In Vivo Degradation of Resin-Bonded Human Dentin After 3 Years of Storage
Howard E. Strassler, DMD
Garcia-Godoy F, Tay FR, Pashley DH, et al. Am J Dent. 2006;19:109-113.
PURPOSE: To test, in vitro, the null hypothesis that there was no difference in the ultrastructure of adhesive-bonded, acid-etched dentin aged under accelerated conditions in mineral oil or artificial saliva. METHODS: Beams of human dentin bonded with three total-etch adhesives that were retrieved from the two storage media after 3 years and prepared for electron microscopy. RESULTS: Hybrid layers from specimens aged in mineral oil exhibited structural integrity of the collagen network. Conversely, abnormal hybrid layers were seen in specimens aged in artificial saliva, with progressive disintegration of the fibrillar network to the extent that it was beyond detection by collagen staining. Self-destruction of collagen matrices can occur in resin-infiltrated dentin and, to a lesser degree, in mineralized dentin in the absence of bacterial or salivary enzymes.
In clinical practice, composite-based restorations are being placed routinely with enamel and dentin adhesive bonding. In the past 10 years there has been considerable evidence both in vitro and in vivo that bonds created to dentin by resin-based adhesives may not be as durable as was speculated.1 Current chemistries being used with resin adhesives employ both hydrophilic and ionic resinous components to address the need to bond to dentin, an inherently wet substrate. Unfortunately, these chemistries are potentially unstable and slowly degrade because of water sorption. This is especially true when the resin–dentin bond is not protected by an etched enamel seal and the adhesive interface is challenged by interactions with moisture.
This study addresses what happens in the hybrid zone, that layer of resin infiltration in peritubular dentin and, over time, into the dentinal tubules. There has been concern that there is a bond degradation because of the potential instability of the demineralized dentin collagen matrix that can be measured with the thinning or disappearance of collagen fibrils from aged and bonded dentin.2
The findings of this study parallel bond strength studies that have demonstrated a significant decrease in adhesion to dentin over time.3,4 After 3 years, the resin infiltration into the hybrid zone demonstrated a self-destruction that in all likelihood accounts for the reported decreases in adhesive bonding. This degradation in adhesive bonding to dentin supports what dentists see clinically.
Bonding to etched enamel is the "gold standard" for adhesion. Clinicians see this when they are preparing teeth for crowns that have existing Class V resin-bonded restorations. These restorations cannot be dislodged from the preparations, mostly because of the enamel bonding. Once the teeth are prepared and the enamel surfaces are removed, these Class V composite resin restorations can be "popped out" with a sharp scaler. The dentin bond over time, however, is questionable. When placing restorations, follow the manufacturer’s instructions to achieve the best adhesion. Whenever possible, try to maintain an enamel interface to seal the restoration—especially with etched porcelain- bonded veneers and crowns. Do not depend on dentin-bonded restorations to be as durable as enamel-bonded restorations.
References1. Pashley DH, Tay FR, Yiu C, et al. Collagen degradation by host-derived enzymes during aging. J Dent Res. 2004;83(3): 216-221.
2. Yiu CK, King NM, Pashley DH, et al. Effect of resin hydrophilicity and water storage on resin strength. Biomaterials. 2004;25(26): 5789-5796.
3. Meiers JC, Young D. Two-year composite/dentin bond stability. Am J Dent. 2001;14(3):141-144.
4. Hashimoto M, Ohno H, Kaga M, et al. In vivo degradation of resin-dentin bonds in humans over 1 to 3 years. J Dent Res. 2000;79(6): 1385-1391.
Howard E. Strassler, DMD
Professor and Director of Operative Dentistry
Department of Endodontics, Prosthodontics and Operative Dentistry
University of Maryland Dental School, Baltimore, Maryland