The present results revealed a higher prevalence of dental erosive wear among young physically active individuals compared with a group of young adults who did not exercise. A high consumption of acidic dietary components, such as beverages, citric fruits and sport drinks, as well as changes in salivary flow, have earlier been shown to increase the risk of erosive lesions [4
]. In the present study, the questionnaire revealed a relatively high consumption of acidic beverages in both groups, particularly among the controls, but there was no significant association with erosive lesions. The consumption of citric fruits was relatively higher in the exercise group compared with the controls. Even though no association could be found with the erosive wear, the consumption may also be an explanation for the higher presence of lesions found among the individuals at the fitness centre. These findings suggest that isolating individual dietary components from other possible factors contributing to dental erosive wear may be too simplistic, and that the relationships between the factors leading to erosive lesions are complex. Furthermore, some studies have demonstrated that sports drinks used during exercise are not associated with erosive lesions in the athletes studied [14
], whereas Järvinen [6
] found a four-fold increase in risk of lesions when sports drinks were consumed. In the present study, consumption of sports drinks was not related to erosive wear. This could be explained by the small number of responders consuming sports drinks (only 3). As the participants were regularly undertaking exercise, but not necessarily competitively, they did not use nutrient replacements. In addition, the participants may have been aware of the fact that, for most individuals, the sports drinks offer no more benefits than water [19
A higher prevalence of erosive wear in patients complaining of reflux symptoms have been reported [6
]. In the study by Bartlett et al.[21
], 64% of the patients with palatal erosion had pathological reflux symptoms. Although no significant association could be found in the present study, more than one fourth of the physically active participants reported occasions of reflux symptoms, a relatively higher frequency than reported in the comparison group. This indicates that physically active individuals may be at risk for development of erosive lesions which can be related to reflux symptoms. Previously, it has been noted that gastroesophageal reflux may be associated with some forms of tough exercise [22
]. The study by Clark et al. [22
] has shown that running and weightlifting induced reflux in healthy individuals, and that reflux persist through a 1-hour run.
While good oral hygiene is of proven value in the prevention of periodontal disease and dental caries, frequent tooth brushing may accelerate dental erosive wear [4
]. It has been suggested that health-conscious individuals tend to have better than average oral hygiene [7
]. The present study revealed that brushing teeth for more than two minutes at time was related to erosive lesions in both groups.
The questionnaire revealed that 82% of the physically active young adults with erosive wear who recently had been to their dentist/dental hygienist had not been informed about the presence of these lesions. This indicates a lack of awareness among dental practitioners regarding dental erosive wear and an increased risk for some physically active people who practice good oral hygiene.
The prevalence of dental erosion increases with age [24
], because older individuals are more likely to have exposed their teeth to acidic diets for a longer time. The findings from the present study support this trend. The older age group (26-32 years) had a higher prevalence and more severe erosive lesions than participants in the age group 18-25 years.
However, the findings should be interpreted with caution since our study has some limitations. There were slightly more women than men among the cases, and the controls were on average four years younger. Furthermore, the conditions of the dental examination differ between the groups which could also have impacted our results. However, with no prevalence studies on dental erosive wear from Norway, and due to the difficulty of comparing studies from other countries because of different populations/age groups studied and examination standards, we decided to include a comparison group even though it was not perfectly matched. Furthermore, assessing the effects of acidic diet and other related factors based on questionnaires may not provide accurate data as the answers are limited by the respondents' ability to recall.
During physical activity, decreased stimulated salivary flow was observed among more than half (64%) of the participants. Earlier studies have demonstrated that saliva flow rate appears to be modified during exercise [9
]. A decrease in salivary flow might be explained by an increase in sympathetic activity during intense exercise, since sympathetic innervations cause a marked vasoconstriction, resulting in reduced salivary volume [25
]. This may also be a consequence of sweat-induced dehydration and restricted fluid intake during exercise. In a study by Horswill [16
], a significantly lower stimulated salivary flow rate and volume was shown even when consuming water during the training session.
Prolonged exercise may reduce the unstimulated salivary flow [26
]. Our results showed no consistency - the unstimulated salivary flow increased as often as it decreased among the participants. One could speculate that the duration of the training session was too short to give measurable changes in unstimulated saliva, since it has been suggested that modification of hydration status can at the earliest be detected three hours after exercise [27
]. Another explanation of variability in the salivary flow rate may be individual variations [28
], as well as consumption of fluids during the exercise [10
]. Furthermore, by providing the saliva sample of only 70 out of 104 participants could have influenced the outcome. With the allocated resources and of convenience the first 70 participants arriving to the fitness centre were asked to provide the saliva samples. Comparing the prevalence of erosive lesions among the "saliva providers" with the "non-saliva providers", no significant difference was observed. Furthermore, there are no reasons to believe that the variations in flow rate between these participants should be different from the others. However, due to this uncertainty the results in the present study should be interpreted with caution. The participants consumed liquid during exercise session as they normally would with the intention to create a "real life situation" for the individuals. This could explain diversity in the unstimulated salivary flow rates and could have influenced the outcome of the present study, as liquid consumption during exercise may help maintain normal salivary function [16
]. Another issue which could influence the salivary flow rates is diet and liquid intake before the exercise. It is known that previous stimulation of less than 1 hour prior saliva collection may influence the flow rate [29
Several studies have demonstrated that reduced salivary flow may increase the risk to the dentition [4
]. Järvinen et al. [6
] found a low stimulated salivary flow in 16 erosion cases and 6 controls, while a reduction in unstimulated flow was seen in 7 erosion cases and 6 controls. These findings are in accordance with the present results. Although most participants studied demonstrated normal salivary flow rate, the stimulated salivary flow of more than one third was in the lower rage and significantly more erosive lesions were registered than in subjects with higher flow rates. Our findings support the statement of Järvinen et al. [6
] that salivary flow rate is an important factor determining whether erosive lesions occur. One explanation could be the findings reported by Amaechi [30
], higher salivary flow contributes to higher clearance and thus a lower erosive potential.