Combating Bond Degradation

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In yesterday’s post I discussed the concept of bond degradation, which is the loss of bond strength over time after a restoration is placed. One of the processes we have become aware of around adhesive dentistry is the presence and production of Matrix Metalloproteinases. MMP’s , as they are referred to, are host-derived proteolytic enzymes that become trapped in the demineralized dentin layer. Despite our best techniques at developing the hybrid zone when bonding tags of demineralized dentin extend beyond the infiltration of resin. The presence of MMP’s in combination with demineralized dentin and water results in breakdown and reduction in bond strength over time, what we refer to as bond degradation.

MMP’s are naturally present in the dentin. What research is looking at is the effect of the etching process on activating the MMP’s and setting off the process of bond degradation. This may account for the difference in decrease in bond strengths we see over time between materials. The acidity of the etch, the ability to demineralize deeper than the resin can infiltrate in combination with moisture, a technique factor all influence the quantity and activity of the MMP”s. So for years we have been working on improving the longevity of our restorations by improving how we etch, and create the hybrid zone, all of which decreases the ability of MMP’s to breakdown what we created.

Many of you know that for more than a decade I have been a raving fan of Gluma Desensitizer by Heraeus. In addition to it’s ability to eliminate post op sensitivity and significantly decrease the risk of post operative pulpal inflammation or death, I now have yet another reason to love using it. The focus these days with MMP’s is looking at ways to deactivate them so bond degradation is minimized if not eliminated. We have incredible research from the medical literature showing that a 3% Glutaraldehyde solution significantly reduces the activity of MMP’s and Gluma contains 5%. Other additives to dentin adhesives such as Galardin, and antibacterial rinses like Chlorhexidine have also been shown to reduce the activity of MMP’s. Dr. ED McLaren, UCLA Center For Esthetic Excellence, has shown in his research that treating the prepared tooth first with 2% Chlorhexidine followed by Gluma may be the magic combination to increase bond strengths and decrease bond degradation.

As with many things in dentistry we do not have all the answers and we are learning more and more everyday. For now, precise use of our materials and precise technique have one more cheerleader, the reduction of bond degradation. Using desensitizers and antibacterial rinses not only saves pulps, but adds to the longevity of our restorations, for a mere dollar or two a prep and 30 seconds worth of time,