All-On-4 is not an invention, but rather a treatment technique that has evolved over time and has the following features:

1. four dental implants to support a full fixed bridge
2. the use of angulated implants in the back to overcome bony deficiencies or anatomical structures
3. immediate loading

THE ALL-ON-4 TREATMENT CONCEPT

All-on-4 is a prosthodontic procedure (i.e replacement of missing teeth) that provides a permanent, screw-retained, same-day replacement for the entire upper and / or lower set of teeth with a bridge or denture. This procedure is best for patients with significant tooth loss or decay and for people whose bone loss in the jaw area prevents them from getting conventionally oriented (vertical) dental implants.

Often, tooth loss is accompanied by loss of the jaw bone which poses the problem of reconstruction of the jaw bone requiring bone grafting. The All-On-4 protocol is considered to be a graftless solution thereby avoiding the long and costly road of rebuilding bone when conventionally oriented implants are used. For the implementation to be successful a careful analysis of the bone structure needs to be made. The most ideal way to evaluate the bone is by a CBCT scan.

The All-On-4 protocol is for at least 4 implants to be placed in a jaw. The back implants are typically angled approximately 30 to 45 degrees from the biting plane. The implant is placed in front of the maxillary sinus in the upper jaw (maxilla) and in front of the mental nerve in the lower jaw (mandible). The head of the implant emerges in approximately the second premolar position. This will allow a molar tooth to be cantilevered posterior resulting in a denture or bridge with approximately 12 teeth.

The All-on-4 treatment concept owes its name to the very nature of the method, which consists of applying a dental prosthesis with at least twelve teeth (bridge) fixed in the jaw, based only on four titanium implants.

via wiki