Mean Value Of Resistance Research Articles

Effect of two Preparation Designs and Methods of Construction on the Fracture Resistance of Glass Ceramics Laminate Veneers

Purpose: To evaluate the effect of marginal finish line design and fabrication techniques on the fracture resistance of lithium disilicate laminate veneer. Materials and methods: A total of 24 veneers were designed, constructed, and divided into two main groups according to preparation design Chamfer 0.3 mm finish line (n=12) and, Chisel finish line (n=12). Each group was then divided into two subgroups according to the technique of veneer construction, veneers constructed by (CAD/CAM system) out of e max CAD blocks (n=6), and veneers constructed by (press on technology) using e max press ingots (n=6). then the veneers bonded to corresponding epoxy resin dies using resin cement. Finally fracture resistance test was done for all specimens using universal testing machine. Results: The highest fracture resistance values were recorded in the group of chisel marginal design fabricated by CAD/CAM technique. The lowest fracture resistance values were recorded in the group of 0.3mm chamfer margin design fabricated by Press technique. Regardless to margin design there was a significant difference between both processing techniques as indicated by two-way ANOVA test (p=0.0178 Press). Irrespective of material type it was found that margin design significantly influenced mean as indicated by two-way ANOVA test (p=0.0001 0.05). It was found that the Chamfer margin design recorded statistically significant higher fracture resistance mean value with CAD/CAM group (245.85±56.37N) than Press group (129.71±19.49 N) as indicated by unpaired t-test (P=0.002<0.05) Conclusions: The technique of fabrication of ceramic laminate veneer restorations has a crucial effect on its performance with the regard to fracture resistance. IPS e.max CAD could be considered as a valid restoration than IPS e.max press.

Impact of Access Cavity Design and Root Canal Taper on Fracture Resistance of Endodontically Treated Teeth: An Ex Vivo Investigation

IntroductionThe susceptibility of endodontically treated teeth (ETT) to fracture is mainly associated with the loss of tooth structure. This study evaluated the effect of the access cavity design and taper preparation of root canals on ETT fracture resistance of maxillary molars. MethodsFor tapering assessment, 30 sound distobuccal roots of maxillary molars were randomly assigned to 1 of 3 groups (n = 10): a .04 taper, a .06 taper, or a .08 taper. Endodontic canal preparations were performed using the Twisted Files rotary system (Kerr Co, Glendora, CA). In addition, 48 intact maxillary first and second molars were randomly assigned to 1 of 3 groups (n = 16) for cavity preparation approaches: intact teeth, traditional access cavity (TAC), or conservative access cavity (CAC). Fracture resistance was tested using a universal testing machine. For statistical analysis, the level of significance was P ≤ .05. ResultsThe .04 taper instrumentation had the highest fracture resistance (259.61 ± 52.06), and the .08 taper had the lowest (168.43 ± 59.63). The .04 and .06 groups did not differ significantly (P > .05); however, these groups differed significantly from the .08 group (P ≤ .05). Regarding the cavity preparation approaches, the 3 groups of intact teeth, CAC, and TAC showed fracture resistance mean values of 2118.85 ± 336.97, 1705.69 ± 591.51, and 1471.11 ± 435.34, respectively, with no significant difference between the CAC and TAC groups (P > .05). ConclusionsIncreasing the taper of the root canal preparation can reduce fracture resistance. Moreover, access cavity preparation can reduce resistance; however, CAC in comparison with TAC had no significant impact.

Fracture resistance of thin occlusal veneers made from hybrid ceramic (Cerasmart) -In vitro study

Statement of the problem: Occlusal veneers represent a conservative alternative to traditional restoration for restoring tooth wear. However, the ability of occlusal veneers with thin (reduced) thickness using hybrid ceramics to withstand masticatory forces in the posterior area is not yet known. Purpose: the purpose of this in vitro study was to evaluate the fracture resistance of thin occlusal veneers made from hybrid ceramic (Cerasmart). Materials and methods: Twelve human first maxillary molars were used in this study collected from patients with untreatable periodontal problems (grade III mobility); Teeth were chosen to be free from any caries, defects or Cracks. (n= 12) Teeth were prepared to receive Cerasmart occlusal Veneers with 1.8 mm thickness at the cusp tip and 1.2 mm at the central groove. A standardized tooth preparation was applied to all specimens using CNC milling machine, with anatomical occlusal surface preparation with 1 mm ferrule and 1mm deep chamfer finish line. Then occlusal veneers were fabricated by CAD/CAM milling using The CEREC AC system. Then all occlusal veneers were checked over their corresponding teeth for Seating. Then cementation using Re1yXTM Unicem (dual cure self-adhesive resin cement). All samples were subjected to thermo-cycling for 1000 cycle, and cyclic loading for 25,000 cycles. The samples testing was done by compressive mode using a universal test machine along the long axis of the occlusal veneers using load applicator in the form of metallic rod with rounded end (5 mm diameter). Data were collected, tabulated and statistically analyzed. RESULTS: The mean values and standard deviation of fracture resistance (N) measured by fracture resistance test as a function of restoration thickness. It was found that occlusal veneers with a thickness of 1.2 and 1.8 mm recorded fracture resistance mean value (1743.7± 387N). CONCLUSIONS: Within the limitations of present in vitro study, Hybrid ceramic thin occlusal veneers with a thickness of (1.2 and 1.8 mm) can withstand the masticatory forces in the posterior area, which providing a conservative treatment for tooth wear.

Fracture Resistance of A Newly Proposed Occlusal Veneer Design Using Two Different CAD/CAM Ceramic Materials

Statement of the Problem: Management of severe occlusal erosive lesions constitutes a challenging therapeutic approach to the restorative dentist. Bonded occlusal veneers have been introduced as a conservative solution to traditional onlays or complete coverage crowns. Still, there is lack of information and conflict in the data concerning the mechanical performance of the occlusal veneer materials and designs.Purpose: The purpose of this in vitro investigation was to evaluate and compare the fracture resistance and failure mode of a newly proposed occlusal veneer design constructed of zirconia reinforced lithium silicate and hybrid ceramic materials with the conventional design restored with the same tested materials.Materials and Methods: Two mandibular first molars of a typodont were chosen to perform the master preparations; one for the conventional planar occlusal veneer design, and the second for the proposed modified design which consisted of occlusal veneer preparation with circumferential chamfer finish line and two shallow proximal slots. Ten elastomeric impressions were taken for each design using the putty and light polysiloxane addition silicone impression material. The twenty impressions were poured using type IV dental stone to produce twenty stone casts, ten for each design. Each group of stone casts was subdivided randomly into two equal subgroups according to the ceramic material to be tested; the zirconia reinforced lithium silicate “Celtra Duo” and the hybrid resin nano ceramic “Lava Ultimate”. All the occlusal veneers were fabricated using the CAD/CAM Cerec InLab SW 4.2.5 System. The veneers were then checked on both the stone casts and the master preparation on the typodont for perfect seating, after the Celtra veneers were crystallized and glazed and the Lava veneers being subjected to finishing and polishing. The preparations were duplicated to obtain twenty epoxy casts over which the occlusal veneers were adhesively cemented using a standard bonding protocol. The samples were then subjected to thermal cycling program. All the samples were individually mounted on the Instron testing machine with a loadcell of 5 KN and fracture test was done by compressive mode of load applied occlusally using a metallic rod with spherical tip (5.6 mm diameter) at cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and tabulated to be statistically analyzed. The fractured specimens were examined to detect the mode of failure. Results: Regardless of the ceramic type, the modified occlusal veneer design showed statistically significant higher fracture resistance mean value (1106.0 N) than conventional design (957.6 N) at P ≤ 0.05. Irrespective of the design, the Lava Ultimate revealed higher statistically significant fracture resistance mean value (1114.1 N) than Celtra (949.5 N) at P ≤ 0.05. The Celtra veneers showed higher fracture resistance mean value (1016.9N) with the conventional design than the modified design (882.2 N), the difference was statistically significant at P ≤ 0.05. While the lava veneers presented higher statistically significant fracture resistance mean value with the modified design (1329.9 N) than the conventional design (898.3 N) at P ≤ 0.05. All the specimens exhibited cracks limited to the veneer material, except one revealed catastrophic failure.Conclusions: 1- The modified occlusal veneer design offered promising results as far as fracture resistance is concerned particularly with the nano-hybrid ceramic which presented the highest statistically significant fracture resistance mean values.2- The conventional planar occlusal veneer design proved to be superior with zirconia lithium silicate ceramic (ZLS) as it presented highly significant fracture resistance mean values than with the modified design.3- Both the conventional and modified occlusal veneer designs presented fracture resistance mean values with the two tested materials “Celtra and Lava Ultimate” that exceed the range of clinical acceptability.4- Rating of the tested occlusal veneers according to their fracture resistance mean values is as follows: the highest for the Lava Ultimate with the modified design, followed by Celtra Duo with conventional design, then Lava Ultimate with conventional design and Celtra Duo with modified design.5- It can be recommended that in cases with increased occlusal stresses, Lava Ultimate occlusal veneer with the modified design be the first choice, followed by the Celtra Duo with the conventional design as a second choice.

Investigation on Performance of No-Insulation Coil Considering the Influence of Stress Distribution on Radial Characteristic Resistivity

The no-insulation (NI) winding technique is a useful approach in high field magnets. As the operation current can pass through adjacent turns, radial characteristic resistance (including the resistance of stabilizer layer, substrate layer and turn-to-turn contact surface) becomes a decisive factor influencing the NI magnet's thermal stability and excitation delay behavior of NI magnet. Radial characteristic resistivity is mainly affected by the tape material and turn-to-turn contact stress. However, stress distribution in most design examples is scarcely considered, and a mean resistivity obtained through an experimental test is often used. To facilitate the NI magnet's realization of faster charging and lower excitation loss, a nonuniform winding prestress method is proposed to adjust the radial resistivity while maintaining the coil's mechanical stability. This paper investigates the pretightening force, thermal stress, and electromagnetic force in the process of manufacturing, cooling, and excitation of a high-temperature superconducting NI magnet. A distribution of the radial resistivity is obtained considering the varying tendency of radial resistivity under changing stress. An equivalent circuit model and finite element model are applied to analyze the NI coil's excitation characteristics. The results are compared with the mean resistivity value model and provide a theoretical basis for NI magnet design.

Electrical Impedance to Assess Facial Nerve Proximity During Robotic Cochlear Implantation.

Reported studies pertaining to needle guidance suggest that tissue impedance available from neuromonitoring systems can be used to discriminate nerve tissue proximity. In this pilot study, the existence of a relationship between intraoperative electrical impedance and tissue density, estimated from computer tomography (CT) images, is evaluated in the mastoid bone of in vivo sheep. In five subjects, nine trajectories were drilled using an image-guided surgical robot. Per trajectory, five measurement points near the facial nerve were accessed and electrical impedance was measured (≤1 KHz) using a multipolar electrode probe. Micro-CT was used postoperatively to measure the distances from the drilled trajectories to the facial nerve. Tissue density was determined from coregistered preoperative CT images and, following sensitivity field modeling of the measuring tip, tissue resistivity was calculated. The relationship between impedance and density was determined for 29 trajectories passing or intersecting the facial nerve. A monotonic decrease in impedance magnitude was observed in all trajectories with a drill axis intersecting the facial nerve. Mean tissue densities intersecting with the facial nerve (971-1161 HU) were different (p <0.01) from those along safe trajectories passing the nerve (1194-1449 HU). However, mean resistivity values of trajectories intersecting the facial nerve (14-24 Ωm) were similar to those of safe passing trajectories (17-23 Ωm). The determined relationship between tissue density and electrical impedance during neuromonitoring of the facial nerve suggests that impedance spectroscopy may be used to increase the accuracy of tissue discrimination, and ultimately improve nerve safety distance assessment in the future.

Seasonal and inter-annual variability of the Bowen smith ratio over a semi-arid grassland in the Chinese Loess Plateau

Energy partitioning between grassland sensible (H) and latent (LE) heat fluxes is critical in determining boundary layer development, the hydrological cycle, weather and climate. In this report, we describe the seasonal and inter-annual variability of the Bowen ratio (β) over semi-arid grassland of the Loess Plateau in the north boundary belt of the summer monsoon of China. β was directly measured by an eddy covariance system over a 6-year period (2007–2012), during which the studied grassland experienced a large range in precipitation, extending from 555.5 mm (2007) to 262.8 mm (2011). The annual Bowen ratio (βa) based on annual energy budgets ranged from 0.90 (2007) to 1.93 (2011) with an annual mean value of 1.32, while the annual midday (10:00–16:00 GMT + 8) β ranged from 2.07 (2007) to 4.19 (2011) with an annual mean value of 3.02. The mean midday β during the dry years (3.66, 2009, 2010 and 2011) was higher than that observed during the wet years (2.39, 2007, 2008 and 2012). The 6-year annual mean values of the bulk surface resistance (Rs), aerodynamic resistance (Ra) and climatological resistance (Ri) varied from 272.27 to 410.10 s m−1, 31.62–34.89 s m−1 and from 64.5 to 87.13 s m−1, respectively, with annual mean values of 337.08, 32.83 and 73.05 s m−1, respectively. The normalized difference vegetable index (NDVI) had a direct influence on β as mediated by Rs, and there was a logarithmic function between ET/ETeq and Rs in the semi-arid grassland. A positive trend between β and the surface resistance (Rs*) normalized by the climatological and aerodynamic resistance was observed at this site. Moreover, the annual effective precipitation frequency was significantly related to the midday β during the growing and non-growing seasons, which indicated that the annual effective precipitation, not the annual precipitation, indirectly affected the annual β through its effect on the shallow soil water content (SWC). The results suggested that inter-annual variations in β was primarily controlled by an annual effective precipitation frequency and seasonal variations in β was directly affected by NDVI as mediated by Rs over the semi-arid grassland in the Chinese Loess Plateau.

The effect of recasting on the Fatigue resistance of Co-Cr alloys

The present study evaluated the effect of recasting cobalt-chromium alloys with the addition of new alloy in different ratios (75% and 50%) on the deflection fatigue resistance using three types of alloys: Wironit (Bego), Remanium (Dentaurum), and Wisil (Wipla). Each alloy was divided into three groups for each test, group I (100% new alloy), group II (75% new alloy +25% recast alloy), and group III (50% new alloy + 50% recast alloy).Fatigue specimens produced were butterfly-shaped and half round at their cross section with 18mm length, 1mm thickness, and 2mm width. For each alloy group, five samples were prepared.The results of this study revealed that recasting with adding 75% new alloy did not significantly affect the fatigue resistance of Wironit and Wisil alloys, while significantly affected that of Remanium. Recasting with the addition of 50% new alloy significantly decreased the fatigue resistance of the three types of alloys.Wironit alloy showed the higher mean values for deflection fatigue resistance compared with Remanium and Wisil alloys.

Electrical resistivity method for groundwater exploration: A case study of ganori village area, Aurangabad District, Maharashtra, India

An attempt is made by geophysical surveys involving VES to depict the fracture zones. A total of twelve VES were established in the part of Ganori village of Aurangabad district, Maharashtra to identify the groundwater potential zones. The quantitative interpretation of the VES curves involves the IX1D technique. The resistivity values and subsurface thickness of first layer is represents the top soil and has a mean resistivity value of 10 meters with mean thickness 0.5 ohm-m. The second layer has a mean resistivity of 21ohm-m to 30 ohm-m with means thickness 5 to 10 meters. This layer represents a murumatic, weathered/fractured rock basement. The third layer has means resistivity of30 ohm-m to 35ohm-m and a mean thickness 30m to 50 meters. This layer represents the Amygdaloidal basalt/zeolitic rocks. Four layers were obtained in three vertical electrical soundings and only VES with a resistivity value 0f 50 ohm-m to 105ohm-m and mean thickness 35 m and below hard Trap devoid of joints and fractures rock in the study area.

Fracture resistance of simulated immature teeth reinforced with different composites after root-end closure

Purpose The purpose of this study was to evaluate fracture resistance of simulated immature teeth reinforced with different bulk-fill flowable composite resin; Smart dentine replacement (SDR) or Filtek bulk-fill flowable (FBF) after application of two apical plug materials; mineral trioxide aggregate (MTA), or Biodentine (BD). Patients and methods Fifty human central incisors with nearly similar dimensions were used. Teeth were sectioned 3 mm above and 10 mm below cement–enamel junction to simulate immature apex. Root canal (RC) instrumentation was done using ProTaper rotary system up to F5; simulations of immature roots were carried out using Peeso-reamers from #1 to #4. Teeth were divided randomly into five groups (n = 10), group 1 (control): received no filling material, group 2: MTA/SDR, group 3: MTA/FBF, group 4: BD/SDR, and group 5: BD/FBF. In the experimental groups, MTA or BD was placed in the apical 4 mm of RCs. The remaining part of RCs was back-filled with composite resins. A load was applied on the palatal surface of teeth at 135° to their long axis until fracture using universal testing machine. Load was recorded in Newton and data were analyzed using one-way analysis of variance at a significant level of P less than or equal to 0.05. Results Group 4 exhibited the highest fracture resistance mean value followed by groups 2, 5, and 3, whereas control group exhibited the lowest value. A statistical significant difference between SDR and FBF groups was recorded, whereas there was no statistical significant difference between MTA and BD groups. Conclusion Using either MTA or BD as an apical plug material with bulk-fill flowable composite resins in simulated immature teeth enhances their fracture resistance. SDR provided better resistance to fracture than FBF.

Fuzzy constrained Lp-norm inversion of direct current resistivity data

We evaluate the use of a fuzzy c-means clustering procedure to improve an inverted 2D resistivity model within the iterative error minimization procedure. The algorithm is coded in MATLAB language for the Lp-norm inversion of 2D direct current resistivity data and is referred to as fuzzy constrained inversion (FCI). Two additional input parameters are required to be provided by the interpreter: (1) the number of geologic units in the model (i.e., the number of clusters) and (2) the mean resistivity values of each geologic unit (i.e., cluster center values of the geologic units). The efficacy of our approach is evaluated by tests carried on the synthetic and field electrical resistivity tomography (ERT) data. Inversion results from the FCI algorithm are presented for conventional L1- and L2-norm minimization techniques. FCI indicates improvement over conventional inversion approaches in differentiating the geologic units if a proper number of the geologic units is provided to the algorithm. Inappropriate clustering information will affect the resulting resistivity models, particularly conductive geologic units existing in the model. We also determine that FCI is only effective when the observed ERT data can recognize the particular geologic units.

Reduction of the frequency of herbaceous roots as an effect of soil compaction induced by heavy grazing in rangelands of SW Spain

Rangelands in SW Spain constitute the most extensive ranching system on the Iberian Peninsula. During the last few decades, a significant increase in livestock numbers, along with a progressive substitution of cattle for sheep, have led to land degradation processes such as the reduction of grass cover and increased soil compaction in heavily grazed areas. Nevertheless, a better understanding of how soil compaction affects grass production is still needed. In this study, some of the effects of soil compaction due to heavy grazing are analysed, mainly the reduction of the frequency of herbaceous roots and its relationships with bulk density and soil penetration resistance. The study was carried out in 22 fenced areas grazed under different intensities (animal stocking rates: 0.19–15.76AUha−1). Undisturbed soil core and bulk samples were collected at 3 depth intervals in order to determine select soil properties (texture, organic matter content, and bulk density). Additionally, soil penetration resistance was quantified at 890 random points at different depths and soil moisture contents. Frequency of herbaceous roots was estimated for each soil horizon in 47 soil profiles and categorized into 4 classes: none, few, common and many. Results showed negative relationships between bulk density (>10cm depth) and the content of soil organic matter from 0 to 5cm (r=−0.061, p<0.05) and 5–10m depth (r=−0.824, p<0.005). Furthermore, a tendency for decreasing mean values of soil penetration resistance as the frequency of herbaceous roots increased was also observed. The values observed confirm that soil compaction provoked by an excessive number of animals reduced the quantity of herbaceous roots. The value of 2MPa traditionally accepted as restrictive for root growth is discussed. Findings presented here could be of interest for policy makers and farm owners to guide decisions about optimum animal stocking rates.

FRACTURE RESISTANCE AND FAILURE MODE OF TWO RESTORATION DESIGNS MADE OF MONOLITHIC HYBRID AND GLASS MACHINABLE CERAMICS ; IN VITRO STUDY

Statement of the problem: Monolithic hybrid and glass ceramics are indicated for intracoronal and extracoronal ceramic restorations. Available data regarding selection of the appropriate ceramic type for each preparation design and its influence on fracture resistance of tooth restoration complex is still scarce.Purpose: The purpose of this study was to evaluate in vitro the fracture resistance and investigate failure mode of two restoration designs (crowns and inlays) made from lithium disilicate glass ceramic and hybrid ceramic constructed by the CAD /CAM technique.Materials and Methods: A total of twenty ceramic restorations restoring lower molars were designed and fabricated in this study. The restorations were divided into two groups; Group 1: Ten full coverage crowns and Group 2: Ten inlays. Each of the previous groups was further subdivided into two equal subgroups; Subgroup 1: Five restorations constructed from lithium disilicate glass ceramics (e.max CAD) and Subgroup 2: Five restorations constructed from hybrid ceramic (VITA ENAMIC) by the CAD/CAM technology. Two ivorine teeth were prepared following the guidelines for full coverage and inlay ceramic restorations, they were duplicated into stone dies followed by scanning, designing and milling of restorations. The stone dies were duplicated into epoxy dies where the restorations were adhesively cemented on them. All cemented samples were exposed to 2000 thermal cycles (5°C and 55°C in water) with a dwell time of 25 seconds in a computer controlled thermocycler. All specimens were loaded in a universal testing machine where fracture test was done by compressive mode of load applied occlusally using a metallic rod with round tip at cross-head speed of 1mm/min until fracture occurred. Fracture resistance values were recorded in Newtons then they were statistically evaluated and failure modes were analyzed. Results: For group 1 representing crown restorations, a statistically significant difference was found between (e.max CAD) and (VITA ENAMIC) subgroups at (p=0.05) where the highest mean value of maximum load was found in (VITA ENAMIC) (951.77 N ± 81.05) and the lowest mean value of maximum load was found in (e.max CAD) (709.35 N± 49.51). While for the second group representing inlay restorations, no statistically significant difference was found between (e.max CAD) and (VITA ENAMIC) subgroups at (p=0.307) where the highest mean value of maximum load was found in (e.max CAD) (627.71 N ± 80.01) and the lowest mean value of maximum load was found in (VITA ENAMIC) (581.26 N± 51.74). For the e.max CAD subgroup, a statistically significant difference was found between (Crown) and (Inlay) groups at (p=0.005) where the highest mean value of maximum load was found in the crown group (790.35 N± 49.51) and the lowest mean value of maximum load was found in the inlay group (627.71N ± 80.01).Regarding the VITA ENAMIC subgroup, a statistically significant difference was found between (Crown) and (Inlay) groups at (p<0.001) where the highest mean value of maximum load was found in the crown group (951.77 N ± 81.05) and the lowest mean value of maximum load was found in the inlay group (581.26N±51.74).Conclusions: 1. All inlays and crowns constructed from hybrid and glass ceramics in this study revealed fracture load values falling in the range of physiologic masticatory forces 2. When considering restoration of molars with full coverage crowns, VITA ENAMIC is more preferred than e.max CAD ceramic in terms of fracture resistance as it showed a higher statistical significant mean values.3. When planning to restore molars with minimally invasive intracoronal restorations, both ceramics can be used as there was insignificant statistical difference between them , however e.max CAD can be recommended due to its more favorable mode of fracture compared to VITA ENAMIC.4. Irrespective of preparation designs, both ceramics showed insignificant difference regarding fracture resistance mean values.

Aerobic exercise training modulates biochemical parameters in type 2 diabetic patients with chronic hepatitis C

Introduction:Recent studies suggested that Hepatitis C Virus (HCV) patients may suffer from insulin resistance (IR), lipid profile abnormalities and poor virological response to the antiviral treatment. The beneficial effects of aerobic exercise have been a matter of controversy in the field of HCV management.This study aimed to measure the impact of aerobic exercise training on insulin resistance, lipid profile abnormalities and virological response in type 2 diabetic patients with chronic hepatitis C.Material and Methods:Eighty non-hypertensive, non-cirrhotic chronic HCV infection Saudi patients with high Triglycerides (TG), Total cholesterol (TC) and Low Density Lipoprotein Cholesterol (LDL-c) & non-insulin dependent diabetic with insulin resistance. Patients were divided in to two equal groups. The first group received aerobic exercise training, three sessions per week for three months in addition to their antiviral treatment. The second group (B) received only their antiviral treatment.Results:The mean values of Homeostasis Model Assessment-Insulin Resistance- index (HOMA-IR), TC, LDL-c, TG, virologic response and Body Mass Index (BMI) were significantly decreased in group (A), where the mean value of High Density Lipoprotein Cholesterol (HDL-c) was significantly increased, while there were no significant changes in group (B) Also; there was a significant difference between both groups at the end of the study.Conclusions:Treadmill walking exercise training is an effective treatment policy to improve insulin resistance, lipid profile abnormalities and virological response in type 2 diabetic patients with chronic hepatitis C.

A randomized comparative trial of OTSC and Padlock for upper GI hemostasis in a standardized experimental setting

Introduction: Upper gastrointestinal bleeding (UGIB) is the key emergency situation in clinical endoscopy and is traditionally treated with injection, thermal or through the scope clipping therapy. Mortality rates are in the range of 8–10% and demand new treatment approaches. The Over-The-Scope Clip (OTSC®) has been described as a very effective hemostatic device in UGIB. We compared OTSC with the Padlock™ device in an established pre-clinical setting.Material and methods: Our test-bed consisted of the biohybrid EASIE model using soft silicone tubes, tunneled into the gastric wall and surfacing at a mucosa defect, representing the bleeding site. After successful deployment of the OTSC and Padlock devices on the spurting ulcer bleed (Forrest Ia) the vessel tubes were pressurized with a manometer to 120 mmHg. Tight closure at this pressure was defined as successful hemostasis (primary endpoint). N = 11 procedures were done with each device. Statistical testing was done using Fisher’s exact test. Sample size was adjusted to an assumed α-error of 5% (two-sided test) and a power of 80%.Results: Technically correct placement of the respective hemostatic device was achieved in all procedures. A statistically significant difference was found in the primary endpoint. In OTSC the success proportion was 100%; 11/11 (95% KI 74.1% to 100%); in Padlock it was 0%; 0/11 (95% KI 0%–25.8%). This means that no bleeding was stopped by Padlock. The mean value of perfusion pressure resistance was 300 mmHg (cut-off) for OTSC and 9.2 ± 8.4 mmHg for Padlock.Discussion: Our data on hemostatic function of OTSC coincide with the clinical literature and earlier pre-clinical studies in the EASIE model, which is widely accepted as a realistic and effective simulation system for clinical conditions. The inability of Padlock to stop hemorrhage may be due to design differences and, thus, its limitation in providing tight sealing of the clipped tissue.Conclusion: Different types of endoscope-tip mounted clips have different performances. OTSC consistently stops simulated spurting bleeding, Padlock fails to do so. These differences are statistically significant.

Influence of sodium chloride content in electrolyte solution on electrochemical impedance measurements of human dentin.

The aim of this study was to investigate the influence of sodium chloride (NaCl) content in electrolyte solution on electrochemical impedance measurements of human dentin by employing electrochemical impedance spectroscopy. Dentin samples were prepared from extracted molars. Electrochemical impedance measurements were carried out over a wide frequency range (0.01Hz-10MHz). After measurements, samples were characterized using scanning electron microscopy. Electrochemical impedance measurements showed that the mean values of dentin electrical resistance were 4284, 2062, 1336, 53 and 48kΩ at different NaCl contents in electrolyte solution. One-way ANOVA test of mean values of dentin electrical resistance revealed a significant difference (P < 0.0001) as a function of NaCl content in electrolyte solution. Comparing electrical resistance values of dentin samples at 0.05% w/v and 0.9% w/v concentrations were found to be significantly different (P < 0.05 at 95% confidence level). Scanning electron microscopy revealed structure of dentin sample with intertubular dentin matrix and distribution of patent dentinal tubules. This in vitro study indicated, through electrochemical impedance spectroscopy measurements, that electrical resistance of dentin was affected by the concentration of NaCl in electrolyte solution. It is clear from the current study that NaCl concentration in electrolyte solution has a marked influence on dentin electrical resistance. Therefore, this baseline data need to be considered in any future study on dental samples.

A Comparative Evaluation of Fracture Resistance of Endodontically Treated Teeth restored with Composite Resin Core using Two Different Designs of Prefabricated Metal Posts: An in vitro Study

ABSTRACTAimTo comparatively evaluate the fracture resistance of endodontically treated teeth restored with light-cured composite resin core using two different designs of prefabricated metal posts.Materials and methodsA total of 30 single-rooted anterior teeth were selected for the study and endodontically treated. Teeth were sectioned 2 mm above the cementoenamel junction and were randomly divided into two groups (n = 15). Teeth in group I were restored with Parallel post—EG post and group II with parallel post with coronal flare—i post. Light-cured composite core buildup was done in all samples using a customized core former. Compressive load was applied at a 135° angle to the long axis of the tooth at a cross-head speed of 1 mm/minute until visible signs of fracture were observed. Levene's test and t-test were used to determine the difference of the failure loads between the groups (α = 0.05).ResultsThe mean values (standard deviation [SD]) for fracture resistance were 295.55 N and 469.59 N for parallel post—EG post and parallel post with coronal flare—i post respectively. Since the p-value for thet-test is less than 0.05, it indicates that we should reject null hypothesis and conclude that the mean fracture load of parallel post with coronal flare—i post is significantly more than that of mean fracture load of parallel post—EG post.ConclusionThe study conducted evaluated that the fracture resistance of endodontically treated teeth with parallel post with coronal flare—i post and core buildup had better strength as compared with parallel post—EG post and core buildup.Clinical significanceThe present study will help the clinician to select the appropriate prefabricated metal post that will fit exactly into the coronal flare of the canal improving clinical performance, thus increasing the longevity of the restoration.How to cite this articleGaikwad AM, Shah N, Ram SM. A Comparative Evaluation of Fracture Resistance of Endodontically Treated Teeth restored with Composite Resin Core using Two Different Designs of Prefabricated Metal Posts: Anin vitroStudy. J Contemp Dent 2017;7(2):97-102.

FRACTURE RESISTANCE OF CAD/CAM FABRICATED IMPLANT - SUPPORTED ALL - CERAMIC CROWNS CEMENTED ON READY AND CUSTOM MADE ZIRCONIA ABUTMENTS

Statement of the problem: Despite their outstanding esthetic characteristics, the adequacy of implant-supported all-ceramic crowns under occlusal loads in the posterior segment of the jaw remains questionable. Aim of the study: Evaluation of the fracture resistance of different CAD/CAM fabricated implant-supported all-ceramic monolithic posterior crowns cemented on ready and custom made zirconia abutments. Materials and methods: 30 internal connection titanium dummy implants were embedded in epoxy resin and randomly divided into three groups (n=10 each) according to the crown material used; Group I: Polycrystalline ceramic (Katana Zirconia), Group II: Hybrid ceramic (Vita Enamic) and Group III: Lithium disilicate glass ceramic (IPS e.max CAD).All crowns were CAD/CAM fabricated as monolithic maxillary right first premolar.In each group, five crowns were cemented on ready made zirconia abutments (subgroup A) while the other five were cemented on custom made zirconia abutments (subgroup B). All samples were thermocycled (5o to 55o,10 seconds dwell time) then compressively loaded under axial static load till fracture using a universal testing machine with a loadcell of 5 kN at a cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and failure modes were visually analyzed. Statistical analyses were performed by Two-way ANOVA and Tukey’s post-hoc test.( P ≤ 0.05)Results: Fracture resistance of implant-supported all-ceramic monolithic posterior crowns was statistically significantly affected by the ceramic crown material and abutment type (P<0.001). Either with ready or custom-made zirconia abutments; zirconia crowns recorded the statistically significantly highest fracture resistance mean value followed by IPS e.max CAD ones while Vita Enamic crowns recorded the lowest values with no statistically significant difference between them and IPS e.max CAD crowns. Zirconia and Vita Enamic crowns cemented on custom made abutments recorded statistically significantly higher mean fracture resistance values than those cemented on ready made one. However, IPS e.max Cad crowns cemented on both abutment types showed statistically insignificant difference. Different failure modes were observed among the tested ceramic crowns without fracture of any abutment.Conclusions: All tested implant-supported all-ceramic monolithic posterior crowns cemented on ready and custom made zirconia abutments had the potential to withstand the physiologic occlusal forces in the premolar region with the superiority of the zirconia crowns cemented on custom made zirconia abutments.

INFLUENCE OF COBALT CHROMIUM FRAMEWORK FABRICATION TECHNIQUES ON MARGINAL ACCURACY AND FRACTURE BEHAVIOR OF IMPLANT-SUPPORTED METAL CERAMIC BRIDGES

Statement of problem: Marginal fit and structural integrity are keys for long term success of implant supported restorations. Little information is available regarding precision of marginal adaptation and fracture behavior of implant supported metal ceramic bridges with recently introduced milled Cobalt Chromium frameworks. Aim of the study: Evaluation of marginal accuracy (before and after porcelain application) and fracture resistance of implant supported metal ceramic bridges with Cobalt Chromium (Co-Cr) frameworks fabricated using the new computer aided designing /computer aided manufacturing (CAD/CAM, soft milling/post sintering) technique in comparison to the conventional casting technique.Materials & Methods: A total of 10 epoxy resin models were constructed into which two titanium dummy implants were inserted in each model and received straight titanium abutments. 10 Co-Cr cement retained frameworks were fabricated on the implant models, 5 with the new CAD/CAM soft milling/ post sintering technique (group I) and the other 5 with the lost wax casting technique (group II). All frameworks were veneered with porcelain by the layering technique. Vertical marginal gap distance between the Co-Cr frameworks and the implant abutments was measured using a stereo microscope at 16 predetermined points/abutment before and after porcelain application. Then metal ceramic bridges were cemented onto their corresponding abutments with temporary resin cement. Samples were loaded compressively under static vertical load till fracture in a universal testing machine with a loadcell of 5 kN at a cross-head speed of 1 mm/min. The load required to fracture was recorded in Newton. Fracture modes of all samples were visually analyzed. Data were statistically analyzed using the repeated measures ANOVA test for vertical marginal gap distance results (P 0.05). Bridges with CAD/CAM fabricated frameworks recorded the lowest statistically insignificant vertical marginal gap distance mean value before porcelain application (24.63±4.27µ), while those with cast frameworks recorded the highest statistically insignificant vertical marginal gap distance mean value after porcelain application (25.21±7.08µ). Implant supported metal ceramic bridges with cast frameworks showed higher fracture resistance mean value (1608.56±215.04 N) than those with CAD/CAM fabricated frameworks (1392.73±160.75 N), the difference between groups was statistically insignificant as indicated by Student’s t -test (P >0.05). Conclusions: CAD/CAM soft milled/post sintered Co-Cr frameworks may be considered promising alternative to conventional cast frameworks for implant supported metal ceramic bridges in terms of marginal accuracy and fracture resistance.

State feedback control for DC-photovoltaic systems

This paper proposes an alternative state feedback-based control strategy to a DC–DC converter applied to regulation purposes in photovoltaic (PV) systems. The PV generation voltage output level is determined through a maximum power point tracking (MPPT) algorithm. Moreover, the proposed control technique also provides a suitable duty-cycle for the switching of the DC–DC converter to improve its dynamics with regards the reference voltage generation, provided by the MPPT algorithm. The control technique relies on a state-space equations description of the PV generator connected to the converter. The controller gains are designed by building a proper characteristic polynomial which takes into account the conditions for system controllability using Ackermann formulation. Moreover in order to experimentally verify the converter system control dynamics, a switched load has been applied and controlled to set constant the converter output voltage. This control for this load secure it a mean value of resistance through a PWM period during the experiment. The proposed method is tested by means of computational simulations in Matlab/Simulink environment. In addition, an experimental apparatus has been mounted to emulate the simulated results and to corroborate the technique efficacy.