Hobin Kang

Nondestructive Assessment of Early Tooth Demineralization Using Cross-Polarization Optical Coherence Tomography

New methods are needed for the nondestructive measurement of tooth demineralization and remineralization to monitor the progression of incipient caries lesions (tooth decay) for effective nonsurgical intervention and to evaluate the performance of anticaries treatments such as chemical treatments or laser irradiation. Studies have shown that optical coherence tomography (OCT) has great potential to fulfill this role since it can be used to measure the depth and severity of early lesions with an axial resolution exceeding 10 μm, it is easy to apply in vivo and it can be used to image the convoluted topography of tooth occlusal surfaces. In this paper, a review of the use of polarization-sensitive-OCT for the measurement of tooth demineralization is provided along with some recent results regarding improved methods for the detection of caries lesions in the earliest stages of development. Automated methods of analysis were used to measure the depth and severity of demineralized bovine enamel produced using simulated caries models that emulate demineralization in the mouth. Significant differences in the depth and integrated reflectivity from the lesions were detected after only a few hours of demineralization. These results demonstrate that cross-polarization-OCT is ideally suited for the nondestructive assessment of early demineralization.

Non-destructive clinical assessment of occlusal caries lesions using near-IR imaging methods.

Enamel is highly transparent in the near‐IR (NIR) at wavelengths near 1,300 nm, and stains are not visible. The purpose of this study was to use NIR transillumination and optical coherence tomography (OCT) to estimate the severity of caries lesions on occlusal surfaces both in vivo and on extracted teeth.

Automated assessment of the remineralization of artificial enamel lesions with polarization-sensitive optical coherence tomography.

Accurate measurement of the highly mineralized transparent surface layer that forms on caries lesions is important for diagnosis of the lesion activity because chemical intervention can slow or reverse the caries process via remineralization. Previous in-vitro and in-vivo studies have demonstrated that polarization-sensitive optical coherence tomography (PS-OCT) can nondestructively image the subsurface lesion structure and the highly mineralized transparent surface zone of caries lesions. The purpose of this study was to develop an approach to automatically process 3-dimensional PS-OCT images and to accurately assess the remineralization process in simulated enamel lesions. Artificial enamel lesions were prepared on twenty bovine enamel blocks using two models to produce varying degree of demineralization and remineralization. The thickness of the transparent surface layer and the integrated reflectivity of the subsurface lesion were measured using PS-OCT. The automated transparent surface layer detection algorithm was able to successfully detect the transparent surface layers with high sensitivity ( = 0.92) and high specificity ( = 0.97). The estimated thickness of the transparent surface layer showed a strong correlation with polarized light microscopy (PLM) measurements of all regions (R(2) = 0.90). The integrated reflectivity, ΔR, and the integrated mineral loss, ΔZ, showed a moderate correlation (R(2) = 0.32). This study demonstrates that PS-OCT can automatically measure the changes in artificial enamel lesion structure and severity upon exposure to remineralization solutions.

Nondestructive monitoring of the repair of enamel artificial lesions by an acidic remineralization model using polarization-sensitive optical coherence tomography

OBJECTIVES It is difficult to completely remineralize carious lesions because diffusion into the interior of the lesion is inhibited as new mineral is deposited in the outermost layers. In previous remineralization studies employing polarization sensitive optical coherence tomography (PS-OCT), two models of remineralization were employed and in both models there was preferential deposition of mineral in the outer most layer. In this study we attempted to remineralize the entire lesion using an acidic remineralization model and demonstrate that this remineralization can be monitored using PS-OCT. METHODS Artificial lesions approximately 100-150 μm in-depth were exposed to an acidic remineralization regimen and the integrated reflectivity from the lesions was measured before and after remineralization using PS-OCT. RESULTS Automated integration routines worked well for assessing the integrated reflectivity for the lesion areas after remineralization. Although there was a high degree of remineralization, there was still incomplete remineralization of the body of the lesion. CONCLUSION This study demonstrated that PS-OCT can be used to non-destructively measure changes in lesion structure and severity upon exposure to an acidic remineralization model. This study also demonstrated that automated algorithms can be used to assess the lesion severity even with the presence of a weakly reflective surface zone.

Longitudinal monitoring of demineralization peripheral to orthodontic brackets using cross polarization optical coherence tomography.

OBJECTIVES The aim of this study was to test the hypothesis that cross-polarization optical coherence tomography (CP-OCT) can be used to longitudinally monitor demineralization peripheral to orthodontic brackets in an extended clinical study. METHODS A high-speed CP-OCT system was used to acquire 3D volumetric images of the area at the base of orthodontic brackets over a period of 12 months after placement. The reflectivity was measured at 3-month intervals for 12 months to determine if there was increased demineralization. Two teeth were monitored on 20 test subjects and the brackets were bonded using two types of adhesives. This was a randomized controlled clinical study with a split mouth design such that each subject served as his or her own control. On one side, the control premolar was bonded with a bonding agent (Adper Scotchbond from 3M ESPE, St. Paul, MN) and composite (Transbond XT from 3M Unitek, Monrovia, CA) that lacked fluoride. On the other side, the experimental premolar was bonded with a fluoride releasing glass ionomer cement (GC Fuji Ortho LC from GC America, Alsip, IL). RESULTS There was a small but significant increase in the calculated lesion depth and integrated reflectivity over that depth (ΔR) for both adhesive types (p<0.0001) indicating increasing demineralization with time. There was no significant difference in the lesion depth (p=0.22) and ΔR (p=0.91) between the groups with the fluoride releasing glass ionomer cement and the conventional composite. CONCLUSIONS CP-OCT was able to measure a significant increase in demineralization (p<0.0001) at the base of orthodontic brackets over a period of 12 months.

Near-IR and CP-OCT imaging of suspected occlusal caries lesions

Radiographic methods have poor sensitivity for occlusal lesions and by the time the lesions are radiolucent they have typically progressed deep into the dentin. New more sensitive imaging methods are needed to detect occlusal lesions. In this study, cross‐polarization optical coherence tomography (CP‐OCT) and near‐IR imaging were used to image questionable occlusal lesions (QOCs) that were not visible on radiographs but had been scheduled for restoration on 30 test subjects.

In vivo Near-IR Imaging of Occlusal Lesions at 1310-nm

Several in vitro studies have demonstrated the potential for transillumination imaging and optical coherence tomography operating at 1310-nm for imaging caries lesions on tooth proximal and occlusal surfaces. Recently, we demonstrated that lesions on proximal surfaces could be imaged in vivo using NIR transillumination and that PS-OCT can be used in vivo to measure early demineralization on tooth buccal and occlusal surfaces. In this paper we report the first in vivo measurements using OCT and NIR imaging of occlusal lesions that have been scheduled for restoration. Occlusal lesions were chosen that were scheduled for restoration based on conventional diagnosis that consists of visual and tactile examination. Occlusal lesions were visible in the NIR. OCT looks promising for confirming the lateral spread of occlusal caries under the dentinal-enamel junction adjacent to fissures. These studies suggest that both near infrared transillumination imaging at 1310-nm and OCT provide valuable information about the severity of caries lesions.

Imaging simulated secondary caries lesions with cross polarization OCT

The clinical diagnosis of secondary caries has been found to account for the replacement of the majority of intra-coronal restorations. Current methods to diagnose the presence of these lesions at early stages are considered insufficient due to their low sensitivity. Polarization-sensitive optical coherence tomography (PS-OCT) imaging studies have confirmed its effectiveness for imaging carious subsurface lesions in enamel and dentin. The objective of this study was to determine if PS-OCT can be used to nondestructively image demineralization through resin restorations on extracted teeth with both simulated and natural lesions. Simulated secondary caries lesions were created by exposing cavity preparations made in extracted human teeth to a demineralizing solution for 48 hours and subsequently restoring with resin. Negative control restorations were also prepared on each tooth. Optical changes in demineralized versus control preparations beneath restorations were measured as a function of depth using PS-OCT. PS-OCT images indicated that a significant increase in reflectivity and depth occurred in the simulated lesions compared with the control preparations. This study suggests that PS-OCT is well-suited to nondestructively detect early caries lesions in enamel beneath composite restorations.

Clinical monitoring of smooth surface enamel lesions using CP-OCT during nonsurgical intervention.

Studies have shown that cross‐polarization optical coherence tomography (CP‐OCT) can be used to image the internal structure of carious lesions in vivo. The objective of this study was to show that CP‐OCT can be used to monitor changes in the internal structure of early active carious lesions on smooth surfaces during non‐surgical intervention with fluoride.

Enhancing the detection of hidden occlusal caries lesions with OCT using high index liquids.

In a previous study, we investigated the influence of several high refractive index fluids on the performance of polarization sensitive optical coherence tomography (PS-OCT). That study showed that these liquids can increase the effective imaging depth and lesion contrast. Other in vitro and in vivo studies have shown that OCT can be used to show whether occlusal lesions have penetrated to the dentinal-enamel junction (DEJ) and spread laterally under the enamel. The purpose of this study was to determine if high index fluids can enhance the ability of OCT to detect hidden occlusal lesions and show if these lesions have penetrated through the enamel into the underlying dentin. Ten extracted teeth with occlusal lesions were imaged using OCT after the application of water, glycerol, BABB (33% Benzyl Alcohol + 67% Benzyl Benzoate) and a Cargille Liquid (Cedar Grove, NJ) (hydrogenated terphenyl 1- bromo-naphthalene) with a refractive index of 1.61. The intensity of the reflectance from the underlying lesion area for each sample was compared with the reflectance of the sound tooth surface for each fluid. The use of high index fluids significantly (P< 0.0001) increased the reflectivity of subsurface occlusal lesions under the surrounding sound enamel.