Four implants per arch, or six?
This is a hotly debated topic, with strong supporters on both sides.
My opinion is quite simple.
Based on literature and my own anecdotal experience, I believe that 4 implants are optimal for an immediately loaded full-arch prosthetic if the composite torque value (CTV) and the Cantilever/AP spread ratio are also optimal.
In layman’s terms:
If I can achieve solid torque (in my hands, 45 N-cm or higher per implant, and a CTV of 180 or greater) and a one-tooth-or-less cantilever, then I feel 4 implants is the correct clinical choice for the patient.
If I cannot meet those parameters with 4 implants, then I feel additional implants are indicated.
I want to reiterate that, if those parameters are met, I feel that a 4-implant distribution is the optimal choice… not merely adequate.
I feel arbitrarily adding more implants without a clear clinical benefit introduces the patient to unnecessary surgery, increased surgical risks, increased anesthesia time, increased patient discomfort, and potentially makes long-term hygiene more difficult.
At times, however, the benefits of additional implants outweigh those risks. If CTV or cantilever length do not meet my requirements, I look to transition to a 6-implant configuration. Certain subsets of patients, such as bruxers or exceptionally young patients, might also (but not always) be included in this group.
Ultimately, I have not noticed any clinically significant difference in the integration rate of 4 versus 6 implant cases – assuming torque and cantilever are accounted for.
Take home: CTV and CL/AP spread ratio are what dictate whether I perform 4 or 6 implants.