Mini implants have limitations and certain indications, and restoring a tooth is where limitations are very real and there are few indications. Mini implants used to restore a tooth is generally a poor long-term decision -- the only teeth I'd ever consider restoring on a mini implant are the smallest teeth we have that are in the least amount of function: lower incisors or upper lateral incisors (the small teeth just next to your two front teeth). Mini's just aren't design to take much biting force, so they won't last if you ask them to do too much work. Investing in a bone graft and a larger implant is a much more predictable long term solution. There are also companies like Biohorizons, Nobel Biocare, and Straumann (3 of the biggest dental implant players in the world) that have come out with 3.0mm implants that are very strong and can withstand long term use. These are just slightly larger than minis, but they will be a better long term choice by far. If you have adequate bone to place a 3.0 or larger size implant, you should go that route. Minis are cost effective in a short term sense, but they will likely fatigue and fail over time. When a failure occurs, it may make placing a second implant difficult or impossible. Plus, if you have to pay for two minis and two crowns, you've probably spent more than you would on one conventional sized implant, abutment, and crown.