Methods: Dentine blocks were obtained from intact human premolars. One sound dentine block was assigned as a positive control. The remaining dentine blocks were demineralised with 4N formic acid. Then they were divided into 6 groups (groups A-F). Each group consisted of 4 specimens. The first specimen of each group was immersed in a commercial nano-HA solution (HAcom) (PlasmaBiotal LTD, UK), the second in an experimental nano-HA solution (HAexp), the third in a colloidal silica solution (SiO2), while the fourth was kept as a non-infiltrated control. Transmission electron microscopy (TEM) was used to visually determine the presence of nanoparticles within the demineralised collagen matrix of group A specimens. Group B specimens were examined with energy dispersive x-ray (EDX) to evaluate the degree of infiltration by quantifying the concentrations of calcium (Ca), phosphorus (P) and silicon (Si). Groups C to F were immersed in a remineralising solution for 1, 4, 8 and 12 weeks. The levels of Ca, P and Si were measured after each respective time period.
Results: TEM images confirmed the presence of nanoparticles in the demineralised dentine matrix in the cases of (HAexp) and (SiO2) solutions. EDX confirmed that all nano-particulate solutions tested had infiltrated human dentine. (HAexp) solution increased the P and Ca levels up to 65.1% and 55.31% of the sound dentine control respectively. After immersion in the remineralising solution, specimens previously infiltrated with (SiO2) had 15 times higher concentration in P and 6 times higher in Ca, when compared to non-infiltrated specimens.
Conclusion: Silica and hydroxyapatite nano-particulate solutions are capable of infiltrating demineralised human dentine. Given the right environment, nanoparticles can promote dentine remineralisation.