Nanoscale chemical surface characterization of four different types of dental pulp-capping materials

The surface of any dental pulp-capping material has important implications for its clinical success because it is in direct contact with dental tissue, which influences its cytotoxicity. The aim was to determine the chemical composition of the first atomic layers of four pulp-protection agents because these atoms can initiate the pulp healing process.

Biodentine (Septodont), ProRoot MTA (Dentsply), Dycal (Caulk) and TheraCal (Bisco) were prepared (n=5) according to manufacturer recommendations. The chemical surface composition was analyzed using X-ray photoelectron spectroscopy (XPS), and the bulk composition was analyzed by Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX). Both survey and high resolution XPS spectra of the elements detected were obtained, with element-dependent probe depths of 4-5nm; the binding energy scale was normalized to the C1s adventitious carbon peak at 285eV.

There was a significant difference between bulk and surface compositions for all the pulp-capping materials. The calcium surface concentrations at 0nm and 70nm were Dycal 7.9% and 15.1%; ProRoot MTA 14.1% and 17%; TheraCal 0% and 3.6%; and Biodentine 17.6% and 33.7%, respectively. Trace amounts of the following elements (<1%) were also found: Ti, S and Zr in Biodentine; Bi in ProRoot MTA and TheraCal; Na, P, Zn and N in Dycal.

The XPS results showed that Ca in the surface layer could vary from 0 to 18%, depending on the material. Aliphatic carbons, from the polymerization reactions, especially in Dycal and TheraCal, were found to mask the other components.

This study compares, for the first time, the chemical composition of the first atomic layers of four pulp-capping materials. This information is relevant because the interaction between pulpar cells and the material's outermost atomic layer is an important factor for leading the pulpal response.