The invention relates to biologically active nanoparticles of a carbonate-substituted non-stoichiometric hydroxyapatite, having:a) a crystallinity degree CD lower than 40%, the crystallinity degree being defined asCD=(1−X/Y)·100wherein: Y=height of the diffraction maximum at 2θ=33°, X=height of the diffraction background at 2θ=33° of the nanoparticles X-ray diffraction pattern；b) a length L ranging from 20 to 200 nm and a width W ranging from 5 to 30 nm； andc) an aspect ratio AR comprised between 2 and 40, the aspect ratio being defined as AR=L/W.The biologically active nanoparticles of the invention find a preferred use in oral or dental hygiene applications and may be formulated as compositions for oral or dental hygiene such as, for example, solutions, suspensions, oils, gels or other solid products. Other aspects of the invention include a process for preparing a suspension for oral or dental hygiene including the aforementioned biologically active nanoparticles, a process for manufacturing a toothpaste comprising the nanoparticles, as well as a method of locally remineralizing the teeth comprising contacting the teeth with the nanoparticles.
