Bar Design for All-On-4 Final Bridge
There are various methods to make immediate All-On-4 implant-supported fixed bridges. The nature of the treatment often precludes the ability to fit the FINAL bridge immediately after surgery. This is due to a number of factors, including:
- Inability to obtain accurate tissue impressions after surgery;
- Complexities in the coordination/integration of the surgical and restorative teams;
- Limitations in relation to accessing a laboratory within the surgical facility;
- Inability to accurately assess the aesthetics and function because of post-operative swelling and/or numbness;
- Laboratory processes and time constraints for production of the final teeth; and,
- Shrinkage/retraction of the soft tissue during healing.
As a result, most clinician would do something temporary initially using ‘denture conversion’ method, where a pre-fabricated denture is retro-fitted to titanium cylinders using cold-cure acrylic, and after 4 months once the gums and tissues have healed, they would resume the process to make their version of a ‘final’ bridge, most commonly an acrylic bridge supported by a milled-titanium frame connected to the implants. This attracts a substantial additional cost for the patient.
At All-On-4 Clinic we have developed unique surgical and restorative methodologies that enable us to deliver the final bridge within 24 hours from surgery. These methodologies have been widely acclaimed internationally by specialists, university professors and many hundreds of highly experienced implant-surgeons who have attended our clinical residency programs. However the system to create an immediate final bridge requires special set up as well as specially-trained technicians, thus they are not easy for most clinics to adopt.
We start planning the treatment and aesthetics prior to the surgery with a full smile design. Immediately after the surgery, our impression system enables us to obtain accurate guided-tissue-impressions, which results in a predictable healed interface with no tissue retraction. Our indexation system then enables us to transfer a template of our digital design into the mouth for real-life functional and aesthetic evaluation within hours, …..once the numbness has gone, …and before any swelling sets in. We are also able to fine-tune the aesthetics and make changes on the spot.
Using special laboratory processes we produce a FINAL metal-reinforced fully processed HIA bridge, not the temporary type. To be able to produce the bridge within 24 hours, we use a different kind of metal bar. We refer to our bar as a ‘floating bar’. Unlike the milled titanium bar, our bar, whilst providing similar rigidity and support, is connected to the implants via the bridge itself through titanium cylinders. Thus it is ‘floating’ within the hard bridge substance instead of being directly connected to the supporting implants.
With the way we process and reinforce our bridges, there is no difference in the ‘finality’ whether it is a floating bar or milled titanium.
In both cases the prosthesis itself is acrylic, so the teeth are the weakest link.
The wear and longevity are exactly the same in both milled and floating versions.
The only advantage of a milled bar is possibly that it allows for a slightly longer posterior cantilever. But then we have to consider the potential adverse loading of the implants.
With documented cases in the thousands, we know that frame/retainer breakages with our floating bar method is extremely rare. The most common complication is not breakage through the bar, but breakage of a tooth/teeth. This happens in 15% of cases. If it happens, then it usually happens within a period of 3 years.
If a tooth would breaks with our floating bar, then it would also break just the same with a milled titanium bar. In those situations “milled” or “floating” will make no difference. The only solution is upgrading to a stronger material like Zirconia.
Apart from the physical properties of the bridge material, and its method of reinforcement, there are 2 other factors that contribute to the finality of a bridge:
- Occlusion – Its important to understand that occlusion in full-arch implant supported restorations is NOT the same as denture occlusion because of its fixed nature. A balanced occlusion, as commonly prescribed, is not only unnecessary but inappropriate. Full-fixed implant occlusion is also NOT the same as natural teeth occlusion, …and its not the same as dentitions intermixed with segmental implants …because there is no proprioceptive feedback with full-fixed restorations. In the absence of proprioception, the focus in occlusal design must be both physiologic and musculo-skeletal, where reduction of excessive biting/clenching forces is attained by eliminating occlusal trigger points that fire up the masseter, and considering the airways to minimise SPO2 depletion due to airway issues from skeletal maloclussion/retrognathic-lock or sleep apnoea, which in turn cause reflexes that fire up other muscles of mastication.
- Restorative Space – in full arch restorations restorative space is paramount for flexibility in the design of the restoration, for improved comfort, better lip support, to hide the transition line, facilitate hygiene (by eliminating mini-flanges), and improved durability. Like I always say …The Space Makes Your Case. Restorative space can be improved with alveoplasty, sinus impaction graft (aka “sinus crush”), and mucoplasty. It can also be increased by opening the OVD, but this is quite limited. The amount of surgical restorative space management is very different from patient to patient, but it is alway an important factor in the ability to achieve the final restoration immediately.
Since there is no difference in practice between a milled or floating frame, and since both are similarly susceptible to 15% breakages, there is no sense in waiting for the production of a milled bar at additional costs, and wearing a sub-optimal ‘denture conversion’ in the interim period, especially when the floating bar offers the necessary support immediately, along with the optimal final aesthetics, comfort and function offered by the All-On-4 Clinic Restorative System.
I have a number of issues with the alternative protocol for a so-called ‘permanent bridge’ with a milled-frame, which involves the fitting of a temporary bridge for a few months, especially when the initial temporary restoration is retrofitted to the implants with cold-cure acrylic, as commonly done when there are no means or resources for another alternative. Primarily, I am concerned by the following:
- ‘temporary’ also translates to unreliable. This means that it is more susceptible to degradation and/or dissociation between the titanium cylinders and the prosthesis, …which means that the support offered by a certain specific implant becomes ineffective causing a concentration of the loads in other areas and accelerating further degradation along the bridge, …which puts the remaining implants under adverse or excessive stress, …and all this during the most critical initial period of osseo-integration. This may likely result in an increased amount of bone loss and/or higher rate of failures.
- on delivery of the ‘permanent’ version with a milled titanium bar, the patient will have paid much more for the actual production of the bar, and yet the acrylic teeth are still susceptible to the same rate of breakages. So the dentist would repair, and keep repairing, …until accepting the inevitable need to upgrade to Zirconia, in spite of having produced what they decribed as the ‘permanent’ bridge. In those situations both the dentist and the patient will be at an economic loss …not an ideal situation for patient satisfaction and referrals.
With All-On-4 Clinic’s protocol, whenever there is a breakage, or when the teeth eventually wear down after 5-10 years, the patients are offered an instant upgrade to Zirconia. They only pay an upgrade fee. Thus, not only do they end up spending much less overall on their implant rehabilitation, they end up with porcelain teeth (not acrylic) that do not wear down and which are far more durable than the acrylic teeth, regardless as to whether those acrylic teeth would be supported by a milled or floating frame.
Written by Dr Alex Fibishenko, All-On-4 Clinic Melbourne.