IADR Abstract Archives
Characterisation of SDF-HAP Reactions Under Remineralising Conditions: an NMR Study
Objectives: To use NMR to characterise the chemical interactions between 38% Silver Diammine Fluoride (SDF) and hydroxyapatite (HAP) powder during remineralisation.
Methods: 2g HAP powder was immersed in 10ml 0.1M acetic acid pH=4.0 solution in a centrifuge tube and placed in a shaking-incubator at 37C for 2hrs to mimic demineralisation. The powder was collected, washed, and then dried for 24hours in an incubator at 37C. Then, the demineralised powder was mixed with 1.5ml 38% SDF (SDI, Aus) for one minute, and air-dried for 3 minutes. The demineralised powder mixture was divided equally into seven parts and each part was immersed in 10ml remineralisation solution (composition- 2mMol CaCl2, 1.2mMol KH2PO4, 150 mMol NaCl, pH=7.0) in individual centrifuge tubes and placed in a shaking-incubator at 37C for 10, 120, 240, 360, 480, 600 and 1440 minutes, respectively. At the end of these times, the powders were collected, washed, dried (as described previously) and then analysed using 19F NMR.
Results: 19F NMR results indicated the formation of CaF2 within 10 minutes depicted by a broad short peak at -107ppm. At 120mins, there was an increase in CaF2 formation followed by a decrease at 240mins. There was a further reduction in CaF2 at 360min but a new peak at -105.8ppm appeared indicating the presence of fluoride substituted hydroxyapatite (FSHA). At 480 and 600mins there was a further reduction in CaF2 formation, but a concomitant increase in FSHA formation. At 1440mins, the FSHA peak downshifted to -104ppm and became sharper.
Conclusions: Initially, a larger proportion of CaF2 was formed during remineralisation following SDF treatment. With time, there is an increase in the proportion of FSHA indicating a chemical transformation from CaF2 to the more stable FSHA phase, slowing progression of dental caries.
Methods: 2g HAP powder was immersed in 10ml 0.1M acetic acid pH=4.0 solution in a centrifuge tube and placed in a shaking-incubator at 37C for 2hrs to mimic demineralisation. The powder was collected, washed, and then dried for 24hours in an incubator at 37C. Then, the demineralised powder was mixed with 1.5ml 38% SDF (SDI, Aus) for one minute, and air-dried for 3 minutes. The demineralised powder mixture was divided equally into seven parts and each part was immersed in 10ml remineralisation solution (composition- 2mMol CaCl2, 1.2mMol KH2PO4, 150 mMol NaCl, pH=7.0) in individual centrifuge tubes and placed in a shaking-incubator at 37C for 10, 120, 240, 360, 480, 600 and 1440 minutes, respectively. At the end of these times, the powders were collected, washed, dried (as described previously) and then analysed using 19F NMR.
Results: 19F NMR results indicated the formation of CaF2 within 10 minutes depicted by a broad short peak at -107ppm. At 120mins, there was an increase in CaF2 formation followed by a decrease at 240mins. There was a further reduction in CaF2 at 360min but a new peak at -105.8ppm appeared indicating the presence of fluoride substituted hydroxyapatite (FSHA). At 480 and 600mins there was a further reduction in CaF2 formation, but a concomitant increase in FSHA formation. At 1440mins, the FSHA peak downshifted to -104ppm and became sharper.
Conclusions: Initially, a larger proportion of CaF2 was formed during remineralisation following SDF treatment. With time, there is an increase in the proportion of FSHA indicating a chemical transformation from CaF2 to the more stable FSHA phase, slowing progression of dental caries.