Of the general households in South Korea, single-person (30.2%) and two-person households (27.8%) formed 58.1%, 1.5% up from 56.5% in 2018; the greatest increase in the number of single-person households (1.12 million) was found among those in their twenties (18.2%) and thirties (16.8%), compared with the previous year (1.02 million), followed by those in their seventies (18.4%) [1]. Such an increase of small-sized households leads to the tendency to replace a meal by semi-cooked or cooked food, which requires no personal cooking at home, and this phenomenon is expected to prevent todayʼs people from having a balanced diet due to the resultant changes in dietary life and adversely affect oral health [2]. In particular, social participation by more women and the increase in the population enjoying leisure activities gradually decrease time to purchase food ingredients and cook at home personally [3].

Approximately 17% of the South Korean adults were found to consume sugar-containing food for snack at least three times a day. The older people were, the more likely they were to have sugar-containing snack and the most frequently consumed type of snack was sweetened coffee: 43% consumed it at least once a day [4]. Reportedly, food consumption supplies the brain with energy, helps secrete serotonin and dopamine, and serves to relieve stress temporarily [5]. The habitual snack consumption, which leads to an increase in added sugar consumption, can increase blood glucose, cause obesity, and become a risk factor for chronic disease and was rather related to anxiety, depression, or excessive stress [6,7]. Overconsump-tion of sugar is known to adversely affect health by causing many different types of adult disease, including obesity and diabetes, and become one of the causes of oral diseases, such as dental caries [8]. Both those in their twenties and thirties largely consumed coffee and vegetable food frequently on a weekly basis [9]; the contemporary diet in which at least a half of total sugar intake comes from processed food [10] is a cause of the increased dental caries and periodontal disease and affects dental caries because it is characterized by refinement to remove the need of hard chewing as well as by easy attachment to the surface of teeth [11].

Dental caries can be managed effectively by removing dental plaque through toothbrushing, which is the most widely applied method of personal oral hygiene management [12].

This study aimed to compare toothbrushing frequency by sugar intake via food, which became a new social issue, among young adults, who form a large percentage of single-person and small-sized households, and provide basic data that could help promote oral health and nutritional status.

1. Subjects

The 2019 raw data from the relevant items and the survey on food consumption frequency in the Korea National Health and Nutrition Examination Survey (KNHANES VIII-1) were combined to make a final sample of 1,141 respondents aged between 20 and less than 40, with the exception of missing data.

2. Instruments

The respondentsʼ general characteristics included gender, age, education, occupation, and household income, and health behavior involved alcohol intake and smoking status. The dependent variable, toothbrushing frequency, was the sum of toothbrushing sessions before and after breakfast, before and after lunch, before and after supper, after snacks, and before going to bed. Both men and women participated in this study, and the age groups were limited to those in their twenties and thirties. The education levels were divided into high school graduates or lower and college graduates or higher; household income was categorized into high, above-average, below- average, and low levels by financial status. Lastly, as for occupation, they were categorized into non-blue-collar workers, including professionals, clerks, salespersons, and service providers, and blue-collar workers, including skilled farmers and fishers, technicians, and simple laborers. The respondents, including stay-at-home moms and students, who were not categorized in terms of occupation, were regarded as jobless.

Sugar-containing food was divided into sweetened drinks, sweetened coffee, fruits, processed fruits, fruit juice, confectionery, simple sugar, ice cream, candies, sauce, beverage with lactic acid bacteria, vegetable drinks, chocolate, and carbonated drinks; the survey was based on the number of consumptions a day rather than on the intake.

3. Statistical analysis

Frequency analysis was performed to determine the general characteristics, health behavior, sugar-containing food consumption, and toothbrushing frequency for the respondents; chi-square test was carried out for variation in the effects of the general characteristics, health behavior, and sugar intake type on toothbrushing frequency. With the independent variables controlled, hierarchical logistic regression analysis was performed to identify the factors increasing toothbrushing fre-quency.

1. General characteristics and health behavior

As for the general characteristics, 529 respondents (46.4%) were male, 612 (53.6%) female; 474 respondents (41.5%) were aged 20 to 29, 667 (58.5%) aged 30 to 39. The mean age was 30.73 years (min 20 and max 39). As for household income, 436 respondents (38.2%) were at the high level, 342 (30.0%) at the above-average level, 276 (24.2%) at the below-average level, and 87 (7.6%) at the low level. 745 respondents (65.3%) were college graduates or at higher education levels, and 396 (34.7%) high school graduates or at lower education levels. 622 respondents (54.5%) were non-blue- collar workers, 131 (11.5%) were blue-collar workers, and 388 (34.0%) were jobless. As for health behavior, 756 respondents (66.3%) were drinkers, and 385 (33.7%) non-drinkers; 236 (20.7%) were smokers, and 905 (79.3%) non-smokers (Table 1).

Table 1 . General characteristics and health behavior

Variable	N (%)	Mean±standard deviation (Min-Max)
Gender
Men	529 (46.4)
Women	612 (53.6)
Age (yr)
20-29	474 (41.5)	30.73±5.79
30-39	667 (58.5)	(20-39)
Household income
High	436 (38.2)
Above-average	342 (30.0)
Below-average	276 (24.2)
Low	87 (7.6)
Education
≥College	745 (65.3)
≤High school	396 (34.7)
Occupation
Other than blue-collar	622 (54.5)
Blue-collar	131 (11.5)
Jobless	388 (34.0)
Alcohol intake
Drinker	756 (66.3)
Non-drinker	385 (33.7)
Smoking
Smoker	236 (20.7)
Non-smoker	905 (79.3)
Total	1,141 (100.0)

Frequency test & descriptive statistics.

2. Frequency of consuming sugar-containing food

As for consuming sugar-containing food at least twice, 10 respondents (0.9%) consumed sweetened drinks and 75 (6.6%) had sweetened coffee. 307 (26.9%) had fruits. 49 (4.3%) had processed fruits. 16 (1.4%) had fruit juice. 120 (10.5%) had confectionery. 707 (62.0%) had simple sugar. 11 (1.0%) had ice cream. 9 (0.8%) had candies. 217 (19.0%) had sauce; 15 (1.3%) beverage with lactic acid bacteria; 19 (1.7%) vegetable drinks; 5 (0.4%) chocolate; and 60 (5.3%) carbonated drinks (Table 2).

Table 2 . Frequency of consuming sugar-containing food

Variable		N (%)	Mean±standard deviation (Min-Max)
Sweetened drink	≥2	10 (0.9)	0.07±0.30 (0-3)
	1	60 (5.3)
	None	1,071 (93.9)
Sweetened coffee	≥2	75 (6.6)	0.29±0.70 (0-6)
	1	144 (12.6)
	None	922 (80.8)
Fruit	≥2	307 (26.9)	1.23±2.09 (0-24)
	1	306 (26.8)
	None	528 (46.3)
Processed fruit	≥2	49 (4.3)	0.28±0.65 (0-8)
	1	199 (17.4)
	None	893 (78.3)
Fruit drink	≥2	16 (1.4)	0.10±0.37 (0-4)
	1	80 (7.0)
	None	1,045 (91.6)
Confectionery	≥2	120 (10.5)	0.48±0.79 (0-7)
	1	264 (23.1)
	None	757 (66.3)
Simple sugar	≥2	707 (62.0)	2.89±2.85 (0-21)
	1	180 (15.8)
	None	254 (22.3)
Ice cream	≥2	11 (1.0)	0.10±0.38 (0-5)
	1	81 (7.1)
	None	1,049 (91.9)
Candy	≥2	9 (0.8)	0.07±0.32 (0-5)
	1	53 (4.6)
	None	1,079 (94.6)
Source	≥2	217 (19.0)	0.80±1.29 (0-10)
	1	259 (22.7)
	None	665 (58.3)
Beverage with lactic acid bacteria	≥2	15 (1.3)	0.11±0.36 (0-3)
	1	90 (7.9)
	None	1,036 (90.8)
Vegetable drink	≥2	19 (1.7)	0.11±0.47 (0-7)
	1	74 (6.5)
	None	1,048 (91.8)
Chocolate	≥2	5 (0.4)	0.05±0.27 (0-4)
	1	47 (4.1)
	None	1,089 (95.4)
Carbonated drink	≥2	60 (5.3)	0.33±0.64 (0-5)
	1	233 (20.4)
	None	848 (74.3)
Total		1,141 (100.0)

Frequency test & descriptive statistics.

3. Toothbrushing frequency by general characteristics and health behavior

In terms of the general characteristics and health behavior, there were gender differences: 494 men (93.4%) and 594 women (97.1%) brushed their teeth at least twice a day (p=0.003). There were differences by education: 725 college graduates and those at higher education levels (97.3%), and 363 high school graduates and those at lower levels (91.7%) brushed their teeth at least twice a day (p<0.001). As for occupation, 602 non-blue-collar workers (96.8%), 121 blue-collar workers (92.4%), and 365 jobless respondents (94.1%) brushed their teeth at least twice a day (p=0.031). There were differences by alcohol intake: 729 drinkers (96.4%) and 359 non-drinkers (93.2%) brushed their teeth at least twice a day (p=0.016). There were differences by smoking: 214 smokers (90.7%) and 874 non-smokers (96.6%) brushed their teeth at least twice a day (p<0.001).

Neither age nor household income made any difference in toothbrushing frequency ≥2 (p>0.05) (Table 3).

Table 3 . Toothbrushing frequency by general characteristics and health behavior

Variable	Toothbrushing frequency		χ2 (p-value)
	≥2	<2
Gender
Men	494 (93.4)	35 (6.6)	8.652 (0.003)
Women	594 (97.1)	18 (2.9)
Age (yr)
20-29	448 (94.5)	26 (5.5)	1.292 (0.256)
30-39	640 (96.0)	27 (4.0)
Household income
High	418 (95.9)	18 (4.1)	7.755 (0.051)
Above-average	330 (96.5)	12 (3.5)
Below-average	262 (94.9)	14 (5.1)
Low	78 (89.7)	9 (10.3)
Education
≥College	725 (97.3)	20 (2.7)	18.627 (<0.001)
≤High school	363 (91.7)	33 (8.3)
Occupation
Other than blue-collar	602 (96.8)	20 (3.2)	6.953 (0.031)
Blue-collar	121 (92.4)	10 (7.6)
Jobless	365 (94.1)	23 (5.9)
Alcohol intake
Drinker	729 (96.4)	27 (3.6)	5.831 (0.016)
Non-drinker	359 (93.2)	26 (6.8)
Smoking
Smoker	214 (90.7)	22 (9.3)	14.694 (<0.001)
Non-smoker	874 (96.6)	31 (3.4)
Total	1,088 (95.4)	53 (4.6)

Values are presented as number (%). Chi-square test.

4. Toothbrushing frequency by frequency of consuming sugar-containing food

As for toothbrushing frequency ≥2 by frequency of consuming sugar-containing food, the less consumption of sweetened drinks, the more likely to brush their teeth at least twice a day: 8 (80.0%) consuming them at least twice, 56 (93.3%) consuming them once, and 1,024 (95.6%) consuming none of them (p=0.049). The less consumption of fruit drinks, the more likely to brush their teeth at least twice a day: 12 (75.0%) consuming it at least twice, 76 (95.0%) consuming it once, and 1,000 (95.7%) consuming none of it (p<0.001) (Table 4).

Table 4 . Toothbrushing frequency by frequency of consuming sugar-containing food

Variable		Toothbrushing frequency		χ2 (p-value)
		≥2	<2
Sweetened drink	≥2	8 (80.0)	2 (20.0)	6.036 (0.049)
	1	56 (93.3)	4 (6.7)
	None	1,024 (95.6)	47 (4.4)
Sweetened coffee	≥2	69 (92.0)	6 (8.0)	2.117 (0.347)
	1	137 (95.1)	7 (4.9)
	None	882 (92.7)	40 (4.3)
Fruit	≥2	293 (95.4)	14 (4.6)	2.171 (0.338)
	1	296 (96.7)	10 (3.3)
	None	499 (94.5)	29 (5.5)
Processed fruit	≥2	45 (91.8)	4 (8.2)	2.621 (0.270)
	1	193 (97.0)	6 (3.0)
	None	850 (95.2)	43 (4.8)
Fruit drink	≥2	12 (75.0)	4 (25.0)	15.260 (<0.001)
	1	76 (95.0)	4 (5.0)
	None	1,000 (95.7)	45 (4.3)
Confectionery	≥2	115 (95.8)	5 (4.2)	2.314 (0.314)
	1	256 (97.0)	8 (3.0)
	None	717 (94.7)	40 (5.3)
Simple sugar	≥2	679 (96.0)	28 (4.0)	2.053 (0.358)
	1	169 (93.9)	11 (6.1)
	None	240 (94.5)	14 (5.5)
Ice cream	≥2	11 (100.0)	0 (0.0)	1.513 (0.469)
	1	79 (97.5)	2 (2.5)
	None	998 (95.1)	51 (4.9)
Candy	≥2	8 (88.9)	1 (11.1)	1.776 (0.411)
	1	52 (98.1)	1 (1.9)
	None	1,028 (95.3)	51 (4.7)
Source	≥2	206 (94.9)	11 (5.1)	0.181 (0.913)
	1	248 (95.8)	11 (4.2)
	None	634 (95.3)	31 (4.7)
Beverage with lactic acid bacteria	≥2	14 (93.3)	1 (6.7)	6.537 (0.038)
	1	81 (90.0)	9 (10.0)
	None	993 (95.8)	43 (4.2)
Vegetable drink	≥2	19 (100.0)	0 (0.0)	1.681 (0.432)
	1	69 (93.2)	5 (6.8)
	None	1,000 (95.4)	48 (4.6)
Chocolate	≥2	4 (80.0)	1 (20.0)	3.338 (0.188)
	1	46 (97.9)	1 (2.1)
	None	1,038 (95.3)	51 (4.7)
Carbonated drink	≥2	54 (90.0)	6 (10.0)	4.532 (0.104)
	1	221 (94.8)	12 (5.2)
	None	813 (95.9)	35 (4.1)
Total		1,088 (95.4)	53 (4.6)

Values are presented as number (%). Chi-square test.

5. Toothbrushing frequency by sugar-containing food consumption

Hierarchical logistic regression analysis performed to identify the factors for the increase in toothbrushing frequency by intake of sugar-containing food type found that in Model 1, with only the general characteristics and health behavior included, the factors for the increase in toothbrushing frequency included education, alcohol intake, and smoking: the odds ratio (OR) for toothbrushing frequency ≥2 was 2.278 times higher for college graduates than for high school graduates (p=0.009), 2.296 time higher for drinkers than for non-drinkers (p=0.006), and 0.436 times higher for non-smokers than for smokers (p=0.011). In Model 2, with the general characteristics, health behavior, and sugar-containing food type included, OR was 2.352 times higher for college graduates than for high school graduates (p=0.008), 2.047 times higher for drinkers than for non-drinkers (p=0.021), and 0.410 times higher for non-smokers than for smokers (p=0.007); the less consumption of fruit drinks and beverage of lactic acid bacteria, the more likely to brush teeth at least twice a day: OR=0.409 (p=0.003) and OR=0.540 times higher (p=0.049), respectively (Table 5).

Table 5 . Factors affecting toothbrushing frequency ≥2

Variable	Model 1				Model 2
	B	Odd rario	p-value		B	Odd rario	p-value
Gender
Women (ref: Men)	0.580	1.786	0.082		0.540	1.715	0.113
Education
College & higher (ref: High school & lower)	0.826	2.278	0.009		0.855	2.352	0.008
Occupation
Non-blue-collar (ref: Blue-collar)	0.352	1.422	0.293		0.415	1.515	0.225
Occupation
Blue-collar (ref: Jobless)	0.168	1.183	0.685		0.114	1.121	0.786
Alcohol intake
Drinker (ref: Non-drinker)	0.831	2.296	0.006		0.716	2.047	0.021
Smoking
Smoker (ref: Non-smoke)	−0.831	0.436	0.011		−0.892	0.410	0.007
Sweetened drink					−0.445	0.641	0.226
Fruit drink					−0.864	0.409	0.003
Beverage with lactic acid bacteria					−0.617	0.540	0.049

Hierarchical logistic regression analysis.

This study was conducted in young adults aged 20 to 39 in South Korea and aimed to determine association between type and frequency of sugar-containing food consumption and toothbrushing frequency and provide basic data that could help promote and maintain oral health so that they could consume sugar-containing food correctly.

Women, those at a higher education level, non-blue-collar workers, drinkers, and non-smokers were more likely to brush their teeth at least twice a day. Consistent with Park and Son [2] and Jung [13], the more educated, the more likely to use oral care products; consistent with Moon and Lee [14], education among the socio-demographic characteristics was reportedly associated with oral care product use. On this basis, it is necessary to give oral health education that meets the socio-demographic characteristics and the environmental factors of individuals rather than a uniform style of oral health education.

The rapid industrialization and Westernization process has also brought about a lot of changes in dietary lifestyle in South Korea and, particularly, increased consumption of processed foods; the increase in processed food consumption causes a problem of overconsumption of fat and sugar [15]. Poor dietary habits are reportedly associated with obesity as well as with behavior related to oral health [16].

Lee et al. [4] found that both dental caries and periodontal disease were associated with dietary behavior of having sugar-containing snacks three times a day. Particularly, frequent consumption of sugar-containing food was significantly associated with the prevalence of periodontal disease even after adjusting the risk factors for periodontal disease, such as toothbrushing and smoking. In contrast, Jung et al. [17] noted that oral disease was affected by methods of toothbrushing to manage oral health after consuming snacks and drinks that cause dental caries rather than by the consumption of such snacks and drinks. To prevent oral disease, therefore, it is essential for individuals to improve their lifestyle and implement efficient preventive measures so that they can manage their oral health properly; the primary way of preventing oral disease is reportedly to manage dental plaque [18].

It is necessary to remove dental plaque regularly and effectively with the objective of preventing them and this can be done by mechanical removal, which involves toothbrushing and dental floss use in the daily course of oral hygiene or professional tooth cleaning on a regular basis; of these, toothbrushing is the most fundamental and effective method. In addition, the causes of any oral disease can be removed effectively to treat the disease through a professional oral hygiene procedure by a dentist and good toothbrushing is crucial to maintain and manage the recovered oral conditions constantly [19]. A combination of selection of oral hygiene products appropriate for individuals, knowledge of how to use them, and professional tooth cleaning on a regular basis probably makes it possible to prevent and manage oral disease [20].

The issue of oral health in adulthood remains at a high level and can be accumulated constantly, even affecting oral health in old age; therefore, it is necessary to intervene actively in the risk factors for oral diseases in adulthood [4]. Chung [21] suggested daily dental plaque management and regular oral examination for young adults, who don’t have a lot of dental problems; Yang et al. [22] proposed good methods of toothbrushing, such as a 1-2-3 toothbrushing campaign, at the level of systemic health.

The World Health Organization recommends putting restrictions on consumption of sugar-containing food as a clinical guidance for obesity and oral disease prevention and management and puts emphasis on dentists and dental hygienists, who can exert a significant influence on good oral health and dietary habit formation for patients and subjects, suggesting the need to enable them to take a leading role in developing relevant education and policies [23].

While oral disease needs to be prevented and managed through oral examination and counseling for patients, South Korea has no comprehensive prevention guidance established and it is necessary to make a prevention plan for each age group.

The 2019 raw data from the Korea National Health and Nutrition Examination Survey (KNHANES VIII-1) were used to make a sample of 1,141 respondents aged 20 to 39, with the exception of missing data. Toothbrushing frequency by sugar-containing food consumption and oral health behaviors was investigated, obtaining the following results:

1. As for the association between the respondentsʼ general characteristics and toothbrushing frequency, those who were female, who were more educated, and who were non-blue-collar workers brushed their teeth more frequently. As for health behavior, drinkers and non-smokers brushed their teeth more frequently.

2. As for toothbrushing frequency by the frequency of consuming sugar-containing food, the more consumption of sweetened drinks, fruit drinks, and beverage with lactic acid bacteria, the higher toothbrushing frequency; in particular, the smaller number of times consuming fruit drinks, the higher frequency of toothbrushing.

3. The logistic regression analysis of toothbrushing frequency by consumption of sugar-containing food type, OR was 2.352 times higher for college graduates than for high school graduates (p=0.008), 2.047 times higher for drinkers than for non-drinkers (p=0.021), and 0.410 times higher for non-smokers than for smokers (p=0.007); the less consumption of fruit drinks and beverage of lactic acid bacteria, the more likely to brush teeth at least twice a day: OR=0.409 (p=0.003) and 0.540 times (p=0.049), respectively.

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