Structural Changes in Human Teeth after Heating up to 1200°C in Argon Atmosphere

Abstract

The phase transformation of hydroxyapatite (HAP, Ca 10 (PO 4) 6 (OH) 2) to the beta tricalcium phosphate phase (β-TCP, β-Ca 3 (PO 4) 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.

On the Nature of the Transparent Teeth of the Deep-Sea Dragonfish, Aristostomias scintillans

“…The resulting value of $80% mineralization (Figure S6) is indeed greater than the average dentin reported for the teeth of humans with $75% mineralization, who have tooth hardness similar to that of piranha and great white shark. 35,36 The minimal amount of dispersed collagen fibrils likely reduces scattering. Additionally, the dragonfish teeth lack microscale features such as dentin tubules.…”

Electron microscopy analysis of the thermal phase transition from hydroxyapatita to β‐TCP observed in human teeth

“…Dental pieces were permanent molar teeth of adult patients (between 25 and 30 years old) extracted for orthodontic reasons. Following the experimental procedure been reported elsewhere (Vargas‐Becerril et al ., ), 12 molars were prepared for this work. After extraction, the dental pieces were observed with the Stereo 2000‐C Carl Zeiss light microscope (Carl Zeiss, Jena, Germany) to use only healthy teeth.…”

“…The thermal decomposition of enamel and dentin can be divided into three temperature ranges characterised by the removal of organic material, adsorbed and structural water, and decarbonisation and dehydroxylation reactions (Vargas-Becerril et al, 2018). At room temperature, only nanometric crystals are present (smaller in dentin, since the DRX peaks are not well defined, and relatively larger in enamel).…”

“…As the dental piece heats up, morphological and chemical changes are evidenced by changes in colour and fractures, as well as changes in hardness and electrical conductivity (Vargas‐Becerril et al ., , ). The understanding of these changes can be useful in the design of new materials and implants for dental use, among others.…”

“…Recently, Vargas‐Becerril et al . (, ) submitted enamel and dentin samples to temperatures from room temperature (25°C) up to 1200°C, both in air and in argon. They analysed the structural changes that occurred and their influence on the mechanical properties of human teeth and commented on the coexistence of two phases: hydroxyapatite (HAP) and tricalcium phosphate (β‐TCP, whitlockite, Ca 3 (PO 4 ) 2 ).…”