Manual Milling Research Articles

Evaluation of marginal adaptation and traction resistance of zirconium crowns made up using two different techniques and cemented on pins with three types of cements

Objective: The aim was to assess marginal adaptation of zirconium crowns made up by manual milling (pantograph) and computerized (computer assisted designing/computer assisted machining [CAD/CAM]) before and after cementation; and the efficiency of 3 types of cements in retaining these crowns: Zinc phosphate, resin modified glass ionomer cement (RelyX Luting 2) and resin cement (RelyX U200). Materials and Methods: Out of 30 zirconium crowns, 15 were milled by the pantograph, and 15 by CAD/CAM. Each group was divided into 3 subgroups according to the cement used. Cementation was done over the analog universal pin 4.5 mm × 4 mm and submitted to mensuration of marginal interface of its four faces with stereoscopic magnifier (×20). Then, they were directed to a machine of universal test (EMIC), and submitted to an axial traction with speed of 0.5 mm/min until its displacement. Results: Before cementation, CAD/CAM crowns (47.60; 40.20; 43.40 μm) demonstrated a greater desadaptation comparing to pantograph crowns (28.20; 35.60; 30.40 μm). RelyX Luting 2 showed less marginal desadaptation postcementation on CAD/CAM crowns (53.80 μm ± 8.43 μm) and pantograph (39.80 μm ± 12.696 μm), when compared with zinc phosphate (62.00 μm ± 12.86; 45.20 μm ± 24.035) and to RelyX U200 (73.80 μm ± 44.49 μm; e 53.00 μm ± 10.817 μm). RelyX Luting 2 also obtained better efficiency on traction resistance (9.48 Kgf ± 2.49 Kgf; e 24.54 Kgf ± 6.73 Kgf), when compared to zinc phosphate (8.71 Kgf ± 4.00 Kgf; and 11.85 Kgf ± 3.15 Kgf) and RelyX U200 (8.08 Kgf ± 0.62 Kgf; and 14.78 Kgf ± 5.94 Kgf). Conclusions: Lower values on marginal discrepancy were found on pantograph crowns comparing to CAD/CAM crowns. RelyX Luting 2 obtained not only a lower marginal desadaptation, but also a better efficiency on traction resistance among the three cements. However, there was no significant statistical difference that could prove the influence of desadaptation on displacement resistance.

Effects of pressure on PbWO4-III

In a hydrostatic pressure environment condition and in manual milling, respectively, investigations of PbWO4-III (P21/n) have been performed by X-ray diffraction and Raman scattering techniques. Experiments found that PbWO4-III keeps its monoclinic structure under hydrostatic pressures with the sample’s anisotropic compressibility up to 14.6 GPa, but transforms to PbWO4-I (I41/a) in a grinding process. The stability and variability of PbWO4-III depending on the strain states were also explored by first-principles calculations of elasticity. Calculations show PbWO4-III has an anisotropic compressibility and a ductile nature with increasing pressure up to 15 GPa.

Comparison of manual rasping and robotic milling for short metaphyseal-fitting stem implantation in total hip arthroplasty: a cadaveric study

Objective: The ROBODOC system offers the theoretical advantage of providing better fit and mechanical stability of the stem in total hip arthroplasty. However, there has been no previous study on short metaphyseal-fitting stem implantation using the ROBODOC system. The aim of the present study was to compare the implant position and primary stability of short metaphyseal-fitting stems implanted by robotic milling and manual rasping in a human cadaveric femoral model.Methods: Eight matched pairs of human cadaveric femora were randomly assigned to a robotic milling group or manual rasping group. Operative time and intraoperative femoral fractures were monitored, and radiographic evaluation of stem alignment was performed by comparison of preoperative planning and postoperative CT data. Stability testing was performed on six matched pairs of femora, excluding two specimens in which intraoperative fractures occurred.Results: The robotic milling procedures took an average of 27 minutes longer than the manual rasping procedures (p < 0.001). The robotic milling group exhibited significantly better anteroposterior alignment and vertical seating, and also showed a significantly reduced variability in both alignment and vertical seating. No intraoperative femoral fracture was detected in the robotic milling group, whereas two femoral fractures and one femoral stem tip perforation were detected in the manual rasping group. Stability testing showed no significant difference in translational and rotational migrations between the two groups, although the robotic milling group showed a trend towards reduced variability of stability.Conclusions: Our cadaveric study suggests that the use of the ROBODOC system for short metaphyseal-fitting stem implantation may have advantages in improving implant fit and reducing the risk of intraoperative femoral fractures without compromising primary stability.

Effects of Ball Milling on the Sintering Process and Superconducting Properties of $(\hbox{MgB}_{2})_{0.96}\hbox{Ni}_{0.04}$ Bulks

Samples of (MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.96</sub> Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.04</sub> prepared by mechanical alloying were sintered at 750°C for 30 min. The reactive process and generating temperature of the second phase were investigated by employing differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. Corresponding microstructures and superconducting properties have also been analyzed. It is found that two-step milling is effective in refining the structure and in eliminating flux jumps, although the corresponding J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is slightly lowered due to the existence of excessive MgO. This observation indicates that the bulk samples prepared by two-step milling possess stable properties of magnetism and heat compared with the sample prepared by manual milling.

Use of Fly Ash as Bonding Material on Low Thermal Expansion Porous Materials

In this work it was determined the effect of fly ash (FA) as bonding material during the fabrication of low thermal expansion porous materials. SiC, fly ash, Vitrified Bonding Material (VBM), and LiAlSiO4 powders were used as raw materials. Porous materials were sintered at 850°C and 950°C after manual milling and mechanical milling in a planetary ball milling at 800 RPM. SEM micrographs showed the presence of porous materials, and it was observed that fly ash particles did not melt at 850°C. However if sintering temperature increases at 950°C, FA starts to melt and it is forming bridges between SiC particles. Thermal expansion values were around 3.0x10-6 K-1. According to these results, it seems that it is possible to have a favorable synergy between FA and VBM to fabricate SiC porous materials with low thermal expansion values.

Histomorphometric analysis of intraoral bone grafts harvested by different methods

Autogenous bone is considered the “gold standard” among graft materials for alveolar ridge augmentation, because of its osteogenic, osteconductive and osteoinductive features. In clinical practice, autogenous bone chips can be obtained by using different methods, and several studies demonstrated the influence of devices used for tissue harvesting on bone chip morphology and vitality. Aim of the present study was to compare histologically and histomophometrically the morphological features and the vitality of bone chips harvested intraorally with five different methods. Material and Methods Five young adult men were recruited for this study. Five bone samples were harvested from the alveolar process of each patient by means of different methods: 1) bone scraper, 2) stainless steel round bur, 3) stainless steel implant spiral bur, 4) piezoelectric device, 5) trephine bur+manual mill. Samples were processed for undecalcified histology and stained with toluidine blue/ pyronine G (Sigma-Aldrich, St Louis, MO). The sections were photographed in a Nikon light microscope (Eclipse E600) equipped with a calibrated digital camera (DXM1200, Nikon, Tokyo, Japan). Histomorphometric analyses were performed to evaluate bone fragment dimensions: fragments with dimensions comprised between 100μm and 1000μm (medium size fragments = MF), fragments smaller than 100μm (small size fragments = SF) and those greater than 1000μm (large size fragments = LF) were differentiated. Total area and percentage area were also evaluated. A stereologic method was used to calculate the percentage of vital bone. Results Five samples for each harvesting procedure were analyzed. Bone fragments harvested using Trephine bur mostly resulted vital and of large dimensions. Spiral and implant bur produced only small and medium fragments but the percentage of nonvital bone was higher than in the other groups. Bone scraper and piezoelectric device produced vital bone fragments with medium-large dimensions. Conclusions Within the limited number of samples evaluated, results of the present study claim that bone scraper and piezoelectric device are the most efficacious procedure on harvesting vital bone fragments.

Technological changes in shea butter production in Ghana: A case study of shea butter production in the Yendi District of the Northern Region of Ghana

This study investigated technological changes in shea butter production in the Yendi District of Ghana and how processing could further be improved. A qualitative research and analysis of six communities and 36 sheabutter processors in the Yendi District indicated that shea butter processors have changed from roasting whole kernels to crushing the kernels before roasting. Shea butter processors have mechanised the milling of roastedkernels and abandoned manual milling. Crushing of kernels and ‘beating’ of shea kernel paste have also been mechanised; however, only few processors are using this method. Shea butter processors need improvement inthe areas of cooking shea kernels, ‘beating’ of shea paste, and packaging of shea butter.

Influence of preparation and storage conditions on photoluminescence of porous silicon powder with embedded Si nanocrystals

The time changes of photoluminescence (PL) characteristics of porous silicon (porSi) powder during storing in different ambients have been reported. A porous silicon material with embedded Si nanocrystals of size of few nanometers was prepared by an electrochemical method from 10 to 20 Ωcm p-type Si wafers, and both constant and pulse current anodization regimes were used. A powder with a submicron average particle size was obtained by simple mechanical lift-off of the porous layer followed by additional manual milling. The air, hexane, and water as storage media were used, and modification by a nonionic surfactant (undecylenic acid) of the porSi surface was applied in the latter case. Dependence of PL characteristics on preparation and storage conditions was then studied. A remarkable blue shift of a position of PL maximum was observed in time for porSi powders in each storage media. In water suspension a many-fold build-up (10–30) of PL intensity in a time scale of few days was accompanied by an observed blue shift. Photoluminescence time behavior of porSi powders was described by a known mechanism of the change of porSi PL from free exciton emission of Si nanocrystals to luminescence of localized oxidized states on the Si nanocrystal surface.

Accuracy analysis of cavities for cochlea implants milled conventionally and manually with navigated control

A new experimental support system for milling cavities for cochlear implants is proposed. In contrast to assisting the milling task by drilling jigs, image-based navigation systems or robots, the approach of “Navigated Control” features a supervision of the power of the user controlled instrument. The main feature is the decrease of the power of an active instrument depending on the location of this instrument relative to a planned volume. A first experiment to determine the accuracy of the system in contrast to conventional manual milling is presented. The accuracy of the manual milling with “Navigated Control” was at 0.2 ± 0.2 mm compared to the lower accuracy of the conventional manual milling without “Navigated Control” at 0.8 ± 0.2 mm. The results are discussed.

Identification of Milling Parameters for Manual Cutting of Bicortical Bone Structures

Within the framework of the development of a new neurosurgical robot system, parameters of conventional manual neurosurgical bone milling had to be determined. These results were used as a reference for the design and validation of the robotic versus manual milling task. Bovine scapulae were used for the tests because their bicortical structure is similar to the bone structure of the skull. The exercise was to cut defined geometries that had been registered on the bone prior to the start of the milling operation. The geometries had to be milled with a depth of 3 mm, which corresponded to the radius of the ball of the cutter. Different parameters like tool position, rotary speed, temperature, forces and time were registered. Eleven experienced neurosurgeons with practical experience of 80-1200 skull operations participated in this study. First results show a large variation in depth along the line. The lateral deviation was up to 5 mm, the depth error up to 2.5 mm, the tool temperature was 22°C to 65°C, and rotary speed varied from 15,000 to 80,000 rpm. Registered forces had maxima of 16 N in the feed direction and 21 N normal to the surface; average forces were approximately 1-2 N.

The Grace Factor: A New Tool for Cement Industry Process Control Engineers

Abstract A method for mill control and supervision is described that is based on measurement of the mill horsepower consumption and the bulk density of the material being ground. Control by horsepower is shown to be possible and to be a more fundamentally based scheme than other commonly used systems. A monitoring and control system is discussed that uses the relationships described to provide a visual indication of mill loading conditions that can be used effectively by nontechnically trained personnel for manual mill control or as an automatic signal for direct control interlock with programmable controllers.

The Vocational Division of Labor and Education of the Youth

Technical progress causes changes in the division of labor in the sphere of material production. "Labor," wrote Karl Marx, "is organized and divided differently depending on what tools are at its disposal. The manual mill presupposes a different division of labor from that of the steam mill." (1, p. 152)