This in-situ study will investigate on extracted teeth the protection of a re-formulated varnish containing fluoride in the same concentration as an existing approved varnish used to treat caries and erosion. Healthy volunteers without caries, periodontal disease or signs of erosive tooth wear and who give consent will be recruited to a cross-over blinded intervention. Custom mouthguards (splints) housing 8 sections of extracted human teeth will wear the appliance for 3 consecutive days and then repeat the study. Extracted teeth will be collected from patients needing tooth extraction for dental reasons. Their participation ceases when they donate the teeth. The teeth will be sterilised with hypochlorite for a minimum of 24 hrs and then sectioned and polished to form a 5mm x 5mm area of enamel and placed in the splint. The varnish, with and without fluoride, will be applied to the surface of the extracted teeth, allowed to dry, and then placed into the mouth of the healthy volunteers for 6 hours, after which, the varnish will be carefully removed. Overnight the splint and teeth will be kept in a clean and moist environment and replaced in the mouth the following day, again for 6 hours. Every 90 minutes, four times over the day, the splint will be removed and immersed in 1% citric acid pH 2.7 for 2 minutes. At the end of the day, 2 sections will be removed and tested in the laboratory for hardness. The splint will be reinserted in the mouth again for 6 hours during which it will be immersed in the acid again every 90 mins. At the end of the day the samples will be removed and measured using profilometry. A few weeks later the process will be repeated with either the fluoride or non-fluoride varnish, the order being randomly determined.
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Microhardness Measurement
Timeframe: day 0 & end of Day 2
Profilometry scanning
Timeframe: at the end of Day 3