1.Background

According to the statistical data of Health Care Bigdata Hub, the number of outpatients for gingivitis and periodontal disease (K05) will be 17.4 million, the most frequent outpatient disease in 2021. The number of patients with gingivitis and periodontal disease more than doubled from 8.03 million 10 years ago. Dental caries (K02) maintains the top rank for long-term frequent disease with 6.35 million in 2021 (4th frequent outpatient)¹⁾. The major risk factors for dental caries and periodontal disease are oral microbes²⁾. When a mass of bacteria adheres to the dental surface as agglomerates with calcium in saliva, as the bacteria multiply, they secrete acidic substances to the surroundings environment, and various proteolytic enzymes are secreted to cause periodontal inflammation as well as dental caries. If the dental plaque on the tooth surface is not removed properly, the teeth and periodontal are exposed to constant risk stimuli, which leads to not only dental caries, but also periodontal pocket inflammation, gingival recession, and destruction of periodontal ligaments and alveolar bone, leading to tooth loss. Therefore, for effective prevention and treatment of dental caries and periodontal disease, continuous oral hygiene management is required to control the dental plaque.

A toothbrush is the most basic oral hygiene management tool, but dental floss, interdental toothbrush, mouthwash, and tongue cleaner are also widely used for oral hygiene³⁾. Although brushing also reduced the incidence of inter-dental papillitis, brushing and interdental cleaning with a rubber cone significantly reduced the incidence of inter-dental papillitis by more than four times⁴⁾. Interdental cleaning is very effective in preventing dental caries and periodontal disease. Therefore, interdental plaque, which is limited in removal by toothbrushing, can be effectively removed using dental floss or an interdental toothbrush. The use of dental floss not only reduces inflammation of the gum in the interdental area, but also prevents dental caries on the adjacent surface and is effective in removing bad breath⁵⁾. About 80% of the plaque on interdental area was removed by using dental floss⁶⁾. Compared to tooth-brushing alone, around 95% of plaque was removed when toothbrushes and interdental brushes were used together⁷⁾.

2.Objectives

Recently, dental floss with various thread thicknesses and coated with wax or functional ingredients is commercially available, allowing users to choose according to their preferences. Floss that is fixed in a holder to help with the difficulty of using floss that is wrapped around your finger is also available. Thread type, C type, and Y type floss according to the shape of the handle are easily available in the market. However, most dental clinics and Korean Dental Association provide oral hygiene education using dental floss that is wrapped around the finger. According to the teeth arrangement and preferences of consumers, education on how to use dental floss for each type is required. In addition, the plaque removal effect of C type and Y type floss has not been experimentally verified. In this study, the degree of dental plaque removal of C type and Y type floss was compared with thread type floss. The high-definition digital imaging equipment quantitative light-induced fluorescence-digital (QLF-D) was used to measure the degree of plaque removal. By elucidating the degree of plaque removal for each type of dental floss, the need for education on how to use each type of floss is derived.

1.Ethic statement

The present study was approved by the Institutional Review Board of Eulji University (IRB No. EU22-70). Written informed consent was provided to participants.

2.Subjects

Thirty adults in their 20s participated in this study. Subjects who had bleeding while toothbrushing their teeth, were undergoing braces, and had been scaling for less than 3 months were excluded from the experiment. This study consisted of 3 groups (thread type floss, C type floss, Y type floss), and 10 people in each group participated. The number of participants was recruited by referring to previous similar studies, and all participated in the experiment⁸⁾.

3.Materials

One representative type for each type of floss was used in the experiment: thread type floss (Oral B waxed floss; P&G, New York, NY, USA), C type floss (Oral B), Y type floss (Daiso, Seoul, Korea) (Fig. 1). The dental plaque images were obtained by Q-ray (AIOBIO, Seoul, Korea). The captured Q-ray image was confirmed with the QLF-D viewer program C3 (AIOBIO), and the fluorescence level was obtained with the QLF-D analysis program QA2.

Fig. 1. Floss types. (A) Thread type floss. (B) C type floss. (C) Y type floss.

4.Methods and image analysis

Before flossing, images of the subject’s upper and lower anterior teeth were obtained by Q-ray. Dental floss was applied to the 6 incisors of the subject’s upper and lower jaw. Flossing of all subjects was performed by one investigator. For the thread type floss group, the middle finger of both hands method was applied. Roll about 45 cm of dental floss around the middle fingers of both hands and adjust them at intervals of 5 to 10 cm. Then, with the thumb and index finger of both hands, hold the dental floss to a length of 2 to 2.5 cm, and place the floss in a C-shape on the tooth surface. The floss was cleaned three times in the vertical direction per tooth surface by sawing operation. In the case of the C type and Y type floss groups, the dental floss was also placed in a C-shape on the tooth surface and cleaned three times in the vertical direction per tooth surface by sawing operation. After flossing, images of the subject’s upper and lower incisors were obtained by Q-ray again. The fluorescence level of the captured Q-ray image was measured using the QLF-D analysis program QA2. The fluorescence level of dental plaque was confirmed with the values of Simple Plaque Score (SPS), Area R30, Area R70, and Area R120. SPS is set on a scale of 0∼5, and a higher score means more plaque or tartar. Area R30, Area R70, and Area R120 represent the fluorescence intensity according to the maturity of dental plaque. Area R30 values are areas sensitive to the recently formed dental plaque, and Area R120 values are areas sensitive to dental plaque accumulated over a long period of time.

5.Statistical analysis

Statistical analysis was performed using SPSS 28.0 (IBM Corp., Armonk, NY, USA). After Shapiro–Wilk normality test was performed, the dental plaque area before and after flossing was analyzed by Wilcoxon signed rank test. The Kruskal–Wallis test was used to compare the plaque removal effect between the three types of dental floss. A p-value ≤0.05 was considered statistically significant.

As a preliminary study, we measured the dental plaque level of the subjects participating in the study by Q-ray and confirmed it with Area R30, Area R70, and Area R120 fluorescence intensities. For most of the subjects, the sensitivity in the area of Area R30 was higher than that of Area R70 and Area R120, so the degree of dental plaque was analyzed using the Area R30 value. Q-ray fluorescence images were obtained before and after flossing for the maxillary and mandibular 6 incisors of three groups of subjects (thread type floss, C type, and Y type) (Fig. 2A). As a result of analyzing the fluorescence image of Area R30 in QA2 program, there was a significant difference in fluorescence intensity before (1.56±2.19) and after (0.92±1.60) of thread type floss application (p=0.018). C type floss also had a significant difference in fluorescence intensity before (2.67±3.20) and after (1.27±1.85) floss application (p=0.012). There was an also significant difference in fluorescence intensity before (1.54±1.56) and after (1.10±1.30) of Y type floss application (p=0.012) (Fig. 2B). These results suggest that the dental plaque removal effect after flossing is effective for all three types of floss.

Fig. 2. Q-ray fluorescence images of the 6 incisors of the subjects before and after flossing. (A) Q-ray fluorescence images were obtained before and after flossing for the maxillary and mandibular 6 incisors of three groups of subjects (thread type floss, C type, and Y type). Representative Q-ray images for each group were provided. (B) The degree of plaque was analyzed using the Area R30 value in the QA2 program, and the Area R30 intensity score was graphed before and after the application of dental floss. *p-value was determined from Wilcoxon signed rank test (n=10/group).

To elucidate the effective type of dental floss for dental plaque removal, the difference between the SPS, Area R30, Area R70, and Area R120 values before and after the application of dental floss was used. As a result of the analysis, there was no significant difference in SPS, Area R30, Area R70, and Area R120 values by floss type (∆SPS, p=0.674; ∆Area R30, p=0.726; ∆Area R70, p=0.504; ∆Area R120, p=0.423) (Table 1). These results suggest that the dental plaque removal effect is similar regardless of the type of floss.

Table 1

Dental Plaque Removal Effect by Floss Types (n=10/group)

Category	Floss	Flossing		Mean±SD	p-valuea
		Before	After
∆SPS	Thread type	1.30±1.89	0.90±1.45	0.40±0.97	0.674
	C type	1.80±1.81	1.30±1.81	0.50±0.71
	Y type	1.20±1.23	0.80±1.23	0.40±0.52
∆Area R30	Thread type	1.56±2.19	0.92±1.60	0.64±1.00	0.726
	C type	2.67±3.20	1.27±1.85	1.00±1.75
	Y type	1.54±1.56	1.10±1.30	0.44±0.39
∆Area R70	Thread type	0.82±1.34	0.45±0.90	0.37±0.73	0.504
	C type	1.55±1.81	0.80±1.81	0.75±1.19
	Y type	0.64±1.23	0.47±1.23	0.17±0.19
∆Area R120	Thread type	0.44±1.45	0.22±0.51	0.22±0.37	0.423
	C type	0.54±1.81	0.29±1.81	0.25±0.50
	Y type	0.22±1.23	0.19±1.23	0.03±0.07

Values are presented as mean±standard deviation.

SPS: simple plaque score.

^ap-value was determined from Kruskal–Wallis test (n=10/group).

1.Interpretation

The acid component produced by bacteria in the dental plaque causes dental caries, and various secreted toxins cause gums inflammation⁹⁾. The initial dental plaque is relatively easy to remove only by toothbrushing, but if it clumps together with the calcium component of saliva for quit long time, it is converted into tartar, which is difficult to remove only by toothbrushing. Since dental calculus, which is difficult to remove by brushing, causes periodontal disease, it is very important to have a preventive habit that controls the growth of the dental plaque in the early stage. As well as dental caries, the number of out-patients for gingivitis and periodontitis is ranked at the top in 2021, making it a high morbidity disease¹⁾.

2.Comparison with previous studies

With the increasing interest in oral health, various oral supplements are being used as well as dental care in terms of prevention and aesthetics. According to the report, about 40% of the total tooth surfaces were not properly controlled despite toothbrushing, and plaque control was insufficient in the molars rather than the anterior teeth, and in the lingual and proximal surfaces rather than the buccal surfaces^6,7,10). The use of dental floss and interdental toothbrush can remove more than 80% of plaque in the interdental area and helps the blood circulation of the gingiva¹⁰⁾. As a result of the survey on the use of oral supplements, the number of users of dental floss, inter-dental brush, and mouthwash besides brushing was about 20%, which did not increase compared to the 2012 survey results (about 18.5%). The American Dental Association recommends cleaning between teeth at least once a day for oral hygiene. 93.8% of subjects with healthy teeth use oral hygiene products¹¹⁾. However, the level of awareness about how to use oral hygiene products such as toothpicks, dental floss, and mouthwash was moderate, and it was investigated that they did not generally know how to use oral hygiene products¹²⁾. Studies have consistently reported that the use of dental floss is very effective in reducing periodontal disease and dental caries^3,5,6). In particular, in the case of a dense tooth structure due to a limited space between teeth or a mismatch between the tooth size and the jaw size, the use of dental floss may be more effective. Since C type and Y type floss as well as thread type floss are commercially available, individuals can choose floss according to their preference. However, the results of studies demonstrating the plaque removal effect of C type and Y type floss have not been sufficiently reported.

Therefore, this study tried to confirm the plaque removal effect of C type and Y type floss compared to thread type floss. For this purpose, a quantitative light- induced fluorescence, Q-ray test method that can determine the location and amount of dental plaque by detecting porphyrin of oral microorganisms present in the dental plaque was applied¹³⁾. The location and amount of dental plaque is usually confirmed by dental disclosing solution staining method or the medical opinion of the dentist. O’Leary plaque control index and PHP index were also applied to determine the biofilm index¹⁴⁾. QLF-D is a high-definition digital imaging device that combines Q-ray and a specialized filter¹⁵⁾. It can detect bacteria on the tooth surface that are difficult to see with the naked eye using fluorescence in real time. Early bacterial colonies older than 3 days are detected, and the location of plaque containing bacteria as well as the amount of plaque can be automatically scored.

With QLF-D analysis program QA2, four values are calculated: SPS, Area R30, Area R70, and Area R120. R30, R70, and R120 are fluorescence intensities. Area R30 values are sensitive to the detection of a relatively recently formed dental plaque, and Area R120 values are sensitive to the detection of accumulated plaque. As a result of measuring Area R30, Area R70, and Area R120 of the dental plaques of 30 adults in their 20s who participated in this study, the values for Area R30 were more sensitive than those of Area R70 and Area R120 for most of the participants.

This means that the participants’ dental plaque score was low, and for this reason, the Area R30 value was applied to compare the degree of dental plaque removal according to the type of dental floss. As a result of this study, the plaque removal effect according to the application of dental floss was confirmed in all types of floss. In comparison of the degree of plaque removal using Area R70 and Area R120, the plaque removal according to the application of dental floss was effective regardless of the type of floss. As a result of comparing the score differences (∆SPS, ∆R30, ∆R70, ∆R120) of the dental plaque before and after floss application by floss type, the largest difference in the dental plaque score was observed with C type floss, followed by Y type and thread type floss. However, the difference was not statistically significant among the floss types. This result means that the C type and Y type floss have the same plaque removal effect as the thread type floss. It also means that central plaque is controlled just by flossing regardless of the floss types. Therefore, as C type and Y type floss are being purchased by consumers, training on how to properly use them need to be prepared.

3.Limitation

Since flossing is easy to remove relatively immature dental plaque and there is a limit to removing calculus, the selection of subjects in their 20s who do not have a high dental plaque index was suitable for the purpose of this study. However, there was a limitation in that the fluorescence score output from QLF-D was low because participants with a significantly lower level of dental plaque were included. Therefore, in an experimental study to prove the plaque removal effect between oral hygiene tools, it is necessary to perform it on subjects with an appropriate plaque score rather than age. Further study will be needed to elucidate the degree of dental plaque removal for each type of floss according to the position of the teeth and various tooth surfaces. In addition, based on the results of this study, education and awareness on the effectiveness and correct use of dental floss for oral hygiene rather than the type of floss should be expanded.

4.Conclusions

In this study, the degree of dental plaque removal according to the dental floss types was compared with the fluorescence image value, and it was confirmed that the use of dental floss was effective in removing plaque and that the plaque removal effect was not related to the type of dental floss. This result suggests that proper instruction on how to use each type of dental floss is necessary.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2022R1F1A1063204).

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

Human experiment was approved by the Institutional Review Board (IRB) of Eulji University (approval No. EU22-70).

Conceptualization: Myoung-Hee Kim. Experiments: Myoung-Hee Kim, Yu Jin Park, and Young Sun Hwang. Data acquisition: Myoung-Hee Kim, Yu Jin Park, and Young Sun Hwang. Formal analysis: Myoung-Hee Kim, Yu Jin Park, and Young Sun Hwang. Funding: Young Sun Hwang. Supervision: Myoung-Hee Kim, Yu Jin Park, and Young Sun Hwang. Writing–original draft: Myoung-Hee Kim and Young Sun Hwang. Writing–review & editing: Myoung-Hee Kim, Yu Jin Park, and Young Sun Hwang.

The data and materials of this article are included within the article. The data supporting the findings of this study are available from the corresponding author upon reaso-nable request.