The great thing about medical school cadavers is that they can't die.

If a surgeon in training makes a mistake, there's always next time. It is the last environment where medical errors have no consequences.

But 3D printing is changing that, giving even experienced operating room teams valuable practice on a model that looks and feels like the real thing. It has life-saving and life-altering implications.

Violet Pietrok was born two years ago with a rare deformity called a Tessier cleft. The bones that normally join to form the fetal face had not fused properly.

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As a result, Violet's eyes were set so far apart, her vision was more like a bird's than a human's. She also had no cartilage in her nose.

Dr. John Meara has begun Violet's series of surgeries. (Boston Children's Hospital) But the corrective operation is extraordinarily complex. So Violet's family turned to one of the world's leading reconstructive surgeons, Dr. John Meara, at Boston Children's Hospital.

He warned them of the danger of making sophisticated cuts through the skull, very close to the optic nerve. "They might be very close to the brain," Meara explained in an interview. "So the ability to make these cuts on the model first and see the trajectory of a sawblade or where that cut would come through in relationship to the eye is absolutely critical."

To get that model, the simulation team at Boston Children's took multiple MRIs of Violet's skull and replicated it on a 3D printer.

It took more than a day to print, but the model is exact. Even the density of the bone is precise.

"We were actually able to do the procedure before going into the operating room," Meara said.

"So we made the cuts in the model, made the bony movements that we would be making in Violet's case and we identified some issues that we modified prior to going into the operating room, which saves time and means that you're not making some of these critical decisions in the operating room."

During the surgery earlier this year, Meara kept a model of Violet's skull close by and referred to it as he went through the complicated steps of the operation. This successful surgery was just the first of several that will be needed to remake Violet's face.

Other hospitals are interested

Boston's success has prompted a lot of calls from hospitals around the world looking to set up their own 3D printing simulations to Dr. Peter Weinstock, who runs the Boston program.

He equates medicine with sports teams. Any team worth its salt, he says, practises before the game.

"We looked at that and thought, why is health care not doing that? If you can see the patient before you see the patient, if you can do the operation before you do the operation, you have the opportunity to tailor your approach, to tailor your team to the specific environment and event. Think about that opportunity."

Weinstock's printer now runs 24/7 preparing for procedures at Boston Children's — well worth the $400,000 investment.

The models are game-changing — giving a whole new meaning to personalized medicine. With each new print, the models are getting more sophisticated. Soon, the replicated veins and arteries will bleed as they would in real-life.

Boston Children's has also found better recovery times. Patients of surgeons who've practised on the models typically leave hospital sooner and get back on their feet more easily.

Weinstock's simulation program really took off a few years ago with Surgical Sam, the world's first operable infant mannequin.

A model of an individual

But Weinstock wanted not just a model of generic human but one of a specific person.

That's also what Adam Stedman needed. Adam was born with arteriovenous malformation or AVM, a tangled mess of arteries and veins in the brain that restricts blood flow and prompts progressively worse seizures that can cause brain damage.

He could have had a stroke at any moment, or a hemorrhage, his mother Amy tearily explained. But surgically tackling the web of tubes inside Adam's brain was also potentially deadly, or it could leave him blind.

The 3D printer re-created Adam's brain — including the AVM — something his surgeon could hold, manipulate, examine, re-examine and ultimately, practice on.

The surgery was a success — taking only a third of the expected time because the entire operating room team had done it before just hours earlier on the practice model.

When Adam came out of the OR, he smiled and his mother broke down. "He just has a blind spot," she said in an interview in her Connecticut home. To her, that's a big improvement.

"I honestly think that the 3D printing has the majority to do with that, as far as where they knew, where to cut and where not to."