The objective of this study was to evaluate the influence of four desensitizers (Seal&Protect, Admira Protect, VivaSens, Hyposen) in situ.The root surfaces of freshly extracted human molars were thoroughly cleaned, thereby removing the cementum. From each tooth root dentin specimens were prepared. Ninety specimens were distributed among the following experimental groups: A: Seal&Protect, B: Admira Protect, C: VivaSens, D: Hyposen, E: control group, untreated. Two dentin specimens of each group were inserted into two buccal aspects of nine intraoral mandibular appliances. The appliances were worn for five weeks day and night. One side was brushed daily with a fluoride-containing toothpaste (Aronal). On the other side, plaque was allowed to grow. Individual oral hygiene techniques were performed without any fluorides. After the in situ period, two slabs (150 microns) were ground. The depth of the demineralized areas was determined using a polarized light microscope. For each group mean value and standard deviation were calculated. Statistical analysis was performed using SPSS 11.0. Concerning lesion depth, ANOVA revealed significant differences between brushed (b) and non-brushed (nb) specimens. Compared to the untreated control, lesion depths in groups A-D were significantly decreased in the brushed and also in the non-brushed subgroups (p Schlagwörter: root dentin, demineralization, in situ, dentin adhesive, desensitizer