Cavities made by the participants of the study were often made too large, which could be due to the Delboeuf illusion, which makes enclosed areas appear smaller than they actually are when seen in a larger context. (DTI/Photo courtesy of Robert P. O’Shea, Australia)

2013-11-21 | News Asia Pacific

LISMORE, Australia: Objects in a mirror appearing to be farther away than they are is a common illusion encountered by car drivers around the world every day. Misleading visual perception of an object could also be the reason that dentists sometimes drill larger cavities than necessary to fill a tooth or prepare a root canal, a team of psychologists and dental researchers from Australia and New Zealand has suggested.

In clinical field tests involving eight practising endodontic specialists from New Zealand and conducted in 2002 and 2006, the researchers found that dental professionals tend to fall trap to the Delboeuf illusion, which makes enclosed areas appear smaller than they actually are when seen in a larger context. In their case, a cavity drilled into a tooth appeared to be smaller when the surrounding tissue was in range of the parameters of the illusion, leading to more healthy tissue being removed at the expense of patients.

The researchers said in the report that it remains unknown whether dentists are aware of this when drilling but recommended that their findings be incorporated into the early stages of clinical training to decrease the risk of cracking or perforating the root end due to having removed too much healthy tissue. It should also be extended to other fields of health-care treatment that could be affected by visual illusions, they added.

“When operating, health-care providers try to save as much healthy tissue as possible. It is important to know that their eyes can deceive them into removing more healthy tissue than necessary,” lead author of the study and psychology expert from the University of Southern Cross in Australia Prof. Robert O’Shea commented.

Named after its creator, Joseph Remi Leopold Delboeuf, a Belgian scientist, the illusion was first documented in 1865. It has been reported to be used by restaurants to trick customers regarding the size of their dishes by using smaller plates, among other things.

For the latest study, more than 20 extracted and root-filled teeth were treated by each participant, who had not been informed about the parameters of the illusion. The participants were asked to remove as little tissue as possible when preparing the teeth and to use their usual hand instruments.