Background and objective: Femtosecond laser (fs-laser) is a novel tooth preparation tool. After cavities were prepared by fs-laser, their axial-wall taper is closely related to the retention force and success of restorations, while the taper after preparation by fs-laser is not clear yet. This study aimed to explore the value of the taper after fs-laser tooth preparation and the effect of laser fluence, scanning line spacing, and scanning layers on taper. Materials and methods: Twenty cavities with a width of 0.5 mm were prepared by an fs-laser both in enamel and dentin to obtain the axial-wall taper (No. PKUSSIRB-201949124). To study the effects of three parameters of fs-laser, five different laser fluence were set as 1.56, 3.13, 4.69, 6.25, and 7.81 J/cm2 of five cavities. Scanning line spacing was set as 6, 12, 25, 30, 40, and 50 μm of six cavities and the scanning layers were 5, 10, 25, 50, 75, 100, 200, 300, and 400, respectively, of nine cavities. Laser pulses irradiated perpendicular to the tooth and the scanning path was controlled via a vibratory mirror. The taper was measured with a laser confocal microscope. Curves of the taper versus different parameters were drawn. Results: There was a significant difference in taper between enamel and dentin. Overall, the taper decreased gradually with the increase of laser fluence. The optimal taper obtained was 20.53° ± 0.28° in dentin and 38.71° ± 0.46° in enamel when the corresponding fluence was 6.25 J/cm2. In comparison, the scanning line spacing has little effect on the taper. The scanning layers significantly affect the taper, which decreased dramatically as scanning layers increased within 75 layers and does not change considerably as it was beyond 100 layers. Conclusions: Reasonable selection of laser fluence, scanning line spacing, and the number of scanning layers can optimize the cavity taper by fs-laser.

In recent years, the concept of minimally invasive endodontics has been proposed, which could be described as preventing or treating diseases by preserving more dental tissue and creating minimal damage. In the process of root canal preparation, it was recommended to use instruments with a smaller taper to preserve more tooth tissue and improve the preservation rate of the affected teeth. Photon-induced photoacoustic streaming (PIPS) was a new type of laser-activated irrigation technology, which was now widely used in endodontic treatment. The purpose of this article was to evaluate the bactericidal effect of PIPS with NaOCl in root canals with different widths or tapers.
Twenty-three maxillary first molars with three independent root canals were included in this study. The mesiobuccal (MB), distobuccal (DB), and palatal (P) root canals were prepared at sizes of #10/.02, #25/.02, and #25/.06, respectively. After being incubated with a bacterial suspension for 4 weeks, the specimen were irrigated with 2% NaOCl activated by conventional needle irrigation (CNI) (n = 10) or PIPS (n = 10). Three specimen were not treated (control group). Before and after irrigation, the presence of bacteria was assessed with an adenosine 5\'-triphosphate (ATP) assay kit and biofilms were assessed using confocal laser scanning microscopy and scanning electron microscopy.
In specimen prepared using PIPS irrigation, the ATP was reduced by more than 98%. When the root canal taper was 0.02, the size #25 root canals had a higher percentage of dead bacteria than the size #10 root canals in all regions (P < 0.05) in the PIPS group. When the root canal width was #25, the 0.02 taper group had a higher percentage of dead bacteria than the 0.06 taper group in the apical region (P < 0.05), except coronal and middle regions (P > 0.05). PIPS irrigation results in a greater percentage of dead bacteria and reduction of ATP in size #10/.02 root canals than CNI in size #25/.06 root canals in three regions (P < 0.05).
Increasing the width from #10 to #25 improves the bactericidal effect of PIPS in the root canal. Increasing the taper of the root canal from 0.02 to 0.06 at size #25 did not affect the bactericidal effects of PIPS. PIPS resulted in more dead bacteria in specimen with smaller tapers and root canal widths than CNI. PIPS can be used to clean the smear layer in the coronal region and open the dentin tubules.
Activation of irrigants with PIPS brought about significant bacterial reduction smaller tapers and width root canals compared to CNI, which was beneficial to prevent excessive loss of tooth tissue and conserve the structural integrity of teeth.

This study explored the effect of the light-off delay setting in a robotically controlled femtosecond laser on the taper and adaption of resin tooth preparations. Thirty resin teeth (divided into six equal groups) were studied under different light-off delay conditions. Tapers from six vertical sections of the teeth were measured and compared among the light-off delay groups. The mean taper decreased from 39.268° ± 4.530° to 25.393° ± 5.496° as the light-off delay increased (p < 0.05). The average distance between the occlusal surfaces of the scanned data and the predesigned preparation data decreased from 0.089 ± 0.005 to 0.013 ± 0.030 μm as the light-off delay increased (p < 0.05). The light-off delay of the femtosecond laser is correlated with the taper and adaption of automatic tooth preparations; this setting needs to be considered during automatic tooth preparation.

This study aimed to compare the use of photon-initiated photoacoustic streaming (PIPS) and conventional needle irrigation (CNI) in conjunction with different concentrations of sodium hypochlorite (NaOCl) to remove Enterococcus faecalis (E. faecalis) suspended bacteria and biofilms from root canal systems with different diameters or tapers.
Artificial root canal samples (n = 480) were randomly divided into three groups (n = 160/group). The canals were prepared to fit file sizes #10/.02, #25/.02, or #25/.06. The size #10/.02 group was incubated for seven days. The size #25/.02 or #25/.06 group was incubated for 2 days. A stable biological model of E. faecalis infection was established. The root canals were washed with distilled water or with 1%, 2%, or 5.25% NaOCl combined with CNI or PIPS. Bacterial suspensions and biofilms were assessed using an ATP assay kit and fluorescence microscopy. Image-Pro Plus was used to analyse the average fluorescence intensity to determine the most suitable root canal irrigation solution.
In the CNI and PIPS groups, the ATP value of the 5.25% NaOCl subgroup was the lowest, followed by that of the 2% and 1% NaOCl subgroups. The ATP value of the distilled water subgroup was the highest (P < 0.05). When the root canal taper was 0.02, the ATP value of the #10/.02 + PIPS group was significantly lower than that of the #25/.02 + CNI group (P < 0.05). The average fluorescence intensity of the #10/.02 + PIPS group was lower than that of the #25/.02 + CNI group (P < 0.05). When the apical diameter was #25, the ATP value of the 0.02 taper in the PIPS group was lower than that of the 0.06 taper in the CNI group (P < 0.05), and the average fluorescence intensity of the 0.02 taper + PIPS group was lower than that of the 0.06 taper + CNI group (P < 0.05). PIPS combined with 2% and 5.25% NaOCl effectively improved the long-term antibacterial effect after irrigation and re-culture for 6 h.
Compared with CNI, PIPS has greater ability to remove bacteria in root canals with a small preparation diameter and a small taper. PIPS with 2% and 5.25% NaOCl exhibited superior antibacterial and bacteriostatic effects.

As the microporous structure has been widely used in the field of precision machining, at the same time, the requirements for the quality of microporous machining are continuously increasing. Water jet-guide laser processing technology (WJGL) has been gradually applied for its high machining precision. However, there are a few researches on the heat conduction process of WJGL processing metal materials. Therefore, it is of great significance to study the transient thermal effect of metal materials and the mechanism of material removal to improve the processing quality. In order to explore the heat conduction model of WJGL processing metal materials, this paper is based on the \"element birth and death\" technique in the finite element method, and the three-dimensional transient temperature field of four typical metal materials (titanium alloy, stainless steel, aluminum alloy, copper) and material removal model are established. Under this model, the removal mechanism of different metal materials and the influence of different process parameters on the temperature field distribution of the material are studied, and the influence of fixed-position drilling and helix drilling on the microporous morphology is compared. The results show that copper and aluminum alloys can obtain a larger depth-to-diameter ratio and a smaller hole taper. Titanium alloy and stainless steel have better hole roundness, lower hole edge temperature, and smaller thermal deformation. Hole roundness error and hole taper decrease with the increase of laser power. The roundness error of each material is reduced to within 10 μm when the laser power is 10 W, and the average hole taper is 8.73°.

In this paper we propose and investigate a novel magnetic field sensor based on a Tri-microfiber coupler combined with magnetic fluid and a fiber Bragg grating (FBG) in a ring. A sensitivity of 1306 pm/mT was experimentally demonstrated in the range of magnetic fields from 0 to 15 mT. The reflection peak in the output spectrum associated with the FBG serves as a reference point allowing to avoid ambiguity in determining the spectral shift induced by the magnetic field. Due to its high sensitivity at low magnetic fields, the proposed structure could be of high interest in low field biosensing applications that involve a magnetic field, such as magnetic manipulation or separation of biomolecules.

In this paper, we propose a novel vertical SU-8 waveguide for evanescent analyte sensing. The waveguide is designed to possess a vertical and narrow structure to generate evanescent waves on both sides of the waveguide\'s surface, aimed at increasing the sensitivity by enlarging the sensing areas. We performed simulations to monitor the influence of different parameters on the waveguide\'s performance, including its height and width. E-beam lithography was used to fabricate the structure, as this one-step direct writing process enables easy, fast, and high-resolution fabrication. Furthermore, it reduces the sidewall roughness and decreases the induced scattering loss, which is a major source of waveguide loss. Couplers were added to improve the coupling efficiency and alignment tolerance, and will contribute to the feasibility of a plug-and-play optical system. Optical measurements show that the transmission loss is 1.03 ± 0.19 dB/cm. The absorption sensitivity was measured to be 4.8 dB per refractive index unit (dB/RIU) for saline solutions with various concentrations.

A novel intensity demodulated refractive index (RI) sensor is theoretically and experimentally demonstrated based on the front-tapered single-mode-multimode-single-mode (FT-SMS) fiber structure. The front taper is fabricated in a section of multimode fiber by flame-heated drawing technique. The intensity feature in the taper area is analyzed through the beam propagation method and the comprehensive tests are then conducted in terms of RI and temperature. The experimental results show that, in FT-SMS, the relative sensitivity is -342.815 dB/RIU in the range of 1.33~1.37. The corresponding resolution reaches 2.92 × 10-5 RIU, which is more than four times higher than that in wavelength demodulation. The temperature sensitivity is 0.307 dB/°C and the measurement error from cross-sensitivity is less than 2 × 10-4. In addition, fabricated RI sensor presents high stability in terms of wavelength (±0.045 nm) and intensity (±0.386 dB) within 2 h of continuous operation.

Objective This study aimed to measure the taper and diameter of root canal, as well as the elastic modulus and hardness in the root dentin of maxillary primary anterior teeth. Methods Patients under general anesthesia who needed root canal therapy in the maxillary primary anterior teeth were selected. Silicone impression material was used to take impressions. The impressions were scanned, and the taper and diameter of root canal were measured. Maxillary primary anterior teeth were collected in vitro. The elastic modulus and hardness of root dentin was tested. Results A total of 74 silicone impressions were obtained. The mean tapers of primary incisor teeth, primary lateral incisor teeth, and primary canine teeth were 0.106, 0.185, and 0.098, respectively. The mean diameters of the root canal 5 mm below the cementum-enamel junction (CEJ) were 1.267, 0.860, and 1.429 mm, respectively. The elastic modulus and hardness of root dentin were measured in 10 primary anterior teeth in vitro. The range of elastic modulus was 19.919-25.017 GPa. The range of hardness was 0.867-1.082 GPa. Conclusion The root canal post used in primary anterior teeth can be produced by the following data: taper of primary incisor teeth and primary canine teeth, 0.1; diameters of their tips, 1.2 mm and 1.4 mm, respectively; taper of primary lateral incisor teeth, 0.2; diameter of their tips, 0.8 mm; range of elastic modulus, 20-25 GPa; and range of hardness, 0.87-1.08 GPa.
目的 测量上颌乳前牙根管锥度、直径及根部牙本质的弹性模量和硬度，为用于上颌乳前牙的可吸收根管桩的制作提供参考。方法 选择全身麻醉下进行上颌乳前牙根管治疗的患儿，采用硅橡胶制取上颌乳前牙根管印模，扫描印模后测量根管的锥度和直径。收集10颗离体上颌乳前牙，测量根部牙本质的弹性模量和硬度。结果 本研究共收集了74颗上颌乳前牙的根管模型，其中乳中切牙28颗，乳侧切牙35颗，乳尖牙11颗。乳中切牙、乳侧切牙、乳尖牙的平均锥度依次为0.106、0.185、0.098，釉牙骨质界下方5 mm处平均直径依次为1.267、0.860、1.429 mm。10颗离体上颌乳前牙根部的牙本质弹性模量范围为19.919~25.017 GPa，硬度范围为0.867~1.082 GPa。结论 制作乳牙根管桩时，乳中切牙及乳尖牙根管桩建议取锥度为0.1，尖端直径为1.2、1.4 mm；乳侧切牙根管桩建议取锥度为0.2，尖端直径为0.8 mm；桩的弹性模量范围为20~25 GPa，硬度范围为0.87~1.08 GPa较为适宜。.

Helical flow has been introduced to improve the hemodynamic performance of vascular devices such as arterial grafts, stents and arteriovenous shunts to overcome the flow induced thrombus formation and intimal hyperplasia. However, the quite low intensity of helical flow in the existing devices may limit their function. To obtain desirably high intensity, inspired by the helical flow and tapered configuration of the arterial system, we proposed a new conceptual design of the medical devices, which take the form of a tapered helical shape. We demonstrated its effectiveness in arterial grafts by numerically comparing the hemodynamic performance of helical grafts with different smooth tapers. The results show that the helicity density quantifying the helical flow enlarges sharply with the increase of the taper under both steady and pulsatile flow conditions. Moreover, the amplified helical flow induced by the taper would lead to highly elevated wall shear stress, remarkably reduced oscillating shear index and relative residence time at both the grafts and the anastomosis of the host vessel. The present findings therefore indicated that the new helical graft with taper would significantly enhance the helical flow in the grafts and host vessel, which may reduce the possibility of thrombus formation in the graft and intimal hyperplasia in the host vessel and hence improve the graft patency. In addition, the concept of helical shape with taper may also be applied to design arterial stents and arteriovenous shunts to obtain better hemodynamic performance.