Corrosion behavior of titanium in response to sulfides produced by Porphyromonas gingivalis.

OBJECTIVE: To investigate the effects of sulfides produced by Porphyromonas gingivalis (P. gingivalis) on the corrosion behavior of titanium. METHODS: Commercially pure titanium disks were mirror-polished and immersed in culture medium (BHI), spent medium after culturing P. gingivalis (BHI-S), and culture medium with P. gingivalis (BHI-P), and incubated aerobically at 37°C for 3-14 days. Titanium corrosion was evaluated through surface observation (using scanning electron microscope: SEM), color change (ΔE*ab), glossiness (Gs(20°)), chemical composition and state (using X-ray photoelectron spectroscopy: XPS), and titanium release. RESULTS: ΔE*ab and Gs(20°) did not significantly differ among specimens placed in test mediums for the study duration (p>0.05). SEM images of specimens showed no signs of localized or overall corrosion. XPS analysis indicated showed clear titanium metal state peaks on all specimens in addition to sulfide and sulfate on BHI-S and BHI-P specimens. Valency fraction of titanium decomposed from Ti2p spectrum of BHI-S and BHI-P specimens indicated no progression of oxidation. No significant levels of titanium release were found regardless of the mediums' sulfide content. Results suggested that sulfides produced by P. gingivalis attached on the surface of titanium specimens but did not cause titanium corrosion over the immersion period of 14 days. SIGNIFICANCE: It is imperative for dental practitioners to be aware of any elements which may influence the clinical success of titanium implants.

Effects of calcium hydroxide reagent on the bond strength of resin cements to root dentin and the retention force of FRC posts.

The aim of this study was to determine the effects of calcium hydroxide (Ca(OH)2) treatment on bond strength of resin cements to root dentin and retention force of fiber-reinforced composite (FRC) posts. Bovine root dentin was endodontically prepared and treated with Ca(OH)2 for 7 days. Root dentin for bond strength test was adhered to resin-composite with resin cements. For pull-out test, posts consisting of FRC posts and resin-composites were fabricated and cemented to root. Shear bond and pull-out tests were performed using a universal testing machine. No significant differences in bond strength and post retention force were found between Ca(OH)2 treated and untreated groups. Significant differences were found among the cements. A positive correlation was indicated between bond strength of cements and retention force of FRC posts. In conclusion, Ca(OH)2 treatment on root dentin did not affect bond strength of resin cements and retention force of FRC posts.

Influence of sulfide concentration on the corrosion behavior of titanium in a simulated oral environment.

This study assessed the corrosion behavior of titanium in response to sulfide by determining the effects of sulfide concentration and pH over immersion period. Corrosion was evaluated through changes in color, glossiness, surface characterization, and titanium release. Sulfide solutions were prepared in 3 different concentrations with Na2S, each in pH unadjusted (sulfide-alkaline) and pH adjusted to 7.5 (sulfide-neutral). Titanium discoloration increased and glossiness decreased as sulfide concentration and immersion period increased in sulfide-alkaline solutions. Coral-like complexes were observed on the surface of these specimens, which became more pronounced as concentration increased. Small amounts of titanium release were detected in sulfide-alkaline solutions; however, this was not affected by immersion periods. Corrosion was indicated through considerable surface oxidation suggesting the formation of a thick oxide layer. No significant changes in color and glossiness, or titanium release were indicated for titanium specimens immersed in sulfide-neutral solutions indicating that pH had a significant effect on corrosion. Our findings suggest that a thick oxide layer on the titanium surface was formed in sulfide-alkaline solutions due to excessive oxidation.

Treatment of hypophosphatasia by muscle-directed expression of bone-targeted alkaline phosphatase via self-complementary AAV8 vector.

Hypophosphatasia (HPP) is an inherited disease caused by genetic mutations in the gene encoding tissue-nonspecific alkaline phosphatase (TNALP). This results in defects in bone and tooth mineralization. We recently demonstrated that TNALP-deficient (Akp2 (-/-) ) mice, which mimic the phenotype of the severe infantile form of HPP, can be treated by intravenous injection of a recombinant adeno-associated virus (rAAV) expressing bone-targeted TNALP with deca-aspartates at the C-terminus (TNALP-D10) driven by the tissue-nonspecific CAG promoter. To develop a safer and more clinically applicable transduction strategy for HPP gene therapy, we constructed a self-complementary type 8 AAV (scAAV8) vector that expresses TNALP-D10 via the muscle creatine kinase (MCK) promoter (scAAV8-MCK-TNALP-D10) and examined the efficacy of muscle-directed gene therapy. When scAAV8-MCK-TNALP-D10 was injected into the bilateral quadriceps of neonatal Akp2 (-/-) mice, the treated mice grew well and survived for more than 3 months, with a healthy appearance and normal locomotion. Improved bone architecture, but limited elongation of the long bone, was demonstrated on X-ray images. Micro-CT analysis showed hypomineralization and abnormal architecture of the trabecular bone in the epiphysis. These results suggest that rAAV-mediated, muscle-specific expression of TNALP-D10 represents a safe and practical option to treat the severe infantile form of HPP.

Development of a Drilling Simulator for Dental Implant Surgery.

The aim of this study was to develop and evaluate a dental implant surgery simulator that allows learners to experience the drilling forces necessary to perform an osteotomy in the posterior mandibular bone. The simulator contains a force-sensing device that receives input and counteracts this force, which is felt as resistance by the user. The device consists of an actuator, a load cell, and a control unit. A mandibular bone model was fabricated in which the predicted forces necessary to drill the cortical and trabecular bone were determined via micro CT image-based 3D finite element analysis. The simulator was evaluated by five dentists from the Department of Implantology at Tokyo Dental College. The ability of the evaluators to distinguish the drilling resistance through different regions of the mandibular bone was investigated. Of the five dentists, four sensed the change in resistance when the drill perforated the upper cortical bone. All five dentists were able to detect when the drill made contact with lingual cortical bone and when the lingual bone was perforated. This project successfully developed a dental implant surgery simulator that allows users to experience the forces necessary to drill through types of bone encountered during osteotomy. Furthermore, the researchers were able to build a device by which excessive drilling simulates a situation in which the lingual cortical bone is perforated--a situation that could lead to negative repercussions in a clinical setting. The simulator was found to be useful to train users to recognize the differences in resistance when drilling through the mandibular bone.

The cricothyroid joint in elderly Japanese individuals.

Using 15 cricothyroid joint (CT joint) specimens obtained from donated cadavers of elderly individuals, we examined the morphologies of the ceratocricoid ligaments as well as the synovial tissue. The ligaments consistently contained abundant elastic fibers: the fibers tended to be straight on the anterior side in contrast to a mesh-like arrangement on the posterior side. Thick and/or long synovial folds were often evident in the CT joint. The synovial tissue usually contained CD68-positive macrophages, but the positive cells were often restricted to certain parts of the tissue. Factor VIII-positive capillaries were present but few in number, and CD3- or IgM-positive lymphocytes were absent in the synovial tissue. Degenerative changes in the joint cartilage, such as roughness or thinning, were often present, but no cartilage defects were evident. Therefore, in contrast to the small, non-weight-bearing joints of the musculoskeletal system, we considered the degeneration of the CT joint to be a specific, silent form of osteoarthritis. For high-pitched phonation and ossification of the laryngeal cartilage, the CT joint in elderly individuals seemed to maintain its anterior gliding and rotation with the aid of elastic fiber-rich tissues compensating for the loss of congruity between the joint cartilage surfaces.

Prevention of Lethal Murine Hypophosphatasia by Neonatal Ex Vivo Gene Therapy Using Lentivirally Transduced Bone Marrow Cells.

Hypophosphatasia (HPP) is an inherited skeletal and dental disease caused by loss-of-function mutations in the gene that encodes tissue-nonspecific alkaline phosphatase (TNALP). The major symptoms of severe forms of the disease are bone defects, respiratory insufficiency, and epileptic seizures. In 2015, enzyme replacement therapy (ERT) using recombinant bone-targeted TNALP with deca-aspartate (D10) motif was approved to treat pediatric HPP patients in Japan, Canada, and Europe. However, the ERT requires repeated subcutaneous administration of the enzyme because of the short half-life in serum. In the present study, we evaluated the feasibility of neonatal ex vivo gene therapy in TNALP knockout (Akp2(-/-)) HPP mice using lentivirally transduced bone marrow cells (BMC) expressing bone-targeted TNALP in which a D10 sequence was linked to the C-terminus of soluble TNALP (TNALP-D10). The Akp2(-/-) mice usually die within 20 days because of growth failure, epileptic seizures, and hypomineralization. However, an intravenous transplantation of BMC expressing TNALP-D10 (ALP-BMC) into neonatal Akp2(-/-) mice prolonged survival of the mice with improved bone mineralization compared with untransduced BMC-transplanted Akp2(-/-) mice. The treated Akp2(-/-) mice were normal in appearance and experienced no seizures during the experimental period. The lentivirally transduced BMC were efficiently engrafted in the recipient mice and supplied TNALP-D10 continuously at a therapeutic level for at least 3 months. Moreover, TNALP-D10 overexpression did not affect multilineage reconstitution in the recipient mice. The plasma ALP activity was sustained at high levels in the treated mice, and tissue ALP activity was selectively detected on bone surfaces, not in the kidneys or other organs. No ectopic calcification was observed in the ALP-BMC-treated mice. These results indicate that lentivirally transduced BMC can serve as a reservoir for stem cell-based ERT to rescue the Akp2(-/-) phenotype. Neonatal ex vivo gene therapy thus appears to be a possible treatment option for treating severe HPP.

Fetal development of the minor lung segment.

The mediobasal segment (S7) of the right lung has been considered to correspond to the cardiac lobe generally seen in mammals. To investigate fetal development of the right mediobasal segmental bronchus (B7), we examined paraffin-embedded serial sections of 15 embrynic and fetal lungs at 7-8 weeks (serial sections) as well as semiserial sections of 8 fetuses at 15-18 weeks (semiserial sections). All of the smaller specimens did not contain B7, but 2 of the 8 larger specimens carried B7: one was found in the immediately anterior side of the inferior pulmonary vein, while in the other, the subdivisions (B7a, B7b) were overriding the vein. Although the incidence might be underestimated because of observations using semiserial sections, the B7 was most likely to develop secondarily during a period from 8 to 15 weeks. Fetal topographical changes (mainly, the descent) of the middle lobe and the inferior pulmonary vein might relate with the secondarily budding of B7. The present result does not reduce a clinical relevance of B7 as a segmental bronchus of the lung segment system.

Association between the peri-implant bone structure and stress distribution around the mandibular canal: a three-dimensional finite element analysis.

The aim of this study was to elucidate the association between the bone structure at implant insertion sites and stress distribution around the mandibular canal by means of three-dimensional finite element (3D FE) analysis. Four FE models were created with slice data using micro-computed tomography (micro-CT), and 3D FE analysis was performed. Mechanical analysis showed that the load reached the mandibular canal via the trabecular structure in all FE models. High levels of stress were generated around the mandibular canal when the distance between the mandibular canal and the implant decreased. High stress levels were also observed when cortical bone thickness and bone volume/total volume (BV/TV) were low. Our findings suggest that load is transmitted to the mandibular canal regardless of differences in the thickness of cortical bone or cancellous bone structure, but excessive load may be generated in bone with thin cortical and coarse cancellous structures.

Distribution of elastic fibers in the head and neck: a histological study using late-stage human fetuses.

There is little or no information about the distribution of elastic fibers in the human fetal head. We examined this issue in 15 late-stage fetuses (crown-rump length, 220-320 mm) using aldehyde-fuchsin and elastica-Masson staining, and we used the arterial wall elastic laminae and external ear cartilages as positive staining controls. The posterior pharyngeal wall, as well as the ligaments connecting the laryngeal cartilages, contained abundant elastic fibers. In contrast with the sphenomandibular ligament and the temporomandibular joint disk, in which elastic fibers were partly present, the discomalleolar ligament and the fascial structures around the pterygoid muscles did not have any elastic fibers. In addition, the posterior marginal fascia of the prestyloid space did contain such fibers. Notably, in the middle ear, elastic fibers accumulated along the tendons of the tensor tympani and stapedius muscles and in the joint capsules of the ear ossicle articulations. Elastic fibers were not seen in any other muscle tendons or vertebral facet capsules in the head and neck. Despite being composed of smooth muscle, the orbitalis muscle did not contain any elastic fibers. The elastic fibers in the sphenomandibular ligament seemed to correspond to an intermediate step of development between Meckel's cartilage and the final ligament. Overall, there seemed to be a mini-version of elastic fiber distribution compared to that in adults and a different specific developmental pattern of connective tissues. The latter morphology might be a result of an adaptation to hypoxic conditions during development.