The Effect of Sintering Temperature on the Behavior of Hydroxyapatite from Different Natural Sources in Artificial Saliva

Raising pH is one of the important factors in preventing dental caries via enhancement of remineralization. This study aimed to evaluate the pH-neutralization behavior of various natural hydroxyapatite (HA) under demineralized artificial saliva (AS). HA derived from bovine, galline, and porcine were sintered at either 800, 1000, or 1200 ℃ to investigate the effect of sintering temperature on HA composition by XRD and its buffering capacity by measuring the change in pH and the time required to raise the pH from 4.0 to 5.5. XRD data showed that the main phase HA extracted from raw bones is highly crystalline and presents minor other calcium phosphate phase tricalcium phosphate via thermal degradation. Crystallite size and crystallinity degree gradually increased with the increase of sintering temperature from 800–1200 ℃. The acid neutralization analysis showed no significant differences in the pH value around HA obtained from bovine, galline, and porcine (p > 0.05). Bovine HA sintered at 800 ℃ required a lesser time to raise the pH from 4.0 to 5.5 and had a higher pH neutralization profile (5.83 ± 0.09) after 24 h than the other HA samples. All HA samples caused a pH increase of the eluate at 24 h; however, HA sintered at 1200 ℃ neutralized demineralized AS to a significantly lesser pH of 5.5. Therefore, this research demonstrated that natural HA’s neutralizing tendency decreased with the increase of sintering temperatures, regardless of the animal HA sources.