Mining-Induced Stress Control by Advanced Hydraulic Fracking under a Thick Hard Roof for Top Coal Caving Method: A Case Study in the Shendong Mining Area, China

Fully mechanized top-coal caving mining with high mining height, hard roofs and strong mining pressure are popular in the Shendong mining area, China. The occurrence of dynamic disasters, such as rock burst, coal and gas outburst, mine earthquakes and goaf hurricanes during the coal exploitation process under hard roof conditions, pose a threat to the safe production of mines. In this study, the characteristics of overburden fracture in fully mechanized top-coal caving with a hard roof and high mining height are studied, and the technology of advanced weakening by hard roof staged fracturing was proposed. The results show that the hard roof strata collapse in the form of large “cantilever beams”, and it is easy to release huge impact kinetic energy, forming impact disasters. After the implementation of advanced hydraulic fracturing, the periodic weighting length decreases by 32.16%, and the length of overhang is reasonably and effectively controlled. Ellipsoidal fracture networks in the mining direction of the vertical working face, horizontal fracture networks perpendicular to the direction of the working face, and near-linear fracture planes dominated by vertical fractures were observed, with the accumulated energy greatly reduced. The effectiveness of innovation technology is validated, and stress transfer, dissipation and dynamic roof disasters were effectively controlled.

Multifragmentary patellar fracture has a distinct fracture pattern which makes coronal split, inferior pole, or satellite fragments

The present study aimed to map the location and frequency of fracture lines on the coronal articular and sagittal planes in multifragmentary patellar fractures. 66 multifragmentary patellar fractures were digitally reconstructed using the 3D CT mapping technique. The coronal articular surface and midsagittal fracture maps were produced by superimposing each case over a single template. Each fracture line was classified based on the initial displacement and orientation. We evaluated the frequency and direction of the fracture line, coronal split fragment area, and satellite and inferior pole fragment presence. Coronal articular surface fracture mapping identified primary horizontal fracture lines between the middle and inferior one-third of the articular surface in 63 patients (95.4%). Secondary horizontal fracture lines running on the inferior border of the articular facet were confirmed (83.3%). Secondary vertical fracture lines creating satellite fragments were mostly located on the periphery of the bilateral facet. Midsagittal fracture mapping of primary and secondary horizontal fracture lines with the main coronal fracture line revealed a predominantly X-shaped fracture map. The consequent coronal split fragment and inferior pole fracture were combined in most cases. In conclusion, the multifragmentary patellar fracture has a distinct pattern which makes coronal split, inferior pole, or satellite fragments.

Comparing the Fracture Resistance and Modes of Failure in Different Types of CAD/CAM Zirconia Abutments with Internal Hexagonal Implants: An in Vitro Study

3 groups of zirconia abutments (n=3) made of different connection design or manufacturers were investigated (All-Zr, ASC-Zr and AM-Zr groups). All-electric dynamic test instrument was used to place static loading on specimen with a crosshead speed set at 1 mm/min. One-way analysis of variance (ANOVA) and post hoc Tukey tests (α=.05) were used for statistical evaluation. The mean fracture resistance was 258.21±68.60 N for All-Zr group, 360.55±29.66 N for ASC-Zr group, and 341.45±25.97 N for AM-Zr group. There was no significant difference in fracture resistance between the 3 groups (1-way ANOVA, P = 0.10). The modes of failure among the 3 types of abutments are different. The All-Zr group showed an oblique fracture line starting from the buccal aspect at the region of the implant platform. While in the ASC-Zr group and the AM-Zr group showed a relatively horizontal fracture line with greater distance from implant platform. The titanium inserts cannot significantly improve the fracture resistance of the zirconia abutment. However, they may alter the modes of failure, allowing buccal fracture surfaces of the zirconia abutments to be placed away from the implant platform, thereby protecting the implant-abutment connection.

Characteristics of Multifragmentary Patellar Fractures: Three-dimensional Computed Tomography-based Fracture Mapping Study

Limited literature is available regarding anatomic patterns of articular injuries in comminuted patellar fractures. The present study aimed to map the location and frequency of fracture lines on the coronal and sagittal planes of the articular surface in AO/OTA 34C3 fractures. The directions of the fracture lines from the CT scans of 66 multifragmentary patellar fractures were highlighted in the coronal plane of the articular surface and in the midsagittal plane. The images of all fractures were then oriented to fit and superimposed over a single template. The primary horizontal fracture lines were identified in 63 patients (95.4%) using coronal articular surface fracture mapping. The average value of the primary horizontal fracture line was located between the middle and inferior facets. The secondary horizontal fracture lines ran frequently on the inferior border of the articular facet (83.3%). The secondary vertical fracture lines created satellite fragments and were mostly located on the periphery of the bilateral facet. Sagittal fracture mapping of the primary and secondary horizontal fracture lines with the main coronal fracture line revealed a predominantly X-shaped fracture map. The presence of the free articular type of coronal split fragment was significantly related to inferior pole fractures (OR: 8.15, P = 0.01).

Well Shear Associated with Conventional and Unconventional Operations: Diagnosis and Mechanisms

Summary Wells are sometimes deformed due to geomechanical shear slip, which occurs on a localized slip surface, such as a bedding plane, fault, or natural fracture. This can occur in the overburden above a conventional reservoir (during production) or within an unconventional reservoir (during completion operations). Shear slip will usually deform the casing into a recognizable shape, with lateral offset and two opposite-trending bends, and ovalized cross sections. Multifinger casing caliper tools have a recognizable response to this shape and are especially useful for diagnosing well shear. Certain other tools can also provide evidence for shear deformation. Shear deformations above a depleting, compacting reservoir are usually due to slip on bedding planes. They usually occur at multiple depths and are driven by overburden bending in response to reservoir differential compaction. Shear deformations in unconventional reservoirs, for the examples studied, have been found to be caused by slip on bedding planes and natural fractures. In both cases, models, field data, and physical reasoning suggest that slip occurs primarily due to fluid pressurization of the interface. In the case of bedding plane slip, fracturing pressure greater than the vertical stress (in regions where the vertical stress is the intermediate stress) could lead to propagation of a horizontal fracture, which then slips in shear.

Minimal Invasive Post Endodontic Monoblock Restorations, II- Sharonlay Crown: Review

The loss of tooth structure owing to caries, iatrogenic cavity preparation, and dentin drying compromises the structural integrity of root canal treated teeth. Because the quantity of remaining tooth structure and the ability to resist occlusal forces have a direct link, it is critical to offer a post endodontic restoration that allows cuspal covering as soon as possible after completion. The decision to place a full crown or an onlay is based on the remaining tooth structure; an onlay can be inserted if the cuspal width to length ratio is 1:2 or above. A full crown must be planned when the ratio is less than 1:2. Cast post and core or a prefabricated post can provide fracture resistance with equivalent outcomes in single-rooted teeth requiring post-endodontic repair. In the case of premolars, however, contrary to the common practice of just providing cuspal covering through onlays, cervical reinforcement would be required to counteract horizontal stresses acting in the cervical region. Only full crown or onlay does not prevent horizontal fracture of tooth that occurs due to shear forces of mastication so many a times radicular support is taken to retain coronal restoration and strengthening of cervical region of tooth. Sharonlay is one of the newer ways being developed by researchers to improve the function of teeth and repair in such circumstances. Sharonlay is a new onlay patented design with I.P. no 1956475 dated 27/04/2010 that has a post extending into the radicular section of the premolar giving the required strengthening in a conservative manner while also protecting it against both vertical and horizontal stresses. It is a potential post-endodontic restoration option for premolars, and it may be indicated in a multirooted tooth primarily for retention, particularly when the clinical crown is too short to support an onlay, crown, or endocrown.

Experimental and Modelling Study of Gravity Drainage in a Three-Block System

Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed, validated and used for monitoring the saturation profiles along with the matrix blocks. Results showed that gas wetting condition of horizontal fracture weakens the capillary continuity and in consequence decreases the recovery factor in comparison with the original liquid wetting condition. Moreover, higher spacers’ permeability increases oil recovery at early times, while it decreases the ultimate recovery factor. Tilt angle from the vertical axis decreases recovery factor, due to greater connectivity of matrix blocks to vertical fracture and consequent channelling. Decreasing horizontal fracture aperture decreases recovery at early times but increases the ultimate recovery due to a greater extent of capillary continuity between the adjacent blocks. Well match observed between the numerical model results and the experimental data of oil recovery makes the COMSOL multiphysics model attractive for application in multi-blocks fractured systems considering block-to-block interactions. The findings of this research improve our understanding of the role of different fracture properties on the block-to-block interactions and how they change the ultimate recovery of a multi-block system.

Horizontal fracture of anterior mandible

A 33-year-old male patient reported to us with the history of assault. The patient was cooperative and oriented, with no sign of head injury. He was assaulted with an axe over the mandible. The patient is having posteroanterior view radiographs of the mandible suggesting isolated horizontal fracture of the anterior mandible. Under general anaesthesia, this unusual fracture was treated by open reduction and internal fixation with a three-dimensional plate and miniplates. The case was managed successfully without any postoperative complications.

Relationship between Fracture of the Ulnar Styloid Process and DRUJ Instability: A Biomechanical Study

Background There has been clinical question in the treatment of ulnar styloid fracture with distal radius fracture, surgical fixation of the styloid fragment, or ignorance of the fragment. We examined relationship between size of the ulnar styloid fracture and distal radioulnar joint (DRUJ) stability biomechanically to answer the above clinical question. Methods Changes in the dorsopalmar stiffness of the DRUJ after experimentally simulating in four types of ulnar styloid fractures were examined in cadavers. After tip, middle, base-horizontal, and base-oblique type of styloid fractures were made sequentially, changes in dorsopalmar DRUJ stiffness were measured using the MTS machine in the intact wrist, for each fracture, at 60 degrees pronation, neutral, and 60 degrees supination, respectively. Additional cutting of the radioulnar ligament (RUL) at the fovea was also simulated with the base-horizontal fracture. Results The tip and middle type fractures did not demonstrate significant loss of stiffness compared with the intact. The base-horizontal fracture demonstrated only significant loss of stiffness in the dorsal direction (radius palmar; ulnar dorsal) with forearm in neutral rotation. The base-oblique fracture demonstrated significant loss of dorsopalmar stiffness of the DRUJ. Additional section of the RUL with the base-horizontal fracture induced significant loss of stiffness of the DRUJ compared with the intact. Conclusions Because the RUL originates from the fovea as well as from the base of the ulnar styloid, these results suggest that DRUJ instability closely correlates with how much of the bony fragment includes the originating portions of the RUL. The findings further suggest that larger base-oblique and base-horizontal fragments with resultant DRUJ instability must be reattached, but that even base-horizontal fragment as well as tip and middle ulnar styloid fragment can be ignored when there is no instability.