The OptiBond product line is evolving once again with OptiBond eXTRa Universal, which is a slightly updated version of OptiBond XTR. While there is only a minor change in the resin component, Kerr should be congratulated for not messing up a good thing. It is still a two component, universal adhesive that can be used in all modes (etch & rinse, self-etch, and selective etch).
The primer includes GPDM (glycero-phosphate dimethacrylate), which is a monomer that has formed the backbone of the OptiBond family since its inception in 1993 and seems to be one of the primary reasons it continues to be a major player in the adhesive category. In addition, the primer has hydrophilic co-monomers including mono and di-functional methacrylate monomers, along with camphorquinone (CQ) as the photo-initiator, all in a solvent of water, ethanol, and acetone. This so-called ternary (3 part) solvent is stated to enhance its self-etching capability and facilitates its penetration into the tooth, which should lead to high bond strengths.
The pH starts out at 2.4, but due to the quick evaporation of the acetone when the primer is applied, it is stated to decrease instantaneously to 1.6, which presumably helps with the enamel etching task. Note that the higher pH (2.4) when it is in the bottle or unidose is also supposed to enhance the primer’s stability during storage.
The adhesive is the second component and includes hydrophobic, structural, and cross-linking monomers, the identification of which is proprietary. It also contains CQ, along with fillers composed of 0.4 micron barium glass and nano-silica, plus sodium hexafluorosilicate in ethanol. This makes it 15% filled by weight. The pH is 3.3 initially, but increases to 6.5-7.0 (neutral) after applying and light curing. Due to its minimal film thickness (stated to be 5-10 microns), it is being recommended for both direct and indirect restorations.
Note: According to Kerr, the odor-causing monomer (present at less than 5% of the formula) in the adhesive (which was not appreciated by most of our evaluators when OptiBond XTR was evaluated) was replaced with a functionally-equivalent monomer but without the pungent odor. Therefore, the net change in formulation is really minimal and should not affect its performance.
To use, dry (blotting is best) but don’t desiccate the preparation. Apply the primer to the tooth for 20 seconds, using a scrubbing technique. Note that “scrubbing” is a relative term, since the applicator included in the kit is quite flexible and only permits a moderate amount of pressure during this scrubbing phase.
Evaporate the solvent with gentle air at first and increase the pressure to moderate air. Even though the primer contains CQ, it is not designed to be light cured. Then apply the adhesive for 15 seconds using gentle agitation, followed by gentle to medium air to thin the layer and evaporate the solvent. If you are applying it to a prep destined for an indirect restoration, your air pressure needs to be strong enough to prevent the adhesive from pooling. If the adhesive layer pools or you have wrinkles, it could prevent complete seating of your restoration. Finally, light cure for 10 seconds. Note that the CQ in the primer is supposed to enhance the light curing propensity of the adhesive.
Using this protocol, here are our bond strength results in MPa using light-cured composite:
With self-cured composite, the 24 hour bond strength in MPa to dentin in the self-etch mode was 18.8.
The packaging is very basic. While it comes in bottles and unidose, we only received the latter for this preview. They are in an easy to stack cardboard box with product identification on three sides and on top. Expiration date is on a label on the back. Taped for security. Inside are the unidose vessels housed in separate recloseable plastic bags.
The unidose vessel has a relatively broad, round base that allows it to stand on its own or it can be used by the assistant as a handle. The cylindrical receptacle for the primer or adhesive sits directly on this base and is flanked by bilateral wings that help stabilize it when the assistant holds it. The top section is a rounded triangle but flat in cross section. To remove the top, merely twist it in either direction using moderate pressure.
Once removed, the top cannot be used to protect the exposed adhesive from ambient light. If you want to use it for multiple preparations but not all at the same time, you'll need to place the bottom section in a light-protected box to keep it from prematurely polymerizing.
The primer comes in a green unidose, while the adhesive is gray. Both are clearly marked as either the primer (1) or adhesive (2). There is also the product name and the expiration date.
If you want the full directions, you need to download them from the Kerr site. In the box you will find a plastic-laminated foldout card with realistic color illustrations described in English.
OptiBond eXTRa Universal, with performance that echoes its 5-star, XTR parentage, should be at or near the top of this category once the full evaluation is completed. Stay tuned on that.