Etchants applied to ceramic materials (except zirconia) are used to create micromechanical retention on the inside of indirect restorations and on intraoral repair sites. Resin cement or restorative materials can then flow into these etched surfaces and form a strong bond to the porcelain, similar to the bond of resin to etched enamel.
It has also been suggested that these products can increase bond strength to composite. However, our tests suggest there is no advantage to treating composite with one of these products compared to using 35% phosphoric acid.
Composition 4% - 10% hydrofluoric acid, which will optimally etch sandblasted porcelain in one minute.
Viscosity Only gels are applicable for intraoral use. But not all gels are created equal. It should have enough flow to adequately wet the restorative material, but not be excessively fluid.
Color Allows you to see where you applied the gel. Should be intense enough for easy visibility, but should not discolor the restorative material you are etching.
Handling and Packaging Should be easy to apply and easy to wash off. A syringe with a fine needle tip definitely simplifies application.
Safety A dental/rubber dam should be used whenever possible. If you cannot place a dental/rubber dam, reliable soft tissue protection should be employed.
Step 1 Place dental/rubber dam, if possible. If you are repairing a restoration adjacent to the gingiva and you are unable to place a dental/rubber dam, cover the tissue with a resin block-out material or a special gel some manufacturers include in their kits for this purpose. Apply wax or a resin block-out material to any area of the restoration you do not want to etch.
Step 2 Sandblast area to be etched, assuming the area to be etched is not very fragile. If you are repairing a ceramic restoration with a thin section of porcelain, skip the sandblasting step.
Step 3 Carefully apply HF gel on the porcelain you want to etch with a fine brush or straight from the syringe, if the gel is packaged in that form. One area that has not been investigated is the effect of HF gels on enamel or dentin. There are times when it is extremely difficult to keep the HF gel off the adjacent tooth structure. There is no doubt that the HF gel will etch tooth structure. However, since these gels are typically placed for at least one minute, it has to be assumed that the adjacent tooth may be overetched during this time. However, our tests suggest HF has minimal, if any, effect on bond strengths. Nevertheless, until we know the biological effect of HF on tooth structure, we continue to advise doing your best to keep it off the adjacent tooth structure.
If you are etching the inside of an indirect restoration, be sure to cover the entire surface, including the margins. It is always better to flow the etchant slightly over the margin rather than taking a chance part of the margin is not properly etched.
NOTE Our tests showed the best etching time was one minute if the porcelain was sandblasted. If you have not sandblasted prior to etching, however, our tests suggest you may want to extend etching time to 3 - 4 minutes. Etching time is also complicated because different ceramic materials seem to etch at different rates.
Step 4 With intraoral repairs, applying EtchArrest to neutralize the HF prior to rinsing seems to be a prudent procedure if you are not using a dental/rubber dam. Place the EtchArrest directly on the HF, stir to mix, and then rinse well. However, our tests suggest that EtchArrest has a slight negative effective on bond strength, so it should only be used if necessary. Otherwise, rinse forcibly for 10 seconds with an air-water syringe. With indirect restorations, wash off the HF at the sink, using a soft brush to facilitate the washing process. Be sure to cover the drain of the sink, just in case the restoration slips out of your hands.
Our tests found all products produced bond strengths that exceeded the cohesive strength of the porcelain specimens.