Pure Screw Research Articles

An Evaluation of the Stress Distribution in Screw Retained Implants of Different Crown Implant Ratios in Different Bone Densities Under Various Loads-A FEM Study.

Studies on stress distribution around screw retained implants in different bone densities are limited. In clinical situations crowns of different heights are placed on the implants and the effect of varying crown implant ratio on the bone is not understood properly. To evaluate and compare the stress distribution in different screw retained implants for different crown-implant ratios in different bone densities under various occlusal loads using three dimensional finite element analyses. In this invitro study the stress distribution was evaluated and compared between two different crown heights (7.5mm, 10mm) retained on implants by using different screw materials (commercially pure titanium, titanium alloy) in two different densities of bone D2, D3 under various load (100N, 200N) applications by using finite element analysis. For crown height of 7.5mm, in D2 bone density when vertical load of 200N was applied, the maximum stress concentration was 1780N/cm(2), for oblique load of 100N it was 2936N/cm(2) respectively and in D3 bone density when vertical load of 200N was applied, the maximum stress concentration was 1820N/cm(2), for oblique load of 100N it was 3477N/cm(2) respectively. When the crown height is increased to 10mm, the maximum stress concentration in D2 bone was 1875N/cm(2) for vertical load, 4015N/cm(2) for oblique load and in D3 bone the maximum stress concentration was 2123N/cm(2) for vertical load and 4236N/ cm(2) for oblique load. In case of titanium screws for crown height of 7.5 mm, when vertical load was applied, stress concentration was 1603 N/cm(2) where as for titanium alloy screw it was 1820N/cm(2). In case of 10mm crown height stress concentration was 1904N/cm(2) for titanium screw and 2123N/cm(2) for titanium alloy screw. In case of oblique loading for 7.5mm crown height stress concentration was 3155N/cm(2) for titanium screw 3477N/cm(2) for titanium alloy screw. For 10mm crown height stress concentration was 4236N/cm(2) for titanium screw, 4663N/cm(2) for titanium alloy screw. Stress concentration was less and stress distribution was better in D2 bone density than in D3 bone density. Stress concentration was less and stress distribution was better in commercially pure titanium screw than in titanium alloy screw. With the increase in the height of crown (i.e., from 7.5mm to 10mm) stress concentration and stress distribution also increased.

Different structural origins for different sized surface pits observed on a-plane GaN film

A correlation study between the observed surface morphology using high-resolution scanning electron microscopy (HRSEM) and the observed structural imperfections using transmission electron microscopy (TEM) has been conducted for a-plane GaN. There are three different sized asymmetric surface pits: large pit of 500 nm–2 µm in side length, medium pit of 50 nm in side length, and small pit with side lengths of less than 5 nm, which originate from incomplete island coalescence, screw dislocation, and partial dislocation (PD), respectively. Both screw dislocation and PD can produce pits on the free surface because they have a perpendicular line tension to the surface, which must remain in balance with the surface tension. The two types of dislocation lead to distinctive pit sizes because the PD has a smaller Burgers vector component along the dislocation line than the pure screw dislocation. A pit that is produced in the island-coalescing process is much larger than those caused by dislocations because island coalescence is a kinetic process that involves large-scale mass transportation, whereas the dislocation mediates the surface in the local area. These three types of surface pits sometimes interact with one another in space. The coalescence of the island determines the surface morphology at large scales, whereas the defects affect the details.

Molecular dynamics simulation of surface step reconstruction and irreversibility under cyclic loading

The mechanical behaviour of surface steps naturally created by the glide of dislocations subjected to cyclic loading is examined using molecular dynamics simulations. Three face centred cubic metals, Al, Cu and Ag are analysed. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. Three different mechanisms of reconstruction are defined. They induce different reconstruction rates and various relief evolutions depending on the temperature. Surface slip irreversibility under cyclic loading is analysed. All surface steps are intrinsically irreversible under usual fatigue laboratory loading amplitude without the arrival of opposite sign dislocations. A surface step is reversible only when an opposite sign dislocation subsequently glides on a nearby atomic plane. Steps created by opposite sign dislocation glides on non neighbouring planes are irreversible. The irreversibility cumulates cycle by cycle and a micro-notch is produced whose depth increases cyclically. A rough estimation of surface irreversibility is carried out for pure edge dislocations in persistent slip bands in wavy materials. This gives an irreversibility fraction between 0.5 and 0.75 in copper. An analysis coupling surface mechanisms with the classical bulk slip irreversibility model proposed by Differt, Essmann and Mughrabi in 1986 and applied to pure screw dislocations gives an irreversibility fraction of 0.62 in copper. Similar estimations in nickel give irreversibility fractions around 0.6 and 0.8 for pure edge and screw dislocations respectively. These values are in agreement with recent atomic force microscopy measurements.

Direct Determination of Burgers Vectors of Threading Mixed Dislocations in 4H-SiC c-Plane Wafers Grown by PVT Method

Threading Screw Dislocations (TSDs) have long been observed in 4H-SiC crystals grown by the Physical Vapor Transport (PVT) method. Recent studies [1] show that a significant proportion of these threading dislocations are actually mixed type dislocations with a Burgers vectors nc+ma (where n and m are integers). With the help of Synchrotron White Beam X-ray Topography, it is straightforward to distinguish these mixed type threading dislocations from pure screw dislocations simply by recording different reflections from an axially cut sample (cut parallel to growth direction) and applying the g.b =0and g.bxl =0 invisibility criteria (g – diffraction vector; b – Burgers vector). However, axial wafers are only cut from the boules slated for research purposes and are usually unavailable for boules from which commercially preferred c-plane oriented wafers are sliced. In this study, Synchrotron Monochromatic X-ray topography was carried out on a 100mm 4H-SiC c-cut commercial wafer and contrast variation was observed for each single threading screw or mixed dislocation image on six different types of 11-28 reflections. The way the contrast varied in the different reflections was also found to be different and actually depends on the nature of the dislocation itself. Ray Tracing Simulation was then carried out to confirm this observation. This simulation method is capable of simulating dislocation contrast in various geometries and it is based on the fact that orientation contrast is the predominant contributor to contrast from threading dislocations in the grazing incidence and back reflection geometries. According to the simulation results and their comparison to the observed contrast, it is in principle possible to determine the Burgers vector of any single threading dislocation using this methodology. [1] F. Wu, H. Wang, S. Byrappa, B. Raghothamachar, M. Dudley, E. K. Sanchez, D. Hansen, R. Drachev, S. G. Mueller, and M. J. Loboda, Mater. Sci. Forum 717-720, 343(2011).[2] X. R. Huang, M. Dudley, W. M. Vetter, W. Huang, W. Si, and C. H. Carter, Jr., J. Appl. Cryst. 32, 516 (1999). Figure 1

Signature of dislocations and stacking faults of face-centred cubic nanocrystals in coherent X-ray diffraction patterns: a numerical study.

Crystal defects induce strong distortions in diffraction patterns. A single defect alone can yield strong and fine features that are observed in high-resolution diffraction experiments such as coherent X-ray diffraction. The case of face-centred cubic nanocrystals is studied numerically and the signatures of typical defects close to Bragg positions are identified. Crystals of a few tens of nanometres are modelled with realistic atomic potentials and 'relaxed' after introduction of well defined defects such as pure screw or edge dislocations, or Frank or prismatic loops. Diffraction patterns calculated in the kinematic approximation reveal various signatures of the defects depending on the Miller indices. They are strongly modified by the dissociation of the dislocations. Selection rules on the Miller indices are provided, to observe the maximum effect of given crystal defects in the initial and relaxed configurations. The effect of several physical and geometrical parameters such as stacking fault energy, crystal shape and defect position are discussed. The method is illustrated on a complex structure resulting from the simulated nanoindentation of a gold nanocrystal.

Depinning-controlled plastic deformation during nanoindentation of BCC iron thin films and nanoparticles

Nanoindentation is commonly employed to study mechanical properties of metallic specimen. In recent years, the use of this technique has been extended to study how mechanical properties of sub-micrometer scale specimens depend on size and dimensionality. In this work, we explore this dependence for α-Fe in molecular dynamics simulations of nanoindentation of thin films and nanoparticles. The simulations show that the strength poorly depends on the dimensions in the lateral directions and that the indentation curves of thin films and nanoparticles are alike. This is in contrast with recent observation in FCC metals. A detailed analysis of the dislocation mechanisms during the deformation reveals that ½ 〈111〉{110} dislocations are nucleated in six possible directions, but these remain pinned to their nucleation sites after nucleation. Load drops in the indentation curve, which corresponds to strain bursts, are attributed to depinning of these dislocations as full or half prismatic loops, i.e., the deformation is depinning-controlled. In nanoparticles, some of the dislocations depin partially, resulting in pure screw dislocations between the indenter and the lateral facet. The locality of the depinning-controlled deformation rationalizes the lack of size effect. Finally, we relate the dislocation mechanisms during the depinning-controlled deformation to the frequency and extent of strain bursts during nanoindentation of BCC specimens.

Glide of threading edge dislocations after basal plane dislocation conversion during 4H–SiC epitaxial growth

Transmission electron microscopy (TEM) and KOH etching were used to analyze the motion of dislocations after the conversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) during 4H–SiC epitaxy. The locations of TED etch pits on the epilayer surface were shifted compared to the original locations of BPD etch pits on the substrate surface. The shift of the TED etch pits was mostly along the BPD line directions towards the up-step direction. For converted screw type BPDs, the conversion points were located below the substrate/epilayer interface. The shift distances in the step-flow direction were proportional to the depths of the BPD–TED conversion points below the substrate/epilayer interface. For converted mixed type BPDs, the conversion points were exactly at the interface. Through TEM analysis, it was concluded that the dislocation shift is caused by a combined effect of H2 etching prior to growth and glide of the threading segments during high temperature epitaxy. The TED glide is only possible for converted pure screw type BPDs and could present a viable means for eliminating BPDs from the epilayer during growth by moving the conversion point below the substrate/epilayer interface.

Ultraviolet-C irradiation to titanium implants increases peri-implant bone formation without impeding mineralization in a rabbit femur model

Objectives. Volume and bone quality of peri-implant supporting bone, in particular, at implant neck region, as well as bone–implant contact ratio, is important for long-term stability of implants. Ultraviolet-C (UVC) irradiation is known to enhance the osseointegration capability of titanium implants. However, the histological determination was performed only on a rat model, but not pre-clinical animal model such as a rabbit model. The purpose of this study was to determine the effects of UVC irradiation on titanium implants on the volume and mineral density of peri-implant supporting bone formation in a rabbit femur model. Materials and methods. Acid-etched pure titanium screw implants with or without 3 mW/cm2 UVC irradiation for 48 h were placed in rabbit femur diaphyses. Peri-implant bone tissue formation was analyzed at 3 and 8 weeks post-operatively by histology and micro-CT-based bone morphometry after calibration with hydroxyl apatite phantoms. Results. UVC pre-irradiated implants accumulated a higher density of cells and thicker and longer bone tissue attachments that continued into the inner basic lamellae of the surface of existing cortical bone at 3 and 8 weeks than the implants without irradiation. Although the bone mineral density around both implants was equivalent to that of the existing cortical bone, bone volume was greater with UVC pre-irradiation in two-thirds or more of the apical region throughout the observation period. Conclusions. These results indicate that UVC treatment increased the volume of cortical-like bone tissue in the coronal region of titanium implants without deterioration of bone mineral density.

Growth and dislocation studies of β-HMX

BackgroundThe defect structure of organic materials is important as it plays a major role in their crystal growth properties. It also can play a subcritical role in “hot-spot” detonation processes of energetics and one such energetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (β-HMX).ResultsThe as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, all with {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two of which could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact of the twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one type of etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgers vector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated with line dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristic of mechanical deformation by dislocation slip.ConclusionsCrystals of β-HMX grown from acetone show good morphological agreement with that predicted by modelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution. Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant at higher super saturations. The twin plane in β-HMX was identified as a (101) reflection plane. The low plasticity of β-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays. On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screw dislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pits are associated with pure screw dislocations with b = [010].Graphical abstractEtch pits on the twinned (010) face of β-HMX.

Electromagnetic Lead Screw for Potential Wave Energy Application

This paper presents a new type electromagnetic lead screw (EMLS) intended for wave energy application. Similar to the mechanical lead screw, this electromagnetic version can transfer slow linear motion to high-rotational motion, offering gearing effects. Compared with the existing pure magnetic lead screw (MLS) employing permanent magnets only, the new EMLS proposed uses dc current to provide the required helical-shape magnetic field, offering a much simpler, robust structure compared with the MLS. The working principle and the performances of this EMLS are analyzed in this paper. Comparison with PM-type lead screw is given. In addition to this, the theoretical analysis to support the use of a 2-D finite element model to analyze the 3-D magnetic-type lead screw is given, which has not been well covered in the existing literature.

Inclination of a threading dislocation in an epilayer of 4H-SiC

Threading dislocations (TDs) are inclined from the [0001] c-axis in 4H-SiC epilayers which are produced by the step-controlled technique. The reason for this inclination is discussed in the framework of isotropic elastic theory of dislocation. The elastic strain energy of a TD in an epilayer is calculated as a function of its orientation, and the minimum energy orientation is used to predict the inclination angle. The results of the calculations are as follows. For a cut-off angle (α) of 4°, a threading edge dislocation (TED) and a threading pure screw dislocation (TpSD) are inclined from the c-axis by 12 and 2°, respectively: Threading near screw dislocations (TnSDs) and threading mixed dislocations (TMDs) are inclined by angles ranging from 8 to 15° from the c-axis, depending on their actual Burgers vectors. Similarly for α of 8°, a TED and a TpSD are inclined from the c-axis by 21 and 4°, respectively: TnSDs and TMDs are inclined from the c-axis by angles ranging from 7 to 17°. These predictions are in good agreement with experiment.

Dynamic strain aging caused by a new Peierls mechanism at high-temperature in iron

In situ straining experiments and post-mortem observations have been carried out in pure Fe in order to investigate the dislocation mechanisms in the temperature range of dynamic strain aging. The results show that dislocations are locked in pure screw orientation at 200 °C and start to move viscously at higher temperatures, up to more than 400 °C. The unexpected reappearance of a Peierls mechanism at such a high temperature is proposed to result from the interaction between screw dislocations and solute carbon atoms.

Analysis of the repair of bone defects filled with β-tricalcium phosphate associated to pure titanium implants.

Objective: The present study aims to develop a histological descriptive analysis on the repair of bone defects filled with β-TCP, associated to pure titanium implants into cavities prepared in the calvarial bone of rats. Materials and method: Eighteen male adult rats were randomly selected and divided into three groups of six rats each, according to their period of death: 15, 30, and 60 days. Four bone defects were made into each one of the calvarial bones of rats and filled with: (a) β-TCP, (b) clot, (c) β-TCP + pure titanium screw, and (d) pure titanium screw. The samples were cut and histologically assessed. Presence and volume of loose connective tissue and newly formed bone tissue were analyzed, as well as the presence or absence of remaining material (β-TCP) into the defect. Results: It was verified an acceleration bone neoformation process in the presence of β-TCP. Conclusion: The results suggest the biocompatibility and osteoconductivity of the biomaterial, even when associated to pure titanium implants. Keywords: Biomaterials. Calcium Phosphate. Bone Substitutes.

GaN/Si(111) Device Defects and HFET Degradation Mechanisms

High Voltage AlGaN/GaN Switching HEMTs The recent advances of AlGaN/GaN HEMTs grown on Si for addressing the needs of the power electronics market in the 0-900 V range have indicated that GaN on Si may be the most cost effective solution. The main problem with this technology is the large lattice and thermal mismatch between Si and III-nitride layers, which result in several electrically active defects affecting both device performance and reliability. Furukawa Electric initially reported that to increase breakdown voltage it is necessary to compensate the GaN buffer layer by using p-type dopants. Such an approach allowed Furukawa to report a breakdown voltage as high as 525 V with a low specific on resistance. This investigation, using elaborate buffer layer configurations did show the direct relationship between threading dislocation density and breakdown voltage. These results and our present investigations show that to achieve a high breakdown voltage, thick buffer layers and carefully designed structures are required. However the growth of thick buffer layers either by MOCVD or MBE is challenging due to both the thermal mismatch as well as the lattice mismatch.The presence of mismatch in lattice parameter and coefficient of thermal expansion between GaN on common substrates like Al2O3, SiC, and (111) Si results in a variety of defects that adversely affect device performance. Among the potential defects, threading dislocations (TDs) are the primary defects seen in GaN epitaxial layers. These dislocations can be categorized as pure edge dislocations, pure screw dislocations, or mixed dislocations. Edge dislocations, defined by the Burgers vector , run parallel to the basal (c-) plane of the wurtzite GaN structure. Screw dislocations are defined by a Burgers vector and run perpendicular to the GaN basal plane/parallel to the c-axis. While dislocations have been observed in all heteroepitaxially grown GaN films, TDs are especially prevalent in GaN on (111) Si substrates. The GaN-(111) Si lattice parameter mismatch (≈17%) and coefficient of thermal expansion mismatch (≈56%) are significantly larger than the mismatch with SiC or Al2O3 substrates, leading to the introduction of greater tensile stresses in the GaN layer during and after growth at elevated temperatures. This stress translates into a greater dislocation density or, in more extreme cases, cracking of the GaN film. A variety of techniques have been employed in order to reduce the negative effects of these tensile stresses. Buffer layers of AlN between the GaN and substrate, buffer stacks of AlN, GaN, AlGaN, or SiN, AlN/GaN superlattice layers, special patterning of the substrate, and lower temperature GaN growth processes have received much attention in attempts to prevent film cracking and reduce the TD concentrations. In any case, the TD areal density in GaN-on-Si still remains on the order of 108-1010 defects/cm2 near the upper film surface; these densities are much higher than the TD densities observed in GaN on Al2O3 or SiC. Effects of Threading Dislocations on Device Performance Threading edge and screw dislocations present near the upper GaN surface regions degrade electronic device performance in several ways. Both varieties of TD can hamper carrier mobility in the active device regions of the GaN films. The dangling bonds associated with edge defects can act as electron acceptor traps that introduce electrostatic interactions and reduce electron mobility in the conduction channel or two-dimensional electron gas in GaN MOSFETS or HEMTs. The associated negative charging of edge defects has been observed experimentally through use of Scanning Kelvin Probe Microscopy by Simpkins, et al. Screw dislocations can also hamper charge transport through scattering interactions as the defects continue upward through the GaN film. However, since edge dislocations are the predominant defect near the upper GaN surfaces, screw dislocations play a lesser role in reducing carrier mobility. Also, the likelihood of charge carrier interactions with TDs has been shown to be highly dependent on the angle between the dislocation line and the carrier velocity; edge and screw defects that are parallel to the electron velocity have minimal effects on the carriers. Therefore, construction of vertical devices in which screw dislocations have minimal effect on carrier transport is possible, leading to higher carrier mobility and lower resistivity.1. Y.Li, M. Krishnan, S. Salemi and A. Christou, “Strain induced buffer layer defects in GaN HFETs and their evolution during reliability testing” DOI: 10.1109/IRPS.2009.5173336

The kinematics of ball-screw mechanisms via the slide–roll ratio

The motion state of balls in the ball screw mechanism is hard to observed or measured because of the complexity of the mechanism consisting of three main components: screw, nut and balls. In this paper, a kinematic model for the basic single arc ball screw mechanism driven by the rotation of the screw is established using the homogenous transformation matrix, and the kinematic characteristics and slide–roll ratios at contact points of the raceways are analyzed. There are five possible relative motion states: a) screw pure rolling and nut rolling–sliding mixed motion, b) nut pure rolling and screw rolling–sliding mixed motion, c) screw pure sliding and nut no relative motion, d) nut pure sliding and screw no relative motion, and e) both rolling–sliding mixed motion between the balls and the raceways of the screw and nut in the tangential direction of the helix path. A parametric study is also carried out to evaluate the effect of motion velocity on the slide–roll ratio based on the numerical calculations of the slide–roll ratio at the contact points.

Investigation of leakage current paths in n-GaN by conductive atomic force microscopy

We have investigated electrical characteristics of leakage current paths in n-GaN layer grown by metal-organic chemical vapor deposition with conductive-atomic force microscopy (C-AFM). The C-AFM mapping shows two kinds of leakage current paths existing in the n-GaN layer: open-core dislocation and pure screw dislocation. From the localized I-V curves measured by C-AFM, we confirmed that the open-core screw dislocation shows more significant leakage current. We explained these results in terms of a modified Schottky band model based on donor states formed by oxygen segregation at the {10−10} sidewall of the open-core screw dislocation.

Synchrotron topography studies of the operation of double-ended Frank–Read partial dislocation sources in 4H-SiC

Synchrotron White Beam X-ray Topography (SWBXT) has been used to image and analyze a distinctive stacking fault pattern observed in 4H-SiC wafers. The pattern often consists of a six-pointed star comprised of multiple layers of rhombus-shaped stacking faults with three different fault vectors of the Shockley type bounded by 30° Shockley partial dislocations. Formation of this stacking fault pattern is associated with a micropipe at its center which can act as nucleation sites for dislocation half-loops belonging to the primary basal (1/3〈11−20〉(0001)) slip system and occasionally the secondary prismatic (1/3〈11−20〉{1−100}) slip systems. In this case, the rhombus-shaped Shockley type stacking faults are nucleated on the basal plane by dissociation of 1/3〈11−20〉 pure screw dislocations cross-slipped from the prismatic plane and subsequent expansion caused by glide of the leading partial and locking of the trailing partial by interaction with 60° 1/3〈−2110〉 dislocations on the basal plane. Based on these observations, a formation mechanism involving the operation of a double-ended Frank–Read partial dislocation source has been proposed. In the limit, this glide and cross-slip mechanism leads to 4H to 3C polytype transformation in the vicinity of the micropipe by a mechanism similar to that proposed by Pirouz and Yang (1993) [21].

Characterization of Vacant Broken Line Defects in A-Face Grown Crystals of Silicon Carbide

A new type of defects, vacant broken line defects, was found to occur in a-face grown crystals of 4H-Silicon Carbide. We characterized the vacant broken line defects by high voltage transmission electron microscope (HV-TEM). The HV-TEM image revealed that the edges of broken line defects were connected by a bundle of dislocations, which elongated to the growth direction on the basal plane. The analysis by gb method for determining Burgers vector indicated that the dislocations were not pure screw dislocations, but complex of screw and edge dislocations. The vacant broken line defect was considered to be a quasi-stable state of a bundle of basal plane dislocations in a-face growth, similar to a micropipe defect in c-face growth.

Dislocation-induced acoustic nonlinearity parameter in crystalline solids

Based on an orientation-dependent dislocation line energy, a solution to the acoustic nonlinearity parameter is obtained for pure and mixed dislocations in anisotropic crystals. The solution is validated by comparison with molecular dynamic simulations. Parametric studies using this new solution show that (i) elastic anisotropy can significantly change the nonlinear behavior of dislocations including “corners” in the bowed dislocation line, much reduced critical stress for instability, sharp peaks in the β versus applied shear relationship, etc., (ii) mixed dislocations may have distinct behavior that is not bounded by the pure edge and screw dislocations, (iii) asymptotic solutions of the acoustic nonlinearity parameter in terms of power series (as high as 5th order) may not be valid even for pure dislocations in isotropic solids.

Pure percutaneous pedicle screw fixation without arthrodesis of 32 thoraco-lumbar fractures: clinical and radiological outcome with 36-month follow-up

To evaluate the outcome of pure percutaneous fixation of unstable single level fractures at the thoraco-lumbar junction (A1 to B2 Magerl/AO Spine). Neurological intact patients were included in a 2-year prospective study (follow-up 36 months). Two groups were considered: the group in which additional short bilateral screws in the fractured vertebra were placed was called lordorizing screw group (LSG), the other was called non lordorizing screw group (nLSG). Clinical outcome was evaluated using the SF-36, the Oswestry disability index and the recovery time needed to go back work. The following radiological parameters were also evaluated on the follow-up exams: the Mid-Sagittal Index, the Cobb's angle and the Sagittal Index. In the LSG, the correction values of MSI, Cobb's angle and SI were statistically significantly higher than in nLSG. When feasible we recommend a pure percutaneous short segment pedicle screw fixation adding a lordorizing screw.