Nitrates of cerium and samarium deposit on human enamel independently of a salivary pellicle

Louis Kopp; Karl-Anton Hiller; Fabian Cieplik; Arno Pfitzner; Florian Pielnhofer; Bastian Höfler; Christian Dolle; Áine M Lennon; Sophia R Bauer; Wolfgang Buchalla; Konstantin J Scholz

doi:10.3389/froh.2024.1455924

Nitrates of cerium and samarium deposit on human enamel independently of a salivary pellicle

Front Oral Health. 2024 Aug 29:5:1455924. doi: 10.3389/froh.2024.1455924. eCollection 2024.

Authors

Affiliations

¹ Department of Conservative Dentistry and Periodontology, University Hospital Regensburg, Regensburg, Germany.
² Department of Operative Dentistry and Periodontology, Faculty of Medicine, Center for Dental Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
³ Institute of Inorganic Chemistry, University of Regensburg, Regensburg, Germany.
⁴ Laboratory for Electron Microscopy, Karlsruhe Institute of Technology, Karlsruhe, Germany.
⁵ Department of Oral and Maxillofacial Surgery, University Hospital Regensburg, Regensburg, Germany.

Abstract

Objectives: The aim of this study was to analyze the precipitation of Cerium(III)nitrate hexahydrate [Ce(NO₃)₃] or Samarium(III)nitrate hexahydrate [Sm(NO₃)₃] solutions on human enamel with and without a salivary pellicle. Investigated parameters were At%Ce and At%Sm measured using energy dispersive x-ray spectroscopy (EDX) after test solution (two concentrations) application.

Materials and methods: Precipitation of Ce(NO₃)₃ and Sm(NO₃)₃ solutions was examined on human enamel with and without a salivary pellicle. 6 enamel specimens each were obtained from 12 freshly extracted human third molars. These specimens were ground flat and polished. A salivary pellicle was created on 3 of the 6 specimens per tooth by storing the samples in human saliva. Subsequently, an aqueous solution of Ce(NO₃)₃ was applied to 2 of the 6 specimens (one with, one without salivary pellicle) for 60 s. The same was carried out with an aqueous solution of Sm(NO₃)₃ on 2 further specimens. The remaining 2 specimens from each tooth were treated with demineralized water (negative control). Ce(NO₃)₃ and Sm(NO₃)₃ solutions were applied at 25 or 50 wt% (aqueous solutions). The test materials and concentrations were distributed using a randomization table. After 60 s exposure and rinsing with demineralized water, the elemental composition (Ce, Sm, Ca, P, O, N, Na, Mg) of the enamel surface was analyzed by EDX. Atomic percentages (At%), differences (ΔAt%) and calcium/phosphorous-ratios (Ca/P-ratios) were calculated and analyzed non-parametrically (α = 0.05).

Results: 2.0-2.3 At%Ce (median) was detected on Ce(NO₃)₃-treated enamel and 0.4-0.7 At% Sm (median) was detected on Sm(NO₃)₃-treated enamel. Ce was only detected on the surfaces after application of Ce(NO₃)₃, Sm only after application of Sm(NO₃)₃. The Ca/P-ratio was significantly lower (1.37-1.59; p = 0.028) after the application of 25% and 50%Ce(NO₃)₃ as well as 50%Sm(NO₃)₃ compared to the control treatment (demineralized water; 1.61-1.63). After treatment with Ce(NO₃)₃, At%Ca and At%Na were significantly lower (p ≤ 0.043) compared to treatment with Sm(NO₃)₃. No significant differences were found between specimens treated with 25% or 50% lanthanide nitrate solution. Presence of a salivary pellicle had no significant influence on the measured At% with the exception of specimens treated with 50% Sm(NO₃)₃ with increased At%Sm (p ≤ 0.046).

Conclusions: Ce(NO₃)₃ and Sm(NO₃)₃ precipitate on human enamel independently of the presence of a salivary pellicle.

Keywords: EDX; SEM; caries; cariostatic; lanthanide; nitrate.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. KJS and FP received funding from the University of Regensburg (UR Fellows program). KJS received funding from the DGZMK (German Society of Dental, Oral and Craniomandibular Sciences; Deutsche Gesellschaft für Zahn-, Mund- und Kieferheilkunde; Science Funding).