The present cross-sectional study was conducted in intermediate schools in Dammam and Khobar, Eastern Province, Saudi Arabia in February-April 2016. The target group was male students (12-15 years of age). Ethical approval was obtained from the Institutional Review Board (IRB-2015-02-187) at the Imam Abdulrahman Bin Faisal University, Dammam. The current report was part of an ongoing study that aimed to describe the oral health status of intermediate schools’ male students. The students were included in the study if they were attending public schools in Khobar or Dammam, their parents or legal guardian consented in writing for their participation, the student himself agreed to be clinically examined, had no health problems and has not been on medication for the last six months. The students who did not return the written informed consent of their parents/legal guardians were excluded from the study. In addition, female students were excluded since the male examiners could not be allowed into females’ schools in conformance to social norms in the country.

Sample size of the original study was calculated using the following assumptions; alpha error=5%, study power=85%, estimated caries prevalence=70% [2] and null percent=66%. The minimum required sample size to assess caries prevalence was calculated (http://www.stat.ubc.ca/~rollin/stats/ssize/b1.html) to be 1207. The sample size was increased to 1,250 to avoid a drop because of non-response. The Directorate of Education in the province was approached to select public schools in the two cities for subjects’ recruitment. The authorities selected three schools which were thus non-statistically selected. All students in these three intermediate schools were asked to join the study.

Data collection included a clinical examination and a questionnaire. Caries was diagnosed based on the World Health Organisation (WHO) criteria [18], using disposable examination mirrors under daylight conditions in the schools. Three examiners had three sessions to train on the diagnostic criteria followed by a calibration session. The examiners had an acceptable agreement with an experienced gold standard examiner (κ ≥0.6). An experienced faculty member of dental public health division served as the gold standard examiner during the process of calibration. Plaque was assessed using the Plaque Index by Löe H [19].

A specially designed questionnaire was developed and was assessed for face and content validity by two independent assessors. The questionnaire was then pilot tested among 30 teenagers whose data were not included in the analysis. Minor modifications were made to minimise ambiguity and enhance clarity of the questionnaire. The self-administered questionnaires were filled by the students. The examiners were there to facilitate data collection by answering any question that the students had in the study.

Data were imported to SPSS, version 20.0 (Armonk, NY: IBM Corp) and analysed at 0.05 significance level. The main independent variable was caries in the first permanent molar (presence and mean number with caries). Covariates included in the study were; parents’ education, home ownership, oral health practices and Plaque Index. Descriptive statistics were calculated. Univariate and multivariate logistic regression were used to assess caries presence in different teeth in relation to the presence of caries in the first permanent molars. Linear (univariate and multivariate) regression was used to assess the association between the number of these various teeth with caries and the number of first permanent molars with caries).

[Table/Fig-1] presents the distribution of socio-economic factors and oral health practices of the study participants. Fifty percent of the students had both parents’ university educated and 53.9% of the parents owned their homes. Most of the students reported using fluoridated toothpaste (60.4%). However, only 25.2% reported having regular visits to the dentist. Seventy-six percent of the students indicated that they frequently used sugary snacks. The mean Plaque Index in the study sample was 1.4 with a standard deviation of 0.9.

The overall prevalence of tooth decay was 57.2% while the mean number of decayed teeth was 1.63 (SD±1.99). [Table/Fig-2] presents the percentage and mean number of carious teeth in the study participants. The first permanent molars had the highest percentage of decay among all teeth (50.4%) with a mean of 1.08 carious molars. The second most affected teeth were the second permanent molars (prevalence=14.7%, mean number of decayed molars=0.25). The mean number of carious canines was 0.02 with a prevalence of 1.8%, which were the least affected among all teeth.

[Table/Fig-2]:

Percentage of teeth with caries and mean number of carious teeth in male teenagers, Khobar and Dammam, 2016.

Different factors were associated with the presence of caries in other permanent teeth [Table/Fig-3]. None of the studied factors (both parents being university educated, living in owned houses, using fluoridated toothpaste, regular dental visits, not using sugary snacks and Plaque Index) were associated with the presence of caries in canines, premolars or second molars. Increased plaque accumulation was associated with higher odds of caries in incisors (OR=1.92) whereas using fluoridated toothpaste was associated with lower odds of caries in first molars (OR=0.47).

Adjusting for the effect of all other variables, significantly higher odds of caries in incisors, premolars and second molars were associated with caries in first molars (OR=4.87, 3.57 and 4.26, respectively [Table/Fig-4]. No significant association was observed between the presence of caries in the first molars and in canines (OR=0.99). Adjusting for the effect of all other variables, a unit increase in the number of carious first molars was associated with a significant increase in the number of carious incisors, premolars and second molars (regression coefficients=0.09, 0.07 and 0.12, respectively) [Table/Fig-5].

Our study demonstrated that caries in first permanent molar is significantly associated with increased risk of caries in second molar, premolars and incisors. Similarly, significant associations between caries in first permanent molar and caries in other permanent teeth were also shown in multivariate linear regression analyses. The highest prevalence of caries in first and second permanent molars was observed in our sample of children. The highest percentage of caries found in first permanent molars followed by second permanent molars in the present study is in accordance with the results shown by other studies [6,10,15,17,20]. In Saudi Arabia, 86% of children (12-year-old) in Riyadh and 75.5% of children aged 9-12 years in Jeddah had caries in their first permanent molars [15,17]. Brazilian children were shown to have 87% of first permanent molar affected with caries [21]. First permanent molars were the most commonly affected with caries in Indian children [10]. Warnakulasuriya S observed similar caries trends in Sri-Lankan children [20]. In Taiwan, 48% of children were caries free in first permanent molars [22]. Macek MD et al., also reported greater caries susceptibility in permanent molars than other permanent teeth [6]. On the other hand, Desai VC et al., found that second permanent molars had greater untreated decay than first permanent molars [11]. King NM et al., observed that 10% of first permanent molars and 45% of second permanent molars became carious within one year of their eruption and 92% of first and 68% of second permanent molars were decayed and filled and missing due to caries by the age of 15 years [23].

Caries susceptibility of first permanent molar can be related to early eruption, age, anatomical features, large crown size, and its posterior location in the mouth [15,21]. There are reports of a relationship between caries in second primary molar and first permanent molar. A recent study found strong correlation between caries in second primary mandibular molar and first permanent mandibular molars in 7-9-year-old children in United Arab Emirates [24]. Leroy R et al., reported the influence of caries in deciduous molars on cavity formation in first permanent molars and the effect was more pronounced in case of second deciduous molar [12]. In addition, reduced susceptibility to caries in first permanent molar was observed when there were sound adjacent primary molars [25].

A previous research in Brazil found that children with caries in other teeth had 1.9 times higher odds of caries in first permanent teeth [26]. Likewise, the present study found a statistically significant relationship between caries in first permanent molars and caries in other permanent teeth. Although caries distribution in permanent central incisors, premolars and second molars was low, however, higher odds of caries in central incisors, premolars and second molars were associated with the presence of caries in first permanent molars. Second permanent molars were 4.28 times more likely to have caries if there was caries in first permanent molars. Similarly, the number of carious second permanent molars increased with an increase in the number of carious first permanent molars (regression coefficient=0.12). Premolars caries was also significantly related to caries in first permanent molars (regression coefficient=0.07).

There could be several reasons for an association between caries in first permanent molars and caries in second permanent molars which include similar occlusal morphological features (fissures and pits) and difficult access for proper tooth brushing. These factors can result in the accumulation of food debris in occlusal surfaces and can increase the risk of caries [8]. Caries initiation and progression within and between teeth could be attributed to the presence of dental plaque. It was shown that first permanent molars with visible plaque were 3.9 times more likely to have caries than those without plaque [26]. Similarly, teeth with abundant plaque were 14.5 times more susceptible to caries than those with hardly detectable plaque [27].

Dental caries is an infectious and transmissible oral condition and it is possible that caries in first permanent molar in addition to its proximity can initiate caries development in second permanent molar and premolars [28]. The accumulation of dental plaque and infectious nature of caries can contribute to the existence of an association between caries in first permanent molar and other permanent teeth. In addition, dietary and oral hygiene habits can also play a role in caries experience in different teeth [12]. Our study findings highlight the significance of preventing caries in first permanent molars and its impact on reducing the occurrence of caries in other permanent teeth by improving oral hygiene behaviours in children. It is known that 42% of tooth extraction occurs because of first permanent molar caries which is higher than for other teeth [29].

The findings of the present study can help dental practitioners better evaluate caries risk in first permanent molars and other individual permanent teeth in children in addition to evaluating the influence of socio-behavioural factors on caries. It is also hoped that health policy-makers will benefit from the results of the present study and will develop caries preventive programs for children with high risk of caries in first permanent molars in Dammam.

There are certain limitations of the study, which are the inclusion of male participants from fewer schools, and exclusion of female children. These factors can compromise the generalisability of the study findings. In addition, a cross-sectional study design precludes investigating cause and affect relationship between socio-behavioural effects and dental caries in different teeth. Under and over-reporting of responses can be seen in cross-sectional studies involving the administration of a questionnaire. Socio-economic status is a complex phenomenon and is usually determined by income, education, and occupation [24]. However; the present study focused more on education. The statistically significant relationship between oral hygiene and dental caries were assessed using Plaque Index. Moreover, a longitudinal study design should be employed in future research to investigate the presence of caries in first permanent molars and its effect on other permanent teeth particularly second permanent molars.

Based on the data analyses of the present study, it is concluded that first permanent molars had greatest caries prevalence followed by second permanent molars. Statistically significant associations were found between caries in first permanent molars and caries in other permanent teeth particularly central incisors, premolars, and second molars. Dental caries develops soon after the eruption of permanent first molars and can transmit to other permanent teeth; therefore, school-based oral health promotion programs should address younger children so that high prevalence of caries can be controlled in adolescents with early prevention. Oral health education should be raised in the community through oral health campaigns. Adequate access to public preventive and restorative dental programs and services should be ensured for all the children.