With the market flooded with attractive ads for “new and improved” cements, the practitioner may wonder if, and when, they are worth the extra money. Since our trust in the quality and sealing ability of composite resins has grown, that has tended to flow over to other uses of resins as well, and we’ve wondered if it’s time to move on to the newer product.
You might have the impression based on bonded restorations that resin cements “bond” better and are therefore more likely to retain your crown. It’s absolutely valid that in any application involving true bonding, such as veneers, resin cements would be the only viable option. But for crowns made with non-bondable materials such as all-metal, PFM, zirconia or lithium disilicate, there is no point to using an expensive resin cement when a glass ionomer will serve just as well for a fraction of the cost. The reality is that if your crowns have 3-4 mm of wall length and approximately 10-12° of taper, the cement you choose is largely a matter of choice.
So what else might influence your decision? Glass ionomers had a reputation for post-operative sensitivity some years ago when clinicians treated the dentin surface as they would a restorative surface and removed the smear layer. This opened all the dentinal tubules, leaving the tooth vulnerable to the acidic pH forced down into the dentinal tubules via hydraulic pressure of crown seating. When the smear layer is left in place, this is not usually a problem.
But what about the seal? Glass ionomers form an ionic bond to the calcium ions in dentin that forms a strong seal, and the low shrinkage of glass ionomer makes it quite stable, and the resin-modified versions are even more stable and less soluble. Self-etching cements, on the other hand, have such a low acid content that there is very little etching or bonding ability to dentin. In fact, most experts recommend a separate etching step on enamel.
All in all, glass ionomer has proven itself to be the luting cement of choice for all non-bondable materials.