Mechanical considerations for the implant tooth-supported fixed partial denture

The implant tooth-supported fixed partial denture presents a biomechanical design problem, because the implant is rigidly fixed within the alveolus, and the tooth is surrounded by a periodontal ligament that allows movement. Nonrigid fixed partial denture designs are advocated by some dentists as a method of compensating for this differential movement. Rigid fixed partial denture designs, however, are advocated by many clinicians. Studies have failed to show the advantage of one design over the other. This study developed an in vitro method for testing such prosthesis designs and measured movement of a natural tooth abutment during simulated function. The movement of the natural tooth abutment was not found to change substantially with the fixed partial denture designs tested.     

Intracrown ring for crown and fixed partial denture abutments

When a tooth prepared for a crown does not comply with the general principles of retention and resistance form, and it is not possible to correct it without damage to the biologic structures of the tooth, consideration must be given to the purpose of the crown, such as whether it is a single crown, a retainer for a fixed restoration, or a retainer for a fixed removable prosthesis with precision attachments. The crown prepared with receptacles for internal attachments will undoubtedly require more retention and resistance to dislodgment than a single crown because of forces that will be applied to it through the removable portion of the restoration. The purpose of this article is to present an alternative procedure that uses the intracrown ring, which provides additional retention for the abutment crown because of the compressible ring. The compressible ring is placed in the groove prepared in the lower third of the abutment during the crown preparation.     

Fabricating abutment crowns for existing removable partial dentures using custom resin clasp analogs

A universal approach for fabricating abutment crowns for existing removable partial dentures is described. A replica (analog) of the clasp assembly is generated and transferred to a traditional working cast, which includes the abutment die. The analog is incorporated into the working cast as a removable component to allow the formation of the crown contours. The article reviews in detail the procedures required to transfer accurately all the essential components and information from the mouth to the working cast while allowing the patient uninterrupted use of the removable partial denture. Prestabilizing the removable partial denture, creating the analog impression, avoiding errors due to soft tissue components, forming a precise analog base, selecting materials, generating a rigid resin analog, and prescribing a path of insertion and withdrawal to the analog are described. The method replicates all types of clasps and can generate all types of fixed prosthodontic retainers to function harmoniously with the existing partial denture.     

The influence of splinting procedures on the periodontal and peri-implant tissue damping characteristics. A longitudinal study with the Periotest device

The aim of the present study was to evaluate the capability of the Periotest device in detecting and monitoring functional changes in the periodontal as well as in the pari-implant damping characteristics. In the first part of this study, 107 teeth were splinted by means of 40 full acrylic fixed prostheses (AFP) and another 37 teeth were splinted by means of 14 ceramometallic fixed prostheses (C-MFP). The Periotest measurements of individual teeth were done the day the fixed prostheses were cemented temporary (PTV 1), and again after a mean observation period of 27.4 days (PTV 2). In the 2nd part, 78 osseointegrated two-stage implants were splinted by means of 23 full acrylic fixed prosthesis (AFP) and other 18 implants were left without it. Using the same abutment length, Periotest measurements were performed, at abutment connections and before installation of the final prosthesis. In a 3rd part, using both implants and teeth as abutments, 29 osseointegrated implants were connected with 25 abutment teeth by means of 7 AFP. The measurements were performed at the beginning of the prosthetic treatment and 2, 4 and 6 weeks later. After splinting teeth by means of AFP for the observation period, no statistically significant reduction in PTVs was found. When on the other hand, a C-MFP was used, PTV 2 showed a significant reduction. The PTVs at abutment connection went down after a period of time, during which some implants were interconnected by means of an AFP and others were not.(ABSTRACT TRUNCATED AT 250 WORDS)     

Single tooth, implant-stabilized crowns replacing anterior teeth: a clinical comparison of two systems

Implant-supported single-tooth crowns are suitable alternative restorations to partial dentures and bridges. A number of systems have been developed to create a good aesthetic result without the display of the standard titanium abutment traditionally used in restorations with complete fixed prostheses supported by titanium endosseous implants. This paper reviews two such systems.     

Repair with a surveyed cast clasp while patient retains the partial denture

A technique is described that allows a removable partial denture with a broken clasp or a removable partial denture in which an abutment has been extracted to be restored by the reattachment of a new cast clasp component or a complete surveyed clasp assembly. The technique is applicable to most clasp designs and can include attachment to the acrylic denture base or the metal major connector. The technique is distinguished from other repair techniques by (1) providing a cast clasp replacement, (2) allowing the patient to retain the prosthesis during the repair, (3) generating a precisely formed surveyed clasp assembly by the laboratory, and (4) including an efficient transfer mechanism for the precision clasp created in the laboratory to be attached to the removable partial denture in the dental office. A two-step impression procedure is used to ensure proper relation of the partial denture to the abutments.     

Large-Scale Flume Tests of Riprap-Apron Performance at a Bridge Abutment on a Floodplain

Laboratory tests using a large-scale model of a spill-through bridge abutment led to important findings about the performance of a riprap apron as an abutment scour countermeasure. Riprap stone is widely used for protecting side slopes of embankments against erosion, and several design guidelines are available in the literature. In contrast, only a few guidelines exist for the design of a riprap apron around an abutment. These guidelines focus only on the armoring effect of riprap, neglecting other effects. This study shows that apron performance involves several mechanisms: armoring the bed, dissipating large-scale turbulence shed from the abutment, reducing the peak unit discharge, reducing the average shear stress, and shifting the scour region away from the abutment. Together, these mechanisms substantially reduce the maximum scour depth. The test findings are compared with those from a much smaller model of riprap-apron performance.     

Local Scour and Riprap Stability at an Abutment in a Degrading Bed

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.     

Countermeasure Toe Protection at Spill-Through Abutments

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.     

Optimizing multiple individual anterior implant restorations with a new generation implant-abutment system; IMZTwinPlus: a case report and treatment rationale

A 53-year-old male with a history of initial oral facial trauma causing the loss of three maxillary incisors, multiple failures of tooth-borne fixed prosthetic reconstructions, and a resultant condition of structural failure of abutment cuspids and lateral incisor was to be retreated. The case contained numerous anatomic and dimensional constraints. The patient's desire to achieve a long-term, dependable prosthetic reconstruction prompted professional consideration of incorporating implants to lend structural support in the edentulous area. An extensive review of current implant-abutment options and their single-tooth implant replacement design and treatment rationales was conducted. The IMZ Generation III (IMZTwinPlus) implant system, a nonhex system, was chosen for treatment of the case of report to optimize mechanics, biomechanics, and esthetics for multiple individual-tooth implant replacement.     

Removable partial prostheses for the elderly

Elderly partially edentulous patients can have teeth replaced with removable or fixed prostheses supported by mucosa, teeth, or implants. Age per se does not influence which option is best. Instead, the relative health of the patient, dental tissues, and the patient's finances determine treatment. A three-level index of these factors, the PTF index, is proposed to assist in the decision-making for treatment. Removable partial prostheses (RPPs) can be indicated for all patients because RPPs offer esthetic, versatile, noninvasive, and reversible features. They are particularly indicated when remaining teeth are questionable. If teeth are lost, they can be more easily added to existing RPPs compared with fixed prostheses. Six changes to ideal designs are illustrated in this article for prostheses with a compromised dentition, to make continued prosthetic service simpler.     

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier–Stokes equations, closed with the k–ω turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, “quiescent,” region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract coherent eddies from the chaotic turbulent flow. Application of this technique to several abutment configurations yielded results that support the numerical findings.     

Load transmission in implant superstructures supported by natural teeth and osseointegrated dental implants. A preliminary report

There is considerable debate as to the effects of using bridges which are supported simultaneously by teeth and implants, due to the marked differences in their displaceability. This in-vivo experiment was carried out on three subjects, and measured the vertical and horizontal movement of implants and teeth, linked with a fixed superstructure, when this was loaded. The results suggest that natural abutment teeth may contribute significantly to bridge support in these circumstances.     

Comparison of intravenous nalbuphine infusion versus naloxone in the prevention of epidural morphine-related side effects

Thirty-nine consecutive patients with 3- and 4-part proximal humeral fractures and fracture dislocations were treated with hemiarthroplasty. After an average of 42 months (range 5 to 98 months) of follow-up, 17 women and 8 men (average age 64.5 years) were evaluated with the University of California-Los Angeles (UCLA) scale, the Constant-Murley scale, the Hospital for Special Surgery (HSS) scale, and the visual analogue scale. Fair, good, or excellent results were achieved in 80% of the patients on the UCLA and Visual scales, in 72% of the patients on the HSS scale, and in 44% of the patients on the Constant-Murley scale. The highest correlation was between the HSS score and the Visual analogue score. According to the UCLA and Constant-Murley results, the outcome after early (<4 weeks) humeral head replacement was significantly better than after late (> or =4 weeks) humeral head replacement (UCLA score, P=.02; Constant-Murley score, P=.01). After early hemiarthroplasty active forward flexion was significantly better (P=.035). Thus the decision to perform prosthetic humeral head replacement in elderly patients should be made as early as possible after trauma.     

Human herpesvirus-6 infection in liver transplant recipients: documentation of pathogenicity

In the posterior partially edentulous jaw, implants may be used to supplement existing natural dentition. Frequently, the maxillary sinuses and the mandibular nerve preclude the fabrication of freestanding implant-retained prostheses. However, if an implant and a natural abutment are combined, a fixed prosthesis can be fabricated, restoring the arch into the premolar area. The histories of three patients with attachments connecting implant-retained ceramotitanium crowns with crowns on natural abutments are described. A design for a rigid custom-made attachment for the Br?nemark system, using standard components with a machine-duplication, spark-erosion technique, is suggested.     

Stress analysis of a cantilevered fixed partial denture with normal and reduced bone support

A two-dimensional finite element model was constructed to analyze the simulated mechanical behavior of a cantilevered fixed partial denture. The variations of the models were made by altering the degree of bone support, the number of splinted abutments, and the length of the pontics. High stress concentrations were observed around the connectors of the fixed prosthesis and the tooth closest to the cantilever. Reduced bone support increased the deflection and stress concentrations. There was reduction in displacement and stress concentration when the teeth were splinted together. To improve the prognosis of the fixed partial denture cantilever, the number of abutments should be increased and the number of pontics decreased.     

One-stage surgery with a nonsubmerged implant system

Although nonsubmerged implant surgery can reduce patient trauma and costs by eliminating the uncovering procedure, one-piece implants cannot be shortened for esthetic results. However, a new implant design that comes preattached on a multipurpose collar is used for insertion, nonsubmerged healing, and as an abutment base. For submucosal margins, the collar can be replaced by an esthetic abutment that connects directly to the implant. Surface treatments include midsections roughened by hydroxyapatite or titanium plasma spray coatings, with smoother, acid-etched necks and self-tapping apical ends. Screw-retained, friction-fit abutments offer prosthodontic stability and uniformity, despite the submucosal implant type.     

Catastrophic Sliding of a Concrete Deck during Its Launching on the Steel Girders of a Composite Bridge

The concrete deck of a 340-m long composite bridge having a general slope of 6.5% was built by increments of 20 m. Forming and concreting were done behind the upper abutment. Increments were successively pushed over the steel girders with cast iron shoes inserted between concrete and steel at regular intervals. As the third increment was in place, it was noticed that the concrete ribbon was slightly curved and laying somewhat eccentrically over the girders. The deformation of the steel flanges induced transverse weight components. Moreover, launching is always accompanied by dynamical effects, which were not correctly understood. As the 10th increment was being pushed, an arresting plate holding the steel structure at the upper abutment in the longitudinal direction failed and transverse weight components helped setting the deck in motion, which then began sliding.     

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.