Photoacoustic Imaging for Periodontal Probing Depth

Engineering research at the University of California San Diego has led to a technique that could update how teeth and gums are imaged. Researchers combined squid ink with light and ultrasound to create a new dental imaging method to examine a patient’s gums in a more comprehensive and accurate way than existing methods and also non-invasive way. The image can show the entire pocket depth around teeth consistent and accurately without prodding the gums of the patient.

The conventional method for dentists to assess gum health is to use an instrument called a periodontal probe which is a thin, hook-like metal tool that is marked like a tiny measuring stick and inserted in between the teeth and gums to see if the gums have shrunk back from the teeth, creating pockets. This method of measuring pocket depth is considered a gold standard in dentistry. A pocket depth measuring one to two millimeters (mm) indicates healthy gums where as three mm and greater is a sign of gum disease. If the pockets are much greater than 3 mm than there is even more severe gum disease. A periodontal probing depth of greater than or equal to 4 mm or when the attachment of the gum to the tooth (attachment loss) is 3 mm or more is used by  the American Association of Oral and Maxillofacial Surgeons (AAOMS) as a cutoff for when they feel wisdom teeth should be extracted due to the increased risk of potentially developing periodontal disease. For more information on periodontal disease and probing deaths see

A periodontal probe is invasive and can be painful and uncomfortable for patients. Measurements sometimes vary greatly between dentists creating discrepancies of how many mm the pocket depth really is. This can lead to conflicting treatment suggestions. In addition, the probe is only capable of measuring the pocket depth one spot at a time.

The method the researchers developed first has patients rinse their mouth with a paste made of commercially available food-grade squid ink mixed with water and cornstarch. The squid-ink-based rinse serves as a contrast agent for the photoacoustic ultrasound imaging method. Squid ink contains melanin nanoparticles, which absorb light. The melanin nanoparticles get trapped in the pockets between the teeth and gums. A light signal, typically a short laser pulse, is shined and heats up and expands generating an acoustic signal. When researchers shine the laser light onto the area, the squid ink heats up and quickly swells, creating pressure differences in the gum pockets detectable via ultrasound. Such a method enables researchers to create a full map of the pocket depth around each tooth.

The researchers tested the photoacoustic imaging method in a pig model containing a mix of shallow and deep pockets in the gums. The results closely matched measurements using a periodontal probe. However, measurements with the periodontal probe varied significantly from one test to another. The researchers were surprised how accurate their method was compared to the standard approach.

The team is currently collobaring with dentists to further develop this technique. They hope to later expand to testing their method in humans. The researchers also plan to minimize the taste of the squid ink oral rinsem which is a bit bitter, and replace laser lights with LEDs which are cheaper. The team hopes to ultimately create a mouthpiece that uses their developed technique to measure periodontal health. It seems such a mouthpiece will help better answer the question in the future if wisdom teeth should be extracted or retained.

Source: C.Y. Lin and et al., Photoacoustic Imaging for Noninvasive Periodontal Probing Depth Measurements, Journal of Dental Research, 2017.

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