Fluoride-Free Toothpastes Containing Ca-TMP Prevent the Formation of Enamel Subsurface Lesions

Objectives: This study aimed to (1) synthesize and characterize a new cyclophosphate salt with total replacement of sodium by calcium in the sodium trimetaphosphate (Na-TMP) molecule, and (2) to assess in vitro its effects on enamel remineralization when added to toothpaste formulations at different concentrations.
Methods: Calcium trimetaphosphate (Ca-TMP) was synthesized by removing Na⁺ ions from commercial Na-TMP using an ionic exchange column, followed by addition of calcium hydroxide (to provide Ca⁺⁺ ions), filtration and drying. The resulting powder was then characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Sound bovine enamel blocks (n=12/group) were treated twice/day with slurries of the following toothpastes: Placebo (“PLA”, without any actives), 1100 ppm F (“1100F”, as NaF); 100% Na-TMP (“Na-TMP100”), and Ca-TMP at 20, 50, 80 or 100% (respectively “Ca-TMP20”, “Ca-TMP50”, “Ca-TMP80”, and “Ca-TMP100”), and subjected to a pH-cycling regimen (7 days). Lesion depth and mineral concentrations (ΔZ) were determined by micro-computed tomography, and the data were analyzed by Kruskal-Wallis and Student-Newman-Keuls’ tests (p<0.05).
Results: SEM analysis showed smaller and more regular crystals of Ca-TMP compared with Na-TMP, while EDS data demonstrated total replacement of Na⁺ by Ca⁺⁺ ions in the TMP molecules. Regarding ΔZ and lesion depth, enamel treated with Ca-TMP50 and Ca-TMP80 showed no mineral loss and no formation of subsurface lesion. The overall pattern observed for ΔZ was PLA = Na-TMP100 < 1100F < Ca-TMP20 < Ca-TMP100 < Ca-TMP50 = Ca-TMP80, while for lesion depth the trend was PLA > Na-TMP100 > 1100F > Ca-TMP100 > Ca-TMP20 > Ca-TMP50 = Ca-TMP80.
Conclusions: The method for the synthesis of Ca-TMP was shown to be effective, and the addition of this salt at 50 or 80% to fluoride-free toothpastes led to the highest protective effect against enamel demineralization in vitro among all groups, having superior effects compared with a conventional fluoride toothpaste.