Multispectral cross-polarization reflectance measurements suggest high contrast of demineralization on tooth surfaces at wavelengths beyond 1300 nm due to reduced light scattering in sound enamel

Monitoring silver diamine fluoride application with optical coherence tomography and thermal imaging: An in vitro proof of concept study

Objectives

The purpose of this study was to show that optical coherence tomography (OCT) and thermal imaging can be used to monitor changes in the structure and activity of caries lesions over time after treatment with silver diamine fluoride (SDF).

Methods

Artificial caries lesions were formed on enamel and dentin bovine blocks. Each block was partitioned into five windows with the central three windows exposed to a demineralization solution to create lesions: one sound window served as a sound control (SC), one sound window was exposed to SDF to serve as a test control (SCT), one lesion window served as a lesion control (LC), one lesion window received one application of SDF (L1), while the other lesion window received two applications of SDF (L2). Each window was scanned using OCT before SDF application, and every week subsequently, for 12 weeks after initial SDF treatment. Changes in the mean intensity and the width of the peak of increased reflectivity due to the lesion and SDF along with the intensity at a depth of 180 µm from the surface representing optical penetration through the lesion were monitored. Changes in the heat lost, ΔQ (temperature integrated over time) of each window during drying with air were also monitored using a thermal imaging camera. Transverse microradiography (TMR), and high‐resolution microscopy were also used for the analysis of selected samples.

Results

The reflectivity and optical penetration of sound and lesion areas of enamel and dentin manifested significant changes in OCT images after SDF application. Thermal imaging showed significant differences in ΔQ indicative of permeability changes in the sound and lesion areas of enamel and dentin after SDF application.

Emerging Technologies for Dentin Caries Detection-A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aimed at assessing the diagnostic accuracy of emerging technologies, such as laser fluorescence (LF), transillumination, light-emitting diode devices, optical coherence tomography (OCT), alternating current impedance spectroscopy, fluorescence cameras (FC), photo-thermal radiometry, and modulated luminescence technology. In vivo and in vitro results of such non-ionizing, non-invasive, and non-destructive methods’ effectiveness in non-cavitated dentin caries detection are sometimes ambiguous. Following the PRISMA guidelines, 34 relevant research articles published between 2011–2021 were selected. The risk of bias was assessed with a tool tailored for caries diagnostic studies, and subsequent quantitative uni- and bi-variate meta-analysis was carried out in separate sub-groups according to the investigated surface (occlusal/proximal) and study setting (in vivo/in vitro). In spite of the high heterogeneity across the review groups, in vitro studies on LF and FC proved a good diagnostic ability for the occlusal surface, with area under the curve (AUC) of 0.803 (11 studies) and 0.845 (five studies), respectively. OCT studies reported an outstanding performance with an overall AUC = 0.945 (four studies). Promising technologies, such as OCT or FC VistaProof, still need well-designed and well-powered studies to accrue experimental and clinical data for conclusive medical evidence, especially for the proximal surface. Registration: INPLASY202210097.

Dehydration imaging of dental fluorosis at 1950 nm

Dental fluorosis is an increasing problem in the U.S. due to excessive exposure to fluoride from the environment. Fluorosis causes hypomineralization of the enamel during tooth development and mild fluorosis is visible as faint white lines on the tooth surface while the most severe fluorosis can result in pitted surfaces. It is difficult to differentiate lesions due to fluorosis from those due to caries. Dental fluorosis appears with extremely high contrast at short wavelength infrared (SWIR) wavelengths of 1450 and 1960 nm coincident with higher water absorption. In this study reflectance measurements at 1450 and 1950 nm were used to monitor the dehydration dynamics of lesions due to fluorosis on extracted teeth. The dehydration dynamics were compared with the lesion structure that was measured with microCT. Sixteen extracted teeth with suspected fluorosis were imaged and microCT showed that the mean surface zone thickness was 118 ± 30 μm and the lesion depth was 284 ± 105 μm for the areas of fluorosis investigated. The dehydration dynamics of lesions due to fluorosis appeared most similar to those of arrested caries lesions. There was no significant correlation (P >0.05) of the intensity change and rate of the intensity change at 1450 or 1950 nm with either the lesion surface zone thickness or the lesion depth.

Use of SWIR dehydration and OCT to assess the complete arrest of simulated incipient caries lesions

Previous studies have shown that optical coherence tomography (OCT) can be used to show the formation of a transparent surface zone on caries lesions indicative of remineralization. Studies have also shown that monitoring changes in the diffuse reflectivity of caries lesions during drying with air can be used to assess lesion activity and that the largest changes occur at SWIR wavelengths coincident with high water absorption at 1450 and 1950 nm. The purpose of this study was to determine when remineralization has occurred by monitoring changes in SWIR reflectance measurements and OCT images of simulated lesions over an extended time period during exposure to a remineralization solution. Eight bovine enamel surfaces each with two treatment windows were exposed to a pH cycling regimen to produce simulated lesions 50-100 μm deep. OCT at 1310 nm was used to image the samples at each time point. An extended range tungsten halogen lamp with a 1450 nm band pass filter and a broadband amplified spontaneous emission source centered near the peak of the water-absorption band at 1950 nm were used as light sources. An extended range InGaAs camera (1000-2340 nm) was used to acquire reflected light images as the samples were dried with air. After 32 days of exposure to the remineralization solution there were no further changes to the samples suggesting they had been completely arrested.

High contrast imaging of dental fluorosis in the short wavelength infrared

Dental fluorosis is an increasing problem due to over exposure to fluoride from the environment. Fluorosis causes hypomineralization of the enamel during tooth development and mild fluorosis is visible as faint white lines on the tooth surface while the most severe fluorosis can result in pitted surfaces. It is difficult to quantify the severity of mild to moderate fluorosis and assessments are limited to subjective visual examinations. Dental fluorosis appears with very high contrast at short wavelength infrared (SWIR) wavelengths beyond 1400 nm and we hypothesize that these wavelengths may be better suited for detecting mild fluorosis and for estimating the severity on tooth surfaces. In this study, the contrast of fluorosis of varying severity on extracted human permanent teeth was measured at SWIR wavelengths ranging from 1300 to 2150 nm using an extended range of InGaAs camera and broadband light sources. The contrast was also measured in the visible range and with quantitative light-induced fluorescence (QLF) for comparison. The depth of hypomineralization and the integrated reflectivity were also measured with cross-polarization optical coherence tomography. The contrast of hypomineralization is significantly higher (P < 0.05) at 1460 and 1950 nm wavelengths than for the visible, fluorescence or other SWIR wavelengths from 1300 to 2150 nm. The highest correlation of the contrast with the depth of hypomineralization measured with cross-polarization-optical coherence tomography (CP-OCT) was at 1950 nm. This SWIR in vitro imaging study exploring wavelengths beyond 1400 nm has shown that hypomineralization on tooth surfaces can be viewed with extremely high contrast at SWIR wavelengths from 1460 to 2000 nm and that SWIR imaging has great potential for monitoring hypomineralization on tooth surfaces. New clinical methods are needed for the measurement of fluorosis that are valid, reliable, and feasible for surveillance at the community level. In addition, methods are needed for the quantitative assessment of fluorosis in vivo.

Dynamic SWIR imaging near the 1950-nm water absorption band for caries lesion diagnosis

SIGNIFICANCE

It is not sufficient to detect caries lesions on tooth surfaces; it is also necessary to measure the activity of the lesions to determine if intervention is needed. Changes in the reflectivity of lesion areas during dehydration with forced air at short wavelength infrared (SWIR) wavelengths can be used to assess lesion activity since these changes represent the evaporation dynamics of water from the lesion.

AIM

The aim of this study is to develop new optical methods for assessing lesion activity on tooth surfaces utilizing the strong water absorption band near 1950-nm.

APPROACH

The time-resolved reflectivity of 20 active and arrested caries lesions on the surfaces of human extracted teeth was monitored at 1300 to 2000 nm using broadband light sources and an extended range InGaAs camera during drying with air.

RESULTS

Multiple parameters representing the rate of change of the lesion reflectivity correlated with the presence of a highly mineralized outer surface zone indicative of lesion arrest measured with x-ray microtomography (microCT). Performance at 1950-nm was higher than for other wavelengths.

CONCLUSIONS

This study demonstrates that SWIR imaging near 1950-nm has great potential for the assessment of lesion activity.

Detection and analyzing plane of non-cavitated approximal caries by cross-polarized optical coherence tomography (CP-OCT)

OBJECTIVE

The objective was to assess the detection ability and the effect of analyzing plane of CP-OCT for non-cavitated approximal caries.

METHODS

Thirty human extracted premolars were selected based on micro-computed tomography [μ-CT: μ- CT = 0: sound (n = 12), μ-CT = 1/2: caries into outer-/inner-half of enamel (n = 6 each), μ-CT = 3: caries into outer one-third of dentine (n = 6)]. Teeth were mounted in a custommade device to simulate approximal contact, and scanned from the marginal ridge above the contact area. CP-OCT images were analyzed by deepest caries extension from horizontal and coronal planes, and repeated 48-hrs later. Sensitivity, specificity,percent correct, area under the ROC curve (Az), intra-examiner repeatability and correlation with μ-CT were determined.

RESULTS

Sensitivity/specificity/Az for Horizontalplane, Coronal-plane, and Deepest from both planes were 94percent/58percent/0.76,81percent/100percent/0.90, and 94 %/58 %/0.82. Coronal-plane had significantly higher specificity than Horizontal-plane and Deepest (p = 0.004) but Horizontal-plane and Deepest were not different (p = 1.00). Horizontal-plane had significantly lower Az than Deepest (p = 0.048), but Coronal-plane was not different than Horizontal-plane (p = 0.07) or Deepest (p = 0.20). Correlation coefficients were Horizontal-plane (0.53, p < 0.001), Coronal-plane (0.84, p < 0.001), and Deepest (0.66, p < 0.001).

CONCLUSION

Within the limitations of this study, CP-OCT could be used to detect non-cavitated approximal caries. Analysis using the Coronal-plane is superior to the Horizontal-plane.

CLINICAL SIGNIFICANCE

It is challenging to detect non-cavitated approximal caries clinically due to the adjacent tooth. CP-OCT is a nondestructive, no ionized-radiation caries detection technique. CP-OCT seems suitable to detect non-cavitated approximal caries and observing the Coronal-plane appears better than Horizontal-plane.

Monitoring silver diamine fluoride application with optical coherence tomography

The objective of this study was to investigate the use of optical coherence tomography (OCT) for monitoring changes in the structure of caries lesions overtime after treatment with silver diamine fluoride (SDF). Artificial caries lesions were formed on dentin bovine blocks. Each block was partitioned into 5 windows: one lesion was covered by nail varnish as control (LC), one sound window was covered with nail varnish (SC), one sound window was exposed to SDF (SCT), one lesion received 2 applications of SDF (L2), while the other lesion received one application of SDF (L1). Each window was scanned using OCT before SDF application, and every week subsequently, for 12 weeks after initial SDF treatment. Parameters such as mean intensity and the width of the peak of increased reflectivity located at the sample surface and the intensity at a depth of 180-μm were monitored. High-resolution microscopy was also used to for the analysis of selected samples. Changes in the parameters measured showed significant changes on dentin lesions after SDF application. OCT resolved structural changes after SDF application as well as changes overtime. High resolution microscopy images confirm penetration of SDF into the samples. Such changes can potentially be monitored to determine if and when re-application of SDF is needed.

High contrast reflectance imaging at 1950 nm for the assessment of lesion activity on extracted teeth

Changes in the reflectivity of lesions on the proximal surfaces of extracted human teeth were measured at SWIR wavelengths from 1300-2000 nm as they were dried with air to assess lesion activity. An extended range tungsten-halogen lamp with bandpass filters of varying wavelength (bandwidth) 1300 nm (90), 1460 nm (85), 1535 nm (80), and 1675 nm (90) along with a broadband ASE source centered near the peak of the water-absorption band at 1950-nm were used as light sources and an extended range InGaAs camera (1000-2340 nm) was used to acquire reflected light images as the samples were dried with air. MicroCT images were used as a gold standard for comparison. SWIR light at 1950 nm yields extremely high contrast of demineralization and appears to be the optimum wavelength for the assessment of lesion activity on tooth coronal surfaces.

Imaging dental fluorosis at SWIR wavelengths from 1300 to 2000-nm

Dental fluorosis is an increasing problem in the U.S. due to excessive exposure to fluoride from the environment. Fluorosis causes hypomineralization of the enamel during tooth development and mild fluorosis is visible as faint white lines on the tooth surface while the most severe fluorosis can result in pitted surfaces. It is difficult to quantify the severity of fluorosis and assessments are limited to subjective visual assessments. Dental fluorosis appears with very high contrast at short wavelength infrared (SWIR) wavelengths beyond 1400-nm and we hypothesize that these wavelengths may be better suited for detecting mild fluorosis and for estimating the severity. In this study the contrast of fluorosis of varying severity on extracted human permanent teeth was measured at SWIR wavelengths ranging from 1300-2000-nm using an extended range InGaAs camera and broadband light sources. Cross polarization optical coherence tomography was used to measure the depth of hypomineralization.

High Contrast Reflectance Imaging of Enamel Demineralization and Remineralization at 1950-nm for the Assessment of Lesion Activity

BACKGROUND AND OBJECTIVES

Previous studies have shown that large changes in the diffuse reflectivity of caries lesions during drying with air can be used to assess lesion activity. The largest changes occur at short wavelength infrared (SWIR) wavelengths coincident with high water absorption. The strongest water absorption in the SWIR occurs at 1950 nm. In this study changes in the reflectivity of simulated lesions with varying degrees of remineralization was measured at 1500-2340 nm and at 1950 nm as the samples were dried with air.

STUDY DESIGN/MATERIALS AND METHODS

Twenty bovine enamel surfaces each with five treatment windows were exposed to two demineralization/remineralization regimens to produce simulated lesions of varying depth, severity, and mineral gradients. An extended range tungsten-halogen lamp with a long pass filter (1500-2340 nm) and a broadband amplified spontaneous emission source centered near the peak of the water-absorption band at 1950-nm were used as light sources and an extended range InGaAs camera (1000-2340 nm) was used to acquire reflected light images as the samples were dried with air. Lesions were also assessed using digital microscopy, polarized light microscopy, optical coherence tomography, and transverse microradiography.

RESULTS

Both wavelength ranges showed extremely high lesion contrast (>0.9) for all six lesion treatment windows in both models. The change in contrast (ΔI) was significantly higher for the 1950 nm broadband source for all the intact lesion windows compared with the 1500-2340 nm wavelength range.

CONCLUSION

SWIR light at 1950 nm yields extremely high contrast of demineralization and appears to be the optimum wavelength for the assessment of lesion activity on tooth coronal surfaces. Lasers Surg. Med. 00:00-00, 2020. © 2020 Wiley Periodicals LLC.

Dual short wavelength infrared transillumination/reflectance mode imaging for caries detection

SIGNIFICANCE

We have developed a clinical probe capable of acquiring near-simultaneous short-wavelength infrared (SWIR) reflectance and occlusal transillumination images of lesions on tooth proximal and occlusal surfaces. We hypothesize that dual images will aid in differentiating between shallow and deep occlusal lesions and reduce the potential of false positives (FPs).

AIM

The aim of this study was to test the performance of the dual reflectance and occlusal transillumination probe on extracted teeth prior to commencing clinical studies.

APPROACH

The dual probe was 3D printed and the imaging system uses an InGaAs camera and broadband superluminescent diode light sources that emit broadband light at 1300 nm for occlusal transillumination and 1600-nm light for cross-polarization reflectance. The diagnostic performance of the dual probe was assessed using 120 extracted teeth with approximal and occlusal lesions. Reflectance and transillumination images were fused into single images to enhance the contrast between sound and lesion areas. The lesion contrast in both modes did not increase significantly with either the lesion depth or the distance from the occlusal surface for approximal lesions. In addition, the diagnostic performance of radiography, the individual reflectance and transillumination images, dual images, and fused images were compared using micro-computed tomography as the gold standard.

RESULTS

Reflectance imaging at 1600 nm yielded the highest diagnostic accuracy for lesions on both occlusal and proximal surfaces while radiography yielded the lowest number of FPs.

CONCLUSION

This study demonstrates that simultaneous acquisition of both reflectance and transillumination SWIR images is possible with a single clinical device.

The contrast of demineralization on tooth occlusal surfaces from 405 to 1950-nm with varying depth

Near Infrared Reflectance (NIR) is a new imaging technology that detects dental caries (decay) on tooth occlusal surfaces and in the interproximal contact sites between teeth. Conventional techniques, mostly dental x-rays, do not provide the high sensitivity and specificity at the vulnerable pits and fissure regions. The contrast of demineralization on tooth surfaces changes with increasing severity and the magnitude of that change with depth depends on the wavelength. The purpose of this study is to determine how the contrast changes with depth as a function of wavelength. Demineralization of varying depth was produced in 1.5 × 1.5 mm exposed windows after 1, 2, 3, 4, and 5 days of exposure to a demineralizing solution at pH 4.5. Lesions were imaged at 405, 630, 850, 1300, 1460, 1535, 1675, and 1950-nm with multiple imaging systems. The highest lesion contrast was measured at 1950-nm.