Researchers are more likely to report positive results about dental treatments if they get paid by the companies marketing the treatments, a new study suggests.
In an analysis of 135 randomized clinical trials from leading dental journals, those in which the authors had a conflict of interest were 2.4 times more likely to have positive results, the study shows.
Researchers from Chile and Canada reported the results at the International Association for Dental Research (IADR) 91st General Session and Exhibition in Seattle, Washington.
University of Toronto researcher Romina Brignardello-Petersen, DDS, told that she was not surprised by the results. “It has already been observed in medicine,” she said. “In some dental specialties there is a lot of potential financial gain.”
A Difficult Problem
Dr. Brignardello-Petersen and her colleagues began by identifying the 10 dental journals with the greatest 2011 impact factors as rated by Journal Citation Reports (Science Edition). Only 7 of these had published a randomized clinical trial in the past year, so the researchers narrowed their study to these: Clinical Implant Dentistry and Related Research, Journal of Dental Research, Dental Materials, Journal of Clinical Periodontology, Journal of Dentistry, Journal of Endodontics, and Oral Oncology.
They then identified 135 randomized clinical trials reported in these journals and looked at which authors had a conflict of interest. They defined a conflict of interest by broad criteria as one in which an author had any type of financial relationship with a company that was being evaluated, including funding to pay for the trial, funding for the author to present the results, and other types of grant.
They defined a conflict of interest by narrow criteria as a more direct financial relationship, such as an author who is an employee, paid consultant, or stockholder of the company being evaluated.
Dr. Brignardello-Petersen acknowledged that some researchers have other kinds of conflicts of interest, such as a personal stake in the outcome, but she and her colleagues could not measure this in their study.
They found that authors in 37.78% of the studies had broad conflicts, and authors in 30% of the trials had a conflict by narrow criteria. Overall, 57.78% of the trials had positive results.
The 2.4-fold increased likelihood of a positive result in which there was a conflict of interest by broad criteria was statistically significant, with 95% confidence that the likelihood was between 1.5 and 5.02 times higher.
They found that authors who had a conflict of interest using the narrow criteria were 12.25 times more likely to report a positive result (95% confidence interval, 1.56 – 96.11).
But the problem is a difficult one to address, said Dr. Brignardello-Petersen. “I think that unfortunately, it would be very hard to conduct clinical research if there was no sponsorship,” she said. “Randomized clinical trials are expensive to conduct, and researchers have a bigger opportunity to conduct research if they work with one of the companies.”
Government funding is meager in dentistry because most oral diseases are not immediately life-threatening.
Dental journals typically ask researchers to disclose conflicts of interest. “Besides being transparent about conflicts of interest and about the way the research was done, the rest is up to the reader,” Dr. Brignardello-Petersen said.
But many readers do not know how to assess the evidence critically, she said. “To be completely honest, probably it does have a big impact because most people who use the literature are not accustomed to doing critical analysis of it.”
On the other hand, Marjorie Jeffcoat, DMD, a former editor-in-chief of the Journal of the American Dental Association and past president of IADR, told that she is confident existing safeguards will keep the dental literature from being distorted. For example, when she worked at the Journal of the American Dental Association, the editors asked researchers not only whether they had a conflict of interest but also how they would manage the conflict.
“Most of the research comes out of industry,” said Dr. Jeffcoat, who was not involved in this study. “That’s who does it.”
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