A mask made on a 3-D printer proved instrumental in healing a California puppy's face after it was severely injured in an attack by another dog.

Loca, a 4-month-old Staffordshire bull terrier, arrived at University of California Davis' School of Veterinary Medicine with a fractured jawbone and cheekbone, as well as a damaged temporomandibular joint (TMJ). The TMJ connects the jawbone to the skull. Loca's doctors weren't too worried about the TMJ — it would almost certainly be fine thanks to Loca's age and natural bone growth — but they saw the seriousness of her other injuries as an opportunity to try a new face mask that had been developed in partnership with the university's biomedical engineering (BME) students, according to a statement released by the university.

A mask that's also a cast

The veterinary hospital's Dentistry and Oral Surgery Service (DOSS) had been working with UC Davis' BME students to design something that would assist in healing face and jaw injuries, the same way a cast helps legs recover from fractures. Basically, the mask would keep bones in place, but it would have to be unique to each patient. The result of that work was the Exo-K9 Exoskeleton, a 3-D printed mask.

When Loca arrived, vets alerted BME students to be ready to print the first-ever Exo-K9 should a computerized tomography (CT) scan reveal that she would be a candidate for the mask. Once under general anesthesia, Loca's doctors performed a cone-beam magnetic resonance imaging test to ascertain the extent of her injuries. In addition to the damaged TMJ and the fractured jawbone and cheekbone, doctors found a small fracture along Loca's neck. They performed a short surgery to remove bone fragments.

While she recovered from surgery, BME students used her CT scan to create an Exo-K9 that "would precisely fit her head, and could optimize the healing process,"

The very next day, after the mask was completed, students walked the half-mile to deliver the mask to the School of Veterinary Medicine. Loca also was fitted with a neck bandage to stabilize her neck fracture and limit her movements during the healing process. For three days in the hospital, Loca ate soft food and was given pain medication to keep her comfortable.

Road to recovery

Over the next month, Loca had to keep wearing the mask and neck bandage except while she was eating or drinking. Additionally, she wasn't allowed to chew on anything hard, including toys and bones. When she returned to UC Davis for a 1-month checkup, another CT scan was performed to see how she was healing. The TMJ was indeed growing a new bone, but it would require harder kibble to make sure the joint was semi-functional and not fusing to her skull.

The CT scan also revealed that she had two developing molars that required extraction.

Loca after her Exo-K9 was removed The Exo-K9 helped Loca's injuries heal. (Photo: UC Davis Vet Med/YouTube)

After three more months with the mask, another CT scan was performed. The surgery sites were healing well, and the TMJ was growing as it should. Doctors had to remove those two molars, but Loca handled the extraction like a champ.

While Loca was the first dog to use the Exo-K9, other dogs have benefited from 3-D printing. A 15-month-old Labrador named Hanna received a printed tooth after she broke her original one chewing on a bone. The 3-D metal tooth allowed Hanna to go back to eating, but she can't apply too much or play tug-of-war. Another dog, this one in Mexico City, received a prosthetic leg created using a 3-D printer following an accident with a lawnmower.