Introduction

Dental caries is still a major public health problem that affects people of all ages in most countries. When fluoride toothpaste was introduced in the 1960s, caries only showed a decreasing trend in Sweden, while in the rest of the Western world, it took several decades to see a reduction in caries incidence. There are indications that caries, especially among growing individuals and the elderly population, is on the rise again [1].

Fluoride toothpaste is one of the main reasons for the decrease in the prevalence of dental caries worldwide [2]. However, there is not enough knowledge about whether individuals in different age groups are aware of the benefits of fluoride toothpaste or not, as well as their daily oral care habits and whether they use fluoride or not [3, 4].

Fluoride toothpaste is widely advertised globally for cosmetic purposes. This trend is in line with the legal definition of regular fluoride toothpaste as a cosmetic and hygiene product, in fact, teenagers use toothpaste for cosmetic purposes. On the other hand, dentists promote fluoride toothpaste due to its therapeutic effect in preventing dental caries. An increasing number of children and teenagers request teeth whitening [5].

Brushing teeth with fluoride toothpaste is considered equally important as fluoride for preventing dental caries. Dental professionals used to think that identifying plaque on teeth is easier for their patients than asking about their use of fluoride toothpaste. The reason for this was that they assumed their patients already had the necessary knowledge about fluoride toothpaste and its use. However, individual intervention by a dental health professional has a significant impact on the use of fluoride toothpaste [6]. One of the most effective ways to prescribe fluoride is through regular use of fluoride toothpaste [7,8,9]. Therefore, the aim of this study was to investigate the knowledge and performance of Iranian students regarding the use of fluoride toothpaste.

Method

This research is a cross-sectional analytical study (Clinical Trial Number: 401,000,590). The target population in this study was the first- and second-year high school students in Kerman city. First, the names of schools were obtained from the Department of Education and then, using cluster sampling, four schools (two girls’ schools and two boys’ schools) from each education district were selected. Then two classes were selected from each school and questionnaires were distributed (z: 1.96; p = q = 0.3; d: 0.03, Number of samples: 700).

The researcher-made questionnaire (Persian language) contained personal questions such as age, gender, and year of enrollment, general questions, and questions related to students’ knowledge and performances about the use of fluoride toothpaste, which were given to students to complete and submit. The nature and purpose of this study were such that students who entered the study, were allowed to leave the study at any time after the interview began. The purpose of this research was explained to each individual, and if they wished, the questionnaire was provided to them. In addition, all individuals were assured that the information on the questionnaire would remain confidential and would only be used for statistical purposes.

The questions in this questionnaire were designed by two dental professionals (Oral Medicine and Operative Dentistry) and one statistics expert.

The scientific validity of the questionnaire was confirmed by providing it to six dental professionals experts, and the level of question content and comprehensibility was discussed. Based on their opinions and text analysis, the content validity of the questionnaire was satisfactory. However, two knowledge questions and two performance questions were removed according to their opinion.

Then, to evaluate the reliability, first, the questionnaire was given to ten students, and then two weeks later, the questionnaire was given to them again. The reliability of the questionnaire was satisfactory regarding the Cronbach’s alpha coefficient of 0.76.

In terms of knowledge questions, each correct answer received 2 points, each wrong answer received 0 points, and “I do not know” received 1 point. The knowledge questions included 12 questions, so the knowledge score ranged from 0 to 24 (Good = 20–24, Average = 10–19, Poor = 0–9). In terms of performance questions, each correct answer received 2 points, each wrong answer received 0 points. The performance questions included 14 questions, so the performance score ranged from zero to 28 (Good = 23–28, Average = 13–22, Poor = 0–12).

Results

The results obtained from the analysis by T-test, Pearson correlation coefficient, Chi-square test, and SPSS version 24 were analyzed. The level of significance in data analysis was P < 0.05.

In this study, 700 forms were completed by students, and 681 forms were analyzed (Response Rate = 97.3%). Of these, 252 (37%) were boys and 429 (63%) were girls. The average age of participants was 14.1 ± 0.4. The minimum age was 13 and the maximum age was 16. Table 1 621 participants (91.2%) reported using toothpaste, and 453 participants (77.8%) reported using fluoride toothpaste.

Table 1 Demographic characteristics of participating in the study
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Table 2 shows the participants’ responses to general questions. 521 participants (76.51%) reported that the price of toothpaste is important in choosing a type of toothpaste. 621 participants (91.19%) used a regular toothbrush. 312 participants (45.81%) reported receiving education on using toothpaste, and in 212 cases (3028%), this education was provided by parents. 609 participants (87%) evaluated their oral health as good.

Table 2 Answers of participants to general questions
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Table 3 shows the participants’ responses to knowledge questions. 621 participants (91.19%) stated that toothpaste promotes oral health. 567 participants (81%) stated that if someone uses toothpaste, it will have less effect on their teeth’s sugar level. 501 participants (71.57%) correctly stated that using toothpaste can make teeth less yellow. The mean ± SD of knowledge score was 16.7 ± 1.2 out of 24, indicating the average level of knowledge among students in this field.

Table 3 Answers of participants to knowledge questions
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Figure 1 show the amount of toothpaste used by students. This study showed that 402 participants (57.42%) used half a centimeter of toothpaste. 102 participants (14.57%) used 2 centimeters of toothpaste, and 112 participants (16%) used 1 centimeter of toothpaste.

Fig. 1
figure 1

How much toothpaste do you use when you brush your teeth?

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Table 4 shows the participants’ responses to performance questions. 543 participants (77.57%) stated that they brush their teeth at least once a day, and 101 participants (14.43%) brushed their teeth twice a day. 502 participants (71.71%) reported brushing their teeth for less than a minute. In this study, only 60 participants (8.9%) used mouthwash after brushing their teeth. 102 participants (14.57%) stated that they clean between their teeth using dental floss.

Table 4 Participant responses to performance questions
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The average performance score was 18.10 ± 2.22 out of 28, indicating a relatively average performance level among study participants. This study showed that there was no significant relationship between performance score and age or gender. Table 5 there was also a positive correlation between knowledge and performance, with a correlation coefficient of 0.731, indicating that increasing knowledge leads to increased behavioral changes.

Table 5 The relationship between knowledge, performance and demographic charecteristics in participants
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Discussion

In this study, 543 participants (79.7%) reported brushing their teeth at least once a day, and 101 participants (14.8%) brushed their teeth twice a day.

In the field of oral hygiene, one of the constant concerns of researchers in this field is daily brushing, and it should be done correctly by every person at least twice a day. According to the finding by Zhu et al., preventive measures are more effective than curative measures [10]. While it is beneficial that more than half of students brush their teeth twice a day, there is a need to increase knowledge about oral hygiene practices, including the recommended amount of toothpaste and frequency of brushing.

A meta-analysis study showed that brushing teeth more than twice a day or less than twice a day does not have a significant effect on the occurrence of dental caries, but they noted that dental caries occur more frequently in primary teeth compared to permanent teeth [6]. Another study showed that the strongest evidence related to dental caries in 12-year-olds is found in the frequency of brushing and dental plaque [11].

In this research, 502 participants (73.7%) reported brushing their teeth for less than a minute. Also, 621 participants (91.2%) reported using toothpaste, and 453 participants (77.8%) reported using fluoride toothpaste.

The Saveanu et al. study [12] showed that about half of the participants did not know the recommended amount of toothpaste to use while brushing. Only a quarter of individuals considered fluoride content when choosing toothpaste. About one-third of students did not know proper brushing techniques and chose their toothbrush based on criteria other than dental guidelines.

The mean ± SD of knowledge score was 16.7 ± 1.2 out of 24, indicating the average level of knowledge regarding the use of fluoride toothpaste among students.

The Saveanu et al. study [12] showed that most students have at least basic knowledge about the frequency, purpose, and timing of brushing. Only about 20.47% of students knew about the beneficial effects of fluoride in toothpaste on mineralizing dental tissue. This lack of knowledge about fluoride and its benefits among students has been shown in other studies as well [13,14,15,16,17,18]. A study showed that Australian preschoolers who used non-fluoride toothpaste had a higher rate of dental caries compared to other regions worldwide [19]. A Cochrane review supports the benefits of using fluoride toothpaste in preventing dental caries compared to non-fluoride toothpaste [20].

The fact that a significant percentage of students do not have knowledge about the amount of toothpaste to use and the frequency of brushing has been shown in other specialized studies as well [19,20,21,22].

The benefits of fluoride-containing toothpaste are well established. Overall, studies are relatively high quality and provide clear evidence that fluoride-containing toothpaste is effective in preventing dental caries [9]. It appears that fluoride-containing toothpaste, frequency of brushing, fluoride concentration in toothpaste, amount of toothpaste on the brush, brushing time, and rinsing with water are effective factors in this area [23,24,25,26].

Differences in studies can be caused by the studied population, the studied country, the level of oral health of the community and the culture of the community.

Although fluoride-containing toothpaste is generally available in northern European countries, around 25% of 14-year-old adolescents do not brush their teeth daily [27, 28]. In Sweden, 90% of adult report brushing their teeth at least once a day [29]. The recent studies showed that almost half of adults brush their teeth for more than two minutes [30, 31] where brushing time was observed to be slightly over one minute. In the study by Koivusilta et al. [28], only 9% of adults used proper rinsing technique after brushing.

This study showed that in 402 participants (56%), the amount of toothpaste used was half a centimeter. 102 participants (15%) used 2 centimeters of toothpaste, and 112 participants (14.5%) used 1 centimeter.

The American Academy of Pediatrics, the American Academy of Pediatric Dentistry, and the American Dental Association recommend fluoride-containing toothpaste for all children and limit the amount of toothpaste used by children under 3 years old to a “smear” (a grain of rice) [12,13,14].

According to Hu et al. controlling the amount of toothpaste consumption is important in reducing the risk of fluorosis. A meta-analysis showed that using a pea-sized amount minimizes the risk of fluorosis in children and maximizes the preventive benefits of tooth decay for all age groups [22].

In this study, 621 participants (91.2%) stated that toothpaste promotes oral health. 567 participants (83.2%) claimed that if someone uses toothpaste, it will have less effect on their teeth. The use of toothpaste can whiten teeth less by 501 participants (73.6%).

Furundzic et al. [7] showed that reasons for using fluoride-containing toothpaste in students include oral health, a substance that strengthens teeth and eliminates bacteria and therefore prevents decay. Additionally, if someone uses toothpaste, it will have less effect on their teeth, and toothpaste can be used to protect against acid because toothpaste is alkaline and therefore increases PH which is compatible with other studies [25, 26, 28,29,30].

Differences in studies can be caused by the studied population, the studied country, the level of oral health of the community and the culture of the community.

This study showed that the average knowledge and performance scores of students were moderate, and there was no significant correlation between performance and knowledge scores with age and gender.

There are multiple studies in specialized articles that analyze the relationship between students’ knowledge level and their knowledge and performance regarding oral hygiene [3, 4]. Kamran et al. [25] showed that women have better grades in knowledge, attitude, and behavior toward oral hygiene compared to men, which is consistent with other studies [27,28,29,30].

There was also a positive correlation between knowledge and performance, and a correlation coefficient of 0.731 was obtained between knowledge and behavior, which indicates that increasing knowledge leads to an increase in behavioral changes that is consistent with the research of Kamran and colleagues [25].

Eleven studies showed a significant positive effect of intervention on awareness, attitude, and behavior (brushing and flossing) of the experimental group. Nakre and Harikiran suggested that involving other groups such as parents and teachers in oral health education and promotion is more effective. Increasing knowledge can improve oral health education [21].

Conclusion

This study showed that students’ knowledge and performance about using fluoride-containing toothpaste is average. There was no significant relationship between performance and knowledge with age and gender. There was also a positive correlation between knowledge and performance that indicating that increasing knowledge leads to an increase in behavioral changes.

Limitation

Non-cooperation of the number of participants.

Non-cooperation of a number of school officials.

Incomplete filling of a number of questionnaires.