Methods: Cores of enamel were removed from extracted human teeth, lightly ground and polished to provide a flat enamel surface. The enamel was air-polished using different powders formulated on the use of a Calcium/Sodium Phosphosilicate (BAG) or Dicalcium Phosphate Dihydrate (DPD) at air pressure of 5 bar (500 MPa) and a distance of 10 mm. A Na-bicarbonate powder (BIC) was also used as control treatment. The specimens were first immersed in artificial saliva (AS) for 24h at 37°C. Subsequently, the specimens were immersed in 0.1M citric acid [pH: 3.4] using a 3-time-cycle; under continuous agitation (30s); (h: 8:00 – 12:00 – 17:00) and stored in AS at 37°C during the intervals. The complete experimental design was repeated for 3 days. Knoop hardness (KHN), scanning electron microscopy (SEM) and confocal laser microscopy (CLSM) were used to examine the specimens.
Results: Specimens treated with DPD showed immediate increase of KHN subsequent to prolonged AS immersion probably due its conversion into octacalcium phosphate. However, the acid challenge induced a significant (p<0.05) reduction of the KHN at the end of the each daily acid challenge. Conversely, the specimens treated with BAG showed immediate increase of KHN subsequent the first 24h of AS immersion and lower KHN reduction (p<0.05) compared to the other treatment groups. In particular, the specimens treated with BAG showed a re-establishment of the surface hardness subsequent to prolonged AS storage. BIC-treated enamel showed the lowest (p<0.05) KHN results. SEM and CLSM confirmed a low degree of surface erosion after citric acid challenge in BAG-treated enamel.
Conclusions: BAG and DPD are excellent biomaterials for enamel remineralisation. However, air-polishing procedures performed using BAG may protect the enamel due to enhanced anti-erosion and remineralising ability.