Background. The design of an orthodontic mini-implant is a significant factor in determining its primary stability and its clinical success. The aim of this study was to measure the relative effect of mini-implant design factors on primary stability of orthodontic mini-implants. Methods. Thirty-two 3-dimensional assemblies of mini-implant models with their surrounding bone were generated using finite element analysis software. The maximum displacement of each mini-implant model was measured as they were loaded with a 2-N horizontal force. Employing Taguchi’s design of experiments as a statistical method, the contribution of each design factor to primary stability was calculated. As a result of the great effect of the upper diameter and length, to better detect the impact of the remaining design factors, another set of 25 models with a fixed amount of length and diameter was generated and evaluated. Results. The diameter and length showed a great impact on the primary stability in the first set of experiments (P<0.05). According to the second set of experiments, increased taper angle in the threaded and non-threaded area decreased the primary stability. There was also an optimum amount of 2.5 mm for threaded taper length beyond which the primary stability decreased. Conclusion. It is advisable to increase the diameter and length if primary stability is at risk. In the second place, a minimum amount of taper angle, both in the threaded and non-threaded area with an approximate proportion of 20% of threaded taper length to MI length, would be desirable for MIs with a moderate size.

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The aim of the present study is to fabricate high volume Al2O3-reinforced Al7075 matrix composite by semi-solid powder processing method as an effective method to achieve the desired wear properties. The alloy powder (20 µm) was mixed with Al2O3 (120 µm) for 10 min and 5 h by planetary ball mill to overcome the powders agglomeration. The wear behavior of the composites was studied using the pin-on-disk tribometer. The effects of milling time, compact pressure, and reinforcement content were investigated to enhance the wear resistance. The results of the tribotests indicated that composites with coarser reinforcing particles (lower milling time) have good wear resistance. The role of compaction pressure in highly loaded composites is remarkable. The maximum wear resistance was observed for the 50% Al2O3 composite. The wear resistance increased as the reinforcement volume increased before reaching a critical value. Abrasive wear is the predominant mechanism in the wear of reinforced composites containing less than the load limit. However, adhesive and laminating wear are the controlling mechanisms at overloads. The results indicate valuable information in the development of aluminum-based composites.

Feasibility of partial remelting process in producing the feedstock for semi-solid processing of M2 high-speed steel (HSS) has been investigated. The effect of reheating parameters, that is, heating rate, holding temperature and holding time on final microstructure of M2 HSS, has been studied. For this purpose, a series of experiments based on Taguchi method was employed to determine the required reheating cycles. The experiments were carried out in a resistance furnace and in an argon-controlled atmosphere to avoid any oxidation and decarburization. During any reheating cycle, the temperature of surface and core of the samples were recorded and compared with the furnace temperature. Microstructural evolution of the samples was then studied and the formation of a globular microstructure in holding time has been evaluated. The particle shape factor and globule size in each stage of experiments have been derived and its relation to other parameters has been studied. Finally, appropriate reheating cycle and parameters has been determined and twodimensional plots of parameters versus shape factor are introduced as a process window for reheating cycle derived.

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