How to Calculate the Decayed, Missing & Filled Teeth Index Ratio

The decayed, missing and filled teeth (DMFT) index is used to describe the prevalence of dental decay in adults. The index includes an individual's number of decayed, missing and filled permanent teeth to quantify his amount of dental decay. Because the presence of third molars, or wisdom teeth, varies throughout the population, considering them in the calculation is not advised.

Things You'll Need

• Dental examination data
• Dental radiographs
• Calculator (optional)

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Instructions

• 1

  Bitewing X-rays help to illustrate decay between two teeth.

  Count the number of teeth that have existing dental decay by using the individual's dental examination data and dental radiographs. The presence of at least one cavity in one tooth means it must be counted.

• 2

  Radiograph showing that 28 teeth are present

  Count the person's number of teeth that are missing using the dental examination data and dental radiographs. A person should have 28 teeth, not including four wisdom teeth.

• 3

  X-ray of three teeth with fillings

  Count the individual's number of teeth that have a filling or fillings using the dental examination data and dental radiographs. Fillings include tooth-colored fillings, silver-colored (amalgam) fillings, crowns and veneers. If a tooth has at least one of those fillings, then include it in this tally unless it also has decay and was included in the tally for decayed teeth.

• 4

  Add the number of decayed teeth, missing teeth and filled teeth. The total should not exceed 28 because wisdom teeth should not be included in the calculation.

• 5

  Using a calculator can help you determine the final DMFT index ratio.

  Divide the total number of decayed, missing and filled teeth you counted by 28 to find the person's DMFT index ratio. Multiply the resulting ratio by 100 to determine the percentage of decayed, missing and filled teeth. If an individual's total number of decayed, missing and filled teeth is seven, for example, then divide seven by 28. The resulting DMFT ratio is 0.25. To convert that individual's DMFT ratio into a percentage, multiply 0.25 by 100, yielding a DMFT of 25 percent.