All-On-4 Digital Workflow Possibilities with milled PMMA

There have been suggestions, and often a “push”, by technicians to streamline their production process with All-On-4 and full arch implant restorations by integrating a digital work flow and using materials that can be milled quickly and accurately to be used as immediate provisional restorations. One such material that is gaining popularity is milled PMMA, but how does this compare to the quality offered by our existing systems?

I have looked at what’s available on PMMA and used in for short span bridges.

PMMA is accurate, aesthetic, easily integrated with a digital workflow and certainly better than any kind of denture-conversion system for All-On-4 and full arch restorations, BUT it still lacks the rigidity and durability required for a permanent/final restoration. This is a critical point because any kind of functional flex or crack will negate the load sharing function between the implants and intensify the load on specific implants. This can then lead to bone loss and failure.

For this reason, and especially with the thousands of implants that we insert each year with All-On-4 treatments, PMMA or any kind of system that is designated as a “provisional” is not a protocol that we can accept at the All-On-4 Clinic group.

We are currently looking at Carbon Fiber and other materials that can more easily be incorporated into a fully digital workflow for an immediate restoration that is permanent, but our results and conclusions are still pending.

Tempting as it may be to be drawn into newer materials and workflows, as clinician we need to focus on creating the most favourable environment for the healing of the implants that we place with the greatest of our skill and effort. An immediate restoration that is non-elastic and “final” in its construction and durability is an important opportunity to provide a self-protective system through reliable load sharing.

Our current system of an immediate final bridge with a milled titanium frame and acrylic teeth is still the only system that can give us what we need in terms of rigidity and durability of the connecting element between the fixtures, and a more forgiving element at the functional occlusal surface. It is also a system that gives us an opportunity to do in-mouth wax try-ins and immediate fine tunning, which is far more reliable for achieving the final aesthetics than any kind of purely digital workflow.

Our data data does show a moderately high rate of cohesive breakages (close to 20%) within a 5 year period, but this does not compromise the bar connection, which is the protective mechanism for the implants, and means that 80% will continue to function beyond that term. The other 20% receive upgrades to Zirconia.

Notwithstanding what I said above, in reality not every surgical facility has access to an onsite lab and milling centre to enable them to produce an immediate final restoration, and especially with a milled titanium framework. As such, offering a digital workflow and provisional options such as with PMMA certainly save time, and are a step (many steps, in fact) above the denture-conversion option (which is sadly still widespread 😟 ). The Aesthetics can always be fine-tuned at the second stage when producing the zirconia restoration.

As an alternative to an immediate final restoration with a milled titanium framework, clinicians who do not have access to an instant milling centre can also attain the required parameters using a floating bar withing the acrylic restoration. I have personally used the floating-bar option for many years, and it is still a better option than PMMA because its final, but perhaps not quite the same as a milled titanium bar.