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PURPOSE To evaluate the effect of different procedures for retightening the abutment screw on the screw stability between the abutment and implant. MATERIALS AND METHODS External hexagon connection (EHC) and internal tri-channel connection (ITC) implants were employed in this study. Each abutment screw was used for the following applications (n = 5 for each group): group 0 = abutment was tightened and retightened with a 10-minute interval; group 1 = abutment was tightened and retightened with a 10-minute interval, then loaded for 500,000 cycles; group 2 = abutment was loaded for 83,000 cycles during tightening and retightening and then loaded for 500,000 cycles; group 3 = abutment was loaded for 167,000 cycles during tightening and retightening and then loaded for 500,000 cycles; and group 4 = abutment was loaded for 250,000 cycles during tightening and retightening and then loaded for 500,000 cycles. Both tightening and retightening torques were set at 35 Ncm, and dynamic oblique loading between 0 N and 200 N was applied on the abutment in all groups. The settlement of the abutments (settling value) after retightening and the abutments' removal torque values (RTVs) after testing were measured. RESULTS No significant differences in settling values were found for EHC or ITC. There were significant differences in the RTVs on EHC implants, but ITC implants showed no difference in RTV with different prosthetic retightening applications. CONCLUSION The retightening application affected the joint stability of EHC implants, but did not affect the settlement or joint stability of ITC implants.

Statement of problem Limited information is available on the differences between tissue-level implants with an ultrathin threaded microsurface conical transmucosal portion and bone-level implants rehabilitated with conical custom abutments. Purpose The purpose of this retrospective study was to assess the outcomes of crowns designed as per the biologically oriented preparation technique (BOPT) cemented on conical titanium abutments on tissue-level and bone-level implants. Material and methods Patients consecutively rehabilitated with a delayed loading protocol with anterior implant-supported single crowns with a feather-edge margin, in function for at least 4 years, were recruited and divided into 2 groups based on the implant type they had received: tissue-level implants with a conical transmucosal portion or bone-level implants rehabilitated with a conical abutment by following the platform switching concept. Bone resorption, pink esthetic score (PES), and white esthetic score (WES) were collected and analyzed. The nonparametric Mann-Whitney test was performed to analyze all parameters (α=.05 for all tests). Results A total of 43 participants (48 implants) were included in the present study. The mean follow-up period was 4.5 years (range 52-64 months). A statistically significant difference (P=.004) was found in the mean ±standard deviation bone resorption between tissue-level implants (0.38 ±0.46 mm) and bone-level implants (0.83 ±0.58 mm). Higher values for both PES and WES were obtained in the tissue-level implant group. Conclusions Within the limitations of the present retrospective study, tissue-level implants with a conical transmucosal portion seem to provide a suitable alternative to bone-level implants in the anterior area.

Various kinds of implants of different diameters and connection types are used for patients with a range of bone densities and tooth sizes. However, comprehensive studies simultaneously analyzing the biomechanical effects of different diameters, connection types, and bone densities are scarce.The purpose of this 3-dimensional finite element analysis study was to evaluate the stress and strain distribution on implants, abutments, and surrounding bones depending on different diameters, connection types, and bone densities.Twelve 3-dimensional models of the implant, restoration, and surrounding bone were simulated in the mandibular first molar region, including 2 bone densities (low, high), 2 implant-abutment connection types (internal tissue level, internal bone level), and 3 implant diameters (3.5 mm, 4.0 mm, and 4.5 mm). The occlusal force was 200 N axially and 100 N obliquely. Statistical analysis was performed using the general linear model univariate procedure with partial eta squared (ηFor bone tissue, low-density bone induced a larger maximum and minimum principal strain (in magnitude) than high-density bone (P.001). As the implant diameter increased, the volume of the cancellous bone in low-density bone at the atrophy region (strain200 με) increased (P.001). For implant and abutment, the internal bone-level connection type was associated with increased peak stress as compared with the tissue-level connection type (P.001). For all models, the stress distribution on the implant complex was influenced by implant diameter (P.001): a decrease in implant diameter increased the stress concentration.The implant connection type had a greater impact on the stress of the implant and abutment than the diameter. A tissue-level connection was more advantageous than a bone-level connection in terms of stress distribution of the implant and abutment. Bone density was the most influential factor on bone strain. The selection of dental implants should be made considering these factors and other important factors including tooth size.

The influence of backfill type and material properties on the performance of field-scale geosynthetic reinforced soil (GRS) abutment models is investigated. Two alternative types of backfill as recommended in the Federal Highway Administration (FHWA) guidelines (called open-graded and well-graded) were used to build two field-scale model abutments and compare their load-bearing performance under a loading beam. Results are presented and discussed relative to the loading beam settlement, facing deformation and reinforcement strains. The well-graded backfill was found to result in smaller beam settlements and facing lateral deformations, especially at smaller loads that were comparable to service load levels. However, it was significantly faster and easier to compact the open-graded aggregate to the unit weight recommended in the guidelines. Nevertheless, performances of both abutment models were found to be satisfactory relative to the limiting requirements on the beam settlement and facing deformations at service load levels.

Statement of problem Computer-aided design and computer-aided manufacturing (CAD-CAM) methodologies allow the fabrication of custom dental implant abutments with a variety of materials and techniques. Studies on the mechanical strength of such components and the wear induced at their coupling interface during mechanical cycling are sparse. Purpose The purpose of this in vitro study was to measure the wear patterns at the hexagonal platform of dental implants induced by the installation and mechanical cycling of custom abutments fabricated by using 4 different CAD-CAM methods and to determine the compressive static resistance of the implant-abutment combinations. Material and methods A CAD software program was used to design a custom abutment for a single-unit screw-retained external hexagon dental implant crown. The same design file was used to manufacture with 4 CAM methods (N=40): milling and sintering of zirconium dioxide (ZO), cobalt-chromium (Co-Cr) sintered by selective laser melting (SLM), fully sintered machined Co-Cr alloy (MM), and machined and sintered agglutinated Co-Cr alloy powder (AM). Prefabricated titanium abutments were used as a control (TI). Each abutment was installed onto a dental implant (4.1×11 mm), and the specimens were mechanically aged (1 million cycles, 2 Hz, 100N, 37 °C). After mechanical cycling, the hexagonal connection of the dental implants was examined with a scanning electron microscope (SEM), and unused dental implants (NI) were examined as a control (n=10). The images were analyzed with a software program to quantify the areas that showed wear. The implant-abutment combinations were reassembled and submitted to a compression test (1mm/min) with a universal testing machine. The data obtained were submitted to 1-way ANOVA (α=.05). Results The mean ±standard deviation fracture load (N) of the specimens of each group were 1005 ±187 (ZO), 1074 ±123 (SLM), 1033 ±109 (MM), 1019 ±149 (AM), and 923 ±129 (TI). These values were statistically similar (P=.213). The mean ±standard deviation wear of the implants in squared-pixels were 1.1 ±0.38×105 (ZO), 2.0 ±0.29×105 (SLM), 1.0 ±0.38×105 (MM), 1.1 ±0.27×105 (AM), 1.1 ±0.33×105 (TI), and 0.51 ±0.29×105 (NI). The results indicated that, although significantly higher than those in in the control group (NI), the wear values found in the groups TI, ZO, MM, and AM were significantly lower than in the SLM group (P Conclusions The CAD-CAM abutments presented the same mechanical fracture load and wear measurements as the TI group, except for the SLM material, which showed increased wear. The failure mode from the load bearing test was the fracture of the abutments for the ZO group. The implants permanently deformed or fractured for the metal abutment groups.

Evidence to validate the routine use of angled screw-channel abutments in the anterior maxilla is sparse. If properly planned, they might provide surgical and prosthetic benefits.The purpose of this observational study was to determine the prevalence of digitally placed implants in the anterior maxilla that would allow screw-retained implant-supported restorations with either a straight or an angled screw-channel abutment.Two hundred cone beam computed tomography (CBCT) scans met the inclusion criteria for retrospective analysis and digital implant planning. Virtual implants were planned for randomly selected anterior maxillary teeth by using the anatomic crown and root position. Virtual abutments of varying angulation were attached to the implants to determine the ability to screw retain a restoration with either a straight or an angled screw-channel abutment.One hundred fifty-two (76%) sites required an angled screw-channel abutment to enable screw retention. Forty-eight (24%) sites allowed screw retention with a straight abutment. The percentage of implants requiring angled or straight abutments varied significantly among anterior teeth (P.005). One hundred nine (71.7%) angled screw-channel abutment sites required a 5-degree abutment, 41 (26.9%) required a 10-degree abutment, and 2 (1.3%) required a 15-degree abutment. Among the anterior teeth, lateral incisors presented a greater need for angled screw-channel abutments. None of the implants in the present study needed cement-retained restorations.Angled abutments allowed for screw-retained restorations on digitally planned implants in the anterior maxilla. The required angular correction to a screw-retained restoration was ≤15 degrees. Screw-retained restorations were frequently achievable (76%) with the use of angled screw-channel abutments or with straight abutments (24%), and lateral incisors presented a greater need for angled screw-channel abutments.

Purpose To measure the retrieval force required to remove 1.5-mm-thick CAD/CAM zirconia copings cemented on zirconia (Zr) and titanium (Ti) stock implant abutments after a single application of erbium-doped yttrium scandium gallium garnet (Er:YSGG) laser. Materials and methods A total of 60 monolithic Zr copings were cemented on Zr and Ti implant abutments with either a resin-modified glass-ionomer (RelyX Luting Plus Cement, 3M ESPE; Rx) or a zinc oxide eugenol cement (Temp-Bond, Kerr; Tb). These abutment-coping specimens were randomly divided into 12 groups based on laser application (vs control [C]), abutment type (Zr vs Ti), cement (Rx vs Tb), and storage condition (dry [D] vs saline water [W]). Er:YSGG laser was applied at 6 W, 30% water-60% air, and 20 Hz (300 mJ/pulse energy) postcementation following a defined pattern. The force required to remove all the cemented copings from their abutments was measured on a universal testing machine (Instron model 4204). Descriptive statistics, multi-factor analysis of variance, and post hoc Tukey honest significant difference tests (α = .05) were performed. Results The mean peak force values at removal of the Zr abutment groups were 470.3 ± 151.33 N (ZrRxC), 161.7 ± 19.29 N (ZrRxD), 316.03 ± 95.24 N (ZrRxW), 103.27 ± 24.53 N (ZrTbC), 39.33 ± 6.21 N (ZrTbD), and 20.33 ± 6.45 N (ZrTbW); and for the Ti abutment groups were 349.80 ± 106.82 N (TiRxC), 84.63 ± 14.02 N (TiRxD), 177 ± 62.57 N (TiRxW), 54.77 ± 9.10 N (TiTbC), 22.67 ± 4.32 N (TiTbD), and 11.57 ± 2.30 N (TiTbW). Conclusion Within the limitations of this study, it can be concluded that Er:YSGG laser allows for easier removal of cemented Zr copings with lower removal forces, with Ti abutment groups requiring lower forces than Zr abutment specimens. No significant difference was seen between laser and control groups for Tb compared to Rx. Er:YSGG laser shows great clinical promise for predictable retrievability of cemented, monolithic Zr implant crowns, especially with stronger resin-based cement such as Rx. With further clinical evidence, this could be very useful for clinicians managing cement-retained implant crown complications.

Statement of problem The use of reduced platform sets (implants and abutments) can help to control crestal bone loss around implants, which is essential for optimizing esthetics and biomechanical behavior. However, the information available on the fracture resistance of implants with a reduced platform is sparse. Purpose The purpose of this in vitro study was to analyze the maximum fracture strength value of implants with different platform designs during quasistatic fatigue, followed by a simulation of different bone levels of cervical insertion. Material and methods One hundred and twenty sets of dental implants and abutments with different diameters and platform designs were tested. All implants had an internal hexagon connection and conical macrogeometry. Four groups (n=30) were studied: O4.0-mm implants with a regular matched platform (rMatch group), O4.0-mm implants with a regular switched platform (PSwitch group), O5.0-mm implants with a wide matched platform (wMatch group), and O5.0-mm implants with a wide switched platform (wSwitch group). Three conditions simulating different levels of bone position around the cervical portion of the implants were proposed: insertion at the implant shoulder level=0 mm (L0), level=3 mm of insertion loss (L3), and level=5 mm of insertion loss (L5). All sets of all groups and proposed insertion level were subjected to a fracture strength test at 30 degrees in relation to the axis of the sets in a universal testing machine. Results Regardless of the insertion levels tested, the switched platform implants (rSwitch and wSwitch groups) showed similar mean fracture strength values (P>.05), while the implants of matched platforms (rMatch and wMatch groups) showed different fracture strength values for all insertion levels tested (P Conclusions The fracture strength values of the switched platform implants were lower at all insertion levels tested. However, for all insertion levels tested, the implants with a switched platform presented less deformation, whereas, in the matched platform implants, there was significant deformation of the implant structure.

Purpose To evaluate the occlusal reproductive trueness of zirconia crowns fabricated using additive manufacturing (AM) and to compare the surface roughness of crowns fabricated using AM and conventional milling (CM). Materials and methods Crowns were manufactured using AM and CM on abutments with total occlusal convergence angles of 16 and 20 degrees. Results The surface roughness of the AM crowns was less than that of the CM crowns. The differences in reproduction of the occlusal morphology of the abutment crown were greater at 16 degrees than at 20 degrees. Conclusion AM could be an effective method for manufacturing zirconia crowns.

Statement of problem A custom emergence profile offers the ideal horizontal dimensions for an anatomic healing abutment. However, developing such an emergence profile can be a time-consuming and complex process. Purpose The purpose of this study was to develop a mathematical formula defining horizontal cervical tooth geometry to design prefabricated, tooth-specific, healing abutments. Material and methods Cone beam computed tomography (CBCT) horizontal cross sections of 989 teeth on 54 participants were measured. For anterior and premolar teeth, 2 perpendicular ellipses were fitted onto the cervical tooth cross section that was defined by 3 parameters. The lingual ellipse followed the lingual outline of the tooth, and its diameter was the largest mesiodistal diameter of the tooth (parameter “a”); its buccolingual radius became parameter “b.” The buccal ellipse was perpendicular to the lingual ellipse and followed the buccal outline of the tooth. The buccolingual radius of the smaller ellipse became parameter “c.” For molars, the first ellipses followed the mesial outline of the tooth, and its larger diameter (parameter “a”) matched the largest buccolingual diameter of the tooth. Its smaller radius became parameter “h1.” The second ellipse was parallel to the first ellipse and followed the distal outline of the tooth. Its larger diameter became parameter “b”, and its mesiodistal diameter became parameter “h2”. Statistical differences between parameters were evaluated by the linear mixed model (α=.05 after Bonferroni adjustment). Pairwise comparisons were made separately for each parameter of the molars and separately for each parameter for the anterior teeth plus premolars. Teeth were put into the same parameter cluster if no significant differences were found between them for a specific parameter. If neither parameter (4 for molars and 3 for the other teeth) was different for 2 teeth, they were put into the same abutment cluster. The abutment clusters determined the type of anatomic healing abutment. The areas were calculated from the developed mathematical formula by using the parameters. In addition, cervical areas of 106 randomly chosen teeth were measured directly with a photo-editing software program. A computer algorithm was used to select 5 CBCT scans from the 54 by using the simple randomization method. The agreement between the 2 methods was evaluated by Bland-Altman analysis. Results The lower and upper limits of agreement between the 2 methods were -8.57 and 7.36 mm2, respectively, with no bias (-0.61 mm2, P=.224). Significant differences were found between most parameters among the 14 tooth types (P Conclusions The cervical tooth cross section can be accurately defined by combining 2 elliptical elements. A comprehensive array of tooth specific emergence profiles can be provided by just 12 different prefabricated abutments, designed as per the recommended parameters.

Excavation is common in the construction of hydropower projects. Monitoring for both stable and unstable slopes is a pressing requirement during progressive excavations with or without cut-slope support measures. The present study is about an excavation carried out in a proposed concrete gravity dam site on the right bank slope of the Punatsangchhu River in western Bhutan. During the excavation, the right bank abutment witnessed multiple events of slope failures of various magnitudes. One major landslide occurred on 23 July 2013 in the toe of the right abutment, where foliation/multiple sheared/fractured zones/seams in quartz-feldspathic biotite gneiss dip towards the valley. During further excavations/piling works, a subsequent landslide on the downstream, within the body of the July 2013 landslide, occurred on 12 August 2016. As a result, a real-time monitoring of the slope became necessary to facilitate further excavations for achieving the dam foundation. Thus, the advanced slope monitoring instrument like Image By Interferometric Survey – Frequency Modulated (IBIS-FM) radar was deployed for monitoring the right bank slope during the excavation for the construction of ∼129 m high dam. The displacement of the hill slope is assessed based on this system by monitoring point locations as well as areas by assigning different threshold values for providing timely alerts. This real-time monitoring was effective in identifying the reactivation of August 2016 landslide that occurred on 22 January 2019. Thus, this study showcases the efficiency of IBIS-FM radar in monitoring slope instability with sub-millimeter accuracy on a near real-time basis.

PURPOSE To assess the conformity of PFNA-II® and introduce clinical implications of new cephalomedullary nail (CMN) by analyzing three-dimensional (3D) modeling with virtual implantation at the actual size. MATERIALS AND METHODS Thirty-four patients (average age; 79 years, range 68-94 years) who sustained the intertrochanteric fracture of the femur were enrolled in the present study. After importing into Mimics® software, the intact femurs on the opposite side were selected as cropping areas to reconstruct the 3D femur model with the medullary canal. PFNA-II® and new CMNs (lateral angle 0° and 2°, CCD angle 130°; CMN0° and CMN2°) were processed at the actual size and ideally placed in the proximal femur using Mimics® software. The virtual entry point (EP), nail conformity, and anatomical relationships with the adjacent structures were assessed. RESULTS The virtual EP of PFNA-II® was placed along the cervico-trochanteric (CT) junction in the posterior half around trochanteric fossa and always medial to the tip of greater trochanter (GT). There were six abutments in PFNA-II® models, one impingement in CMN 0°, and no impingement in CMN 2°. All the models with cortical abutment showed increased anterior and lateral bowing of the proximal shaft owing to age-dependent changes. Compared with PFNA-II®, with a decreasing tendency on the mediolateral angle of new CMNs, the virtual EP shifted to the medial and anterior side towards the CT junction. By simulating the intentional positioning in the media-to-lateral direction, the abutments in the PFNA-II® model could not be avoided. Furthermore, the lag screw of CMN 0° was placed ideally at the center or inferior side of the femoral head < 10 mm in any direction without a cortical abutment. CONCLUSION To avoid cortical abutment of CMN in the Asian geriatric femur, the virtual EP would be technically placed in the medial to the GT tip, and the implant design should be changed to decrease the mediolateral angle.

Statement of problem. Polyetheretherketone (PEEK) has been advocated to replace metal components in dentistry. Although PEEK is a high-performance polymer with a white color, adequate biological response, and resistance to fracture, data to support PEEK as an alternative material for implant abutments are lacking. Purpose. The purpose of this in vitro study was to assess the mechanical and functional properties of PEEK implant abutments as a nonmetallic alternative to titanium abutments, which presents esthetic limitations and greater difficulty to customize clinically. Material and methods. Implant abutments manufactured by using PEEK (n=24) or titanium grade 5 (n=24) were attached to MIS Implants type M4 3.75×16 mm with an internal screw tightened to 25 Ncm. Screw loosening and microleakage was assessed by submersion in a 2% methylene blue solution for 48 hours at 37 C. Both groups were compared with and without applying dynamic loading; fatigue testing was performed following the International Organization for Standardization (ISO) 14801:2016 standard. All specimens were observed under a stereomicroscope at ×8 magnification. Statistically significant differences among the PEEK and titanium implant abutments were tested with 2-factor ANOVA and the chi-square analysis for nonpaired and paired data, respectively (a=.05). Results. The implant abutments made of titanium were better in all mechanical tests. The torque loss of titanium abutments was approximately 10%, while PEEK showed a significantly higher (P

Statement of problem How axial displacement may be affected by the mechanical properties and internal discrepancy of a cement-retained implant-supported prosthesis is unclear. Purpose The purpose of this in vitro study was to assess the difference in internal discrepancy and axial displacement according to the prosthesis material in cement-retained prostheses splinting nonparallel implants. Material and methods Computer-aided design and computer-aided manufacture (CAD-CAM) titanium abutments were fabricated for a vertically placed implant and a 15-degree tilted implant. Three types of prostheses, in zirconia, cobalt-chromium (Co-Cr) alloy, and polymethylmethacrylate resin (PMMA), were fabricated (n=10). The internal discrepancy between the CAD-CAM titanium abutment and the prosthesis was measured by using the replica technique. After luting with an interim cement, they were mounted in Type IV gypsum. The specimens were cyclic loaded, and axial displacement of the prosthesis was measured after 3, 10, 100, and 106 cycles. The internal discrepancy and cumulative axial displacement were assessed by using a 3-way analysis of variance and repeated measures analysis of variance (α=.05). Results The internal discrepancy of the prosthesis did not differ based on the prosthesis material (P=.869); however, it was significantly different based on the measurement location, with the occlusal discrepancy (224 ±29 μm) being greater than the axial discrepancy (21 ±10 μm) (P Conclusions Prostheses made with high-elastic moduli materials exhibited less axial displacement than PMMA prostheses, even though the internal discrepancy was not different. Moreover, vertically placed implants presented a greater axial displacement of the prosthesis than implants with angled placement.

PURPOSE: To assess the clinical, radiographic, and patient-reported outcome measures, including the success of screw-retained monolithic zirconia implant-supported restorations with CAD/CAM titanium abutments in the posterior region during a 1-year follow-up.METHODS: In a prospective case series, 50 molar sites in the posterior region of 46 patients with a minimum age of 18 years and sufficient bone volume and anatomical conditions for placing an implant (≥8 mm) and an anatomical restoration were included. Parallel-walled implants with a conical connection were inserted in a two-stage surgical procedure. Implant uncovering and healing abutment placement occurred 12 weeks after insertion. Two weeks after mucosa healing, a screw-retained monolithic zirconia restoration with a CAD/CAM titanium abutment was placed. Clinical, radiographic, and patient-reported outcome measures were collected at baseline before implant placement and then during the 1 month and 1 year follow-ups.RESULTS: At the 1 year follow-up, 49 restorations could be evaluated. The plaque accumulation, presence of calculus, bleeding tendency and peri-implant inflammation indices were low, representing healthy peri-implant conditions. The mean marginal bone level change between the 1 month and the 1 year follow-up was -0.17 ± 0.46 mm. The mean patient satisfaction was high. The restoration success was, according to the modified USPHS criteria, 95.9%.CONCLUSION: Monolithic zirconia implant-supported restorations with CAD/CAM titanium abutments have very good clinical, radiographic and patient-reported outcomes after 1 year in function.

In long-span fixed partial denture restoration, especially when pier abutment is present, a non-rigid connector as a stress breaker is indicated. The Non-rigid connector is classified into a dovetail, loop connector, split pontic, cross-pin, and wing. Split pontic is an attachment placed entirely inside the pontic, particularly indicated in the tilted abutment case, to prevent the box preparation of distal pier abutment. This case report presents A pier abutment case treated with long span porcelain fused to the metal fixed movable bridge using dovetail shaped attachment, assembling the split pontic as a non-rigid connector. Split pontic acts as the stress breaker to prevent the pier abutment acts as a fulcrum. Split pontic also transfers the shear stress to the alveolar bone, minimalizes the mesiodistal torquing of the abutment teeth, and enables individual tooth movement. The advantages of this design are preparation with minimal reduction and better esthetic outcome as the porcelain build up can be done. Thus, there is no metal exposure of the restoration. Longevity and success of fixed partial denture restoration depend on the size, shape, type, and connector position. In pier abutment cases, a non-rigid connector must be considered one of the treatment choices to restore the missing teeth and preserve the abutments.KEYWORDS: pier abutment, split pontic, non-rigid connector

Untreated conductive and mixed hearing losses as a result of middle ear pathology or congenital ear malformations can lead to poor speech, language and academic outcomes in children. Lack of access to centralised hearing healthcare in resource-constrained environments limits opportunities for children with hearing loss. Red Cross War Memorial Children's Hospital (RCWMCH) is one of only two dedicated paediatric hospitals in sub-Saharan Africa. Between 2016 and 2021, 29 children received implanted bone conduction hearing devices, and 104 children were fitted with bone conduction devices on softbands. The authors' experience at RCWMCH suggests that bone-anchored hearing devices, either fitted on softbands or on implanted abutments, can provide solutions in settings where patients have limited access to hearing healthcare and optimal classroom environments. Hearing healthcare should be accessible and delivered at the appropriate level of care to mitigate the adverse effects of hearing loss in children. CONTRIBUTION: This article describes strategies employed at RCWMCH such as fitting bone conduction hearing devices on a softband immediately after hearing loss diagnosis and conducting follow-up via remote technology to make hearing healthcare more accessible to vulnerable populations.

PURPOSE The optimal abutment material and design for an angled implant-abutment connection in the esthetic zone is unclear. The purpose of this finite element analysis (FEA) study was to compare different abutment models by evaluating the stress values in the implant components and strain values on the simulated bone around an anterior maxillary implant with different angled abutment models and loading conditions. MATERIALS AND METHODS One O3.5×12-mm implant was placed in 3D FEA models representing the anterior left lateral segment of the maxilla. Three different contemporary implant models were created with 17- or 25-degree angled abutments (Ti base abutment, zirconia abutment, and titanium abutment) and 3D-modeled. The implant abutment model was an angled Ti base abutment (TIB), an angled zirconia abutment (ZIR), or an angled titanium abutment (TIT). Vertical and oblique loads of 100 N for the central incisors were applied as boundary conditions to the cingulum area and incisal area in a nonlinear FEA. RESULTS The TIB model resulted in reduced stress conditions. According to the von Mises stresses occurring on the screw, abutment, crown, and implant, especially under oblique loads, the TIB model was exposed to less stress than the ZIR or TIT models. Strain values in simulated cortical and trabecular bones were obtained lower in the TIB model. CONCLUSIONS When a standard implant was placed in the esthetic zone at an increased angle, the implants, abutments, and screws had more unfavorable stress levels; therefore, using a Ti-base abutment may reduce stress. The amount of contact surface of the implant with the simulated cortical bone is also an important factor affecting stress and strain. This article is protected by copyright. All rights reserved.

Fixed partial dentures (FPDs) made of metal ceramic are a popular treatment option for missing teeth. Studies have shown that posterior abutments of FPDs had a higher pulp survival rate than anterior abutments. Postoperative sensitivity following the cementation of a fixed prosthesis is a frequent symptom, especially when the abutments include important pulp. Dentinal hypersensitivity affects between 4 and 74 percent of people. Females are found to have a somewhat greater DH incidence than males. While DH can affect individuals of any age, there have been several theories on what causes abutment sensitivity after tooth preparation and cementation. In this review we included some of it. Also, we discussed methods of management of postoperative sensitivity and Management of fractured abutment screw.

Taken overlying strata of fully mechanized top coal caving mining (FMTCCM) in 15 m extra thick coal seam as the research object, the comprehensive research methods such as field investigation, theoretical calculation, and numerical analysis are used to systematically analyze. During the mining of extra thick coal seam, the overlying strata form the structure of lower cantilever beam and upper hinged rock beam. The downward transmission caused by the interaction of this combined structure is the fundamental reason for the strong periodic ground pressure behavior of working face and roadway blow. The movement process of overlying strata movement is divided into four stages, and dynamic distribution characteristics of lateral abutment pressure in different stages are obtained. It is considered that the gob side roadway can be in a relatively stable overburden structure and stress environment during the stable stage of abutment pressure. The distribution range of the internal and external stress fields is determined, which provides a theoretical basis for the reasonable roadway layout. At last, the fracture position and abutment pressure evolution process of overlying strata along the goaf side of the extra thick coal seam are further verified by drilling stress measurement.

Coal wall spalling is regarded as a key technical problem influencing safe and efficient mining of large-mining-height working faces while the distribution of abutment pressure within the limit equilibrium zone (LEZ) influences coal wall spalling within a large-mining-height working face. This research attempted to explore the distribution characteristics of abutment pressure within the LEZ in a large-mining-height working face. For this purpose, the influences of the orientation of joints on mechanical characteristics of coal with joints and on the distribution of abutment pressure within the LEZ in the large-mining-height working face were analysed by theoretical analysis and numerical simulation. Research results show that the damage variable of coal with joints first rises, then decreases, and finally increases with increasing dip angle of the joints; as the azimuth of the joints increases, the damage variable first declines, then increases; the damage variable gradually declines with increasing joint spacing; an increase in the dip angle of joints corresponds to first reduction, then growth, and a final decrease of the abutment pressure at the same position in front of the coal walls; on certain conditions, the abutment pressure at the same position within the LEZ first rises, then declines as the azimuth of joints increases; with the growth of the joint spacing, the abutment pressure at the same position within the LEZ rises. The dip angle and azimuth of joints marginally affect the abutment pressure within the LEZ.

OBJECTIVES There is no information today about the impact of abutment type on the crestal bone stability. This retrospective study was aimed to evaluate the crestal bone levels (CBL) and failures of implants with prefabricated and customized abutments after the long term. MATERIALS AND METHODS The mesial and distal CBL around dental implants with prefabricated and custom abutments were recorded. Measures were completed at 5- and 10-year endpoints. RESULTS Sixty-three patients with 249 implants were included. One hundred twenty-seven implants (51%) were restored with prefabricated and 122 implants (49%) with customized abutments. All the patients received fixed restorations. The results showed that the CBL was higher in patients with custom abutments than the CBL of patients with prefabricated abutments. The mean bone loss around implants with prefabricated abutments was 0.29 mm mesial/0.45 mm distal after 10 years. Meanwhile, the mean bone loss at implants with custom abutments was 1.19 mm mesial/1.27 mm distal (p

Landslide tsunamis are complex fluid–solid coupling processes that often cause enormous catastrophes. In this study, the smooth particle hydrodynamics (SPH) and discrete element method (DEM) coupling algorithms are used to simulate the tsunami which was induced by the 1963 Vajont landslide, Italy. In order to simulate the failure process of the landslide, a DEM numerical model is constructed based on the geological structure of the landslide, and contact parameters for the DEM particles are inverted according to the laboratory tests. Based on the numerical results, the whole process of the tsunami by the Vajont landslide is reproduced in detail. Comparisons show that the simulated motion and accumulating characteristics of the landslide, the climb-up and peak overtopping flow of the tsunamis, and the load on the dam by the tsunamis agree well with the published results. The simulation also indicates that the right bank slope of Vajont Dam is the major spillway of the flood, thereby significantly reducing the flow directly over the dam, which is helpful to stabilize the dam; and the concrete of the left abutment is damaged by the mixture flow of water and geomaterials with a higher velocity (approx. 35 m/s at the max.). The overtopping depth decreases from the north bank to the south bank. The maximum depth on the right abutment and the left abutment is approximately 80 and 65 m, respectively, lower than the reported estimation of ~ 150 m. This study shows that the coupled SPH–DEM method and the developed code—CoSim—work well for the analysis and research on landslide tsunami.

Toe formation is a phenomenon resulting from unconnected cracks between blastholes, which occurred during blasting excavation of the abutment slot at Baihetan hydropower station. Analysis of crack development has tended not to focus on the high in-situ stress environment at the slope corner. Therefore, this study aimed to explore the toe formation process through theoretical analysis and numerical simulation. Firstly, a three-blasthole model was established to analyze the effects of blasting load and in-situ stress on crack extension. Then, a finite-element model of the abutment slot was built to simulate crack propagation under different in-situ stress environment. Finally, optimization measures for avoiding toe were proposed. The results demonstrate that cracks grow preferentially in the direction of the maximum tangential tensile stress and are influenced by the blasting load and in-situ stress. On the lateral side of the abutment slot, the crack initiation and extension occur far from the centerline due to the deviation of the maximum tangential tensile stress. The deviation increased as the in-situ stress. Consequently, cracks between blastholes not being able to connect with each other results in toe formation. Increment of the linear density of the charge and optimization of the excavated profile are both effective in reducing the impact of the stress concentration caused by in-situ stress and preventing toe formation.

This computational study analyzed the strain magnitude and distribution within trabecular bone structure around different materials and finish line (FL) configurations of implant abutments loaded axially. Differences in fracture resistance of these abutments were also assessed. Sixteen endosseous screw vent implants were embedded in eight bio-faithful mandibular simulators resembling D2 and D3 bone density (n = 4 models per bone type) in the second premolar and second molar positions. These models were further subdivided into eight subgroups with different FL configurations and abutment materials. Strain gauges were mounted adjacent to the implants, and the superstructures were successively placed on the abutments. A universal dynamometrical testing apparatus was used for a static compression load. Finally, all samples were subjected to load until fracture. Three-way analysis of variance for strain analysis showed a significant overall interaction between the three variables (bone type, FL configuration, and abutment materials; P < .001), while the analysis for fracture resistance showed significant two-way interactions between bone type and FL configuration (P < .001) and between bone type and abutment material (P < .001). The implant abutment material, the FL configuration of the abutment, and the bone type can influence the mechanical behavior of the abutment used. Zirconia abutments with anatomical FL configurations possess better fracture resistance than zirconia and titanium abutments with circular FL configurations in D2 bone density.

Purpose: to study the mechanical properties and Finite Element Stress Analysis of three implant abutment materials. Materials and Methods : Fifteen bars (25mm length, 4mm. thick and 5mm.width)of three abutment materials ;High Performance Polymer Hybrid abutments , Nano-Fiber Reinforced Composite and Fiber Reinforced Composite divided into three groups were exposed to Flexure Strength and Deflection tests. Fifteen implant abutments (two parts abutment) covered by all ceramic crowns divided into three groups were exposed to Static Fracture Resistance test and Finite Element Stress Analysis .Results: Flexure Strength tests mean and standard deviation of bar specimens showed significant difference, where Gp I, II, III were 519.29±0.46), 200.74±0.33and 315.43±0.59) .Also, Deflection test mean and standard deviation were 3.052±0.040, 0.984±0.106, 2.028±0.027 receptively revealed significant difference. The comparison between fracture resistance mean and standard deviation of the tested abutment three groupswere 642.00±.5.637,306.00±30.496 and 514.40±12.915 respectivelyand revealed significant difference. Finite Element Stress Analysis of applied vertical load on the three abutment materials did not have clear difference but the least stresses created on bone with Nano-FRC abutment(16.2) followed with FRC (17.32) then BioHPP abutment (18.55).Conclusion: Fracture strength of BioHPP abutments with ceramic crowns had the potential to withstand maximum occlusal forces, also showed better fracture patterns than the FRC and NFRC abutments. and showed a better stress distribution on the set, suggesting a good mechanical behavior.

In this paper, the seismic behavior of a total of 84 reinforced concrete bridges, including 12 straight and 72 curved bridges was studied. The bridges were designed and detailed according to the American Association of State Highway and Transportation Officials (AASHTO) regulations. To evaluate the accuracy of the seismic response predictions obtained using elastic analyses, as suggested by AASHTO, both linear and nonlinear time history analyses were performed and the results were compared. In addition, to investigate the accuracy of the code provisions regarding the limitations on the bridge subtended angle for the use of equivalent straight bridges, the results obtained for the curved bridges were compared with those obtained for the equivalent straight bridges. Furthermore, the effects of different types of irregularity on the predicted displacement demands from equivalent straight bridges were investigated. To study the effects of different types of irregularity on the results, different irregular arrangements of spans, various column heights, different abutment conditions, and different subtended angles were considered. Also the effect of combination of different types of irregularity was investigated by considering bridges with different configurations. The results indicated that the deviation of the results obtained from the linear and nonlinear analyses is significant, particularly in the transverse direction of the bridges with irregularity in columns height for different subtended angles. Also, it was shown that in bridges with restrained abutments, unlike the bridges with unrestrained (i.e., free) abutments, the equivalent straight bridges cannot be used in lieu of the curved bridges, since the differences between the results from the two models are significant and become larger with increasing the subtended angle of the bridges. It was shown that some modeling assumptions widely used for seismic analysis of bridge structures can be unrealistic and may lead to inaccurate predictions. It was shown that the AASHTO specifications regarding the use of elastic analysis for some irregular bridges and the limitations on the subtended angle for the use of equivalent straight bridges need to be reevaluated.

Expansion of bridge girders in summer moves integral bridge abutments toward backfill, causing high lateral earth pressures behind the abutment. Some backfill material slumps downward and toward the abutment when the abutment moves away from the backfill due to bridge girder contraction in winter. Placement of geogrids within the backfill can increase stability of the backfill while placement of compressible inclusions (e.g., Expanded Polystyrene (EPS) foam) can reduce lateral earth pressures behind the abutment caused by bridge girder expansion. In this study, six physical model tests were conducted with 30 abutment top movement cycles due to simulated seasonal temperature changes to study the performance of integral bridge abutments with different mitigation measures. The test results showed that geogrid reinforcements caused higher maximum lateral earth pressures at the same abutment movement, but geogrids with wrap-around facing significantly reduced the backfill surface settlements. The combination of the EPS foam and geogrids could minimize lateral earth pressure increase and backfill settlement. The EPS foam reduced the abutment toe outward movement when the abutment top was pushed against the backfill; however, the mitigation effects by the EPS foam was limited due to its small thickness and relatively high elastic modulus in this study.

Objective: To evaluate and compare the effect of implant supported versus implant retained removable partial denture restoring Kennedy's class I cases on the supporting structures by measuring marginal bone loss and bone density around implant. Subjects and Methods: Twelve patients were selected from the outpatient clinic, Prosthodontics Department, Faculty of Dentistry, Minia University. Both groups were classified into two equal groups; according to the implant superstructures either dome shaped abutment -and-ball and socket attachment. Each Patient of both groups had two implants in second molar position and received removable partial denture of the same design. Patients were followed up for one year radiographicaly regarding marginal bone loss and bone density around each implant. Group I: Six patients received RPD supported by dome shaped short abutments. Group II six patients received RPD retained by ball and socket attachments. Results: Results revealed that there was Significant increase in marginal bone loss in group II implant retained with ball abutment than group I implant supported with dome shaped abutment and Significant increase in bone density in group I (implant supported) than group II (implant retained) Conclusion: The use of dome shaped abutment produce less marginal bone loss and increase of bone density than the use of ball abutment.

Objective: The objective of this study is to evaluate the clinical effect of two abutment materials with two different types of superstructure metal free restoration on the platform switched implant. Subjects and Methods: Twenty human patients with missing maxillary central incisor were selected for implant placement and divided randomly into two groups according to abutment type Titanium abutment and PEEK abutment( n= 10 in each) .Each group was subdivided into two subgroubs according to superstructure crown (PEEK and VITA ENAMIC crown, n=5) All groups were evaluated clinically through measuring implant stability, determining screw loosening and color stability at base line, 3, 6 and 12 months . Results: As regarding to implant stability , there was no significant difference between four groups Ti PEEK ,Ti VIT , PEEK PEEK and PEEK VIT group (73.40 ± 3.44,73.80 ± 2.17,76.0 ± 1.87,73.40 ± 2.30). There is no screw loosening of all tested group. PEEK VIT group show the highest color change between all groups but the change is not significant . Conclusion: PEEK abutment with PEEK crown gives better result but in general implant stability is comparable with other groups. There is no screw loosening occur in all group. Color stability was better when use titanium abutment however the difference between all group was non significant. VITA ENAMIC crown with PEEK abutment show the higher color change, however the difference is non significant.

Aim: The aim of this study was to evaluate the effect of PEEK abutments, an alternative to titanium abutments, with temporary acrylic restorations using immediate loading protocol on the marginal bone loss and peri-implant tissues. Methodology: This study was performed with temporary restorations using 32 titanium and PEEK abutments (14 titanium and 18 PEEK) on 32 implants performed on 21 patients (13 females, 8 males). Before surgical placement of the implants, intraoral and radiographic examinations were performed. The patients were divided into two groups as titanium abutment group (Grup Ti) and PEEK abutment group (Grup PEEK). In both groups, all implants were placed according to the manufacturer's recommendations. After surgery, impressions were taken using polyvinyl siloxane impression material and closed tray impression technique. The gingiva, which is thought to be formed on the model, was scraped and screwed onto the appropriate titanium or PEEK abutment analogue according to the groups and temporary restoration was prepared and applied on the implant. Results: The results of the statistical analysis show that abutment types have no significant effect on ISQ values (p>0.05), but the diameter of the implant significantly affected ISQ values independently from abutment type (p0.05). Conclusion: Within the limitations of this study, there was less bone loss in the PEEK abutment group (p0.05). How to cite this article: Gül İ, Zortuk M, Öztürk C. Effects of abutment materials on the tissues surrounding dental implants immediately after loading: An in vivo study­. Int Dent Res 2021;11(Suppl.1):1-6. https://doi.org/10.5577/intdentres.2021.vol11.suppl1.1 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Objective: To evaluate and compare the effect of implant supported versus implant retained removable partial denture restoring Kennedy's class I cases on the supporting structures by measuring modified gingival index and probing depth for abutment teeth and implants. Subjects and Methods: Twelve patients; who had Kennedy class I mandibular partially edentulous ridge extending distal to the first or second premolar, were selected from the outpatient clinic, Prosthodontics Department, Faculty of Dentistry, Minia University. The patients were classified into two equal groups; according to the implant superstructures either dome shaped abutment or ball and socket attachment. Each Patient of both groups had two implants in second molar position (one in each side) and received removable partial denture of the same design. Patients were followed up for one year clinically. Group I: Six patients received RPD supported by dome shaped short abutments. Group II six patients received RPD retained by ball and socket attachments. Results: Results revealed that, there was no statistically significant difference between the two groups regarding modified gingival index and probing depth around the abutment teeth and implant abutment. Conclusion: The use of dome shaped abutment or ball and O-ring attachment have the same effect on gingival index and probing depth around natural abutments and implants in Kennedy class I mandibular situations.

Purpose To systematically review all in vitro studies focusing on the durability of different bonding protocols applied to zirconia restorations with different types of tooth or implant abutments. Materials and methods English-language articles published in dental journals up to March 2020 were searched using a combination of free text words and MeSH terms, as follows: zirconia; Y-TZP; zirconium; zirconia restoration; enamel; dentin; titanium abutment; titanium base; ceramic abutment; dental core; ceramic or metal post and core; composite build-up; bonding; adhesive cement; resin cement; adhesion; cementation; test; material testing; laboratory; and in vitro. Studies were identified for review based on certain inclusion and exclusion criteria. Results A total of 3,339 titles were identified. After a successive filtering process, a final total of 28 studies were included. The included studies featured different types of surface pretreatment methods, primers, resin cements, tooth and implant abutments, laboratory test outcomes, and designs. The relatively limited number of the identified studies and the heterogeneity of the extracted data did not allow for meta-analysis. Conclusions Zirconia surface pretreatment is an essential step in the bonding protocol. Airborne-particle abrasion surface pretreatment had a positive influence on zirconia resin bonding to most types of tooth and implant abutments identified. Chemically activating the treated zirconia surfaces with an MDP monomer-based primer, along with an MDP monomer or phosphate ester monomer-based resin cement, seems to be a durable bonding protocol. Type of resin cement seems to be a less influential factor.

The morphology and histology of the soft tissue around the implant are different from the periodontal tissue, but the difference in the regulation of blood flow is not known. The aim of the study was to compare the resting blood flow and the vasodilatation capacity of the gingiva between implants and teeth. Twenty-six healthy volunteers with single-tooth implants were involved. The implant-borne crown was retained on either a zirconia or titanium abutment. The vasodilatation capacity of the gingiva was assessed by a postocclusive reactive hyperemia test. Blood flow was measured by a laser speckle contrast imager at the buccal gingiva of the implant-borne crown and an analog natural tooth. No significant differences in baseline gingival blood flow were observed between the different abutments and the teeth in either region. The hyperemia after compression was significantly attenuated at the zirconia abutments in all regions during the entire investigation period (20 minutes) compared to the titanium abutments and the teeth. No differences were observed between titanium abutments and the teeth. The resting microcirculation seems to be the same at implants and teeth. However, the vascular reactivity might be disturbed at the zirconia, but not at the titanium, abutment.

PURPOSE To evaluate the mechanical stability and complication rates of titanium (Ti) or zirconia (Zr) abutments restored with cantilevered fixed dental prostheses (cFDPs) when supported by 1 or 2 implants. MATERIALS AND METHODS A total of 32 samples were fabricated. Half of the samples received 1 implant, and the other half received 2 implants (Bone Level Implant, O 4.1, 13 mm, Straumann) to simulate the clinical situation of 2 or 3 missing maxillary incisors, respectively. Each group was divided into two subgroups (n = 8). Ti-I and Ti-II groups received Ti abutments (Anatomic Abutment, Straumann) supporting 2- or 3-unit metal cFDPs, respectively, while Zr-I and Zr-II groups received Zr abutments (IPS e.max Anatomic Abutment, Straumann). Following the cementation of cFDPs using resin cement (Multilink Automix, Ivoclar Vivadent), the samples were subjected to thermomechanical fatigue load and were subsequently loaded until fracture in a universal testing machine. Following the static loading test, stereomicroscopic analyses (Carl Zeiss) were done to identify the weakest component of the cFDP, abutment, and implant assembly. Mann-Whitney U test was used to evaluate the effect of the number of supporting implants and abutment material on fracture strength values, and the level of statistical significance was set at 5% (α = .05). RESULTS All specimens survived the aging, and no screw loosening or fracture was recorded. The mean fracture strength values were 226 N (± 26.45 ), 551.12 N (± 82.19 ), 601 N (± 41.51 ), and 664.5 N (± 37.59 ) for Zr-I, Zr-II, Ti-I, and Ti-II, respectively. The difference between fracture strength values of Ti and Zr groups was significant in favor of Ti abutments (P < .001). The number of supporting implants showed a significantly positive effect on the fracture strength of Zr abutments. CONCLUSION Zirconia abutments demonstrated lower fracture strength values than titanium abutments independent from the number of supporting implants when used under cFDPs. Two-implant supported cFDPs with zirconia abutments have the potential to withstand physiologic forces applied in the anterior region.

Steel in bridge constructions is often associated with very large span bridges due to its favorable relationship between strength and weight. But even for bridges with small and medium spans of up to 60 m, steel combined with concrete as a composite bridge can lead to economically justifiable constructions, especially when the performance during the complete life-cycle is integrated. In this paper, two life-cycle oriented calculation methods (life-cycle costs and external costs) are introduced and applied. As a result, comparisons between two abutment solutions (conventional reinforced concrete abutment and a permanent steel sheet pile abutment) and two superstructure variants (steel composite construction and in-situ prestressed concrete superstructure) are presented. It is shown that accelerated construction processes, durable materials, and a smart bridge-design considering actual technological developments lead to economically advantageous solution for traffic infrastructures.

To control rockbursts in mining roadways in ultrathick coal seams, a new method for preventing rockbursts through dual pressure relief by roof cutting through cumulative blasting in medium-deep boreholes from the conveyor gateway and return airway was proposed. The mechanical characteristics of key overlying strata of the working face under the effect of dual pressure relief were theoretically investigated. Furthermore, a mathematical relationship between the roof-cutting depth and the advanced abutment pressure on the working face was established to reveal the mechanism of dual pressure relief in controlling rockbursts. Moreover, the effect of the dual pressure relief method on controlling rockbursts was validated through numerical simulation and field testing. Results showed that artificially increasing the caving height of gangues in goaf based on the dual pressure relief method can restrict the subsidence of key strata, thus reducing the advanced abutment pressure of the working face; the method influences a range of 20 m in front of the working face along the strike and areas 30 m away from the two roadways along the dip. The average energy density of coal in the side of the conveyor gateway is decreased by 15.4%, while that in the side of return airway is reduced by 13.8% within the range of influence. The field test results indicated that the average pressure on support declines by 21.4% within 30 m from the working face to the conveyor gateway, while it decreases by 20.5% within that region 25 m from the return airway by using the dual pressure relief method. After conducting dual pressure relief, the total number of microseismic (MS) events during mining of the working face is decreased by 25.4%. The number of MS events with energy release exceeding 103 J falls by 36.6%, while the number of events releasing less than 103 J is increased by 28.6%. The characteristics of MS energy release change from coexistence of low-energy events and a small number of high-energy events to the occurrence of numerous low-energy events. Results can verify the effectiveness of the dual pressure relief method in controlling rockbursts in the mining roadway of ultrathick coal seams.

Partial supporting piles removal from deep foundation pit may lead to large-scale foundation pit collapse, resulting in severe consequences. Various studies have investigated the underpinning technology of cutting abutment piles by combining field monitoring and numerical simulation, but there are few studies on cutting supporting piles of foundation pit by the shallow excavation method. Taking an actual deep and large foundation pit as an example, the finite element method (FEM) was adopted to study the surface settlement and the changing trend of the force and displacement of the supporting pile caused by cutting piles during the shallow excavation of double tunnels. The FEM results were verified with the field monitoring data. The simulation results show that the surface settlement around the foundation pit mainly occurs at the pile cutting stage under different excavation sequences (0D, 1D, 2D), and the main distribution area is the one-fold diameter area outside the double tunnel. After the supporting piles are partially cut, the bending moment and displacement of the lower part of the broken piles differ significantly due to different excavation sequences, but the bending moment and displacement of the upper part of the broken piles are basically similar. In the process of removing the supporting piles, the Earth pressure behind the piles is redistributed, and the load is mainly transferred to the adjacent supporting piles outside the tunnel within the radius of one time of the tunnel diameter. However, the load is not evenly transferred to the adjacent supporting piles. Some recommendations for the reinforcement scheme of the supporting structure during cutting supporting piles in deep foundation pit are also proposed. The research results can provide theoretical basis and practical guidance for the construction of similar projects in the future.

The excavation-induced stresses transferred from the panels or pillars in upper coal seams play a key role in the occurrence of rockbursts in driving roadways during close-distance coal seam mining, which has become a common problem and threat to many underground mines. The authors established a 3D finite-difference numerical model via FLAC3D software using the close-distance coal seam mining conditions in the Zofiowka Mine as a case example to reveal the rockburst mechanism in such conditions. The excavation-induced vertical stresses are analyzed, which provides a basis to build a conceptual model to explain the possible source mechanism of the rockburst under such conditions. Nine typical rockburst indicators considering different contributing factors are then selected as the evaluation criteria to assess rockburst potential in the study site. The results suggest that the superposition of multiple excavation-induced stresses of the main drift and tailgate provides an environment for stress concentration and energy accumulation. The side abutment stress induced by mining in the upper coal seam has a “strengthening” effect to the rockburst occurrence. The great deviatoric stress induced by complex excavating situations is another important exterior cause. A strict calibration procedure should be implemented before using indicators to predict rockburst potential. A methodology was proposed to estimate the location and magnitude of rockbursts combined with numerical modeling, laboratory tests, and feedbacks from the field. The study could provide some references and guidelines for preventing and mitigating rockbursts in underground mines under similar engineering conditions.

Many field observations have shown that rock bursts occur frequently near the terminal mining line (TML) and dip coal pillar area in deep coalfaces. Taking the “7.26” rock burst in coalface 3302 in Xingcun Coal Mine as an example, the rock burst mechanism was investigated based on theoretical analysis and field observations, and a combined evaluation method using the stress field under seismic wave excitation was established to determine the reasonable TML of coalface 3302. Firstly, the static geological data revealed during roadway excavation were used for preevaluation of rock burst risk at the working face. By theoretically analyzing the stress transfer mechanism of the two types of the roof structure, the computational model of abutment pressure was established and the calculation method giving the abutment stress was proposed. Subsequently, a dynamic evaluation method that adopts microseismic and stress online monitoring system to monitor dynamic information, such as mine tremors and stress during coalface mining, was developed to define stress anomaly areas and then dynamically determine the TML. Finally, the proposed model was used to optimize the position of the TML of LW3302 in Xingcun Coal Mine; findings obtained in this study provide theoretical guidance for safe coal mining. Combined with the results of theoretical analysis (255 m), online stress monitoring (200 m), microseismic (MS) monitoring (262 m), and passive seismic velocity tomography (220–250 m), it can be finally determined that the width of the protective coal pillar for the TML of coalface 3302 should be at least 262 m.

Directivity of fault ruptures modifies the ground motion in the direction of rupture (forward directivity) to have large amplitude shorter duration pulses, and the ground motion opposite to the rupture propagation (backward directivity) to have long duration low amplitude pulses, compared to the ground motion at locations perpendicular to the direction of rupture at similar rupture distances (Rrup). Directivity is prominent in the fault-normal component of ground motion. Multiple extents of directivity scenarios (4 scenarios; 1 symmetric bilateral, and 3 directivity scenarios of different unilaterality) of magnitude 7 on a vertical strike-slip fault (analogous to the San Andreas fault in Southern California) are simulated at a few racetrack locations, of which one forward and one backward directivity station are included. Three racetracks (Rrup 5 km, 10 km, and 15 km) are considered within the near-field where NGA West-2 relations suffer for limited data. The simulated ground motion is applied as base excitation to 2-span seat abutment pre-1970 Californian skew bridges of different skew angles (0°, 15°, 30°, 45o, and 60°), with bridges oriented parallel to the fault and perpendicular to the fault. Probabilistic seismic demand models (PSDMs) are computed for each skew angle at each rupture distance and scenario. Collapse fragility curves are derived from PSDMs, and the median and dispersion are compared with those of HAZUS prescribed values.

Deep mining has become the normal state of coal mining; compared with the mine with shallow buried depth, the consequent high level of in situ stress and complex distribution have brought severe threats to the stability of the stope and the surrounding rock of the roadway. In this research, taking the 121304 working face of Kouzidong Mine as the engineering background, the characteristics of mining-induced stress distribution under complex in situ stress environment in deep mining are analyzed by using on-site measurement of the original rock stress and mining stress, establishing a theoretical model centered on the middle section of the working face, and establishing large-scale numerical calculation models for different advancing directions. It was found that under deep mining conditions, the maximum stress of the original rock is 25.12 MPa, and the direction is vertical. The advanced influence range of mining stress is about 150 m, and the abutment pressure presents a three-peak distribution characteristic in front of the working face. The research results provide important theoretical guiding value for guiding the mining of coal mines with similar geological conditions.

In this study, inorganic sodium nitrate salt (NaNo3) was used as the tracer and BX2 piezometer was selected as an injection point and 10 other piezometers were selected as sampling points. After conducting the tracer test and sampling from piezometers and transferring all samples to the laboratory, the electrical conductivity of the samples was measured. After analyzing the results, two possible routes were identified for the leakage from the body and abutment of Shahghasem dam. The results show that the main pathway of the leakage flow was diagnosed toward the right abutment and the reason may be due to dissolution and formation of limestone holes and karstification phenomenon. Finally, it can be concluded that the sodium nitrate as tracer moved in the body and abutment of Shahghasem dam and was not adsorb by clay and silt materials; therefore, it is suggested for future tracer works.

At present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

It is well-known that seismic pounding is detrimental to curved bridges since it can not only amplify the global displacement demands of the bridge deck but also cause stress concentration and localized damage to the bridge components like abutment backwall and expansion joints. In this study, a shake table experiment was performed on a 1/25 scale curved bridge model with a pounding buffer zone made of natural rubber pad or aluminum foam at the expansion joint location to mitigate the pounding effect. This model consisted of a single-span segment, a two-span segment and an expansion joint in-between. For comparison purpose, the buffer zone was also made of steel in order to achieve a steel-on-steel interaction. Two historical ground motions including a pulse-type near-field motion and a non-pulse type near field motion, were selected to excite the bridge model to study the effects of motion characteristics. The results show that the buffer zones of rubber and aluminum can effectively reduce seismic impact forces, and hence alleviate the localized damage. Meanwhile, these two buffer zones can also effectively reduce the global response of the bridge such as bridge deck accelerations, seat width demand at the joint location, and in-plane rotation of the bridge deck. However, when comparing with the aluminum foam, the rubber buffer zone demonstrated better performance in reducing the pounding force, bridge deck accelerations, and seat width demand at the expansion joint locations. In addition, for the same bridge model, the pulse-like record can result in significantly large response than the nonpulse-like record, regardless of the buffer zone materials. It was also found that seismic collision of the curved bridge could also induce significantly large friction force along the contact surface, which could also influence the response of the bridge system.

Various bridge portfolios and modeling parameters will influence the seismic response of bridges differently. These features are typically fixed prior to modeling bridges, while there is inherent uncertainty associated with choosing them. Sensitivity analysis of analytical seismic demands with respect to the changing bridge attributes helps to improve estimated seismic demand models which are eventually used in the reliability assessment of bridges. To this end, the current study implements statistical approaches such as analysis of covariance to evaluate the impact of common bridge portfolios such as abutment types on the primary engineering demand parameters such as deck displacement. Moreover, this paper proposes a machine learning algorithm, Random Forest ensemble learning method, to assess the level of importance of modeling parameters on estimating seismic demands. The framework is presented for analyzing concrete box-girder bridges with tall piers that are typically constructed in response to the complex topography of the construction site such as mountain or valley regions. However, the proposed framework is applicable to other types of bridges. Furthermore, although previous research revealed distinctive seismic performance for bridges with tall piers compared to the bridges with ordinary configurations, there is still a lack of understanding of the variability of their seismic demands. Thereby, the findings of this study provide a better understanding of the seismic performance of this class of bridge.

This study compared the marginal and internal fit of implant-supported fixed dentures fabricated using CAD/CAM systems.A lower jaw model representing partial edentulism was produced. Two dental implants were inserted in the area of teeth 35 and 37, onto which cemented abutments were screwed. The model was scanned using a laboratory scanner and transferred to a design software program for substructure fabrication. Sixty substructures were fabricated out of each group for six substructure types (n = 10), cast Co-Cr (control), milling Co-Cr, laser sintering Co-Cr, titanium (Ti), zirconium, and polyetheretherketone (PEEK) substructures. The marginal and internal fit was evaluated using a silicone replica viewed under a stereomicroscope. The data were analyzed using the statistical package program for social sciences (SPSS, Chicago, IL, USA, v. 17) at a significance level of 0.05. Marginal and internal gaps were compared using the one-way ANOVA test and Tukey's post hoc test. The differences between abutment teeth were determined using the independent sample t-test.There was a significant difference in the marginal gap between PEEK and Ti groups (p 0.05) but no difference between other groups (p 0.05). There was a significant difference in the internal gap between PEEK, laser sintering Co-Cr, and milling Co-Cr groups (p 0.05) but no difference between other groups (p 0.05). The PEEK group had a higher marginal gap than the Ti group and a higher internal gap than the DMLS Co-Cr group (p 0.05).All substructures have a marginal and internal fit within acceptable clinical limits.This in vitro study suggests that materials and techniques used in CAD/CAM systems improve the fitting accuracy of implant-supported fixed restorations.

Based on the geological conditions of the 15,600 working face in Pingba Mine, this paper establishes the mechanical model of the stress distribution in the pre-working face under the influence of mining pressure based on a hemispherical stress distribution theory. The analytical formula for the stress distribution is determined. A numerical model for the mining pressure under the influence of key layer is also constructed, and dynamic stress interruptions under various roof-cutting relief schemes in different horizontal positions are simulated. The stress distribution of the stope under different pressure relief schemes is analyzed and compared with the theoretical results. Results show that blasting roof cutting blocks the transmission of the abutment pressure to the working surface to the coal and rock mass in front of the working face, reducing the significant working face mining pressure influence range, which decreases as blasting pressure relief position moves toward the working face. Stress accumulation in the coal in front of the working face also increases as the blasting pressure relief position moves toward the working surface. Engineering practice results show that blasting cutting can effectively block the propagation of mining pressure, and the stress impact range is shortened by approximately 1/3.

AIM To evaluate 1-year bone-level changes around subcrestal platform-switching implants with 1 or 3 mm definitive abutments. The influence of mucosal thickness on bone-level alterations was further analysed. MATERIALS AND METHODS Implants were placed in the posterior sextants and positioned 1.5 mm subcrestally with an abutment of 1 or 3 mm height. Final restorations were delivered after 16 weeks. Radiographic measurements of inter-proximal bone level were the primary outcome and were adjusted by vertical mucosal thickness. Peri-implant clinical conditions and resonance frequency analysis were also compared. RESULTS A total of 65 subjects with 99 implants were analysed. The overall 1-year implant survival rate between the 1- and 3-mm groups was 96.4% and 94.4%, respectively. Statistically significant lower inter-proximal marginal bone-level changes were observed in the 3-mm group (1 mm: -0.17 ± 0.02 mm at mesial and -0.21 ± 0.02 mm distal; 3 mm: -0.03 ± 0.02 mm at mesial and -0.03 ± 0.02 mm and distal; mesial: p = .001; distal: p

Bridge scour is soil erosion around the bridge foundation (pier or abutment), which may cause foundation damage. Thus, effective, real-time, reliable, and robust monitoring methods are imperative. This study proposes a distributed fiber optic sensing method based on an ultra-weak fiber Bragg grating (UWFBG) array for scour monitoring and estimation. In this method, most of the optical fiber is installed freely on the surface of piers/abutments in spiral form. The unconstrained optical fiber can deform randomly and easily under flowing water, and the deformation can be collected by the UWFBGs written in the optical fiber. The scour estimation can be realized by analyzing the difference between signals of the optical fiber embedded in the sand and those immersed freely in the water. A series of experiments were designed and carried out to demonstrate the proposed method. The effects of flow velocity and temperature were investigated experimentally. Standard deviation was employed as the scour indicator, because it can indicate the discrete degree of signals. Experimental results show that the proposed method can estimate the scour in real time.