e.max: Bond or Cement?

Lithium disilicate has definitely taken the dental profession by storm – and Ivoclar to new heights of profitability. The company that released Empress to us so many years ago, and saw it proliferated by every manufacturer who could deconstruct it, was much more careful to guard their product when Empress II, the original name of the lithium disilicate that we know today as e.max, was introduced. It has also been named Empress Eris in the past.

I love this stuff. Lithium disilicate has made it possible for us to have an all-ceramic crown material that actually works reliably in almost every situation. While it originally was less-than-perfect for many esthetic applications, the technical modifications that have been made over the past few years have given us a material that can be used with esthetic confidence in both posterior and anterior teeth. The one remaining application in which it struggles to fully displace other materials is in situations where a very thin occlusal thickness is required, such as second molars in cases where a cant is being corrected. Fortunately, zirconia has appeared to fill that need, although I’ve seen some unusual esthetic results in cases that are not a bright and light shade. That being said, pretty much everyone I know in dentistry is using e.max lithium disilicate in their practice.

I get to spend some time at our Anterior Restorative Dentistry workshop discussing the history and current science around bonding. In that regard, there is one question that never fails to come up quickly and often in that workshop and in others as well: "Should I seat all of my e-max restorations by bonding them in?"

Before we investigate that, let’s limit our conversation to lithium disilicate since that is the material for which the question is asked. There are two e.max products that are lithium disilicate: e.max Press and e.max CAD.

e.max Press

Full contour, can be cut back for stacking, can be pressed as a core for stacking with e.max Ceram.

e.max CAD

Milled, conditioned, can be cut back for stacking with e.max Ceram.

e.max ZirPress, e.max Ceram, and e.max ZirCAD all share the e.max name, but they are not lithium disilicate.

e.max ZirPress

Fluorapetite glass ceramic ingot that can be pressed over a ZirCAD framework.It can then be cut back for stacking with e.max Ceram. That’s three kinds of e.max in one restoration.

e.max Ceram

Nano-fluorapetite layering ceramic powder that can be applied over any of the e.max materials.

e.max ZirCAD

Yttrium stabilized zirconium oxide block that is milled and then sintered. The milled ZirCAD is 20 percent larger than the resulting sintered product. It can then be covered with e.max ZirPress and/or e.max Ceram.

If you find all of this confusing, you are not alone. How many of us can name all of the ingredients in all of the e.max products? For the record, it’s the Yttrium stabilizer that most people forget.

So now that we are crystal clear, we can discuss the question at hand: Should I cement or bond my e.max (lithium disilicate) restorations?

First of all, can we all agree that all partial coverage e.max restorations will be bonded? Partial coverage restorations require a connection to the tooth to have adequate strength. Crowns are where the option appears and the questions begin.

If there is a difference in strength between the two methods of connecting to the tooth, I am betting most of us would opt for more strength, yes? When Bob Winter and I visited Ivoclar's U.S. headquarters a few years ago, they showed us some impressive data regarding strength. They also showed us some very loud tests that they use for measuring that strength. Bonded on e.max lithium disilicate restorations tested stronger. Case closed?

Just because you can make something stronger, does it mean you have to? My favorite analogy is hanging up a picture. I’m betting that your art is not falling off the walls, and yet you could put more nails there to make it stronger. Sometimes enough is good enough. If the strength is adequate for what the restoration will be asked to do, is it necessary to give it more strength? My answer is: if you want to.

I believe, and we teach this here at Spear, that lithium disilicate crowns can be cemented or bonded. Your decision on which to do is driven by the preparation and the patient. In the case of short prep, too much taper, get the help of adhesive materials to attach it.

A bruxing patient who has destroyed all of your excellent dentistry in the past: same thought.

Adequate resistance and retention form, a patient who only eats and talks with his teeth: cement it if you want to.

I’ve referenced a couple of fairly recent articles that show us one nail can and does keep the art on the wall. In Vivo use of cementation does not change the predictability of the lithium disilicate restoration.

Relish the freedom to do what feels right at the time and what works best in your hands.

References:

Clin Oral Investig. 2013 Jan;17(1):275-84. doi: 10.1007/s00784-012-0700-x. Epub 2012 Mar 7.Clinical results of lithium-disilicate crowns after up to 9 years of service. Gehrt M1, Wolfart S, Rafai N, Reich S, Edelhoff D.
J Am Dent Assoc. 2012 Mar;143(3):234-40.Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic.Kern M1, Sasse M, Wolfart S

Comments

Joe G.
January 7th, 2016

I have always felt doing the kind of dentistry you would want done in your mouth is the best way to practice. With that said, I cannot think of a case where I would prefer NOT to have an Emax crown bonded in my own mouth.

Gary D.
January 7th, 2016

Thanks for the thought Joe, and I would agree wholeheartedly that you should always DO the dentistry you would want in your mouth. You SHOULD have any and all full coverage lithium disilicate restorations BONDED because you feel strongly about it being better. I have both bonded and cemented lithium disilicate restorations in my mouth so I believe I am also living by that same belief. IF I believed it was better to bond every full coverage lithium disilicate restoration I would. Because I believe cementation can satisfy every requirement within a given set of parameters I do that when I want to. I am not suggesting you SHOULD cement, I am putting forth the option, the ability to choose. The research supports no difference in success when the requirements for cementation are met. I apologize if my writing seemed to suggest you SHOULD cement, that was most certainly not my intent. Thanks again.

Joshua K.
September 25th, 2017

Thanks for this article Gary. I came from an office that ONLY cemented E.max crowns and there were several failures on 2nd molars but it worked well everywhere else. Cutting off a bonded crown is a miserable experience IMHO so I would rather cement when possible (not to mention the additional steps involved in bonding). It's certainly a judgment call on a case by case basis, but I follow your recommendation to bond anything that is NOT full coverage every time.

David S.
February 5th, 2018

What about the marginal integrity? Are there any studies to show that you have a better chance of getting recurrent caries around the margin with cementation versus bonding? David

Gary D.
February 8th, 2018

Thanks for posting David - I am not aware of any studies that show that. I just did a quick Pub-med search to try and check without success. My personal opinion is that resin-modified glass ionomer is less likely to degrade than resins when the margin is dentin and oral fluids are present. I have no data to support that so please hear it for what it is. Thanks again for posting.

Sean R.
April 17th, 2018

Gary, thanks for the article and your thoughts. I have a similar experience with e.max and will both bond and cement depending on the situation. I have often wondered (and have asked a number of speakers) about the strength of the material in those situations. Specifically, is the restoration stronger when it is bonded instead of cemented. I understand that lithium disilicate has an inherent flexural, compressive, etc properties but how does this change? If I have 1mm of occlusal thickness and I bond how does the strength of that restoration compare to the same restoration cemented?

Gary D.
April 18th, 2018

Thanks for the post Sean. When I wrote the article, Ivoclar said 1.5mm of thickness was required, so 1mm of thickness would put lithium disilicate (e-Max) into the "must be bonded" category because the restoration IS more resistant to failure when bonded. Today Ivoclar says only 1mm of thickness is required. As you note, the material itself has properties that are constant, the bonding simply reduces fracture probability since the material is directly and completely attached to a stable substrate. No question it is "stronger" when bonded. You could hang every picture in your home with 10 nails. The question is still whether the picture on the wall will be stable for generations with one nail. If it would, either is an acceptable selection.

W. Chris E.
October 4th, 2018

Gary, Great topic. I am a Cerec guy and use Emax almost exclusively, except Enamic for implant TI base crowns. I have also placed many pressed restorations. I have tried a variety of cements and bonding systems. From an esthetic standpoint nothing has compared to Multilink for it's chameleon like finish, I marginate as occlusal as possible. I do use Fuji plus for cementation of crowns where there was recurrent root caries, usually these are longer more retentive preps, and I sacrifice a more visible margin. For bonding it is all about the preparation of the two surfaces and control of that environment. We always air abrade both crown and prep at about 30 PSI ( Crystalmark is the best unit that I have found) and ozone and acid etch the tooth and then "scrub" in the A and B primer for 20-30 seconds before thinning and bonding. Instead of cleaning up the excess with a brush I use a rubber tip stimulator to wipe away the excess and avoid "plucling fo the margin. Clean up is key, I often masque the adjacent contacts, under microscope. I say bond it if possible. Variolink for thin veneers in anterior and bond with the pen. PS I have fractured some second molars, usually thin around 1 mm. I have also seen zirconia fracture.

Gary D.
October 5th, 2018

Thanks for posting Chris!