A study published in The Journal of Evidence-Based Dental Practice recently examined how dentin bonds degrade over time. This was the first in vivo human study on bond degradation. It showed expected results. Over a 3 year time period, the bind between dentin and resin. After 3 years, bond strength decreased almost 60%. The study did indicate some clinical steps that dentists can easily do to maximize bind strength. These included using a 4th generation three step dentin bonding system, improving impregnation of the hybrid layer by using multiple applications of resin primer, and ensuring adequate polymerization of the adhesive system.
Of course there is much in vivo human work to do studying bonding. This study goes a long way but there are still some questions. After the dentin bond has deteriorated, does the enamel bond that is theoretically there keep the restoration viable? Certainly in traditional amalgam restorations there is no dentin bond yet they seem to last for years with no problem. Does the resin’s affinity for water absorption cause problems long term after the dentin bond has deteriorated. These are all questions we should be pondering when placing resin composite restorations.
Study citation: In vivo degradation of resin-dentin bonds in humans over 1 to 3 years. Hashimoto M, Ohno H, Kaga M, Endo K, Sano H, Oguchi H. J Dent Res 2000;79(6):1385-91