Etching tooth structure, especially enamel, prior to applying a bonding agent used to be as routine as using a handpiece to prepare a cavity. However, with the surge of self-etching bonding agents, there are some in the profession preaching doom and gloom for more conventional etchants. Nevertheless, with the inability of many self-etch products to be effective on unprepared enamel, conventional etchants should still be part of every dentist's restorative aramentarium.
Composition 30% - 40% phosphoric acid, which will optimally etch both enamel and dentin in 15 - 20 seconds.
Viscosity Gels are favored over liquids due to our ability to exercise more control over the application of a gel. The lone exception may be for etching occlusal surfaces prior to applying a sealant. In this situation, a liquid etch is quite effective and may even be better at reaching into the depths of the pits and fissures. However, not all gels are created equal. It should have enough flow to get into line angles and between tooth structure and tight matrices, but not be excessively fluid. An etchant gel should also have a smooth consistency and not be jelly-like. We have included a flow test for these products.
Color Allows you to see where you applied the gel. Should be intense enough for easy visibility, but should not discolor any base material or tooth structure.
Silica vs. No Silica Silica thickeners may deposit silica particles on the dentin surface and could interfere with bonding. However, our tests found no advantages as far as bond strength is concerned regardless of whether the etchant contained silica or not.
Antimicrobial Additives We have only seen two studies on this subject, one saying you do need it and the other casting doubt on that need. The latter study found no difference in zones of inhibition around dentin/enamel discs that had been treated with etchants containing or not containing an antimicrobial, all of which were then placed in contaminated agar. The antimicrobial in this study was benzalkonium chloride (BAC). Therefore, we don't believe you should base your choice of etchant on whether it contains an antimicrobial agent or not.
Handling and Packaging Should be easy to apply and easy to wash off. A syringe with a fine needle tip definitely simplifies application.
Step 1: Apply for 15 seconds. Apply etchant to enamel, keeping it off dentin if possible at this point. On enamel, there is a wide range of acceptable etching times, from 15-60 seconds. Our tests also show dentin may not be as etch-sensitive as we may have thought. With OptiBond Solo Plus, bond strengths were highest when dentin was etched 5, 10, or 15 seconds, while 30 or 60 seconds were lower but still seemingly acceptable. The two-minute etch was the worst. For Prime & Bond NT, bond strengths dropped off after 15 seconds, while two minutes was again definitely the worst. Therefore, 15 seconds continues to be our recommended etching interval for dentin and enamel. Never etch for longer than 60 seconds.
Step 2: Lightly agitate the etchant. Flow the etchant over the dentin and immediately start to time 15 seconds. Use a disposable brush or applicator tip, if necessary, to push the etchant into any restricted areas of the cavity. Lightly agitating the etchant during this brief application period may also be beneficial just to make sure the entire preparation is properly coated with etchant.
Step 3: Rinse for 5 seconds. Have the air-water syringe and suction ready to go. Begin rinsing as soon as the 15 seconds is up. Rinse well for five seconds, which had significantly higher bond strengths than when a 10-second rinse was tested. However, the five-second guideline is contingent on all the etchant being rinsed off the teeth in that time period. Otherwise, continue rinsing until this goal is accomplished.
Our tests have shown some differences between the products, but it is uncertain whether these differences are clinically significant. These values can be found in each product's narrative.