Evaluation of Cortical Bone Microdamage and Primary Stability of Orthodontic Miniscrew Using a Human Bone Analogue.

Orthodontic miniscrews have gained popularity; however, they have some drawbacks, including screw loosening that results from bone resorption caused by excess microdamage created during screw insertion. Pilot hole preparation through the cortical bone is considered beneficial to avoid such microdamage, while an overly large pilot hole impairs primary stability. Hence, we used a human bone analogue to evaluate the microdamage and primary stability to estimate the optimal pilot hole size that would minimize the screw loosening risk. Ti6Al4V orthodontic miniscrews and 1.0-mm-thick synthetic cortical bone pieces were prepared. Various compressive loads were applied in indentation tests to test pieces' surfaces, and the microdamaged areas were confirmed as stress-whitening zones. Screw insertion tests were performed in which a miniscrew was inserted into the test pieces' pilot hole with a diameter of 0.7-1.2 mm in 0.1-mm intervals, and the stress-whitening area was measured. The insertion and removal torque were also measured to evaluate primary stability. The stress-whitening areas of the 1.0-1.2 mm pilot hole diameter groups were significantly smaller than those of the other groups (p < 0.05), whereas the 0.9 and 1.0 mm pilot hole diameter groups showed higher primary stability than other groups. In conclusion, the bone analogue could be utilized to evaluate microdamage in cortical bones and the primary stability of miniscrews.

Enhanced bone formation onto the bone surface using a hydroxyapatite/collagen bone-like nanocomposite.

The process of bone formation onto the bone surface using a hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) was investigated. Immersion tests were performed to evaluate the impact of pH on the degradation of the specimens in an aqueous environment. The specimens were soaked in aqueous solutions of pH 4.0, 5.0, and 7.0. Using standardized images, the top-view areas of the specimens were measured. Animal experiments were performed to investigate the bone formation process onto the bone surface. The specimens were placed under the rat calvarial periosteum, and µCT image analysis and histological observation were performed on samples harvested on postoperative Days 3, 5, and 7. In all experiments, ß-tricalciumphosphate (ß-TCP) was adopted as the control. HAp/Col turned to gel in acidic environments below pH 5.0. In contrast to the ß-TCP, the HAp/Col specimens placed under the periosteum expanded and attained a hollow structure with a gel-filled center, accompanied by larger volume of new bone and appearance of TRAP-positive multinucleated cells on postoperative Day 5. Therefore, HAp/Col can enhance bone formation onto the bone surface via induction of TRAP-positive multinucleated cells, and may have clinical applications.

Effect of incorporation of surface pre-reacted glass ionomer filler in tissue conditioner on the inhibition of Candida albicans adhesion.

We investigated the effects of incorporation of surface pre-reacted glass ionomer (S-PRG) filler in tissue conditioner (TC) on Candida albicans adhesion. We prepared specimens containing 0, 5, 10, or 20 wt% of S-PRG filler, and measured the amount of C. albicans on the surface using a colony forming unit (CFU) assay and scanning electron microscopic images. In addition, we measured the consistency, penetration depth, and surface roughness (Ra). CFU values for 10 and 20 wt% were significantly lower than that for the control (p<0.05). Hyphal density on the surface was greater in the control. The 10 and 20 wt% specimens showed significantly higher consistency and Ra, lower penetration depth ratio than control (p<0.05). These results suggest that incorporation of S-PRG filler may reduce C. albicans adhesion onto TC surface; however, the optimal amount of filler is dictated by the influence of filler incorporation on mechanical and surface characters of TC.

Enhanced biological fixation of ligaments to bone tissues utilizing chitin fabrics.

In ligament reconstruction involving anterior cruciate ligament surgery, biological fixation between the transferred ligament and bone tissue is critical for achieving successful outcomes. Here, we administered chitin fabrics into the bone tunnels and evaluated their efficacy in promoting biological fixation. An animal model on the rat's patellar ligament was employed. First, bone tunnels were created in the lateral condyle of the femur. The ligament was then separated from the tibial tuberosity, and half was inserted into the tunnel and fixed with the use of end button. Animals in the experimental group were treated with microfiber nonwoven chitin fabric, whereas control animals received no treatment. Specimens were collected at 2, 4, and 6 weeks after surgery, and the fixation strength was measured by mechanical tests. Histological sections were prepared from samples prepared 4 weeks after surgery, and the diameter of bone tunnel and the width ratio of collagenous tissue in the bone tunnel were measured. Administration of chitin significantly increased the mean fixation strength at 4 and 6 weeks after surgery. Furthermore, chitin also promoted bone formation in the bone tunnel and increased the density of collagen fibers. Thus, microfiber nonwoven chitin fabric enhanced the biological fixation of the ligament to the bone tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2355-2360, 2018.

Shape Optimization of Bone-Bonding Subperiosteal Devices with Finite Element Analysis.

Subperiosteal bone-bonding devices have been proposed for less invasive treatments in orthodontics. The device is osseointegrated onto a bone surface without fixation screws and is expected to rapidly attain a bone-bonding strength that successfully meets clinical performance. Hence, the device's optimum shape for rapid and strong bone bonding was examined in this study by finite element analyses. First, a stress analysis was performed for a circular rod device with an orthodontic force parallel to the bone surface, and the estimate of the bone-bonding strength based on the bone fracture criterion was verified with the results of an animal experiment. In total, four cross-sectional rod geometries were investigated: circular (Cr), elliptical (El), semicircular (Sc), and rectangular (Rc). By changing the height of the newly formed bone to mimic the progression of new bone formation, the estimation of the bone-bonding strength was repeated for each geometry. The rod with the Rc cross section exhibited the best performance, followed by those with the Sc, El, and Cr cross sections, from the aspects of the rapid acquisition of strength and the strength itself. Thus, the rectangular cross section is the best for rod-like subperiosteal devices for rapid bone bonding.

Wound healing efficacy of a 660-nm diode laser in a rat incisional wound model.

This study aimed to elucidate the optimum usage parameters of low reactive-level laser therapy (LLLT) in a rat incisional wound model. In Sprague-Dawley rats, surgical wounds of 15-mm length were made in the dorsal thoracic region. They were divided into groups to receive 660-nm diode laser irradiation 24 h after surgery at an energy density of 0 (control), 1, 5, or 10 J/cm2. Tissue sections collected on postoperative day 3 were stained with hematoxylin-eosin and an antibody for ED1 to determine the number of macrophages around the wound. Samples collected on day 7 were stained with hematoxylin-eosin and observed via polarized light microscopy to measure the area occupied by collagen fibers around the wound; day 7 skin specimens were also subjected to mechanical testing to evaluate tensile strength. On postoperative day 3, the numbers of macrophages around the wound were significantly lower in the groups receiving 1 and 5 J/cm2 irradiation, compared to the control and 10 J/cm2 irradiation groups (p < 0.01). The area occupied by collagen fibers in day 7 was largest in 5 J/cm2 group, followed by 1 J/cm2 group, although this difference was not significant. The day 7 tensile test demonstrated significantly greater rupture strength in healing tissues from 1 and 5 J/cm2 irradiation groups, compared to the control group (p < 0.05). Thus, LLLT with a 660-nm diode laser with energy density of 1 and 5 J/cm2 enhanced wound healing in a rat incisional wound model. However, a higher radiation energy density yielded no significant enhancement.

Impact of Dynamic and Static Load on Bone Around Implants: An Experimental Study in a Rat Model.

PURPOSE: This study aimed to evaluate peri-implant bone reactions to dynamic and static loads in a rat model. MATERIALS AND METHODS: Two cylindrical titanium implants were placed in the left tibia diaphysis of 39 rats, which were divided into three groups: static load for 4 weeks (S4), static load for 8 weeks (S8), and static load for 4 weeks followed by dynamic load for 4 weeks (S4D4). All implants received a mechanical lateral load. After the experiment, the implants were extracted to determine the attachment strength around the bone and implant. The new bone formation and bone-to-implant contact were measured using plain and polarized light microscopy. RESULTS: Histologic tissue analysis revealed good contact between the bone and implant, and new bone formation around all implants. The S4D4 group had the greatest attachment strength, new bone formation, and complex collagen fiber orientation in the new bone tissue, compared with the other groups. No statistically significant differences in bone-to-implant contact were observed among the three groups. CONCLUSIONS: Applying dynamic and static loads to osseointegrated implants increased the amplification of new bone. The attachment strength was significantly improved when dynamic load was used for 4 weeks, compared with when static load was used.

Comparison of nerve regenerative efficacy between decellularized nerve graft and nonwoven chitosan conduit.

BACKGROUND: Recently decellularized nerves with various methods are reported as highly functional nerve grafts for the treatment of nerve defects. OBJECTIVE: To evaluate the efficacy of decellularized allogeneic nerve, compared with oriented chitosan mesh tube, and an autologous nerve. METHODS: Sciatic nerves harvested from Sprague-Dawley (SD) rats were decellularized in combination with Sodium dodecyl sulfate and Triton X-100. A graft into the sciatic nerve in Wistar rats was performed with the decellularized SD rat sciatic nerves or oriented chitosan nonwoven nanofiber mesh tubes (15 mm in length, N=5 in each group). A portion of sciatic nerve of Wistar rat was cut, reversed and re-sutured in-situ as a control. Nerve functional and histological evaluations were performed 25 weeks postoperatively. RESULTS: It was revealed that functional, electrophysiological and histological recoveries in the decellularized nerve group match those in the autograft group. Recovery of sensory function and nerve maturation in the decellularized nerve group were superior to those in the chitosan mesh tube group. CONCLUSIONS: Nerve regeneration in the decellularized nerves could match that in the autografts and is somehow superior to artificial chitosan mesh tube. Detergents wash of SDS and Triton X-100 could obtain highly functional nerve grafts from allografts.

Comparative study of the efficacy of decellularization treatment of allogenic and xenogeneic nerves as nerve conduits.

The objective of this study was to compare the results of allogenic and xenogeneic nerve grafts that were treated using decellularization. The sciatic nerves of Sprague-Dawley rats and the median nerves of Japanese white rabbits were decellularized with sodium dodecyl sulfate and Triton X-100 and examined with a scanning electron microscope and immunofluorescence staining. A bridge-graft into the sciatic nerve in Wistar rats was performed with the decellularized nerves (10 mm in length for short-term evaluation; 15 mm in length for long-term evaluation). As a control, an isograft was performed. The specimens were harvested at 4 weeks postoperatively and prepared for immunohistochemistry. Function, electrophysiological and histomorphological analyses were performed to evaluate nerve recovery at 24 weeks postoperatively. The 3-dimensional structure of the basal lamina column, on which the cell adhesion molecules were integrated, was preserved through the decellularization protocols. Limited ED1-positive macrophage invasion was observed, and abundant NF 160-positive axons, which were accompanied by S-100-positive Schwann cells, penetrated through the implanted nerves. The sciatic nerve function and electrophysiological and histomorphological analyses suggest that the xenogeneic nerve graft was statistically indistinguishable from the allogenic nerve graft but slightly inferior to the isograft in supporting the axonal regeneration and functional recovery.

Reduction of Candida biofilm adhesion by incorporation of prereacted glass ionomer filler in denture base resin.

OBJECTIVES: This study investigated the influence of surface reaction-type prereacted glass ionomer (S-PRG) fillers on Candida albicans adhesion on denture base resin. METHODS: Discs were prepared by incorporating the S-PRG filler into the polymer powder of a polymethyl methacrylate (PMMA)-based, heat-polymerizing resin at 0 (control), 5%, 10%, and 20% (w/w). The surface roughness of all disc surfaces was measured. Elemental analysis of released Na(+), Sr(2+), SiO3(2-), Al(3-), BO3(3-), and F(-) was performed after water immersion. Each disc was placed in a well with artificial saliva to form acquired pellicle, incubated, washed with phosphate-buffered saline, and immersed in a C. albicans (JCM2085) cell suspension standardized at 10(4) cells/ml. After aerobic incubation at 37 °C for 24 h, the metabolic mitochondrial activity, total biofilm biomass, and biofilm thickness were evaluated. The morphogenetic transition of C. albicans in the early culture stage (1 and 3 h) was observed. RESULTS: There was a slight but significant increase in the surface roughness with an increase in the filler content. The metabolic activity and total biomass volume were significantly lower in all filler groups than in the control group, although there were no significant differences among the filler groups. Groups with at least 5% filler content exhibited a thinner biofilm compared with the control group. All filler groups showed hyphal forms at 3 h, with the length of the hyphae being lesser than those in the control group. CONCLUSIONS: Although the incorporation of S-PRG filler slightly increases the surface roughness of denture base resin, it reduces the adhesion of C. albicans. CLINICAL SIGNIFICANCE: The S-PRG filler has the potential to reduce Candida albicans adhesion on denture base resin and may lower the risk of denture stomatitis. However, filler incorporation can increase the surface roughness of heat-polymerizing denture base resin.

In vivo evaluation of a Ti-based bulk metallic glass alloy bar.

Ti-based bulk metallic glasses are reported with high strength, low Young modulus and high corrosion resistance, suggesting their potentials in biomedical applications. However a thorough in vivo evaluation of its biocompatibilities has not been conducted yet. In this study, we implanted bars of Ti-based bulk metallic glass in the femoral bone of rats, followed up local tissue reaction as well as its component ions' diffusion in local area and whole body. The Ti-based BMG (Ti40Zr10Cu34Pd14Sn2) alloy exhibited favorable features of both high strength and high elasticity. In vivo implant evaluation showed that it has a good tissue compatibility, equivalent bone integration and bonding ability with Ti sample. No component ion diffusion was detected up to 3 months post implantation. The possibility and efficacy of its use for bone implant is confirmed. Thus further long term implant study is recommended.

An Experimental Study to Bridge a Nerve Gap with a Decellularized Allogeneic Nerve.

BACKGROUND: The authors evaluated the efficacy of decellularized nerve as a scaffold for nerve regeneration. METHODS: Sciatic nerves harvested from Sprague-Dawley rats were decellularized in combination with sodium dodecyl sulfate and Triton X-100, and examined with scanning electron microscopy and immunofluorescence staining. A graft into the sciatic nerve in Wistar rats was performed with the decellularized Sprague-Dawley rat sciatic nerves [allograft: 10 mm long (n = 3) for short term and 15 mm long (n = 5) for long term]. As a control, a portion of sciatic nerve of Wistar rats was cut, reversed, and resutured in situ [autograft: 10 mm long (n = 3) and 15 mm long (n = 5) for different terms, respectively]. Samples were harvested 4 weeks postoperatively and prepared for immunohistochemistry. Von Frey hair test, static toe spread factor measurement, and electrophysiologic and histomorphologic analyses were carried out to evaluate nerve recovery 24 weeks postoperatively. RESULTS: Scanning electron microscopic images revealed the honeycomb structure, and immunohistology showed that the three-dimensional structure of the basal lamina column on which cell adhesion molecules are integrated is preserved through the decellularization protocols. Limited ED1-positive macrophage invasion was found through the decellularized sciatic nerves, suggesting that antigenicity remained more or less after this treatment. Nevertheless, NF160-positive axons accompanied by S100-positive Schwann cells penetrated through the decellularized sciatic nerves. Sciatic nerve function had recovered, and there were no significant differences in the electrophysiologic and histomorphologic recovery in the groups. CONCLUSION: These results suggest that the decellularized allogeneic nerve is a suitable scaffold to bridge a nerve gap.

Laser perforated accordion nerve conduit of poly(lactide-co-glycolide-co-ɛ-caprolactone).

Accordion nerve conduit of poly(lactide-co-glycolide-co-ε-caprolactone) with perforations was developed by excimer laser processing. We evaluated its in vivo function for nerve repairing and discussed the influence of pore size and density. It was found that perforations help inner nerve regeneration remarkably, which effect is unrelated to pore size or density, and is not parallel with revascularization increment. Inducing of permeability only to allow substance exchange but not vessel ingrowth could facilitate nerve regeneration too. Perforating micropores with the size of 100 µm and the density of 25/cm provides permeability and vessel ingrowth both, therefore promotes the axon extension the best, larger, and more pores do not advance axon regeneration more.

Development of oral and extra-oral endosseous craniofacial implants by using a mesh structure for connective tissue attachment.

Connective tissue attachment to a mesh structure incorporated on the surface of oral implants and extra-oral endosseous craniofacial implants (EOECI) was investigated. Two types of implants were prepared: TI and TI-Mesh. TI was composed of an upper and a lower component, both comprised of a titanium cylinder, which could be connected using a titanium screw. The composition of the TIMesh was similar, but the lower cylinder had a lateral groove that was covered with a titanium mesh. In animal experiments performed using rat calvaria, the lower component was first implanted and was left submerged for 3 weeks, then the upper component was mounted percutaneously. After an additional 2 weeks, each implant and the surrounding tissues were harvested and evaluated. Histological observations revealed collagen fibers originating from surrounding hypodermal tissues anchored to the mesh structures of the TI-Mesh whereas no such collagen fibers were observed around TI. Significantly greater values of the attachment strength, the thickness of the dermal tissue, the thickness of hypodermal tissue, and the attachment lengths were observed in TI-Mesh than those of TI. Thus connective tissue attachment with collagen fibers anchored to the mesh was achieved by incorporating mesh structures into the percutaneously placed implants.

Reconstruction of small diameter arteries using decellularized vascular scaffolds.

Although artificial vessels are available for large diameter arteries, there are no artificial vessels for small diameter arteries of < 4 mm. We created a decellularized vascular scaffold (length, 10 mm; outer diameter, 1.5 mm; inner diameter, 1.3 mm) from rat abdominal arteries. We measured the biomechanical characteristics of the scaffolds, implanted them to defects made in rat carotid arteries, and evaluated their patency and the endothelial cell linings. Silastic grafts were implanted as controls. The decellularized scaffolds demonstrated similar mechanical characteristics to normal arteries. All of the control grafts were occluded. Fibroblast-like cells were discovered in the thrombus, and fibrous organization was apparent. In contrast, patency of the grafts in 10 of 12 animals was observed 4 weeks after implantation. The internal cavity of the patent scaffold was completely lined by endotheliallike cells. Thus, the possibility of small artery reconstruction using decellularized scaffolds was demonstrated.

Enhanced osteoconductivity of titanium implant by polarization-induced surface charges.

This study introduces the application of method for electrically polarizing titanium implants coated with anatase TiO2 using microarc oxidation. It also describes the features of the electrically polarized titanium implants, on which surface charges are generated by the dipole moment of the TiO2 , and describes how the surface charges affect the implants' in vivo bone-implant integration capability. A comprehensive assessment using biomechanical, histomorphological, and radiographic analyses in a rabbit model was performed on polarized and nonpolarized implants. The electrically polarized surfaces accelerated the establishment of implant biomechanical fixation, compared with the nonpolarized surfaces. The percentage of the bone-implant contact ratio was higher using polarized implants than using nonpolarized implants. In contrast, the bone volume around the implants was not affected by polarization. Thus, using the polarized implant, this study identified that controlled surface charges have a significant effect on the properties of titanium implants. The application of the electrical polarization process and the polarization-enhanced osteoinductivity, which resulted in greater bone-implant integration, was clearly demonstrated.

Hydroxyapatite/collagen nanocomposite-coated titanium rod for achieving rapid osseointegration onto bone surface.

This article proposes less-invasive subperiosteal bone-bonding devices capable of realizing rapid osseointegration and the acquisition of fundamental knowledge required for their development. Three candidates were prepared: titanium rod specimens with a machined surface (Bare), hydroxyapatite (HAp) coating, and hydroxyapatite/collagen (HAp/Col) nanocomposite coating. To investigate bone formation around these rods, each specimen was placed under the periosteum of a male Sprague-Dawley rat calvarium. Four weeks after surgery, the samples were evaluated via histomorphometrical analyses and bonding strength tests. All the Bare specimens and more than half of the HAp specimens were encapsulated with fibrous tissue, whereas all the HAp/Col specimens were almost completely surrounded by new bone tissue without encapsulation. Histomorphometrical analyses showed that the HAp/Col group had the greatest bone contact ratio among all candidates (p < 0.05). Further, a bonding strength test indicated that the HAp/Col group exhibited the greatest bonding strength to bone (p < 0.05). Thus, HAp/Col-coated rods are considered as the best candidate materials for achieving rapid osseointegration onto a bone surface.

Mechanical attachment of soft tissue to dental and maxillofacial implants with mesh structures: an experiment in percutaneous model.

Soft tissue attachment is a major concern for the improved design of dental and maxillofacial implants. This study evaluated the efficacy of mesh structures for soft tissue attachment in a rat percutaneous model. Four kinds of implant specimens were prepared - TI implants made of titanium cylinders, HA implants of hydroxyapatite-coated titanium, TI-Mesh implants with a titanium mesh covering a groove machined around a titanium cylinder, and similar HA-Mesh implants with a hydroxyapatite-coated mesh. These specimens were implanted percutaneously into the skin tissue of rats. The detachments of the implants were examined during the experimental period of 4 weeks. Survived implants were subjected to mechanical tests for the attachment strength and histological examinations. TI and HA implants demonstrated 0% of survival rates, while TI-Mesh and HA-Mesh showed significantly higher rates of 93.3% and 100% respectively. The attachment strengths were 159 ± 47 kPa in the TI-Mesh and 135 ± 16 kPa in the HA-Mesh. Histological observations revealed that collagen fibers originating from surrounding subcutaneous tissues were anchored to the mesh structures of the TI- and HA-Mesh implants. The results demonstrated the efficacy of the mesh structures for the attachment of soft connective tissues to implants.

Evaluation of platelet aggregability during left ventricular bypass using a MedTech MagLev VAD in a series of chronic calf experiments.

The impact of continuous flow left ventricular assist device (LVAD) pumping on platelet aggregation was investigated in animal experiments utilizing six calves. A single-use MagLev centrifugal blood pump, MedTech MagLev, was used to bypass the calves' hearts from the left atrium to the descending aorta at a flow rate of 50 ml/kg/min. The LVAD's impact on blood coagulation activities was evaluated based on the platelet aggregability, which was measured with a turbidimetric assay method during the preoperative, operative, and postoperative periods. Heparin and warfarin were used for anticoagulation, while aspirin was used for the antiplatelet therapy. A decrease in platelet aggregation immediately after the pump started was observed in the cases of successful long-term pump operation, while the absence of such a decrease might have caused coagulation-related complications to terminate the experiments. Thus, the platelet aggregability was found to be significantly affected by the pump, and its initial trend may be related to the long-term outcome of the mechanical circulatory support.

Reproducibility of probing depth measurement by an experimental periodontal probe incorporating optical fiber sensor.

BACKGROUND: An experimental periodontal sensor probe (SP) equipped with an optical fiber for recording function was developed. The aim was to test the intraexaminer reproducibility of probing using the SP and to assess the consistency with the manual probe (MP). METHODS: The SP was assembled with an external sheath covering the probe tip of an MP. The sheath was slid backward by the free gingival margin while probing and the sliding distance was detected by the sensor. The probing was conducted with the walking stroke at six sites for four first molar teeth in six maintenance patients with the SP and the MP at a 1-hour interval. The deepest reading in the vicinity of each site was recorded. The measurements were rerecorded 1 week later. RESULTS: The mean depth was 3.03 and 3.08 mm recorded by the MP and SP, respectively. Although no significant difference was found between the probes (P >0.05) in all measurement sites, the mean depth at the lingual site of the upper left first molar was noticeably lower with the SP. For sites ≥7 mm, significantly lower depth was recorded by the SP (P <0.05). Zero discrepancy in duplicate measurements was found in 76% of all sites with MP and 92% with SP. CONCLUSIONS: The reproducibility of the SP was comparable to that of the MP. The results indicate that for sites of maintenance patients with probing depth <7 mm there was excellent agreement obtained by a single examiner using the SP compared to the MP.