The effect of etching cavity after preparation by dental gel containing silver on the structure and mechanical properties of the boundaries of «dentin — filling» and «enamel — filling» in permanent teeth with low caries-resistant hard tissues is studied. The samples were cut from teeth that were extracted from patients aged 18–60 years old according to the Ethic Protocol of the Ural State Medical University. The filling was made with the adhesive systems of IV and V generations, flowable and packing composites were chosen as filling materials. The samples for metallographic study were cut perpendicularly to the main axis of a tooth. Their surfaces were mechanically abraded and etched in concentrated phosphoric acid. The observations were carried out on light and scanning electron microscopes. It is shown that no etching gel reduces the cohesive strength of the borders, despite the presence therein of silver.