The volunteers were randomly allocated into one of 3 groups: 5 mins erosion repeated x3, 10 mins erosion repeated x3 or 15 mins erosion repeated x3 and a coin was flipped to determine which side the samples were to be removed for ex vivo immersion with tails for left and heads for right. . At the beginning of the study visit the splints were inserted and worn for 30 minutes. Following which the enamel samples (1 polished and 1 unpolished) were removed from one side to begin the erosion regime. For in vivo erosion each participant was asked to rinse with orange juice for their either time 5, 10 or 15 minutes. This was standardised by setting up cups with 10 mL of the orange juice and a timer set at 1 minute. The participant was asked to insert the liquid into their mouths start the time and when the alarm sounded expectorate and repeat until they completed his/her time allocation of either 5, 10 or 15 minutes. Simultaneously the ex vivo samples were immersed in 20 mL of orange juice and agitated at 62 rpm for the allocated time using an orbital shaker (Stuart Scientific, Mini Orbital Shaker S05, Bibby). This completed one cycle after which the removed samples were reinserted into the splint which was worn for a further hour after which the rinsing/immersion regime was repeated. The process was repeated a further instance to complete 3 cycles of erosion. After the 3rd and final erosion cycle the participants were given a desensitising toothpaste Sensodyne Repair & Protect (GSK, Weybridge, UK).