Hydroxyapatites (nHAp and µHAp) with two types of morphology were prepared from the following substrates: calcium hydroxide Ca(OH)2 (CAS:1305-62-0, pure p.a. Chempur, PL), ortho-phosphoric acid H3PO4, 85% (CAS:7664-38-2, pure p.a. Chempur, PL), ammonia NH4OH 25% (CAS: 1336-21-6, pure p.a. Chempur, PL), calcium nitrate tetrahydrate Ca(NO3)2•4H2O (CAS:13477-34-4, pure p.a. Chempur, PL), sodium dihydrogen phosphate NaH2PO4 (CAS:7558-80-7, pure p.a. Chempur, PL), urea CH4N2O (CAS: 57-13-6, pure p.a. Chempur, PL). Nanohydroxyapatite Ca10(PO4)6(OH)2 was synthesised by the aqueous precipitation method from calcium hydroxide and orthophosphoric acid added dropwise over 45 min with constant stirring under alkaline conditions (pH=11) by adding ammonia solution, if necessary. Appropriate amounts of substrates with a Ca/P molar ratio of 1,67 were used. The synthesis was carried out at 50 °C for 2 h. The precipitate was rinsed 4 times with deionised water and centrifuged (3700 rpm for 3 min) until the excess ammonia solution was removed. The resulting nanoHAp was dried at 90 °C for 24 h. The synthesis of µHAp particles was carried out by homogenous precipitation method. The main substrates used for the synthesis of the HAp were: calcium nitrate tetrahydrate, sodium dihydrogen phosphate and urea for pH control. The appropriate amounts of substrates with Ca/P molar ratio of 1,67 were mixed with deionised water in a three-necked flask with a reflux condenser. The synthesis was carried out at 90 °C for 48 h. Finally, the precipitated solid phase obtained was washed with boiling distilled water and dried at 90 °C for 24 h. The use of two different synthesis methods resulted in products with different morphologies (irregular-shaped nanohydroxyapatite (Fig. ) and microfibrous (whisker-shaped) hydroxyapatite (Fig. )). The exact particle size characterisation of both fillers is given in section 3.2. Both products obtained were characterized by Xray powder diffraction as a single phase (100% of hydroxyapatite) (Fig. ). However, the hydroxyapatite particles obtained differed in the size of the specific surface area (BET). Clearly, the nanohydroxyapatite particles exhibited a significantly larger specific surface area (SBET = 80.68 ± 0.12 m²/g) than the micrometric particles (SBET = 5.73 ± 0.02 m²/g). The size ratio of the specific surface area of nHAp/µHap is approximately 14.