The thesis consists of two parts. The first part provides basic information concerning the microscopic structure of the human enamel, focusing especially on the superficial enamel and organic films covering it. In this part we have also included the effect of acid etching and the pathologic condition erosion. The second part consists of our own research project and is presented as a manuscript entitled: The effect of brushing, acid etching and fluoride dentifrice on the human enamel surface as observed with the scanning electron microscope (SEM) . The aim of the present in vitro experiment was to examine the effects on the enamel surface of various combinations of acidic and abrasive challenges. The method of examination was scanning electron microscopy (SEM). A total of 48 teeth were included in the study. The conclusions were that no obvious effect on the enamel surface was detected after the brushing treatment alone, with or without toothpaste. Brushing with toothpaste, with or without fluoride gave no additional effect other than leaving a fluffy-grainy material on the surface. A very obvious modulating effect of brushing on etched enamel was observed. After brushing with fluoride paste individual crystals tended to be more obvious compared to brushing without paste and brushing with nonfluoridated paste, but the sample size is not large enough to conclude any further with regards to this subject. On the molars it was observed a coating over the enamel. It varied in thickness, but was generally in the order of about 10-40 μm. The nature of the coating observed on molars is not clear, but it is suggested that it may in part be of an odontogenic origin.