What Properties of a Dental Adhesive System Are Most Important?

Tuesday, July 30, 2013

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In the war for the title of best dental adhesive, does strength matter anymore?

I recently had a patient come in with consistent pain in one of his back teeth. We had placed a composite filling in tooth #18 about 7 years ago. What we found was a fracture that started on the occlusal, and wrapped around toward the distal. The tooth was sensitive to pressure and to percussion and the x-ray showed a periapical radiolucency around the distal root. Considering the vertical bone loss on the distal, the fracture was most likely present for a while.

We ended up referring the patient to the endodontist we work with, and while the clinical findings were interesting, what I thought was most compelling was the actual presentation of the fracture. The original filling was placed using Kuraray’s Clearfil SE Bond and 3M ESPE’s Filtek Supreme. The picture below that we shot was with our DexCam 3 intraoral camera. What you can see is the bond has not failed on the filling. Instead, the occlusal pressure causing the tooth to crack split the filling in half. What this says to me is the internal strength of the filling failed before the adhesive bond did.

While bond strengths used to be one of those key points of comparison between bonding systems from different manufacturers, this case makes me question whether or not it remains a significant point of interest. I’m not saying it is not significant, but almost everyone has approached or broken the 30 MPa mark in terms of shear bond strength. If we have achieved a certain level of strength where the tooth is failing before the bond does, maybe there are other key attributes everyone should be using to better distinguish products. This is not so different from the way power windows used to be a key upgrade when buying a car, but now most cars have them and power windows have morphed into a minimum standard.

These days the two key attributes I am looking for in a bonding system are simplicity and a lack of post-op sensitivity. Considering the latter, I have had great success with self-etching systems, and I rarely get called a few days later to hear someone is still having trouble. So while the patient unknowingly benefits from my choice of bonding system, I want a system that to make my life easier as well.

Lately, I have been using Scotchbond Universal. It is a self-etching system that employs a similar monomer to what is found in Clearfil SE Protect. It is also packaged with silane primers, so I can use it to bond a post, a porcelain crown, a zirconia restoration or a direct filling.

So while bond strengths are still important, the chemistry has reached a point where when properly applied, I am confident in the ability of most adhesives to keep a restoration where it has been placed. These days I’m looking more intently at an adhesive’s ability to improve both my workflow and my patients’ comfort.

Drop a comment below if you have a similar case, or have something you find most valuable in your adhesive of choice.

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