The first generation of methacrylate-based root canal sealers appeared in the 1970s [1
]. The material, Hydron, was removed from the market because it absorbed too much water, swelled out of the confines of the root canal and leached 2-hydroxyethyl methacrylate into the periapex, causing chronic inflammation. The second generation [3
] was designed to bond to NaOCl/EDTA-treated dentin. This dual-cured sealer, EndoREZ (Ultradent, South Jordan, UT), can be used with conventional gutta-percha or resin-coated gutta-percha points. The third generation utilizes a self-etching acidic primer to etch into the smear layer, followed by a dual-cured flowable composite. An example of such a sealer is Resilon (Resilon Research LLC, Madison, CT) [5
]. The fourth generation is essentially a self-etching flowable composite (RealSeal SE, SybronEndo, Orange, CA) that combines an etchant, a primer, and a sealer into an all-in-one self-etching, self-adhesive composite [6
]. As the etching ability of these sealers is sufficient to uncover and activate MMPs in apical dentin, the thin hybrid layers created by these sealers may be susceptible to MMP-induced degradation. Dental adhesives obtain their adhesion by flowing into the spaces between adjacent collagen fibrils. Once polymerized, this resin-infiltrated demineralized zone is called a “hybrid layer”. Hybrid layers provide micromechanical retention between overlying filling materials and the underlying mineralized dentin. The only continuous connection between mineralized dentin and filling materials are the collagen fibrils of the hybrid layer.
Dentin collagen fibrils contain inactive proforms of proteolytic enzymes called matrix metalloproteinases (MMPs) [7
]. Once mineralized, the MMPs in the dentin matrix are inactive. They are exposed and activated by acid-etching during adhesive bonding procedures. If these matrix-bound, activated MMPs are not fully infiltrated with adhesive resin, they can slowly degrade the collagen fibrils that anchor the fillings to dentin. This can cause loss of adhesion [8
] and gap formation. This has lead to a number of investigations on the use of MMP-inhibitors to inactivate exposed, activated MMPs [9
]. The functions of MMPs are diverse but are mainly associated with degradation of the extracellular matrix including collagens. Dentin contains endogenous MMP-2, -8, -9, -20 [7
] and are involved in degradation of resin-dentin bonds both in vivo
and in vitro
]. MMP-2 and -9 have traditionally been considered as gelatinases. However, more recent work showed that they also exhibit collagenolytic activity [11
] When these inactive zinc- and calcium-dependent endopeptidases are exposed and activated by self-etch or total-etch adhesives [14
], they can degrade type I collagen [18
]. As collagen fibrils are incompletely resin-infiltrated during dentin bonding procedures [19
], strategies to prevent bond degradation are necessary to increase the longevity of methacrylate resin-based root fillings and orifice barriers.
Several materials have been shown to inhibit MMPs, including some root canal irrigants. Both 2% chlorhexidine and 17 wt% ethylenediaminetetraacetic acid (EDTA) have been shown to inhibit MMP activity induced by self-etching adhesives [15
]. Although the anti-MMP activity of EDTA is well-known, it is often used at only 0.34–0.68 wt% in anti-MMP assays. What is not known is how rapidly 17 wt% EDTA can inactivate matrix-bound MMPs when the latter is used in the context of a root canal irrigant. Thus, the aim of the present study was to determine the time necessary for 17 wt% EDTA to display anti-MMP effects on demineralized dentin. The null hypothesis tested was that different exposure times to 17 wt% EDTA has no effect on MMP activity of demineralized human dentin.