Four implants and six implants show similar implant survival. Pooled across studies with one to five years of follow-up, implant survival was 99.66% for All-on-4 and 98.55% for All-on-6. In a separate cohort of 943 patients whose 5,989 implants spanned both jaws, the mandibular subgroup (2,954 implants) showed five-year implant survival of 98.6% for four implants and 99.4% for six, a gap that did not reach statistical significance (p=0.136).12
Six implants are still preferred where the mechanics are harder: severe ridge atrophy, documented bruxism, high occlusal forces, or systemic risk factors. The decision is about load and anatomy, not about survival statistics.2
What the survival numbers show
The clearest evidence comes from a 2026 systematic review that pooled implant survival across three follow-up windows rather than giving a single figure for the entire follow-up. Broken down that way, survival with four implants and with six stays close.1
| Follow-up | All-on-4 | All-on-6 |
|---|---|---|
| 1 year | 99.20% | 100% |
| 1 to 5 years | 99.66% | 98.55% |
| 5 years or more | 98.14% | 97.50% |
At every follow-up interval in the table the two approaches sit within a percentage point or two of each other. In the first year All-on-4 trails All-on-6 by less than one point.1
A separate cohort points the same way, but the whole cohort and the subgroup these figures come from need to be kept apart. Researchers followed 943 patients with 5,989 immediately loaded implants supporting fixed full-arch prostheses, in both the upper and lower jaw, for a mean of 5.0 years. The mandibular subgroup within it totals 2,954 implants. Five-year cumulative implant survival in that subgroup came to 98.6% for four implants and 99.4% for six, a gap that did not reach statistical significance (p=0.136).2
Neither the pooled review nor the cohort's mandibular subgroup found that adding two implants changed implant survival enough to reach statistical significance.
Marginal bone loss
Survival only asks whether the implant is still in place. It says nothing about how much bone has been lost around it, and on that measure the pooled estimates for the two designs differ.1
Pooled estimates from studies with shorter follow-up show a small gap: 0.77 mm of marginal bone loss around All-on-4 fixtures against 0.85 mm around All-on-6.1 Pooled estimates from studies with five-year follow-up show a wider gap running the other way: 1.28 mm of marginal bone loss for All-on-4, against 0.94 mm for All-on-6.1
That is a difference of roughly a third of a millimeter in the five-year estimates (1.28 mm minus 0.94 mm). These short-term and five-year figures come from different follow-up windows in the pooled data rather than the same patients tracked over time, so this is not two curves diverging within one group. These pooled figures do not establish why the gap runs in this direction.
The consensus statement adds a caveat for the upper jaw: survival between four and six implants looks similar there too, but marginal bone loss has been reported inconsistently across studies and patient groups. The mandibular subgroup figures above should not be assumed to carry over to the maxilla.2
When six implants are chosen
With survival and bone loss this close, the choice depends less on published outcomes than on whether the patient's jaw can safely carry the load on fewer fixtures.
- Severe ridge atrophy. Less bone volume to spread the load across favors more implants, not fewer.
- Documented bruxism. Grinding puts sustained extra force through every fixture in the arch.
- High occlusal forces. A strong bite works the same way as bruxism, without the grinding habit behind it.
- Systemic risk factors. Conditions that make bone healing less predictable make each implant less predictable.
These four situations are the ones the Italian consensus statement lists as reasons to add the extra pair.2 Four implants remain the standard choice when the picture is more favorable: enough bone at the front of the mandible to anchor all four fixtures, good spread from front to back, a cantilever kept short, and an occlusion the surgical team can control and adjust.2
Part of what makes four implants work in a shorter arch is how the back two are placed. They are usually angled rather than set straight up and down, reaching further into available bone and shortening the cantilever without a bone graft. A pooled analysis across axial and tilted implants found no failure-risk difference between the two designs that reached statistical significance (RR 1.02, 95% CI 0.85 to 1.23).3 The consensus statement reports the same pattern within full-arch cases specifically: no failure-risk difference reaching statistical significance, though a small difference in long-term marginal bone loss does reach significance.2
Questions patients ask
Is four implants enough for a whole jaw?
In most standard cases, yes. The consensus statement describes four implants as sufficient for the typical edentulous mandible, with survival close to a six-implant arch. Whether it applies to a given jaw depends on four surgical conditions: enough anterior bone, a good spread front to back, a short cantilever, and an occlusion the team can control.2
Why would a surgeon choose six implants?
No statistically significant difference in failure risk between four and six implants has been found. Six is chosen for mechanical reasons instead: heavier ridge atrophy, bruxism, unusually high biting force, or a medical condition that makes any single implant less reliable. Spreading the load across six fixtures reduces how much any one of them has to carry.2
Does the upper jaw follow the same rule?
Survival is similar between four and six implants in the maxilla as well. Marginal bone loss is the part that is less settled there, with results varying across studies and patient groups, so the mandibular subgroup figures above should not be read as a maxillary guarantee.2
What is the prosthesis made of?
Monolithic zirconia is one material option for the full-arch prosthesis. The consensus statement reports an average survival of 97.23% and a complication rate of 2.25% for monolithic zirconia prostheses, over a mean follow-up of 49.7 months. Zirconia prostheses finished with a layered veneer perform worse: chipping affects 15% to 54% of them.2
References
- Shao WH, Chen R, Wang S, Duan SY, Zhang XD, Tang YL. All-on-4 and All-on-6 implant-supported fixed prostheses for the edentulous jaw: a systematic review and meta-analysis. International Journal of Oral and Maxillofacial Surgery, 2026;55(9):1098–1112. doi:10.1016/j.ijom.2026.04.002
- Rapone B, Ferrara E, Tomarelli F, Giovannico G, Bacci C, Dalmaschio G, et al. Consensus Statement on Full-Arch Implant Rehabilitations: Evidence-Based Recommendations from the Italian Consensus Conference. Journal of Clinical Medicine, 2026;15(10):3695. doi:10.3390/jcm15103695
- Malak AA, El Masri Y, El Masri J, Issawi HA, Salameh P, Aoun G. Implant Failure and Marginal Bone Loss Between Axial and Tilted Implants: An Umbrella Review with Meta-analysis. The International Journal of Oral & Maxillofacial Implants, 2024;39(6):875–883. doi:10.11607/jomi.10885
This page describes published clinical practice. It is not a treatment plan, and it does not replace an examination.