You may have heard the term “Teeth in a Day”. This usually refers to the all on 4 technique. However, it typically requires multiple pre-op appointments, similar to the “Teeth in an Hour” technique. With the Teeth in an hour technique, the final prosthesis is made prior to placing the implants, the implants are placed extremely accurately, on adjustable abutments, the final prosthesis fits in and you are done. With all-on-4, the 4 implants per arch are placed. A temporary prosthesis is usually fashioned from a denture to fit on the implants, and 3-6 months later you get a final set of teeth. Since the temporary prosthesis is hand made on short notice, it can be fought with problems such as broken prosthesis or teeth in the first few weeks.
In an effort to decrease the cost of replacing all the teeth in a dental arch, the all on 4 technique has been developed. By angling the implants up to 30 degrees in a front-back direction, it spreads them out, allowing a more even distribution of bite forces on just 4 implants. In some cases it allows the elimination of bone grafting procedures.
Unfortunately, there are a several compromises to take into consideration with the all-on-4 technique. The osseo-integration of an implant – where the bone fuses to the implant takes 16 weeks to mature, with some initial integration occurring by 8 weeks. When the implants are loaded with teeth the day they go in, you rely only on the mechanical stability of the “screw pattern” only, achieving only 40-50% of the implant’s bony attachment potential. With the All-on-4 technique, long-term success for implant maintenance at only 10 years is low – at about 94%. Studies do not exist for longer periods. In addition, the prosthesis with the fewer implants also typically requires more repairs. Also, the prosthesis tend to be shorter, with 10-12 teeth per arch rather than 14. In addition, the angled implants require costly angled abutments, utilize small screws with lower torque values, breaking more often and requiring repairs.
Typical prosthetic guidelines as determined by engineering analysis usually calls for 5 implants in the lower arch, and 6-8 implants in the upper arch. With the additional implants being placed posteriorly in the molar area where the large bite forces exist. With these traditional reconstructions using 5 lower and 6-8 upper implants, long-term success after 25 years is high, 98-99% for being trouble free. The usual issue is the teeth wearing out after 20 plus years. For this reason, this becomes the better value. The All-on-4 is an effective functional solution if you understand the shortcomings and likely need to eventually rebuild your arch of teeth in 8-12 years, or sooner, placing additional implants as well.