Most of the review articles were focusing on the success rate and the predictability of implant systems, rarely discussing about the causes of failure. The failure of implant therapy can be defined as early and late stages. The early failure due to failed osseointegration; the late failure happened after initial osseointegration due to physiological or pathological deosseointegration. Systemic diseases could increase the risk for surgery, but we do not have enough reports about the influence on the success rate of implant. This article is trying to review some clinical factors, which might have influence on the success of implant therapy and become our consideration at the time of implant therapy.