One of the options we have when seating porcelain inlays and onlays is to use a dual cure resin cement. As with all products there are material properties and handling considerations to know about this family of products. One of the most commonly discussed risks with dual cure resin cements is color shift of the cement after seating caused by the chemical catalyst. For this reason I only use dual cure resin cements on posterior teeth, and do not use it on maxillary bicuspids that are in the esthetic zone. With that said, I have to say that none of the dual cure resin cements currently on the market have had issues with color shifting that is dramatic enough to affect the success of the restoration. One major advantage of dual cure resin cements is all of the research that supports improved predictability and longevity of the restoration over light cured products, even in clinical situations where we believe light can penetrate. The next advantage is bond strengths and the ability to predictably seal and retain restorations that have been prepared without significant retention form. Balancing these out, I opt for a dual cure resin cement on most of my all porcelain inlays, onlays and full coverage posterior restorations..
One of the questions you have to answer when seating indirect restorations is whether you will cure the dentin adhesive prior to placement, or leave it uncured and have it cure simultaneously with the resin cement. The primary concern with curing first is film thickness of the adhesive and marginal gap. Another concern is that many of the current self-etching light cured dentin adhesives on the market are not compatible with dual cure products. The acidity of the material, or the oxygen inhibited layer after curing will prevent the chemical cure of the resin cement. So with these issues in mind, a dual cure resin cement requires a dual cure dentin adhesive, right? Maybe not!
Recently Kerr announced the release of a new dentin adhesive in the Optibond family. Optibond XTR, is a self-etching system, with the etch and primer in one bottle, and the resin in a separate bottle. What caught my eye about this new product is that the catalyst in Kerr’s NX3 dual cure resin cement polymerizes Optibond XTR. When using this system, I etch the enamel only with phosphoric acid for 15 seconds ( we can debate the necessity of this in a later post). Following rinsing and drying I apply the first application of adhesive, which etches and primes. Air dry, then apply the resin. Now with this uncured apply my NX3 either to the prep, or in the restoration. Seat, clean and light cure as you normally would, and rest assured that whether by chemical or light activation the adhesive and resin cement are cured.
I think I remember you mention that in previous posts you tend to favor total etch in your direct restorative and indirect anterior partial coverage procedures. Are you sticking to that and using XTR for only cementation or have you considered making a complete switch. Thanks.
Aly Sergie DDS
Aly, Great question. I do still feel more confident with total etch, that is why with this technique I am etching the enamel only first for 10 seconds, then applying the XTR, to get a total time of acid on the enamel of 25 seconds. With that said, more and more the evidence is showing that self etching products have excellent bond strengths and clinical results. This is actually also a common technique people are doing for direct restorations and light cure only indirect bonding. I do use more then one system based on the technique, so I use total etch for my direct composites and when I bond veneers, and XTR for this technique. There are also other techniques that self etching products are great for like temporary cementation of veneer provisionals, sealing exposed root surfaces for sensitivity just to name a few.
How do you prepare the e.max or ceramic with this technique?
Ray, you need to have the lithium disilicate etched with hydrofluoric acid( 5%) for 20 seconds (https://leeannbrady.com/dental-materials/etching-protocol-for-e-max-lithium-disilicate), most other ceramic is 5% for 60-120 seconds. Then you apply a porcelain coupling agent like Silane or Monobond Plus.