Laser-induced autofluorescence study of caries model in vitro

Development of a Visualisation Approach for Analysing Incipient and Clinically Unrecorded Enamel Fissure Caries Using Laser-Induced Contrast Imaging, MicroRaman Spectroscopy and Biomimetic Composites: A Pilot Study

This pilot study presents a practical approach to detecting and visualising the initial forms of caries that are not clinically registered. The use of a laser-induced contrast visualisation (LICV) technique was shown to provide detection of the originating caries based on the separation of emissions from sound tissue, areas with destroyed tissue and regions of bacterial invasion. Adding microRaman spectroscopy to the measuring system enables reliable detection of the transformation of the organic–mineral component in the dental tissue and the spread of bacterial microflora in the affected region. Further laboratory and clinical studies of the comprehensive use of LICV and microRaman spectroscopy enable data extension on the application of this approach for accurate determination of the boundaries in the changed dental tissue as a result of initial caries. The obtained data has the potential to develop an effective preventive medical diagnostic approach and as a result, further personalised medical treatment can be specified.

Development of a Fluorescence-Based Caries Scoring System for an Intraoral Scanner: An in vitro Study

OBJECTIVES

To develop an automated fluorescence-based caries scoring system for an intraoral scanner and totest the performance of the system compared to state-of-the-art methods.

METHODS

Seventy-three permanent posterior teeth were scanned with a three-dimensional (3D) intraoral scanner prototype which emitted light at 415 nm. An overlay representing the fluorescence signal from the tissue was mapped onto 3D models of the teeth. Multiple examination sites (n = 139) on the occlusal surfaces were chosen, and their red and green fluorescence signal components were extracted. These components were used to calculate 4 mathematical functions upon which a caries scoring system for the scanner prototype could be based. Visual-tactile (International Caries Detection and Assessment System, ICDAS), radiographic (ICDAS), and histological assessments were conducted on the same examination sites.

RESULTS

Most index tests showed significant correlation with histology. The strongest correlation was observed for the visual-tactile examination (rs = 0.80) followed by the scanner supported by the caries classification function that quantifies the overall fluorescence compared to sound surfaces (rs = 0.78). Additionally, this function resulted in the highest intra-examiner reliability (κ = 0.964), and the highest sum of sensitivity (SE) and specificity (SP) (sum SE-SP: 1.60-1.84) at the 2 histological levels where the comparison with visual-tactile assessment was possible (κ = 0.886, sum SE-SP = 1.57-1.81) and at the 3 out of 4 histological levels where the comparison with radiographic assessment was possible (κ = 0.911, sum SE-SP = 1.37-1.78); the only exception was for the lesions in the outer third of dentin, where the radiographic assessment showed the highest sum SE-SP (1.78).

CONCLUSION

A fluorescence-based caries scoring system was developed for the intraoral scanner showing promising performance compared to state-of-the-art caries detection methods. The intraoral scanner accompanied by an automated caries scoring system may improve objective caries detection and increase the efficiency and effectiveness of oral examinations. Furthermore, this device has the potential to support reliable monitoring of early caries lesions.

The Effect of Photodynamic Therapy and Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) on the Remineralization Rate of Non-Cavitated Root: an In-vitro Study

Using laser treatments and calcium and phosphate compounds to enhance remineralization has been investigated in this study. Seventy two premolar teeth were divided into four groups of 18: 1) control group; 2) laser therapy group; 3) CPP-ACP paste group; and 4) laser therapy and CPP-ACP group. Mineralization and remineralization of samples were investigated by Diagnodent. Data were reported using descriptive statistics (mean, standard deviation) and One Way ANOVA; they were analyzed using SPSS.16 statistical software. Statistical analysis showed that groups 3 and 4 had the highest rate of remineralization compared to groups 1 and 2. According to the results of this study, mineralization ranged decreasingly from group 4 to groups 3, 2, and 1, respectively. The antibacterial effect of laser therapy, leading to remineralization of calcium and phosphorus compounds, was the most effective on controlling root decay.

Demineralization detection in orthodontics using an ophthalmic optical coherence tomography device equipped with a multicolor fluorescence module

OBJECTIVES

Demineralizations such as white spot lesions are among the most prevalent side effects during orthodontic treatment. Fluorescence devices, including quantitative light-induced fluorescence (QLF), exploiting the intrinsic fluorescence of enamel and teeth and most recently optical coherence tomography (OCT) were introduced for early demineralization detection. In addition to near-infrared OCT scanning, multicolor modules allow for imaging with different laser wavelengths and the detection of reflective- and fluorescent light. The aim of this study was to evaluate a modified multicolor ophthalmic OCT device for the detection of early carious lesions in vitro and in vivo.

MATERIALS AND METHODS

Twenty-seven extracted lesion free human teeth were randomly assigned to three different demineralization protocols. Carious lesion detection was performed using macrophotography, OCT, and reflectance/fluorescence imaging using green laser and blue laser light. In addition, teeth of 5 orthodontic patients were OCT scanned, and fluorescence imaging using blue laser light was performed to assess demineralization after orthodontic therapy.

RESULTS

Both in vitro and in vivo, OCT allowed for precise determination of lesion depth and enamel loss. Fluorescence imaging using blue laser light was most sensitive for the detection of early demineralization in vitro and in vivo. However, established and severe demineralizations were also reliably detected by macrophotography in vitro and in vivo.

CONCLUSION

Demineralization can be detected with high sensitivity using blue fluorescence imaging with multicolor OCT devices.

CLINICAL RELEVANCE

In the future, OCT fluorescence imaging might be considered for longitudinal monitoring of dental hard tissue during orthodontic treatment in clinical trials.

Classification of dental diseases using hyperspectral imaging and laser induced fluorescence

PURPOSE

Early diagnosis of tooth enamel demineralization, and dentin caries lesions, present a valuable solution to avoid or decrease their deleterious effect. The aim of this study was to design a simple, effective, and non-invasive technique, employing a novel laser wavelength to classify and differentiate between various tooth abnormalities in-vitro, by estimating wavelengths, showing distinctive appearance for each tooth class.

METHODS

This study implies a fluorescence hyperspectral imaging system employing a 395-nm laser diode source, irradiating a pre-diagnosed 12 molars and premolars teeth. The obtained reconstructed images were displayed and processed by HSAnalysis2XL, accompanied by a custom made digital, and image signal processing algorithms, revealing the exact wavelengths, characterizing the fluorescence of each tooth pre-diagnosed class.

RESULTS

The proposed hyperspectral imaging system was able to discriminate between normal, and abnormal dental classes for the entire specimens. Furthermore, a series of wavelengths, noting each lesion individually were obtained from the spectroscopic hyperspectral output. The root calculus, white spot, dentin caries, and enamel caries have a bright visual appearance at λ₃ = 702 nm, λ₅ = 771 nm, and λ₆ = 798 nm respectively. Consequently, these abnormalities exhibit a dark appearance at λ₁ = 421 nm, λ₂ = 462 nm, and λ₄ = 734 nm. The wavelength selections were confirmed by the grayscale image outcomes.

CONCLUSIONS

This study provides a set of wavelengths that can be employed by dentists to diagnose white spot, root calculus, and enamel dentin caries lesions under the irradiation of a new UV-vis laser illumination source without, any hazardous thermal or mechanical effects.

Clinical validation and assessment of a modular fluorescent imaging system and algorithm for rapid detection and quantification of dental plaque

Background

Significant numbers of adults and children have untreated plaque due to poor oral hygiene and consequently suffer from associate dental and systemic diseases.

Methods

A handheld device equipped with 405 nm light-emitting diodes was constructed to examine the prevalence of red fluorescence signatures associated with dental plaque. This device was used for in vivo imaging of all four incisors and all four canines of twenty-eight consenting human subjects. The same areas were further imaged under white light illumination with a commercial image-processing based plaque-imaging device, and evaluated by a hygienist and dentist. A custom computer vision algorithm using pixel information was developed to calculate plaque coverage ratios ranging from 0 (no plaque) to 1 (complete plaque coverage) for images captured by both devices.

Results

The algorithm calculated red fluorescence-based plaque coverage ratios ranging from 0.011 to 0.211 for the subjects imaged. Clinical assessment and statistical analyses of associated plaque ratios of the 405 nm device images indicated high sensitivity and specificity in detecting dental plaque by the experimental device compared to the commercial reference device.

Conclusions

The low-cost and open source 405 nm device and the associated computer vision algorithm successfully captured red fluorescence signatures associated with dental plaque and demonstrated comparable performance to a commercially available device. Therefore, a proof of concept validation was provided for the construction and application of a sensitive cost-effective plaque-detecting device. A miniaturized mobile adaptable version of the device was also provided, together with and a step-by-step guide for device assembly and webhost the associated software, to facilitate open-source access to a cost-effective at-home, in-clinic oral care technology.

Trial registration

ClinicalTrials.gov NCT03379337, December 19 2017. Retrospectively registered.

Electronic supplementary material

The online version of this article (doi: 10.1186/s12903-017-0472-4) contains supplementary material, which is available to authorized users.

Objective identification of dental abnormalities with multispectral fluorescence imaging

Sensitive methods that can enable early detection of dental diseases (caries and calculus) are desirable in clinical practice. Optical spectroscopic approaches have emerged as promising alternatives owing to their wealth of molecular information and lack of sample preparation requirements. In the present study, using multispectral fluorescence imaging, we have demonstrated that dental caries and calculus can be objectively identified on extracted tooth. Spectral differences among control, carious and calculus conditions were attributed to the porphyrin pigment content, which is a byproduct of bacterial metabolism. Spectral maps generated using different porphyrin bands offer important clues to the spread of bacterial infection. Statistically significant differences utilizing fluorescence intensity ratios were observed among three groups. In contrast to laser induced fluorescence, these methods can provide information about exact spread of the infection and may aid in long term dental monitoring. Successful adoption of this approach for routine clinical usage can assist dentists in implementing timely remedial measures.

Early diagnosis of teeth erosion using polarized laser speckle imaging

Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, altering the tooth structure and making it more sensitive to mechanical erosion. Medical diagnosis of dental erosion is commonly achieved through a visual inspection by the dentist during dental checkups and is therefore highly dependent on the operator's experience. The detection of this disease at preliminary stages is important since, once the damage is done, cares become more complicated. We investigate the difference in light-scattering properties between healthy and eroded teeth. A change in light-scattering properties is observed and a transition from volume to surface backscattering is detected by means of polarized laser speckle imaging as teeth undergo acid etching, suggesting an increase in enamel surface roughness.

Effectiveness of Fluorescence-based Methods in Monitoring Progression of Noncavitated Caries-like Lesions on Smooth Surfaces

Although there has been a significant decrease in caries prevalence in developed countries, the slower progression of dental caries requires methods capable of detecting and quantifying lesions at an early stage. The aim of this study was to evaluate the effectiveness of fluorescence-based methods (DIAGNOdent 2095 laser fluorescence device [LF], DIAGNOdent 2190 pen [LFpen], and VistaProof fluorescence camera [FC]) in monitoring the progression of noncavitated caries-like lesions on smooth surfaces. Caries-like lesions were developed in 60 blocks of bovine enamel using a bacterial model of Streptococcus mutans and Lactobacillus acidophilus. Enamel blocks were evaluated by two independent examiners at baseline (phase I), after the first cariogenic challenge (eight days) (phase II), and after the second cariogenic challenge (a further eight days) (phase III) by two independent examiners using the LF, LFpen, and FC. Blocks were submitted to surface microhardness (SMH) and cross-sectional microhardness analyses. The intraclass correlation coefficient for intra- and interexaminer reproducibility ranged from 0.49 (FC) to 0.94 (LF/LFpen). SMH values decreased and fluorescence values increased significantly among the three phases. Higher values for sensitivity, specificity, and area under the receiver operating characteristic curve were observed for FC (phase II) and LFpen (phase III). A significant correlation was found between fluorescence values and SMH in all phases and integrated loss of surface hardness (ΔKHN) in phase III. In conclusion, fluorescence-based methods were effective in monitoring noncavitated caries-like lesions on smooth surfaces, with moderate correlation with SMH, allowing differentiation between sound and demineralized enamel.

Determination of porphyrins in oral bacteria by liquid chromatography electrospray ionization tandem mass spectrometry

Biofilms in the oral cavity can be visualized by fluorescence and a common assumption is that the endogenously produced porphyrins in certain bacteria give rise to this fluorescence. Porphyrin content in oral bacteria has been sparingly investigated, and non-selective detection techniques such as utilizing the Soret fluorescence band of porphyrins are often used. In the present study, a quantitative and selective method for the determination of porphyrins in oral bacteria has been developed and validated using high performance liquid chromatography-tandem mass spectrometry. Lysis of bacteria using Tris-EDTA buffer together with ultrasonication showed high microbial killing efficiency ≥99.98 %, and sample clean-up using C₁₈-solid phase extraction resulted in low matrix effects ≤14 % for all analytes. Using this method, the porphyrin content was determined in the two oral pathogens Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, as well as for baker’s yeast, Saccharomyces cerevisiae. Uroporphyrin, 7-carboxylporphyrin, 6-carboxylporphyrin, coproporphyrin, and protoporphyrin IX were identified in the investigated microorganisms, and it was shown that the porphyrin profile differs between the two bacteria, as well as for S. cerevisiae. To our knowledge, this is the first time the porphyrin profile has been determined for the bacterium A. actinomycetemcomitans.

Graphical Abstract

Discrimination of healthy and carious teeth using laser-induced breakdown spectroscopy and partial least square discriminant analysis

In the laser drilling of teeth, a microplasma is generated which may be utilized for elemental analysis of ablated tissue via a laser-induced breakdown spectroscopy (LIBS) technique. In this study, LIBS is used to investigate the possibility of discrimination of healthy and carious tooth tissues. This possibility is examined using multivariate statistical analysis called partial least square discriminant analysis (PLS-DA) based on atomic and ionic emission lines of teeth LIBS spectra belonging to P, Ca, Mg, Zn, K, Sr, C, Na, H, and O elements. Results show an excellent discrimination and prediction of unknown tooth tissues. It is shown that using the PLS-DA method, the spectroscopic analysis of plasma emission during the laser drilling, would be a promising technique for caries detection.

Imaging carious dental tissues with multiphoton fluorescence lifetime imaging microscopy

In this study, multiphoton excitation was utilized to image normal and carious dental tissues noninvasively. Unique structures in dental tissues were identified using the available multimodality (second harmonic, autofluorescence, and fluorescence lifetime analysis) without labeling. The collagen in dentin exhibits a strong second harmonic response. Both dentin and enamel emit strong autofluorescence that reveals in detail morphological features (such as dentinal tubules and enamel rods) and, despite their very similar spectral profiles, can be differentiated by lifetime analysis. Specifically, the carious dental tissue exhibits a greatly reduced autofluorescence lifetime, which result is consistent with the degree of demineralization, determined by micro-computed tomography. Our findings suggest that two-photon excited fluorescence lifetime imaging may be a promising tool for diagnosing and monitoring dental caries.

Caries Detection Methods Based on Changes in Optical Properties between Healthy and Carious Tissue

A conservative, noninvasive or minimally invasive approach to clinical management of dental caries requires diagnostic techniques capable of detecting and quantifying lesions at an early stage, when progression can be arrested or reversed. Objective evidence of initiation of the disease can be detected in the form of distinct changes in the optical properties of the affected tooth structure. Caries detection methods based on changes in a specific optical property are collectively referred to as optically based methods. This paper presents a simple overview of the feasibility of three such technologies for quantitative or semiquantitative assessment of caries lesions. Two of the techniques are well-established: quantitative light-induced fluorescence, which is used primarily in caries research, and laser-induced fluorescence, a commercially available method used in clinical dental practice. The third technique, based on near-infrared transillumination of dental enamel is in the developmental stages.

Combining casein phosphopeptide-amorphous calcium phosphate with fluoride: synergistic remineralization potential of artificially demineralized enamel or not?

Recaldent is a product of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). The remineralizing potential of CPP-ACP per se, or when combined with 0.22% Fl gel on artificially demineralized enamel using laser florescence, is investigated. Mesial surfaces of 15 sound human molars are tested using a He-Cd laser beam at 441.5 nm with 18-mW power as an excitation source on a suitable setup based on a Spex 750-M monochromator provided with a photomultiplier tube (PMT) for detection of collected autofluorescence from sound enamel. Mesial surfaces are subjected to demineralization for ten days. The spectra from demineralized enamel are measured. Teeth are divided into three groups according to the remineralizing regimen: group 1 Recaldent per se, group 2 Recaldent combined with fluoride gel and ACP, and group 3 artificial saliva as a positive control. After following these protocols for three weeks, the spectra from the remineralized enamel are measured. The spectra of enamel autofluorescence are recorded and normalized to peak intensity at about 540 nm to compare spectra from sound, demineralized, and remineralized enamel surfaces. A slight red shift occurred in spectra from demineralized enamel, while a blue shift may occur in remineralized enamel. Group 2 shows the highest remineralizing potential. Combining fluoride and ACP with CPP-ACP can give a synergistic effect on enamel remineralization.

Spectroscopic investigations of carious tooth decay

We report on the elemental composition of healthy and infected part of human tooth using laser induced breakdown spectroscopy (LIBS). We have used prominent constituent transitions in laser-excited tooth to diagnose the state of the tooth. A nanosecond laser pulse (355nm, 5ns) was used as an ablating pulse and the sodium (3s2S-3p2P) at 588.99 and (3s2S-3p2P) at 589.99nm, strontium (5s21S-1s5P) at 460.55nm, and calcium (3d3D-4f 3F0) at 452.55nm transitions for spectroscopic analysis. The spectroscopic observations in conjunction with discriminate analysis showed that calcium attached to the hydroxyapatite structure of the tooth was affected severely at the infected part of the tooth. The position-time plots generated from two-dimensional (2D) images conclusively showed a decrease in calcium concentration in the infected region of the irradiated tooth. Using the technique, we could distinguish between the healthy and carious parts of the tooth with significant accuracy.

Time-correlated single-photon counting fluorescence lifetime confocal imaging of decayed and sound dental structures with a white-light supercontinuum source

We report the demonstration of time-correlated single-photon counting (TCSPC) fluorescence lifetime imaging (FLIM) to ex vivo decayed and healthy dentinal tooth structures, using a white-light supercontinuum excitation source. By using a 100 fs-pulsed Ti:Sapphire laser with a low-frequency chirp to pump a 30-cm long section of photonic crystal fibre, a ps-pulsed white-light supercontinuum was created. Optical bandpass interference filters were then applied to this broad-bandwidth source to select the 488-nm excitation wavelength required to perform TCSPC FLIM of dental structures. Decayed dentine showed significantly shorter lifetimes, discriminating it from healthy tissue and hard, stained and thus affected but non-infected material. The white-light generation source provides a flexible method of producing variable-bandwidth visible and ps-pulsed light for TCSPC FLIM. The results from the dental tissue indicate a potential method of discriminating diseased tissue from sound, but stained tissue, which could be of crucial importance in limiting tissue resection during preparation for clinical restorations.