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Permeability of Demineralized Marginal
Hybrid Layer

C. PRATI (University of Bologna, Italy), P. SUPPA (University of Bologna, Italy), S. MARCHIONNI (University of Bologna, Italy), S. CHERSONI (University of Bologna, Italy), and L. BRESCHI (University of Trieste, Italy)


Marginal hybrid layer (MHL) is defined as the resin-dentin interdiffusion layer in correspondence of external margins of the restoration. Its role is obviously extremely important in reducing the risk for micro and nanoleakage.

Objectives:
The tested hypothesis of this study was that acid cariogenic solutions are able to modify in vitro the morphology of MHL and to increase its permeability.

Materials and Methods:
Standardized class II cavities (n= 18) were made in vitro with cervical margin at approx. 1 mm below the CEJ. Two different dentin bonding systems were used: Quadrant UniBond (CAVEX) and Clearfil SE Bond (Kuraray) in association with a composite material (APX Kuraray).
  After finishing with SofLex PopOn abrasive disks (3M-ESPE), specimens were immersed in water for 1 week. An impression was taken by vinyl polyxiloxane (President Jet light, Coltene). The restorations were then immersed in acid lactic solution (pH 4.4) for 3 days. A second impression was taken after demineralization procedure. Replicas were obtained by polyether impression material (Permadyne Garant, 3M-ESPE). Replica and original samples were observed under SEM.

pict 1963
  Results:
Original and replica specimens showed a thin MHL (0.5-1.2 microns) along dentin margins before demineralization. Water droplets were detected in replica samples in correspondence of MHL. Replica samples obtained after storage in cariogenic solution showed degradation of the margins and a greater number of irregularities, gaps. After exposure to cariogenic solution the number and dimensions of droplets slightly increased.

Conclusions:
Marginal hybrid layer and perimarginal dentin morphology resulted severely damaged by demineralizing solution. The droplets formation along MHL is an index of its capability to adsorb and release water.
The increased number of droplets after storage in acidic solution suggests that MHL acts as a permeable substrate and its water permeability is increased by cariogenic acidic solutions.