Improvement of Biological Effects of Root-Filling Materials for Primary Teeth by Incorporating Sodium Iodide

Abstract

Therapeutic iodoform (CHI₃) is commonly used as a root-filling material for primary teeth; however, the side effects of iodoform-containing materials, including early root resorption, have been reported. To overcome this problem, a water-soluble iodide (NaI)-incorporated root-filling material was developed. Calcium hydroxide, silicone oil, and NaI were incorporated in different weight proportions (30:30:X), and the resulting material was denoted DX (D5~D30), indicating the NaI content. As a control, iodoform instead of NaI was incorporated at a ratio of 30:30:30, and the material was denoted I30. The physicochemical (flow, film thickness, radiopacity, viscosity, water absorption, solubility, and ion releases) and biological (cytotoxicity, TRAP, ARS, and analysis of osteoclastic markers) properties were determined. The amount of iodine, sodium, and calcium ion releases and the pH were higher in D30 than I30, and the highest level of unknown extracted molecules was detected in I30. In the cell viability test, all groups except 100% D30 showed no cytotoxicity. In the 50% nontoxic extract, D30 showed decreased osteoclast formation compared with I30. In summary, NaI-incorporated materials showed adequate physicochemical properties and low osteoclast formation compared to their iodoform-counterpart. Thus, NaI-incorporated materials may be used as a substitute for iodoform-counterparts in root-filling materials after further (pre)clinical investigation.

Keywords: iodoform; primary teeth; root canal treatment; root resorption; root-filling material; sodium iodide.

Figure 1

Physical properties of NaI-incorporated paste (NaI@P). (a) Flowability. (b) Film thickness. (c) Viscosity. (d) Radiopacity. (e) Water absorption by weight change over 28 days. (f) Solubility from specimen. (g) Solubility from extract. Statistical significance was calculated using a one-way analysis of variance (ANOVA) followed by Tukey’s honestly significant difference compared to the control (I3O). * p < 0.05, *** p < 0.001.

Figure 2

Optical images and extraction analysis of NaI-incorporated paste (NaI@P). (a) Optical images. (b) Iodine, sodium, and calcium ion releases. (c) The pH. (d) Molecules extracted by liquid chromatography/mass spectrometry (LC/MS) (m/z = mass to charge ratio). Statistical significance was calculated using one-way analysis of variance (ANOVA) followed by Tukey’s honest significant difference compared to the control (I30). ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 3

Cytotoxicity of the extract of NaI-incorporated paste (NaI@P). (a) Cell viability results from the CCK-8 assay. (b) Live/Dead staining results. The statistical significance of (a) was calculated using a one-way analysis of variance (ANOVA) followed by a two-sided Dunnett’s multiple comparison test compared to the control. *** p < 0.001, **** p < 0.0001, n = 6.

Figure 4

Osteoclast differentiation from the extract of NaI-incorporated paste (NaI@P) by (a) TRAP staining, and (b) Actin ring staining. (c) Number of osteoclast differentiation from TRAP staining. (d) The gene expression of c-FOS, NFATc1, cathepsin K, and TRAP measured by qPCR. The statistical significance of (c) was calculated using a one-way analysis of variance (ANOVA) and that of (d) was calculated using two-way ANOVA followed by a two-sided Tukey’s multiple comparison test. (*) compared to the positive control, (#) compared to the I30 group. */# represents p < 0.05, **/## p < 0.01, ***/### p < 0.001, ****/#### p < 0.0001, n = 3.

Figure 5

Development of NaI-incorporated paste (NaI@P). (a) Schematic illustration of the fabrication of strained NaI. (b) Graph comparing the particle size distribution of strained NaI and existing iodoform. (c) The composition of NaI-incorporated pastes (NaI@P) in a different proportions and iodoform-incorporated paste (Io@P).