In vitro hydroxyapatite formation of a tetracalcium phosphate and anhydrous dicalcium phosphate based dentine desensitiser: TRIS buffer vs artificial saliva

Background: Calcium phosphates (CPs) form hydroxyapatite (HA) in physiological solutions. These are commonly used to treat dentine hypersensitivity (DH) as they mimic the mineral composition of the natural tooth. Aim: The present study aims to characterise the apatite formation ability of a commercially available calcium phosphate TeethmateTM (TM) in physiological-like media. Materials and Methods: In this study, 4mm (D) x 6mm (L) cylindrical samples of TM were produced and immersed in tris(hydroxymethyl)aminomethane (TRIS) buffer (pH: 7.3) and artificial saliva (AS) (pH: 6.5) for up to 24 hours. This was followed by characterisation of the samples after immersion using 31P magic angle - nuclear magnetic resonance spectroscopy (MAS-NMR), X-ray powder diffraction (XRD) and dentine treated with the material using scanning electron microscopy (SEM). Results: 31P MAS-NMR and XRD analyses revealed that samples immersed in TRIS buffer solution formed hydroxyapatite within approximately 6 hours of immersion. This change was observed at around 12 hours for samples soaked in AS.  The pH of the immersion media increased with increasing immersion time. SEM analysis showed a transitional phase formation of structures exhibiting plate-like morphology. Conclusion: This study shows that TM converts to HA in vitro rapidly and provides an effective option for the treatment of dentine hypersensitivity.