The role of host-derived dentinal matrix metalloproteinases in reducing dentin bonding of resin adhesives / 国际口腔科学杂志·英文版

Dentin matrix metalloproteinases (MMPs) are a family of host-derived proteolytic enzymes trapped within mineralized dentin matrix, which have the ability to hydrolyze the organic matrix of demineralized dentin. After bonding with resins to dentin there are usually some exposed collagen fibrils at the bottom of the hybrid layer owing to imperfect resin impregnation of the demineralized dentin matrix. Exposed collagen fibrils might be affected by MMPs inducing hydrolytic degradation, which might result in reduced bond strength. Most MMPs are synthesized and released from odontoblasts in the form of proenzymes, requiring activation to degrade extracellular matrix components. Unfortunately, they can be activated by modem self-etch and etch-and-rinse adhesives. The aim of this review is to summarize the current knowledge of the role of dentinal host-derived MMPs in dentin matrix degradation. We also discuss various available MMP inhibitors, especially chlorhexidine, and suggest that they could provide a potential pathway for inhibiting collagen degradation in bonding interfaces thereby increasing dentin bonding durability.

Effect of the thickness of periodontal ligament on the fracture resistance of root and post-core system / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To assess the effect of the thickness of periodontal ligament on the fracture resistance of root and post-core system.</p><p><b>METHODS</b>Forty-five simulated roots in the same length, taper and diameter were made of polymethacrylate (PMMA). Then the wax patterns of post-cores were cast. Soft lining material was used to simulated periodontal ligament. And each specimen was embedded in acrylic resin and then fixed in a special jig on the universal load-testing machine. A compressive load was applied at a 90-degree angle to the long axis of the core until fracture, at a crosshead speed of 1 mm/min. The maximum of load and the displacement were recorded.</p><p><b>RESULTS</b>The mean values of load in root and post-core system were 148.033 N, 161.889 N, 168.667 N, 181.589 N, 194.622 N, and the mean values of displacement were 1.965 mm, 2.837 mm, 3.327 mm, 3.927 mm, 5.326 mm.</p><p><b>CONCLUSION</b>The fracture resistance and displacement of root and post-core system with the same quality and altitude periodontal ligament are associated with the thickness of periodontal ligament when the range of thickness is from 0.2 mm to 1.0 mm.</p>