Marginal discrepancy of all-ceramic crowns cemented on implant abutments

PURPOSE: The purpose of this investigation was to determine the mean marginal discrepancy of all-ceramic crowns cemented on implant abutments. MATERIALS AND METHODS: Five Br?nemark CeraOne abutments were connected to implant fixtures embedded in acrylic resin blocks. The marginal discrepancy was measured using a video camera connected to a digitizing board at four locations on each abutment for five samples in each of the following groups: all-ceramic caps (caps), all-ceramic crowns (crowns), and all-ceramic crowns cemented with zinc phosphate cement (cemented crowns). RESULTS: The mean marginal discrepancies were as follows: caps, 99.0 micrometers (SD, 16); crowns, 117.8 micrometers (SD, 20); and cemented crowns, 168.8 micrometers (SD, 23). Statistically significant differences were found between all three groups at the 99% level of confidence. In addition there were two significant differences between abutments. CONCLUSIONS: Subgingival marginal discrepancies of the magnitude measured in this study have been shown to cause periodontal problems. It is probable that the marginal discrepancy of CeraOne restorations, as tested, can be improved. Efforts should be made to enhance the marginal accuracy of these restorations.     

T cells and cytokines in Crohn''s disease

Complete-arch implant prostheses continue to exhibit horizontal and vertical misfit between frameworks and abutments. It has been suggested that these gaps may be eliminated and that restoration-induced stresses may be reduced by luting frameworks to screw-retained abutments intraorally. This study measured and compared the strains generated by clinically acceptable, conventional frameworks were made from a single master cast representing a bone simulant model of an edentulous mandible with five Nobel Biocare implants and 4-mm abutments. Two strain gauges were also embedded in the bone simulant model to measure strains at two locations. Resin-luted frameworks were made by securing abutments to the clinical model with five gold slot screws tightened to 10 Ncm. Strain-indicator readings were recorded at a standardized time following the initial fastening of each prosthesis (n = 3). Mean principal strains were determined and compared using a one-way repeated measures analysis of variance. A statistically significant difference was found in the principal strains between the conventional cast and the resin-luted frameworks. Overall, there was a decrease in the magnitude of strain for the resin-luted frameworks. Intraoral luting of frameworks may decrease the strains produced in the bone around implants.     

The extent of undiagnosed gestational diabetes mellitus in New South Wales

Rapid, accurate seating of screw-retained implant abutment heads, where timing is controlled by internal or external hex designs, can be readily accomplished with individual, custom-cast abutment head location devices. The devices are especially useful when the abutment head-implant body complex is to be permanently cemented. The use and design of abutment seating jigs for single tooth implants and completely implant or implant and natural tooth-supported prostheses are described.     

Replacing posterior teeth with freestanding implants: four-year prosthodontic results of a prospective study

This article presents prospective four-year prosthetic results of the placement of 432 posterior freestanding, conventionally cemented prosthetic tooth implants in posterior edentulous spaces using the Bicon Dental Implants system (Bicon Dental Implants). Over four years, 0.74 percent of the abutments loosened, 0.5 percent of the abutments fractured, and 2.47 percent of the crowns experienced porcelain fracture, (all porcelain fractures occurred at time of placement). This low rate of problems appears to make free-standing single-tooth implant restorations a reliable solution to treating posterior edentulism.     

Wortmannin sensitizes mammalian cells to radiation by inhibiting the DNA-dependent protein kinase-mediated rejoining of double-strand breaks

STATEMENT OF PROBLEM: The cone-screw abutment has been shown to diminish micromovement by reducing the burden of component loosening and fracture. However, anecdotal concern for cold welding of cone-screw joints in implant design has been identified as a potential source for lack of retrievability. PURPOSE: This comparative study evaluated the loosening torque, as a percentage of tightening torque, for the ITI Straumann and Astra Tech (3.5 and 4.0 mm diameters) implant systems, which use an 8-degree and 11-degree internal cone, respectively. MATERIAL AND METHODS: Implants and abutments from each system were mounted in a torque device, and a range of tightening torques was applied. Loosening torques were then measured, and the influence of conus angle, interfacial surface area, saliva contamination, and time delay to loosening were all assessed. RESULTS: The loosening torque only exceeded tightening torque at the highest levels, just before component failure, when plastic deformation was expected. For all clinically relevant levels of torque, both in a dry environment and with components bathed in artificial saliva at 37 degrees C, loosening torque was always seen to be 80% to 90% of tightening torque, demonstrating that cold welding does not occur. There was a high correlation between loosening and tightening torque for all systems tested, but no statistical difference when comparing wet versus dry or comparing individual data for each system. CONCLUSIONS: It can be concluded that for clinically relevant levels of tightening torque, no problems are anticipated with respect to retrievability.     

Sinus inlay bone augmentation: comparison of implant positioning after one- or two-staged procedures

PURPOSE: This study was undertaken to compare implant angulation and position after one- or two-stage sinus inlay bone augmentation. PATIENTS AND METHODS: Twenty patients were retrospectively selected; group 1 (n = 10) was operated on with a one-stage procedure, and group 2 (n = 10) with a two-stage operation. Casts processed for the final permanent or temporary bridgework were collected and photographed from an oblique anterior view paralleling the alveolar crest on the right and left sides, as well as from an occlusal view. The angle between impression pins inserted in the abutments relative to the true vertical was recorded. In the occlusal view, the midpoints of the abutments were related to an individual computerized superimposed parabola. RESULTS: The implants inserted during the one-stage procedure were generally placed more palatally (Wilcoxon rank sum test, P = .0101) and angled more palatally (P = .0009) compared with those placed with the two-stage operation. CONCLUSION: This study showed that the two methods of treating patients by sinus inlay bone augmentation differed significantly with regard to placement and angulation of the implants. A two-stage procedure seems to offer the surgeon more optimal conditions for positioning the implants.     

Esthetic and prosthetic procedures in single-tooth replacement

Loss of anterior maxillary teeth always results in bone resorption and loss of interdental papillae, and the resorption makes a single tooth replacement by a dental implant very difficult. When infections have been present and the patient's history shows previous surgery at the apex of the root, bone destruction is substantial, which results in an increased resorption defect, thereby further increasing the aesthetic and prosthetic problems. This paper describes the steps necessary for implant surgery and the prosthetics; a brief summary is provided. The quality and quantity of bone, along with the space available between the adjacent teeth, are the basic factors in treatment planning and determine the type of implant to be used. Some resorption and bone defects are usually present after a tooth extraction, and bone regeneration procedures can be performed either before or simultaneously with the implant placement, with numerous flap designs available. Soft tissue augmentation can be achieved by taking a connective tissue graft from the palatal side. Antirotational devices (eg, hex lock abutments) are necessary for all implants in single tooth replacement. Screw-retained abutments can be used in posterior areas and in angled positions in facial areas as well. With proper single tooth implant position, cementation of laboratory fabricated crowns can be considered.     

Restoring the single lower incisor implant with esthetics, antirotation, and retrievability

The long-term success of restoring the lower incisor implant is partially dependent on retrievability of all components down to the implant. Because this implant is usually placed vertically or buccally in the bone, the ability to achieve esthetics without seeing the screw access hole becomes critical. The emergence profile of the crown overlying the implant fixture ultimately dictates the esthetics. The single crown can also become loose during function and, therefore, antirotation of the abutment is imperative. The Octa-Hex Implant Restoration System presents an alternative method of achieving gingival seal with a titanium-alloy connector to the implant, emergence profile with a custom-fabricated casting on this connector, antirotation from intimate contact with implant indexing, and retrievability by a fixation screw and cementation. With the lower incisor, this system offers retrievability without the screw access hole affecting esthetics.     

Is retrievability grouping good for recall?

Most theories suppose that during unconstrained retrieval easy-to-retrieve items will be accessed before hard-to-retrieve items. Recent free-recall studies have supported a different access order, the cognitive triage pattern, in which hard-to-retrieve items are accessed first. The present experiments demonstrated that this pattern enhances total recall. In Exps 1–3, clustering type measures of goodness of triage (grouping output according to items' levels of retrievability) predicted total recall in children and adults. In Exps 4 and 5, goodness-of-triage measures predicted total recall when they were derived from on-line information about retrievability (error–success histories), but not when they were derived from normative information about retrievability (frequency and meaningfulness ratings). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of Vanes for Control of Scour at Vertical Wall Abutments

Rock vanes are single-arm structures angled to the flow with a pitch into the streambed such that the tip of the vane is submerged even during low flow. Vanes have primarily been used in recent years for treatment of bank erosion in stream stability projects. These structures roll the water away from the eroding banks, thus limiting erosion of the channel banks. They have proven to be very effective treatments over a range of flow conditions. In this project, the effectiveness of vanes for preventing scour at single-span bridges with vertical wall abutments was evaluated based on laboratory experiments. The vanes were tested in small-scale experiments in a recirculating flume and subjected to a range of flow conditions, including bank full and a number of overbank flows, which were forced to return to the channel at the abutment. The results showed that the vanes were highly effective in moving the scour away from the abutment into the center of the channel under all flow conditions tested. Based on the experimental results, optimum design settings for the vane angle and height, most effective number of vanes, and distance upstream for placement of the first vane were determined.     

Histologic evaluation of osseointegrated implants restored in nonaxial functional occlusion with preangled abutments

Of concern with the use of preangled abutments on implants is the transmission of masticatory forces and the angle at which they occur. Nineteen endosseous implants were placed in two subhuman primates. After 6 months, to allow for osseointegration, the implants were fitted with preangled abutments of various degrees and restored with type IV alloy castings. Straight abutments were used as control. Histologic evaluation revealed that, after 1 year of service, the implants exhibited complete osseointegration. Implants, whether restored with straight or preangled abutments, had no adverse effect on the surrounding bone. Soft tissue pockets measured, on average, from 2.2 to 2.6 mm; acute and chronic inflammatory cells were present. When crown loss was observed, it was caused by mechanical failure of components, such as gold screws and the screws used to secure the preangled abutments to the implants. Preangled abutments appear to be a valuable adjunct in implant dentistry, although long-term studies are needed for confirmation.     

Biomechanical and esthetic considerations for maxillary anterior overdenture abutment selection

Maxillary canine teeth traditionally have been selected as overdenture abutments. Undesirable aspects associated with the use of maxillary canines as overdenture abutments are described. The use of maxillary lateral incisors as overdenture abutments offers vertical support to the prosthesis, favorable stress distribution, improved esthetics, and preservation of the premaxilla.     

Long term clinical evaluation of three luting materials

A last critical step in the completion of a cast restoration is permanent cementation. With the development of new luting agents the practitioner has to be aware of the physical and biological properties as well as the long term clinical performance of these materials. In this study three commonly used luting agents were evaluated over a four year period. The three cements, a zinc phosphate, a glass ionomer and a resin cement were tested for their reaction to periodontal tissues, pulpal response and other clinical parameters. In twenty six patients, 61 crowns, onlays or bridge abutments were cemented. Evaluations were made at 0 hour, after 7 days, 6 and 12 months and 4 years. In general the cements performed satisfactorily. Health of periodontal tissues adjacent to the crowns improved considerably after 7 days. Postcementation hypersensitivity appeared to be a negligible problem, which was attributed to the time span between preparation and cementation, which exceeded in most instances four weeks. The choice of a final luting agent should be based on anticipated postoperative pulpal reactions, rather than exclusive reliance on physical properties.     

Behavior of a Semiintegral Bridge Abutment under Static and Temperature-Induced Cyclic Loading

This paper presents the results of an experimental study of semiintegral bridge abutments. Primary interests were to investigate (1) potential problems with the particular detail tested; (2) rotational characteristics of the semiintegral abutments; and (3) ability of the specimens to withstand cyclic loading induced by temperature variations during the expected life of the bridge. Sixteen experiments were conducted on three large-scale specimens. The results of the tests have shown that semiintegral abutments can significantly reduce the moments transferred from the superstructure to the foundation piles. Test results have also shown that semiintegral abutments can tolerate the number of displacement cycles that a bridge will experience during the course of its economic life.     

螺纹牙形对特殊螺纹接头弯曲性能的影响

为分析特殊螺纹接头弯曲性能,采用有限元方法,对比正角度螺纹、负角度螺纹和齿侧过盈螺纹3种牙形对特殊螺纹接头密封面上密封性能的影响。有限元分析结果表明,负角度螺纹可以提高拉伸性能,而齿侧过盈螺纹有利于提高压缩性能。综合来看,齿侧过盈螺纹有利于弯曲性能。这些结果可为抗弯曲特殊螺纹接头设计提供参考。     

Simulating the Behavior of GRS Bridge Abutments

Geosynthetic-reinforced soil (GRS) bridge-supporting abutments are similar in principle to GRS retaining walls, except that GRS abutments are typically subjected to a much higher area load, and that the loads are close to the wall face. The GRS abutment technology is relatively new, but it has great potential, and it has been gaining some popularity in recent years. This paper describes the finite element analyses of two full-scale loading tests of GRS bridge abutments referred to as the “National Cooperative Highway Research Program (NCHRP) experiment.” The analysis was carried out using the computer program Dyna3d, developed at the Lawrence Livermore National Laboratory. The finite element analysis of the NCHRP experiment will help with the understanding of the complex behavior of GRS structures in general, and the behavior of GRS bridge abutments with modular block facing in particular. The analysis of the two full-scale loading tests allows the loading conditions that are of greatest concern in the design of the bridge abutments to be examined rationally. The analysis shows that the performance of a GRS abutment, resulting from the complex interaction among the various components, while subject to a service load or a limiting failure load can be simulated in a reasonably accurate manner. In addition, a parametric study was conducted to investigate the performance of the modular block facing GRS bridge abutments subjected to live and dead loads from a bridge superstructure. This study investigated the performance of the GRS bridge abutments as they are affected by backfill properties, reinforcement stiffness properties, and reinforcement vertical spacing.     

Allowable Bearing Pressures of Bridge Sills on GRS Abutments with Flexible Facing

Compared to geosynthetic-reinforced soil (GRS) retaining walls, GRS abutment walls are generally subjected to much greater intensity surface loads that are fairly close to the wall face. A major issue with the design of GRS abutments is the allowable bearing pressure of the bridge sill on the abutments. The allowable bearing pressure of a bridge sill over reinforced soil retaining walls has been limited to 200?kPa in the current NHI and Demo 82 design guidelines. A study was undertaken to investigate the allowable bearing pressures of bridge sills over GRS abutments with flexible facing. The study was conducted by the finite element method of analysis. The capability of the finite element computer code for analyzing the performance of GRS bridge abutments with modular block facing has been evaluated extensively prior to this study. A series of finite element analyses were carried out to examine the effect of sill type, sill width, soil stiffness/strength, reinforcement spacing, and foundation stiffness on the load-carrying capacity of GRS abutment sills. Based on the results of the analytical study, allowable bearing pressures of GRS abutments were determined based on two performance criteria: A limiting displacement criterion and a limiting shear strain criterion, as well as the writers’ experiences with GRS walls and abutments. In addition, a recommended design procedure for determining the allowable bearing pressure is provided.     

Integral Abutment-Backfill Behavior on Sand Soil—Pushover Analysis Approach

This paper presents a study on the behavior of the abutment-backfill system under positive thermal variation in integral bridges built on sand. A structural model of a typical integral bridge is built, considering the nonlinear behavior of the piles and soil-bridge interaction effects. Static pushover analyses of the bridge are conducted to study the effect of various geometric, structural, and geotechnical parameters on the performance of the abutment-backfill system under positive thermal variations. The shape and intensity of the backfill pressure are found to be affected by the height of the abutment. Furthermore, the internal forces in the abutments are found to be functions of the thermal-induced longitudinal movement of the abutment, the properties of the pile, and the density of the sand around the piles. Using the pushover analysis results, design equations are formulated to determine the maximum forces in the abutments and the maximum length of integral bridges based on the strength of the abutments. Integral bridges with piles encased in loose sand and oriented to bend about their weak axis, abutment heights less than 4?m, and noncompacted backfill are recommended to limit the magnitude of the forces in the abutments.     

新型纳米晶硬质合金的研究现状及发展趋势

纳米晶硬质合金以其优异的性能在电子信息、汽车制造、航空航天、国防军事等领域被广泛应用。本文概述了近年来纳米晶硬质合金的发展状况,包括新型粘结相纳米晶硬质合金、无粘结相纳米晶硬质合金、梯度纳米晶硬质合金以及涂层纳米晶硬质合金等一系列新型纳米晶硬质合金,展望了纳米晶硬质合金在各个领域的发展前景和研发重点,为现代硬质合金材料及技术的发展提供新思路。     

Patients with epilepsy who die suddenly have cardiac disease

This paper describes the design and fabrication of a soft liner-retained, implant-supported overdenture used in 10 patients over a period of 1 to 6 years. A final complete denture impression is made of the dental arch, including implant abutments extending 5 mm above the gingival tissue. The master cast is fabricated with actual abutments placed in the impression. After the final wax try-in, the denture is flasked in the usual manner with the metal abutments in place. Before packing with acrylic resin, plastic tubing 1 to 2 mm thick is placed around each abutment. The denture is trial packed and allowed to bench cure over night. The plastic tubing is then removed and a soft denture lining material is placed in these areas only. The flask is closed and cured according to the manufacturer's recommendation. The denture is delivered as a conventional overdenture.