Today’s modern restorative materials allow for minimally invasive preps and partial restorations, as well as traditional full coverage crowns and bridges. The material options can be dizzying, with more and more available choices to meet the high demand for esthetic outcomes. And, the driving force behind the treatment plan tends to focus on the material that will be used; however, it’s important not to forget the materials unsung sidekick – the cement!
For example, if it is impossible to isolate the restoration site from moisture, care should be taken to use restorative materials that allow for conventional cementation, because these cements can accept some moisture; whereas, with an adhesive cement technique, moisture control is critical. If thinking about implant-based restorations that need easy and reliable clean-up, they can benefit from conventional cementation if the restoration margin cannot be placed supragingivally. Additionally, check the manufacturer’s minimum thickness of your chosen restorative material to ensure longevity and prep the tooth accordingly. As the tooth is being prepped, whether or not it is retentive is a very important factor in the success of your material/cement choice.
Is the prep retentive, and if it is what are my options?
Any dental professional who has ever dabbled in woodworking, or even just admired some custom cabinetry or furniture, could draw a rough comparison between the principles of joinery used and the principles behind cementing a crown prep. A butt joint and a tapered crown prep have similar non-retentive properties, requiring a stronger glue, or cement, respectively to have success. On the other end of the spectrum, a dovetail joint has strong mechanical retention and requires minimal gluing. In much the same way a prep with parallel walls and at least 3-4 mm of wall height offers solid mechanical retention which allows a simple GI or RMGI cement to be used. Of course, this analogy only goes so far and dental professionals have to take into account additional factors including the strength of the material being used. So, what is a retentive prep really telling me about material and cement selection? A retentive prep for a crown or a bridge generally allows for any type of cement as no extra bond strength is needed because of the mechanical retention provided by the preparation design. So, retentive preps can be cemented using a conventional cement, without a bonding agent, like a glass ionomer cement or a resin modified glass ionomer cement. This is especially valid if the restorative material is strong (like metal-based or zirconia) and therefore does not need a strong bond to help it stay in place. If the restoration material is weaker - like a glass ceramic - the use of a material forming a chemical bond using a self-adhesive resin cement (no separate bonding step needed) is recommended for a simple and reliable outcome. This choice also comes with the advantage of shade choices to answer potential esthetic needs.
If the prep is non-retentive, how does that change decisions?
A self-adhesive resin cement may also be the first choice for a strong restoration material and a non-retentive prep or a prep with a smaller surface area. If the prep is non-retentive and the restoration material is weaker, i.e. made of glass ceramic or a hybrid material and retention is low, bonding with an adhesive resin cement is generally recommended to give extra support for the restoration to stay in place. Again, this choice allows for excellent esthetic outcomes as there are several shades from which to choose. For non-retentive preps and partial preps - especially if they are mostly on enamel (i.e., veneers) - adhesive resin cements with a separate bonding system and enamel etch are the first choice. This is also true for inlays, and inlay- or Maryland bridges where there are only very small bonding surfaces. Hybrid materials should always be bonded with an adhesive resin cement with a separate adhesive. They need extra bond strength due to their resilient nature.
Conclusion
In summary, high strength materials allow for more cement choice options. Conventional cementation or a self-adhesive cement approach are recommended depending on the situation and retention level. For glass ceramic materials the self-adhesive or adhesive approach are the best options as they allow for good esthetics and strength, whereas for hybrid materials only adhesive resin cements with a separate bonding agent are recommended. Many different cement options have been created to account for so many different material needs. This sometimes makes the choice of the correct cement a bit confusing; however, a few simple guidelines, as noted in the chart above, can help in making the correct cement call in any clinical situation.
