Introduction

Dental erosion appears to be a relatively recent condition. The interest in studying dental erosion has arisen in recent decades, especially following the decline in prevalence of dental caries in children from developed countries [1-4]. Dental erosion has been defined as a progressive irreversible loss of dental hard tissues by a chemical process, not involving bacteria [5-7]. The typical clinical features of dental erosion in anterior teeth include silky-glazed appearance (absence of perikymata) of intact enamel along the gingival margin; while posterior teeth are manifested with cupping and grooving on occlusal surfaces [8]. The fact that some individuals are more prone to develop dental erosion reflects the multifactorial nature whereby interaction of chemical, biological and behavioural factors explains such variation [9,10]. Erosion is most often found in association with other forms of tooth wear such as abrasion and attrition [11]. The majority of tooth wear in childhood is due to dental erosion [12-16]. Adequate preventive measures can be implemented only when the risk factors are known [17].

Dental erosion is caused mainly by intrinsic or extrinsic acids; intrinsic acids from gastro-oesophageal reflux or frequent vomiting, while the source of extrinsic acids may be frequent consumption of acidic foods and beverages, particularly fruits and fruit juices, soft drinks, herbal tea, wines and vinegar and frequent swimming in heavily chlorinated water [1,11,13,18-23].

Poor salivary flow associated with insufficient buffering capacity exacerbate dental erosion [24]. Dental erosion in children, which is caused mainly by frequent intake of acidic food and drinks, is a common condition with early damage to the teeth potentially affecting oral health for an entire lifetime and requiring extensive, difficult and complicated treatment [25]. Therefore, early diagnosis and prevention of erosion in children and adults is important. The decline in caries has made dental erosion become increasingly recognized as a public health concern amongst children and adolescents [26].

Several epidemiological studies showed increasing interest in the study of tooth wear and more particularly dental erosion. Several studies offered a better understanding of tooth wear and dental erosion and their potential risk factors. These published studies include in vitro and in situ studies [27-33], case-control studies [34-37], cross-sectional studies [38-46] and longitudinal studies [47-49]. The main aims of these studies were assessment of the prevalence of dental erosion or tooth wear and recognition of possible factors associated with its development and progression.

Most dental erosion data are derived from European studies; only a few epidemiological studies of dental erosion prevalence have been undertaken in developing countries [23,43, 50-53].

There are a few published epidemiological studies relating to the prevalence of dental erosion in Libya. The aims of this study were to determine the prevalence and severity of dental erosion and to examine gender differences in relation to the prevalence and severity of dental erosion amongst 12 year-old schoolchildren in Benghazi, Libya. Early diagnosis and prevention of erosion in children and adults is important not only to control erosion and prevent further complications, but also to minimize the costs of the complex extensive treatment.

Subjects and Methods

Ethical approval and permissions from local authorities

Ethical clearance and permissions to conduct the study in Benghazi was obtained from the local authorities, Education Ministry, Health Ministry, schools and consents obtained from parents and children.

Obtaining the sample

A cross-sectional observational study was conducted in Benghazi. There is no governmental classification of areas based upon socioeconomic information in Libya. Therefore, a cluster sampling within the schools was used for school sampling. These children were studying at the sixth grade in 36 elementary co-educational public schools drawn from the 15 different districts with different socioeconomic groups and cultures. First, a random sample of schools was selected; at least one school from each district, and at least two schools from districts with 6 or more schools. Then a random selection of boys and girls from each elementary school was made. From the children with parental written consent, a sample was randomly selected. Using a list of randomly generated numbers between 1 and 99 a selection of the children was made using columns, for example starting with column 2 to sample 7 children from within a school. Seven children were randomly selected from each of 36 randomly selected schools to achieve a sample of 252 subjects. The target sample size for completion was 175 which would provide 95% power to detect a correlation coefficient of 0.3 assuming a Type 1 error rate of 5%. The target for recruitment was set at 252 to allow for attrition.

Dental examination

Dental erosion was determined according to the index of the oral health component of the UK National Diet and Nutrition Survey (NDNS) [40] (Table 1). The labial and palatal surfaces of all permanent maxillary incisors and the occlusal surfaces of the first permanent molars were assessed for the depth and area of erosive loss, recorded on the oral health assessment sheets. The screened teeth surfaces were examined for a range of appearances from loss of surface enamel to exposure of dentine or pulp.

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   Table 1:

   Criteria used to assess dental erosion [40].
   
   

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   Table 1: Criteria used to assess dental erosion [40].
   Code	Depth	Area of surface affected
   0	Normal	Normal
   1 2 3 9	Enamel only Enamel and dentine Enamel, dentine and pulp Assessment cannot be made	Less than one third of surface involved One third up to two thirds of surface involved Two thirds or more of surface involved Assessment cannot be made

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Depth of dental erosion on a surface was scored as code 1 if erosion was seen in enamel only, code 2 if erosion was seen in enamel and dentine, code 3 if involving enamel, dentine and pulp. The area of dental erosion on a surface was scored as code 1 if dental erosion affected less than one third surface, code 2 if a affected up to two thirds of the surface and code 3 if it was more than two thirds. In cases where there was doubt over the assessment of a surface, the lower score was assigned [40].

Reproducibility of the study

For the purpose of reproducibility, in each school, 10% of the dentally examined children was randomly re-examined on the same day as the dental examination to determine the reproducibility of the application of diagnostic criteria and to provide data for intra-examiner reproducibility. The results of the dental examination were analysed for reproducibility by Cohen’s Kappa and the following thresholds were considered; score 0 (total disagreement), score 0.4-0.6 (moderate agreement), score 0.6-0.8 (substantial agreement), score >0.8 (good agreement) and score =1 (perfect agreement) [54].

Statistical analysis

Dental erosion data were copied into a database designed within the Statistical Package for Social Sciences-SPSS 15.0 for Windows. A second database, with data from subjects who had been examined in duplicate, was developed to measure the level of intra-examiner agreement in assessing dental erosion. The prevalence of erosion was calculated as the number and proportion of subjects affected. Dental erosion for area and for depth was cross tabulated with gender.

Results

Study sample

Two hundred and fifty two children were randomly selected in thirty six randomly selected public schools: seven children per school. Written consents were obtained from one hundred and eighty subjects (71%) who attended the clinical dental examination. There were 92 boys (51.1 %) and 88 girls (48.9 %). The mean age of the 180 children was 12.3 years (SD ± 0.29).

Dental examinations

Dental examinations were conducted at schools. Ten per cent of the total sample size was randomly selected and dentally examined for a second time during each dental examination session to assess the reproducibility of this study. The dental examination was undertaken in any available space, such as class rooms, libraries, and laboratories. The dental examination was conducted under artificial light, with additional lighting via a headlamp which was used throughout the dental examination as the diagnostic source of light. The subjects were seated in an ordinary chair, in front of the examiner. For the dental examination the examiner used pre-packed sterilised oral examination kits which contained, a plain mouth mirror and a probe to help detect dental caries by removing food debris.

Dental erosion was recorded by depth and area and a subject number was used throughout the study keeping the name and subject number separate. The teeth surfaces were examined for loss of surface enamel and exposure of dentine or pulp. The date of examination was recorded. The date of birth was recorded from school files.

Prevalence of dental erosion

Of the 180 subjects, 70 (38.9%) had experience of dental erosion. There were 110 subjects (61.1%) had no evidence of dental erosion. A higher experience of erosion was observed amongst girls than boys, but this difference was not statistically significant (Fisher’s exact test; p= 0.647) (Table 2).

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   Table 2:

   Significance of association (P) between the number (N) and proportion (%) of subjects with or without experience of dental erosion in the sub-sample and gender.
   
   

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   Table 2: Significance of association (P) between the number (N) and proportion (%) of subjects with or without experience of dental erosion in the sub-sample and gender.
   Experience of dental erosion
   Gender	Girls			Boys			Both
   	Yes	No	Total	Yes	No	Total	Yes	No	Total
   No. of subjects %	36 40.9	52 59.1	88 100.0	34 37.0	58 63.0	92 100.0	70 38.9	110 61.1	180 100.0
   Fisher’s exact test; p= 0.647 OR= 1.18 (95% CI 0.65, 2.15).

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Reproducibility of the study

The levels of intra-examiner agreement in the assessment of dental erosion, as measured by Cohen’s Kappa statistic [54], for code 1 by depth (erosion into enamel only) was 89% for the incisors and 77% for molars. This indicated a good level of agreement for incisors and substantial agreement for molars.

Discussion

This study was conducted in Benghazi, the second largest city in Libya after the capital, Tripoli. The study sample, which consisted of 180 schoolchildren, was collected from 36 public elementary schools distributed in 15 districts More than 88% of the whole Libyan population live in cities [55]. This study aimed to determine the prevalence and severity of dental erosion in children and investigate the gender differences in relation to dental erosion

Even though the study concept in Benghazi was received with encouragement and support from the authorities, schools and parents, there were some difficulties and limitations. Because the dental examinations took place in schools some challenges were encountered such as interruption of dental examinations due to school activities or only small space being available within the school for dental examination, or rooms with poor lighting conditions, which necessitated the use of the headlamp. However, co-operation of the School teachers, the staff and subjects helped to finish the dental examination smoothly.

The erosion index and criteria used in the present study had been validated in National Surveys in the UK [19,40]. This index was selected because it is simple, easy to use and can evaluate severity and affected tooth surface area. It had been specially designed to assess erosive tooth surface loss in the children and has been used in large epidemiological studies. The age of 12 years was selected because of the exposure of the index teeth, which should have been fully erupted, to dental erosive factors for about six years.. In addition, at this age group comparison with results from other studies is made possible.

All subjects were examined clinically by the one expert examiner (RH). A good level of intra-examiner agreement was achieved using the Cohen’s Kappa statistic [54], for dental erosion into enamel only (score 1 for depth). It is difficult to detect dental erosion at an early stage but, the most important feature for dental professionals to diagnose dental erosion is change in the clinical appearance of the tooth surfaces especially in early stage of erosive tooth wear [17].

A good level of intra-examiner agreement was achieved using the Cohen’s Kappa statistic [54], for dental erosion into enamel only (score 1 for depth). This has been shown to be the most difficult erosion score to diagnose [19,39], and it was re-assuring to find that the reproducibility was similar to that found in previous studies assessing dental erosion [43,50,53,56-58].

The results of the present study showed that the mouth prevalence of dental erosion was 38.9%. This figure was lower than the value found in the UK NDNS for 11-14 year-olds, in which 52% of the children examined were affected [40]. On the other hand, the prevalence in this study was higher than 33% for 12 year-olds [19], found in the 2003 UK CDH Survey. When comparing the present findings with other studies which have used the same index and criteria, the prevalence of erosion in this study was found to be higher than the prevalence of erosion found in 13-14 year-old Brazilian children (34%) [43]. Conversely the prevalence found in this study was lower than the 60% found amongst 12 year-olds in the UK [56]. It was also much less than the prevalence of 95% recorded in 862 12-14 year-old Saudi Arabian boys [50]. Both these figures were higher than the findings of the present study; the reason might be due to the high consumption of acidic drinks by Saudi Arabian subjects which was reported by Saudi Arabian studies [23,50], and 27% of 12-14 year-old Saudi Arabia boys consumed acidic drinks at night reported by Al-Majed et al. [50]. The UK National Diet and Nutrition Survey amongst 11-14 year-olds reported a mean daily intake of 240 grams of carbonated drinks [40]. In contrast with other studies which used different methodology and indices, the prevalence of dental erosion in the present study was lower than the prevalence of 57% found for 11-14 year-olds in London using the Smith and Knight tooth wear index [59] and lower than the 66.9% found among 12-14 year-old Sudanese children also using Smith and Knight tooth wear index [51], but it was higher than the one reported in a study in San Antonio, US in12-17 year-olds, in which 5.5% of the children affected by dental erosion [60], an Australian study in 5-14 year-olds using a modified erosion index, in which 25% of the subjects with permanent teeth were found to have erosion [61], the 26% of12 year-old Brazilian children using O’Sullivan index [62], the 37% of 11-13 year-old children in the UK and 41% of 11-13 year-old children in US [63], the 37% amongst 13 year-old children in United States using the modified Smith and Knight Tooth Index [26] and higher than the 38.1% amongst 12 year-old children in Iran using O’Sullivan index [64].

Dental erosion and gender

A higher experience of erosion was observed amongst girls (40.9%) than boys (37%) in the present study. This difference was not statistically significant. Similar results, with girls more affected by erosion than boys, were reported in a Cuban study on 12 year-olds [65]. Other studies have reported no significant gender differences [40,53,58,59,63,66]. In contrast, several studies have reported that boys had more experience of dental erosion than girls [15,40,43,67-69]. The differences in the prevalence of dental erosion between boys and girls in the present study may be explained by a difference of exposure to risk factors in this population.

Conclusions

Of 180 subjects, 70 (38.9%) had evidence of dental erosion, which was over one third of the subjects and higher amongst girls than boys. The null hypothesis of this study was accepted; there is no difference in the prevalence and severity of dental erosion in 12 year-old children in Benghazi, Libya children compared to children from other countries.

Epidemiological studies using a unified approach to determine dental erosion are needed in different regions in Libya. These will provide a clearer picture regarding the prevalence of dental erosion and to determine if dental erosion a cause of concern in terms of public oral health in Libya.

Acknowledgements

The authors would like to thank the Ministry of Education and Ministry of Health. The authors also thank all the schoolchildren, parents, and schools staff in Benghazi for their cooperation with the study.