Monitoring lesion activity on primary teeth with CP‐OCT and SWIR reflectance imaging

Abstract

Objective: The purpose of this study was to use cross polarization optical coherence tomography (CP-OCT) and short wavelength infrared imaging (SWIR) reflectance imaging to monitor changes in the structure and activity of early occlusal caries on primary teeth over a period of 6 months during intervention with fluoride. Methods: Participants (n = 29) aged 6−10 each with two suspected active occlusal lesions on primary teeth completed the study. Fluoride varnish was applied to tooth surfaces every 3-months and participants were instructed to brush twice daily with a fluoride toothpaste. Images were acquired using CP-OCT every 3 months for 6 months. SWIR reflectance images were acquired during forced air-drying of the lesions for 30 s at 0 and 6-months. Results: Most of the 42 lesions appeared initially active at baseline. Only 6 lesions appeared arrested at baseline based on the presence of a highly mineralized transparent surface layer (TSL) in CP-OCT images. At 6 months, 14 of the lesions appeared arrested including the 6 initially arrested lesions and the TSL thickness increased significantly (p < 0.0001). The mean lesion depth (Ld) and the integrated reflectivity over the lesion depth (ΔR) increased significantly (p < 0.05) after 6 months for the 42 lesions analyzed. SWIR reflectance images showed that there was a significantly higher (p < 0.05) delay before changes in intensity were measured for active lesions versus arrested lesions during lesion drying. Conclusion: CP-OCT was able to monitor changes in lesion structure and activity including the formation of a highly mineralized TSL indicative of lesion arrest during nonsurgical intervention. Time-resolved SWIR reflectance imaging also shows that there are differences in the dehydration kinetics between active and arrested lesions. This study demonstrates two independent imaging methods that can be used to monitor changes in lesion activity over time.

Time‐resolved SWIR imaging for the assessment of the activity of occlusal caries lesions

“…Based on this study and recent studies [25, 26], it appears that %Δ I is not a reliable parameter to discriminate between active and arrested lesions and is not suitable for in vivo measurements since the depth and severity of the lesions is not known ahead of time. The other three parameters that reflect the kinetics of the dehydration process; delay, % I fin , and rate are less dependent on the lesion depth and severity and are better suited for clinical use.…”

“…Such surfaces are more challenging for lesion activity assessment using time‐resolved SWIR reflectance imaging due to the highly convoluted topography. In the first clinical study to assess lesion activity in vivo using time‐resolved SWIR reflectance imaging, lesions located on the occlusal surfaces of primary teeth were chosen to ensure that most of the lesions would be active [26]. The study showed the potential of using the delay to discriminate between active and arrested lesions however there was considerable difficulty in sufficiently dehydrating lesions in these areas in 30 s. In addition, many of the acquired curves were noisy or incomplete preventing the calculation of kinetic information from the curves such as rates or % I fin [26].…”

“…This was achieved for all the active lesions using both the benchtop system and the handpiece within 30 s. In contrast, complete dehydration can take hundreds of seconds for arrested lesions, however the entire curve is not needed to calculate suitable values of % I fin and rate as they are sufficiently different from active lesions due to the much slower rate of dehydration for arrested lesions. Dehydration devices using the probe with the air flow shown in Figure 1A were used in two clinical studies; one on root surfaces [21] and the second on the occlusal surfaces of primary teeth [26]. In both studies the test subjects did not complain about any pain or air sensitivity at delivery pressures of 10–15 psi.…”

“…In existing probes, the air dehydration channels are directed parallel to the probe surface (Figure 1B). This nozzle design has worked well on tooth root surfaces [21], however dehydration in the pits and fissures of tooth occlusal surfaces has been more difficult [26]. We experimented with new preliminary nozzle designs and found that the dehydration rate can be increased markedly for occlusal surfaces by narrowing the nozzle opening and angling the nozzle.…”

“…The first clinical study to utilize SWIR reflectance dehydration measurements was recently carried out on the occlusal surfaces of primary teeth using a compact InGaAs camera and 1400–1750 nm light [26]. The presence of a highly mineralized transparent surface layer was also assessed using cross polarization optical coherence tomography (CP‐OCT).…”