Objective: This study compared the effect of an experimental NaF/TiF 4 mouth rinse with a commercial tin/F mouth rinse on the prevention of tooth wear in situ., Methods: Fifteen subjects took part in this crossover and double-blind study, in which they wore a palatal appliance with 8 bovine teeth samples (4 enamel and 4 root dentine) in each of 3 phases (5 days each). Half of the samples were subjected to erosive challenges, and the other half to erosive plus abrasive challenges. The phases corresponded to the use of 1) Experimental solution containing NaF/TiF 4 (189 ppm Ti +4 , 500 ppm F - , pH 4.4); 2) commercial solution containing SnCl 2 /NaF/AmF (800 ppm Sn +2 , 500 ppm F - , pH 4.5, Elmex ® /GABA, positive control); 3) distilled water (negative control). Erosive challenges were performed using 0.1% citric acid (pH 2.5) for 90 s 4 times per day. The abrasion was done using a toothbrush and slurry of fluoride toothpaste, for 15 s 2 times per day. Thereafter, the subjects rinsed with the tested mouth rinse for 60s. Tooth wear was measured using contact profilometry (μm) and submitted to a two-way RM ANOVA/Bonferroni test (p < 0.05)., Results: No significant differences were detected between the experimental and the commercial mouth rinses, regardless of the challenge. Both fluoride mouth rinses were able to significantly reduce tooth wear compared to the negative control (p < 0.0001). No significant differences were detected with respect to tooth wear between the challenges (erosion and erosion plus abrasion)., Conclusion: The experimental NaF/TiF 4 mouth rinse has a similar protective effect to the commercial one against tooth wear in situ., Clinical Significance: The experimental NaF/TiF 4 solution protected against tooth wear in situ, regardless of the challenge (erosion or erosion plus abrasion), for both enamel and dentine, similarly to a commercial solution (tin/F-Elmex ® ) applied for this proposal. This result supports the conduction of clinical trials and a possible application of this solution in the future., (Copyright © 2018 Elsevier Ltd. All rights reserved.)