Membrane permeability properties of dental adhesive films

Abstract

This study evaluated the permeability properties of five experimental resin membranes that ranged from relatively hydrophobic to relatively hydrophilic to seal acid-etched dentin saturated with water or ethanol. The experimental resins (R1, R2, R3, R4, and R5) were evaluated as neat bonding agents or as solutions solvated with ethanol (70% resin/30% ethanol). The quality of dentin sealing by these experimental resins was expressed in terms of reflection coefficients calculated as the ratio of the effective osmotic pressure to the theoretical osmotic pressure of test solutions. The effective osmotic pressure produced across resin-bonded dentin was induced in hypertonic solutions (CaCl(2) or albumin) at zero hydrostatic pressure. The outward fluid flow induced by these solutions was brought to zero by applying an opposing negative hydrostatic pressure. The least hydrophilic resins blends, R1 and R2, exhibited significantly (p < 0.05) higher reflection coefficients than the most hydrophilic resins (R4 and R5) in both conditions of dentin saturation (water and ethanol). The reflection coefficients of neat resins were, in general, significantly higher when compared with their corresponding solvated versions in both conditions of dentin saturation. In dentin saturated with ethanol, bonding with neat or solvated resins, resulted in reflection coefficients that were significantly higher when compared with the results obtained in dentin saturated with water. Reflection coefficients of CaCl(2) (ca. 1 x 10(-4)) were significantly lower (p < 0.05) than for albumin (ca. 3 x 10(-2)). Application of hydrophobic resins may provide better sealing of acid-etched dentin if the substrate is saturated with ethanol, instead of water.

Figure 1

Schematic of the degree of selectivity of membranes based on their reflection coefficients. A. Non-selective; B. Semi-permeable (permeable only to solvent molecules); C. Partial selectivity (permeable to molecules of solvent and solutes with a certain size).

Figure 2

Schematic of apparatus used to measure osmotically-induced fluid flow across resin-bonded dentin at zero hydrostatic pressure and how flow was stopped by applying negative hydrostatic pressure (i.e. lowering outflow tubing). The schematic of the specimen shows cross-sectional appearances of crown segment, water-filled the pulp chamber and the microscopic dentinal tubules that were covered at the surface by experimental resins that, in turn, were covered with test solution.

Figure 3

Correlations between the polymer Hoy’s solubility parameters for hydrogen bonding forces (δ_h) and the respective reflection coefficients (σ) of ethanol-saturated dentin (ESD) bonded with neat (R) or solvated (R+E) resins when using CaCl₂ (A and B) or in (C and D).