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This paper presents findings from an extensive, laboratory-based study of scour at bridge abutments located in compound channels. The study considered aspects of abutment construction, including abutment and floodplain erodibility, and examined how these aspects influence scour development. Its findings show that three basic scour conditions can develop at abutments in compound channels: scour of the main-channel bed, when the floodplain is far less erodible than the bed of the main channel (Scour Condition A); scour of the floodplain around an abutment, for abutments set back on a floodplain (Scour Condition B); and scour at an abutment column exposed once an abutment is breached (Scour Condition C). These conditions may combine, depending on abutment location and site circumstances. The authors present laboratory observations and data associated with Scour Conditions A and B. The data are analyzed in terms of a formulation concept that treats Scour Conditions A and B as essentially scour at a short contraction (the bridge opening), for which flow nonuniformity and turbulence amplify scour depth associated with a long contraction. The amplification is greatest for small contractions and diminishes for larger contractions that force greater magnitude and uniformity of flow velocity through a bridge opening. [ABSTRACT FROM AUTHOR]

Background Microleakage through the interface has been documented in implant systems with titanium ( Ti) abutments. There is a current increase in the use of zirconia ( Zi) abutments especially in esthetic zone in where higher risk of visible metal color through the peri-implant tissues exists. Purpose The aim of the present in vitro study is to evaluate the leakage at the implant fixture-abutment interface with two different screw-retained abutment systems at different torque values in a nonloading condition. Materials and Methods In vitro study design included four groups ( Ti and Zi torqued at 25 and 15 Ncm [ N = 8/group]). Microcomputed tomography (micro- CT) was chosen to detect microgap. Microleakage from the implant chamber to the external milieu was evaluated using limulus amebocyte lysate ( LAL) test, while microleakage from external milieu to the implant chamber was evaluated using toluidine blue dye ( TBD) and colorimeter. Results Micro- CT images did not reveal any microgap. LAL test showed that there is a time-, abutment-, and torque-dependent increase in microleakage ( p = .001) with Zi torqued at 15 Ncm having higher leakage with time compared with Ti torqued at 15 Ncm ( p = .002), as well as Zi torqued at 15 Ncm having higher leakage with time compared with Zi torqued at 25 Ncm ( p = .01). TBD test showed a nonsignificant increase in microleakage with higher leakage related to titanium abutment groups ( p > .05). Repeated torque/antitorque handling differentially affected microleakage ( p = .01). Conclusions Within the limits of this study, there is a statistically significant difference in bidirectional microleakage with time, abutment type, and torque values being major players for leakage from internal implant chamber to external milieu, while the abutment type and time but not the torque value being important factors for leakage from external milieu into implant chamber in nonloading condition. Future studies are needed to determine peri-implant health around Zi abutments. [ABSTRACT FROM AUTHOR]

An in vitro experimental model was designed and tested to determine the influence that peri-implant strain may have on the overall crestal bone. Strain gages were attached to polymethylmethacrylate (PMMA) models containing a screw-type root form implant at sites 1 mm from the resin-implant interface. Three different types of crown superstructures (cemented, 1-screw [UCLA] and 2-screw abutment types) were tested. Loading (1 Hz, 200 N load) was performed using a MTS Mechanical Test System. The strain gage data were stored and organized in a computer for statistical treatment. Strains for all abutment types did not exceed the physiological range for modeling and remodeling of cancellous bone, 200-2500 µε (microstrain). For approximately one-quarter of the trials, the strain values were less than 200 HE the zone for bone atrophy. The mean microstrain obtained was 517.7 µε. In conclusion, the peri-implant strain in this in vitro model did not exceed the physiologic range of bone remodeling under axial occlusal loading. [ABSTRACT FROM AUTHOR]

Background. Because no information was found in the dental literature regarding the fracture resistance of all-ceramic crowns using CEREC (Sirona) computer-aided design and computer-aided manufacturing (CAD-CAM) system on solid abutments, the authors conducted a study. Methods. Sixty synOcta (Straumann) implant replicas and regular neck solid abutments were embedded in acrylic resin and randomly assigned (n = 20 per group). Three types of ceramics were used: feldspathic, CEREC VITABLOCS Mark II (VITA); leucite, IPS Empress CAD (Ivoclar Vivadent); and lithium disilicate, IPS e.max CAD (Ivoclar Vivadent). The crowns were fabricated by the CEREC CAD-CAM system. After receiving glaze, the crowns were cemented with RelyX U200 (3M ESPE) resin cement under load of 1 kilogram. For each ceramic, one-half of the specimens were subjected to the fracture resistance testing in a universal testing machine with a crosshead speed of 1 millimeter per minute, and the other half were subjected to the fractured resistance testing after 1,000,000 cyclic fatigue loading at 100 newtons. Results. According to a 2-way analysis of variance, the interaction between the material and mechanical cycling was significant (P = .0001). According to a Tukey test (α = .05), the fracture resistance findings with or without cyclic fatigue loading were as follows, respectively: CEREC VITABLOCKS Mark II (405 N/454 N) was statistically lower than IPS Empress CAD (1169 N/1240 N) and IPS e.max CAD (1378 N/1025 N) (P < .05). The IPS Empress CAD and IPS e.max CAD did not differ statistically (P > .05). According to a t test, there was no statistical difference in the fracture resistance with and without cyclic fatigue loading for CEREC VITABLOCS Mark II and IPS Empress CAD (P > .05). For IPS e.max CAD, the fracture resistance without cyclic fatigue loading was statistically superior to that obtained with cyclic fatigue loading (P < .05). Conclusions. The IPS Empress CAD and IPS e.max CAD showed higher fracture resistance compared with CEREC VITABLOCS Mark II. The cyclic fatigue loading negatively influenced only IPS e.max CAD. Practical Implications. The CEREC VITABLOCS Mark II, IPS Empress CAD, and IPS e.max CAD ceramic crowns cemented on solid abutments showed sufficient resistance to withstand normal chewing forces. [ABSTRACT FROM AUTHOR]

Live bed scour experiments were conducted using four types of non-cohesive bed sediments with median diameters d = 0.26 mm, 0.42 mm, 1.06 mm and 1.92 mm and five 45°wing-wall abutments of lengths l = 0.04 m, 0.06 m, 0.08 m, 0.10 m and 0.12 m. The tests were conducted in the range of flow velocity varies from 0.71 to 5 times of the critical velocity. The plotting of non-dimensional scour depths (scour depths/abutment lengths) vs non-dimensional flow intensity (flow intensity/critical velocity) show one peak value of scour depth close to the threshold velocity and thereafter, it reduces and again attain a live-bed maximum in the range of flow intensity 3 to 5 times of the critical velocity. It is also observed that the scour depth increases with the increase in sediment sizes up to threshold value of flow for all sediment sizes and abutment lengths. Further, the scour depth decreases with the increase of non-uniformity under all flow conditions. A design equation is proposed for estimating maximum scour depth at 45° wing-wall abutment under live-bed condition. The calculated values of scour depths using proposed equation, and also with three different live-bed local scour equations, are compared with the measured values of scour depths. [ABSTRACT FROM AUTHOR]

Aim To test in vitro the mechanical resistance, rotational misfit and failure mode of three original implant-abutment connections and to compare them to two connections between non-original abutments connected to one of the original implants. Material and Methods Three different implants with small diameters (3.3 mm for Straumann Roxolid, 3.5 mm for Nobel Biocare Replace and Astra Tech Osseospeed TX) were connected with individualized titanium abutments. Twelve implants from each system were connected to their original abutments ( Straumann CARES, Nobel Biocare Procera, Astra Tech Atlantis). Twenty-four Roxolid implants were connected with non-original abutments using CAD/ CAM procedures from the other two manufacturers (12 Nobel Biocare Procera and 12 Astra Tech Atlantis). For the critical bending test, a Zwick/ Roell 1475 machine and the Xpert Zwick/ Roell software were used. Results The rotational misfit varied when comparing the different interfaces. The use of non-original grade V titanium abutments on Roxolid implants increased the force needed for deformation. The fracture mode was different with one of the original connections. Conclusions Non-original abutments differ in design of the connecting surfaces and material and demonstrate higher rotational misfit. These differences may result in unexpected failure modes. [ABSTRACT FROM AUTHOR]

The article offers step-by-step instructions for implant restorations in a timely and predictable manner.

Background/purpose: A bacterial adhesion to implant surfaces is a first stage of peri-implant mucositis and peri-implantitis. The aim of this longitudinal study was to examine the quantitative and qualitative biofilm formation on healing screws and the presence of peri-odontal pathogens in peri-implant crevicular fluid (PCF). In each of the 30 participants, one healing screw was adapted to every single implant. Materials and methods: Thirty patients, 18 females and 12 males, were selected. Thirty heal-ing abutments were left in situ for 20, 30 and 90 days. At regular times, the presence/ absence of bleeding on probing (BOP) was determined. The specific periodontal pathogens were determined in PCF, by polymerase chain reaction (PCR). After 20, 30 and 90 days, the healing screws were removed and analyzed to establish the total bacterial count by a cul-ture method. Results: BOP+ increased significantly after 90 days. Biofilm was detected on all healing abut-ments and the number of cultivable oral flora showed a significant increase from 20 days to 30 days and to 90 days. At 90 days, the anaerobic counts constituted the bulk of plaque exam-ined and Veillonella spp. were present in higher percentages levels (19.82%) among the Gram-negative bacteria. No significant differences among the experimental groups were de-tected in the frequencies of detection of each monitored bacteria in PCF. Conclusion: The healing screws left in situ for a period of 90 days caused a peri-implant inflammation and the presence of periodontal pathogenic bacteria in the peri-implant sulcus, due to the plaque accumulation on screw surfaces. [ABSTRACT FROM AUTHOR]

Abutment teeth are called upon to withstand the forces normally directed to the missing teeth, in addition to those usually applied to the abutments. Whenever possible, an abutment should be a vital tooth. Normally, teeth with active periodontal problem should not be used as abutment teeth. The use of multiple splinted abutment teeth, non-rigid connectors or intermediate abutments makes the procedure much more difficult and often the result compromises the long-term prognosis. In cases where tooth preparation cannot solve the problem, the use of various attachments and a telescopic retainer must be considered. Understanding the basic concepts of how to retain various restorative components and how to protect the remaining tooth structure, will enable us to answer the numerous questionable situations that arise during the restorative process will be facilitated. Thus, this will result in final restorations that are based on sound design principles. [ABSTRACT FROM AUTHOR]

Purpose: A stable oral mucosa is crucial for long-term survival and biofunctionality of implants. Most of this evidence is derived from clinical and animal studies based solely on implant-supported prosthesis. Much less is known about the dimensions and relationships of this soft tissue complex investing tooth-implant-supported bridgework (TISB). The aim here was to obtain experimental evidence on the dimensional characteristics of oral mucosa around TISB with two different abutment designs. Methods: Sixteen 3-unit TISB were constructed bilaterally in the mandible of eight adult Macaca fascicularis. An implant system with a standard progressive thread design was the bone-anchoring implant in the second mandibular molar region while the second mandibular premolar served as the natural tooth abutment. Eight implants were connected with the tapered abutment, the remaining with butt-joint abutment, in a split-mouth design. These were allowed to functional load for 6 months before sacrification for histomorphometry. Six soft tissue indices were scored: coronal gingival mucosa-to-implant top distance (DIM); sulcus depth (SD); junctional epithelium (JE); connective tissue contact (CTC); implant top to first bone-to-implant contact distance (DIB); and biologic width (BW=SD+JE+CTC); corresponding parameters in the natural tooth abutment were also measured. Results: Mucosal dimensions in tapered implants (*BW=3.33±0.43; SD=1.03±0.24; JE=1.08±0.13; CTC=1.22±0.23 mm) were comparable with those of natural tooth abutments (BW=3.04±0.18; SD=0.93±0.1; JE=0.78±0.1; Attachment=1.33±0.09 mm), but differed from butt-joint implants (*BW=4.88±1.24; SD=1.47±0.38; JE=1.49±0.4; CTC=1.92±0.93 mm) (* P<0.05). Conclusions: Results suggested that soft tissue dimensions around TISB are influenced by the implant-abutment interface and abutment material used. Mucosa investing tapered abutment tends to recapitulate soft tissue physiologic dimensions of natural tooth. To cite this article: Siar CH, Toh CG, Ali TBT, Seiz D, Ong ST. Dimensional profile of oral mucosa around combined tooth-implant-supported bridgework in macaque mandible. Clin. Oral Impl. Res. 23, 2012 438-446. doi: 10.1111/j.1600-0501.2010.02145.x [ABSTRACT FROM AUTHOR]

Abstract: The recent concepts of implant dentistry are not only to restore the function of mastication, but the newly applied surgical and prosthetic techniques are enabling dentists to fulfill patients'' esthetic expectations as well. A diagnostic wax-up of planned final restoration is crucial as it establishes the final goal toward which all treatment is directed. The esthetic restoration must possess a form that compliments the surrounding tissues and facilitates proper plaque control and occlusal function. It often presents reconstructive and restorative challenges and requires a comprehensive treatment plan. Implants used to replace missing teeth in the esthetic zone have many advantages ranging from preservation of unrestored adjacent teeth, halting the resorption of edentulous spaces to provide support for the prosthesis. Advanced papilla reconstruction procedures can enable the dentist in achieving the ultimate and most sophisticated goal of ideal esthetic restoration both in anterior and in posterior regions of human dentition. Hence, this is helping patients smile with confidence and dignity. [Copyright &y& Elsevier]

This randomized clinical trial was carried out to compare post cementation sensitivity in vital abutments of metal-ceramic fixed partial dentures using glass ionomer luting cement and resin based luting cement. It analyzed the results of 182 patients whose records were completed during study duration of 09 months at Department of Prosthodontics, AFID, Rawalpindi. Cold sensitivity tests were used to compare post cementation sensitivity in vital abutments of fixed partial dentures using resin based luting cement and glass ionomer luting cement. Sensitivity was assessed on a modified visual analogue scale of 0-10; scores of 1-4 signified mild sensitivity, 5-7 moderate sensitivity, 8-10 severe sensitivity and score of 0 signified no response. The sensitivity results were checked at base line, at 1 week, at 1 month, at 3 months. Data of 182 subjects of mean age 26.15±3.15 was evaluated. Chi-sqaure test was used to see the association of type of cement used and the postoperative sensitivity. The p values for the chi square test were insignificant P- values (P>0.05) at all appointments in abutments of fixed partial denture with either resin based or glass ionomer luting cement. The study showed that there is no significant difference between resin based luting cements and glass ionomer luting cements in terms of post cementation sensitivity in vital teeth. [ABSTRACT FROM AUTHOR]

In October of 2007 the AASHTO LRFD Bridge Design Specification became the mandatory design specifications for highway structures in the United States. This has introduced a number of changes in the design and analysis procedures that engineers have to follow. This paper evaluates the differences between the ASD standard specifications and the LRFD specification and how they apply to the design of earth retaining structures. Several design examples were carried out to examine the effect of the new design standards on structural proportioning and cost. For cantilever abutments and retaining walls 4.6 m and taller, the difference between the LRFD specifications and the ASD standard specifications was insignificant. However, designing shorter abutments and retaining walls using the LRFD specifications can result in an increase in footing length of about 30% and an increase in cost of approximately 10% of the cost of the retaining structures. While these cost impacts to a structure can be significant in some designs, the AASHTO LRFD specifications provides a safe and reliable method of design which is of paramount importance to engineers and the public. [ABSTRACT FROM AUTHOR]

Steel restrainer cables for multiple-frame bridges in California in the United States showed the effectiveness to prevent the unseating at the internal hinges during the past several earthquakes. After that, the steel restrainer cables are being tried to apply for multiple-span-simply-supported (MSSS) bridges in the central and the southeastern regions in the United States. In addition, shape memory alloy (SMA) bars in tension are being studied for the same application. In multiple-frame bridges, the developed seismic forces are transferred to piers through the restrainers; however, in MSSS bridges, the seismic forces are transferred to abutments by the restrainers. Therefore, the abutment’s behavior should be investigated as well. This study assesses the seismic performance of the three types of restrainers—steel restrainer cables, SMA bars in tension, and SMA bars in bending for MSSS bridges—due to moderate to strong ground motions using a deterministic seismic analysis. Also, a fragility analysis is conduced to assess the seismic resistance for the overall bridge system. For these analyses, the bending test of an SMA bar is conducted and its analytical model is determined. Then, nonlinear time history analyses are conducted to assess the seismic responses of the as-built and the retrofitted bridges. The deterministic analysis illustrates how the restrainers influence the components of the bridge. However, it could not explain the effects on the whole bridge system. The fragility analysis shows the effects of the three restrainers on the overall bridge system. The fragility analysis indicates that the SMA bars in bending are the most effective ones. [ABSTRACT FROM AUTHOR]

Scour is one of the main causes of bridge failures. It accounts for about 60% of bridge failures in the United States. Scour failures tend to occur suddenly without prior warning and are very difficult to monitor during flood events. This paper presents a comprehensive review of the up-to-date work on scour at bridge piers and abutments. First, a general introduction of bridge scour including the current situation of bridge scour problems and different types of bridge scour is given. Then, different approaches developed for predicting bridge scour are reviewed. Numerical and laboratory models established for bridge scour studies are also presented. Moreover, laboratory experiments and field tests conducted for bridge scour are reviewed. Different techniques and instruments developed for bridge scour monitoring are also presented with their advantages, disadvantages, and relative cost summarized in a table. Finally, various mitigation countermeasures developed for bridge scour are discussed. [ABSTRACT FROM AUTHOR]

Abutment-backfill soil interaction can significantly influence the seismic response of bridges. In the present study, we provide numerical simulation models that are validated using data from recent experiments on the lateral response of typical abutment systems. Those tests involve well-compacted clayey silt and silty sand backfill materials. The simulation methods considered include a method of slices approach for the backfill materials with an assumed log-spiral failure surface coupled with hyperbolic soil stress-strain relationships [referred to as “log-spiral hyperbolic (LSH) model”] as well as detailed finite-element models, both of which were found to compare well with test data. Through parametric studies on the validated LSH model, we develop equations for the lateral load-displacement backbone curves for abutments of varying height for the two aforementioned backfill types. The equations describe a hyperbolic relationship between lateral load per unit width of the abutment wall and the wall deflection and are amendable to practical application in seismic response simulations of bridge systems. [ABSTRACT FROM AUTHOR]

The flow field around a bridge abutment is analyzed by means of large eddy simulation. The geometrical configuration corresponds to the initial condition of a scour process (flat bed). The three-dimensional flow structure in front of the abutment is analyzed with special emphasis on its effects on shear stresses and pressure gradients on the bottom wall which, in turn, are discussed with respect to their potential scouring action. Both first- and second-order statistics around the abutment are quantitatively discussed, together with probability density distributions of stresses in specific locations. The investigation shows that several terms may play a relevant role in sediment transport around the obstacle. Specifically, the mean horizontal pressure gradient may reach values as large as two orders of magnitude that of a canonical boundary layer, whereas the instantaneous vertical pressure gradient may give an uplifting force comparable to the immersed weight of the sediment. The analysis suggests that local scour models should incorporate the contribution to the destabilizing force coming from pressure stresses and from turbulent fluctuations. [ABSTRACT FROM AUTHOR]

Objectives: This in vitro study was aimed to investigate the attachment, spreading and proliferation of human gingival fibroblasts to milled and polished non-veneered ceramic surfaces in alumina and zirconia and to ceramic surfaces veneered by two different types of porcelain baseliners. Materials and methods: Fibroblasts were cultured on discs of pressed alumina or zirconia, on discs which had been milled, on discs comprising alumina or zirconia which had been polished, on discs of alumina veneered with NobelRondo baseliner Al, on discs of zirconia veneered with Cercon-S baseliner, and on alumina or zirconia discs veneered with the above baseliners and then polished. The surfaces were analyzed using an optical interferometer and scanning electron microscopy (SEM). Cell profile areas were measured using SEM and an image analyzer. Cell attachment was determined after 3 and 24 h as a ratio of the cell profiles and the total micrograph area and was expressed as percent of attachment. MTT analyses were undertaken to determine cellular attachment after 3 h of incubation and cellular proliferation after 7 days. Results: The polished zirconia specimens had the smoothest surface in terms of average height deviation ( Sa=0.03 μm): the roughest were the zirconia specimens with milled surfaces ( Sa=0.36 μm). The application of the baseliners resulted in surfaces smoother than those of the non-veneered discs. The milled surfaces of both alumina and zirconia had significantly higher percentages of cell attachment and proliferation than the other surfaces whereas the milled surfaces in zirconia demonstrated better cellular attachment after 3 and 24 h of culture than the one in alumina. Fibroblasts attached and grew effectively on the surfaces veneered with NobelRondo throughout the experiments, whereas the zirconia surfaces veneered with Cercon-S had the lowest percentage of cell attachment and proliferation. Conclusions: Although the roughness of all surfaces investigated was <0.4 μm, the study disclosed significant differences in cellular attachment and proliferation associated with the various surface modifications. [ABSTRACT FROM AUTHOR]

Surgical guides have evolved to the point that they can be created with the aid of computer-assisted tomography (CT) technology. Surgical guides also are used in construction of the prosthesis prior to implant surgery. With existing guide techniques, the prosthesis is screw retained, or cone-shaped temporary abutments may be used to overcome the lack of parallelism of the implants. With the New Twist technique, we are able to create the surgical guide in such a way that optimum bone may be used and the rotational position of the implant may be established for the surgeon and for the laboratory. Custom abutments are inserted at the time of surgery, as is an esthetic, functionally provisional cemented prosthesis. Castings for the finished ceramo-metal bridge are fabricated before surgery is performed. The final prosthesis then is easily constructed by the restorative dentist during just 3 simple patient visits. [ABSTRACT FROM AUTHOR]

The paper reports on an experimental investigation concerning two important issues: (1) local scour and (2) riprap stability at a 45° wing-wall abutment in a degrading river bed of noncohesive sediment. The abutment considered was short (that is abutment length/flow depth <1). From the experimental observations, no influence of abutment inclusion on bed degradation was evident, as bed profiles with and without abutment were quite identical apart from the immediate vicinity of the abutment. Total scour depth at an abutment is found to be the maximum abutment scour depth in addition to the reduction of bed elevation due to bed degradation. The maximum abutment scour depth can be estimated from the equation given by Kandasamy and Melville in their 1998 paper. For scouring time beyond 24 h, the local abutment scour depth remains independent of time. In a degrading bed, the bed forms cause edge failure of the riprap at an abutment when the dunes propagate over the riprap layer. Initially, the dune height is significant causing the maximum damage of riprap layer. As the flow velocity reduces, the resulting bed-shear stress diminishes with the degrading bed and gradually the formation of dunes ceases. An additional experiment reveals that the damaged riprap layer is significantly vulnerable against a subsequent flood accompanied by large dunes. [ABSTRACT FROM AUTHOR]

Stream rehabilitation projects often involve the installation of instream structures such as flow deflectors. The objective of this study is to use the output of a three-dimensional numerically simulated flow field over a flat, predeformation bed to predict the planform extent of the equilibrium scour hole near stream deflectors of varying angles. It is shown that the upstream extent of the simulated flow separation zone determines the upstream limit of scour, whereas the lateral scour extent at the nose of the deflector is determined by the width of the separation zone. Further, scour depths are greatest in regions where strong downwelling (negative vertical velocity) exists, and the position of the local minimum dynamic pressure point in the simulated flow field defines the downstream limit of scouring. The results have implications for future design of habitat improvement structures where different angles and lengths of structures could potentially be tested prior to their implementation to determine the resultant scour geometry. [ABSTRACT FROM AUTHOR]

Integral bridges can significantly reduce maintenance and repair costs compared with conventional bridges. However, uncertainties have arisen in the design as the soil experiences temperature-induced cyclic loading behind the abutments. This paper presents the results from an experimental program on the behavior of Atherfield clay, a stiff clay from the United Kingdom, behind embedded integral abutments. Specimens were subjected to the stress paths and levels of cyclic straining that a typical embedded integral abutment might impose on its retained soil. The results show that daily and annual temperature changes can cause significant horizontal stress variations behind such abutments. However, no buildup in lateral earth pressure with successive cycles was observed for this typical stiff clay, and the stress–strain behavior and stiffness behavior were not influenced by continued cycling. The implications of the results for integral abutment design are discussed. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical models of flow over complex bed geometry are becoming widely used in river and coastal engineering. Boundary-fitted coordinate grids are typically used to deal with this problem in natural channels. Recently, a regular structured grid method based on numerical porosity has been developed for high-resolution gravel-bed models. A simpler alternative approach is to use a Cartesian mesh with an interpolated 3D solid object representing the river bed. The objective of this study is to assess the impact of these three methods of mesh generation on the simulated flow field above complex bed topography around stream deflectors in a laboratory setting. Results show marked differences between the three types of simulations when running mesh sensitivity analysis. Because the bed porosity approach uses the digital elevation model (DEM) information in each cell to represent bed topography, it requires a finer mesh resolution in order to reach an accurate solution. Although there was good qualitative agreement between the simulated flow fields and Acoustic Doppler Velocity measurements, the quantitative comparison showed relatively poor agreement for all mesh design types. However, the three mesh types were in good agreement when compared to each other for velocity and pressure variables (average correlation coefficient, r, of 0.95), with the 3D object bed and bed porosity showing the best agreement (r = 0.97). Simulated turbulence variables (KE and EP), however, showed more scatter (r = 0.85) and slopes markedly different from unity. [ABSTRACT FROM AUTHOR]

Abstract: Geotechnical properties of pure fine and coarse grained tire-chips and their mixtures (10, 20, 30, 40 and 50%) with a cohesive clayey soil were investigated through a series of soil mechanical tests in order to investigate possibilities of their usage as a lightweight fill material. Grain size and Atterberg limits analysis, permeability, direct shear and compaction tests were performed on the clayey soil, tire chips (both fine and coarse) alone and their mixtures. The results indicate that the use of used tire-chips mixed with clayey soils as a fill material is possible. The mixtures up to 20% coarse grained tire-chips and 30% fine grained tire-chips can be used above ground water tables where low weight, low permeability and high strength are needed in fills such as highway embankments, bridge abutments and backfills behind retaining structures especially when they are to be built on weak foundation soils with low bearing capacity and high settlement problems. They should not be used where drainage is needed to prevent the development of pore pressures during loading of fills under saturated conditions. In these cases, they may, however, be used by mixing with high permeability material such as sand and gravel. [Copyright &y& Elsevier]

An experimental study of scour countermeasures for wing-wall abutments under mobile-bed conditions is reported. The purpose of the study was to determine the required apron size to protect a wing-wall abutment from scour under mobile-bed conditions, for different flow depths, flow velocities, and apron placement level. Riprap and cable-tied block countermeasures were investigated. It was observed that scour at the abutment undermines the apron, causing the outer edge of the apron to settle. Scour at the abutment can be a combination of localized scour (i.e., contraction scour and local scour) and scour due to the troughs of the bed forms that migrate past the abutment, the latter being the focus of the study presented. As the flow depth and flow velocity are increased, the outer edge of the apron settles into the sand, to a depth proportional to the height of the bed forms developed in the flume. Localized scour may additionally influence the depth of settlement. When the apron width is increased, the depth to which the outer edge settles remains reasonably constant. When the apron is preburied below the average bed level, the settlement of the outer edge is less, but the depth of the outer edge of the apron below the average bed level is the same as for the corresponding apron placed on top of the bed. Riprap and cable-tied block aprons respond in different ways. Stones at the outer edge of riprap aprons tend to roll away from the abutment as they settle, pushing the erosion zone further away from the abutment. Conversely, because cable-tied block mats remain attached to the abutment, apron settlement allows the scour to occur closer to the abutment face. It is concluded that the scour at abutments under mobile-bed conditions is often governed by the size of the bed forms that pass the abutment. Therefore, the design of armored scour countermeasures for abutments under mobile-bed conditions should be based upon the largest expected bed forms, which can be predicted based on existing expressions, together with any effects of localized scour. This will enable the settlement of the outer edge of the apron to be determined, and the required apron width to be chosen, depending on the tolerable distance between the deepest scour and the abutment. An equation is given for prediction of the minimum width of apron remaining horizontal after erosion. [ABSTRACT FROM AUTHOR]

An experimental study of scour countermeasures for spill-through abutments situated on the flood plain of a compound channel is reported. The purpose of the study was to determine the variations in the scour hole geometry under clear water conditions by varying the compound channel and abutment geometries, and to determine the extent and type of scour countermeasure toe protection provided. This approach avoids one of the inherent difficulties in conducting scour countermeasure experiments—that is, the subjectivity of determining whether the countermeasure used in the experiment is a success or a failure. Riprap and cable-tied block countermeasures are incorporated. The results show that for most cases, as the countermeasure apron width (i.e., the extent of toe protection) is increased, the scour hole is deflected further away from the abutment and reduces in size. However, for abutment and compound channel configurations where the scour hole forms close to the main channel bank, the scour hole increases in size as the apron width is increased. The results also show that cable-tied block mats allow the scour hole to form closer to the abutment than equivalent riprap aprons and result in deeper scour holes. A suggested design methodology for the extent of apron protection is presented. The method is an improvement on the current, rather-simplified practice of providing aprons of fixed width equal to twice the flow depth. [ABSTRACT FROM AUTHOR]

Experiments were conducted to measure the three-dimensional turbulent flow field, using the acoustic Doppler velocimeter, at a short vertical-wall abutment (ratio of abutment length to approach flow depth less than unity) before and after the development of a scour hole under a clear water scour condition. In the upstream, the presentation of flow field through vectors at vertical sections shows a primary vortex associated with the downflow. In the downstream, the upward flow is comprised of with irregularities owing to the vortex shedding. The flow separation near the bed and within the scour hole is evident from the turbulent kinetic energy distribution. Using Reynolds stresses, the bed shear stresses are calculated. [ABSTRACT FROM AUTHOR]

Drilled shaft groups are often designed to resist lateral loads for transportation structures. The shaft group capacity usually corresponds to a load being applied at the shaft cap level. However, in abutment wail applications, the lateral load is, in fact, applied well above the cap elevation. Thus, the load is transferred to the cap with an additional moment, causing the cap to deflect and rotate more than if this added moment were absent. As a result, the lateral capacity for a given allowable deflection of the group should be reduced because of this effect. Design engineers usually select or approve the allowable deflection at the top of the abutment wall. However, deflection at the cap level is needed to design the group capacity. The main objective of this paper is to report the results from a series of finite-element analyses on abutment wail cap configurations to study the effect of moment on the capacity of the shaft group under lateral load. A scaling factor is defined as the ratio between the group capacity for load applied at a given height above the cap and the group capacity for load applied at the bottom of the cap, and it was found to be dependent on the wall height, the spacing between shafts, and the cap deflection level, and more or less independent of the soil type, the cap thickness, and the shaft diameter. The ratio between the deflection at the top of the abutment wall and the deflection at the cap was found to be dependent on the wall stiffness (wall thickness to wall height ratio). [ABSTRACT FROM AUTHOR]

Arguably the greatest controversy in implant dentistry is that of linking a natural tooth and an implant together in a fixed restoration. Some researchers have absolutely contradicted the inclusion of the two, while others have suggested different options such as design considerations in the restoration or in the implant itself. Further more an outcome of a situation in linking a periodontally compromised abutment with an implant in a restoration itself lacks investigation. The study was designed to evaluate stresses transmitted to supporting structures by a fixed partial restoration under different abutment situations using a rigid / movable connector in the prosthesis. Also to evaluate stresses transmitted and the outcome of linking a periodontally compromised abutment with the implant in a fixed restoration. Photoelastic models were fabricated depicting a partially edentulous posterior mandible. The situations depicted were of a completely tooth supported, tooth implant supported and a completely implant supported situations. 20% and 35 % periodontal damages were also incorporated in the anterior abutment in the models. The fixed restorations were fabricated with movable and rigid type connectors. Vertical point loads were applied on fixed points on the restoration and the transmitted stresses under different simulated situations of the study were then recorded and analyzed. The fringe orders were recorded photographically and the fringe orders were tabulated for interpretation. After thorough analysis of the results obtained the study concluded that it is indeed beneficial to connect natural tooth to implants in a fixed partial restoration and that the type of connector advocated is a rigid one. Also conclusive is the fact that periodontally compromised teeth can be integrated in the restoration in combination with an implant as a conservative treatment option. The use of non rigid connectors in any situation may be erroneous. [ABSTRACT FROM AUTHOR]

This article presents a bimodal procedure for a patient with an implant-supported fixed partial denture (FP2 class of Misch) where endosteal implants (EOIs) and a subperiosteal implant (SPI) were indicated in different sections of the same arch. In edentulous patients, heterogeneous bone volume and density may be encountered in different regions of the same arch. When the available bone is favorable, the use of EOIs is simpler and less time consuming. An SPI is indicated when the available bone is severely resorbed, as in the type I division C, type II divisions C and D, and type III divisions C and D. The main advantage of the described combined technique is that it offers an alternative to invasive surgeries such as iliac crest bone grafts or various surgical augmentation procedures. The second advantage is the very brief healing period after insertion of the SPI before prosthetic loading. Planning, design, laboratory construction, surgical application, and prosthetic rehabilitation for bimodal implant treatment are described. Prefabricated titanium tissue abutments are used in the fabrication of the posts of the anterior titanium SPI. Titanium tissue abutments are placed in the waxup stage of the SPI before the casting of the titanium SPI. Posterior fixtures are EOIs. An anterior SPI with 4 posts and 4 posterior EOIs provides a combination of support for the screw-retained fixed maxillary denture of Misch's FP2. [ABSTRACT FROM AUTHOR]

The anterior maxillary jaw is frequently called the "esthetic zone" because of its high visibility and influence on facial appearance. Implant placement and single-tooth restoration in this region can present some esthetic challenges for the clinician. The underlying titanium abutment, for example, can diminish porcelain translucency and result in a darkened prosthesis. Subsequent changes in soft-tissue margins can also result in the visibility of titanium at the gingival crevice. In recent years, all-ceramic restorations have gained popularity in response to increasing patient demands for improved esthetics. This article describes the clinical use of a new, tooth-shaped, ceramic coping system in the restoration of single teeth in the esthetic zones of 3 patients. Four tapered screw implants were placed in the locations of the central incisors (n = 3) and bicuspid (n = 1). Conventional ceramic protocols were used to fabricate all-ceramic crowns that were cemented onto small core abutments attached to the implants. All prostheses restored the biomechanical needs of the patients and achieved excellent esthetic results. [ABSTRACT FROM AUTHOR]

This paper is a review of the scour conditions, and scour-estimation difficulties, associated with scour at abutments of bridges over rivers and streams. A recent survey of abutment-scour problems in the U.S., Korea, and abroad, shows that several scour conditions can occur, and that existing relationships for scour estimation, besides being inaccurate do not match the scour conditions. Moreover abutment scour is found to be primarily a concern for bridges over smaller rivers and streams than for larger rivers, because inadequate design and monitoring attention has been give to abutment scour at the many small bridges. This paper also discusses the difficulties confronting accurate estimation of abutment-scour depth. The difficulties, which include similitude aspects of laboratory experiments on scour at bridge abutments, complicate the development of reliable scour-estimation relationships. In a practical sense, the difficulties imply that design relationshipsfor scour-depth estimation inevitably have to be of approximate accuracy given the great variability of channel conditions at most abutments. [ABSTRACT FROM AUTHOR]

Experiments on local scour at short abutments (ratio of abutment length to approaching flow depth less than unity), namely vertical-wall, 45° wing-wall, and semicircular, embedded in a bed of relatively fine noncohesive sediment overlain by a thin armor-layer of coarser sediment, were conducted for different flow conditions, thickness of armor-layers, armor-layer, and bed sediments. The abutments were aligned with the approaching flow in a rectangular channel. The armor-layer and the bed underneath it were composed of different combinations of uniform sediments. In the experiments, the approaching flow velocities were restricted to the clear-water scour condition with respect to the armor-layer particles. Depending on the approaching flow conditions, three cases of scour at abutments in armored beds were identified. Effects of different parameters pertaining to scour at abutments are examined. The comparison of the experimental data shows that the scour depth at an abutment with an armor-layer in clear-water scour condition under limiting stability of the surface particles (approaching flow velocity nearly equaling critical velocity for the threshold motion of surface particles) is always greater than that without armor-layer for the same bed sediments. The characteristic parameters affecting the maximum equilibrium nondimensional scour depth (scour depth-abutment length ratio), identified based on the physical reasoning and dimensional analysis, are excess abutment Froude number, flow depth-abutment length ratio, armor-layer thickness-armor particle diameter ratio, and armor particle-bed sediment diameter ratio. The experimental data of clear-water scour condition in thinly armored beds under limiting stability of surface particles were used to determine the equation of maximum equilibrium scour depth through regression analysis. The estimated scour depths were in agreement with the experimental scour depths. Also, an equation of maximum equilibrium scour depth in uniform sediments was obtained. [ABSTRACT FROM AUTHOR]

Two types of HL hexed abutments of a Steri-Oss system, gold/plastic coping and gold coping, were compared in terms of corrosion behavior. The anodic polarization behavior and the galvanic corrosion between abutments and Type III gold alloys, before and after casting, were analyzed. In addition, the crevice corrosion of the casting samples was analyzed with cyclic potentiodynamic polarization tests using the |Er-Ecorr| value and scanning electron microscopy. Before casting, gold/plastic coping and gold coping were shown to have similar corrosion patterns in the anodic polarization test. Type III casting gold alloy was shown to have a lower higher than that of gold coping, but the passive region for the gold/plastic coping was smaller than that of gold coping. The contact current density between the cast gold alloys and gold/plastic before casting was higher than that between gold coping and cast gold alloy. The contact current density of the samples after casting was shown to be similar to that before casting. The crevice corrosion resistance of cast samples using gold coping was lower than that of cast samples using gold/plastic coping, and severe corrosion was observed by SEM at the abutment-casting gold alloy interface. [ABSTRACT FROM AUTHOR]

The esthetics and function of a tissue borne, implant retained overdenture are two of the most important factors that define a patient's acceptance of the prosthesis. In this clinical report, an existing implant overdenture, which was esthetically acceptable to the patient but which had no incorporated retentive components in the substructure framework, was retrofitted to a newly designed and fabricated implant framework. The added retentive components on the new framework increased the patient's overall masticatory function, reduced the frequency of dental visits, and allowed the patient to retain the original overdenture. [ABSTRACT FROM AUTHOR]

This paper presents the use of the trial load method and the block element method with elastoviscoplastic discontinuities for analysis of arch dams. The arch dam is considered as an arch-cantilever system and the foundation as a block element system. With the displacement compatibility condition at the contact surface of the dam and the foundation (including abutment), the governing equations of the arch dam and foundation are established. These methods are used for the analysis of the double curvature arch dam with complex geology conditions of the Xiaowan Hydroelectric Project in China. The deformation and stress states in both the dam body and the foundation are determined. Furthermore, the stability safety factors of the foundation and the abutment are calculated at the same time, which allows for an optimal design of the arch dam considering the strength, the deformation and the stability of the dam and foundation. [ABSTRACT FROM AUTHOR]

The fatigue behavior and FEA analysis of different ceramic materials cemented over distinct substrates for implant-supported crowns were evaluated in this study. Discs of 10 mm in diameter of both restorative and substrate materials were made and randomly allocated into pairs (n = 15) considering the two study factors: 'restorative ceramic material' (1 mm thickness) – polymer-infiltrated ceramic network (PICN), lithium disilicate (LD), zirconia-reinforced lithium silicate (ZLS), or translucent zirconia (TZ); and 'foundation substrate' (2 mm thickness) – polyetheretherketone (Peek) or yttrium-stabilized zirconia (YZ). Adhesive cementation was made with a dual cure resin cement. Fatigue testing was run using the step-stress methodology: initial load of 200 N for 5000 cycles, followed by steps of 10,000 cycles starting at 400 N up to 2800 N or until failure, step size of 200 N, frequency of 20 Hz. Data were analyzed by the Kaplan Meier and log-rank post-hoc tests. Fractography analysis (stereomicroscope and SEM) and FEA were also performed. Both factors under study and their interaction statistically influenced the fatigue failure load (FFL), cycles for failure (CFF) and survival rates (p < 0.001). The restorative materials bonded to YZ had higher FFL and CFF than when adhering to Peek, while restorative materials with more crystalline content (TZ and ZLS) showed higher FFL and CFF than LD and PICN. The fractography analysis showed that all materials bonded to YZ resulted in failures starting at the occlusal surface (Hertzian cone cracks), while materials bonded to Peek had radial cracks from the ceramic-cement intaglio surface. FEA analysis showed that tensile stress concentration decreased in the intaglio surface when testing the restorative material over a stiffer (YZ) foundation substrate. In addition, the higher the restorative material's crystalline content, the more the stress is concentrated within the material (TZ > ZLS ≥ LD > PICN) when bonded to the same foundation substrate. Thus, it concluded that a stiffer foundation substrate (YZ) enhances the load-bearing capacity under fatigue of the restorative set; that restorative materials with higher crystalline content results in higher fatigue performance of the set, regardless of the foundation used; and that the foundation material influences the failure pattern of the restorative set. • Stiffer foundation substrate enhances the fatigue performance of a restorative set. • Restorative materials with higher crystalline content show higher fatigue strength. • The foundation substrate influences the failure pattern of a restorative set. [ABSTRACT FROM AUTHOR]

Owing to anatomic considerations, implants could be inadvertently placed in less than ideal positions. These misaligned Implants in partially edentulous arches can be difficult to restore with conventional abutments and may necessitate implant removal in severe angulations. We present a case restored with a UCLA abutment due to buccal angulation of implant fixture in the posterior mandible and emphasize the need for adequate running room in such cases. [ABSTRACT FROM AUTHOR]

The Aim of the Study: Comparative study of the precision of the junction of modern implant systems with standard and custom abutments., Materials and Methods: The study was carried out by the method of computed X-ray microtomography on an X-ray microtomograph Heliscan micro CT using the ImageJ program in the laboratory «Systems for Microscopy and Analysis» of the Skolkovo Technopark. The measurement of the gap width between the implant and the abutment for each sample was carried out at 20 points according to the algorithm: the total length of the connection between the implant and the abutment; step (distance) between 5 equidistant points along the contact between the abutment and the implant; the measurements were repeated in 2 perpendicular sections along the joint node axis. The study was conducted on the example of seven implant systems common in Russia. The effect on the implant-abutment assembly of a multiple functional load of 250 N at an angle of 45° (7.6 million cycles) was studied., Results: It has been established that the precision of the junction of modern implants with standard abutments is different and is characterized by the length of the contact from 268 to 1300 µm, the gap at the level of the platform from 5.0 to 11.7 µm, and the asymmetry of the contact in diameter by 2.4-14.2 µm. Abutments individually made in modern CAD/CAM laboratories do not have significant dimensional differences with standard abutments, but they have technological defects. The functional load expands and deforms the gap between the implant and abutment junction in the upper half of their contact., Conclusion: The results obtained demonstrate the capabilities of the computer X-ray microtomography method, which can be used to control the quality of manufacturing collapsible dental implants, the accuracy of manufacturing individual abutments in CAD/CAM laboratories, as well as in the development of new dental implant systems. The dimensional parameters of the junction node determine the advantages of the deep cone connection of the implant and the abutment.

The peri-implant soft tissue with inferior adhesion takes a long healing period to form, which is undesirable for the reaction around the peri-implant soft tissues. The aim of this study is to improve the physicochemical properties of titanium (Ti) and zirconia (ZrO 2 ) implant abutments and shorten the formation period of periabutment epithelium tissue. A nonthermal atmospheric plasma brush (NTAPB, N) was employed for Ti and ZrO 2 activation. The surface topographies, roughness, crystallinity, wettability, and chemical elements of the abutment materials were examined. The epithelial cell behavior analysis and tissue remodeling of the periabutment epithelial tissue were performed in vitro and in vivo. N-Ti and N-ZrO 2 had a similar good surface wettability, with a 65 and 70% increase in oxygen content and a 70 and 75% decrease in carbon content, respectively. Both N-Ti and N-ZrO 2 showed excellent adhesion, spread, and proliferation of epithelial cells in vitro, with improved adhesion molecule expression levels compared to untreated samples. N-Ti and N-ZrO 2 abutments were placed in the implantation sites of rats. From week 2 to week 6 after implantation, N-Ti and N-ZrO 2 had similar periabutment epithelium tissue formation, and both had increased plectin-positive and laminin γ2-positive cell numbers compared to Ti and ZrO 2 . The NTAPB shows promising abutment modification abilities. It promotes the expression levels of adhesion molecules and the epithelial cell performance, which later leads to a quicker formation and remodeling of the important periabutment epithelial tissue.