Evidence of Chemical Bonding at Biomaterial-Hard Tissue Interfaces

Abstract

For many years, glass-polyalkenoate cements have been described as possessing the unique properties of self-adherence to human hard tissues, such as bones or teeth. However, direct experimental evidence to prove the existence of chemical bonding has not been advanced. X-ray Photoelectron Spectroscopy (XPS) was used to analyze the chemical interaction of a synthesized polyalkenoic acid with enamel and synthetic hydroxyapatite. For both enamel and hydroxyapatite, the peak representing the carboxyl groups of the polyalkenoic acid was detected to have significantly shifted to a lower binding energy. De-convolution of this shifted peak disclosed two components with a peak representing unreacted carboxyl groups and a peak suggesting chemical bonding to hydroxyapatite. On average, 67.5% of the carboxyl groups of the polyalkenoic acid were measured to have bonded to hydroxyapatite. XPS of hydroxyapatite also disclosed its surface to be enriched in calcium and decreased in phosphorus, indicating that phosphorus was extracted at a relatively higher rate than calcium. Analysis of these data supports the mechanism in which carboxylic groups replace phosphate ions (PO4(3-)) of the substrate and make ionic bonds with calcium ions of hydroxyapatite. It is concluded that an ultrathin layer of a polyalkenoic acid can be prepared on a hydroxyapatite-based substrate by careful removal of non-bonded molecules. With this specimen-processing method, XPS not only provided direct evidence of chemical bonding, but also enabled us to quantify the percentages of functional groups of the polyalkenoic acids that bonded to calcium of hydroxyapatite.

Effect of Substrate Age and Adhesive Composition on Dentin Bonding

“…12,13,16 Carboxylate groups replace phosphate ions of the substrate and bond ionically with calcium of hydroxyapatite. 13 This chemical bonding mechanism is explained by the adhesion-decalcification concept. 10 A different reaction occurs with resin-modified GIC.…”

“…4 Polycarboxylic or polyalkenoic acids promote a stable chemical bonding between the carboxylate groups (COO À ) and calcium in hydroxyapatite. [12][13][14] Glass ionomer cements (GICs) are the only direct restorative material to bond chemically to hard dental tissues as a result of the formation of ionic bonds between carboxylate groups and calcium, enhanced by a shallow interfacial absorption layer into the dentin for the newest resin-modified GIC. 12,14,15 The chemical adhesion provided by GIC has led some manufacturers to introduce carboxylate-based polymers in the composition of dental adhesives.…”

The role of poly(acrylic acid) in conventional glass polyalkenoate cements

“…Furthermore, a study by Yoshida et al [135] showed the capability of using novel biomaterial characterization techniques such as x-ray photoelectron spectroscopy (XPS) in identifying the chemical bonding at biomaterial-hard tissue interfaces. They demonstrated, using XPS, that the PAA component of the glass ionomer system significantly influences the chemical bonding potential.…”

Shear bond strength of resin cements to human dentin

“…However, resin cements require skilful handling: the preparation of the hydrophilic dentin surface for the application of the hydrophobic resin cement is a technique sensitive procedure and is time consuming [11].…”