Chemical Interaction of RMGI with Hydroxyapatite via ESCA and FTIR

Objectives:  Characterize the chemical interaction of a resin-modified glass ionomer, 3M™ ESPE™ Vitrebond™ Plus Liner/Base (VBP), to hydroxyapatite.

Methods:  

The liquid component of VBP was applied to a hydroxyapatite disk for 1hr; sonicated in ultrapure (18milliohm) water 3min to remove excess; dried under nitrogen.  XPS spectra were collected on the disk before and after treatment, and on VBP-liquid; elemental concentrations were calculated, and analyzed via one-way ANOVA and Tukey's T-test (p<0.05). 

A Ca-VBP-polymer salt was synthesized and measured for comparison.  FTIR spectra were collected for VBP-liquid, hydroxyapatite powder, and a liquid-hydroxyapatite mixture; also, for mixed VBP liner, periodically during 24 hr after light-curing. 

Results:   Concentrations via XPS are shown below, atomic%(SD).  Superscript letters in each column denote groups that are not statistically different.

The elevated carbon and nitrogen on treated HAP indicate that the methacrylate-modified polyalkenoic acid in the VBP-liquid adhered to the HAP; the apparent reduction in calcium and phosphorous is attributed to signal attenuation by adherent polyacid.  In the XPS spectra the O-C=O (289eV) peak of  the liquid broadened and shifted slightly for the treated hydroxyapatite, indicative of a chemical bond.  FTIR spectra of  the liquid/hydroxyapatite mixture compared to the VBP-liquid or hydroxyapatite alone show a decrease in the COOH peak (1713 cm^-1) and increase in carboxylate absorption peaks at 1563 cm^-1 and 1411 cm^-1 due to the formation of calcium carboxylate.  FTIR spectra of setting reaction of VBP liner reveals progress of the acid-base GI reaction by the appearance of the carboxylate peak at ~1720 cm^-1 together with concomitant decrease of the carboxylic acid peak at ~1570 cm^-1.

Conclusions:

ESCA and FTIR evidence show that the methacrylate-modified polyalkenoic acid component in Vitrebond Plus chemically bonds to hydroxyapatite; and, that VBP exibits the carboxylate crosslinking reaction of a true glass ionomer.