10:42am Wednesday 19 February 2020

Mathematics provides better attachment for dental crowns

 The method is expected to result in significantly cheaper and faster treatment, with reduced risks of patients having problems with their crowns.

Each year, dentists put hundreds of thousands of new dental crowns into the mouths of Swedish patients. First they have to grind down the teeth to which the crowns are to be attached. This is a  ”handicraft” job that currently is entirely dependent on the individual dentist’s eye and skill. But dentists will soon benefit from a computer program being produced by a group of researchers at Chalmers, at the initiative of the company Nobel Biocare. The researchers are now planning to run clinical tests.

“In our software, you can feed in the existing tooth’s measurements, done by laser scanning the tooth,” explains Chalmers researcher Evan Shellshear. ”The software then calculates how much of that tooth should be ground down, and the output is a 3-D model of the optimal shape of the tooth. You also get a 3-D animation showing precise suggestions for manoeuvring the grinding tool in order to achieve the objective without colliding with the teeth or mouth parts.”
The software is based on advanced mathematical models and on state-of-the-art visualisation technology. The researchers have based their work on international guidelines for how teeth should be shaped before being fitted with dental crowns. The guidelines cover things like the ratios between the height and width of the tooth, and how thick a layer needs to be ground down in order to leave enough space for the crown.
The researchers have converted every guideline into an equation, dividing each tooth into 10,000 sections. From that, the software performs an optimisation, leaving as much of the tooth as possible.
“Most dentists are very skilful, but no human being can achieve this sort of optimisation as efficiently as a computer program,” says the Chalmers researcher and dentist Matts Andersson. “If the tooth does not have a good fit with the crown, bacteria can accumulate in the gaps, resulting in caries and loosening of the teeth. A bad fit can also lead to problems with the jaw joint – or that the dental crown simply falls off.”
The researchers’ new method should therefore reduce the risk of patients suffering such problems. It would also shorten the time needed for treatment, and save large amounts of money.
“I estimate that the treatment sessions would be 10% shorter,” says Matts Andersson. ”That would result in savings of SEK 176 million per year. But the biggest benefit would probably be an improvement in quality, increasing the life of the dental crowns and reducing the number of remakes.”
The Chalmers researchers have also produced 3-D software that dental students can use for learning how to grind teeth. Currently, students have no access to simulation programs with defined objectives. In the new software, the objective is the optimum tooth shape, and those undergoing training will know how close to the objective their effort has come.
The research into tooth grinding is based on methods originally produced for vehicle manufacturing. It takes place at the Wingquist Laboratory, which is part of Chalmers Production Area of Advance.  The research is derived from automatic path planning for industrial robots, something that production researchers and mathematicians at Chalmers are working on jointly with the motor industry.
The project is a cross-disciplinary collaboration, financed by Nobel Biocare and Vinnova. The parties in the collaboration are the Department of Product and Production Development, the Fraunhofer-Chalmers Research Centre for Industrial Mathematics and Nobel Biocare.
Factsheet: The cost of dental crowns in Sweden
Between July 2009 and July 2010, 477,060 dental crown treatments were made in Sweden. The Chalmers researchers have calculated that the treatments cost more than SEK 1.7 billion, of which a large proportion was paid from tax monies through dental health insurance. A crown manufactured in a laboratory costs around SEK 5,000.
For further information, please contact:
Staffan Björkenstam, Fraunhofer-Chalmers Research Centre Industrial Mathematics, staffan@fcc.chalmers.se, + 46 31 772 42 84, +46 73 336 66 95
Evan Shellshear, Fraunhofer-Chalmers Research Centre Industrial Mathematics, evan.shellshear@fcc.chalmers.se, + 46 31 772 42 37
Matts Andersson, Department of Product and Production Development, Chalmers,
manderss@chalmers.se, + 46 31 772 13 21

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