Dental caries and periodontal disease, which are representative oral diseases that hinder oral health, are specific chronic diseases that undergo a continuous deterioration process once they occur and are significant targets of management in the field of oral health [1]. Oral diseases cause problems such as pain, sleep disorders, chewing and eating disorders, and pronunciation disorders, causing various activity restrictions [2]. It has been reported that a disability caused by oral injury affects daily life and can cause severe dysfunction [3,4]. These oral diseases should be managed comprehensively and preventively. However, people often use dentistry when pain or oral problems occur rather than dental use for prevention, resulting in the deterioration of oral health [5]. Diagnosing and treating dental caries early through regular dental checkups is very important to reduce the incidence of dental caries and periodontal diseases. In Korea, general health checkups have been conducted for all citizens aged 19 or older since 2019, and oral checkups are also included [6].

According to the Health Examination Statistical Yearbook (2017), 31.7% of 17.81 million people subject to general health examinations had oral examinations, and only 31.3% of 1.02 million people subject to life-changing health examinations had oral examinations, indicating that the rate of oral examination was lower than that of general health examinations [7]. Unmet dental treatment means not receiving appropriate dental treatment when necessary [8]. It can be seen that it stems from a tendency to delay treatment due to low awareness of oral examination and the seriousness of the oral disease.

Despite the well-established institutional mechanisms, such as improved access to medical care and expanding medical security to bridge the medical gap, the rate of non-metric satisfaction has remained the same [9].

Therefore, the purpose of this study is to use data from the National Health and Nutrition Examination Survey (NHANES), which is representative nationwide, to find out the factors related to unmet dental treatment, the need for dental treatment, and the unmet dental treatment over the past year, and to find out the correlation.

1. Subjects

This study used data from the 8th NHANES (2019) conducted by the Korea Disease and Control Prevention Agency (decayed, missing, and filled permanent teeth). The NHANES used a stratified colony sampling method with survey districts and households as extraction units. The total number of subjects was 10,859, and 8,110 participants were at least one of the health survey, examination survey, and nutrition survey. This study analyzed 5,581 adults aged 19 or older who participated in the health survey and oral examination.

2. Methods

As for the general characteristics, sex, age, marital status, education level, economic activity, medical insurance type, private insurance subscription, and subjective health status were used, and variables were reclassified as necessary. The ignorance and non-response of all questionnaire responses were treated as missing values, and the difference in the total frequency of the study results was due to the omission of the missing values. In general characteristics, reclassified economic activities were divided into six occupational groups, and the unemployed were reclassified into current economic activities (Yes or No). In addition, in the form of medical insurance, 'health insurance local subscribers and workplace subscribers' were reclassified as one 'health insurance subscriber'.

In the oral interview, items such as oral health status, toothache, tooth brushing timing, oral hygiene supplements, oral examination, visits to dental clinics over the past year, chewing problems, and discomfort issues were used. In addition, tooth brushing was reorganized into the number of toothbrushes by summing up all the times performed, and the use of oral hygiene aids was reorganized into 'Yes' if any of the supplies were used and 'No' if not.

Unmet dental care was measured as a case of responding 'Yes' or 'No' to the question, 'Have you ever needed dental care (examination or treatment) in the past year?'

In the oral examination, dental conditions (decayed, missing, and filled permanent teeth), prosthetic conditions, dental treatment needs, and dental fluorosis were investigated. In this study, subjects with more than one tooth score of "one surface's Restorative treatment required" were classified as "Need for dental treatment," and those without were classified as "Needlessness for dental treatment".

3. Statistical analysis

In this study, a composite sample statistical analysis was conducted to ensure that the results of the NHANES were representative. In order to generate a plan file for statistical analysis, stratified variables were applied by calculating integrated weights for the variance estimation layer, the cluster variable was the surveying district, and the weights were calculated and applied to the health questionnaire, examination survey, and oral examination variables.

In order to analyze the general characteristics of the study subjects, whether or not they experienced unmet dental care, and the cause, the survey response was reclassified, and frequency analysis was conducted. In addition, the Rao-Scottchi-square test and complex sample design multi-logistic regression analysis were conducted to determine the relationship between general characteristics, oral health behavior, oral condition, and dental treatment. Data were analyzed using the SPSS Statistics version 25.0 (IBM Corp., Armonk, NY, USA).

1. General characteristics and oral conditions

As a result of analyzing the general characteristics of the subjects who participated in the examination survey and oral examination, the sex was 2,476 male (49.6%), 3,105 female (50.4%), 659 female (17.5%) aged 19-29, 803 people (16.6%) aged 30-39, 985 people aged 40-49 (19.6%), 1,040 people aged 50-59, and 2,094 people (26.7%) aged 60 or older. In addition, there were 938 single people (22.8%) and 4,642 married people (77.2%), and the education level was 1,022 primary school graduates (13.2%), 510 middle school graduates (7.9%), 1,753 high school graduates (35.7%), and 2,008 college graduate or higher (43.2%). Economic status was found to be 2,101 people (35.8%) who were 'no' and 3,176 people (64.2%) who were 'yes'. Medical social security were 5,353 (96.8%) national health insurance and 227 (3.2%) medical benefits. Private health insurance was found to be 1,138 (16.4%) who were 'no' and 4,410 (83.6%) who were 'yes'.

Based on the oral examination survey results, the number of permanent teeth conditions, prosthetics, and implants was confirmed, and 4,502 subjects had fewer than 19 caries in permanent teeth, and 119 subjects had 20 or more teeth.

The subjects with one or more prostheses in the oral cavity were 2,376, and the subjects with one or more implants were 1,147 (Table 1).

Table 1 . General characteristics of subjects

Variables	N (%)a)	Standard errora)
Sex
Male	2,476 (49.6)	0.6
Female	3,105 (50.4)	0.6
Age
19-29	659 (17.5)	0.8
30-39	803 (16.6)	1.0
40-49	985 (19.6)	0.8
50-59	1,040 (19.6)	0.7
≥60	2,094 (26.7)	1.2
Marital status
Single	938 (22.8)	1.0
Married	4642 (77.2)	1.0
Education level
≤Primary school	1,022 (13.2)	0.8
Middle school	510 (7.9)	0.5
High school	1,753 (35.7)	1.0
≥College	2,008 (43.2)	1.4
Employment status
No	2,101 (35.8)	1.0
Yes	3,176 (64.2)	1.0
Medical social security
National health insurance	5,353 (96.8)	0.3
Medical benefits	227 (3.2)	0.3
Private health insurance
No	1,138 (16.4)	0.9
Yes	4,410 (83.6)	0.9
Oral health status
DMFT
0-19	4,502 (97.7)	0.3
≥20	119 (2.3)	0.3
Presence of prosthetics
No	3,205 (64.5)	1.0
Yes	2,376 (35.5)	1.0
Presence of Implant
No	4,434 (81.9)	0.7
Yes	1,147 (18.1)	0.7

Values are presented as number (%). ^a)Weighted DMFT: Decayed/ Missing/Filled Teeth.

2. Unmet dental care and need for dental treatment of variables

Table 2 shows whether or not it has experienced unmet dental care and whether it needs dental treatment.

Table 2 . Characteristics of unmet dental care and dental treatment needs

Variables	N (%)a)	Standard errora)
Unmet dental care
No	2,998 (74.4)	0.9
Yes	1,062 (25.6)	0.9
Dental treatment needs
No	1,389 (25.9)	1.0
Yes	4,192 (74.1)	1.0

Values are presented as number (%). ^a)Weighted.

1,062 people (25.6%) had unmet dental experience, and 2,998 people (74.4%) had no experience. 4,192 (74.1%) people needed dental treatment, and 1,389 (25.9%) people did not need dental treatment.

3. Need for dental treatment according to general characteristics

Table 3 shows the results of analyzing the relationship between the general characteristics of the subject and the need for dental treatment. In terms of sex, 2,414 female (77.7%), 801 (76.9%) in the 50-59-year-old group, and 3,554 (76.1%) in the married group showed a high need for dental treatment (p<0.001). The level of education was high in 1,551 (76.2%) in the college or higher group, and 1,606 (75.4%) in the no employment status group showed a high need for dental treatment. However, there was no statistically significant difference (p<0.05). Depending on the type of Medical social security, 4,043 (74.4%) were found in the national health insurance group, and 3,359 (75.6%) were not subscribed to private health insurance, indicating a high need for dental treatment (p<0.05).

Table 3 . Dental treatment needs according to general characteristics of subjects

Variables	Dental treatment needs		χ2 (p-value)
	No	Yes
Sex			36.671*** (<0.001)
Male	698 (29.4)	1,778 (70.6)
Female	691 (22.3)	2,414 (77.7)
Age			35.864*** (<0.001)
19-29	206 (31.0)	453 (69.0)
30-39	236 (30.4)	567 (69.6)
40-49	238 (23.8)	747 (76.2)
50-59	239 (23.1)	801 (76.9)
≥60	470 (23.2)	1,624 (76.8)
Marital status			36.230*** (<0.001)
Single	301 (32.3)	637 (67.7)
Married	1,088 (23.9)	3,554 (76.1)
Education level			9.796 (0.074)
≤Primary school	262 (26.3)	760 (73.7)
Middle school	124 (25.6)	386 (74.4)
High school	471 (28.0)	1,282 (72.0)
≥College	457 (23.8)	1,551 (76.2)
Employment status			2.065 (0.265)
No	495 (24.6)	1,606 (75.4)
Yes	815 (26.4)	2,361 (73.6)
Medical social security			6.131* (0.028)
National health insurance	1,319 (25.6)	4,034 (74.4)
Medical benefits	70 (33.8)	157 (66.2)
Private health insurance			27.528*** (<0.001)
No	1,051 (24.4)	3,359 (75.6)
Yes	328 (32.7)	810 (67.3)

Values are presented as number (Weighted %). By complex sample Rao-Scott chi-square test. *p<0.05, ***p<0.001.

4. Unmet dental treatment according to oral conditions and oral hygiene behavior

Table 4 shows the results of analyzing whether or not it has experienced unmet dental treatment according to oral conditions and hygiene behavior.

Table 4 . Unmet dental care according to general characteristics of subjects

Variables	Unmet dental care needs		χ2 (p-value)
	No	Yes
DMFT			11.626** (0.005)
0-19	2,603 (75.0)	899 (25.0)
≥20	54 (58.1)	33 (41.9)
Subjective Oral health status			257.221*** (<0.001)
Very good	32 (94.3)	2 (5.7)
Good	429 (89.3)	55 (10.7)
Fair	1,459 (81.1)	337 (18.9)
Poor	665 (61.0)	452 (39.0)
Very poor	72 (49.3)	86 (50.7)
Toothache (within one year)			28.387*** (<0.001)
No	2,125 (76.7)	661 (23.3)
Yes	532 (67.3)	271 (32.7)
Use of toothbrushing			35.375*** (<0.001)
≤1	189 (70.2)	73 (29.8)
2	1,059 (69.9)	468 (30.1)
3	1,233 (77.9)	377 (22.1)
≥4	478 (79.0)	121 (21.0)
Oral care product use			53.381*** (<0.001)
No	913 (64.5)	493 (35.5)
Yes	1,598 (75.8)	535 (24.2)
Chewing difficulty			190.517*** (<0.001)
No	1,923 (76.0)	610 (24.0)
Yes	387 (49.9)	392 (50.1)
Oral examination			190.517*** (<0.001)
No	1,075 (57.2)	827 (42.8)
Yes	1,923 (89.5)	235 (10.5)
Subjective health status			4.077 (0.515)
Very good	135 (70.9)	51 (29.1)
Good	729 (73.3)	268 (26.7)
Fair	1,486 (74.5)	536 (25.5)
Poor	404 (77.0)	125 (23.0)
Very poor	88 (71.6)	33 (28.4)

Values are presented as number (Weighted %). By complex sample Rao-Scott chi-square test. **p<0.01, ***p<0.001. DMFT: Decayed/Missing/Filled Teeth.

The group with more than 20 permanent teeth left was 33 (41.9%), and 86 (50%) answered "very poor" when asked about their subjective oral conditions (p<0.001). There were 271 patients (32.7%) in the group who experienced toothache within one year, and 30.1% of the group brushed twice for the number of times of brushing, showing the highest level of unsatisfied dental care experience (p<0.001). Depending on the use of Oral care product use, the non-use group was 493 (35.5%). The unsatisfied dental experience was high (42%) even in the group with problems during chewing (p<0.001). In terms of subjective health status, the group that answered "very good" showed 51 patients (29.1%) that were more likely to have unmet dental care needs. But, there was no statistically significant difference (p>0.05).

5. Relationship between the need for dental treatment for unmet dental care

Table 5 shows the results of examining the relationship between unmet dental experience and dental treatment needs.

Table 5 . Relationship between dental treatment needs and unmet dental care needs

Characteristics	unmet dental care needs				met dental care
	Odd ratio	95% confidence interval	p-value		Odd ratio	95% confidence interval	p-value
Sex
Male			0.003**				0.141
Female	0.770	0.648-0.916			0.916	0.815-1.030
Marital status
Single			0.028*				0.090
Married	1.306	1.030-1.656			1.166	0.976-1.393
Presence of prosthetics
No	1.364	1.138-1.634	0.001***		1.069	0.937-1.218	0.320
Yes
Presence of Implant
No	1.302	1.074-1.578	0.007**		0.897	0.760-1.058	0.198
Yes

Values are presented as number (Weighted %). By complex sample multiple logistic regression. *p<0.05, **p<0.01, ***p<0.001.

In the unmet dental care group, when dental treatment was needed, sex, marital status, presence of prosthetics and implant were significant. For sex, female were 0.770 times more likely to receive dental treatment than male, and marriage was 1.306 times more likely than single. In the presence of prosthetics were 1.364 times more likely to receive dental treatment than without prosthetics and In the presence of implants were 1.302 times more likely to receive dental treatment than without implants (p<0.01).

This study attempted to examine the relationship between unmet dental care and dental treatment needs of Korean adults using data from the NHANES conducted in 2019. In previous studies, there is a disadvantage in that objectivity is somewhat insufficient because the need for dental treatment is limited to a specific disease, or the need for dental treatment was confirmed through a questionnaire rather than an oral examination. Therefore, this study uses NHANES data to secure the limitations of previous studies. Since it is the result of the oral examination of verified dentists, it is representative of using NHANES data to secure objectivity. Therefore, it is considered that angularity is sufficiently secured.

Due to its retrospective cross-sectional design, the study only included participants of the 8th NHANES, limiting its ability to establish causal relationships.

In this study, the proportion of unmet dental care was 25.6%, and the result was similar to that of 27.4% in Moon and song [10]. In addition, the unmet dental care rate was higher in the university or higher, married, and health insurance groups with high educational standards, especially for female high-educated people, due to the simultaneous performance of work and housework [11-12].

It was reported that the Missing Index was significantly higher, and the subjective oral health status was also negative when dental examinations were not performed periodically [13,14].

Many studies have been conducted on the causes of unmet dental care among Koreans, and the biggest reason why Koreans cannot go to the dentist is economical, and Korea has a well-equipped medical security system, but many people in need of dental treatment may feel that financial burden [15]. In selecting subjects who have experienced unmet dental treatment, the need for dental treatment was more clearly defined in that it was limited to those who were diagnosed as necessary for dental treatment during the oral examination. In addition, this study is meaningful in that it used a complex sample design analysis based on data from the NHANES representing Korea and calculated the analysis results to generalize to the entire population of Korea. In addition, it was found that those who needed dental treatment had a high level of education, were economically active, and experienced unmet medical care, which affected the need for dental treatment. In the future, it is believed that the cause of unmet dental care should be identified through further research on general characteristics such as education level, sex, oral condition, and possible causes.

In this study, the analysis results using raw data from the NHANES to understand the effect of oral health behavior and unmet dental treatment on the dental treatment needs of adult subjects over the age of 19 in Korea.

1. As a result of analyzing the need for dental treatment according to the subjects' general characteristics, female and those aged 50-59 showed the highest need for dental treatment, and married people showed the highest need for dental treatment. As for the level of education, the need for dental treatment was higher in the group with a college degree or higher and the group without economic activity, but there was no statistically significant difference. In terms of health insurance type, the health insurance group and the non-private insurance group showed a high need for dental treatment.

2. As a result of analyzing unmet dental care according to oral health behavior and oral conditions, subjects with more than 20 teeth left were more likely to have unmet dental care needs. And subjective oral health status responded 'very bad' were more likely to have unmet dental care needs (p<0.01). Those who had a toothache within 1 year and those who brushed their teeth twice were more likely to have unmet dental care needs (p<0.01). Subjects without used oral care products were more likely to have unmet dental care needs. Those who had chewing difficulty were more likely to have unmet dental care needs (p<0.01). Subjective oral health status, subjects with responded 'very good' were more likely to have unmet dental care needs. but there was no statistically significant difference (p>0.05).

3. To understand the general characteristics, oral health behavior, and the effect of unmet dental treatment on dental needs, a multi-logistic regression analysis showed no association with dental needs in the group without unmet dental experience. Sex was found to be 0.770 times more likely for female to receive hyper therapy, 1.306 times more likely for married female, and 1.36 times more likely to receive dental treatment when they have prosthetics or implants, respectively.

No potential conflict of interest relevant to this article was reported.