Surface Accumulation of Cerium, Self-Assembling Peptide, and Fluoride on Sound Bovine Enamel

Abstract

The accumulation of caries-preventive compounds on sound enamel is crucial in order to improve the inhibition of carious lesion initiation. The aim of this research was to investigate the initial accumulation of cerium, oligopeptide p11-4, and fluoride from NaF or amine fluoride (AmF) on sound enamel in vitro by means of energy dispersive X-ray spectroscopy (EDX). Polished bovine enamel specimens (n = 120 from 60 teeth) were fabricated. Out of these, 12 specimens each were treated with CeCl3 (cerium(III) chloride 25%), oligopeptide p11-4 (Curodont Repair, Credentis), NaF (10,000 ppm F−), AmF (amine fluoride, Elmex Fluid, CP-GABA GmbH, 10,000 ppm F−), or Aqua demin (control). After rinsing with water, the surface elemental composition (Ce, N, F, Ca, P, O, Na, Mg) was measured (EDX; EDAX Octane Elect detector, APEX v2.0), expressed in atomic percent (At%) and analyzed (non-parametric statistics, α = 0.05, error rates method). Another 12 specimens per treatment group were fabricated and used for analyzing accumulation in cross-sections with EDX linescans and two-dimensional EDX-mappings. The surface median atomic percent of cerium (At%Ce) was 0.8 for CeCl3, but no Ce was found for any other group. N, specifically for oligopeptide p11-4, could not be detected. Fluorine could only be detected on fluoridated surfaces. The median atomic percent of fluorine (At%F) was 15.2 for NaF and 17.0 for AmF. The Ca/P ratio increased significantly compared to the control following the application of NaF and AmF (p < 0.001), but decreased significantly for CeCl3 (p < 0.001). In cross-sectioned specimens of the CeCl3-group, 12.5% of the linescans revealed cerium at the enamel surface, whereas 83.3% of the NaF linescans and 95.8% of the AmF linescans revealed fluorine at the enamel surface. Following the application of oligopeptide p11-4, no traces of N were detectable. In the depth of the samples, no signal was detected for any of the corresponding elements exceeding the background noise. Cerium and fluorine (from both NaF and AmF), but not the oligopeptide p11-4, precipitated on sound enamel.

Elemental Compositions of Enamel or Dentin in Human and Bovine Teeth Differ from Murine Teeth

“…Using EDX, it was possible to determine specific fields on each specimen without processing the specimens into particles. In low vacuum mode (LV), the specimens could be measured directly after preparation without extensive exsiccation, as additional drying and sputtering were not necessary [ 23 , 28 ]. Due to the water vapor in the chamber, fewer exsiccation artifacts are expected, but a loss of resolution due to deflection of the electron beam by gas atoms in the SEM chamber ( skirt effect ) is also to be expected [ 23 , 29 ].…”

“…In low vacuum mode (LV), the specimens could be measured directly after preparation without extensive exsiccation, as additional drying and sputtering were not necessary [ 23 , 28 ]. Due to the water vapor in the chamber, fewer exsiccation artifacts are expected, but a loss of resolution due to deflection of the electron beam by gas atoms in the SEM chamber ( skirt effect ) is also to be expected [ 23 , 29 ]. To reduce this skirt effect described for LV-EDX analyses, all our measurements were carried out using a pressure limiting aperture (PLA), which shortens the path of the electron beam through the chamber gas [ 30 ].…”

“…To surely differentiate Fe (L α1 -peak 0.705 keV) from F (K α1 -peak 0.677 keV), additional field scans were performed on murine incisor enamel using an accelerating voltage of 15 kV, additionally aiming for the K α1 -peak, which is present for iron (6.403 keV) but not for fluorine. Standard customized coefficient (SCC) factors aiming for improved analysis of elements with atomic numbers < 10 and, thus, lower energy X-ray lines, in particular nitrogen, were applied for all 6 kV measurements [ 22 , 23 ].…”

“…EDX systems of previous generations did not allow reliable detection of elements with atomic numbers below 10 [ 21 ]. More recent EDX systems with Si 3 N 4 windows show a higher transmittance of X-rays compared to widespread polymer windows, especially for low keV X-rays emitted by elements of lower atomic numbers, and thus, allow detection of elements with atomic numbers < 10, such as nitrogen [ 20 , 22 , 23 ]. Accurate knowledge of structural properties and elemental composition is inevitably required to use extracted animal teeth as substitutes for human teeth for in vitro and in situ research [ 24 ].…”