One of the most common questions I get asked is: “Which material should I use when restoring a patient with a worn dentition?”

I think the answer to this question has become easier as ceramics have evolved. Today, our selection mainly includes three materials: lithium disilicate, translucent zirconia and high-strength zirconia. The key to clinical success is knowing when and how to use different materials.

To begin, we first need to understand that we choose materials differently depending on where the restoration is in the mouth. In the posterior, the restoration needs to be strong, while in the anterior, the restoration needs to be esthetic. Typically, the most esthetic restorations have at least the incisal 1/3 cut back and layered by hand. This creates a much more esthetic restoration, compared to just an external stain or glaze, as the technician can layer translucency and characterization into the incisal edge. In turn, layering the incisal edge will create the “weak link” of the restoration.

No matter how strong the base ceramic material is:

  • Lithium disilicate = 500 MPa
  • Translucent zirconia = 500-800 MPa
  • High strength zirconia = 1000-1400 MPa

It is the veneering ceramic (approximately 89 MPa) that typically fails. In the posterior, where forces are higher and strength is important, it is preferable to use materials in their monolithic form – meaning the restoration is the same material through and through with no layered or veneering ceramic added.

In general, when choosing a material in the posterior it is important to remember that with less thickness, the strength of the material will need to be higher. But as the strength of the material goes up, the esthetics of the material goes down (Figs. 1- 2). In a worn dentition patient, I’m OK with sacrificing esthetics, since an opaque restoration is better than a fractured restoration.

However, if you want to enhance the esthetics of monolithic restorations, there are a few options. The restorations can be externally stained or glazed, milled with a multilayer block/puck (zirconia) or pressed with a multilayer ingot (lithium disilicate).

Initial presentation and preparation.
Monolithic restorations using a variety of restorative materials were fabricated and tried in to compare fit and esthetics.

Greggory Kinzer, D.D.S., M.S.D., is a member of Spear Resident Faculty.


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Comments

Commenter's Profile Image Victor K.
February 7th, 2020
What are your thoughts on materials like Enamic? My concern with a material like Zirconia is the wear against the opposing tooth
Commenter's Profile Image Greggory K.
February 12th, 2020
Thank you for your question. I have personally not used Vita Enamic, but I would consider it to essentially be a "composite" (any restorative material that you cannot run up in the porcelain furnace, cannot be considered ceramic). This in turn would make the material very kind to the opposing dentition. That being said, so is polished monolithic zirconia. I know it goes against our beliefs (since zirconia is so strong), but due to it's grain size and the the fact that the particles are so closely packed together, polished monolithic zirconia is one of the kindest materials against opposing dentitions. This paper published in 2019 (In vitro wear behavior between enamel cusp and three aesthetic restorative materials: Zirconia, porcelain, and composite resin. Jang YS, Nguyen TT, Ko YH, Lee DW, Baik BJ, Lee MH, Bae TS J Adv Prosthodont. 2019 Feb;11(1):7-15) showed that both composite and zirconia were considered the most desirable restorative materials against the opposing. Zirconia actually becomes abrasive when it is glazed (because of the added ceramic). So, if the material is glazed to add chroma, always make sure the technician polishes the occlusal surface by hand (back to the monolithic zirconia).
Commenter's Profile Image Sam G.
February 12th, 2020
What would be the best material for cementation?
Commenter's Profile Image Greggory K.
February 12th, 2020
Thanks for your question...it's one I get a lot. I basically think of if like this: - High strength zirconia does not need to be bonded for increased strength. So, if the preparation requirements for resistance and retention form are met in the prep design, I will typically cement with a RMGI. If however the prep is short or excessively tapered, I would recommend bonding. - Translucent zirconia and Lithium Disilicate can be bonded or cemented. The literature will show that you will have increased strength if you bond these restorations (unless they are partial coverage). I have done way more lithium disilicate in my practice and although I have more of them bonded, I do have a significant amount that are conventionally luted with RMGI. I have seen no difference in success rates whether they are bonded or luted. This is also supported in the literature (Clinical results of lithium-disilicate crowns after up to 9 years of service. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clin Oral Investig. 2013 Jan;17(1):275-84). The reason I think I have had an equal amount of success whether it's bonded or cemented is that I follow these guidelines. I bond the restoration if: 1. I need additional retention due to short or excessively tapered tooth preparations 2. The tooth has been under prepared (the material is too thin). 3. There is "sharpness" in the tooth preparation (it's not smooth) as this will increase the risk for crack propagation. 4. I want additional strength (ie. seconds molars) 5. Anything that is partial coverage or anything where the full coverage restoration isn't monolithic.
Commenter's Profile Image Mike S.
February 21st, 2020
Nice Article Gregg! In regards to the question on Enamic. It's a nice idea to have a "hybrid" of ceramic/composite... but I would say that it behaves much more like a composite than a ceramic. Although the resilience of the material is quite high, the low modulus makes it more prone to debonding in many clinical scenarios and it has trouble retaining it's polish... and needs quite a bit of maintenance compared to a glass ceramic or zirconia.