Last time we examined some key concepts to evaluate in your direct composite protocol before you even pick up a handpiece. This month I’d like to explore today’s options for dentin/enamel adhesive options in order to help you make the best selection for your practice.
One of the first things to consider is the difference between enamel and dentin substrates and the need to respect that difference. Our bonds to enamel after exposure to acid etching are micromechanical, strong, and consistent. Dentin poses a different set of concerns. It can vary from patient to patient, from one tooth to another, and even within the depth of a preparation. Dentin is also composed of roughly 12-13% water and we are asking a basically hydrophobic material (resins within an adhesive) to attach or bond to it. There is also the issue of the smear layer – whether to remove it or incorporate it into the final product. That has been a source of debate for decades, but it seems the current consensus is to leave it on the surface and utilize chemistries to infiltrate it with the hope of reducing the potential for the feared “post-operative sensitivity.”
Today’s bonding systems come in all shapes and sizes, but can be grouped into three basic categories: Total-Etch (Etch and Rinse), Self-Etch, and the newly developed Universal adhesives. The Total-Etch technique has been the “gold standard” in direct composites since the concept was first pioneered by Buonocore, and involves applying a phosphoric acid of 30-40% concentration to the enamel and dentin for a prescribed length of time (usually 15-20 seconds on enamel and 10 seconds on dentin), then rinsed off with a water spray. This method presents several challenges to the practitioner such as over or under etching of the tooth surfaces, inability to remove all the acid when rinsing, over drying the dentin, or leaving too much water on the surface. All of these can pose a problem and might contribute to sensitivity for the patient after placement of the composite, especially in the posterior. As a result, these concerns led to the creation of the Self-Etch systems as a way to circumvent some of these issues.
The Self-Etch adhesive systems eliminate the separate phosphoric etch step, but still allow for the demineralization process to take place. However, because these self-etch products rely on water to initiate the demineralization, excess water remaining during the polymerization sequence has been shown in some studies to compromise bond strength, so the manufacturers may suggest rubbing or scrubbing of their self-etch adhesives, plus the use of multiple coats to ensure more predictable results. Enamel etch patterns have also come under scrutiny with the self-etch systems, especially if the enamel was not cut with a rotary instrument. The use of a phosphoric acid as a “selective-etch” on enamel only, then rinsed off prior to the application of the self-etch resin, has been suggested as a way to improve this shortcoming.
The newest players in the game are the Universal adhesive systems. Several are based on previously developed chemistry with their key advantage being the ability to bond to a multitude of materials including composite, ceramic, lithium disilicate and zirconium. They can be used with or without a separate acid-etch step to achieve a good result and offer you more flexibility when selecting an adhesive system to purchase.
For me, the bottom line is if you are achieving good clinical results with the system you are using, then there is really no need to make a change. However, if you have experienced sensitivity issues that can be attributed to unsealed dentin, or just wish to be able to bond multiple substrates with one kit, perhaps a self-etch or universal adhesive system might elevate your bonding game.
Drop in next month as we look at the importance of using contemporary matrices to elevate your anterior and posterior composite techniques!