Early morphological and immunological alterations in the spleen during magnesium deficiency in the rat

PURPOSE: Materials used to fabricate the most dimensionally accurate implant casts have not been identified experimentally. The purpose of this investigation was to examine the dimensional accuracy of implant casts fabricated with different materials. Measurements of linear horizontal dimensional change and strain produced on a master framework were evaluated and correlated. MATERIALS AND METHODS: A master framework was fabricated to fit an aluminum five-implant model. Forty polyether implant impressions of the aluminium model were randomly grouped and poured in either Vel-mix, Die Keen, Resin Rock, or Low Fusing Alloy. A digital veneer caliper was used to measure linear distance between the most distal abutments on each of the experimental implant casts and the master model. In addition, strain values were recorded from strain gauges bonded in the mesiodistal axis of the framework, which was secured by prosthetic retaining screws torqued to 10 Ncm. RESULTS: A one-way ANOVA showed a significant difference among the four die materials in dimensional change of the experimental casts (p = .0001). A post-hoc Duncan's multiple-range test (p < .05) showed that casts fabricated with Low Fusing Alloy had the least linear dimensional change from the master cast, but the material exhibited the greatest dimensional variability. A MANOVA (Wilks' Lambda) showed significant differences in strain on the framework based upon die material (p = .015). A post-hoc Duncan's multiple-range test (p < .05) showed that Resin Rock casts induced significantly less strain on the framework than the other materials. Negligible correlation was found between the linear horizontal dimensional change and the total absolute strain on the framework. CONCLUSION: Experimental implant casts made of Resin Rock minimized strain on the master framework and decreased the amount of framework distortion on casts of this material. Low Fusing Alloy yielded accurate casts, but highly variable linear dimensional changes in the horizontal dimension may preclude its clinical benefit.     

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.     

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.     

Evaluating dementia screening tests: methodologic standards to rate their performance

A stable record base is essential for accurate interocclusal centric relation records in a completely edentulous patient. In implant prosthodontics, several procedures have been suggested for the fabrication of a stable record base. However, these procedures necessitate removal of the healing abutments during the interocclusal record procedure and the trial denture placement, which makes the procedures tedious and time-consuming. When the implant-prosthesis interface is subgingival, the patient may also experience discomfort during these procedures. This article describes a procedure for fabricating a stable record base that uses the healing abutments, which eliminates the necessity of the healing abutment removal and its consequences. Advantages and disadvantages of this procedure are also discussed.     

Acute liver failure

PURPOSE: This article reviews the literature on radiographic imaging techniques and image interpretation for dental implant treatment. MATERIALS AND METHODS: MEDLINE was used to identify published peer-reviewed literature for this report. RESULTS: Radiographic images are indispensable in the evaluation of osseous structures when planning treatment for dental implants. Potential bone sites for implant placement can be assessed clinically by means of palpation or probing through the mucosa; however, diagnostic imaging provides the best means for indirectly measuring bone dimensions. After healing of the implant site, the application of radiology is useful to verify the amount of bone adjacent to the implant and that the transmucosal abutments fit the implant. Upon completion of the implant prosthesis, radiology may be used to monitor initial and long-term success of implant treatment. CONCLUSION: Recommendations for the application of radiology over the course of treatment are made for various implant cases ranging from the overdenture to the single-tooth implant.     

Full-arch implant framework casting accuracy: preliminary in vitro observation for in vivo testing

PURPOSE: Conventional techniques for implant metal framework fabrication produce error of a magnitude that is inconsistent with the passive-fit requirement for osseointegrated implants. To understand the correlation between prosthesis fit and the implant-tissue response, evaluation of the interface tissue reactions to customary levels of fit is required. The purpose of this study is to determine the accuracy of torch casting full arch frameworks using a high palladium alloy and a ringless phosphate-bonded investment technique. MATERIALS AND METHODS: Three different variables were considered relative to casting accuracy effect. The first variable, completeness of mold-fill, compared cast specimens where the entire sprue system was filled as part of the casting and cast specimens without the sprue system filled. The second variable, phosphate-bonded investment special liquid concentrations, compared groups of castings produced from 0%, 12%, 25%, and 50% special liquid. The third variable, investment mold shape, compared casting produced from a conventional ringless mold shape with a modified ringless mold shape where the investment in the same horizontal plane as the pattern was equal in thickness at the internal and external surfaces. Horizontal and vertical distances on the wax pattern and resulting framework were measured using a machinists microscope to determine casting error. Combined vertical and horizontal error was used for comparison between groups (one-way analysis of variance). RESULTS: No significant differences existed among the three groups compared (P > 0.05). The mean error comparison between the complete and incomplete mold-fill groups showed no statistical difference, while the incomplete fill group was found to be more porous. The mean error of all groups (0.130 mm) exceeded the recommended level of fit needed to satisfy the passive fit requirement by more than 10-fold. CONCLUSIONS: These results verify clinical observation and suggest that the use of conventional lost wax casting technique to cast one-piece full arch implant frameworks is both imprecise and inaccurate as judged against the passive fit requirement. The consequences of screw-fastening misfitting prostheses to osseointegrated implants is currently under investigation.     

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.     

Retrievable cemented crown options on implant-supported angled abutments: a case report

Nonaxial implant alignment often predicates the use of cemented of screw-retained angled abutments with inherent disadvantages, including reduced retrievability on screw loosening. The purposes of this article are to review the relative merits of cemented and screw-retained angled abutments and to present a method of ensuring retrievability of cemented angled abutments.     

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.     

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.     

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.     

A laboratory evaluation of the construction of resin-bonded cast restorations

OBJECTIVE: To compare the effect of two construction techniques and two pattern materials on the fit of resin-bonded cast restorations. DESIGN: In-vitro study carried out by one operator. SETTING: Postgraduate university hospital. SUBJECTS AND METHODS: 65 nickel-chrome castings were constructed using refractory die and lift-off techniques with wax and acrylic resin pattern material. They were cemented onto master silver dies, embedded in self-curing acrylic resin and sectioned along their long axes. Interfacial distance between the master silver die and casting was measured. RESULTS: A significant different between the range of figures in each group (Mann-Whitney Test, P < 0.01) was found. Construction techniques can be ranked in order of fit of castings: 1. Refractory die, wax patterns: 42.6 microns (SD 12.03). 2. Refractory die, acrylic resin patterns: 53.7 microns (SD.16.06).3. Conventional technique, acrylic resin patterns: 85.5 microns (SD 31.62). 4. Lift-off technique, wax patterns: 139 microns (SD 53.15).5. Lift-off technique, acrylic patterns: 172.8 microns (SD 74.04). CONCLUSIONS: Castings constructed using refractory die technique and subsequently cemented resulted in a more accurate and less variable fit than those produced with the lift-off technique. Wax patterns lead to more accurate castings than acrylic resin and locating indentations may interfere with the cementation of castings when lift-off techniques are used.     

Tripodal mandibular subperiosteal implant: basic sciences, operational procedures, and clinical data

A tripodal mandibular subperiosteal dental implant is a three piece cast metal framework that fits on the residual ridge beneath the periosteum and provides support for a dental prosthesis by means of posts or other mechanisms protruding through the oral mucosa. This implant is indicated in patients with advanced atrophy of the mandible where the unstable alveolar bone has completely disappeared, leaving in place the more stable basal bone with specific anatomical contours. The authors present their experience of 317 cases carried out in three different centers related to this implant modality and underline the importance of the basic anatomic, physiologic, and medical knowledge required to optimize the results.     

The mucosal attachment at different abutments. An experimental study in dogs

The present experiment was performed to examine if the material used in the abutment part of an implant system influenced the quality of the mucosal barrier that formed following implant installation. 5 beagle dogs were included in the study. The mandibular premolars and the 1st, 2nd and 3rd maxillary premolars were extracted. Three fixtures of the Br?nemark System were installed in each mandibular quadrant (a total of 6 fixtures per animal). Abutment connection was performed after 3 months of healing. In each dog the following types of abutments were used: 2 "control abutments" (c.p. titanium), 2 "ceramic abutments" (highly sintered Al2O3), 1 "gold abutment", and 1 "short titanium abutment". This "short titanium abutment" was provided with an outer structure made of dental porcelain fused to gold. Following abutment connection a plaque control program was initiated and maintained for 6 months. The animals were sacrificed and perfused with a fixative. The mandibles were removed and each implant region was dissected, demineralized in EDTA and embedded in EPON. Semithin sections representing the mesial, distal, buccal and lingual aspects of the peri-implant tissues were produced and subjected to histological examination. The findings from the analysis demonstrated that the material used in the abutment portion of the implant influenced the location and the quality of the attachment that occurred between the periimplant mucosa and the implant. Abutments made of c.p. titanium or ceramic allowed the formation of a mucosal attachment which included one epithelial and one connective tissue portion that were about 2 mm and 1-1.5 mm high, respectively. At sites where abutments made of gold alloy or dental porcelain were used, no proper attachment formed at the abutment level, but the soft tissue margin receded and bone resorption occurred. The abutment fixture junction was hereby occasionally exposed and the mucosal barrier became established to the fixture portion of the implant. It was suggested that the observed differences were the result of varying adhesive properties of the materials studied or by variations in their resistance to corrosion.     

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.     

Study of mechanical properties of micromachined dental implants

Advancements in technologies and techniques within the dental industry have given rise to new and effective tooth replacement procedures for damages resulting from causes such as trauma or aging. While these treatments are widely available for patients, they remain highly expensive, preventing patients from much-needed dental care. The elevated cost of dental implants is in part associated with their components that are mainly available through third-party companies at a premium cost. To be cost effective, dental laboratories are exploring the option of producing their own dental implant components, and are therefore acquiring knowledge of manufacturing techniques and quality assurance expertise to produce quality components. In order to ensure high quality and reliability, the fabricated components must be tested and benchmarked against current implants on the market. The present study examines the micro machining process of dental implants, specifically for the abutments and screws, and its impact on the mechanical properties of the components. To achieve this, dental implant abutment and screw prototypes were fabricated, experimentally tested, and compared. The impact of different machining processes on the mechanical properties of the implants was comparatively determined and analysed. The fabricated implant testing results show coherent mechanical properties displayed by good hardness, and material microstructures similar to market components, indicating a high level of prototype quality.     

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.     

Establishing soft tissue integration with natural tooth-shaped abutments

The disparity in dimensions between implant fixtures and the exposed extraction sockets has resulted in the development of anatomically shaped abutments. Systems have been recently introduced that facilitate the fabrication of abutments to the configuration of natural teeth in the anterior maxilla. These systems permit development of an aesthetic emergence profile and contours for easy access in maintenance of oral hygiene of maxillary anterior single-tooth implant-supported restorations. The rationale for the development, indications, advantages, and clinical utilization of a recently introduced abutment system is discussed.     

The nonsubmerged osseointegrated dental implant

Implant patients are seeking means of restoring their health and appearance with minimal side effects. Dental implant surgery must react to these demands by continuing to develop minimally invasive implant surgery techniques, imaging that customizes surgical procedures, and materials and drugs that reduce surgical costs and complications, shorten recovery, and increase the longevity of components, enabling patients to live active lifestyles. Nonsubmerged osseointegrated implants fit nicely into the future of dental surgery.     

Initial stability of a modular uncemented, porous-coated femoral stem: a mechanical study

A versatile modular hip system was used to evaluate the initial stability of a cementless femoral stem in anatomically consistent composite bones. Four implant bone configurations of varying proximal and distal fit/fill were tested. The implanted femurs were tested on an Instron 1331 materials testing machine in neutral loading and flexion loading; both translational micromotions and rotations of the implant relative to the bone were recorded on all three axes of motion, accounting for all 6 degrees of freedom of joint motion. Implants were then sectioned, and both endosteal canal fit and intramedullary canal fill were measured. Results indicate that (1) loading the implant in flexion by out-of-plane forces significantly increases both relative translation and rotation at the interface, (2) increasing the proximal fit reduces implant rotation about its longitudinal axis in flexion loading and (3) increasing the distal canal fit and fill increases prosthesis rotation about its longitudinal axis in flexion loading. These results indicate that the femoral stem is more unstable in out-of-plane loading, such as during stair climbing, and that increasing the proximal fit may enhance the initial rotational stability of an uncemented femoral stem.