Cement selections for zirconia, other restoratives

This is the final part of a three-part DPR series discussing cement selection and related issues with dentists from a variety of practices. We’re asking them about their individual priorities and techniques with cementation and how their practice focus affects the materials they choose.

For part three, we’re speaking with Gary Alex, DMD, who has a solo practice in Huntington, N.Y. Dr. Alex’s practice is strictly referral-based and focuses on cosmetic and prosthetic dentistry. He is a graduate of Tufts University Dental School and is one of only approximately 350 dentists worldwide to be accredited by The American Academy of Cosmetic Dentistry.

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DPR: What considerations play a role when you choose a cement?
DR. ALEX: When it comes to cementation, there are many factors to consider before deciding on the use of a specific class of cement and placement protocol, including the nature of the tooth and restoration substrate being cemented or bonded to, inherent retentiveness of the preparation, access and control of the working area, ease of use and cleanup and esthetics (will the color of the cement affect the esthetic result?). I also think manufacturer reputation and brand recognition is a factor.

DPR: What are the go-to cements in your practice?
DR. ALEX: While other cementation options exist (and excluding porcelain veneers), the majority of dentists today use of one of three distinct classes of materials for the final cementation of their restorations:
1. Resin-modified glass ionomers (e.g. RelyX Luting Plus, 3M ESPE; FujiCem-2, GC)
2. Dual-cure self-adhesive resin cements that are placed without the use of a separate dentin bonding agent (e.g. RelyX Unicem 2, 3M ESPE; Maxcem, Kerr; Bis-Cem, BISCO; G-Cem, GC)
3. Dual-cure resin cements that are used in conjunction with a separately placed dentin bonding agent (e.g. RelyX Ultimate Adhesive Resin Cement, 3M ESPE; Dual-Link, BISCO; Multilink, Ivoclar).
I use all three genres of cements depending on the specific case requirements.

Related reading: Talking cement selections with a pediatric dentist

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DPR: How compatible is a self-adhesive cement with the most common restorative materials?
DR. ALEX: There are many studies that show self-adhesive resin cements are compatible with most commonly used restorative materials. There are two important factors to consider when using any class of cement: How should you treat the tooth surfaces? How should you treat the intaglio surface of the restoration prior to cementation?

In the case of cementing or bonding in zirconia restorations, my personal preference and recommendation is to sandblast the intaglio surface of the zirconia regardless of the class of cement being used. This helps clean away surface impurities, increase surface roughness, raise surface energy and significantly improve the bond to the zicronia. (I have discussed this, as well as concerns some have regarding sandblasting zirconia, in great detail in a recent paper.)  

I recommend using a sandblaster with 30 μm to 50 μm aluminum oxide at 30-40 psi of air pressure (2.0 to 2.8 bar) at a distance of approximately 10mm. This should be done after the restoration has been tried in and prior to primer and cement placement. If you don’t have a sandblaster, you can ask your laboratory to sandblast the restoration and then use a solution of sodium hydroxide, polyethylene glycol, water and zirconia oxide (Ivoclean, Ivoclar) to clean the restoration after try-in and before primer placement and cementation.

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DPR: How important is efficiency in your cement selection?
DR. ALEX: The ability to accomplish the job with a minimum expenditure of time and effort is very important. Factors such as ease of use and removal of set cement are in the minds of all seasoned dentists when cementing and/or bonding in restorations.  

However, there are times when the “easiest” cement to use may not be the best for the job at hand, depending on many clinical factors, including retentiveness of the preparation and the specific type of restoration being placed. As an example, RMGI cements such as RelyX Luting Plus are relatively easy to use and clean up but probably not the best choice in situations where maximum retention is required or where the inherently white opaque color of RMGI cements may “show through” more translucent restorations, creating unacceptable esthetics.  

In such situations, self-adhesive resin cements (such as Rely X Unicem 2) or resin cements used in conjunction with a dentin bonding agent (such as RelyX Ultimate and Scotchbond Universal, 3M ESPE) are better choices even though they may take longer to use and make cleaning excess set cement more difficult.

Related reading: Using esthetic adhesive cement to blend CAD/CAM posterior restorations to surrounding dentition

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DPR: What role do your assistants play in the cementation process, and how do cement features impact that?
DR. ALEX: I have taught my assistants the specific cementation and bonding protocols for various dental materials and cements. This includes the proper way to treat the intaglio surfaces of various restorative materials (sandblasting, use of hydrofluoric acid) and the placement of surface primers such as silane and MDP-containing primers, depending on the nature of the restoration being placed. They also are responsible for mixing the cement and loading in into the restoration being placed. Most of the cements we use are available in auto-mixing syringes, making the mixing process simpler, faster and more predictable.   

DPR: How do you recommend dentists stay informed about all the new materials out there so they can make the best choices for their practices?
DR. ALEX: Dentists need to sort through the plethora of articles and look for unbiased, independent, peer-reviewed articles published in reputable journals that present the actual science without embellishment and marketing hype. Look for courses given by knowledgeable independent speakers that really understand the chemistry and inner workings of dental materials, including adhesives and cements, along with their practical indications and use in a busy dental practice.  
For those who really want to take it to the next level, research meetings such as the IADR (International Association of Dental Research), IAAD (International Academy for Adhesive Dentistry) and AADR (American Academy of Dental Research) provide a treasure trove of scientific information on virtually all aspects of dentistry. 

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DPR: So do you think dentists have pretty solid options, given the progress cements have made in recent years?
DR. ALEX: Dental manufacturers have made great strides in developing quality cements, primers and adhesives that meet the requirements for virtually all cementation needs. Clearly, one of the trends has been toward simplification in terms of mixing, product versatility and clean-up. It is the dentist’s responsibility to learn the specific differences between the various classifications of cements, how to optimize their performance and which to use depending on the material being placed and specific clinical situation.   

Watch the video below for step-by-step instruction of cementing a monolithic zirconia crown: