An optical illusion that can make the area of tooth decay appear larger tricks dentists into drilling bigger holes than necessary, a study has found.
An Australian visual perception expert teamed up with New Zealand dentistry researchers to determine whether visual illusions affect dental treatment.
The study, published in the journal Plos One, involved eight New Zealand dentists preparing 21 teeth for root canals by drilling cavities in each.
Professor Robert O'Shea, a psychology expert in visual perception from Southern Cross University, says all of the dentists drilled larger holes than necessary.
He said this was due to an optical illusion which makes a small enclosed area (the decay) appear larger when surrounded by a larger area (the tooth).
"We do not know if dentists are aware of this," Prof O'Shea said.
"The critical aspect for the illusion is the ratio between the size of the tooth and the size of the small area.
"We think that dentists think, either consciously or unconsciously, after they have made a hole of a particular size: 'That looks rather small - I need to make that hole bigger'."
Dental researcher Nicholas Chandler, an associate professor at New Zealand's University of Otago, says removing more of the tooth than required can lead to the tooth splitting or cracking.
Prof O'Shea says in light of the new research dentists should consider measuring the area that needs to be drilled, rather than relying on their eyes to determine how big the hole needs to be.
The study could be helpful to other healthcare providers, such as doctors, to ensure as much healthy tissue is saved as possible when carrying out treatment, he says.
"It is important for them to know that their eyes can deceive them into removing more healthy tissue than necessary," he said.
© AAP 2018