We all use ceramic restorations in our practices and will always complete a try-in step before bonding the restoration to the tooth. Some dentists mill these restorations in house and then acid etch and apply silane, and some restorations come from the lab pre-etched.
We know that if the bonding surface is contaminated with blood or saliva or try-in paste, then the bonding strength will be affected. I always paid attention to the fact that if there was blood on the intaglio surface I would have to re-etch it, but if it didn’t have copious amounts of saliva on it, I would probably have just washed and dried it and applied my silane. In a material confused state, I was doing the wrong thing.
I have asked many dentists what their protocol is and many have responded that they don’t necessarily clean the crown after trying. They didn’t have a clear understanding of the advantage of cleaning and silanating the restoration. A recent inquiry on SpearTALK addressed the efficacy of etching/silane vs Ivoclean/silane.
A scientific study back in 2009 looked at this and concluded that these restorations are best cleaned with either 37 percent phosphoric acid (e.g. Total Etch gel) or a 5 percent hydrofluoric acid.1 Additionally, if you use any fit-checker, silicone-type material, you have to use hydrofluoric acid. The study examined other techniques like using isopropanol and just water air spray, which did nothing to improve bond strength.
The part of this that I and many of my colleagues were missing was that in getting any saliva contamination was harmful, and here’s why. Saliva contains alkaline phosphatase and other phosolipids that more or less react with the surfaces of the crown rendering it inert to your primer silane. Therefore, you have to clean it. Using acid etch will render it clean and increase the bonding strength, as long as it wasn’t pre-etched.
If your restoration was pre-etched from the lab, it still requires cleaning, but you don’t want to re-etch it. Doing so removes more filler particles and renders the restoration less strong. In this case, you will want to use Ivoclean. Ivoclean consists of an alkaline suspension of zirconium oxide particles in water (which is why you have to shake the bottle well). It is strongly alkaline and thus corrosive, so you have to be really careful to wear gloves and eye protection.
The concentration and size of the particles render them more attractive to the phosphate contaminants. They absorb them like a sponge and leave behind a clean oxide surface. It in essence becomes an acid-base reaction.
Here’s the take home lesson. You can have your lab etch your restorations, but if you are trying it in first, which you undoubtedly will, you have to re-clean it. Since you don’t want to re-etch it, which will remove too many of the filler particles, you need to use Ivoclean. If you have chosen not to have your lab etch the restoration, you can etch it yourself but will need to know your ceramic as well as the concentration and time of the acid that the manufacturer recommends.
If you follow these recommendations, your incidence for crowns coming off will be greatly reduced and your satisfaction for doing all ceramic restorations will escalate.
Mary Anne Salcetti, DDS, PC, Spear Visiting Faculty www.maryannesalcettidds.com
1. K.Klosa, S.Wolfart, F. Lehmann, H.-J. Wenz, M. Kern. The effect of storage conditions, contamination modes and cleaning procedures on the resin bond strength to lithium dislocate ceramic: J.Adhes. Dent. 11,127 (2009)