All-on-4 vs All-on-6: Which Full-Arch Solution Is Right for You?

Patients who are considering fixed teeth on implants almost always arrive with the same question: are four implants enough, or are six the safer decision. The short answer is that both methods work well, but a greater number of implants does not automatically mean a better solution. The longer answer depends on the quantity, quality and distribution of your bone, on which dental arch is being restored and on what you expect over the next ten years and more. Here we explain the difference without exaggerating in either direction.

What the numbers 4 and 6 actually mean

Both All-on-4 and All-on-6 are concepts in which an entire dental arch, upper or lower, is carried by a few strategically positioned implants and loaded immediately with a fixed temporary bridge. With All-on-4, four implants are placed, most often two straight at the front and two tilted at the back, which makes it possible to avoid important anatomical structures such as nerves or sinuses and to make the fullest use of the bone that is still present. All-on-6 adds two implants, usually in the posterior region, so that the load is distributed across more points of support.

The logic behind the two additional implants is simple: more points of support can mean a better distribution of forces across the implants and the prosthetic structure. That does not automatically mean that six is always better. The choice depends on whether your bone offers the space and the conditions for six strategically positioned implants with good primary stability.

Implant survival: the results are very similar

If you look only at whether the implants remain in the bone, the difference between four and six is smaller than most patients expect. In a five year multicentre randomised study of the upper jaw, implant survival was 100 per cent in the four implant group and 99.3 per cent in the six implant group, with only one early loss.1 A large retrospective analysis of 943 patients and almost 6,000 implants produced a similar picture: after five years, survival was 98.4 per cent for four and 98.7 per cent for six implants, with no statistically significant difference.2

The All-on-4 concept itself also has a solid foundation over the longer term. A systematic review of 24 studies with more than 11,000 implants reported survival above 99 per cent over a shorter period and a success rate of around 94.8 per cent after ten years.3 Those are figures on which a lasting solution can be built.

Where the methods do differ

The difference appears when we look deeper than the mere survival of the implants. A meta-analysis of the upper jaw found no significant difference in the survival of either the implants or the restoration, but it did record significantly greater marginal bone loss with four implant solutions.4 The authors conclude that a greater number of implants can reduce the load on the bone and the number of complications.

The pattern on the technical side is interesting too. In the five year randomised study mentioned above, technical complications such as screw loosening or fractures of the temporary bridge were more frequent in the four implant group (16.6 against 0 per cent), while the difference in bone loss remained clinically negligible.1

The message is not that one method is better than the other. Additional implants can provide a biomechanical reserve and a better distribution of load, but only if we can position them strategically and achieve high quality bone anchorage. Four well positioned implants can therefore be a better solution than six implants placed in biomechanically less favourable sites.

What matters, then, is not only the number of implants, but the individual anatomy of the patient, the knowledge and experience of the implantologist, high quality and complete diagnostics, precise treatment planning and an equally precise surgical execution.

When we usually propose All-on-4

All-on-4 is a frequent choice in the lower jaw, where the bone is generally denser and often allows good primary stability of the implants. We also use it when the anatomy and the distribution of the remaining bone allow four strategically placed implants to provide a stable and biomechanically favourable foundation for the entire fixed dental arch.

The tilted rear implants make it possible to use the existing bone to the full, to avoid important anatomical structures and to move the rear point of support as far back as possible. In selected cases this makes it possible to avoid additional bone augmentation procedures and, in the upper jaw, sinus floor elevation as well.

When four correctly distributed implants provide everything needed for a safe and durably stable fixed solution, placing additional implants simply for the sake of a higher number makes no sense. All-on-4 in this way opens the path to fixed teeth for many patients, without lengthy preparation and bone augmentation.

When All-on-6 has the advantage

We consider six implants above all when the anatomy and the available bone allow the two additional implants to be placed strategically and to be biomechanically useful. This can be particularly important in the upper jaw, where the bone is often of lower density. Additional points of support can then allow a better distribution of load and provide an extra biomechanical reserve.

All-on-6 can also have the advantage in patients with pronounced teeth grinding, that is bruxism, and in other situations in which we judge that additional points of support will be biomechanically useful in the long term. The condition is always the same: there has to be enough good quality bone and a suitable distribution for placing six implants with good primary stability.

A poorly positioned fifth or sixth implant brings no advantage simply because it increases their total number. The aim is not to place as many implants as possible, but a sufficient number of implants in the right places.

What if there is not enough bone even for four

There are patients for whom even four standard implants are a challenge, most often because of a severely resorbed upper jaw. For them, the classic division into 4 and 6 is often not the real issue. In such cases, at Ortoimplant DENTAL SPA we use rarely available advanced implantology techniques such as zygomatic (Zygoma), pterygoid, transnasal and transsinus implants.

These techniques allow us, depending on the individual 3D anatomy of the patient, to find other safe zones of bone anchorage and to make the fullest use of the existing bone, instead of the treatment necessarily relying on extensive procedures to build that bone up.

With a severely resorbed lower jaw the options are different. Depending on the available bone and the position of the inferior alveolar nerve, short or ultrashort implants may be the solution, while in particularly demanding cases Dr Zdenko Trampuš also performs lateralisation or transposition (repositioning) of the inferior alveolar nerve, extremely demanding surgical techniques which, in carefully selected patients, make it possible to place implants in the posterior part of the lower jaw.

The principle we follow is that there is no patient to whom a solution cannot be offered. When standard implants are not possible, we do not only ask whether there is enough bone for a classic All-on-4 or All-on-6. The question is where, in the individual anatomy of the patient, there is safe bone anchorage for a durably stable fixed solution.

How we make the decision

We do not choose the number of implants in advance, nor from a price list. At the first examination, which is free of charge at our clinic, we carry out a clinical examination and complete digital X-ray diagnostics, including a 2D orthopantomogram and a 3D CBCT scan, and we plan the position of every implant digitally before we begin the procedure. Only once we can see the actual volume, quality and three dimensional anatomy of the bone and its relationship to important anatomical structures can we assess whether four implants will be entirely sufficient or whether six will bring a genuine biomechanical advantage.

In doing so we plan not only where we can place the implants, but where we need to place them so that the future fixed restoration has optimal support and distribution of forces. As Dr Zdenko Trampuš puts it: “We plan the surgery around the teeth, not the teeth around the implants.”

For patients with pronounced fear, dental anxiety or dental phobia, analgosedation is available, while we apply potentiated intravenous analgosedation as a matter of protocol for more extensive implantology and oral surgery procedures analgosedation. With DENTAL SPA treatments we give the body further support before, during and after the procedure and create more favourable conditions for healing and a more comfortable recovery DENTAL SPA.

The goal is always the same: durably stable fixed teeth, not the largest possible number of implants.

Frequently asked questions