This in situ study aimed to analyse the impact of different tetrafluorides (TiF(4), ZrF(4) and HfF(4)) and AmF on erosion and erosion plus abrasion of enamel and dentin. Ten volunteers took part in this crossover and double-blind study performed in 8 phases of each 3 days. In each phase, 2 bovine enamel and 2 dentin specimens were fixed in intraoral appliances. One enamel and one dentin sample were pretreated once with TiF(4), ZrF(4), HfF(4) or AmF (all 0.5M F) for 60s, while the other samples remained unfluoridated and served as control. Then, all samples were subjected to either erosion only (4 times/day, 90 s) or to erosion and abrasion (2 times/day, 30 s/sample). Toothbrushing abrasion was performed 90 min after the first and last erosion with an electrical toothbrush and fluoridated toothpaste at 1.2N. After 3 days, enamel and dentin loss was assessed by profilometry (microm) and analysed by repeated measures ANOVA and paired t-test (p<0.05). All fluoride solutions reduced enamel and dentin loss significantly compared to the controls. Generally, eroded samples showed less wear than eroded and abraded samples. The protective potential of the fluorides was not significantly different and was only slightly, but mostly not significantly, decreased by abrasion. The protective effect of the fluoride solutions was similar in enamel and dentin. Tetrafluorides and AmF are able to reduce erosion and erosion plus abrasion in situ and are almost equally effective.