In spite of recent pioneering advances and remarkable evolution in the design and development of surgical and dental implant materials, failures do occur. One of the reasons for these failures can be corrosion of dental implants. The most favorable implant is the one which is capable of resisting the most extreme conditions that could possibly be encountered in the mouth. The choice of the materials used for the implant as well as implant borne suprastructures become vital, and can be made by way of evaluating their galvanic corrosion behaviors. When the mechanisms that ensure implant bioacceptance and structural stabilization are fully understood, implant failures will become a rare occurrence, provided that they are used properly and placed in sites for which they are indicated. Titanium dental implants can cause corrosion and wear. Particles and ions of titanium and titanium alloy components due to corrosion and wear can be deposited in surrounding tissues, and inflammation can occur. The buildup of titanium ions and particles can occur systemically as well as in the neighboring tissues, which can lead to toxic reactions in other tissues including yellow nail syndrome. Additionally, there are cases where the metal material is hypersensitive. Currently, zirconia/ceramic implants are considered to be an alternative; however, there are still limitations due to a lack of long-term clinical data. Within the limitation of this lecture, it suggests that we should be aware of the rare problems of titanium toxicity, allergy & hypersensitivity.