Our aim was to investigate the effect of TiF4 solutions on mineral loss on enamel and dentine in vitro. Samples were fluoridated 1 × 5 min per day with 1.64% w/v TiF4 or 2.2% w/v NaF solutions, each with a pH of 1.2, and then subjected to a cyclic de- and remineralization procedure for 5 days. Demineralization was performed for 6 × 10 min per day with citric acid (pH 2.3). In controls no fluoridation was performed. Mineral content was determined by longitudinal microradiography. Enamel mineral loss was markedly reduced by both fluoride solutions, but TiF4 was significantly more effective than NaF: cumulative mineral loss on day 3 was 61.7 ± 15.0 µm in the NaF and 34.2 ± 13.1 µm in the TiF4 group (p ≤ 0.001) compared with 121.0 ± 27.0 µm in the control group. Dentine mineral loss ceased after both TiF4 and NaF applications (cumulative mineral loss on day 5 in controls: 61.0 ± 17.0 µm, in the TiF4 group: 15.4 ± 13.4 µm and in the NaF group: 21.8 ± 11.8 µm). Both TiF4 and NaF application reduced mineral loss both on enamel and dentine, which could open new possibilities for a symptomatic therapy of erosions.