“Four vs. Six Implants” in Full‑Arch Therapy
Evidence‑Based Truths to Help You Avoid Regret
Full‑arch fixed implant treatment—supporting a complete set of teeth on implants—has become a mainstream solution after tooth loss. One crucial decision many patients face is whether to place four implants (All‑on‑4) or six implants (All‑on‑6).
“Fewer implants are cheaper and easier?” “More implants feel safer?”
A recent meta‑analysis focused on the maxilla (upper jaw)—considered more challenging surgically—offers compelling evidence to answer these questions (Sharaf et al., 2024). Here are the key findings from a specialist’s perspective.
1) Surprising result: Implant “survival” is not driven by the number of fixtures
In the maxilla, the proportion of implants remaining integrated (survival) showed no statistically significant difference between four and six implants.
Pooled survival rates in the latest meta‑analysis:
– Implant survival: 4 implants 98.5% vs 6 implants 97.0%
– Prosthesis (fixed bridge) survival: 4 implants 99.8% vs 6 implants 99.6%
In other words, “fewer” does not mean “fails sooner.” Although maxillary bone is less dense and complicated by the sinus, contemporary surgical and prosthetic protocols can achieve very high survival with four implants. However, survival alone doesn’t define long‑term health over 10–20 years.
2) The “invisible health” gap: bone loss progresses twice as fast with four implants
The most consequential difference concerns the supporting bone. For marginal bone loss (MBL), four versus six implants showed a striking divergence:
“Significantly higher MBL was observed in the 4‑implant group than in the 6‑implant group (p < 0.01).”
Over a mean 3.8 years, average bone loss was:
– Four implants (4‑IG): 1.02 mm
– Six implants (6‑IG): 0.46 mm
That’s more than double the rate of bone loss with four implants. The mechanism is mechanical: with only four fixtures, distal cantilevers are typically longer to replace missing posterior support, acting as a lever that concentrates stress on the terminal implants and adjacent bone. With six fixtures, cantilevers shorten, load distribution improves, and long‑term bone health is easier to maintain.
3) Early warning signs: subtle differences in complication risk
Technical/mechanical complications (per 100 prostheses):
– Four implants: 20.7%
– Six implants: 17.9%
Biologic complications (e.g., peri‑implantitis) (per 100 prostheses):
– Four implants: 2.0%
– Six implants: 0.8%
Technical issues trend slightly higher with four implants (each fixture carries more load), but both groups show very low biologic complication rates (~1%). This underscores that the “hidden” risk—accelerated bone loss with four implants—is the more critical determinant of long‑term maintainability.
4) Technology matters: CAD/CAM and strategic “positioning” drive success
Simply adding more implants is not enough; precision fit becomes more demanding. In six‑implant cases, using CAD/CAM‑milled frameworks significantly improved implant survival versus conventional casting (p < 0.01). Digital workflows reduce misfit across multiple fixtures and lock in the mechanical advantages of additional support.
Equally important is distribution planning (e.g., V‑II‑V layouts) to optimize anterior‑posterior spread in the maxilla.
5) Conclusion: Finding your optimal choice
Guidance for regret‑free decisions based on the data:
– Four implants (All‑on‑4): Highly efficient with reduced surgical burden and rapid restoration of function. However, loads are more concentrated and bone loss tends to progress faster, so closer long‑term follow‑up is essential.
– Six implants (All‑on‑6): Superior “mechanical balance” with better load distribution—particularly advantageous for heavy biters or patients with bruxism, helping protect bone over time. To fully realize the benefit, a precise digital (CAD/CAM) workflow is essential.
Implant therapy does not end on the day of placement. The true value is how your bone holds up and how comfortably you continue to chew years later. When consulting your clinician, review your bite force, lifestyle, and—most importantly—how you will protect bone—then weigh “four vs. six” accordingly.
To safeguard your smile a decade from now, which do you prioritize today: simplicity or stability?
References
Sharaf, M. A., Wang, S., Mashrah, M. A., Xu, Y., Haider, O., & He, F. (2024). Outcomes that may affect implant and prosthesis survival and complications in maxillary fixed prosthesis supported by four or six implants: A systematic review and meta‑analysis. Heliyon, 10(3).
Book your consultation today
Tokyo International Dental Roppongi (map)
Address: 2F, TIDS Building, 5‑13‑25 Roppongi, Minato‑ku, Tokyo (Otafuku‑zaka)
Phone: 03‑5544‑8544
Nearest stations:
– Toei Oedo Line “Azabu‑Juban” Exit 7 — 5 min walk (see route video)
– Tokyo Metro Namboku Line “Azabu‑Juban” Exits 4/5 — 5 min walk (see route video)
– Tokyo Metro Hibiya Line “Roppongi” Exit 3 — 10 min walk
(Behind Toyo Eiwa Jogakuin JHS grounds, along Otafuku‑zaka)
Supervisor: Hiroshi Miyashita, Director, Tokyo International Dental Roppongi
