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Biomedical subjects

A B Carr

Publications and source records attributed to A B Carr.

At least 19 recordsLinked to original sources
PubMed2006

Interventions for tobacco cessation in the dental setting.

BACKGROUND: Tobacco use has significant adverse effects on oral health. Oral health professionals in the dental office or community setting have a unique opportunity to increase tobacco abstinence rates among tobacco users. OBJECTIVES: This review assesses the effectiveness of interventions for tobacco cessation offered to cigarette smokers and smokeless tobacco users in the dental office or community setting. SEARCH STRATEGY: We searched the Cochrane Tobacco Addiction group Specialized Register (CENTRAL), MEDLINE (1966-2004), EMBASE (1988-2004), CINAHL (1982-2004), Healthstar (1975-2004), ERIC (1967-2004), PsycINFO (1984-2004), National Technical Information Service database (NTIS, 1964-2004), Dissertation Abstracts Online (1861-2004), Database of Abstract of Reviews of Effectiveness (DARE, 1995-2004), and Web of Science (1993-2004). SELECTION CRITERIA: We included randomized and pseudo-randomized clinical trials assessing tobacco cessation interventions conducted by oral health professionals in the dental office or community setting with at least six months of follow up. DATA COLLECTION AND ANALYSIS: Two authors independently reviewed abstracts for potential inclusion and abstracted data from included trials. Disagreements were resolved by consensus. MAIN RESULTS: Six clinical trials met the criteria for inclusion in this review. Included studies assessed the efficacy of interventions in the dental office or a school community setting. All studies assessed the efficacy of interventions for smokeless tobacco users, one of which included cigarettes smokers. All studies employed behavioural interventions and only one offered pharmacotherapy as an interventional component. All studies included an oral examination component. Pooling of the studies suggested that interventions conducted by oral health professionals increase tobacco abstinence rates (odds ratio [OR] 1.44; 95% confidence interval [CI]: 1.16 to 1.78) at 12 months or longer. Heterogeneity was evident (I(2) = 75%) and could not be adequately explained through subgroup or sensitivity analyses. AUTHORS' CONCLUSIONS: Available evidence suggests that behavioural interventions for tobacco use conducted by oral health professionals incorporating an oral examination component in the dental office and community setting may increase tobacco abstinence rates among smokeless tobacco users. Differences between the studies limit the ability to make conclusive recommendations regarding the intervention components that should be incorporated into clinical practice.

Counseling↗
PubMed2001

Histomorphometric comparison of implant anchorage for two types of dental implants after 3 and 6 months' healing in baboon jaws.

STATEMENT OF PROBLEM: A complete understanding of dental implant prognosis requires better knowledge of the bone anatomy after implant healing. Such baseline data are necessary to compare against load-induced changes in anatomy. PURPOSE: The purpose of this article is to describe and compare measures of implant support (percentage [%] integration and percentage [%] bone area) for various implants in baboon jaws after healing times of 3 and 6 months. MATERIAL AND METHODS: Commercially pure titanium (cpTi) and titanium alloy (Ti-alloy) screw-shaped implants were placed in the posterior jaws of 9 female baboons after 2 months of postextraction healing. Specimens were harvested after 3 months (5 baboons: 8 cpTi, 7 Ti-alloy) and after 6 months (4 baboons: 8 cpTi, 8 Ti-alloy). Each implant provided 6 polished horizontal sections for data collection, which was accomplished from digitized images with the IMAGE analysis system (reliability at 1.6%). Three- and six-month data for each parameter were compared with the use of ANOVA (P<.01). RESULTS: The results revealed a significant increase in the % integration (cpTi 39.1 to 56.2; Ti-alloy 40.0 to 55.2) and the % bone area (cpTi 38.8 to 47.9; Ti-alloy 38.9 to 49.2) from 3 to 6 months for both implants. This significant increase was also true for comparisons by jaw for each implant material (P<.01 for overall and by jaw comparisons). CONCLUSION: A time-dependent increase in jawbone anchorage was measured in this nonhuman primate population, and it was shown that the 6-month maxillary data were comparable to the 3-month mandibular data. These results lend support to the clinical strategy of waiting longer to load implants in the maxilla.

Alloys↗
PubMed2000

Hierarchy of research design used to categorize the "strength of evidence" in answering clinical dental questions.

The purpose of this article is to highlight important features of research design that clinicians can use to determine which articles are useful when attempting to answer clinical questions and determine the best therapy for a particular patient. This article offers a systematic means of categorizing the quality of research reports for clinicians and clinical investigators. A recurring clinical theme of hygiene education is used to exemplify how phrasing the clinical question determines the type of study design that could be used. The article describes the continuum of research reports, and categorizes them by their inherent strengths and weaknesses. The report describes why the research designs in the supreme position of the research hierarchy, are the most valuable to clinicians seeking evidence that defines the best therapy for their patients.

Clinical Trials as Topic↗
PubMed1999

Distortion of three-unit implant frameworks during casting, soldering, and simulated porcelain firings.

PURPOSE: The aim of this study was to assess distortion inherent in casting, soldering, and simulated porcelain firings of screw-retained, implant-supported three-unit fixed partial dentures (FPDs). MATERIALS AND METHODS: Ten wax patterns were fabricated on a die-stone cast containing two implants, 20 mm apart from center to center. Five specimens were cast in a high-palladium alloy, exposed to simulated porcelain firings, sectioned, and then soldered with low-fusing solder. Five specimens were cast, sectioned, soldered with high-fusing solder, and then exposed to simulated porcelain firings. For each specimen, two horizontal and six vertical distances between appropriately scribed reference points were measured with a traveling microscope. Comparisons were made among the various measurements taken after wax-pattern fabrication, casting, high- and low-fusing soldering, and each porcelain firing. Data were analyzed using a repeated-measures factorial ANOVA (alpha = 0.05). RESULTS: Significant difference was detected in the amount of horizontal distortion during casting (53 +/- 24 microns) and high-fusing soldering (-49 +/- 50 microns), as well as in the amount of horizontal distortion during high-fusing soldering (-49 +/- 50 microns) and low-fusing soldering (17 +/- 26 microns). However, no clinically significant difference was found in the amount of horizontal distortion during casting, low-fusing, and high-fusing soldering. The greatest amount of distortion during the simulated porcelain firings took place during the oxidizing cycle. CONCLUSIONS: Soldering did not improve the casting misfit of a three-unit implant-retained FPD model. Metal-ceramic implant frameworks should be oxidized before intraoral fit evaluation.

Analysis of Variance↗
PubMed1998

Effects of dental laboratory processing variables and in vitro testing medium on the porcelain adherence of high-palladium casting alloys.

PURPOSE: This study assessed the effects of dental laboratory processing variables and testing medium on porcelain adherence of representative high-palladium alloys. MATERIAL AND METHODS: The processing variables were recasting two and three times, porcelain stripping with hydrofluoric acid and rebuilding, and changing the recommended oxidation procedures. The testing medium was air for these four groups and the nontreatment group. In the last group, the specimens were stored and tested in artificial saliva. The metal ceramic specimens were fractured with biaxial flexure in constant strain. The area fraction of adherent porcelain (%) was calculated with a standardized spectrometric technique. A gold-palladium alloy served as the control. RESULTS: Recasting without adding new alloy negatively affected some high-palladium alloys. Porcelain stripping did not cause a decrease in adherence of the tested alloys. The alternate oxidation treatment reduced significantly the porcelain adherence of the Au-Pd and one Pd-Cu-Ga alloy. Storage and testing in artificial saliva did not significantly affect the porcelain adherence of the alloys. The Au-Pd alloy exhibited the highest porcelain adherence.

Adhesiveness↗
PubMed1997

Effect of prosthetic superstructure accuracy on the osteointegrated implant bone interface.

OBJECTIVE: This study evaluated the biologic result of forces induced by a misfitting prosthetic superstructure on implants placed in a New Zealand white rabbit tibia model. STUDY DESIGN: Nine rabbits had two dental implants placed in both right and left proximal tibias. After 6 weeks, one animal was sacrificed for baseline integration data, and the remaining animals had fitting or misfitting prosthetic superstructures attached to the implants for 12 weeks. Implants were evaluated clinically, radiographically, and histomorphometrically at the scanning electron microscopic level. RESULTS: No clinical, radiographic, or histomorphometric evidence exists of integration failure with implants subjected to superstructure strain, although bone remodeling is noted. CONCLUSIONS: Given the limitations of sample size, animal model used, duration of prosthetic superstructure attachment, and loading confounders possible, the study of prosthetic framework misfit must be evaluated with another animal model, such as an intraoral primate model, to determine the relationship between clinical performance and histologic findings.

Adaptation, Physiological↗
PubMed1996

The response of bone in primates around unloaded dental implants supporting prostheses with different levels of fit.

Implant failure as a consequence of prosthetic loading following clinical determination of successful stage I healing is poorly understood. A basic premise of accepted prosthetic protocol is passive connection of multiunit prostheses to the implant support. To better understand mechanical factors related to implant failure, this basic passivity premise was experimentally tested prior to study of functional loading research. The purpose of this preliminary study was to measure the bone response around implants placed in the mandible of baboons that supported prostheses exhibiting two levels of fit and not loaded occlusally. Screw-retained prostheses that exhibited a mean linear distortion of 38 microns and 345 microns made up the fit and misfit groups respectively. The results failed to distinguish a difference in bone response between the two levels of prosthetic fit. Although the finding can be argued as a sample size limitation, the data strongly suggest an opposite response than is clinically expected and, consequently, does not warrant the use of additional animals in this initial study. Because the design of this study does not mimic the clinical application of misfitting prostheses (where dynamic functional loads are superimposed with misfit loads), it cannot be inferred that, in clinical application, fit does not alter the osseointegrated interface. Ongoing investigation of failure due to nonpassive connections under dynamic loading conditions of mastication will help clarify the clinical significance of passivity.

Analysis of Variance↗
PubMed1996

Characterization of noble metal implant cylinders: as-received cylinders and cast interfaces with noble metal alloys.

A common procedure in the fabrication of implant prostheses is the use of premade wrought cylinders in cast frameworks. Although manufacturers outline some precautions in the use of these components, detailed information about the metal interface between cylinders and cast alloys is lacking. This article, following a previous report that compared titanium-based implant cylinders used with two different classes of cast alloys, compares conventional noble metal cylinders from three different manufacturers combined with these two classes of cast noble alloys. Analysis of the as-received cylinders revealed that the implant cylinders as a group are predominantly composed of metals commonly found in noble dental alloys, namely, platinum, palladium, gold, and silver. The interfaces created by casting both high-fusing and low-fusing alloys around the cylinders exhibited a general elemental concentration variability compared with the bulk alloy regions, but continuous concentrations for shared elements suggested alloy-cylinder compatibility. Vickers hardness values, which ranged from 212 to 276 for the as-received cylinders, decreased from 12% to 43% for the various cylinders after casting. This study suggests characteristics of an ideal cast interface that include maintenance of the cylinder and casting alloy microstructures up to the interface, absence of interfacial reaction regions, lack of porosity created by volatilization of components from either alloy or the casting process, and sufficient strength to maintain anticipated loads.

Dental Alloys↗
PubMed1996

Comparison of strains transferred to a bone simulant between as-cast and postsoldered implant frameworks for a five-implant-supported fixed prosthesis.

PURPOSE: To measure and compare the strains transferred by screw-fastening one-piece full-arch prostheses as cast and after sectioning and soldering. MATERIALS AND METHODS: Photoelastic resin was applied directly to five 3.75 x 13-mm Brånemark implants, situated 7 mm apart, in a silicone mold of an edentulous mandible. Four strain gauge rosettes were also incorporated in the resin to allow strain measurements at four locations. Three frameworks were made from a single master cast produced from an impression of the five-implant model with 4-mm abutments. These frameworks were sequentially secured to the master model with five gold slot screws tightened to 10 N cm. Strain indicator readings were recorded at a standardized time following the initial fastening of each prosthesis. The test was repeated three times. Each of the three castings were subsequently sectioned and soldered in two locations, mesial to the two terminal fixtures. After soldering, the three superstructures were returned to the master model for measurement of postsolder strains three times each. A one-way repeated-measures ANOVA was performed to determine differences between mean principal strains between the as-cast and postsoldered groups. RESULTS: A statistically significant difference was found in the principal strains between the as-cast and soldered frameworks. Overall, there was a decrease in the magnitude of strain for the soldered frameworks. CONCLUSIONS: Sectioning and soldering improved the as-cast accuracy as far as the amount of strain transferred to the bone simulant.

Alveolar Process↗
PubMed1996

The accuracy of implant verification casts compared with casts produced from a rigid transfer coping technique.

PURPOSE: Prosthodontic techniques for implant-supported prostheses continue to evolve in an effort to facilitate treatment and minimize costs. Because research has shown no impression transfer technique to be without error, some clinicians have attempted to control the fit of prosthetic frameworks by reorienting sections of patterns or frameworks intraorally, fabricating a verification cast, and completing the prosthesis to fit such a cast. One manufacturer has attempted to meet both impression-making and verification-cast objectives by providing metallic impression copings (MICS) with extensions that allow contact between the copings for rigid fixation with acrylic resin before impression making. The purpose of this study was to determine the accuracy of casts produced from the MICS transfer process compared with casts produced from sectioned frameworks, where both techniques used a low-polymerization-shrinkage acrylic resin polymer to rigidly join the sections. MATERIALS AND METHODS: Using stainless steel measurement spheres as a reference point on each implant analog, the distances between analogs on the experimental casts were compared with the distances measured on the master cast. Seven casts were produced for each group and measured with a machinist's microscope at a 4-micron level of precision. RESULTS: The results revealed that the MICS transfer exhibited a mean error of 41 microns, which was significantly less than the verification-cast group mean error of 57 microns (p < .01, Student's t test). CONCLUSIONS: Given these results, clinicians can consider the rigid transfer technique as provided in the MICS transfer to be more accurate than the verification technique as outlined in this study.

Analysis of Variance↗
PubMed1995

X-ray diffraction studies of as-cast high-palladium alloys.

OBJECTIVES: The purpose of this study was to use x-ray diffraction (XRD) to investigate four representative high-palladium alloys in the as-cast condition and obtain new information about the metallurgical phases. METHODS: Two Pd-Cu-Ga alloys and two Pd-Ga alloys were cast into plate-shaped specimens (20 mm x 1.5 mm) which were bench-cooled. Polished and etched specimens were analyzed using two different x-ray diffractometers and CuKa radiation. RESULTS: All four alloys exhibited strong XRD peaks for the face-centered cubic (fcc) palladium solid solution matrix, and variations in the lattice parameter were consistent with alloy compositions. Comparison of the relative peak intensities for the alloys and the pure palladium powder standard indicated that the as-cast microstructures had preferred crystallographic orientation. Because the two Pd-Cu-Ga alloys contained appreciable amounts of near-surface lamellar interdendritic or eutectic constituents, it was possible to determine previously unreported XRD peaks for the Pd2Ga phase in these alloys. Low-intensity peaks in the Pd-Ga alloys were attributed to small amounts of secondary phases observed in the microstructures. SIGNIFICANCE: Knowledge of the metallurgical structures of these high-palladium alloys can be important for interpretation of microstructural observations, mechanical properties, corrosion behavior and clinical performance.

Dental Alloys↗
PubMed1995

Comparison of strains transferred to a bone simulant among implant overdenture bars with various levels of misfit.

PURPOSE: To measure and compare strains transferred to a bone simulant by screw-fastening implant overdenture bars with various levels of fit or misfit. MATERIALS AND METHODS: Photoelastic resin was cast directly to two 3.75 X 13-mm Branemark fixtures (Nobelpharma USA Inc, Chicago, IL) situated 20 mm apart in a silicone mold of an edentulous mandible. Two strain-gauge rosettes were also incorporated in the resin to allow precise determination of principal stresses at two locations. Four groups of three overdenture bars with 0-, 180-, 360-, and 500-micrometer vertical gaps were fabricated. These bars were sequentially secured to the abutments with gold slot screws tightened to 10 N-cm. Strain indicator readings were recorded at a standardized time following the initial fastening of each bar. The test was repeated three times for each overdenture bar. RESULTS: Mean principal stresses and strains at the location of the rosettes were determined. The magnitude of these stresses and strains increased significantly with each increase in gap size. Strains were several times larger mesial to the fixture than they were distal. CONCLUSIONS: Strains are transferred to the bone when misfitting prostheses were secured. Some of the strains mesial to the fixture appeared to be unfavorable for regions of lower bone density when the groups with designed gaps were secured. These data will be compared with those in ongoing animal studies regarding the cellular response to prosthesis misfit.

Alveolar Process↗
PubMed1993

Porcelain adherence to high-palladium alloys.

The adherence of porcelain to four representative high-palladium alloys of the first generation (Pd-Cu-Ga) and second generation (Pd-Ga) was measured by use of a gold-palladium alloy as a control. The area fraction of adherent porcelain after metal-ceramic specimens were debonded in biaxial flexure at constant strain was calculated from the characteristic Si x-ray intensity with a standardized scanning electron microscope/energy-dispersive spectroscopy technique (SEM/EDS). The gold-palladium alloy exhibited the highest percentage of cohesive fracture through the porcelain, the two first-generation alloys were intermediate, and the two second-generation alloys exhibited the lowest area fractions. This study demonstrated that conventional visual (naked eye) or microscopic examination of the fractured metal-ceramic specimens at moderate magnification and the use of standard quantitative metallographic techniques were inadequate to provide accurate measurements of the area fraction covered with porcelain.

Analysis of Variance↗
PubMed1993

Titanium alloy cylinders in implant framework fabrication: a study of the cylinder-alloy interface.

Titanium alloy has been proposed as a suitable alternative to noble metal alloys in premanufactured metal cylinders for fabricating implant prosthesis frameworks. The interfaces produced by standard lost wax procedures that use titanium and conventional noble metal implant cylinders with both high-fusing (high-palladium) and low-fusing (high-gold) noble metal casting alloys were compared. Elemental analysis by scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDS) of the two titanium cylinders revealed that one commercial product had a composition similar to that for commercially pure titanium and the other had a composition consistent with that for Ti-6Al-4V alloy. The SEM observations and complementary elemental line scans indicated that the interfaces between the titanium cylinders and the two noble metal casting alloys did not meet proposed criteria for acceptable metal-to-metal unions. The interfaces between the noble metal cylinders and noble metal casting alloys did exhibit acceptable unions. The SEM observations and elemental analyses were supported by push-shear test results that showed that the resistance to failure was appreciably greater for interface specimens produced with alloy cast to noble metal cylinders compared with titanium cylinders.

Alloys↗
PubMed1993

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.

Analysis of Variance↗
PubMed1992

Comparison of impression techniques for a two-implant 15-degree divergent model.

To consistently provide passively fitting implant superstructures, an understanding of the accuracy and precision of all phases of fabrication and connection is required. The initial phase of fabrication, ie, impression making and cast forming, was investigated in an earlier report for a mandibular five-implant model. The current study evaluates the accuracy of working casts produced from impressions using two different transfer copings in a 15-degree divergent two-implant posterior mandibular model. While the indirect method is less cumbersome to use, it was found to be less accurate in the prior study. The purpose of this study was to see if the direct method is more precise for this clinical situation. A transfer was deemed effective in producing experimental casts if distances between specified points on the cast agreed with the corresponding distances on the master cast. The absolute value of the difference in distances between experimental and master casts was compared for the two techniques (two-sample t tests). No significant differences were noted (P > .05), and the power of the tests ranged from 0.70 to 0.96 against the one-sided hypothesis that the direct method had a smaller mean absolute difference in distance than the indirect method. This suggests no clear advantage in using the direct method in similar clinical situations. Comparison of these findings to other impression accuracy studies is made.

Dental Implantation, Endosseous↗