title: Mechanisms of degradation of the hybrid layer in adhesive dentistry and therapeutic agents to improve bond durability--A literature review.
abstract: OBJECTIVE
  Success in adhesive dentistry means long lasting restorations. However, there is substantial evidence that this ideal objective is not always achieved. Current research in this field aims at increasing the durability of resin-dentin bonds. The objective of this paper is to examine the fundamental processes responsible for the aging mechanisms involved in the degradation of resin-bonded interfaces and the potential approaches to prevent and counteract this degradation.
  
  
  METHODS
  PubMed searches on the hybrid layer degradation were carried out. Keywords were chosen to assess hybrid layer degradation for providing up-dated information on the basis of scientific coherence with the research objective. Approaches to prevent and counteract this degradation were also reviewed.
  
  
  RESULTS
  148 peer-review articles in the English language between 1982 and 2015 were reviewed. Literature shows that resin-dentin bond degradation is a complex process, involving the hydrolysis of both the resin and the collagen fibril phases contained within the hybrid layer. Collagen fibers become vulnerable to mechanical and hydraulic fatigue, as well as degradation by host-derived proteases with collagenolytic activity (matrix metalloproteinases and cysteine cathepsins). Inhibition of the collagenolytic activity and the use of cross-linking agents are the two main strategies to increase the resistance of the hybrid layer to enzymatic degradation.
  
  
  CONCLUSIONS
  This review analyzes the issues regarding the durability of the adhesive interface, and the techniques to create stable resin-dentin bonds able to resist the collagenolytic hydrolysis that are currently studied.
authors.affiliation: Department of Medical Sciences, University of Trieste, Piazza dell'Ospitale 1, Trieste, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Frassetto
authors.affiliation: Department of Biomedical and Neuromotor Sciences, DIBINEM, University of Bologna, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Breschi
authors.affiliation: Department of Medical Sciences, University of Trieste, Piazza dell'Ospitale 1, Trieste, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Turco
authors.affiliation: Department of Medical Sciences, University of Trieste, Piazza dell'Ospitale 1, Trieste, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Marchesi
authors.affiliation: Department of Medical Sciences, University of Trieste, Piazza dell'Ospitale 1, Trieste, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Di Lenarda
authors.affiliation: Department of Oral Biology, Georgia Regents University, College of Dental Medicine, Augusta, GA, USA.
authors.forename: Franklin R
authors.initials: FR
authors.lastname: Tay
authors.affiliation: Department of Oral Biology, Georgia Regents University, College of Dental Medicine, Augusta, GA, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Pashley
authors.affiliation: Department of Medical Sciences, University of Trieste, Piazza dell'Ospitale 1, Trieste, Italy. Electronic address: mcadenaro@units.it.
authors.forename: Milena
authors.initials: M
authors.lastname: Cadenaro
mesh_terms: D002403:Cathepsins / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000737:chemistry; D001840:Dental Bonding; D003804:Dentin / Q000737:chemistry*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D006801:Humans; D006868:Hydrolysis; D020782:Matrix Metalloproteinases / Q000378:metabolism; D019279:Resin Cements / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D017220:Dentin-Bonding Agents; D019279:Resin Cements; D003094:Collagen; D002403:Cathepsins; D020782:Matrix Metalloproteinases
keywords: Collagen; Cross-linking agent; Dentin; EDC; Hybrid layer degradation; Metalloproteinases