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

Objectives: The aim of this study was to analyze the precipitation of Cerium(III)nitrate hexahydrate [Ce(NO)] or Samarium(III)nitrate hexahydrate [Sm(NO)] 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(NO) and Sm(NO) 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(NO) 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(NO) on 2 further specimens. The remaining 2 specimens from each tooth were treated with demineralized water (negative control). Ce(NO) and Sm(NO) 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 ( = 0.05).

Results: 2.0-2.3 At%Ce (median) was detected on Ce(NO)-treated enamel and 0.4-0.7 At% Sm (median) was detected on Sm(NO)-treated enamel. Ce was only detected on the surfaces after application of Ce(NO), Sm only after application of Sm(NO). The Ca/P-ratio was significantly lower (1.37-1.59;  = 0.028) after the application of 25% and 50%Ce(NO) as well as 50%Sm(NO) compared to the control treatment (demineralized water; 1.61-1.63). After treatment with Ce(NO), At%Ca and At%Na were significantly lower ( ≤ 0.043) compared to treatment with Sm(NO). 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(NO) with increased At%Sm ( ≤ 0.046).

Conclusions: Ce(NO) and Sm(NO) precipitate on human enamel independently of the presence of a salivary pellicle.