Tooth eruption sequence and dental crowding: a case-control study.

UNLABELLED: When cases of dental crowding are identified and diagnosed promptly, interceptive orthodontics is particularly successful. AIM: To assess the differences in the eruption sequence of the mandibular canine and first premolar teeth in children with and without dental crowding. MATERIALS AND METHODS: Children who attended the Shiraz Dental School's orthodontic clinic (Iran) from September to December 2012 were enrolled in this case-control study. Tooth size arch length discrepancy (TSALD) of all 8-10 year olds was calculated from patients' dental models. Thirty-six children were randomly selected from those with TSALD of equal or less than 4mm (those with crowding). Each selected case was matched for sex and age with another child (as control) with TSALD>-4mm attending the same clinic, in the same time period. The existing panoramic radiographs were traced and the eruption percentages were measured for mandibular canine and first premolar teeth. The mean difference between canine and first premolar eruption percentages was compared between the case and control groups using the SPSS (version PASW 18) software and a paired sample t-test. RESULTS: Canine and first premolar eruption percentages in the case group were 65.82±13.00 and 78.92±10.15 percent, respectively. The mean eruption percentages for canines and first premolars of the control group were 74.12±14.55 and 75.47±11.60 percent, respectively. There was a significant difference in pre-eruptive positions of canine and first premolar teeth in those with moderate to severe crowding when compared to the control group (p<0.001). CONCLUSION: These findings may improve the early diagnosis of children with high risk of developing moderate to severe crowding during mixed dentition

Novel User-friendly Device for Human Bite Force Measurement

Statement of Problem: Bite force is generated due to the consonance between different parts of the masticatory system. In dentistry, measurement of the bite force is quite common through several methods and devices. Objective: The aim was to present a novel bite force-measuring device that could help reducing the costs. Materials and Methods:This study presented the design, fabrication, and calibration method of a novel low-cost bite force-measuring device based on a force-sensitive resistor and application of strain gages. The FSR 402 was the selected sensor, which was suitable in size for placement in mouth, sterilizable for reuse, and contained biocompatible material.It could measure a large bite force of up to 90 kg with high repeatability.The device had a liquid crystal display (LCD) for immediate visualization of the results and a system for quick calibration of the device in office. To assess the accuracy of the device, some forces were applied to the sensor in nine values from11 to 80kg. The mean of measured force, absolute error, and error percentage were measured and recorded. Results: The mean relative error was almost 2% within the range of 11-80kg. The lowest error percentage was 0.46% at the load of 52kg and the highest error percentage was 3.97% at the load of 28 kg.Error percentage was 2.51% in the lowest range (11kg) and 2.65% in the highest range (80kg).The relative error in different ranges did not follow a particular trend. Conclusions:The bite force-measuring device is an economical and user-friendly appliance that can be simply used for routine practice in the office. The device shows good linearity and repeatability. It also has a calibration apparatus that can help maintaining the device accuracy

Enhancement of grain structure and mechanical properties of a high-Mn twinning-induced plasticity steel bearing Al–Si by fast-heating annealing

Abstract In this study, a cold-rolled Fe-0.01C-21.3Mn–3Al–3Si (wt.%) TWIP steel was undergone a fast-heating (FH) annealing at high temperatures of 1000–1200 °C and 2 s soaking time for grain refinement and controlling the phase structure and thereby to enhance the mechanical properties. For comparison, recrystallization annealing was conducted at lower temperatures of 650 and 700 °C for 180 s. The microstructural evolution of the FH annealed steel was surveyed using electron backscatter diffraction. The strain hardening behavior of the FH structures was studied by tensile tests. The tensile flow curves were also predicted by a phenomenological model based on the evolution of dislocation density during deformation. Fine mainly austenitic structure was promoted by FH annealing at 1000 and 1100 °C. At the lower temperatures of 650 and 700 °C, bands of finer grains, indicative of some inhomogeneity, were evident in the mostly austenitic recrystallized microstructure. However, at 1200 °C, the structure consisted of coarse austenite and ferrite with almost equal fractions. The FH annealed structures exhibited a remarkable improvement in the mechanical properties (a better combination of yield and tensile strength and ductility) compared to conventional long annealing cycles

A new processing route to develop nano-grained structure of a TRIP-aided austenitic stainless-steel using double reversion fast-heating annealing

Abstract A novel processing route comprising double reversion annealing (DRA) was designed for developing bulk nano-grained (NG) structure of an austenitic stainless steel (Type 301LN). The new processing concept of DRA comprised two subsequent intrinsic type processes i.e., two times cold reductions (∼53 % and 63 %) followed by fast induction heating (∼200 °C/s) and short duration annealing at different temperatures (first at 690 °C/60s and second at 750–900 °C/0.1–1s). The NG structure revealed a remarkable improvement of the mechanical properties compared to the counterparts processed by single reversion annealing. Furthermore, outstanding combination of strength and formability is achieved for the DRA structures, significantly higher than those of high-Mn TWIP steels, low-alloy TRIP steels and 304 stainless steel. For instance, a superior combination of yield strength (∼950–1030 MPa) and formability index (11.8–12.5 mm) obtained after DRA at 750 °C/0.1s and 800°C/1 s, respectively. However, the corresponding values are 300 MPa and 12 mm for TWIP steels, 500 MPa and 10 mm for TRIP steels, and 270 MPa and 12 mm for 304 stainless steel. In order to reveal the effect of DRA on the stretch formability, Erichsen cup testing was conducted of both the initial and DRA steel specimens. Moreover, Erichsen cup testing also simulated by the finite element method (FEM) to survey further details of their deformation

Optimization of the tensile-shear strength of laser-welded lap joints of ultra-high strength abrasion resistance steel

Abstract The tensile-shear strength of laser-welded lap joints developed in abrasion resistance ultra-high strength ARS-600 steel was optimized by evaluating the joints achieved with different welding parameters and various configurations of weld patterns, including multiple continuous longitudinal and transverse weldments. The microstructural evolution of the fusion zone was characterized by electron backscatter diffraction (EBSD) after welding with different values of energy input (60–320 J/mm). Furthermore, in order to better comprehend the shear response of different weld patterns, stress analysis of various longitudinal and transverse lap joints was conducted by the finite element method (FEM)

High-speed Erichsen testing of grain-refined 301LN austenitic stainless steel processed by double-reversion annealing

Abstract Austenitic Cr–Ni stainless-type 301LN steel was subjected to a double-reversion annealing (DRA) treatment to develop bulk grain-refined microstructures. The tensile properties and formability of the DRA structures were determined by high-speed tensile and Erichsen cupping tests at a strain rate of 1.5 s⁻¹ (50 mm s⁻¹) and compared with those of coarse-grained steel. Detailed microstructural features of the DRA structures were characterized using the electron backscatter diffraction technique and X-ray diffraction analysis. The DRA structures achieved by annealing for 1 second at 800 °C and 900 °C exhibited a superior combination of yield (~ 950 and 770 MPa, respectively) and tensile (~ 1050 and 950 MPa, respectively) strengths and ductility (~ 35 and 40 pct, respectively, as well as reasonable Erichsen index values under high-speed biaxial strain. Due to adiabatic heating, the DRA structures had higher austenite stability during high-speed stretch forming, i.e., were less prone to strain-induced martensitic transformation. The finite-element method (FEM) was used to conduct coupled field thermomechanical analyses of the high-speed deformation processes for the coarse-grained and DRA structures. Comparison of the FEM analyses with the experimental results revealed a considerable influence (~ 20 pct) of martensitic transformation on the adiabatic temperature rise. The balance of the yield strength and Erichsen index value of the developed nanograined microstructure is comparable to that of coarse-grained commercial steel

Promotion of thermomechanical processing of 2-GPa low-alloyed ultrahigh-strength steel and physically based modelling of the deformation behaviour

Abstract A low-alloyed ultrahigh-strength steel comprising CrNiMoWMnV was designed based on thermodynamic calculations and by controlling the microalloying elements to promote various strengthening mechanisms upon processing. The hot deformation behaviour and mechanism were correlated with the processing parameters, that is, strain rate and temperature. The fine features of the deformed microstructures were analysed using electron backscatter diffraction (EBSD) and MATLAB software, combined with the MTEX texture and crystallographic analysis toolbox. The flow stress behaviour at high temperatures was modelled using the dislocation density-based Bergström's model, which could be applied up to the peak strain. However, the diffusional transformation (i.e. recrystallisation)-based Kolmogorov–Johnson–Mehl–Avrami model has been applied to fit the flow stress over a wide deformation strain. The effective grain size (EGS) of martensite and prior austenite grain size (PAGS) were correlated with the deformation temperature and strain rate. Because the PAGS was significantly refined from 16 μm in the initial microstructure to 6 μm after processing at 850 °C/0.01 s-1, the corresponding martensite EGSs were 1.38 and 1.01 μm, respectively. Therefore, these fine-controlled characteristics of the processed microstructures at high temperatures help to enhance the mechanical properties, such as the strength and toughness, of the designed ultrahigh-strength steel