Ring-Polymer Molecular Dynamics and Kinetics for the H- + C2H2 → H2 + C2H- Reaction Using the Full-Dimensional Potential Energy Surface.

The H- + C2H2 → H2 + C2H- reaction is important in understanding the production mechanisms of anionic molecules in interstellar environments. Herein, the rate coefficients for the H- + C2H2 → H2 + C2H- reaction were calculated using ring-polymer molecular dynamics (RPMD), classical molecular dynamics (MD), and quasi-classical trajectory (QCT) approaches on a newly developed ab initio potential energy surface (PES) in full dimensions. PES was constructed by fitting a large number of ab initio energy points and their gradients using the permutationally invariant polynomial basis set method. There was no barrier in the reaction coordinates, which was a collinear-dominated reaction, and the reaction proceeded exothermically. It is found that the fitted PES provides the appropriate thermal rate coefficients based on all RPMD, classical MD, and QCT simulations at higher temperatures. The evaluation of the rate coefficients at lower temperatures should be conducted carefully because the fitting of the PES associated with the long-range interaction should be further improved. The spatial distribution of the nucleus allows a more effective attraction between the reactants.

On-the-Fly Ring-Polymer Molecular Dynamics Calculations of the Dissociative Photodetachment Process of the Oxalate Anion.

The dissociative photodetachment dynamics of the oxalate anion, C2O4H- + hν → CO2 + HOCO + e-, were theoretically studied using the on-the-fly path-integral and ring-polymer molecular dynamics methods, which can account for nuclear quantum effects at the density-functional theory level in order to compare with the recent experimental study using photoelectron-photofragment coincidence spectroscopy. To reduce computational time, the force acting on each bead of ring-polymer was approximately calculated from the first and second derivatives of the potential energy at the centroid position of the nuclei beads. We find that the calculated photoelectron spectrum qualitatively reproduces the experimental spectrum and that nuclear quantum effects are playing a role in determining spectral widths. The calculated coincidence spectrum is found to reasonably reproduce the experimental spectrum, indicating that a relatively large energy is partitioned into the relative kinetic energy between the CO2 and HOCO fragments. This is because photodetachment of the parent anion leads to Franck-Condon transition to the repulsive region of the neutral potential energy surface. We also find that the dissociation dynamics are slightly different between the two isomers of the C2O4H- anion with closed- and open-form structures.

Quantum calculations of the photoelectron spectra of the OH-·NH3 anion: implications for OH + NH3→ H2O + NH2 reaction dynamics.

We present the results of quantum dynamics calculations for analyzing the experimentally measured photoelectron spectra of the OH-·NH3 anion complex. Detachment of an excess electron of OH-·NH3 initially produces a molecular arrangement, which is close to the transition-state structure of the neutral OH + NH3→ H2O + NH2 hydrogen abstraction reaction due to the Franck-Condon principle, and thus finally leads to the OH + NH3 or H2O + NH2 asymptotic channel. We used both the path integral method and the reduced-dimensionality quantum wave packet method to simulate the photoelectron spectra of the OH-·NH3 anion. The calculated spectra were found to be in qualitative agreement with the experimental spectra. It was found that the photodetached complex mainly dissociates into the OH + NH3 channel; however, we found that the hydrogen exchange process also contributes to the photodetachment spectra.

Discrepancy Between Clinical Diagnosis and Whole-exome Sequencing-based Clonality Analysis of Synchronous Multiple Oral Cancers.

BACKGROUND/AIM: The definition of multiple oral cancers is based on the distances between the tumors. However, it is not possible to accurately predict tumor origins based only on clinical criteria. PATIENTS AND METHODS: We performed whole-exome sequencing (WES) to analyze the genetic alterations in five tumors of two patients who underwent surgery in our hospital. RESULTS: In case 1, the distances between tumors on the right mandibular gingiva and buccal mucosa were more than 15 mm, leading to a clinical diagnosis of multiple primary tumors. WES revealed common mutations between tumors, suggesting that the tumors were derived from the same clone. In contrast, in case 2, the distance between tumors on the right side of the tongue was only 10 mm, but the tumors were diagnosed as double primary tumors because their mutations were completely different. CONCLUSION: WES, rather than the available clinical criteria, can clarify the clonal origins of multiple oral cancers.

Theoretical Analysis of the Formylmethylene Anion Photoelectron Spectrum: Importance of Wolff Rearrangement Dynamics.

Photoelectron spectroscopy of a molecular anion is very useful for investigating the transition state and intermediate regions on the reactive potential energy surfaces of a neutral system. In this work, we theoretically analyzed the previously measured photoelectron spectrum of the formylmethylene anion, HCCHO-. We simulated the photoelectron spectra for both the singlet and triplet states using the semiclassical method with quantum nuclear densities and Franck-Condon factor calculations with harmonic vibrational analysis. We also performed real-time quantum dynamics calculations to elucidate the importance of the Wolff rearrangement process, which leads to the stable product ketene from the carbene intermediate on the neutral singlet potential energy surface.

Appropriate surgical margin for odontogenic myxoma: a review of 12 cases.

OBJECTIVE: Odontogenic myxoma (OM) is a rare benign tumor that is frequently nonencapsulated and invades the surrounding bone, resulting in a high risk of recurrence. However, the optimal surgical technique and appropriate surgical margin remains controversial. Here, we report our clinical investigation of 12 patients with OM diagnosed histopathologically. STUDY DESIGN: We retrospectively reviewed the records of 12 patients treated at our institution. Osteotomy or bone shaving with enucleation was generally performed with 5-mm bony margins from the radiologic extent of the tumor. RESULTS: One half of the cases occurred in the maxilla and the other half in the mandible. Treatment for maxillary OM was enucleation in 2 patients and maxillectomy in 4 patients. Treatment for mandibular OM was enucleation with shaving of the surrounding bone in 1 patient and segmental mandibulectomy in 5 patients. Radiographs of surgical specimen removed by segmental mandibulectomy indicated that the mean distance between the tumor and the margin was 5.4 (range 3.4-7.0) mm. Tumor recurrence was noted in 1 patient who had undergone enucleation alone. CONCLUSION: The 1-cm surgical margin for OM, as reported conventionally, might not be necessary. A prospective study is needed to determine the appropriate surgical margin for OM.

Comparison of magnesium alloys and poly-l-lactide screws as degradable implants in a canine fracture model.

The aims of this study were to evaluate in vivo the biological responses to implants composed of biodegradable anodized WE43 (containing magnesium yttrium, rare earth elements and zirconium; Elektron SynerMag®) magnesium alloy, monolithic WE43 magnesium alloy and poly-l-lactic acid (PLLA), which are commonly used materials in clinic settings, and to evaluate the effectiveness of the materials as bone screws. The effectiveness of the magnesium alloy implants in osteosynthesis was evaluated using a bone fracture model involving the tibia of beagle dogs. For the monolithic WE43 implants, radiological, and histological evaluation revealed that bone trabeculae around the implanted monolithic WE43 decreased because of an inflammatory response. However, there was no damage due to hydrogen gas or inflammatory response in the bone tissue around the anodized WE43 implants. After 4 weeks, all the PLLA implants (n = 3) had broken but the WE43 implants had not (n = 6). These results suggest that the WE43 implants had sufficient strength to fix bone fractures at load-bearing sites in orthopedic and oral maxillofacial surgery. Therefore, these biodegradable magnesium alloys are good candidates for replacing biodegradable polymers. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1282-1289, 2016.

Effects of platelet-poor plasma, platelet-rich plasma, and platelet-rich fibrin on healing of extraction sockets with buccal dehiscence in dogs.

Alveolar bone resorption generally occurs during healing after tooth extraction. This study aimed to evaluate the effects of platelet-poor plasma (PPP), platelet-rich plasma (PRP), and platelet-rich fibrin (PRF) on healing in a ridge-augmentation model of the canine socket with dehiscence of the buccal wall. The third mandibular premolars of 12 beagle dogs were extracted and a 3 mm buccal dehiscence from the alveolar crest to the buccal wall of the extraction socket was created. These sockets were then divided into four groups on the basis of the material used to fill the sockets: PPP, PRP, PRF, and control (no graft material) groups. Results were evaluated at 4 and 8 weeks after surgery. The ultrastructural morphology and constructs of each blood product were studied by a scanning electron microscope (SEM) or calculating concentrations of platelets, fibrinogen, platelet-derived growth factor, and transforming growth factor-ß. A total of five microcomputed tomography images of specimens were selected for measurement, and the area occupied by the newly formed bone as well as the horizontal bone width were measured. Moreover, decalcified tissue specimens from each defect were analyzed histologically. The median area of new bone at 4 and 8 weeks and median horizontal bone width at 8 weeks were the highest in the PPP group. However, bone maturation in the PRF and the PRP groups was more progressed than that in the PPP and control groups. By SEM findings, the PRF group showed a more highly condensed fibrin fiber network that was regularly arranged when compared with the PPP and PRP groups. The growth factors released from platelets in PRP indicated higher concentrations than that in PRF. Under more severe conditions for bone formation, as in this experiment, the growth factors released from platelets had a negative effect on bone formation. This study showed that PPP is an effective material for the preservation of sockets with buccal dehiscence.

Application of a new material (ß-TCP/collagen composites) in extraction socket preservation: an experimental study in dogs.

PURPOSE: A bone defect model simulating an extraction socket with buccal dehiscence was designed to investigate the usefulness of a composite of beta-tricalcium phosphate (ß-TCP) and a collagen sponge, ß-TCP/collagen (TCP/Col) for socket preservation. MATERIALS AND METHODS: Following the extraction of the maxillary second and third premolars of 13 beagle dogs, a bone defect with buccal dehiscence (5 × 3 × 7 mm) was prepared. The defects were filled with either TCP/Col, ?-TCP, collagen, or left intact (control) and evaluated at 4 and 8 weeks after surgery. A total of three micro-computed tomography (micro-CT) images were selected, and the area size occupied by the newly formed bone and residual TCP was measured. Newly formed bone and residual TCP in the bone defect site of the specimens was also measured and evaluated. RESULTS: No evidence of postoperative infection was found in all cases. At 4 weeks after surgery, the TCP granule was retained in the bone defects and active bone formation was observed in the TCP/Col group and the ß-TCP group, whereas in the collagen and the control groups, connective tissue grew into the defect. In the TCP/Col and ß-TCP groups, morphologically well-preserved alveolar ridges were observed; most TCP granules grafted in the defects were resorbed and only a few residuals were evident at 8 weeks after surgery. CONCLUSIONS: These results exhibited that the TCP/Col composites could sufficiently maintain bone width and height for the preservation of the extraction socket with buccal dehiscence while preventing epithelial in-growth. In addition, TCP/Col in an easily handled spongeous form could provide a better intraoral manipulation capability than TCP granules alone and was considered to be suitable as a bone grafting material used for alveolar ridge preservation.

The effect of covering materials with an open wound in alveolar ridge augmentation using beta-tricalcium phosphate: an experimental study in the dog.

PURPOSE: This study aimed to examine the effectiveness of a grafting technique using beta-tricalcium phosphate (Β-TCP) covered with different materials in alveolar bone defects with dehiscences. MATERIALS AND METHODS: In five beagle dogs, all premolars in the mandible were extracted bilaterally. After a 12-week healing period, two bone defects (length, 5 mm; width, 5 mm; depth, 7 mm) were created on each side of the mandible, and the buccal bone plate was resected. The four bone defects were randomly assigned to one of the following treatments: group 1, Β-TCP alone (TCP group); group 2, Β-TCP graft covered with collagen sponge (TCP+collagen group); group 3, Β-TCP graft covered with free buccal mucosa (TCP+mucosa group); group 4, no treatment (control group). The microarchitecture of the regenerated bone was observed using microcomputed tomography, and the area of newly formed bone was measured. Specimens from each defect were selected and subjected to histologic and histomorphometric analysis; areas of newly formed bone and the ridge width were measured in the specimens. RESULTS: Significant differences were found between the control group and all test groups. The median horizontal width of the ridge 2 mm from the top of the alveolar crest in the TCP+mucosa group was significantly greater than that of the TCP group. There was no significant difference between the TCP+mucosa and TCP+collagen groups in any measurement. CONCLUSIONS: Application of Β-TCP grafts to alveolar bone defects with dehiscence and covering of the open wound with free buccal mucosa or collagen sponge may be useful for ridge augmentation. Compared to no treatment or leaving the wound uncovered, these approaches resulted in more new bone formation and provided adequate horizontal mandibular width.