It's easy to think about the dental implant procedure as one thing, but there are actually a few options that may be considered depending on what your situation is. Let's look at some of the options for folks considering dental implants.
The Standard, Single-Tooth Implant
As you can guess, this is an implant intended to replace a single tooth that's missing. A post, usually made of a material like titanium, is inserted into the supporting dental bone structure between the jaw and where the tooth used to be. This post has a porous structure to encourage new bone to grow in around it, making it more secure when someone chews.
It is possible to use this approach to replace multiple missing teeth. Most doctors, however, would consider that approach radical if you're trying to replace several missing teeth in a row. If you've lost a single front tooth, such as having one knocked out from a fall or due to tooth decay, the single-tooth approach is a good option. That's especially the case compared to some alternatives, as single-tooth partial dentures can have a hard time staying in place unless they're in the perfect spot.
This is a dental implant procedure meant to deal with situations involving massive tooth loss. All remaining teeth in your upper or lower mouth will be removed. A set of four posts, hence the name all-on-four, are then implanted as they would be for a typical single-tooth procedure. Two arcs of artificial teeth are then mounted to the posts, replacing all of the previous teeth.
You can have a doctor do the procedure on both the top and bottom of your mouth. Your doctor will decide how to approach removing any remaining teeth and which sets get put in first.
This method is mostly reserved for situations where a standard bridge can be installed. For example, suppose you had all your molars removed. There won't be a rear-most tooth for the usual bridge to attach to.
In this situation, the idea is simple. One healthy tooth will be used as an attachment point, just like it would happen with normal bridgework. An implant post will then be put in at the other end to provide a point of attachment. The bridge will then span between the real tooth and the post, providing close to the same level of stability expected from a regular bridge.