Mini implants are not ideal for long-term support of any type of prosthesis. They are mainly used as interim or transitional implants. Complications such as failure or fracture are common with mini-implants. While they are cheaper to do, their long-term prognosis is unknown. If you don't have enough bone for regular implants, then grafting should be considered. If cost is of issue and mini implants are being offered for that reason, then you should know of questionable prognosis and how long they may work. Your dentist should provide you some level of what to expect so you can make the best decision. See link below for more information.