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Craniofacial Implants and Prosthetics by Dr. Vladimir Frias

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Categories: Prosthodontics;
Craniofacial Implants and Prosthetics 

The digital revolution has helped dentists create lifelike prostheses even outside of the mouth

by Dr. Vladimir Frias

Soon after I graduated from dental school and was preparing to join my prosthodontic program, I happened to mention to a patient that I was going to leave my associateship because I was returning to school to specialize. The patient smiled and said, “That’s great! Do you, um, specialize in different kinds of teeth?”

Of course, I was taken aback. This was a reasonably well-educated lady who had been through four years of orthodontics and had four wisdom teeth removed and yet, despite her interactions with at least two dental specialists, she had no idea that there were dentists who had chosen to limit their practices to eliminate gum disease, straighten teeth or treat root canal infections.

It comes as no surprise to me, then, that patients often turn up to Roswell Park’s maxillofacial clinic with a concern that they’re in the wrong place. Obturators and mandibular resection prostheses are easier to relate to in a dental setting because, of course, there are teeth involved. But when patients are missing a nose or an eye, it often seems to be a stretch that their treating doctor is a doctor of dental surgery.

I often explain it to them in the same way that I explain it to other doctors and dentists who have an interest in facial reconstruction: Craniofacial implants are a derivative of dental implants, and the rules and procedures for placing them are similar. ENT and plastic surgeons can place them, but dentists and oral surgeons place them every day.

This extrapolates to the actual prosthetic. Dentures and facial prostheses start with a physical or digital impression. The sculpting and processing of both are also similar and so are the adjustments at delivery. Who better than a dentist to create these prostheses? Last but not least, I am proud to tell patients and other doctors that the originator of modern facial prosthetics, Dr. Arthur Bulbulian, and the originator of modern plastic surgery, Dr. Varaztad Kazanjian, were not medical doctors but dentists who began their careers working on denture prosthetics.

Why not plastic surgery?

Most patients and many doctors assume that the field of plastic surgery has evolved to a point where a facial prosthesis is no longer necessary. However, there are many limitations on the plastic surgical reconstruction of facial defects, and in some cases plastic surgery is used as an adjuvant, not as a primary treatment. In other cases, the defect is restored entirely with a prosthesis. Plastic surgery cannot replace the contents of the eyeball, or an entire nose or ear when the bone and cartilaginous support is missing, and in general, the larger the defect is, the more likely prosthetic intervention will be required.

Another reason for the use of facial prostheses is if the patient is considered a poor risk for surgery, either because of a systemic medical issue or local reasons such as surgical scarring or radiation treatment to the affected site. The likelihood of tumor recurrence is also a factor, and often the use of a prosthesis is considered advantageous because it allows oncologic surgeons to visually inspect the resection site at recall visits.

Adequate communication with the head and neck oncologic surgeon or plastic surgeon before surgery is extremely important, especially when plastic surgical procedures are combined with a prosthesis. Over- or underfilling a surgical defect with grafted tissue can change the outcome of a prosthetic reconstruction drastically, and this becomes even more important when implants are part of the treatment plan. Having the maxillofacial prosthodontist in the operating room to surgically place the implants or to ligate a surgical prosthesis at the time of ablative or reconstructive surgery makes the delivery of treatment seamless and improves the final result.

The advent of implants

Most facial prostheses used to be created with anatomical or adhesive retention to keep them in place. I have found this to be the most discouraging part of wearing a facial prosthetic for most patients. Any kind of moisture—be it sweat, rain or a dip in the pool—will loosen the adhesive and cause the prosthesis to dislodge. The use of spectacles or other mechanical retention is uncomfortable and, of course, the moment the spectacles dislodge, so does the prosthesis.

The advent of craniofacial implants did as much for the field of facial prosthetics as it did for intraoral prosthodontics by giving us a reliable method to affix prostheses to tissue. The first craniofacial implants were based on the Branemark intraoral implant except that they had much shorter lengths (3–4 mm) that allowed placement into the mastoid, orbital or nasal bones. Current versions like the Vistafix 3 implant by Cochlear Limited possess a beveled flange that can be recessed against the cortex for support and allows for smooth tissue coverage (Fig. 1).

A cylindrical tissue-penetrating abutment similar to a multiunit abutment can be placed at the time of initial surgery or at a second stage through a punch incision. Impression material such as vinyl polysiloxane is often used to capture abutment copings (Fig. 2), then encased in a layer of fast-setting stone, acrylic or rigid impression material to prevent the impression from flexing during pouring.

Craniofacial Implants and Prosthetics
Fig. 1
Craniofacial Implants and Prosthetics
Fig. 2
 

The result is similar to a splinted intraoral implant impression where transfer copings are embedded in a representation of the surrounding soft tissues (Fig. 3). Abutment analogs can then be attached (Fig. 4) and once a stone model is created, a magnetic or a bar-and-clip-style attachment system can be fabricated by soldering prefabricated components or casting wax patterns (Fig. 5). I prefer bar-and-clip retention in young patients with enough dexterity to lock the clips onto the bars and access the tissues beneath for hygiene. Magnets work well in patients with poor dexterity and poor hygiene habits; however, they have reduced retentive values.

Craniofacial Implants and Prosthetics
Fig. 3
Craniofacial Implants and Prosthetics
Fig. 4
Craniofacial Implants and Prosthetics
Fig. 5
 

Fig. 6 shows the postoperative view of a patient with a postoncologic defect after implant placement and magnetic abutment connection. Magnetic retention devices can be picked up in an impression and a silicone prosthesis is created from a wax pattern using investing and processing techniques similar to denture laboratory techniques (Fig. 7). After final coloration, the prosthesis can then be delivered to the patient (Fig. 8).

Craniofacial Implants and Prosthetics
Fig. 6
Craniofacial Implants and Prosthetics
Fig. 7
Craniofacial Implants and Prosthetics
Fig. 8
 

Digital techniques in facial prosthetic construction

The traditional method of creating an impression-based moulage is often uncomfortable to the patient, because of the presence of highly sensitive residual structures. The use of digital techniques such as CT-derived data or laser scanning in the creation of facial prosthetics improves not only the workflow but also the comfort level of patients during the capture.

Using technology to replace physical impressions is only part of the digital revolution in facial prosthetics. The impressions can also be digitally altered as necessary and models, frameworks and molds can be printed in resin while patterns can be printed in wax.

In this case, a patient presented after rhinectomy with very sensitive nasal tissue (Fig. 9) and a digital impression was created and modified (Fig. 10). A digital framework was then created (Fig. 11), and replicated as a physical model with matching resin framework (Fig. 12). The wax pattern can be printed from a presurgical scan or completed by hand (Fig. 13).

Craniofacial Implants and Prosthetics
Fig. 9
Craniofacial Implants and Prosthetics
Fig. 10
Craniofacial Implants and Prosthetics
Fig. 11
 

Craniofacial Implants and Prosthetics
Fig. 12
Craniofacial Implants and Prosthetics
Fig. 13
 

Most final processing of silicone is still done by hand, because of the poor aesthetics of printed silicone or flexible resin; however, improvements in these technologies virtually ensure the application of directly printed prostheses in the future. Another time-saving digital technology is the Spectromatch shade system, which allows the recording of a patient’s skin color with a click and replicates this in silicone, again saving the significant chair time involved in manually matching shades (Fig. 14).

Because all the sculpting, silicone processing and painting is done chairside by the dentist and not by a laboratory technician, the use of digital technologies helps improve the efficient delivery of care and cost of production of these prostheses, and the final result can be a lifelike durable prosthesis (Fig. 15) with minimal investment of time by the patient or provider.

Craniofacial Implants and Prosthetics
Fig. 14
Craniofacial Implants and Prosthetics
Fig. 15
 

Orbital prosthetics are often not quite as amenable to an entirely digital workflow due to the fact that the iris, the sclera and the silicone replacement of the surrounding bone and tissue are replaced with separate prosthetic components; however, digital techniques can also be used as part of the treatment.

In this case, a patient had his eyeball and part of his eye socket removed because of a meningioma and the resultant defect was overfilled with grafted tissue (Fig. 16). There was no room to place implants and the conventionally created prosthesis (Fig. 17) was overcontoured. The patient complained that the extra weight of the prosthesis caused it to detach even with routine reapplications of the adhesive, and he was especially conscious that it had a protruded appearance.

Craniofacial Implants and Prosthetics
Fig. 16
Craniofacial Implants and Prosthetics
Fig. 17
 

To reduce the contours, the impression was scanned in a laboratory in a box scanner (Fig. 18) and the entire base of the prosthesis was created in a single piece of printed resin with a virtual location for the pupil. The iris was then hand-painted and attached with cyanoacrylate (Fig. 19), and a soft-tissue overlay was then waxed and processed conventionally. The added space from the printed base and the use of shadowing techniques in the borders of the extrinsic coloration give the illusion of a prosthesis that seats further into the eye socket (Fig. 20).

Craniofacial Implants and Prosthetics
Fig. 18
Craniofacial Implants and Prosthetics
Fig. 19
Craniofacial Implants and Prosthetics
Fig. 20
 

The future of digital prosthetics

I think we aren’t far off from a touchfree facial prosthetic where scanned facial structures can be used to create digital prosthetics that can be virtually tried onto a patient. The approved patterns can then be converted into a printed prothesis, colored and delivered with minimal chair time. Because the lifetime of silicone prostheses is short—many last only a year before requiring replacement—and because many patients travel from hours away for treatment, the ability to fabricate multiple duplicate prostheses from digital images or scans is a huge advantage.

But why stop there? The most important application of digital technology in maxillofacial prosthetics will be the printing of resorbable 3D scaffolds for human stem cells. Currently confined to lab experiments, the use of digital scans and 3D printing will allow us to replicate the form and contour of a patient’s missing oral and facial structures in a bioresorbable structure that can be used as a scaffold to grow a patient’s own skin, cartilage and bone. These lab-grown replacements can eventually be grafted onto a patient to reconstruct a defect or to replace his or her prosthesis. It sounds like science fiction, but we are currently able to grow all the individual cellular materials required, and it will only be a matter of time before we are able to re-create entire structures in replicant anatomy.

I’ve heard some dentists joke that by inventing and using digital technologies, we will soon put ourselves out of business, but I think it actually goes the opposite way. Clinging to old-fashioned treatments and methods ensures our demise as a profession; the adaptation and use of new technology not only improves outcomes for our patients but also ensures that dentistry stays relevant as a medical specialty in the future.

Acknowledgment
The author thanks Andy Jakson, Colin Chairmonte and the team at Evolution Dental for their expertise in the scanning and printing of the prosthetic frameworks.

Author Bio
Vladimir Frias Dr. Vladimir Frias received his Doctor of Dental Surgery and Master of Science degrees from Columbia University, where he completed specialty training in prosthodontics, followed by fellowships in maxillofacial prosthetics and surgical implantology. Frias, a diplomate of the American Board of Prosthodontics, has been published in multiple scientific journals in the fields of craniofacial and implant reconstruction. His current research includes 3D printing for craniofacial cellular frameworks. He maintains a private practice in prosthodontics and implant surgery and is the director of maxillofacial prosthetics at the Roswell Park Comprehensive Cancer Center in Buffalo, New York.
 

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