The hole truth

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The holes you drill are too big because an optical illusion which makes a small enclosed area (the decay) appear larger when surrounded by a larger area (the tooth).
The holes you drill are too big because an optical illusion which makes a small enclosed area (the decay) appear larger when surrounded by a larger area (the tooth).

A new study has found dentists may be visually tricked into drilling larger holes than necessary in teeth. The study, published in the online journal PlosOne, was led by Professor Robert O’Shea, from the Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Southern Cross University. He studied eight New Zealand dentists preparing 21 teeth for root canals by drilling cavities in each.

The results are important, he wrote in the abstract for the study, because “health care depends, in part, on the ability of a practitioner to see signs of disease and to see how to treat it. Visual illusions, therefore, could affect health care. Yet there is very little prospective evidence that illusions can influence treatment.”

His findings were that 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 told a local newspaper in this report.

“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, also told the newspaper that 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.

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2 COMMENTS

  1. This study is seriously flawed in many aspects.

    A very small sample size of eight dentists and then concluding that “all dentists drill larger holes than necessary” leaves a lot to be desired. Having all dentists in the one jurisdiction (all from New Zealand) would also create bias which was not mentioned.

    Maybe the Professor should stick to their own field because they clearly know nothing about dentistry.

    To choose root canal therapy to illustrate such flawed statement shows a serious lack of knowledge in the field in which the professor is trying to conclude. Root canal therapy requires the removal of tooth necessary to access the canals so that a necrotic, pulpless or pulp that is irreversibly inflammed can be removed, disinfected and filled. An access cavity needs to remove that amount of tooth in order to achieve this outcome, regardless of whether that part of the tooth is healthy or infected. Many molar teeth can have up to four or even more root canals and without accessing these canals, the root canal system will still remain infected. In root canal therapy, its call about access and disinfection which may require removal of healthy tooth to access these canals ie- especially in deep narrow decayed teeth

    furthermore, reference to removal of more teeth results in splitting and cracking is true. However, the context is unrelated to the procedure that is being described. Most dentists either cusp cap or crown root treated teeth so that this is not an issue.

    The results are skewed. Concluding that “health care depends, in part, on the ability of a practitioner to see signs of disease and to see how to treat it” completely fails to mention a much LARGER part in health care in that knowing the procedure necessary and the possible complications involved in treating such disease. Again, this goes to the nature of knowing the field of dentistry and is an issue of informed consent.

    Its surprising that this study made it through a rigorous peer review process.

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