Influence of custom-made implant designs on the biomechanical performance for the case of immediate post-extraction placement in the maxillary esthetic zone: a finite element analysis

Due to the increasing adoption of immediate implantation strategies and the rapid development of the computer aided design/computer aided manufacturing technology, a therapeutic concept based on patient-specific implant dentistry has recently been reintroduced by many researchers. However, little information is available on the designs of custom-made dental implant systems, especially their biomechanical behavior. The influence of the custom-made implant designs on the biomechanical performance for both an immediate and a delayed loading protocol in the maxillary esthetic zone was evaluated by means of the finite element (FE) method. FE models of three dental implants were considered: a state of the art cylindrical implant and two custom-made implants designed by reverse engineering technology, namely a root-analogue implant and a root-analogue threaded implant. The von Mises stress distributions and micro-motions around the bone-implant interfaces were calculated using ANSYS software. In a comparison of the three implant designs for both loading protocols, a favorable biomechanical performance was observed for the use of root-analogue threaded implant which approximated the geometry of natural anterior tooth and maintained the original long-axis. The results indicated that bone-implant interfacial micro-motion was reduced and a favorable stress distribution after osseointegration was achieved.     

A three-dimensional finite element study on the biomechanical behavior of an FGBM dental implant in surrounding bone

Dental implants made of functionally graded biomaterials (FGBM) have been receiving increasing attention due to their unique advantage of being able to simultaneously satisfy biocompatibility, strength, corrosion resistance, etc., which a single composition with a uniform structure cannot satisfy. This paper investigates the biomechanical behavior of a threaded FGBM dental implant/surrounding bone system under static and harmonic occlusal forces by using a three-dimensional finite element method. The implant is a mixture of a bioceramic and a biometal with a smooth gradient in both the material composition and properties in the longitudinal direction. The interaction of the implant and the supporting bone tissues is considered. Three contact conditions at the implant-bone interface are used to model different osseointegration stages. A comprehensive parametric study is conducted to highlight the influence of the material properties, the volume fraction index, the occlusal force orientation, and the osseointegration quality on the maximum von-Mises stress, deformation distribution, natural frequencies, and harmonic response.     

An electronic device for accelerating bone formation in tissues surrounding a dental implant

A dental implant is a unique structure which can be used with a noninvasive method because it is inserted into the bone in part and extended extracorporally. This study presents an electronic device that is temporarily connected with the dental implant, and reports its effect on accelerating bone formation in the surrounding tissues in a canine mandibular model. A small sized and low power consumption biphasic electrical current (BEC) stimulator ASIC was developed and the surrounding tissue was exposed to continuous BEC stimulation for 7 days with the parameters of 20 µA/cm², 125 µs duration, and 100 pulses/s. After 2 (n = 5) and 5 weeks (n = 5), animals were sacrificed and the specimens were histomorphometrically evaluated. The newly formed bone area (BA) was 1.30 times (3 weeks, P < 0.05) and 1.35 times (5 weeks, P < 0.05) higher in the experimental group compared to the control group, respectively. Bone‐implant contact (BIC) in 3‐week specimens was 1.62 times (P < 0.05) greater in the experimental group, while there was no statistically significant difference in 5‐week specimens. Based on these results showing accelerated bone formation on and around the dental implant, it could be suggested that the latent time for osseointegration in dental implants can be reduced, and the success rate of implants in poor quality bone can be increased by using our device with BEC. Bioelectromagnetics 30:374–384, 2009. © 2009 Wiley‐Liss, Inc.     

Nanoindentation measurements of biomechanical properties in mature and newly formed bone tissue surrounding an implant

The characterization of the biomechanical properties of newly formed bone tissue around implants is important to understand the osseointegration process. The objective of this study is to investigate the evolution of the hardness and indentation modulus of newly formed bone tissue as a function of healing time. To do so, a nanoindentation device is employed following a multimodality approach using histological analysis. Coin-shaped implants were placed in vivo at a distance of 200 μm from the cortical bone surface, leading to an initially empty cavity of 200 μm * 4.4 mm. Three New Zealand White rabbits were sacrificed after 4, 7, and 13 weeks of healing time. The bone samples were embedded and analyzed using histological analyses, allowing to distinguish mature and newly formed bone tissue. The bone mechanical properties were then measured in mature and newly formed bone tissue. The results are within the range of hardness and apparent Young's modulus values reported in previous literature. One-way ANOVA test revealed a significant effect of healing time on the indentation modulus (p < 0.001, F = 111.24) and hardness (p < 0.02, F = 3.47) of bone tissue. A Tukey-Kramer analysis revealed that the biomechanical properties of newly formed bone tissue (4 weeks) were significantly different from those of mature bone tissue. The comparison with the results obtained in Mathieu et al. (2011, "Micro-Brillouin Scattering Measurements in Mature and Newly Formed Bone Tissue Surrounding an Implant," J. Biomech. Eng., 133, 021006). shows that bone mass density increases by approximately 13.5% between newly formed bone (7 weeks) and mature bone tissue.     

Optimal designs for evaluating a series of treatments

Several articles in this journal have studied optimal designs for testing a series of treatments to identify promising ones for further study. These designs formulate testing as an ongoing process until a promising treatment is identified. This formulation is considered to be more realistic but substantially increases the computational complexity. In this article, we show that these new designs, which control the error rates for a series of treatments, can be reformulated as conventional designs that control the error rates for each individual treatment. This reformulation leads to a more meaningful interpretation of the error rates and hence easier specification of the error rates in practice. The reformulation also allows us to use conventional designs from published tables or standard computer programs to design trials for a series of treatments. We illustrate these using a study in soft tissue sarcoma.     

Influence of anisotropic bone properties on the biomechanical behavior of the acetabular cup implant: a multiscale finite element study

Although the biomechanical behavior of the acetabular cup (AC) implant is determinant for the surgical success, it remains difficult to be assessed due to the multiscale and anisotropic nature of bone tissue. The aim of the present study was to investigate the influence of the anisotropic properties of peri-implant trabecular bone tissue on the biomechanical behavior of the AC implant at the macroscopic scale. Thirteen bovine trabecular bone samples were imaged using micro-computed tomography (μCT) with a resolution of 18 μm. The anisotropic biomechanical properties of each sample were determined at the scale of the centimeter based on a dedicated method using asymptotic homogenization. The material properties obtained with this multiscale approach were used as input data in a 3D finite element model to simulate the macroscopic mechanical behavior of the AC implant under different loading conditions. The largest stress and strain magnitudes were found around the equatorial rim and in the polar area of the AC implant. All macroscopic stiffness quantities were significantly correlated (R² > 0.85, p < 6.5 e-6) with BV/TV (bone volume/total volume). Moreover, the maximum value of the von Mises stress field was significantly correlated with BV/TV (R² > 0.61, p < 1.6 e-3) and was always found at the bone-implant interface. However, the mean value of the microscopic stress (at the scale of the trabeculae) decrease as a function of BV/TV for vertical and torsional loading and do not depend on BV/TV for horizontal loading. These results highlight the importance of the anisotropic properties of bone tissue.     

Isolation of clinically relevant fungal species from solid waste and environment of dental health services

Aims: This study was undertaken to detect, identify and determine antifungal susceptibility of yeast strains isolated from dental solid waste and to evaluate airborne fungi in the Brazilian dental health care environment and in the waste storage room. Methods and Results: A group of 17 yeast strains were identified by macroscopic and microscopic characteristics, API 20C Aux system and Multiplex PCR. All 104 airborne fungal colonies were identified by macroscopic and microscopic morphology. The CLSI broth microdilution method was utilized as the susceptibility test. Candida parapsilosis was the prevailing yeast species recovered from waste, followed by Rhodotorula glutinis. Three strains of Candida guilliermondii presented minimal inhibitory concentration values considered to be susceptible dose dependent (2 μg ml^?1) to voriconazole. Of all airborne fungal species, 69% were recovered from the waste storage room and 31% were recovered from the clinical/surgical environment. Most of them were identified as Cladosporium spp. Conclusions: These findings reinforce the potential risk of waste handling and point out the need for safe management to minimize the spread of these agents to the environment. Filamentous fungi isolation in almost all sampled environments indicates that a periodic monitoring of airborne microbiota in the dental health care service environment is required. Significance and Impact of the Study: The survival of yeast strains for 48 h suggests that dental waste should be carefully controlled and monitored.     

Proteomics as a tool for clinically relevant biomarker discovery and validation

The excitement associated with clinical applications of proteomics was initially focused on its potential to serve as a vehicle for both biomarker discovery and drug discovery and routine clinical sample analysis. Some approaches were thought to be able to "identify" mass spectral characteristics that distinguished between control and disease samples, and thereafter it was believed that the same tool could be employed to screen samples in a high-throughput clinical setting. However, this has been difficult to achieve, and the early promise is yet to be fully realized. While we see an important place for mass spectrometry in drug and biomarker discovery, we believe that alternative strategies will prove more fruitful for routine analysis. Here we discuss the power and versatility of 2D gels and mass spectrometry in the discovery phase of biomarker work but argue that it is better to rely on immunochemical methods for high-throughput validation and routine assay applications.     

Optimization of a sample preparation method for the metabolomic analysis of clinically relevant bacteria

Metabolomics, or metabolite profiling, is an approach that is increasingly used to study the metabolism of diverse organisms, elucidate biological processes and/or find characteristic biomarkers of physiological states. Here, we describe the optimization of a method for global metabolomic analysis of bacterial cultures, with the following steps. Cells are grown to log-phase, starting from an overnight culture and bacterial concentrations are monitored by measuring the optical density of the cultures at 600 nm. At an appropriate density they are harvested by centrifugation, washed three times with NaCl solution and metabolites are extracted using methanol and a bead-mill. Dried extracts are methoxymated and derivatized with methyltrimethylsilyltrifluoroacetamide (MSTFA) then analyzed using gas chromatography coupled to time-of-flight mass spectrometry (GC-MS/TOF). Finally, patterns in the acquired data are examined by multivariate data modeling. This method enabled us to obtain reproducible metabolite profiles of Yersinia pseudotuberculosis, with about 25% compound identification, based on comparison with entries in available GC-MS libraries. To assess the potential utility of the method for comparative analysis of other bacterial species we analyzed cultures of Pseudomonas aeruginosa, Salmonella typhimurium, Escherichia coli and methicillin-sensitive Staphylococcus aureus (MSSA). Multivariate analysis of the acquired data showed that it was possible to differentiate the species according to their metabolic profiles. Our results show that the presented procedure can be used for metabolomic analysis of a wide range of bacterial species of clinical interest.     

Influence of eccentric strength of knee extensor muscles on biomechanical factors of a vertical drop jump

During a vertical drop jump (VDJ), the human neuromuscular system absorbs and reuses external loads applied to the lower extremity by coordinating the musculoskeletal system. This study aims to investigate the influence of the eccentric strength of the knee extensor muscles on the biomechanical factors of a VDJ. Participants were divided into two groups based on the eccentric strength of their knee extension muscles: low eccentric (L_ECC) and high eccentric (H_ECC) strength groups. The VDJ joint kinematics and kinetics of the lower extremity, the fascicle behavior of the vastus lateralis, and the muscle activation of the knee extensor muscles were simultaneously recorded during maximum-effort VDJ. Compared with the L_ECC group, the H_ECC group showed a higher jump, greater knee and ankle joint stiffness, and smaller fascicle length change. These findings suggest that the eccentric strength capacity of the knee extensor muscles accounts for the different biomechanical strategies (bouncing-type for H_ECC and absorbing-type for L_ECC) observed between the groups. Consequently, the eccentric strength of the knee extensor muscle may be an essential factor in determining the biomechanical strategy for VDJ and should be considered in the jumping performance enhancement training paradigm.     

FT-IR microspectroscopy for early identification of some clinically relevant pathogens

AIMS: To investigate the potentials and limitations of Fourier transform-infrared (FT-IR) microspectroscopy as a tool to identify, at the level of microcolonies, pathogenic bacteria frequently isolated in the clinical environment. METHODS AND RESULTS: A total of 1570 FT-IR spectra from 164 gram-positive and gram-negative bacteria isolated from patients were recorded from 6 to 10-h old microcolonies of 50-150 microm size. A classification of 100% was obtained for the most frequent gram-positive bacteria, such as Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Enterococcus faecium at the species level. An average accuracy of about 80% was reached with Gram negative bacteria from the Enterobacteriaceae and Pseudomonaceae families; Enterobacter aerogenes, Enterobacter cloacae, Klebsiella spp., and Citrobacter koseri; and Proteus mirabilis and Escherichia coli. Results were comparable with FT-IR measurements on dried suspensions from 18-h cultures. CONCLUSIONS: Early identification of young microcolonies is feasible with FT-IR microscopy with a very high accuracy for gram-positive bacteria. Some improvement in the transfer of microcolonies is necessary to increase the accuracy for gram-negative bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: Combination of FT-IR microscopy and multivariate data analysis could be a complementary, rapid, and reliable tool for screening and discriminating, at species and subspecies level, micro-organisms of clinical, food-borne, or environmental origins.     

Selections of the cylinder implant neck taper and implant end fillet for optimal biomechanical properties: a three-dimensional finite element analysis

In this paper, effects of the implant neck taper and the implant-end fillet on the maximum Von Mises stresses were evaluated in jaw bones, and maximum displacements examined in an implant-abutment complex by a finite element method (FEM). The implant-neck tapers (T) ranged from 45 degrees to 70 degrees , and fillets of implant ends (R) ranged from 0.5 to 1.5mm. Results suggested that under axial load by the maximum Von Mises stresses in cortical and cancellous bones decreased by 71.6% and 14.8%, respectively, and under 45 degrees buccolingual load by 68.2% and 11.0%, respectively. The maximum displacement of implant-abutment complex decreased by 9.1% and 22.8% under axial and 45 degrees buccolingual load, respectively. When T ranged from 64 degrees to 73 degrees and R exceeded 0.8mm, minimum stress/displacement was obtained and the evaluating targets were more sensitive to T than to R. Data indicated that the taper of implant neck favored stress distribution in cortical bones more than the fillet of implant end did; taper of implant neck affected implant stability more than the fillet of implant end did; and the taper of implant neck of 64-73 degrees and fillet of implant end exceeding 0.8mm were optimal selections for the type B/2 bone in a cylinder implant by biomechanical consideration.     

Investigation of critical inter‐related factors affecting the efficacy of pulsed light for inactivating clinically relevant bacterial pathogens

Aims: To investigate critical electrical and biological factors governing the efficacy of pulsed light (PL) for the in vitro inactivation of bacteria isolated from the clinical environment. Development of this alternative PL decontamination approach is timely, as the incidence of health care–related infections remains unacceptably high. Methods and Results: Predetermined cell numbers of clinically relevant Gram‐positive and Gram‐negative bacteria were inoculated separately on agar plates and were flashed with ≤60 pulses of broad‐spectrum light under varying operating conditions, and their inactivation measured. Significant differences in inactivation largely occurred depending on the level of the applied lamp discharge energy (range 3·2–20 J per pulse), the amount of pulsing applied (range 0–60 pulses) and the distance between light source and treatment surface (range 8–20 cm) used. Greater decontamination levels were achieved using a combination of higher lamp discharge energies, increased number of pulses and shorter distances between treatment surface and the xenon light source. Levels of microbial sensitivity also varied depending on the population type, size and age of cultures treated. Production of pigment pyocynanin and alginate slime in mucoid strains of Pseudomonas aeruginosa afforded some protection against lethal action of PL; however, this was evident only by using a combination of reduced amount of pulsing at the lower lamp discharge energies tested. A clear pattern was observed where Gram‐positive bacterial pathogens were more resistant to cidal effects of PL compared to Gram negatives. While negligible photoreactivation of PL‐treated bacterial strains occurred after full pulsing regimes at the different lamp discharge energies tested, some repair was evident when using a combination of reduced pulsing at the lower lamp discharge energies. Strains harbouring genes for multiple resistances to antibiotics were not significantly more resistant to PL treatments. Slight temperature rises (≤4·2°C) were measured on agar surfaces after extended pulsing at higher lamp discharge energies. Presence of organic matter on treatment surface did not significantly affect PL decontamination efficacy, nor did growth of PL‐treated bacteria on selective agar diminish survival compared to similarly treated bacteria inoculated and enumerated on nonselective agar plates. Conclusions: Critical inter‐related factors affecting the effective and repeatable in vitro decontamination performance of PL were identified during this study that will aid further development of this athermal process technology for applications in health care and in industry. Very rapid reductions (c. 7 log₁₀ CFU cm^?2 within ≤10 pulses) occurred using discharge energy of 20 J for all tested clinically relevant bacteria under study when treated at 8 cm distance from xenon light source. While no resistant flora is expected to develop for treatment of microbial pathogens on two‐dimensional surfaces, careful consideration of scale up factors such as design and operational usage of this PL technique will be required to assure operator safety. Significance and Impact of the Study: Findings and conclusions derived from this study will enable further development and optimization of this decontamination technique in health care and in food preparation settings, and will advance the field of nonthermal processing technologies.     

Detection of clinically relevant point mutations by a novel piezoelectric biosensor

Piezoelectric sensing is here applied to point mutation detection in human DNA. The mutation investigated is in the TP53 gene, which results inactivated in most cancer types. TP53 gene maps on chromosome 17 (17p13.1). It contains 11 exons and codifies for the relative protein, involved in cell proliferation. The TP53 gene has a wide mutation spectrum that is related to different tumours. In particular, those occurring in the structurally important L2 and L3 zinc-binding domains, have been linked to patient prognosis and more strongly to radiotherapy and chemotherapy resistance in several major cancers. For this reason, the identification of these mutations represents an important clinical target and biosensors could represent good candidate for fast mutation screening. In this paper, a DNA-based piezoelectric biosensor for the detection of the TP53 gene mutation at codon 248 is reported. A biotinylated probe was immobilised on the sensor surface via dextran-streptavidin modified surfaces. The sensor was optimised using synthetic oligonucleotides. Finally, the sensor system was successfully applied to polymerase chain reaction (PCR)-amplified real samples of DNA extracted from two cell lines, one normal (wild-type) and one mutated, carrying the mutation at codon 248 of the TP53 gene. The results obtained demonstrate that the DNA-based piezoelectric biosensor is able to detect the point mutations in PCR-amplified samples showing the potentialities of this approach for routine analysis.     

Effects of a novel medial meniscus implant on the knee compartments: imaging and biomechanical aspects

Biomechanics and Modeling in Mechanobiology - The altered biomechanical function of the knee following partial meniscectomy results in ongoing articular cartilage overload, which may lead to...     

Structural basis of antigen mimicry in a clinically relevant melanoma antigen system

Although mimics of human tumor antigens are effective immunogens to overcome host unresponsiveness to the nominal antigen, the structural basis of this mimicry remains poorly defined. Therefore, in this study we have characterized the structural basis of the human high molecular weight-melanoma-associated antigen (HMW-MAA) mimicry by the mouse anti-idiotypic (anti-id) monoclonal antibody (mAb) MK2-23. Using x-ray crystallography, we have characterized the three-dimensional structure of the anti-id mAb MK2-23 Fab' and shown that its heavy chain complementarity-determining region (CDR3) (H3) and its light chain CDR1 (L1) are closely associated. These moieties are the source of HMW-MAA mimicry, since they display partial amino acid sequence homology along with a similar structural fold with the HMW-MAA core protein. Furthermore, a 15-residue peptide comprising the H3 loop of anti-id mAb MK2-23 demonstrates HMW-MAA-like in vitro and in vivo reactivity. This peptide in conjunction with the structural data will facilitate the characterization of the effect of the degree of antigen mimicry on the induction of a self-antigen-specific immune response by a mimic.     

Refinement of a thyroid cultured cell system used in clinically relevant bioassays

Thyroid cultured cells are now used worldwide in clinical bioassays of TSH and of thyroid autoantibodies. Having originally developed the thyroid cell cultures (Ambesi-Impiombato et al. 1980) from rat glands in our laboratory, we now aim to improve the system, moving in two directions: a) TSH-independent mutants have been produced and characterized, which can be used in clinical bioassays without starvation from the hormone. b) Human cultures have been attempted using our experience with rat cells, as well as innovative strategies. Preliminary results now indicate that human normal differentiated cells may be available for clinical studies in vitro, when species-specific differences may be critical.