Mathematics Provides Better Attachment For Dental Crowns

Dental treatment involving crown replacements costs the Swedish tax payers hundreds of millions SEK each year. Researchers at Chalmers University of Technology are developing a new method for determining exactly how to optimally prepare a tooth to place a crown on it. The method is expected to result in significantly cheaper and faster treatment, and improved quality and reliability of the crown replacements.

Each year, dentists put hundreds of thousands of new dental crowns into the mouths of Swedish patients. They firstly have to grind the teeth to which the crowns are to be attached. This is a procedure that is still much of an art and depends completely on the individual dentist's 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.

"With current software, you can measure the damaged tooth's dimensions by laser scanning," explains Chalmers researcher Evan Shellshear. "The software then computes the optimal shape of the ground tooth, and the output is a 3-D visualisation of it. You also get a 3-D animation showing precise suggestions for manoeuvring the cutting tool in order to achieve the final tooth shape safely."

The software is based on advanced mathematical models and on state-of-the-art visualisation technology. The researchers have based their computations on roughly a dozen 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 tens of thousands of sections. From that, the software performs an optimisation, leaving the patient with as much of the healthy 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.