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Nerve repair advances lead to improved restoration of facial sensation

Jun. 9, 2021, 9:00 AM

Nashville resident Sheala Smartt had long thought that her face looked asymmetrical, and as she turned 15, she also began experiencing a troubling sensation.

Oral and Maxillofacial Surgeon Susie Lin, MD, poses for a photo with patient Sheala Smartt, 16, at Belcourt Oral Health Center.

“There was this tightness I felt right under my lip,” she said. “If I were to visualize it, I’d imagine a string connected to two points, and if you were to pull the string right in the middle, that’s the feeling I had. I was describing this to doctors before they found out what it really was. I was super proud of myself because I was right on the mark.”

Smartt, then a freshman at Nashville School of the Arts High School, said the odd sensation didn’t overly concern her dentist or physician, so she focused on school and other activities. Then, her right lower jaw and gums became markedly swollen, and she and her family sought an answer for the dramatic change.

It was discovered that a benign tumor had been growing steadily, destroying part of her lower jaw and even displacing teeth, and Smartt was referred to Susie Lin, DDS, MD, an assistant professor in the Vanderbilt University Medical Center Department of Oral and Maxillofacial Surgery.

Lin knew removing the tumor would require transecting or cutting the third division of the trigeminal nerve, if it hadn’t already been damaged by the tumor. The trigeminal nerve’s third division includes the inferior alveolar and the mental nerves which supply sensation to the lower teeth, lip, chin, and part of the gums.

Recent advances in allograft nerves — nerves harvested from human donors — combined with advances in complex microsurgical repair now allow Lin and other VUMC oral and maxillofacial surgeons to more successfully restore feeling to patients’ faces after trigeminal nerve damage.

An injury to the trigeminal nerve — the largest and most complex of the cranial nerves — can be caused by trauma, such as a gunshot or vehicle accident; tumor growth and removal; removal of wisdom teeth, and more rarely, local anesthetic injections. Increasingly, dental procedures such as the placement of implants also cause injury to this critical nerve.

While a trigeminal nerve injury typically results in loss of sensation, in some cases these injuries cause debilitating neuropathic pain that disrupts everyday activities such as eating and drinking, brushing teeth, shaving and applying makeup, Lin said.

“Dental and oral surgical treatments often involve procedures being performed near the third division of the trigeminal nerve, and despite using the best care and techniques to reduce the risk of injury, dental providers who limit their practice to low-risk procedures, such as dental restorations, fillings, and root canal treatments, see an average of about two trigeminal nerve injury cases during their career,” said Lin. “In a dental practice with specialists performing root canal therapy, removal of impacted teeth or dental implant placement, they will definitely see more of this type of injury.”

According to the American Academy of Implant Dentistry, approximately 500,000 individuals in the United States get dental implants annually. As digital technology continues to improve to support these procedures, dental implants are predicted to continue increasing.

VUMC’s oral and maxillofacial surgeons care for patients with facial trauma and perform orthognathic surgery, which corrects jaw irregularities and realigns the jaws and bite. These specialists also perform benign tumor and cyst resection and reconstructive surgery, so they are very familiar with measures to preserve and, in some cases, repair the trigeminal nerve.

When trauma or surgery causes an open or witnessed injury to the trigeminal nerve, prompt referral to a specialist is critical, but a closed injury in which nerve injury isn’t witnessed or suspected can delay such a referral. That’s why it’s important for people to report and seek treatment for persistent facial numbness or pain, especially following a dental or facial procedure, Lin said.

“Individuals with a closed injury need to be monitored closely for four weeks after the suspected injury occurs,” Lin said. “During that time, we recommend neurosensory testing to see if they regain sensation. If there’s no significant improvement at the four weeks’ mark, then there needs to be a referral to a specialist. If surgery is indicated, it should ideally be performed within three months of the injury. Surgery is recommended even sooner if a branch of the nerve has been cut.”

After successfully removing the tumor in Smartt’s face, Lin used an allograft nerve to bridge the gap between the ends of the remaining nerve. Performing the nerve graft during the same surgery as the tumor resection is a new service at VUMC.

In the past, nerve autografts were used in which a nerve segment from another part of the patient’s body was relocated to the injured area. Using an autograft meant the donor area would be left with reduced sensation and two surgical areas needed to heal rather than just one.

Using nerve allografts from human donors is an increasingly popular alternative, evidenced by published clinical data showing favorable outcome comparisons with other techniques. Previously these allografts required immunosuppressive therapy after surgery to prevent rejection, and they were not often successful if the nerve gap was larger.

Decellularized nerve allografts have been developed in recent years in an effort to eliminate the need for immunosuppression. Human nerve tissue is carefully processed to make the grafts less likely to be rejected while retaining the structure necessary for nerve regeneration.

In Smartt’s case, the resulting nerve gap was “very sizeable” at about six or seven centimeters, Lin said. After more than 10 hours of surgery to remove the tumor, connect the nerve graft and relocate bone from Smartt’s hip to become part of her new jaw, Lin and Smartt documented the slow, but steady return of facial sensation during follow-up appointments.

“If you were to circle around the bottom part of my lip, slowly the circle with no feeling got smaller and smaller until only the tiny part in the middle was where it couldn’t feel,” Smartt said. “Now, it’s completely back.”

More than a year after the initial surgery, Smartt is ready for the next steps. She’ll have bone grafts to further reinforce her lower jaw, followed by dental implants to replace missing teeth.

“I’d like to commend all doctors and everyone working with me,” she said. “I was super shy, so I appreciate them being confident and making me feel confident in the procedure. I definitely appreciated them wanting to make sure my face was symmetrical, because that was one of my big concerns.”

Smartt said she’s ready to concentrate on finishing high school, then earn earn a paired business and art degree in college. She plans to join a production team creating concept art.

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