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Dentists around the world are dying of a rare, incurable lung disease, according to Morbidity and Mortality Weekly Report by the US Centers for Disease Control and Prevention (CDC).

Of total 894 patients, nine patients had been suffering from Idiopathic Pulmonary Fibrosis (IPF) over almost two decades among which seven had already died, as per the CDC report. IPF is described as a rare chronic and progressive lung disease which can be treated but nor cured totally.

Symptoms of IPF include shortness of breath, a dry, chronic cough, weight loss, joint and muscle pain and clubbed fingers or toes.

"Dentists and other dental personnel have unique exposures at work. These exposures include bacteria, viruses, dust, gases, radiation, and other respiratory hazards," Randall J. Nett, lead author of the study told CNN. "At this time, we do not know what caused this cluster of idiopathic pulmonary fibrosis cases in dental personnel."

In the aforementioned case, the nine patients — eight dentists and one dental technician — were referred as a cluster. However, all the IPF patients were treated at a Virginia hospital. Defining the cluster, Nett told CNN, it is a term used to define a collection of cases "grouped in place and time that are suspected to be greater than the number expected."

Although the number of nine patients may not seem a lot — it is just 1 percent of all. But according to Nett, this number "was about 23 times higher than expected."

While the doctors cannot find what caused the scarring condition to the cluster of dentists, some experts have suggested viral infections, cigarette smoking, and occupations where exposure to dust, wood dust, and metal dust are common, as the contributing factors to IPF.

"Although IPF has been associated with certain occupations, no published data exist regarding IPF in dentists," the CDC said. "Dental personnel are exposed to infectious agents, chemicals, airborne particulates, ionizing radiation and other potentially hazardous materials. Inhalational exposures experienced by dentists likely increase their risk for certain work-related respiratory diseases."

Speaking of health hazards related to dentistry, Paul Casamassimo, chief policy officer of the American Academy of Pediatric Dentistry's Pediatric Oral Health Research and Policy Center, told CNN, "We do work with materials and with human bioproducts that are potentially damaging to our bodies if we inhale them,"

Even though CDC investigators have not figured out the reasons of IPF, Nett said, "More work has to be done before we can make any conclusions about the risk dentists or other dental personnel have. CDC will follow up on this newly recognized cluster."