There is no upper limit to the number of dental implants you can have as long as there is sufficient jawbone to support them. Implants can be used to replace a single tooth, multiple teeth, or all teeth in the mouth. In cases of substantial tooth loss, implant-supported bridges or dentures can be used, which require fewer implants to support more prosthetic teeth. So when you hear about All on 4 or All on 6 it is that an entire arch of teeth may be supported by 4 or 6 implants or more.