Characterisation of Enamel Mineralisation by Calcium Silicate

Objectives: To use the techniques of scanning/transmission electron microscopy (SEM/TEM), energy dispersive x-ray spectroscopy (EDX), focused ion beam (FIB) and selected area electron diffraction (SAED) for the characterisation of enamel mineralisation induced by calcium silicate containing products.
Methods: Bovine teeth specimens were polished, and a subset was treated with 1% citric acid (pH=3.6) for 3 minutes. Specimens were tested in three groups (n=3): Group 1: acid softened enamel treated with calcium silicate (CaSi) and sodium phosphate salts toothpaste containing 1450ppm fluoride for 3 minutes; Group 2: sound enamel treated with a dual phase gel containing CaSi, sodium phosphate salts and fluoride for 3 minutes, and Group 3: acid softened enamel treated as per Group 2. Specimens were then immersed in simulated oral fluid for at least 2 hours (Group 1) or the rest of the day (Groups 2 & 3). This cycle was repeated up to 28 times (Group 1) or 7 times (Groups 2 & 3). The surface deposition was analysed by SEM and EDX. An approximate 100nm slice near the surface was prepared via FIB and examined with TEM and SAED.
Results: SEM and EDX characterisation revealed significant deposition onto the enamel substrates for all three groups, where calcium, phosphate and oxygen were the major elements present. The deposition for all 3 groups had similar elemental compositions to its parental enamel substrate, and had a crystalline nature identical to hydroxyapatite (HAP), as demonstrated by the very good agreement between the plane constants derived from SAED and from the HAP standard reference, as shown below for Group 1.
Conclusions: Calcium silicate containing products can induce the formation of HAP onto acid eroded and sound enamel.