The Effect of Potassium Iodide on Silver Diammine Fluoride-Treated Hydroxyapatite

Objectives: The aim of this study is to evaluate the effect(s) of adding potassium iodide (KI) following silver diammine fluoride (SDF) reaction with hydroxyapatite (HAP) aqueous solution.
The null hypothesis is that the application of KI following the reaction between SDF and HAP will not alter the formation of silver phosphate (Ag₃PO₄), and therefore will not interfere with the caries-arresting mechanism of SDF.
Significance:
The dental literature has proposed that KI application may overcome the blackening of SDF-treated tooth structure. This study tests if KI addition would shift the chemical reaction between SDF and HAP in any way that would compromise the caries-arresting effect of SDF on tooth structure.
Methods: HAP solutions were prepared by mixing 2.4 mg (4.78 µmol) HAP powder (Sigma Aldrich) in 993.9 µL deionized water (Barnstead) in glass vials. After equilibration, 6.1 µL of 2.36 M SDF (38% w/v Advantage Arrest) was added to each vial. SDF-treated HAP specimens were allowed to equilibrate before KI (Fisher Scientific) addition. Four different groups were analyzed based on the quantities of a 3.0 M KI solution (0, 1.6, 3.2, 4.8 µL) added to the vials. Control studies were performed with Ag₃PO₄ standards and equivalent quantities of KI. Raman spectroscopy (532 nm) was used to detect the reaction products. The reaction products analyzed were Ag₃PO₄, HAP, fluorapatite (FAP), and calcium fluoride (CaF₂).
Results: - Adding KI to the SDF-treated HAP interfered with Ag₃PO₄ and FAP formation.
- Adding KI to Ag₃PO₄ standards exhibited a greater (negative) impact on Ag₃PO₄ vs. that formed from SDF-treated HAP.
- The initial pH of the HAP-H₂O solutions was 7. It increased to 10 after the addition of SDF and did not change following KI application.
Conclusions: The desired products (Ag₃PO₄ and FAP) as caries-arresting agents are impacted by KI addition. Increasing the concentration leads to removal of both of these products.