The World Health Organization defines health as a condition of physically, mentally, and socially complete well-being as well as absence of disease or injury [1] and suggests equality in health; that is, everyone should be given an equal chance to realize their own health potential and not be at any disadvantage [2]. As one of the major elements of life, oral health is a part of general health, is one of the elements indispensable for health promotion and maintenance, and is a condition of oral tissues that is not susceptible to disease and causes no mental or social disorder [3,4].

Most of the oral diseases progress slowly; however, they can hardly be cured naturally, once they occur, and make it difficult to recover the natural condition even with treatment; therefore, prophylaxis and early treatment are important to oral disease [5]. Prevention and early treatment of oral disease require continuous oral care, which is required to be combined with living practice for oral health and regular oral examination. However, most of the South Korean adults rarely take preventive treatment or oral examination for oral health because of time, financial status, accessibility, and so on before they feel pain or discomfort. It results in dental caries and periodontal disease, which lead to tooth loss in the worst case [3]. As the top two oral diseases, dental caries and periodontal disease may become chronic and are multifactorial conditions, which are irreversible once they occur. Most of the oral diseases can be detected by oral examination, and early treatment prior to pain can prevent them from progressing or worsening and relieve the burden of medical expenses. It is therefore vital to perform preventive health behavior based on good measures, such as regular visit to a dental clinic, good dietary habits, and tooth-brushing, which are factors for oral disease, with the objective of keeping oral condition healthy [6,7].

The Korea National Health and Nutrition Examination Survey (KNHANES) IV-3(2009) reported that the most frequent cause of trauma was bumping, followed by fall and sliding and transportation accidents and that the incidence rate of trauma requiring treatment in clinics, hospitals, or emergency rooms was 8.0% for the respondents aged 1-18, 6.8% for those aged 19-64, and 6.6% for those aged ≥65 [8]. These days, injury to oral tissues from strenuous sports tends to be on the remarkable increase and the incidence rate of accidents requiring treatment for trauma is on the gradual increase. In particular, the oral and maxillofacial region, which is directly exposed to the outside, is susceptible to injury from external force and exposes the oral tissues, including teeth, to the risk of injury. Dental care service for dental trauma is less likely to be covered by health insurance and involves more non-benefit items, and its narrow coverage is due to the relatively large amount of medical expenses. Teeth, once injured, generally cannot be treated at low cost [9]. As for orthodontic treatment involving a lot of non-benefit items, it is known that children's experience of orthodontic treatment is affected by their oral conditions, parents, and the dental care system of the society [10]. Despite the health policies for wider coverage of health insurance, people fail to get dental treatment fully because of the relatively larger number of non-benefit items [11]. Dental treatment with high-priced non-benefit items may cause problems with equality in oral health, and the variation in the oral health level is affected by the socio-economic characteristics.

This study aimed to investigate oral examination, experience of dental caries in permanent teeth, dental trauma from exercise or accidents, and experience of orthodontic treatment on the basis of KNHANES data and provide basic data necessary to make practical oral health policies for promoting oral health.

1. Subjects

This study used the raw data from 4,788 respondents aged ≥19 to the 5th KNHANES and the data were given according to the procedure described on its website. 39.0% of the respondents were men, and 61.0% women; 18.9% were aged 60-69; and 33.0% were high school graduates. 23.6% had average monthly income of at least 5 million won; 87.1% were married and 12.9% unmarried (Table 1).

Table 1 . Socio-demographic characteristics

Item	Division	n (%)
Gender	Men	1,892 (39.0)
	Women	2,916 (61.0)
Age (yr)	<30	499 (10.4)
	30-39	800 (16.7)
	40-49	783 (16.4)
	50-59	899 (18.8)
	60-69	901 (18.9)
	≥70	896 (18.8)
Educational level	Elementary and below graduation	1,316 (27.5)
	Middle school graduation	509 (10.7)
	High school graduation	1,576 (33.0)
	University graduation and above	1,377 (28.8)
Average monthly income (million won)	<1	854 (17.9)
	1 to <2	780 (16.3)
	2 to <3	823 (17.2)
	3 to <4	657 (13.8)
	4 to <5	538 (11.3)
	≥5	1,126 (23.6)
Marital status	Married	4,160 (87.1)
	Unmarried	618 (12.9)

By frequency analysis.

2. Method and variable

The survey contents included the socio-demographic characteristics (gender, age, educational level, average monthly income, and marital status), oral examination (No, Yes), experience of dental caries in permanent teeth (No, Yes), dental trauma from exercise or accidents (No, Yes), and experience of orthodontic treatment were reviewed (No, Yes).

3. Data analysis

The collected data were computationally processed using an IBM SPSS Statistics for Windows ver. 20.0 (IBM Co., Armonk, NY, USA) to meet the goal of the data analysis. Frequency analysis was performed for the socio-demographic characteristics of the respondents, and cross-tabulation analysis was carried out for oral examination, experience of dental caries in permanent teeth, dental trauma from exercise or accidents, and experience of orthodontic treatment by the socio-demographic characteristics, with the statistical significance level set at 0.05.

1. Oral examination by socio-demographic characteristics

Oral examination differed statistically significantly by age, educational level, and average monthly income. The respondents aged <30, 60-69, and ≥70 were more likely to answer 'No', and those aged 30-39, 40-49, and 50-59 were more likely to answer 'Yes.' Elementary school graduates and those at lower education levels and middle and high school graduates were more likely to answer 'No', and university graduates and those at higher education levels were more likely to answer 'Yes.' The respondents with average monthly income of less than 1 million won, 1-2 million won, 2-3 million won, and 4-5 million won were more likely to answer 'No', and those with 3-4 million won and at least 5 million won were more likely to answer 'Yes' (Table 2).

Table 2 . Centrality analysis of the network structure

Item	Division	Oral examination			x2(p)a
		No	Yes	Not applicable (medical check-up was taken)
Gender	Men	467 (25.1)	421 (22.6)	974 (52.3)	0.333 (0.846)
	Women	711 (24.4)	672 (23.0)	1,533 (52.6)
Age (yr)	<30	124 (24.8)	109 (21.8)	266 (53.3)	66.560 (0.000)
	30-39	162 (20.3)	184 (23.0)	454 (56.8)
	40-49	162 (20.7)	209 (26.7)	412 (52.6)
	50-59	224 (24.9)	235 (26.1)	440 (48.9)
	60-69	260 (28.9)	218 (24.2)	423 (46.9)
	≥70	246 (27.5)	138 (15.4)	512 (57.1)
Educational level	Elementary and below graduation	356 (27.1)	202 (15.3)	758 (57.6)	84.940 (0.000)
	Middle school graduation	140 (27.5)	212 (23.8)	248 (48.7)
	High school graduation	386 (24.5)	358 (22.7)	832 (52.8)
	University graduation and above	296 (21.5)	412 (29.9)	669 (48.6)
Average monthly income
(million won)	<1	213 (24.9)	135 (15.8)	506 (59.3)	69.934 (0.000)
	1 to<2	206 (26.4)	144 (18.5)	430 (55.1)
	2 to<3	201 (24.4)	194 (23.6)	428 (52.0)
	3 to<4	138 (21.0)	16 (24.5)	358 (54.5)
	4 to<5	139 (25.8)	131 (24.3)	268 (49.8)
	≥5	281 (25.0)	328 (29.1)	517 (45.9)
Marital status	Married	1,040 (25.0)	959 (23.1)	2,161 (51.9)	3.671 (0.160)
	Unmarried	138 (22.3)	134 (21.7)	346 (56.0)

Values are presented as number (%). ^a By chi-square test, p<0.05.

2. Experience of dental caries in permanent teeth by socio-demographic characteristics

The experience of dental caries in permanent teeth differed statistically significantly by gender and average monthly income. They were more likely to have experienced dental caries in permanent teeth in terms of gender and average monthly income (Table 3).

Table 3 . Experience of dental caries in permanent teeth by socio-demographic characteristics

Item	Division	Experience of dental caries in permanent teeth		x2(p)a
		No	Yes
Gender	Men	207 (11.1)	1,655 (88.9)	21.019 (0.000)
	Women	212 (7.3)	2,704 (92.7)
Age (yr)	<30	43 (8.6)	456 (91.4)	4.551 (0.573)
	30-39	64 (8.0)	736 (92.0)
	40-49	74 (9.5)	709 (90.5)
	50-59	73 (8.1)	826 (91.9)
	60-69	73 (8.1)	828 (91.9)
	≥≥70	92 (10.3)	804 (89.7)
Educational level	Elementary and below graduation	138 (10.5)	1,178 (89.5)	8.184 (0.052)
	Middle school graduation	38 (7.5)	471 (92.5)
	High school graduation	138 (8.8)	1,438 (91.2)
	University graduation and above	105 (7.6)	1,272 (92.4)
Average monthly income (million won)	<1	93 (10.9)	761 (89.1)	15.863 (0.007)
	1 to <2	64 (8.2)	716 (91.8)
	2 to <3	89 (10.8)	734 (89.2)
	3 to <4	52 (7.9)	605 (92.1)
	4 to <5	45 (8.4)	493 (91.6)
	≥5	76 (6.7)	1,050 (93.3)
Marital status	Married	356 (8.6)	3,804 (91.4)	1.801 (1.081)
	Unmarried	63 (10.2)	555 (89.8)

Values are presented as number (%). ^a By chi-square test, p<0.05.

3. Dental trauma from exercise or accidents by socio-demographic characteristics

Dental trauma from exercise or accidents differed statistically significantly by gender and age. They were more likely to have no dental trauma from exercise or accidents in terms of gender and age (Table 4).

Table 4 . Dental trauma from exercise or accidents by socio-demographic characteristics

Item	Division	Dental trauma from exercise or accidents		x2(p)a
		No	Yes
Gender	Men	1,805 (96.9)	57 (3.1)	15.424 (0.000)
	Women	2,756 (94.5)	160 (5.5)
Age (yr)	<30	406 (81.4)	93 (18.6)	364.670 (0.000)
	30-39	727 (90.9)	73 (9.1)
	40-49	748 (95.5)	35 (4.5)
	50-59	891 (99.1)	8 (0.9)
	60-69	897 (99.6)	4 (0.4)
	≥70	892 (99.6)	4 (0.4)
Educational level	Elementary and below graduation	1,312 (99.7)	4 (0.3)	9.622 (0.141)
	Middle school graduation	502 (98.6)	7 (1.4)
	High school graduation	1,504 (95.4)	72 (4.6)
	University graduation and above	1,243 (90.3)	134 (9.7)
Average monthly income (million won)	<1	847 (99.2)	7 (0.8)	5.766 (0.835)
	1 to <2	757 (97.1)	23 (2.9)
	2 to <3	788 (95.7)	35 (4.3)
	3 to <4	622 (94.7)	35 (5.3)
	4 to <5	510 (94.8)	28 (5.2)
	≥5	1,037 (92.1)	89 (7.9)
Marital status	Married	4,044 (97.2)	116 (2.8)	1.330 (0.514)
	Unmarried	517 (83.7)	101 (16.3)

Values are presented as number (%). ^a By chi-square test, p<0.05.

4. Experience of orthodontic treatment by socio-demographic characteristics

The experience of orthodontic treatment differed statistically significantly by gender, educational level, and average monthly income. They were more likely to have no experience of orthodontic treatment in terms of gender, educational level, and average monthly income (Table 5).

Table 5 . Experience of orthodontic treatment by socio-demographic characteristics

Item	Division	Experience of orthodontic treatment		x2(p)a
		No	Yes
Gender	Men	1,805 (96.9)	57 (3.1)	15.424 (0.000)
	Women	2,756 (94.5)	160 (5.5)
Age (yr)	<30	406 (81.4)	93 (18.6)	8.051 (0.153)
	30-39	727 (90.9)	73 (9.1)
	40-49	748 (95.5)	35 (4.5)
	50-59	891 (99.1)	8 (0.9)
	60-69	897 (99.6)	4 (0.4)
	≥70	892 (99.6)	4 (0.4)
Educational level	Elementary and below graduation	1,312 (99.7)	4 (0.3)	151.828 (0.000)
	Middle school graduation	502 (98.6)	7 (1.4)
	High school graduation	1,504 (95.4)	72 (4.6)
	University graduation and above	1,243 (90.3)	134 (9.7)
Average monthly income
(million won)	<1	847 (99.2)	7 (0.8)	62.857 (0.000)
	1 to <2	757 (97.1)	23 (2.9)
	2 to <3	788 (95.7)	35 (4.3)
	3 to <4	622 (94.7)	35 (5.3)
	4 to <5	510 (94.8)	28 (5.2)
	≥5	1,037 (92.1)	89 (7.9)
Marital status	Married	4,044 (97.2)	116 (2.8)	8.070 (0.055)
	Unmarried	517 (83.7)	101 (16.3)

Values are presented as number (%). ^aBy chi-square test, p<0.05.

This study aimed to use the data from the 5th KNHANES to investigate oral examination, experience of dental caries in permanent teeth, dental trauma from exercise or accidents, and experience of orthodontic treatment by the socio-demographic characteristics in South Korean adults and provide basic data necessary to make dental care service more accessible, remove inequality, and improve relevant policies and systems.

Oral examination differed statistically significantly by age, educational level, and average monthly income among the socio-demographic characteristics. The respondents aged <30, 60-69, and ≥70 were more likely to answer 'No', and those aged 30-39, 40-49, and 50-59 were more likely to answer 'Yes.' Lee et al. [12] found that people aged 34-44 (80.8%), 45-54 (79.1%), and 55-64 (74.4%) were more likely to answer 'No', and Lee [13] and An et al. [14] also found that each age group was more likely to answer 'No.' Elementary school graduates and those at lower education levels and middle and high school graduates were more likely to answer 'No', and university graduates and those at higher education levels were more likely to answer 'Yes.' While elementary school graduates and those at lower education levels and middle and high school graduates were more likely to answer 'No', and university graduates or those at higher education levels were more likely to answer 'Yes'. Lee et al. [12], Lee [13], and An et al. [14] found that middle school graduates and those at lower levels and high school and university graduates were more likely to answer 'No.' The respondents with average monthly income of less than 1 million won, 1-2 million won, 2-3 million won, and 4-5 million won were more likely to answer 'No', and those with 3-4 million won and at least 5 million won were more likely to answer 'Yes.' The respondents with average monthly income of less than 1 million won, 1-2 million won, 2-3 million won, and 4-5 million won were more likely to answer 'No', and those with 3-4 million won and at least 5 million won were more likely to answer 'Yes.' Lee et al. [12] found that people with less than 4 million won and at least 4 million won were more likely to answer 'No', and Lee [13] found that those at low, middle-low, middle-high, and high levels were more likely to answer 'No.' An et al. [14] found that those with less than 2 million won, 2-3 million won, 3-4 million won, and at least 4 million won were more likely to answer 'No.' While it is vital to get oral examination and required dental treatment on a timely basis with the aim of extending dental life expectancy and improving the quality of life related to oral health, they failed to perform it, in agreement with the finding of this study. It is necessary to investigate the state of taking oral examination and failing to get required dental treatment, analyze relevant factors, and develop a plan for making dental care more accessible.

The experience of dental caries in permanent teeth differed statistically significantly by gender and average monthly income among the socio-demographic characteristics, and they were more likely to have experienced dental caries in permanent teeth in terms of gender and average monthly income. Lee [15], Lee [16], and Jang and Kim [17] found that women were more likely to have experienced it and men were more likely to have no such experience, and Choi and Kim [18] found that women were more likely to have no such experience and men were more likely to have experienced it. Lee [15] found that people with average monthly income of at least 2 million won were more likely to have experienced it and those with not more than 2 million won were more likely to have no such experience; Choi and Kim [18] found that those with not more than 1 million won were more likely to have experienced it and those with at least 3 million won were more likely to have no such experience. Lee [16] found that people with not more than 1 million won were more likely to have experienced it and those with 1-1.5 million won were more likely to have no such experience. This is probably because women having more time than men in principal charge of socio-economic activity may visit a dental clinic more frequently, take examination for other regions than the targeted one, and find new teeth to treat. They may fail to visit a dental clinic easily because of the psychological burden of dentist's fees and to take good prophylaxis and treatment.

Dental trauma from exercise or accidents differed statistically significantly by gender and age among the socio-demographic characteristics. They were more likely to have no dental trauma from exercise or accidents in terms of gender and age. Lee [19] found that 8.9% of the men and 8.3% of the women got dental trauma from exercise and that 10.1% of the men and 16.6% of the women got it from an accident. Shin et al. [20] found that males showed higher rates of dental trauma than women.

The experience of orthodontic treatment differed statistically significantly by gender, educational level, and average monthly income among the socio-demographic characteristics. They were more likely to have no experience of orthodontic treatment in terms of gender, educational level, and average monthly income. Park et al. [21] and Jin and Lee [10] found that 72.2% and 46.6% of the women, respectively, had experienced orthodontic treatment and 27.8% and 53.4% of the men, respectively, had experienced it. Kim et al. [22] and Park [23] also found that women were more likely to have experienced orthodontic treatment than men. Park [23] found that 56.8% of the university students and those at higher education levels, 23.9% of the high school graduates, and 19.3% of the middle school graduates had experienced orthodontic treatment; Kim et al. [22] found that 90.48% of the university graduates and those at higher education levels, 72.41% of the university students, and 19.77% of the high school students had experienced it. Kim et al. [22] found that people with 4 million to less than 5 million won were more likely to have experienced orthodontic treatment; Jin and Lee [10] found that those at the high level of monthly household income were most likely to have experienced it. Women were more likely to have experienced orthodontic treatment than men because the former might have greater interest in and needs for good appearance and attach more importance to intra-oral aesthetic factors; the higher educational level, the more likely to obtain and accept information and have experienced orthodontic treatment for preventive and therapeutic purposes. It is expected that the higher monthly household income, the more knowledgeable about good time for orthodontic treatment and the easier to perform oral health behavior and access dental treatment. It is necessary to control medical resources with the objective of making dental treatment more accessible to meet the demand for orthodontic treatment, which involves a lot of non-benefit items.

This study is cross-sectional research using the data from the 5th KNHANES and has limitations in explaining causal relations but is significant in that it used a national survey. It is necessary to use many different indexes at the same time, supplement with longitudinal study design, and conduct continuous research that can determine causal relations among factors.

This study used the data from KNHANES to analyze oral examination, experience of dental caries in permanent teeth, dental trauma from exercise or accidents, and experience of orthodontic treatment by the socio-demographic characteristics in people aged ≥19 and drew the following conclusion:

1. Oral examination differed statistically significantly by age, educational level, and average monthly income and the experience of dental caries in permanent teeth differed statistically significantly by gender and average monthly income.

2. Dental trauma from exercise or accidents differed statistically significantly by gender and age, and the experience of orthodontic treatment differed statistically significantly by gender, educational level, and average monthly income.

On the basis of these results, it is necessary to change the perception in pursuit of a higher rate of participation in oral examination in an effort at oral health care, develop many different types of education for oral care, and control medical resources that allow people to get dental treatment with a lot of non-benefit items more easily.

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