The given paper as well as the whole complex of problems is closely connected with the investigation of the selected materials which are used for dental implants manufacture. The investigated implants had to be removed prematurely from the patient's mouth cavity due to the occurrence of critical states (CS) in relation to the manufacturing material. These critical states of the material led to the malfunction and unacceptability of the dental implants from the aspect of the health condition and the hypersensitivity of the patient to degraded implant material. This work is mainly based on the combination of the theoretical as well as practical knowledge along with predetermination and specification of the needed testing procedures for materials which are commonly used for dental implants. Samples were prepared from the cut sections of the implants in a metallographic (ceramographic) way and subsequently, they were investigated in the terms of their structural properties. The main aim of this paper was to present the microscopic evaluation of the materials for implants and to analyse the undesirable defects that led to their destruction.