Background: The preventative role of topical fluoride in dental caries has long been established. Exposures to low levels of fluoride have been shown to reduce dental caries by 50%. However, excessive exposure to systemic fluoride during enamel development can lead to development of dental fluorosis. The metabolism of fluoride may be affected by many factors including genetics, diet and exercise. However, the methods to measure fluoride absorption and fluoride excretion which provide an indication of fluoride metabolism often involve practicality and ethical issues, especially in relation to blood collection in young children.
Aims: This thesis aimed to assess the use of Dry Tips and Lashley cups for the collection of ductal saliva (Study 1), as well as collecting and investigating the relation between fluoride concentrations in whole blood and plasma (Study 2A) and blood plasma, whole saliva and sublingual-submandibular (SL-SM) saliva (Study 2B). The main aim of this thesis was to investigate the effect of different intensities of continuous exercise on fluoride metabolic responses in adults (Study 3). This was followed by aiming to develop a feasible and ethically sound protocol for an experimental study on the effects of exercise on fluoride excretion in children (Study 4).
Methods: Study 1: The endogenous fluoride contents of Dry Tips were investigated using three pre-preparation methods: 1) Direct Ashing, 2) NaOH as an ashing aid, and 3) No ashing. Lashley cups were manufactured at Teesside University and tested at three different levels: 1) Teesside University, 2) Newcastle University, and 3) Sao Paulo University. Study 2: Phase A involved the collection of 1) venous whole blood, 2) venous plasma and 3) capillary whole blood (n= 15). Phase B involved the collection of 1) whole saliva, 2) sublingual-submandibular saliva and 3) venous plasma (n= 24).
Study 3: In a 4-treatment, 4-session cross-over study, 8 healthy adults (18 - 35 years) were invited to attend the laboratory early morning in fasting conditions. Baseline urine and plasma measurements were obtained. Participants were provided with low fluoride breakfast and a 1-mg fluoride tablet. At each session, participants were asked to either rest (control) or exercise on a cycle ergometer at light, moderate and vigorous intensities (relative workload, %VO2 max), for 20 minutes. Blood samples were taken at 0, 30, 45, 60 and 90 minutes post fluoride ingestion. Time-controlled urine samples were also collected over 24-hours to measure the rate of UFE. Each session was separated by a wash-out
period of one week. Data were corrected for baseline and analysed using linear mixed model analysis. Study 4: An initial protocol was developed to assess the feasibility and ethical acceptance of a protocol for a prospective study on the effects of exercise on fluoride excretion in children.
Results: Study 1: Dry Tips contained high endogenous fluoride and challenges were faced in the collection of ductal saliva using Lashley cups. No saliva samples were collected. Study 2: A significant correlation was found between venous whole blood and venous plasma with a ratio of 0.65. Whole saliva and venous plasma had a mean ratio of 1.30. SL-SM saliva and venous plasma had a mean ratio of 0.18. Study 3: Mean±SD baseline-adjusted rate of UFE over 0-8 hours post fluoride ingestion was 73.8±96.5, 54.3±53.3, 44.1±43.4 and 50.9±74.4 μg/hour and mean±SD baseline-adjusted peak plasma fluoride concentrations (Cmax) at 45 minutes post fluoride ingestion were 23.6±14.3, 102.7±58.2, 226.2±115.6 and 94.2±58.1 ng/ml for no, light, moderate and vigorous exercise, respectively. Statistically significant differences in Cmax were found between i) control and moderate exercise and ii) light and moderate exercise (p <0.05). Study 4: Ethical approval was gained for a protocol designed to investigate the effects of exercise on urinary fluoride excretion in children. The pilot study was conducted with ease and great acceptability from both, the parent and child participant.
Conclusion: Study 1: Dry Tips are not suitable for studies measuring fluoride and Lashley cups pose practicality issues in the wider population. Study 2: Blood plasma was found to be the most suitable biomarker for fluoride absorption. Study 3: The results indicate that moderate intensity exercise might increase absorption and reduce urinary excretion of fluoride, however further understanding the mechanisms involved is required. Study 4: Although challenging, it is possible to gain ethical approval for studies investigating fluoride metabolism in children. Larger trials are required to confirm the acceptability of the protocol.
|Date of Award||30 Nov 2018|
|Supervisor||Vida Zohoori (Supervisor), Liane Azevedo (Supervisor), Alan Batterham (Supervisor), Marilia A.R. Buzalaf (Supervisor) & Anne Maguire (Supervisor)|