During a one-year observation period eleven patients treated with fixed appliances and 164 brackets which had been bonded in pairs, were checked at periodic intervals. Every patient had brackets positioned on the teeth in the first and fourth quadrant without graphite marking and in the second and third quadrant with graphite marking. In a parallel in-vitro study with eight pairs of teeth the above described conditions were applied. These specimens were examined in an universal testing machine in order to determine the magnitude of the shear forces. In the in-vivo as well as in the in-vitro study no statistically significant correlations were revealed between the graphite marking and the durability of adhesion as well as the required shear force of the examined brackets. Utilising light microscopy studies, the penetration of adhesive was determined in relation to the position of the graphite marking in etched enamel; at was harmlessness of the reference medium.