Investigation of Hydroxyapatite Growth from Novamin™ Technology Using Electron Microscopy

Methods: For initial experiments water was condensed onto Novamin™ dispersed on carbon coated TEM grids. The ESEM conditions used were 4^oC at 6 torr pressure (resulting in ~95% humidity). At set time intervals over a 4 day period energy dispersive spectroscopy (EDS), environmental secondary electron and wet scanning transmission electron microscopy imaging were performed. In further experiments Novamin™ was dispersed in artificial saliva fluid and then onto 100nm thick micro-tomed dentine slices. The same ESEM conditions as in the first experiments were used.

Results: For the experiments using condensed water from the ESEM these conditions enabled the growth of silicon and calcium/phosphorous rich areas on and around the dispersed Novamin™ to be followed. The majority of these growths had relatively high Ca/P ratios (>3) but some areas had values near to 1.6. In experiments using artificial saliva it was found possible to observe the growth over time of SiO and Ca/P rich areas on and at the edges of the dentine slices. The EDS analysis showed that the majority of the growths had a Ca/P ratio close to 1.6. Post ESEM analysis of the growths on the carbon membrane and dentine by electron diffraction and high resolution electron microscopy indicated that parts of the growth regions contained crystalline apatite.

Conclusion: This work indicates that time lapse ESEM imaging and analysis, (even at low growth temperatures required for water condensation in the ESEM) has the potential to further the understanding of the growth steps of crystalline apatite from Novamin™ technology.