The periodontal probe is the gold standard tool for periodontal examinations, including probing depth measurements, but is limited by systematic and random errors. Here, we used photoacoustic ultrasound for high-spatial resolution imaging of probing depths. Specific contrast from dental pockets was achieved with food-grade cuttlefish ink as a contrast medium. Here, 39 porcine teeth (12 teeth with artificially deeper pockets) were treated with the contrast agent, and the probing depths were measured with novel photoacoustic imaging and a Williams periodontal probe. There were statistically significant differences between the 2 measurement approaches for distal, lingual, and buccal sites but not mesial. Bland-Altman analysis revealed that all bias values were < ±0.25 mm, and the coefficients of variation for 5 replicates were <11%. The photoacoustic imaging approach also offered 0.01-mm precision and could cover the entire pocket, as opposed to the probe-based approach, which is limited to only a few sites. This report is the first to use photoacoustic imaging for probing depth measurements with potential implications to the dental field, including tools for automated dental examinations or noninvasive examinations.

The gold-standard periodontal probe is an aging tool that can detect periodontitis and monitor gingival health but is highly error-prone, does not fully characterize the periodontal pocket, and causes pain. Photoacoustic imaging is a noninvasive technique that can address these limitations. Here, a range of ultrasound frequencies between 16–40 MHz were used to image the periodontium and a contrast medium based on cuttlefish ink was used to label the pockets. A 40 MHz ultrasound frequency could spatially resolve the periodontal anatomy, including tooth, gum, gingival margin, and gingival thickness of tooth numbers 7–10 and 22–27. The photoacoustic-ultrasound measurements were more precise (0.01 mm) than those taken with physical probes by a dental hygienist. Furthermore, the full geometry of the pockets could be visualized with relative standard deviations of 10% (n = 5). This study shows the potential for non-invasive monitoring of periodontal health with photoacoustic-ultrasound imaging in the dental clinic.

The interaction between methylene blue (MB) and sodium dodecyl sulfate (SDS) has been widely studied spectroscopically, but details about their interactions remain unclear. Here, we combined photoacoustic (PA) imaging with nanoparticle tracking analysis (NTA) and spectroscopy to further elucidate this interaction. PA imaging of 0.05 mM MB showed a 492-fold increase in intensity upon the addition of 3.47 mM SDS. Higher concentrations above SDS’s critical micelle concentration (CMC) at 8.67 mM decreased the PA intensity by 54 times. Relative quantum yield measurements indicated that PA intensity increased as a result of fluorescence quenching. Meanwhile, NTA indicated an increased number of nonmicellar MB/SDS clusters at SDS concentrations below the CMC varying in size from 80 to 400 nm as well as a decreased number above the CMC. This trend suggested that MB/SDS clusters are responsible for the PA intensity enhancement. Comparison of PA intensities and spectral shifts with MB/hexadecyltrimethylammonium bromide, MB/sodium octyl sulfate, and MB/sodium chloride demonstrated that MB was bound to the sulfate moiety of SDS before and after micellization. Our observations suggest that MB forms aggregates with SDS at premicellar concentrations, and the MB aggregates disassociate as monomers that are bound to the sulfate moiety of SDS at micellar concentrations. These findings further clarify the process by which MB and SDS interact and demonstrate the potential for developing MB-/SDS-based contrast agents.

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