The dentist and the ex-cop first met about five years ago at a pain management seminar at Tufts University.

"He asked me what I was doing there," recalls Carlos Aquino, who spent 23 years on the Philadelphia police force before retiring in 1995 as a sergeant specializing in narcotics investigations. "When I told him, he understood."

Elliot Hersh, a professor at the University of Pennsylvania dental school who specializes in pharmacology, understood so well that he soon had Aquino lecturing his students on the dangers of overprescribing painkillers, including opioids such as Percocet and Vicodin.

"He said he wanted me to scare the hell out of them," said Aquino, who also worked for the Drug Enforcement Administration and now advises pharmacies on DEA compliance issues.

Every fall, Aquino spends a couple of hours with Hersh's pharmacology class, explaining what can happen to patients who overuse opioids and to dentists who illegally prescribe them. Hersh devotes 12 hours to this subject in an 88-hour course.

They are part of a nationwide push to get dental schools to help fight opioid addiction.

In April, U.S. Surgeon General Vivek Murthy announced a campaign that included a special plea to dentists and other medical professionals.

A Harvard research team reported recently in the Journal of the American Medical Association (JAMA) that "dentists are among the leading prescribers of opioid analgesics," particularly for surgical tooth extractions.

Hersh points out that some dentists are prescribing opioid combinations that are both unnecessary and less effective than other painkilling drugs. "There are some cases where the pain is so bad you need an opioid," he says, "but it shouldn't be the first thing you prescribe. Opioids have their place but only in special situations."

Hersh said he has found that Advil is usually at least as effective as Vicodin for dental pain. He and his frequent research collaborator Paul Moore of the University of Pittsburgh are hoping to conduct a larger study to confirm this and similar findings.

Back in 2011, they wrote in the Journal of the American Dental Association, dentists were prescribing 12 percent of immediate-release opioids in the United States.

In another study published in JAMA in 2011, data from 2009 showed that dentists were the largest source of opioid prescriptions for patients age 10 to 19. Hersh says this is the age when wisdom teeth are likely to be removed surgically.

The downside of opioids is well-known: They are potentially addictive, can lead to the use of street drugs such as heroin, and can have side effects such as nausea, vomiting, constipation and dizziness. Drugs prescribed for adults can find their way into the hands of children.

Why, then, do dentists frequently prescribe them?

In some cases, Hersh says, nonsteroidal anti-inflammatory medicines have side effects that some patients can't tolerate. Naproxen and Aleve, for example, can cause stomach issues. Acetaminophen should not be prescribed for anyone with liver disease.

But except for these cases, Hersh blames habit: Some practitioners have been writing opioid prescriptions for years and haven't kept up with the effectiveness of alternate drugs.

In other cases, they are anticipating a pain level that might occur in only a small minority of patients. For this he cites "patient expectation" as a major cause of overprescribing.

"They want a strong pain reliever and they have a perception that something with an opioid is better. And the dentists and physicians cave in."

Patient demand is a bigger factor in recent years with the spread of clinician-rating sites on the internet: An unhappy patient delivers a bad rating that can damage a dental or medical practice.

And then there are the patients seeking opioids to feed a drug habit - which in many cases started with a painkiller prescription.

George Downs, dean emeritus at the University of the Sciences, says that in about 85 percent of cases, a well-trained physician, dentist or pharmacist should be able to spot addiction.

Hersh says that warning flags include patients who come a long way to see a dentist for no discernible reason, who want to pay only in cash, or who claim to have a list of ailments that preclude about every over-the-counter pain management drug.

"Some of them know their pharmacology better than the physician or the dentist," he says.

Aquino said that in his law enforcement career he saw cases in which patients were so desperate to get drugs from a dentist that they sliced their gums so they would get infected.

Improvements in electronic record-keeping are making doctor-shopping more difficult, Hersh says, but there is still room for error.

State health guidelines adopted last year and endorsed by the Pennsylvania Dental Association call on dentists to refer patients with chronic pain to pain management specialists.

Aquino says he warns dental students to stick with what they know.

"Your field is dentistry, not pain management," he tells them. "But if you get involved in pain management, you'd better do a lot of education on it."