Ultrastructural features of dentinoenamel junction revealed by focused gallium ion beam milling

Effect of cigarettes smoke on bonded polymeric restorations: OCT study

Background

Up to date, the effect of cigarette smoke (CS) on the adhesive properties of the restorative materials bonded to tooth structure is still unclear. It is still questionable if it interferes with the durability and clinical success of these restorations. Few numbers of studies reported the assessment of microgaps of dental composite using cross-polarization optical coherence tomography (CP-OCT). The aim of this study was to evaluate the presence of interfacial microgaps between composite resin restoration and the tooth structure with or without exposure to CS under the CP-OCT.

Materials and methods

In this in-vitro study, a standardized round class-V cavities were prepared in twenty extracted, caries-free human molar teeth, and they were divided randomly into two groups (n = 10). Adhesive system (Gluma universal, Kulzer GmbH) was applied followed by filing the prepared cavities with flowable composite restoration (Charisma, Kulzer GmbH). Then, exposure to CS (40 cigarettes/day) was carried out for 14 days and the samples were stored in normal saline solution after each smoke exposure cycle. Next, all samples were immersed in ammoniac silver nitrate for 24 h, followed by immersion in a photo-developing solution for 8 h. Optical comparison was carried out by CP-OCT to assess microgaps percentage between smoke (SG) and non-smoke groups (NSG) at the axial walls (AW) and cavity floor (CF).

Results

Independent T-test showed that there was a significant difference between the two groups (SG, NSG) in AW microgaps percentage (p = 0.008), while there was no difference in CF (p = 0.15).

Conclusion

It can be inferred from the current finding that OCT can be used to predict the adaptability of the bonded restoration under the thermochemical influence. CS has a negative effect on the marginal integrity of the bonded polymeric restorations.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Advanced imaging of dentin microstructure

This study aimed to demonstrate the feasibility of using optical coherence tomography (OCT) for locating the sectioning site of a specimen before characterizing the ultrastructural features of dentin surfaces as well as the inner wall of the dentinal tubules (DT) using a field emission scanning electron microscope (FESEM). Eight sound human molar teeth were extracted, examined via cross-polarization optical coherence tomography (CP-OCT), embedded, and hemisectioned using a low-speed diamond sawing machine. Next, each sectioned surface was further trimmed, polished, and examined under a confocal laser scanning microscope (CLSM) to locate the target area on the superficial dentin. Subsequently, each section was gold-coated and examined using FESEM. Backscattered reflection from the dentin layer was less than that from the enamel under CP-OCT. Distinct reflections from certain enamel and dentin microstructures were observed before sectioning the specimens. Areas with enamel cracks and dentin defects were identified and avoided during sectioning. At the micron level, the CLSM images exhibited a homogenous distribution of the DT orifices. Low magnification FESEM images showed intertubular dentin as a loosely condensed globular layer with shallow grooves in between, whereas peritubular dentin exhibited more organized condensation of apatite crystals surrounding the DT orifices. High magnification of the DT revealed a cross-linking layer of mineralized collagen network extending in the peri-intratubular lumen, with scattered globules of matrix vesicles. CP-OCT enabled the realization of rapid initial scanning and image acquisition with high contrast at the micron scale before profound insights into dentin ultrastructures at the nano scale were provided by FESEM. The variations in structural densities of the dental tissues significantly affected the image contrast and helped identify underlying structures.

Tomographic Evaluation of the Internal Adaptation for Recent Calcium Silicate-Based Pulp Capping Materials in Primary Teeth

Objectives

To evaluate the internal adaptation of recent pulp capping materials (TheraCal and Biodentine) relative to MTA when used as indirect pulp capping for primary teeth.

Materials and Methods

Thirty primary molars were randomly allocated into three groups, group (A) was TheraCal, group (B) was Biodentine, and MTA was the control group (C). A standardized round class-V cavity (1.5 mm diameter and 2 mm depth) was prepared using a milling machine on the buccal surface of each tooth with the pulpal floor located on the dentin. Then, pulp-capping materials were applied. Finally, all teeth were restored by composite restoration. The internal adaptation of the pulp-capping materials to the dentinal surface was investigated by microcomputed tomography (Micro-CT) to determine the internal gap volume, and by optical coherence tomography (OCT) to determine the high-intensity reflection of light from the floor.

Results

Based on Micro-CT findings, TheraCal showed significantly higher internal gap volume than both MTA and Biodentine (p < 0.001), while MTA and Biodentine did not show a significant difference in the gap volume. Based on the OCT findings, TheraCal showed a significantly higher intensity of light reflection than both MTA and Biodentine (p < 0.001); however, there was no significant difference between MTA and Biodentine. Pearson's correlation test showed that there was a strong positive correlation between Micro-CT and OCT (r = 0.686, N = 30, p < 0.001).

Conclusions

Biodentine and MTA showed a comparable result in terms of their internal adaptation on the dentinal surface of the primary teeth, and both were better than TheraCal. There is a moderate to a strong positive correlation between Micro-CT and OCT in the measurement of internal adaptation of the tested pulp capping materials. OCT can be helpful and beneficial for the clinical setting and allow dentists to screen and evaluate restorations during follow-up.

Optical comparison between micro-CT and OCT in imaging of marginal composite adaptation: Observational study

Dental composite is the most used aesthetic restorative biomaterial worldwide. However, it undergoes polymerisation shrinkage that could lead to loss of the interfacial seal between tooth and resin in some circumstances. This demands high-resolution imaging technologies to detect these defects. This study carried out a comparison between microcomputed tomography (micro-CT; Shimadzu, Japan) and swept-source optical coherence tomography (SS-OCT; Santec, Japan) in the detection of marginal adaptation defects at the tooth-resin interface. Unlike in micro-CT, it was possible to outline interfacial gaps along with tooth-resin interfaces with SS-OCT, which was attributed to the Fresnel diffraction of light. This in vitro comparison demonstrates SS-OCT has great potential in dental imaging to effectively assess dental composite adaptation and marginal defects when high resolution is desired in real time. LAY DESCRIPTION: Detection of tooth-colored restoration defects had been assessed by different radiographic methods. However, most of these methods are either invasive or suffer from low-resolution. In this study, a comparison has been carried out between two different high-resolution imaging systems; microcomputed tomography and optical coherence tomography, to explore their potentials in detecting restorations defects. The results showed optical coherence tomography has a great accuracy in locating the underlying defects when the obtained images were validated against confocal laser scanning microscopy images.

Effect of light irradiation condition on gap formation under polymeric dental restoration; OCT study

OBJECTIVE

To investigate the effect of two light-curing systems; quartz tungsten-halogen (QTH) and light-emitting diode (LED), and irradiation time on interfacial gap formation of dental composite resin restorations bonded with an adhesive resin using optical coherence tomography (OCT).

MATERIALS AND METHODS

Forty cavities were prepared in extracted human molar teeth and divided into four groups (n=10) based on the type of light curing system QTH (LITEX 680A) and LED (Demi Plus) and curing duration (10 s or 40 s). A single-step self-etching dental adhesive (Tetric® N-Bond; Ivoclar Vivadent AG, Schaan, FL, Liechtenstein) was applied and polymerized with QTH for 10 s (QTH-10), or for 40 s (QTH-40). Similarly, the adhesive in LED-10 and LED-40 groups was polymerized with an LED for 10 s or 40 s, respectively. Then, all specimens were restored with Filtek™ Z350 XT flowable composite (3M ESPE AG, St. Paul, MN, USA) and immersed in ammoniacal silver-nitrate contrasting solution. Cross-sectional images were recorded at every 250μm using cross-polarization OCT system (CP-OCT; IVS-300, Santec, Komaki, Aichi, Japan). Image analysis to quantify the percentage of gap at resin-dentin interface was performed using a custom plugin for ImageJ software.

RESULTS

Data analysis using one-way ANOVA showed a significant difference in mean gap percentage between the four test groups (p<0.0001). Mean gap percentage values were 75.8%, 53.2%, 9.9% and 5.6%. The highest for LED-10 followed by LED-40 (p <0.05). QTH-40 revealed a slightly better adaptation compared with QTH-10, but the difference between them was not significant (p <0.05).

CONCLUSION

CP-OCT with a contrast agent is a useful non-invasive imaging tool for dental composite resin materials. QTH showed better results than LED under the experimental conditions. When using an LED light-curing unit, prolonged irradiation improved interfacial adaptation of dental composite bonded with a self-etching adhesive.

Development of protocols for the first serial block-face scanning electron microscopy (SBF SEM) studies of bone tissue

There is an unmet need for a high-resolution three-dimensional (3D) technique to simultaneously image osteocytes and the matrix in which these cells reside. In serial block-face scanning electron microscopy (SBF SEM), an ultramicrotome mounted within the vacuum chamber of a microscope repeatedly sections a resin-embedded block of tissue. Backscattered electron scans of the block face provide a stack of high-resolution two-dimensional images, which can be used to visualise and quantify cells and organelles in 3D. High-resolution 3D images of biological tissues from SBF SEM have been exploited considerably to date in the neuroscience field. However, non-brain samples, in particular hard biological tissues, have appeared more challenging to image by SBF SEM due to the difficulties of sectioning and rendering the samples conductive. We have developed and propose protocols for bone tissue preparation using SBF SEM, for imaging simultaneously soft and hard bone tissue components in 3D. We review the state of the art in high-resolution imaging of osteocytes, provide a historical perspective of SBF SEM, and we present first SBF SEM proof-of-concept studies for murine and human tissue. The application of SBF SEM to hard tissues will facilitate qualitative and quantitative 3D studies of tissue microstructure and ultrastructure in bone development, ageing and pathologies such as osteoporosis and osteoarthritis.

Adaptation Assessment of Three Bonded Resin Restorations at the Cavity Floor Using Cross-Polarization Optical Coherence Tomography

Objective: The aim of the study was to compare the composite adaptation of three systems by using cross-polarization optical coherence tomography (CP-OCT). Background data: Most polymer-based restorations suffer from polymerization shrinkage that affects the interfacial seal. This shrinkage cannot be detected by conventional X-ray methods. Optical coherence tomography was proved to be a reliable non-invasive imaging tool to examine biological structures and biomaterials at micron scale. Methods: Twenty-four cylindrical class-V cavities were prepared on the buccal surfaces of the extracted human molars. After cavity preparation, samples were randomly divided into three groups (n = 8) according to the restoration system: one-step self-etch Clearfil Tri-S Bond Plus with Clearfil Majesty ES-2 composite (TS; Kuraray Noritake Dental), Single Bond Universal in self-etch mode with Filtek Z350 XT composite (SB; 3M ESPE), and one-step self-etch Plafique Bond with Plafique LX 5 composite (PB; Tokuyama Dental). The restoration placement was carried out according to the manufacturers' recommendations. Later, the specimens were immersed in a contrasting agent; then, image acquisitions were taken by CP-OCT to calculate the adaptation percentage by using an image analysis software. Results: Mann-Whitney U test showed no statistical significant difference in the adaptation percentage between TS (91.72 ± 11.6) and SB (93.43 ± 6.9) groups (p > 0.05). However, the adaptation percentage in PB (41.83 ± 28.5) was significantly lower than in the other tested groups (p < 0.05). Conclusions: Within the limitation of the study, TS and SB groups showed better adaptation than PB. Moreover, CP-OCT is a useful imaging tool that can display composite adaptation at micron scale.

Micro and nanostructural analysis of a human tooth using correlated focused ion beam (FIB) and transmission Electron microscopy (TEM) investigations

In this study, natural molar human tooth specimens were investigated for determining their micro- and nanoscale structural morphology, chemistry and crystallinity. The differences were tracked comparatively for both enamel and dentin layers and at their interfaces. Although dental material structures are hard and tough and the cross-sectioning of these materials using mechanical methods is challenging, FIB-SEM dual-beam instruments serve for preparing ultra-thin homogenous lamella sections. In this work, both FIB-SEM and TEM based advanced characterization methods were applied to reveal different morphological characteristics of dental tissue via complementary imaging and diffraction analysis. In addition, SEM-EDS and Raman spectroscopy techniques provided additional information about the elemental distribution and the chemical composition differences of the dental tissues. According to electron microscopy examinations at the intersection between the enamel and the dentin layers, it was shown that the enamel was denser and polycrystalline, while the dentin layer was porous, fibrillar and of negligible long-range order, due to its tubular structure and organic components. In particular, EDS mapping and linescan analyses showed almost no differences in the elemental distribution. Raman results confirmed that both tissues had similar chemical composition except dentin showed spectral background effects in the spectrum due to its tubular structure and organic components.

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.