Noninvasive cross-sectional imaging of incomplete crown fractures (cracks) using swept-source optical coherence tomography

Assessment of the Accuracy in Measuring the Enamel Thickness of Maxillary Incisors with Optical Coherence Tomography

Although the clinical assessment of enamel thickness is important, hardly any tools exist for accurate measurements. The purpose of this study was to verify the precision of enamel thickness measurements using swept-source optical coherence tomography (SS-OCT). Human extracted maxillary central and lateral incisors were used as specimens. Twenty-eight sites were measured in each specimen. The optical path length (OPL) at each measurement site was measured on the OCT images, and enamel thickness (e1) was calculated by dividing OPL by the mean refractive index of enamel, 1.63. The specimens were then sectioned, and a light microscope was used to measure enamel thickness (e2). e1 and e2 were then compared. Measurement errors between e1 and e2 for the central and lateral incisors were 0.04 (0.02; 0.06) mm and 0.04 (0.02; 0.07) mm [median value: (25%, 75% percentile)], respectively. No significant differences between measurement sites were noted for measurement errors between e1 and e2. These results demonstrate that OCT can be used for noninvasive, accurate measurements of enamel thickness.

New technique for detecting cracked teeth and evaluating the crack depth by contrast-enhanced cone beam computed tomography: an in vitro study

Background

Cracked teeth may cause various clinical symptoms depending on the extension depth of the crack and the subsequent bacterial infections. However, techniques to reliably determine the extension depths of cracks in teeth before treatment are lacking. The aim of this study was to develop a new technique based on contrast-enhanced cone beam computed tomography (CBCT) to improve the accuracy of crack depth evaluation in vitro.

Methods

We developed an in vitro artificial simulation model of cracked teeth. Pre-experimental CBCT (pre-CBCT), and micro-computed tomography (micro-CT) were first performed for all cracked teeth (n = 31). Contrast-enhanced CBCT was then performed by infiltrating the crack with ioversol under vacuum conditions. The sensitivities of pre-CBCT and contrast-enhanced CBCT for the diagnosis of cracked teeth were calculated. According to the K-means clusters, crack depths measured by micro-CT were changed into categorical variables. Bland–Altman plot and the intraclass correlation coefficient (ICC) were used to analyze the consistency of the crack depths between the pre-CBCT and contrast-enhanced CBCT, as well as the ICC between the contrast-enhanced CBCT and micro-CT. Receiver operating characteristic (ROC) curves were generated to assess the ability for predicting crack depth in the differential diagnosis using pre-CBCT and contrast-enhanced CBCT. Restricted cubic splines were also used to model the non-linear relationship between the crack depths of contrast-enhanced CBCT and micro-CT.

Results

The sensitivities of pre-CBCT and contrast-enhanced CBCT were 48.4%, and 67.7%, respectively. The ICC value of crack depth as measured by pre-CBCT and contrast-enhanced CBCT was 0.847 (95% confidence interval [CI] 0.380–0.960; P < 0.001). The areas under ROC curves (AUC) of pre-CBCT and contrast-enhanced CBCT were different: the AUC of pre-CBCT was 0.958 (P = 0.000, 95% CI 0.843–1.074), and the AUC of contrast-enhanced CBCT was 0.979 (P = 0.000, 95% CI 0.921–1.037), and the difference was not statistically significant (Z = − 0.707, P = 0.480). The ICC value of crack depth as measured by contrast-enhanced CBCT and micro-CT was 0.753 (95% CI 0.248–0.911; P < 0.001).

Conclusion

Contrast-enhanced CBCT under vacuum conditions with a contrast medium can significantly improve the crack detection rate of cracked teeth; however, it cannot measure the crack depths accurately.

A method of crack detection based on digital image correlation for simulated cracked tooth

Background

Early clinical cracked tooth can be a perplexing disorder to diagnose and manage. One of the key problems for the diagnosis of the cracked tooth is the detection of the location of the surface crack.

Methods

This paper proposes an image-based method for the detection of the micro-crack in the simulated cracked tooth. A homemade three-axis motion platform mounted with a telecentric lens was built as an image acquisition system to observe the surface of the simulated cracked tooth, which was under compression with a magnitude of the masticatory force. By using digital image correlation (DIC), the deformation map for the crown surface of the cracked tooth was calculated. Through image analysis, the micro-crack was quantitatively visualized and characterized.

Results

The skeleton of the crack path was successfully extracted from the image of the principal strain field, which was further verified by the image from micro-CT. Based on crack kinematics, the crack opening displacement was quantitatively calculated to be 2–10 µm under the normal mastication stress, which was in good agreement with the value reported in the literature.

Conclusions

The crack on the surface of the simulated cracked tooth could be detected based on the proposed DIC-based method. The proposed method may provide a new solution for the rapid clinical diagnosis of cracked teeth and the calculated crack information would be helpful for the subsequent clinical treatment of cracked teeth.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01897-2.

Optical coherence tomography's current clinical medical and dental applications: a review

Optical coherence tomography (OCT) is a non-invasive investigative technique that is used to obtain high-resolution three-dimensional (3D) images of biological structures. This method is useful in diagnosing diseases of specific organs like the eye, where a direct biopsy cannot be conducted. Since its inception, significant advancements have been made in its technology. Apart from its initial application in ophthalmology for retinal imaging, substantial technological innovations in OCT brought by the research community have enabled its utilization beyond its original scope and allowed its application in many new clinical areas. This review presents a summary of the clinical applications of OCT in the field of medicine (ophthalmology, cardiology, otology, and dermatology) and dentistry (tissue imaging, detection of caries, analysis of dental polymer composite restorations, imaging of root canals, and diagnosis of oral cancer). In addition, potential advantages and disadvantages of OCT are also discussed.

The effect of flowable composite lining and dentin location on microtensile bond strength and internal fracture formation

The objective of this study was to determine the effect of flowable composite lining and dentin location on internal dentin fracture formation in the microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT). MTBS test beams (1.0×1.0 mm) were prepared from human superficial and deep dentin, which was bonded with a self-etch adhesive (Clearfil SE Bond) and hybrid composite resin (Clearfil AP-X), with or without flowable lining (Clearfil Majesty ES-Flow). We tested 4 groups according to placement technique (with vs. without flowable liner) and dentin (superficial vs. deep) locations. Cross-sectional 2D images of the bonded interface were obtained before and after the MTBS test. Internal dentin fracture after MTBT was observed as a bright zone in SS-OCT. Flowable lining significantly reduced internal fracture formation in dentin (p<0.05). Dentin location significantly influenced MTBS (p<0.05), and this was reduced by flowable lining usage.

Detection of Simulated Periradicular Lesions in Porcine Bone by Optical Coherence Tomography

INTRODUCTION

The accurate detection of periradicular lesions located under a nonperforated cortical plate poses a challenge in endodontic microsurgery. Optical coherence tomography (OCT) is a noninvasive imaging method that has been successfully used in many dental applications. In this study, we investigated if spectral-domain OCT (SD-OCT) could be used to determine simulated periradicular lesions.

METHODS

Twenty-eight cavities with different depths were prepared on bone plates obtained from 5 porcine mandibles. Both 3-dimensional SD-OCT imaging and micro-computed tomographic (micro-CT) imaging were used to image the bottom of the air-filled cavity and the cavity filled with soft tissue for comparison. The residual bone thickness under the cavity was measured by SD-OCT and micro-CT imaging and compared using the Pearson correlation.

RESULTS

The air-filled lesions were readily detected; yet, filling of the cavity with soft tissue diminished the appearance of the lesion boundaries in the SD-OCT images. The optical values of residual bone thickness obtained from SD-OCT ranged from 0.14-2.11 mm, which corresponded to the range of 0.26-1.18 mm from micro-CT imaging. A strong correlation was found between the 2 imaging modalities (r = 0.96; range, 0.94-0.98). The slope (1.56) of the linear regression matched the bulk refractive index of bone tissues.

CONCLUSIONS

SD-OCT allows for visualization of the lesion boundaries via intact bone surfaces and may be a promising, practical, and nonirradiating adjunct tool for chairside localization of periradicular lesions in bone.

Is Optical Coherence Tomography a Potential Tool to Evaluate Marginal Adaptation of Class III/IV Composite Restorations In Vivo?

OBJECTIVE

Margin analysis of Class III and IV composite restorations in vitro and in vivo occurred by scanning electron microscopy (SEM) and optical coherence tomography (OCT). The results were compared and related to clinical evaluation.

METHODS AND MATERIALS

Eight Class III composite restorations were imaged in vitro using OCT and SEM. The margins were analyzed quantitatively. OCT signals were verified by assignment to the criteria perfect margin, gap, and positive/negative ledge. In vivo quantitative margin analysis of Class III/IV composite restorations made of the micro-hybrid composite Venus combined with the self-etch adhesive iBond Gluma inside (1-SE) or etch-and-rinse adhesive Gluma Comfort Bond (2-ER) (all Heraeus Kulzer) was carried out using OCT and SEM after 90 months of clinical function. The results were compared with clinical evaluation (US Public Health Service criteria; marginal integrity, marginal discoloration).

RESULTS

In vitro, the correlation between OCT and SEM was high for all four margin criteria (Kendall tau b [τ_b] correlation: 0.64-0.92, p_i≤0.026), with no significant differences between OCT and SEM (p_i≥0.63). In vivo, a moderate correlation was observed (τ_b: 0.38-0.45, p_i<0.016). Clinically, the cumulative failure rate in the criterion marginal integrity was higher for the 1-SE group (baseline 90 M, p=0.011). Similarly, OCT and SEM detected higher percentages of the criterion gap in the 1-SE group (p: 0.027/0.002), in contrast to perfect margin. Both, gap and perfect margin ranged widely between 0.0% and 88.7% (OCT) and between 0.0% and 89.0% (SEM).

CONCLUSION

Despite the positive selection bias after 90 months with only a few patients left, quantitative margin analysis allows for differentiation between the two adhesives at this specific date. OCT in particular offers the possibility to evaluate marginal integrity directly in vivo.

The Use of Optical Coherence Tomography in Dental Diagnostics: A State-of-the-Art Review

Optical coherence tomography provides sections of tissues in a noncontact and noninvasive manner. The device measures the time delay and intensity of the light scattered or reflected from biological tissues, which results in tomographic imaging of their internal structure. This is achieved by scanning tissues at a resolution ranging from 1 to 15 μm. OCT enables real-time in situ imaging of tissues without the need for biopsy, histological procedures, or the use of X-rays, so it can be used in many fields of medicine. Its properties are not only particularly used in ophthalmology, in the diagnosis of all layers of the retina, but also increasingly in cardiology, gastroenterology, pulmonology, oncology, and dermatology. The basic properties of OCT, that is, noninvasiveness and low wattage of the used light, have also been appreciated in analytical technology by conservators, who use it to identify the quality and age of paintings, ceramics, or glass. Recently, the OCT technique of visualization is being tested in different fields of dentistry, which is depicted in the article.

Detection of Apical Root Cracks Using Spectral Domain and Swept-source Optical Coherence Tomography

INTRODUCTION

This study aimed to evaluate the ability of 2 optical coherence tomographic (OCT) systems to detect apical dentinal microcracks.

METHODS

Twenty extracted human single-rooted mandibular incisors were selected. After root canal preparation with an R40 Reciproc file (VDW, Munich, Germany), the specimens presenting apical microcracks were identified using micro-computed tomographic (micro-CT) scanning as the gold standard. Then, the apical portions of the roots were imaged with spectral domain OCT (SD-OCT) and swept-source OCT systems, and the resulting images were blindly evaluated by 3 independent examiners to detect microcracks. The diagnostic performance of each OCT device was calculated, and statistical analysis was performed.

RESULTS

Based on the micro-CT images, 12 (60%) roots presented dentinal microcracks in the apical region. The images generated by the OCT systems were able to show microcrack lines at the same location as the corresponding micro-CT cross sections. Although the diagnostic performance of the SD-OCT device was superior, there were no statistically significant differences between the 2 OCT devices (P > .05). Interexaminer agreement was substantial to almost perfect for the SD-OCT system and moderate to almost perfect for the swept-source OCT system, whereas intraexaminer agreement was substantial to almost perfect for both OCT devices.

CONCLUSIONS

The detection ability verified for both OCT systems renders them promising tools for the diagnosis of apical microcracks.

Automatic detection of tooth cracks in optical coherence tomography images

PURPOSE

The aims of the present study were to compare the image quality and visibility of tooth cracks between conventional methods and swept-source optical coherence tomography (SS-OCT) and to develop an automatic detection technique for tooth cracks by SS-OCT imaging.

METHODS

We evaluated SS-OCT with a near-infrared wavelength centered at 1,310 nm over a spectral bandwidth of 100 nm at a rate of 50 kHz as a new diagnostic tool for the detection of tooth cracks. The reliability of the SS-OCT images was verified by comparing the crack lines with those detected using conventional methods. After performing preprocessing of the obtained SS-OCT images to emphasize cracks, an algorithm was developed and verified to detect tooth cracks automatically.

RESULTS

The detection capability of SS-OCT was superior or comparable to that of trans-illumination, which did not discriminate among the cracks according to depth. Other conventional methods for the detection of tooth cracks did not sense initial cracks with a width of less than 100 μm. However, SS-OCT detected cracks of all sizes, ranging from craze lines to split teeth, and the crack lines were automatically detected in images using the Hough transform.

CONCLUSIONS

We were able to distinguish structural cracks, craze lines, and split lines in tooth cracks using SS-OCT images, and to automatically detect the position of various cracks in the OCT images. Therefore, the detection capability of SS-OCT images provides a useful diagnostic tool for cracked tooth syndrome.

Fractography of interface after microtensile bond strength test using swept-source optical coherence tomography

OBJECTIVE

To determine the effect of crosshead speed and placement technique on interfacial crack formation in microtensile bond strength (MTBS) test using swept-source optical coherence tomography (SS-OCT).

MATERIALS AND METHODS

MTBS test beams (0.9×0.9mm(2)) were prepared from flat human dentin disks bonded with self-etch adhesive (Clearfil SE Bond, Kuraray) and universal composite (Clearfil AP-X, Kuraray) with or without flowable composite lining (Estelite Flow Quick, Tokuyama). Each beam was scanned under SS-OCT (Santec, Japan) at 1319nm center wavelength before MTBS test was performed at crosshead speed of either 1 or 10mm/min (n=10). The beams were scanned by SS-OCT again to detect and measure cracks at the debonded interface using digital image analysis software. Representative beams were observed under confocal laser scanning microscope to confirm the fractography findings.

RESULTS

Two-way ANOVA showed that for MTBS the crosshead speed was not a significant factor (p>0.05), while there was a difference between placement techniques (p<0.001), with flowable lining yielding higher mean values. On the other hand, for crack formation, there was a significant difference between crosshead speeds (p<0.01), while the placement technique did not show up as a statistically significant factor (p>0.05). The interaction of factors were not significant (p>0.05).

SIGNIFICANCE

Testing MTBS samples at higher crosshead speeds induced more cracks in dentin. Lining with a flowable composite improved the bonding quality and increased the bond strength. SS-OCT can visualize interfacial cracks after restoration debonding.

Comparison of caries diagnostic modalities: A clinical study in 40 subjects

BACKGROUND AND OBJECTIVES

Few studies have been published that evaluate the usefulness of different caries- diagnostic modalities in general dental practice. The goal of this study was to compare the results of screening for coronal dental caries in a general dental practice using clinical observations, radiographs, laser fluorescence (DIAGNOdent™) (LF), and optical coherence tomography (OCT). Diagnostic agreement between OCT and LF versus standard clinical techniques for detecting caries was determined in 40 subjects.

STUDY DESIGNS/MATERIALS AND METHODS

Forty patients with >1 coronal carious lesion as determined by prescreening using clinical examination and radiographs were enrolled in this study. Subjects with gross caries were excluded. Subsequently each patient underwent a full detailed dental examination by an experienced clinician, using visual examination and radiographs according to standard clinical practice. The coronal surfaces of a total of 932 teeth were examined and charted. Teeth were then photographed, rediagnosed using the LF system, and imaged using OCT. Two blinded pre-standardized examiners reviewed radiographic and OCT images and assigned caries status.

RESULTS

Based on manufacturer's cutoff values, sensitivity and specificity for coronal caries using LF technique (i) on unaltered tooth surfaces were 73.7% and 94.1%, respectively and (ii) in previously restored or sealed teeth, they were 19.2% and 95.8%, respectively. LF technique was unable to assess tissue health underneath sealants and restorations. Clinician agreement (kappa [k]) regarding caries diagnosis using OCT imaging was overall 0.834 (SE = 0.034). Sensitivity and specificity for caries using OCT technique (i) on unaltered tooth surfaces approximated 74.1% and 95.7%, respectively and, (ii) in previously restored or sealed teeth, they approximated 76.0% and 95.6%, respectively. Although OCT was able to detect lesions beneath many resin restorations and sealants, results varied considerably between materials. OCT imaging was unable to detect caries when caries was >2 mm below the tooth surface.

CONCLUSION

These findings support the usefulness of LF for primary caries detection, and the clinical utility of OCT for early caries detection and monitoring under dental resin restorations and sealants. Lasers Surg. Med. 48:924-928, 2016. © 2016 Wiley Periodicals, Inc.

Detection and Analysis of Enamel Cracks by Quantitative Light-induced Fluorescence Technology

INTRODUCTION

The ability to accurately detect tooth cracks and quantify their depth would allow the prediction of crack progression and treatment success. The aim of this in vitro study was to determine the capabilities of quantitative light-induced fluorescence (QLF) technology in the detection of enamel cracks.

METHODS

Ninety-six extracted human teeth were selected for examining naturally existing or suspected cracked teeth surfaces using a photocuring unit. QLF performed with a digital camera (QLF-D) images were used to assess the ability to detect enamel cracks based on the maximum fluorescence loss value (ΔFmax, %), which was then analyzed using the QLF-D software. A histologic evaluation was then performed in which the samples were sectioned and observed with the aid of a polarized light microscope. The relationship between ΔFmax and the histology findings was assessed based on the Spearman rank correlation. The sensitivity and specificity were calculated to evaluate the validity of using QLF-D to analyze enamel inner-half cracks and cracks extending to the dentin-enamel junction.

RESULTS

There was a strong correlation between the results of histologic evaluations of enamel cracks and the ΔFmax value, with a correlation coefficient of 0.84. The diagnostic accuracy of QLF-D had a sensitivity of 0.87 and a specificity of 0.98 for enamel inner-half cracks and a sensitivity of 0.90 and a specificity of 1.0 for cracks extending to the dentin-enamel junction.

CONCLUSIONS

These results indicate that QLF technology would be a useful clinical tool for diagnosing enamel cracks, especially given that this is a nondestructive method.

Noninvasive Quantitative Evaluation of the Dentin Layer during Dental Procedures Using Optical Coherence Tomography

A routine cavity preparation of a tooth may lead to opening the pulp chamber. The present study evaluates quantitatively, in real time, for the first time to the best of our knowledge, the drilled cavities during dental procedures. An established noninvasive imaging technique, Optical Coherence Tomography (OCT), is used. The main scope is to prevent accidental openings of the dental pulp chamber. Six teeth with dental cavities have been used in this ex vivo study. The real time assessment of the distances between the bottom of the drilled cavities and the top of the pulp chamber was performed using an own assembled OCT system. The evaluation of the remaining dentin thickness (RDT) allowed for the positioning of the drilling tools in the cavities in relation to the pulp horns. Estimations of the safe and of the critical RDT were made; for the latter, the opening of the pulp chamber becomes unavoidable. Also, by following the fractures that can occur when the extent of the decay is too large, the dentist can decide upon the right therapy to follow, endodontic or conventional filling. The study demonstrates the usefulness of OCT imaging in guiding such evaluations during dental procedures.

Application of Optical Coherence Tomography (OCT) for Diagnosis of Caries, Cracks, and Defects of Restorations

Optical coherence tomography (OCT) is a noninvasive technique providing cross-sectional images of a tooth structure. This review describes the use of OCT for detecting dental caries, tooth fractures, and interfacial gaps in intraoral restorations. OCT can be a reliable and an accurate method and a safer alternative to X-ray radiography.

Dental optical coherence tomography

This review paper describes the applications of dental optical coherence tomography (OCT) in oral tissue images, caries, periodontal disease and oral cancer. The background of OCT, including basic theory, system setup, light sources, spatial resolution and system limitations, is provided. The comparisons between OCT and other clinical oral diagnostic methods are also discussed.

Facilitatory effect of AC-iontophoresis of lidocaine hydrochloride on the permeability of human enamel and dentine in extracted teeth

OBJECTIVES

The objectives of the present study were to quantitatively evaluate chemical permeability through human enamel/dentine using conductometry and to clarify if alternating current (AC) iontophoresis facilitates such permeability.

MATERIALS AND METHODS

Electrical impedance of different concentrations of lidocaine hydrochloride was measured using a bipolar platinum impedance probe. A quadratic curve closely fitted to the response functions between conductance and lidocaine hydrochloride. For analysis of the passage of lidocaine hydrochloride through human enamel/dentine, eight premolars that were extracted for orthodontic treatment were sectioned at the cemento-enamel junction. The tooth crowns were held between two chambers with a double O-ring. The enamel-side chamber was filled with lidocaine hydrochloride, and the pulp-side chamber was filled with extrapure water. Two platinum plate electrodes were set at the end of each chamber to pass alternating current. A simulated interstitial pulp pressure was applied to the pulp-side chamber. The change in the concentration of lidocaine hydrochloride in the pulp-side chamber was measured every 2min using a platinum recording probe positioned at the centre of the pulp-side chamber. Passive entry without iontophoresis was used as a control.

RESULTS

The level of lidocaine hydrochloride that passed through enamel/dentine against the dentinal fluid flow increased with time. Electrical conductance (G, mho) correlated closely to the concentration (x, mmol/L) of lidocaine hydrochloride (G=2.16x(2)+0.0289x+0.000376, r(2)=0.999).

CONCLUSIONS

Lidocaine hydrochloride can pass through enamel/dentine. Conductometry showed that the level of lidocaine hydrochloride that passed through enamel/dentine was increased by AC iontophoresis.