光学相干断层成像检测牙釉质表层脱矿与再矿化的实验研究

目的利用光学相干断层成像技术(OCT)观察不同制剂对年轻恒牙釉脱矿和再矿化效果的影响。方法 将正畸拔除的年轻恒前磨牙制成60个釉质块,随机均分为4组。每天进行如下处理:A组蒸馏水湿敷30min;B组含氟牙膏湿敷30min;C组护牙素湿敷30min;D组多乐氟湿敷30min,置于脱矿液1.5h,最后置于人工唾液中22h。每个步骤间用去离子水冲洗实验样品。实验周期重复30天。在处理前和第 7、15、30天,使用扫频光源OCT完成对样本的扫描和成像,同时使用显微硬度计测量各样本表面的显微硬度。结果 釉质脱矿深度:7天后,A组与其他各组相互比较,差异有统计学意义( P <0.05),B、C、D组组间比较差异无统计学意义( P >0.05)。30天后,C组和D组比较,差异无统计学意义( P >0.05),其余各组之间两两比较,差异均有统计学意义( P <0.05)。显微硬度测量:30天后,各处理组较处理前显微硬度值降低,A组显微硬度值最低,C组与D组显微硬度值高于B组,且差异有统计学意义( P <0.05)。C组和D组间釉质块显微硬度值差异无统计学意义( P >0.05)。结论 OCT可以较准确的显示釉质脱矿部位,在早期龋的诊断方面具有临床意义。护牙素和多乐氟均能有效的抑制牙釉质表面脱矿。     

Three-dimensional assessment of proximal contact enamel using optical coherence tomography

Objective

The purpose of this study was to detect and investigate the association of enamel microcracks with demineralization at proximal contact areas of premolars, using 3D swept-source optical coherence tomography (SS-OCT).

In vitro longitudinal evaluation of enamel wear by cross-polarization optical coherence tomography

ObjectivesEnamel thickness determination by Cross-Polarization Optical Coherence Tomography (CP-OCT) is a promising approach for quantitative monitoring of tooth wear progression. This study evaluated the ability of CP-OCT to quantify the thickness of natural enamel before, during and after tooth wear simulation.Materials and MethodsNatural, unpolished human dental enamel slabs were submitted to five wear stages (Wear 1: to level the surfaces; Wear 2 to Wear 5: 0.05 ± 0.02 mm reduction each) simulated by an automatic grinding/polishing machine. Enamel thickness was evaluated with CP-OCT and a gold-standard method (micro-CT) at baseline and after every wear stage. Data were analyzed using ANOVA with pairwise comparisons for wear stages’ impact on the thickness and wear depth measurements. The inter-method agreement was analyzed using intra-class correlation coefficients, the difference between means, and Bland-Altman plots.ResultsEnamel thickness measurements (mean ± standard error, in mm) with natural (1.40 ± 0.05) and worn surfaces (1.08 ± 0.02) by CP-OCT did not differ significantly from those measured by micro-CT (natural = 1.39 ± 0.05; worn = 1.09 ± 0.02; p-values = 0.30 and 0.39, respectively). CP-OCT and micro-CT showed excellent agreement on natural (ICC = 0.98) and worn surfaces (ICC = 0.98) enamel thickness measurements. Among and between wear stages, there were significant differences in enamel thickness and wear depth measurements for both methods (p-value <0.0001 for all). Both methods yielded similar measurements’ mean (0.14 ± 0.01; p-value = 0.87) and were in good agreement (ICC = 0.77) for wear depth estimation.SignificanceCP-OCT allows accurate measurement of enamel thickness on natural tooth surfaces. Enamel thickness measurement by CP-OCT allows quantitative monitoring of enamel thickness changes and wear depth following progressive wear.     

Non-destructive examination of interfacial debonding using acoustic emission

Objectives

This study aims to assess the viability of using the acoustic emission (AE) measurement technique to detect and monitor in situ the interfacial debonding in resin composite restorations due to build-up of shrinkage stresses during polymerization of the composite.

Materials and methods

The non-destructive testing technique that measures acoustic emission (AE) was used to detect and monitor the interfacial debonding in resin composite during curing of the composite. Four groups of specimens, n = 4 each, were tested: (1) intact human molars with Class-I cavities restored with the composite Z100 (3M ESPE, USA); (2) intact human molars with Class-I cavities restored with the composite Filtek™ P90 (3M ESPE, USA); (3) ring samples prepared from the root of a single bovine tooth and ‘restored’ with Z100; (4) freestanding pea-size specimens of Z100 directly placed on the AE sensor. The restorations in Groups (1)-(3) were bonded to the tooth tissues with the adhesive Adper™ Scotchbond™ SE Self-Etch (3M ESPE, USA). The composites in all the specimens were cured with a blue light (3M ESPE, USA) for 40 s. The AE signals were recorded continuously for 10 min from the start of curing. Non-destructive 3D imaging was performed using X-ray micro-computed tomography (micro-CT) to examine the bonding condition at the tooth-restoration interface.

Results

The development of AE events followed roughly that of the shrinkage stress, which was determined separately by the cantilever beam method. The number of AE events in the real human tooth samples was more than that in the ring samples, and no AE events were detected in the pea-size specimens placed directly on the AE sensor. The number of AE events recorded in the specimens restored using Z100 was more than that found in specimens restored with Filtek P90. The micro-CT imaging results showed clear interfacial debondings in the tooth specimens restored with Z100 after curing, but no clear debonding was found in the P90 specimens.

Conclusions

The AE technique is an effective tool for detecting and monitoring in situ the interfacial debonding of composite restorations during curing. It can potentially be employed to evaluate the development of shrinkage stress and the quality of interfacial bonds in teeth restored with different composite materials, cavity geometries, and restorative techniques.     

Non-invasive quantification of resin-dentin interfacial gaps using optical coherence tomography: Validation against confocal microscopy

Objectives

Regardless of the cause, gap formation at the tooth-restoration interface may result in treatment failure; non-destructive assessment and monitoring of these defects are important. The aim of this in vitro study is to assess the tooth-restoration interface using a non-invasive technique; swept source optical coherence tomography (SS-OCT) and to confirm the findings with confocal laser scanning microscope (CLSM).

Methods

Cylindrical class-I cavities (3 mm in diameter and 1.5 mm in depth) were prepared in the occlusal surface of human premolars. Each cavity was restored using an all-in-one adhesive system (Clearfil Tri-S Bond) and one of the three types of composites placed in bulk; Majesty Posterior, AP-X and Majesty LV (all by Kuraray Medical, Japan). Ten serial cross-sectional images of the whole restored cavity were obtained by SS-OCT at 1319 nm center wave length, to which locations the specimens were later trimmed, polished and observed under CLSM. An image analysis software was used to detect significant peaks in the signal intensity at the resin-dentin interface of the cavity floor. The presence and dimensions of gaps at the interface were also confirmed by CLSM.

Results

Increased SS-OCT signal intensity along the interface corresponded well to the interfacial gaps detected by CLSM. The actual gap size detected ranged from 26 μm to 1.9 mm in length, and the universal composite APX showed lowest interfacial gaps.

Conclusion

SS-OCT imaging technology can be used to non-invasively detect and quantify micrometer gaps at the bottom of composite restorations, and potentially become a monitoring tool for composite restorations both in the laboratory research, and in the clinics.     

An acoustic emission study on interfacial debonding in composite restorations

Objective

This paper studied in vitro the effect of the C-factor on interfacial debonding during curing of composite restorations using the acoustic emission (AE) technique. Finite element (FE) analyzes were also carried out to evaluate the interfacial stresses caused by shrinkage of the composite resin in restorations with different C-factors.

Materials and methods

Twenty extracted third molars were divided into 4 groups of 5. They were cut to form Class-I (Groups 1 and 2) and Class-II (Groups 3 and 4) cavities with different C-factors. The average C-factors of the four groups were 3.37, 2.88, 2.00, and 1.79, respectively. The cavities were then applied with an adhesive and restored with a composite, which was cured by a halogen light for 40 s. A 2-channel AE system was used to monitor the interfacial debonding, caused by shrinkage stress, between the tooth and restoration through an AE sensor attached to the surface of the specimen. Recording of the AE started at the same time as curing of the composite and lasted 10 min. Simplified FE models were used to evaluate the interfacial stresses in restorations with different C-factors, with a thermal load (temperature decrease) being applied to the composite resin to simulate its shrinkage.

Results

The mean and standard deviation of the total number of AE events for the four groups were 29.6 ± 15.7, 10.0 ± 5.8, 2.6 ± 1.5, and 2.2 ± 1.3, i.e. the number of AE events increased with an increase in the C-factor. The FE results also showed that, the higher the C-factor of the restoration, the higher the interfacial tensile stress between the tooth and restoration.

Significance

From the results of the AE tests and FE simulations, it can be concluded that, the higher the C-factor, the higher the shrinkage stress and the more likely is interfacial debonding.     

Evaluation of oral vascular anomalies using optical coherence tomography

Optical coherence tomography (OCT) is a new method of biomedical imaging that can generate high-resolution, cross-sectional images of microstructures. The purpose of this study was to present the first OCT images of oral vascular anomalies using a new advanced OCT scanner that we have developed, and to discuss the application of our system for oral soft tissues. Knowledge of the size and area of the vascular structures can be useful for the diagnosis and choice of the best treatment. Before excision, oral vascular malformations were assessed by OCT in vivo. Histopathological sections were taken and compared with the OCT images to make clinicopathological correlations. OCT provided clear images of all the vascular lesions examined. Oval to roundish, signal-poor areas sharply demarcated by a surrounding signal-rich layer correlated well with the histopathological diagnosis. OCT images provide information about subsurface structure non-invasively that is otherwise obtainable only by examination of a biopsy specimen. The analysis of oral vascular lesions by OCT provides new insights into non-invasive diagnosis and can be helpful in the selection of the most appropriate treatment.     

Marginal analysis of resin composite restorative systems using optical coherence tomography

Objectives

To analyze marginal integrity of resin composites dental restorations using optical coherence tomography (OCT).

Methods

Thirty extracted human premolars had occlusal cavities prepared and were randomly divided according to the restorative systems evaluated: Filtek P90™/P90 Adhesive System™, Filtek Z350™, and Filtek Z250™/Single Bond™ (3 M/ESPE). The teeth were then stored in the dark for 24 h in 0.9% saline solution. Restorations were finished and polished and stored again for 24 h before thermocycling (500 cycles, 5–55 °C). A commercially available OCT system was used (SR-OCT: OCP930SR/Thorlabs) with 930 nm central wavelength. Cross-sectional images were obtained every 250 μm and evaluated using Image J. A-scans were analyzed using the Origin 8.0 program, after a filter treatment using Matlab.

Results

The qualitative analysis of the internal margins did not observe gaps even after A-scan examination, although distinctive patterns were found for each restorative system. Penetration of Single Bond and Filtek P90 self-etch primer into dentin was also observed. A thick adhesive layer was found for Filtek P90 bonding agent.

Significance

Considering the characteristics of the OCT system, the setup used in this study was capable of evaluating the marginal integrity of resin composite restorations and detecting some interaction between dental bonding agents and dental substrates. OCT can be considered a promising method for the evaluation of the internal margins of restorations in vivo.     

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 3 M ESPE, St. Paul, MN) and composite (Transbond XT from 3 M 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.     

In vitro examination of suspicious oral lesions using optical coherence tomography

We compared findings of optical coherence tomography (OCT) with histopathological results of suspicious oral lesions to assess the feasibility of using OCT to identify malignant tissue. Thirty-four oral lesions from 27 patients had swept-source frequency-domain OCT. Four variables were assessed (changes in keratin, epithelial, and sub-epithelial layers, and identification of the basement membrane) and from this we calculated whether or not there were architectural changes. These data were then compared with histopathological results. Two clinicians, who were unaware of the clinical and histopathological diagnoses, decided whether biopsy was necessary. The basement membrane was recognised in only 15 oral lesions. OCT could identify diseased areas but could not provide a diagnosis or differentiate between lesions. The two clinicians, who recommended biopsy agreed in all cases. This pilot study confirms the feasibility of using OCT to identify architectural changes in malignant tissues.     

Evaluation of the integrity of dental sealants by optical coherence tomography

Objectives

The purpose of the present research was to demonstrate images of failures into the structure of pit and fissure sealants using optical coherence tomography (OCT).

Methods

Five human third molars were selected and the sealant ALPHA SEAL LIGHT/DFL was applied according to the manufacturer instructions. For evaluation of the structure of pit and fissure sealants, twenty OCT images of each tooth were performed before and after application of sealant. A total of 200 images were evaluated. A home built spectral OCT system used was operating in spectral domain (SD-OCT), at 840 nm and a measured spatial resolution of 10 μm. The system is based on the Michelson interferometer set-up and is controlled by the software OCT 800 - Complex Square/LabView, that collects data and generates the image. The occlusal surfaces were scanned in a bucco-lingual direction and tomographic images parallel to long axis of tooth were obtained. After the achievement of the images by OCT, the crown of each tooth was sectioned in a occlusogingival direction (buccolingually). Images from each section were obtained and evaluated by an optical microscope. OCT and microscopic images were compared.

Results

Representative images showed that OCT image provides the insight into sealant material. It was possible to clearly identify the internal structure of sealant and the subjacent enamel. Sealant and enamel are very well distinguished, and failures at the interior and at surface are well detected.

Significance

OCT could generate images of the features of fissures, bubbles and failures in the adaptation of sealants, opening up possibilities in the future to monitoring sealant application and retention in short and long term.     

釉质早期龋的光学相干断层成像与定量研究

目的 探讨光学相干断层成像技术（OCT）对釉质早期龋的成像和量化评估效能,为其在早期龋临床诊断中的应用提供实验依据。方法 采用OCT扫描牛牙光滑面早期人工龋模型和脱矿模型,获取釉质图像和光学信息,并与偏振光显微镜图像和原子吸收光谱测得的矿质损失量进行对比,采用SPSS软件包配对t检验和Pearson相关性分析进行数据分析。结果 早期龋及脱矿釉质OCT图像与偏光显微镜图像基本相符;OCT测得的早期龋组釉质的总反射率改变量低于脱矿组（P<0.05）,脱矿深度在两组间无统计学差异（P>0.05）。釉质总反射率改变量与矿质损失量呈正相关（P<0.05）。结论 OCT能够无创地、较准确地显示釉质早期龋的矿质改变,量化其病变范围和程度,在早期龋的临床诊断方面具有广阔的应用前景。     

光学相干成像无创检测不同漂白方法对釉质白斑治疗效果的实验研究

目的 探讨采用光学相干成像技术(OCT)检测不同漂白方法对釉质白斑的治疗效果,评价其用于釉质白斑治疗效果监测的可行性。方法 选取因正畸拔除的完整离体前磨牙48颗,在牙冠颊面正中切取4 mm×4 mm×2 mm釉质块。在其表面(除颊侧面外)涂布抗酸指甲油后,置于脱矿溶液中浸泡18 d,建立釉质白斑体外脱矿模型。将样本随机分为4组(n=12),A组为对照组仅脱矿处理;B组为40%过氧化氢漂白处理;C组为Icon渗透树脂处理;D组为40%过氧化氢漂白联合Icon渗透树脂处理。每组随机抽取8个样本,应用OCT扫描釉质块颊侧面,观察各组釉质表层成像变化并测量表层光强改变;将釉质块用环氧树脂包埋固定(仅暴露颊侧面),显微硬度仪测量并记录各组硬度值变化。各组剩余4个样本纵向切开,扫描电镜观察各组样本超微结构变化。结果 OCT显示,各组釉质表层光散射特性均发生改变,可见高亮层形成,但C、D组的高亮层厚度显著低于A、B组(P<0.05)。各组样本显微硬度值分别是(214.99±31.70)、(250.66±33.64)、(312.42±18.01)、(286.53±26.65)kg/mm^...     

Evaluation of dental caries,tooth crack,and age-related changes in tooth structure using optical coherence tomography

Optical coherence tomography (OCT) is an imaging technique that can visualize the internal biological structure without X-ray exposure. Swept-source OCT (SS-OCT) is one of the latest version of OCT, wherein the light source is a tunable laser that sweeps near-infrared wavelength light to achieve real-time imaging. The imaging depth of OCT is highly influenced by the translucency of the medium. The medium that does not transmit light and the deeper structure beyond the range of light penetration depth are not relevant for OCT imaging. In OCT, sound enamel is almost transparent at the OCT wavelength range, and enamel and dentin can be distinguished from each other as the dentin–enamel junction (DEJ) appears as a dark border. Demineralized enamel and dentin are imaged as bright zones because of the formation of numerous micro-porosities where the backscatter of OCT signal is increased. In cavitated caries at interproximal or occlusal hidden zone, the upper margin of the cavity reflects the signal showing a distinct bright border in the SS-OCT image. SS-OCT is capable of determining crack penetration depth even when the cracks extended beyond the DEJ. SS-OCT has a high degree of sensitivity and specificity for the detection of dental caries and tooth cracks. SS-OCT is also capable of detecting non-carious cervical lesions and occlusal tooth wear in cross-sectional views to estimate the amount of tooth structure loss.     

Sealing performance of resin cements before and after thermal cycling: Evaluation by optical coherence tomography

Objectives

Self-adhesive resin cements have been recently introduced; however, there is little data available on their long-term performance. In this in vitro study, swept-source optical coherence tomography (OCT) at 1310 nm center wavelength was used for monitoring adaptation of indirect resin restorations after thermal cycling.

Methods

Resin inlays were luted to class-I cavities of extracted human teeth using three resin cements; Clearfil SA Luting (SA; Kuraray), Bistite II DC or Multibond II (Tokuyama Dental). Each cement was applied with or without pre-coating of dentin by a self-etch adhesive (Clearfil SE Bond) and a low-viscosity microfilled resin. OCT imaging was performed after 24 h, after 2000 and after 10,000 thermocycles (n = 5). Selected samples were sectioned for interfacial observation by confocal laser scanning microscope (CLSM). Floor adaptation (percentage) was analyzed by software on 20 B-scans throughout each specimen, and subjected to statistical analysis by three-way ANOVA test at a significance level of 0.05.

Results

Resin cement type, resin coating and thermal aging all significantly affected adaptation (p < 0.05). Initially, SA showed the highest adaptation; however, thermal aging significantly affected its sealing. The best results for all the cements were consistently achieved when the resin coating technique was applied where no deterioration of interfacial integrity was observed in the coated groups. CLSM closely confirmed OCT findings in all groups.

Significance

OCT could be used for monitoring of composite inlays with several interfacial resin layers. The application of a direct bonding agent in the resin-coating technique improved interfacial sealing and durability of all resin cements.     

光学相干断层成像技术在龋病诊断中的研究进展

早期诊断龋病能够及时干预病变,终止或逆转龋病进程,降低治疗成本。现有的临床及影像学检查手段对龋病诊断的敏感性较低。光学相干断层成像作为一种无创、无辐射的高敏感性和特异性的检测手段,在龋病的诊断中有着良好的应用前景。本文就光学相干断层成像检查原理以及其在平滑面龋、窝沟龋、邻面龋和继发龋诊断中的研究进展作一综述。     

光学相干层析技术用于早期龋检测的研究进展

早期发现龋损病变并进行及时正确地干预可以逆转龋病的进程,最大限度地保存牙齿,减少创伤性治疗;因此,龋病的早期准确诊断就显得非常重要。目前,临床上使用的常规检测龋病的方法无法客观、有效地检测早期龋,更不能对龋损进程进行定量监测,这就往往使患者丧失了保守治疗的最佳时机;因此,迫切需要安全、准确、可量化的技术来检测早期龋并对治疗干预措施进行监控。近年已开发出一系列检测早期龋的无创、定量检测新技术,本文就光学相干层析技术(OCT)用于检测早期光滑面釉质龋、早期牙骨质龋、早期窝沟龋等方面的研究作一综述。     

Evaluation of bacteria-induced enamel demineralization using optical profilometry

ObjectivesStreptococcus mutans is considered a major causative of tooth decay due to its ability to rapidly metabolize carbohydrates such as sucrose. One prominent excreted end product of sucrose metabolism is lactic acid. Lactic acid causes a decrease in the pH of the oral environment with subsequent demineralization of the tooth enamel. Biologically relevant bacteria-induced enamel demineralization was studied.MethodsOptical profiling was used to measure tooth enamel decay with vertical resolution under one nanometer and lateral features with optical resolution as a result of S. mutans biofilm exposure. Comparison measurements were made using AFM.ResultsAfter 72 h of biofilm exposure the enamel displayed an 8-fold increase in the observed roughness average (R_a), as calculated over the entire measured array. Similarly, the average root mean square (RMS) roughness, R_RMS, of the enamel before and after biofilm exposure for 3 days displayed a 7-fold increase. Further, the direct effect of chemically induced enamel demineralization using biologically relevant organic acids was shown. Optical profiles of the enamel surface after addition of a 30% lactic acid solution showed a significant alteration in the surface topography with a corresponding increase in respective surface roughness statistics. Similar measurements with 10% citric acid over seconds and minutes give insight into the demineralization process by providing quantitative measures for erosion rates: comparing surface height and roughness as metrics.SignificanceThe strengths of optical profilometry as an analytical tool for understanding and analyzing biologically relevant processes such as biofilm induced tooth enamel demineralization were demonstrated.