Optical coherence tomography characterizes the roughness and thickness of the heterogeneous layer on cortical bone surface induced by Er:YAG laser ablation at different moisture contents

Abstract

Background: As an innovative bone ablation tool, pulsed erbium: yttrium-aluminum-garnet (Er:YAG) laser is being used in clinical practice. It faces the same problems as traditional tools: the water content of bone usually changes with the position, while the amount of water spray in the process of laser irradiation is also uncertain. Real-time monitoring of the effects of laser bone ablation is necessary, but effective tools are still lacking. In this study, we examined the feasibility of rapidly and non-destructively evaluating the surface properties of bone after Er:YAG laser irradiation at different moisture contents by optical coherence tomography (OCT).Methods: Bone specimens (n=90) collected from pig cortical bone were used in this study. All bone specimens had similar volume and surface characteristics after machining. To display the baseline level before Er:YAG laser ablation, a control group (n=10) without dehydration or Er:YAG laser ablation was examined with OCT, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The remaining specimens were randomly divided into four groups (n=20/group) with different moisture content: dried (Group 2 and Group 4) or not dried (Group 1 and Group 3). Pulsed Er:YAG laser (120 mJ/pulse, 20 Hz, 100 μs) was used for perpendicular irradiation with (Group 1 and Group 2) or without (Group 3 and Group 4) water spray. The treated specimens were subjected to SEM, EDX spectroscopy, OCT, and then processed for histological evaluation.Results: After Er:YAG laser ablation, the melting effect was obvious in the SEM results of the dry groups and non-sprayed groups (Groups 2-4). EDX spectroscopy showed that the content of calcium and phosphorus and their ratios remained unchanged in the undried and with water spray group (Group 1) were the closest to the control group. Three-dimensional (3D) OCT could evaluate the depth and shape of ablation grooves. The roughness of the laser-ablated surface could be visualized by extracting the surface lines from cross-sectional OCT images. The results illustrated that the laser ablation with water spray could achieve a smoother surface. Furthermore, OCT results demonstrated that a layer with high image intensity was generated on the bone surface after laser irradiation. The thickness of these layers showed a correlation with whether or not the laser irradiation was sprayed with water. Histology showed that thin eosin-stained layers were created in all experimental groups, which matched well with OCT results of the layers with high image intensity. No denatured layer was observed in the non-irradiated areas of bone tissues.Conclusions: OCT could rapidly and non-destructively visualize the bone surface before and after Er:YAG laser ablation at four different moisture contents. The morphology of ablation grooves, as well as the roughness and thickness of the heterogeneous layer on the bone surface, could be characterized quantitatively with good correlation with SEM and histology. This study will promote the development ...

Real-Time Monitoring and Quantitative Evaluation of Resin In-Filtrant Repairing Enamel White Spot Lesions Based on Optical Coherence Tomography

“…Twenty locations on each OCT image of Rabbits #1 and #2 were randomly selected, and the light signal reflection/scattering bright band thickness of the enamel layer and dentin layer of each tooth was measured according to the change of light intensity. Baseline calibration was performed on each surface line of the selected locations, and the surface roughness of the sample was measured according to the arithmetic mean of the absolute value of the distance between each point on the sample surface and the baseline [23]. The surface roughness and the differences of changes in the light signal reflection/scattering bright band thickness of the enamel layer and dentin layer were subjected to one-way analysis of variance (ANOVA) followed by the Bonferroni post hoc test for multiple comparisons at a 5% significance level.…”

“…Immediately after every preparatory step, the specimens of Rabbits #1 and #2 were scanned by an OCT system (as it was shown in Figure 1A) in our medical imaging innovation laboratory that was described in the previous study [23] and was observed and recorded under an SM (Leica, Wetzlar, Germany) at 35 magnifications. The OCT system used 840 nm central wavelength (λ), 40 nm bandwidth (∆λ), 5 MW power (P), and 7.24 µm axial resolution.…”

“…The spectrometer collects coherent signals and sends the coherent signals to the computer. By reconstructing the profile of optical coherence between the light from the reference arm and the sample arm, OCT can obtain the twodimensional or three-dimensional image of the sample [20][21][22][23]. The spatial resolution of the OCT image is about 10 µm.…”

Use of both the diode and Er: YAG lasers in esthetic crown lengthening with the aid of digitally guided dual technique: 3 years follow‐up

“…3,6 The use of erbium lasers for performing procedures that require bone tissue removal has been proposed by several authors, and it is possible to use this wavelength to perform precise sections, with minimal damage to adjacent tissues. [17][18][19][20] The use of lasers in osteotomies could reduce the level of trauma and contamination during the procedure, since the device is working effectively at a distance from the target tissue, which can lead to an improvement in the tissue network. 17 The erbium laser used in this case report was efficient in performing the osteotomy, although some studies have shown that the surgery time can be longer with the use of a laser.…”

Rare earth smart nanomaterials for bone tissue engineering and implantology: Advances, challenges, and prospects

“…189 The results from their study showed that OCT could quickly and accurately evaluate the differences between the moisture content, as compared to histology and scanning electron microscope (SEM). 233 NaYF 4 :Yb, Er@CaF 2 nanoparticles with a small size (10-13 nm) robustly enhance (ca. 300 times) upconversion emission compared with the pristine nanoparticles.…”