After protecting a site from access of saliva, after cleaning and drying, etching procedure can be started. In order to obtain enamel etch, acid solution has to be spread on intercusp fissure surface for 15 seconds. The recommended concentration of phosphoric acid is 37%. The introduction of gel etches allowed to limit the impact of acid used to prepare enamel surface before application of sealant and to decrease the risk of uncontrollable contact of etch with dentine. Gels are applied only once, whereas liquid solutions of acids require multiple application. Etches in the gel form penetrate fissure enamel to the same degree as liquid etches. Acid penetration is hampered by impurities left over after mechanical cleaning of fissures.
It is advisable to repetitively moisten enamel with acid solution during etching, in order to unblock dentine microtubules by removal of calcium salts precipitated during chemical reaction, which limit the effect of etching. After introduction of one-stage etching (of enamel and dentine), dentists have been using self-etching systems based on non-washable acid monomers (low-concentration acids, 10% phosphoric or maleinic acid, 2.5% nitric acid or their mixtures including extra ingredients such as metal ions, glycerin) (2), which eliminate the rinsing phase thus shortening application time and greatly limit the risk of infection of the operative site by saliva and the risk of a mistake during application, which makes the procedure insusceptible to operator's manual "skills".
A soft brush is recommended for etch application, whereas cotton wool balls are not advisable as they contain bubbles of trapped air hampering even spreading of etching solution. Acid solution leads to creation of microfissures in enamel, whose presence enables sealant's penetration deep into tissues. Microscopically, enamel surface becomes rough and appears matt, in electron microscope view - pits of various shapes are visible which were created by a loss of some enamel prisms. The pits are 50-52|im deep.
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