It requires at least 4 implants in either jaw (6 is preferred for the upper) to make a screw retained denture. Also, they must be spread out further. Some people start out by placing 4 full size implants in the lower jaw and converting their denture to a snap-in to save money now because they plan to convert their snap in denture to screwed in denture at a later date.
Truth be told, this rarely happens! Most people are so satisfied with their denture held in by 4 Locators that they never get the conversion to a screwed in or “fixed” denture. To spread the costs out even more, some people have 2 implants in the front of the lower jaw one year, then the other 2 added the next year, then a fixed, screwed-in denture made the next year. Rome wasn’t built in a day and your teeth don’t have to be restored completely in a day either!
The biggest issue with snap-in dentures is they can’t be connected to the implants the day the implants are placed!!! Because of the excessive stress on the implants when the dentures are taken in and out, they will not heal to the bone! You have to wait 6-12 weeks before they can be connected.
But with screw in dentures, all of the implants are held still so they can be connected to the dentures the day they are placed. THIS IS A BIG THING TO CONSIDER FOR MANY PEOPLE.
But with mini implants they can often be connected to the denture the same day. It’s difficult to explain why…just take my word for it.
Personally, for snap in dentures, I say save the money and go with the minis. If you want screw-in teeth, I prefer placing 5 or more implants per arch, if possible. That way if you do lose an implant sometime in your life, you will still have your teeth because it takes 4 to hold them in.
All About Dental Implants and Dentures 