TITLE:
Structural Changes in Human Teeth after Heating up to 1200°C in Argon Atmosphere
AUTHORS:
Nancy Vargas-Becerril, Ramiro García-García, José Reyes-Gasga
KEYWORDS:
Human Tooth, Heating Treatment, Phase Transformation, SEM, X-Ray Diffraction, FTIR
JOURNAL NAME:
Materials Sciences and Applications,
Vol.9 No.7,
June
28,
2018
ABSTRACT: The
phase transformation of hydroxyapatite (HAP, Ca10(PO4)6(OH)2)
to the beta tricalcium phosphate phase (β-TCP, β-Ca3(PO4)2)
at 1100°C is well known. However, in the case of human tooth, the HAP phase
transformation is still an open area. For example, the CaO phase has sometimes
been reported in the set of phases that make up the teeth. In this study, physical
changes of human teeth when subjected to heat treatment in inert atmosphere
(argon) were studied. The results were compared with those obtained in air
atmosphere, from room temperature (25°C) up to 1200°C. Morphological changes
were analyzed by light and scanning electron microscopy (SEM). The HAP to β-TCP phase transformation was followed
in powder samples by X-ray diffraction (XRD) and Fourier transform infrared
spectroscopy (FTIR). Heating of teeth results in the removal of organic
material and structural water before the HAP to β-TCP phase transformation, the increment in hardness and the
induced crystal growth. The percentage of the phases, crystal growth and
lattice parameter variations as a function of temperature was quantified by
Rietveld analysis. The black color was observed in dentin heated under argon
atmosphere. Differences in expansivity produce fractures in dentin at 300°C in
argon and at 400°C in air. In dentin, the coexistence of the HAP and β-TCP phases was observed after 800°C in
argon and after 600°C in air; in enamel it was observed at 600°C in argon
compared with 400°C in air. In general, the role played by the argon atmosphere
during the thermal treatment of the teeth is to retard the processes observed
in air.