Formation of hydroxyapatite on tooth surfaces by calcium hypophosphite in saliva

This in vitro study aimed to investigate whether calcium hypophosphite (CaP) mediates hydroxyapatite (HAP) formation in artificial and human saliva and, in a proof-of-principle toothbrushing model, promotes mineral deposition and occlusion of dentinal tubules. A CaP solution was added to artificial saliva and human saliva, respectively. The resulting precipitate was analyzed using X-ray powder diffraction (XRD). For the toothbrushing simulations, human dentin specimens were allocated to a test group treated with 2 wt% CaP solution and a control group treated with deionized water (n = 5 per group). The specimens were immersed in artificial saliva and subjected to five consecutive 30 s brushing treatments. Confocal laser scanning microscopy (LSM) was used to assess changes in dentinal tubule occlusion before and after treatment, scanning electron microscopy (SEM) was used to examine the morphology of the deposits, and energy-dispersive X-ray spectroscopy (EDX) was used to analyze their elemental composition. In artificial saliva and human saliva, CaP led to the formation of HAP. XRD analysis of the precipitates showed characteristic HAP peaks, with a mean crystallite size of (5.7 ± 0.6) nm and crystallographic parameters of a = (9.484 ± 0.003) Å, c = (6.868 ± 0.002) Å and V = (535.0 ± 0.4) Å3 for the formation in human saliva. LSM and SEM demonstrated mineral deposition within open dentinal tubules following toothbrushing simulations with CaP in artificial saliva, while EDX showed that the deposits contained calcium, phosphorus, and oxygen. CaP mediated HAP formation in artificial and human saliva. The proof-of-concept dentin experiment demonstrated mineral deposition within open dentinal tubules. Although firm conclusions regarding efficacy cannot be drawn, these promising findings merit further exploration in properly powered studies. With further confirmatory studies, CaP has potential as a desensitizing agent for oral care formulations.