Cells and Materials Volume 3 Number 4 Article 5 1993 Heating of Calcium Phosphate Crystals: Morphological Consequences and Biological Implications W. Bohne Faculte de Chirurgie Dentaire, Nantes J. A. Pouezat Faculte de Chirurgie Dentaire, Nantes L. Peru Faculte de Chirurgie Dentaire, Nantes G. Daculsi Faculte de Chirurgie Dentaire, Nantes Follow this and additional works at: https://digitalcommons.usu.edu/cellsandmaterials Part of the Biomedical Engineering and Bioengineering Commons Recommended Citation Bohne, W.; Pouezat, J. A.; Peru, L.; and Daculsi, G. (1993) "Heating of Calcium Phosphate Crystals: Morphological Consequences and Biological Implications," Cells and Materials: Vol. 3 : No. 4 , Article 5. Available at: https://digitalcommons.usu.edu/cellsandmaterials/vol3/iss4/5 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Cells and Materials by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. Cells and Materials, Vol. 3, No. 4, 1993 (Pages 377-382) 1051-6794/93$5.00 +. 00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA HEATING OF CALCIUM PHOSPHATE CRYSTALS: MORPHOLOGICAL CONSEQUENCES AND BIOLOGICAL IMPLICATIONS W. Bohne*, J.A. Pouezat, L. Peru, G. Daculsi Laboratoire de Recherche sur les Tissus Calcifies et les Biomateriaux, Faculte de Chirurgie Dentaire, Place A. Ricordeau, F-44042 Nantes, France (Received for publication October 27, 1993, and in revised form December 29, 1993) Abstract Introduction Sintering hydroxyapatite (HA) and 13-tricalcium Synthetic calcium phosphates are applied in ortho­ phosphate ((3- TCP) affects the chemical composition , the paedic, maxillofacial, otorhinoplastic, and in dental crystallinity, and the morphological features as demon­ preprosthetic and periodontal surgery in order to fill strated by means of X-ray diffraction (XRD) , infrared bone defects and to enhance bone repair (Nery and spectroscopy (IR), and scanning electron microscopy Lynch , 1978; de Groot, 1983; LeGeros, 1988; Passuti (SEM). When heated to 1230°C, 16.7% ofHA had de­ and Daculsi, 1989; Daculsi et al., 1990, 1992; Hamel, composed to IJ-TCP. SEM investigations showed homo­ 1992). Before use, many are sintered at high tempera­ geneous, sharp angular polyhedric blocks of 30 to 50 Jlffi tures. Besides the modification of the chemical compo­ with rare surface pores. On heating at 1230°C, IJ -TCP sition and crystallinity of these materials, sintering also had entirely transformed to a-TCP. During sintering, causes modifications of the size, shape and surface tex­ the size of the powder grains increased and progressive ture of the powder grains. These modifications are tem­ bridging between the grains was observed. At 1230°C, perature dependent. They affect the surfaces in contact a network within round-shaped polyhedric blocks of 50 with tissue fluids and bone cells, and are thought to in­ to 90 Jlm was formed. In both, HA and IJ-TCP, surfaces fluence the biological reactions of these materials and were smooth. The chemical composition and the their solubility properties. The morphological modifica­ crystallinity of calcium phosphate ceramics determine tions have not been taken in account sufficiently by cli­ their dissolution behavior and osteogenic properties. nicians in dental prosthetics, periodontology, and osteo­ Nevertheless, their temperature dependent morphological articular surgery in choosing an appropriate material. features, such as, particle shape and size, surface The aim of this study was to point out the modifi­ texture, and porosity, as demonstrated in the present cations of the chemical composition and the crystallinity study, also influence the resorption rates, tissue of hydroxyapatite (HA) and 13-tricalcium phosphate ({3- responses, and wound healing duration. This should be TCP) during calcination, to demonstrate the size, shape emphasized more by clinicians in choosing an appro­ and surface texture modifications which affect the pow­ priate material for bone substitution. der grains and to discuss possible biological conse­ quences of those modifications. Key Words: Calcium phosphate crystals, sintering, size Materials and Methods and shape modifications, surface texture, chemical com­ position, crystallinity, biological implications, dental Sample preparation preprosthetic surgery, periodontal surgery, bone defect Carbonated HA and 13- TCP powders prepared by filling. Dr. R.Z. LeGeros (University of New York) were used. Both HA and 13- TCP were passed through a 100 /lm sieve. In free atmospherical conditions, the samples *Address for correspondence: were heated from room temperature to respectively W. Bohne 900°C and 1230°C with a Vectra furnace. Each heating Laboratoire de Recherche sur les Tissus Calcifies et les period was for one hour followed by maintaining the Biomateriaux, Faculte de Chirurgie Dentaire, specified temperature for 90 minutes. Cooling was per­ Place A. Ricordeau, formed for one hour. Then , all heated and unheated 44042 Nantes, powder samples underwent X-ray diffraction (XRD), in­ France frared (I R) and scanning electron microscope (SEM) ex­ Telephone number: 33-40 41 29 16 aminations. FAX number: 33-40 08 37 12 377 W. Bohne, J.A. Pouezat, L. Peru, G. Daculsi Table 1. FWHM and D-value variations at different Results temperatures. Hydroxyapatite (HA) Temp. FWHM D (A) The FWHM-values at hkl reflections 002 and 310 oc (002) (310) (002) (310) had increased from room temperature to 900°C and had strongly decreased at 1230°C. Consequently, the D­ HA 20 0.1436 0.1409 614.7 626.5 value variations, which do not give the crystal sizes HA 900 0.1449 0.1575 609.2 560.4 directly but represent crystal size variations (Vetter et HA 1230 0.1113 0.1246 793.1 708.4 al., 1991), indicated crystal size decrease at 900°C and high crystal growth at 1230°C (Table 1). Infrared scans showed C03 peaks at 670 and 878 Table 2. FWHM and crystallinity index (Cl) value cm-1. Furthermore, when heated to 1230°C, a t3-TCP variations at different temperatures. phase appeared at 944 cm- 1. X-ray diffraction investi­ gations confirmed that HA had partly decomposed to Temp. CCC) FWHM D (A) 13-TCP. The degree of decomposition to /3-TCP, esti­ mated by the relative peak heights of the strongest apa­ t3-TCP 20 0.1457 0.620 tite (211) and t3-TCP (0210) hkl reflections (Apfelbaum t3-TCP 900 0.1470 0.625 et al., 1990), was 16.7%. {3- Tricalcium phosphate ({3- TCP) X-ray diffraction The FWHM-values calculated at the hkl reflection The powders were examined using an INEL XRG 2010 and the crystallinity indices (CI) measured on IR­ 3000 CPS diffractometer at 40 kV and 30 rnA connected scans exhibited little differences from 20 to 900°C to a CATO Multianalyser. The samples were exposed which do not seem to be significant (Table 2). for about 30 minutes to a Cu-radiation (A = 1.5406 A). At 1230°C, X-ray diffraction investigations The 20 reflections, relative peak intensities, and full showed that t3 -TCP had transformed to a-TCP. width at half maximum (FWHM) values were calculated Scanning electron microscopy (SEM) observations using a computer program developed at the "Institut des Materiaux", Nantes, France. Peak broadening is in­ Scanning electron microscopy investigations of versely related to both crystal size and internal lattice HA, for room temperature and 900°C samples, showed perfection (Vetter et al., 1991). So, using Scherrer's loosely packed clusters of round-shaped powder grains equation (Posner et al., 1963; Bonar et al., 1983; of about 0.2 Jlffi in diameter. Spaces between clusters Chantraineetal., 1988; Vetteretal., 1991) were about 1 to 3 Jlffi. All surfaces appeared rough, bridging between powder grains was not observed. D = Al(t3 cosO) [1] When sintered at 1230°C (Figs. 1 and 2), the particles D (the mean crystallite size in A) values could be deter­ and clusters had coalesced to form sharp angular poly­ mined; these are not absolute values and used only for hedric blocks of about 30 to 50 Jlffi, without or with rare comparison (Chantraine et al., 1988). A is the X-ray surface pores of 0.2 to 2 Jlffi. The boundaries of the wavelength (A) employed; t3 the FWHM measured; and original particles were either visible or had disappeared. 0 the reflectance angle. As t3 and e were measured in The surfaces seemed to be smooth. degrees, not in radians, these values were divided by At room temperature, t3-TCP showed loose bridg­ 57.3, the radian-degree conversion factor, before apply­ ing between round-shaped particles of about 2 Jlffi in di­ ing the above equation for D (Vetter et al., 1991). ameter. At 900°C, bridging between powder grains had progressed. The diameter of the bridged particles had Infrared spectroscopy increased to 4 to 6 Jlffi. The grain boundaries could be From unheated and heated HA and t3-TCP sam­ seen. The width of the free spaces was about 1 to 4 Jlffi. ples, pellets of 300 mg KBr/ 1 mg HA and 300 mg KBr/ 1 When sintered at 1230°C (Figs. 3 and 4), general bridg­ mg t3- TCP were prepared and examined by means of a ing was observed forming a true network within polyhe­ Nicolet 20 SXC FTIR spectrometer (32 scans) with dric blocks of about 50 to 90 Jlffi without any sharp an­ 1 gles. The spaces between the powder grains were about 4 cm- resolution. On HA scans, C03 peaks were identi­ fied. On t3 -TCP scans, the crystallinity indices were 1 to 6 Jlffi. The boundaries between bridged powder calculated (Rey et al., 1991). grains persisted; all surfaces seemed to be smooth (Fig. 5). Scanning electron microscopy Ali powder samples were carbon coated and ex­ Discussion amined at 7 kV in a JEOL JSM 6300 scanning electron microscope to assess the size, shape, and surface texture With regard to HA, the variability of the chemical modifications of the powder grains.