt^hʌrɯl parɯsio/, and /suk^hiɰ tɯresɯrɯl posip˺s’io/ and very high reliability for the sentence patterns /mami mami mami/ and /ʌmmanɯn remontɕusɯrɯl mandɯrʌjo/.

The test–retest using the Smart Naso™ in the hypernasality group with the inspection words /p’ap’i p’ap’i p’ap’i/, /nani nani nani/, and /aŋiŋ aŋiŋ aŋiŋ/ demonstrated very high reliability of 0.889, 0.895, and 0.793, respectively, and maintained high reliability (≥90%) for the remaining inspection words.

In the test–retest using the Nasometer II 6450 on the normal group, we observed that the inspection words /a/, /i/, /papi papi papi/, /nani nani nani/, /aŋiŋ aŋiŋ aŋiŋ/, and /ʌmmanɯn remontɕusɯrɯl mandɯrʌjo/ demonstrated high reliability of 0.861, 0.896, 0.751, 0.751, and 0.858, respectively, while exhibiting moderate reliability of 0.597 for the inspection words /p’ap’i p’ap’i p’ap’i/ and 0.689 for /p^haiɛ pʌt^hʌrɯl parɯsio/. Low reliability (0.019) was observed for the inspection word /p^hap^hi p^hap^hi p^hap^hi/.

In the test–retest using the Nasometer II 6450 in the hypernasality group, the inspection word of /ʌmmanɯn remontɕusɯrɯl mandɯrʌjo/ demonstrated low reliability of 0.190, and the inspection words of /papi papi papi/, /mami mami mami/, /nani nani nani/, /aŋiŋ aŋiŋ aŋiŋ/, and /suk^hiɰ tɯresɯrɯl posip˺s’io/ exhibited high reliability of 0.857, 0.886, 0.856, and 0.864, respectively, while the inspection words /a/, /i/, /p^hap^hi p^hap^hi p^hap^hi/, /p’ap’i p’ap’i p’ap’i/, and /p^haiɛ pʌt^hʌrɯl parɯsio/ exhibited very high reliability of 0.935, 0.953, 0.946, 0.962, and 0.951, respectively.

Consequently, the Nasometer II 6450 was shown to be highly effective and reliable for the hypernasality group, and Smart Naso^TM was similarly determined to be highly effective and reliable for clinical use.

While nasometer evaluations are characterized by a high level of validity not replaceable by instrumental techniques, they remain reliant on human sense and memory, thus potentially introducing subjectivity for each evaluator and leading to inconsistent results [24]. The nasometer method was developed to supplement auditory perceptual evaluation, which may still present reliability issues. Although nasometer research has extensively reported that various factors, such as vowel type, speech intensity, pitch, and frequency analysis, could affect nasalance, many researchers have verified its reliability and validity in clinical studies and practice, resulting in its widespread use [11,12].

The nasometer revealed that a higher proportion of nasal sounds in the typical inspection words developed by Fletcher [25] correlated with a higher nasalance value. As demonstrated in this study, this device proved highly useful for patients in the hypernasality group, with hypernasality typically observed in conditions such as cleft lip and palate, submucosal cleft palate, and deafness. Smart Naso™ exhibited a reliability >0.7 for all inspection words, suggesting that this device also can be a clinically valid evaluation tool for patients with hypernasality with the existing Nasometer II 6450. Further clinical research is required regarding the factors affecting nasalance in order to measure nasalance with high reliability.

Although nasometers have been used extensively for measuring nasalance and speech therapy, the weight of the separator and its contact with the philtrum have been reported to limit the natural movement of the patient’s upper lip and place uncomfortable pressure on the philtrum. This limits their use in clinical settings because nasometers require bulky and inconvenient hardware [18]. In addition, it has been claimed that nasometers are inconvenient and unsuitable for home use [19].

Although it has been shown that the newly developed device has the potential to be used for clinical evaluation, the small sample size of this study limits the generalizability of its findings showing lower similarity in the normal group comparison. A systematic clinical study with the expanded sample should be performed to compare the performance of Smart Naso™ with Nasometer II 6450.

5. Conclusions

This study compared the similarity and reliability of the nasalance measurement device (Smart Naso™), which was recently developed to evaluate resonance disorders, with an existing product through clinical evaluation. The quantitative analysis of the Smart Naso™ and Nasometer II 6450 devices, as well as an analysis of their suitability and effectiveness, led to the conclusion that Smart Naso™ exhibits clinical utility for patients with hypernasality. Moreover, our findings show that this device can also be useful for patients diagnosed with cleft lip and palate, cleft palate, and submucosal cleft palate.