1,720,984 research outputs found
Impianti ibridi in pazienti sani e parodontalmente compromessi: studio clinico e radiografico preliminare
No full textQuesto studio clinico e radiologico preliminare ha esaminato la sopravvivenza, la perdita di osso marginale (MBL) e l’influenza dell’altezza dell’abutment protesico (AH) sulla MBL intorno a impianti ibridi posizionati in due gruppi di pazienti parzialmente edentuli: pazienti parodontalmente sani (HP) e parodontalmente compromessi (PCP). In totale, sono stati trattati 93 pazienti che necessitavano di restauri implantari singoli o multipli, in entrambe le arcate, con applicazione di restauri protesici cementati. Sono stati posizionati 54 impianti (35 nell’arcata superiore e 19 in quella inferiore) in 45 HP e 56 impianti (31 nell’arcata superiore e 25 in quella inferiore) in 48 PCP. Tutti i 110 impianti ibridi posizionati in osso intatto hanno fatto registrare una percentuale di sopravvivenza del 100% sia negli HP sia nei PCP. Non sono state registrare differenze statistiche nel confronto dei valori di MBL dell’arcata superiore con quelli dell’arcata inferiore. In HP e PCP, è stata registrata una quantità similare e limitata di MBL ed è stato trovato che maggiore era l’AH, minore era la MBL. In conclusione, i risultati indicano che gli impianti ibridi esaminati possono ridurre il rischio di perimplantite dovuta alla superfici coronali macchinate e migliorare l’osteointegrazione grazie alle loro superfici apicali ruvide
Manufacturing and Properties of High-Velocity Oxygen Fuel (HVOF)-Sprayed FeVCrC Coatings
No full textThis paper studies the microstructure, sliding wear behavior and corrosion resistance of high-velocity oxygen fuel (HVOF)-sprayed FeVCrC-based coatings. Various process parameters were tested to evaluate their effects on the coating properties, which were also compared to those of HVOF-sprayed NiCrBSi and Stellite-6 coatings. The Fe alloy coatings are composed of flattened splats, originating from molten droplets and consisting of a super-saturated solid solution, together with rounded particles, coming from partially unmolten material and containing V- and Fe-based carbide precipitates. All process parameters, apart from “extreme” settings with excess comburent in the flame, produce dense coatings, indicating that the feedstock powder is quite easily processable by HVOF. These coatings, with a microhardness of 650-750 HV0.3, exhibit wear rates of ≈2 × 10−6 mm3/(Nm) in ball-on-disk tests against sintered Al2O3 spheres. They perform far better than the reference coatings, and better than other Fe- and Ni-based alloy coatings tested in previous research. On the other hand, the corrosion resistance of the coating material (tested by electrochemical polarization in 0.1 M HCl solution) is quite low. Even in the absence of interconnected porosity, this results in extensive, selective damage to the Fe-based matrix. This coating material is therefore unadvisable for severely corrosive environments
HyFlex EDM rotary Ni-Ti prototypes: the effect of an innovative machining technology on Ni-Ti wear
No full textAim. HyFlex EDM files were recently introduced pre- senting an innovative electro discharge machining (EDM) process of fabrication. The aim of this study was to evalua- te the surface and microstructural alterations of new and in vitro used HyFlex EDM Ni-Ti rotary prototypes.
Methods. The surface and microstructural characteristi- cs of 15 new HyFlex EDM instruments were analyzed by ESEM equipped with energy dispersive x-ray spectropho- tometry (EDS) and optical metallographic imaging. Instru- ments were subjected to instrumentation tests on severely curved root canals (ranging between 50° and 70°) of ex- tracted multi-rooted teeth. Once that canal patency was verified with a #10 K-file, the working length was determi- ned by subtracting 1mm. HyFlex EDM files were used with a 16:1 reduction handpiece X-Smart (Dentsply Maillefer, Baillagues, Switzerland) following the manufacture’s direc- tion, at 500 rpm and 2.5Ncm, with slightly apical pressure and pecking motion. The operative sequence was: 25/12 at 2/3 of the WL, 10/05 and 25/08 at WL. Irrigation was per- formed at every change of instrument, with a total amount of3mlof5%NaOCland3mlof10%EDTA(Ogna,Mug- giò, Italy). Each instrument was used in 10 curved canals, washed in an ultrasonic bath containing detergent for 10 min and then autoclaved at 134°C. Surface and microstruc- tural characterizations were repeated on used instruments at same points and with same angulations to compare the pre- and postoperative micrographs, in order to verify the appearance of fractures, unwinding, microcracks, blade di- sruption and tip deformation.
Results. Surface and microstructural characteriza- tion of new instruments revealed the typical features of a NiTi ED-Machined alloy with an irregular and “craters-like” surface. High magnification microgra- phs disclosed a non-uniform structure were pits, po- res and voids caused the peculiar aspect of a “rough- spark-machined” surface. No fractures were registered during instrumentation of curved canals. Surface and microstructural characterization of used files revealed no wear and no degradation of the 25.12 and 25.08 files. The tip segment was confirmed as the most me- chanically stressed portion of 10.05 prototypes. All the instruments, after several uses, well-preserved the “craters-like” irregular surface without cutting edge al- terations. The metallographic inspection on the cross section of brand new HyFlex EDM files showed an homogeneous martensitic phase. The microstructure appeared uniform from the surface to the bulk, and no microcracks or defect were identified, even at high optical magnification (1000X).
Conclusion. Unaltered spark-machined surface and low microstructural degradation are the main features of recently introduced HyFlex EDM. Caution would be re- commended regarding reuse of small HyFlex EDM files. Instruments exhibited a safe in vitro use in presence of severely curved canals
Rheological characterization of fly ash-based suspensions
No full textThe importance of flow properties in most handling techniques requires specific characterizations of geopolymer rheology in the fresh state. In this work, a Design of Experiment (DOE) approach was used to evaluate the influence of solid load, temperature and dispersant on apparent viscosity and yield stress of fly ash-based geopolymers. The solid load was found to be the most influential variable on viscosity. An increase in solid load led to an increase in apparent viscosity but also of yield stress. Apparent viscosity was found to have an Arrhenius type relationship with temperature. The influence of dispersant on yield stress and viscosity appeared to be minor
Hybrid and fully-etched surface implants in periodontally healthy patients: A comparative retrospective study on marginal bone loss
No full textBackground: Human studies on implants with the same design but with different surfaces are lacking at the present time. Purpose: The aim of this study was to compare the survival rate of and marginal bone loss (MBL) around 2 types of implants with the same design, but with different surfaces: fully "sandblasted and double-etched" (SDE) implants and hybrid (H) implants, with an apical SDE-surface and a coronal machined-surface. Materials and methods: The SDE- and H-surfaces were previously analyzed under SEM and profilometer. Implants were placed in partially edentulous periodontally healthy patients requiring single implant-restoration, in either mandible or maxilla, with cement-retained prosthetic restoration. Twelve months after prosthetic loading, MBL in relation to prosthetic abutment height (AH), calculated radiographically, was statistically analyzed. Results: SEM and profilometer analyses revealed no differences between the SDE-surfaces of either SDE- or H-implants. Transverse ridges and grooves characterized the machined portion of H-implants, clearly influencing the profilometer analysis. In 75 patients, 37 SDE and 38 H-implants were placed and all functioned completely after 12 months. In both SDE- and H-groups, MBL had a significant inverse relationship with AH, with greater intercept and negative slope for SDE-group and intersection of the 2 regression lines at AH=2 mm. Conclusions: A 100% survival rate was recorded for SDE- and H-implants placed in pristine bone of periodontally healthy patients; MBL was limited and similar in both SDE- and H-groups; the higher the prosthetic AH, the lesser the MBL around implants; H-implants could reduce bone loss most effectively with abutments lower than 2 mm, realistically exploitable on thin biotypes; SDE-implants could reduce bone loss most effectively with abutments greater than 2 mm, realistically exploitable on thick biotypes
Hybrid Implants in Healthy and Periodontally Compromised Patients: A Preliminary Clinical and Radiographic Study
Full text linkThis preliminary clinical and radiographic study examined the survival of, the marginal bone loss (MBL) around, and the influence of prosthetic abutment height (AH) on MBL around hybrid implants placed in two groups of partially edentulous patients: healthy (HPs) and periodontally compromised (PCPs) patients. A total of 93 patients requiring single or multiunit implant restoration, in the mandible or maxilla, were treated while undergoing cement-retained prosthetic restoration. A total of 54 implants (35 in the maxilla and 19 in the mandible) were placed in 45 HPs, and 56 implants (31 in the maxilla and 25 in the mandible) in 48 PCPs. All 110 hybrid implants positioned in pristine bone provided a 100% survival rate in both HPs and PCPs. No statistical differences were recorded comparing the MBL values of maxillae with those of mandibles. In HPs and PCPs, a similar and limited amount of MBL was recorded, and it was found that the higher the AH, the less MBL. In conclusion, results indicate that the hybrid implants examined could reduce the risk of peri-implantitis due to their coronal machined surfaces and improve osseointegration due to their apical rough surfaces
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The maintenance of inserted titanium implants: in-vitro evaluation of exposed surfaces cleaned with three different instruments
No full textObjective: Changes to titanium implants smooth-surfaces after instrumentation were comparatively analyzed using low-vacuum scanning electron microscopy (LV-SEM) and white-light confocal (WLC) profilometry, to accurately evaluate curved surfaces. Material and methods: Sixty titanium implants screwed to their abutments were randomly split into three groups for cleaning treatment with (S) stainless-steel Gracey-curettes, (T) titanium Langer-curettes, and (P) an ultrasonic-device with the probe covered with a plastic-tip. One sector of each implant was left unprocessed (U). The other sectors were cleaned for either 60 s, to simulate a single cleaning session, or 180 s to simulate a series of sessions. Surface morphology was analyzed by LV-SEM, without metal sputtering. Quantitative evaluations of the roughness of surfaces were performed using a WLC-profilometer. The Wilcoxon and the Mann-Whitney tests were used in statistical comparisons. Results: U-surfaces showed that thin transverse ridges and grooves, i.e. a polarized surface roughness was substantially compromised after S-instrumentation. Small surface alterations, increasing with time, were also recorded after T-·and·P-instrumentation, although to a lesser degree. The gap of the fixture-abutment connection appeared almost completely clean after T-, clotted with titanium debris after S-, and clotted with plastic debris after P-treatment. The mean roughness (Ra) was unchanged after P-, significantly increased after S- and decreased after T-treatment, when compared with U. The Rz roughness-parameter, calculated along the fixture Y-axis, of S, T, and P resulted similar and significantly lower than that of U. Rz (X-axis) resulted unchanged after P-, slightly increased (+40%) after T-, and greatly increased (+260%) after S-treatment, this latter being statistically significant when compared with U. Conclusions: The careful use of titanium-curettes could produce only minimal smooth surface alteration particularly over prolonged treatments, and avoid debris production that could endanger implant preservation
Properties of HVOF-sprayed TiC-FeCrAl coatings
No full textAs an alternative to WC-CoCr and Cr3C2-NiCr coatings for wear and corrosion protection, a TiC – 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder, free from hazardous and/or supply-critical elements (Ni, Co, W), was produced by high-energy ball-milling and processed by High Velocity Oxygen-Fuel (HVOF) spraying, obtaining dense ( 12 GPa) layers with reasonably good deposition efficiency of ≈ 54%. Tribological testing revealed that the TiC-FeCrAl coatings are particularly promising for sliding contacts, as their ball-on-disc wear rates against an Al2O3 counterpart were lower than those of an HVOF-sprayed Cr3C2-NiCr reference, both at room temperature and at 400 °C, although they could not match the performance of WC-CoCr. At room temperature, brittle fracture along oxidized lamellar boundaries caused localized spallation, releasing debris in the contact region, but, in the incubation period before spallation cracks could propagate, remarkably low friction (≈0.27) was recorded. At 400 °C, spallation was largely suppressed by thermal softening, whilst coarser abrasive grooving became the dominant wear mechanism. TiC-FeCrAl coatings appeared less suited to high-stress abrasion, since extensive brittle fracture resulted in higher wear rates than HVOF-sprayed Cr3C2-NiCr, and to (acidic) corrosive environments. Electrochemical polarisation tests in 0.1 M HCl indeed revealed limited corrosion resistance of the FeCrAl matrix
- …
