Light-Cured-Only
Since they are single-component materials with no chemical catalysts, they are very color-stable, do not have to be mixed, and can be used with virtually any adhesive. They usually do not require refrigerated storage and still have a multi-year shelf life. And, just like their restorative composite analogs, they have unlimited working time as long as you turn down your dental unit light or use a light filter while you are seating restorations.
Because they have no self-curing properties, they are typically used for luting relatively thin, metal-free restorations such as veneers. However, at least one published retrospective study and anecdotal reports have shown they can be used with even thicker restorations as long as you expose the restoration to a current generation curing light from all directions and for an adequate curing interval (usually 40-60 seconds) from each direction. In addition, it is also helpful to use a translucent cement, which is easier to cure than an opaque version. They are meant to be used in combination with either an etch & rinse or self-etch bonding agent of your choosing.
Tests
Consistency and Handling
These properties refer to whether the cement is easy to load into a veneer, for example, and easy to clean off a restoration. Included in this property is the degree of stickiness.
Flow
If a material is too thick, it may prevent positive seating of the restoration as well as possible fracture from the force needed to seat it. A material that is too thin may not have enough body to fill the gap between the restoration and the tooth. We performed flow tests on all the products in this category. Flow is graded on a grid going from 0-5, with 0 being very runny and 5 having virtually no flow.
Shades
2-3 shades of a resin cement is usually more than sufficient. This is due to several factors. In the first case, there are minimal differences in cement shades when they are viewed in clinically relevant thicknesses. This can be demonstrated when we perform the translucency/opacity test.
Second, the effect of the shade of the cement is highly dependent on the thickness of your restoration. The thicker the restoration, the less effect the shade of the cement will have. In restorations thicker than 1.0mm, there are instances where the cement has no effect whatsoever.
Third, the opacity of the restoration may block out any shading effect of the cement. Therefore, this is one category where buying a few shades a la carte makes much more sense than investing in an entire kit.
The most utilized shade will definitely be clear, which some manufacturers may call translucent or something similar. For patients who just have to have the toilet bowl effect, you will probably also need white opaque. And you may want to purchase a dark, medium opacity shade that can tone down a thin restoration that is too bright.
Translucency/Opacity
Discs of all products in 100 micron thicknesses (to simulate the thickness of the cement under a restoration) were measured for relative degrees of translucency/opacity in a spectrophotometer. The scale was 0-100, with 0 being totally clear and 100 being totally opaque. Our findings are in the commentary of each product.
Try-In Pastes
Water-soluble try-in pastes color-keyed to cement shades. These pastes (gels) greatly simplify color matching. When a system has no try-in pastes, you must use the actual material and guard against premature light polymerization. We tested these shades in the same manner as the actual cement and compared each pair (cement and try-in paste) to see if the shades did actually match.
Shade Shift after Curing
Shows how much the color changes after light curing the material. This is only important if you want to do a shade check with the actual cement instead of a try-in paste. If the material does not have a shade shift, it can be used for the try-in.
