Effect of rare earth ion substitution on phase decomposition of apatite structure.

The paper describes an investigation of phase decomposition of apatite lattice doped with rare earth ions (cerium, samarium, and holmium) at temperatures ranging from 25 to 1200 ºC. The rare-earth ion-doped apatite minerals were synthesized using sol-gel method. In situ high-temperature powder X-ray diffraction (XRD) was used to observe phase changes and the lattice parameters were analyzed to ascertain the crystallographic transformations. The expansion coefficient of the compounds was determined, and it was found that the c-axis was the most expandable due to relatively weak chemical bonds along the c-crystallographic axis. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the decomposition properties of the materials. Due to rare earth ion doping, the produced materials had slightly variable decomposition behaviour. The cerium and samarium ions were present in multiple oxidation states (Ce3+, Ce4+, Sm3+, Sm2+), whereas only Ho3+ ions were observed. Rare earth ion substitution affects tri-calcium phosphate proportion during decomposition by regulating concentrations of vacancies. X-ray photoelectron spectroscopy (XPS) analysis indicated that cerium and samarium ion-doped apatite yielded only 25% tricalcium phosphate during decomposition. This finding advances our understanding of apatite structures, with implications for various high-temperature processes like calcination, sintering, hydrothermal processing, and plasma spraying.

Effect of fluoride sustained slow-releasing device on fluoride, phosphate and calcium levels in plaque biofilms over time measured using ion chromatography.

OBJECTIVES: To determine whether there are any differences in fluoride (F), calcium (Ca) or phosphate (PO(4)) concentrations in natural plaque biofilms between the upper right and left quadrants using a fluoride sustained slow-releasing device (FSSRD) placed in the upper right quadrant after 7 and 21 days. To report and validate a new methodology in measuring very low concentrations of F in dental plaque and saliva using ion chromatography. METHODS: Twenty-one participants were divided into two groups with 11 participants in group one and 10 in group two. Each participant had a FSSRD attached to the upper right second permanent molar and two plaque generating devices (PGDs) attached to the upper right and left first permanent molars. The PGDs were recovered after 7 days in group one and 21 days in group two. RESULTS: At both 7 and 21 days (right, left), F (1.081±1.517 ppm, 0.736±0.840 ppm) and (0.459±0.888 ppm, 0.203±0.139 ppm), PO(4) (1053±533 ppm, 654±246 ppm) and (865±1099 ppm, 474±304 ppm) and Ca (136±132 ppm, 74±36 ppm) and (130±109 ppm, 77±24 ppm), were higher in the quadrant containing the FSSRD but not significantly so (p>0.05). Fluoride and PO(4) fell in both quadrants between 7 and 21 days, though not significantly. CONCLUSIONS: Intriguingly while not statistically significant, 21 day plaque contained less fluoride than those investigated after 7 days. While the data was not statistically significant, it seems possible that F, Ca and PO(4) accumulated around the device to a limited extent but were washed away fairly quickly and distributed around the oral cavity. CLINICAL IMPORTANCE: The FSSRD was found to reduce dmfs/DMFS by 76% and raise salivary F levels by ∼10 folds. This device is very helpful in reducing dental decay where compliance is impaired such as in patients with special needs. This study further investigates the anti-cariogenic effect of this device.