When is All-on-4 the best option? 5 factors to consider when creating your dental treatment plan

Full-arch fixed implant bridges—often referred to as All-on-4 (figure 1)—are taking the dental field by storm. These bridges are usually supported by four to six dental implants, which are fabricated from materials such as acrylic fused to titanium, monolithic zirconia, and porcelain stacked to a cobalt-chromium frame. They are often presented with package pricing, which simplifies case presentation, and some practices promote All-on-4 as the best treatment option for their soon-to-be-edentulous patients.

Thanks to aggressive marketing by companies such as ClearChoice and the extensive information available on the internet, patients are more aware than ever of the benefits of All-on-4 bridges. Five to 10 years ago, most patients were unaware that All-on-4 bridges existed. Today, it is common for patients to specifically request this treatment, but is it always in their best interests? As wonderful as All-on-4 bridges are, when are they a disservice?

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It would take a very long article, or more likely a book, to cover everything we should consider when recommending All-on-4 treatment, but these are the five factors that I encounter on a regular basis in my dental implant practice:

• Speech issues
• Difficulty adapting to bridge thickness
• Proprioception
• Parafunction
• High caries index

Let's take a closer look at each of these aspects and, one by one, see how each might affect treatment considerations.

Speech issues

Speech issues are a major concern for patients. What may seem to us to be a minor speech flaw can become an overwhelming concern for the All-on-4 patient. Implant-supported bridges require both vertical and horizontal bulk for strength. Vertical needs vary with different restorative materials, but most bridges require 15 mm or more of height. As a result, clinicians are forced to replace more than just the volume of the missing teeth in order to achieve these measurements. We must often replace bone and soft-tissue volume, even if it is healthy. The result is that the portion of the bridge adjacent to the soft tissue will be bulkier than the original bone and soft-tissue volume that it replaced (figure 2). Consequently, this can have an impact on speech sounds such as "D," "T," and "N," as the tongue contacts the hard palate lingual to the central incisors to form the sound

(figure 3).¹ Likewise, horizontal bulk in the posterior can affect the "S" sound, where the lateral borders of the tongue flare upon making the sound. This can result in slurring.²

All-on-4 patients need to be made aware of this compromise. They can often retrain their tongues with time and practice, but it is likely to be a significant source of anxiety for them. If speech is a major concern, clinicians must be prepared to offer alternative treatments, such as a plan that saves healthier teeth and replaces missing teeth with short-span bridges or individual dental implants. If the teeth are terminal, a bridge that only replaces missing tooth structure can be an option. However, this will often require more implants, more bone grafting, and more expensive prosthetics, so patients will need to be prepared for the additional treatment time and cost.

Difficulty adapting to bridge bulk

patients an All-on-4 model and then a model of a traditional bridge (they’ll get the idea even if it’s tooth-borne) (figures 4 and 5). If the bulk will be an issue, then they should consider options that only replace tooth volume. Due to the reduced bulk of these restorations, both vertically and horizontally, more implants likely will be required to support the bridge to reduce pontic spans and the risk of fracture. Distal cantilevers may need to be shortened and the implants placed more posteriorly, which could result in the need for grafting. Patients may choose the traditional All-on-4 bridge after consultation due to lower cost and reduced treatment time. In any case, patients are more likely to accept any compromises when they have options to choose from and know about any limitations prior to treatment.

Proprioception

With teeth, feedback from PMRs assists with refined motor movements, so chewing efficiency is improved. With dual-arch implants, less refined movements result in poorer chewing efficiency and greater stress on the restoration and implants due to angled forces.⁷

being subjected to the traumatic forces of the opposing implant-supported bridge.

Parafunction

Parafunctional habits—such as bruxism, clenching, and irregular chewing cycles—may impact your treatment decision. As discussed in the last section, teeth can detect forces much more readily than implants.⁹ Including a few saved natural teeth in your treatment plan may enable patients to sense the parafunction better (figure 7), which will increase the chances of them modifying the negative behavior.

If it is necessary to replace all of the teeth when parafunction is present, you may want to consider recommending a bar-supported overdenture (figure 8).

This is still technically an All-on-4 procedure, but it may be a modification from your patients' visions of fixed bridges. I use bar overdentures for patients who brux aggressively. The overdenture can be removed at night and replaced with a flat-planed night guard that snaps onto the bar for retention. This protects the final prosthesis and reduces strain on the supporting implants and bone.

High caries index

It’s an all-too-common scenario: A patient presents with an upper full denture—maybe even an upper All-on-4—and decayed and missing lower teeth. The patient wants a lower All-on-4 fixed bridge. He has a square-shaped jaw, likes to eat steak, and you suspect he’s a bruxer. Teeth Nos. 18, 19, and 30 are fractured to the gumline, having had previous root canals and crowns. Tooth No. 31 has furcation involvement and is mobile. Teeth Nos. 23 through 26 are covered with calculus and have 7 mm pockets, but teeth Nos. 20 through 22 and Nos. 27 through 29 have minimal bone loss and mobility. Should you save the teeth? What are the risks and benefits?

These are my thoughts: If the bicuspids and canines have minimal mobility and are mostly intact (perhaps one needs a crown and one needs a filling), then I would consider saving them. The risk of developing further periodontal disease or failure from decay is likely less than the risk of fracturing the prosthesis or damaging the implant/bone complex due to overly aggressive chewing or parafunction.

Now, let’s consider the same scenario, except five of the six bicuspids and canines have Class V decay, four have interproximal decay, and the teeth are covered in plaque. The cavities aren’t that big—you can fix them—but how are you feeling about the future prognosis? I’m an optimist, but my optimism has gotten me into trouble in cases such as these. It’s difficult to change a habit. And in this scenario, we are asking the patient to improve his home care, visit the dentist more frequently, and significantly reduce his sugar intake. That’s a lot to ask. The risk of losing these teeth to decay in the not-too-distant future likely exceeds the risk of prosthesis fracture or bone loss. Maybe the best treatment for this patient is an All-on-4 bar overdenture. Aside from the ability to lessen stress, this treatment will accommodate a simplified oral hygiene protocol. You will want to invest plenty of time with this patient prior to the final treatment decision.