761 research outputs found
Evolution of fermionic systems as an expectation over Poisson processes
We derive an exact probabilistic representation for the evolution of a
Hubbard model with site- and spin-dependent hopping coefficients and
site-dependent interactions in terms of an associated stochastic dynamics of a
collection of Poisson processes.Comment: 4 pages, contribution to the proceedings of tenth International
Conference on Recent Progress in Many-Body Theories, Seattle, 199
Exact ground state for a class of matrix Hamiltonian models: quantum phase transition and universality in the thermodynamic limit
By using a recently proposed probabilistic approach, we determine the exact
ground state of a class of matrix Hamiltonian models characterized by the fact
that in the thermodynamic limit the multiplicities of the potential values
assumed by the system during its evolution are distributed according to a
multinomial probability density. The class includes i) the uniformly fully
connected models, namely a collection of states all connected with equal
hopping coefficients and in the presence of a potential operator with arbitrary
levels and degeneracies, and ii) the random potential systems, in which the
hopping operator is generic and arbitrary potential levels are assigned
randomly to the states with arbitrary probabilities. For this class of models
we find a universal thermodynamic limit characterized only by the levels of the
potential, rescaled by the ground-state energy of the system for zero
potential, and by the corresponding degeneracies (probabilities). If the
degeneracy (probability) of the lowest potential level tends to zero, the
ground state of the system undergoes a quantum phase transition between a
normal phase and a frozen phase with zero hopping energy. In the frozen phase
the ground state condensates into the subspace spanned by the states of the
system associated with the lowest potential level.Comment: 31 pages, 13 figure
Effect of airborne particle abrasion on microtensile bond strength of total-etch adhesives to human dentin
Aim of this study was to investigate a specific airborne particle abrasion pretreatment on dentin and its effects on microtensile bond strengths of four commercial total-etch adhesives. Midcoronal occlusal dentin of extracted human molars was used. Teeth were randomly assigned to 4 groups according to the adhesive system used: OptiBond FL (FL), OptiBond Solo Plus (SO), Prime & Bond (PB), and Riva Bond LC (RB). Specimens from each group were further divided into two subgroups: control specimens were treated with adhesive procedures; abraded specimens were pretreated with airborne particle abrasion using 50 mu m Al2O3 before adhesion. After bonding procedures, composite crowns were incrementally built up. Specimens were sectioned perpendicular to adhesive interface to producemultiple beams, which were tested under tension until failure. Data were statistically analysed. Failure mode analysis was performed. Overall comparison showed significant increase in bond strength (p < 0.001) between abraded and no-abraded specimens, independently of brand. Intrabrand comparison showed statistical increase when abraded specimens were tested compared to no-abraded ones, with the exception of PB that did not show such difference. Distribution of failure mode was relatively uniform among all subgroups. Surface treatment by airborne particle abrasion with Al2O3 particles can increase the bond strength of total-etch adhesive
Extraction socket preservation using porcine-derived collagen membrane alone or associated with porcine-derived bone. Clinical results of randomized controlled study
The aim of present randomized controlled clinical trial was to clinically evaluate hard tissue changes after extraction socket preservation procedures compared to natural spontaneous healing
Implant survival and success rates in patients with risk factors: results from a long-term retrospective study with a 10 to 18 years follow-up
OBJECTIVE:
Risk factors for implant therapy are represented by all general and local conditions that through various mechanisms can increase either short-term and long-term failure risk. The aim of this study is to assess the implant survival and implant success rates with single and multiple risk factors.
PATIENTS AND METHODS:
To address the research purpose, a retrospective cohort study was designed and implemented, including a sample of 225 patients with a total of 871 implants placed. The following risk factors were considered: smoking, bruxism, bone augmentation procedures and the presence of load risk (implants with crown/implant relation > 0.8; angulation > 25°; presence of cantilever). Follow-up ranged from 10 years to 18 years (average follow-up 13.6 years). Failures were subdivided into short-term failures, before the prosthetic phase, and long-term failures, after definitive prosthesis. The success criteria published by Albrektsson and Zarb were adopted. A Cox proportional hazard regression model was used to calculate hazard ratio, with a statistically significant p-value <0.05.
RESULTS:
Out of the 871 implants placed, 138 did not meet the success criteria, (success rate 84.16%), sixty (43.47%) were classified as "early failure" and seventy-eight as "late failure" (56.53%). A total of 70 dental implants were removed, with a survival rate of 91.96%.
CONCLUSIONS:
The presence of a single risk factor does not imply a marked increase of failure risk. Among the analyzed factors, the one that proved to be the most dangerous was bruxism, even when presented as the only risk factor. Bruxism with load risk proved to be the most dangerous association (success rate 69.23%) and could be included among the absolute contraindications for implant treatment
A randomized clinical trial about presence of pathogenic microflora and risk of peri-implantitis: comparison of two different types of implant-abutment connections
OBJECTIVE:
The aim of this in vivo study was to evaluate two different types of implant-abutment connections: screwed connection and cemented connection, analyzing peri-implant bacteria microflora as well as other clinical parameters.
PATIENTS AND METHODS:
Twenty implants were selected, inserted in 20 patients, 10 with a screwed implant-abutment connection (Group 1) and 10 with a cemented implant-abutment connection (Group 2). The peri-implant microflora was collected, after at least 360 days from the prosthetic rehabilitation, using paper points inserted in peri-implant sulcus for 30 s. Polymerase chain reaction (PCR) Real-time analyzed the presence of 9 bacteria periodontal-pathogens and Candida albicans.
RESULTS:
Our findings showed that bacteria colonized all Groups analyzed, the average bacterial count was 3.7 E +08 (±1.19) in Group 1, compared to 2.1 E +08 (±0.16) in Group 2; no statistically significant differences were observed (p>0.0.5). In Group 1, however, bacterial colonization of peri-implant sulci was over the pathogenic threshold for 5 bacteria, indicating a high-risk of peri-implantitis. Also in Group 2, results showed a microflora composed by all bacteria analyzed but, in this case, bacterial colonization of peri-implant sulci was over the pathogenic threshold for only 1 bacterium, indicating a lower risk of peri-implantitis. Moreover, clinical parameters (PPD > 3 mm and m SBI > 0) confirmed a greater risk of peri-implantitis in Group 1 compared to Group 2 (p<0.05).
CONCLUSIONS:
We concluded that, also after only 360 days, implants with screwed connection showed a higher risk of peri-implantitis that implants with cemented connection
Analytical probabilistic approach to the ground state of lattice quantum systems: exact results in terms of a cumulant expansion
We present a large deviation analysis of a recently proposed probabilistic
approach to the study of the ground-state properties of lattice quantum
systems. The ground-state energy, as well as the correlation functions in the
ground state, are exactly determined as a series expansion in the cumulants of
the multiplicities of the potential and hopping energies assumed by the system
during its long-time evolution. Once these cumulants are known, even at a
finite order, our approach provides the ground state analytically as a function
of the Hamiltonian parameters. A scenario of possible applications of this
analyticity property is discussed.Comment: 26 pages, 5 figure
Accuracy and precision of an intraoral scanner in complex prosthetic rehabilitations: an in vitro study
The main purpose of this study is to measure the accuracy and the precision of the intraoral
optical scanner CS3500® (Carestream Dental LLC, Atlanta, USA) in complex clinical situations as
full arch rehabilitations on impl
ants.
50 scans of the acrylic resin model were performed by using CS3500® (Carestream Dental
LLC, Atlanta, USA) scanner. Each scan was compared with the virtual model derived from scanning
with the laboratory scanner Dscan3® (Enhanced Geometry Soluti
on, Bologna, Italy) to measure a
possible misalignment.
The alignment error was found to be 79,6 (
±
12,87)
m. The measurement was taken at the
level of 2 distal scan
-
abutments. The scanner's precision ranges from 24 to 52
m , depending on
the dist
ance between scan
-
abutment.
CS3500® (Carestream Dental LLC, Atlanta, USA) intraoral scanner has detected a valid device
in the execution of complex rehabilitations on implants. His accuracy and precision values fall within
the range established in li
terature to define acceptable the prosthetic fitting on full arch implant
rehabilitation
- …