Biomechanical Effects (biomechanical + effects)

Distribution by Scientific Domains

Selected Abstracts

Biomechanical effects of double or wide implants for single molar replacement in the posterior mandibular region

Y. Sato
Double implants have been thought to have biomechanical advantages for single molar replacement. To evaluate the effectiveness of double implants versus a wide implant, the vertical forces and torque on each implant were calculated by three-dimensional geometric analysis. Buccal load (100 N) perpendicular to cuspal inclination (20) was applied at the occlusal surface of the superstructure. The three kinds of load points (A, B, C) were 15, 35, and 55 mm from the mesial contact point, respectively. Three implants were compared: mesial and distal double implants (, 33 mm), and a wide implant (, 5 mm). The wide implant showed torque around the long axis (18,150 N cm) whereas double implants had no torque. On the other hand, the vertical forces on the mesial double implant were both smaller (60%: loaded at point C) and larger (140%: loaded at point A) than the wide implant. Given the smaller surface area of the mesial double implant, this large force may generate much higher stress in the peri-implant bone. These results suggest that the biomechanical advantage of double implants for single molar replacement is questionable when the occlusal force is loaded at the occlusal surface near the contact point. [source]

Biomechanical effects of medial,lateral tibial tunnel placement in posterior cruciate ligament reconstruction

Keith L. Markolf
With most posterior cruciate (PCL) reconstruction techniques, the distal end of the graft is fixed within a tibial bone tunnel. Although a surgical goal is to locate this tunnel at the center of the PCL's tibial footprint, errors in medial,lateral tunnel placement of the tibial drill guide are possible because the position of the tip of the guide relative to the PCL's tibial footprint can be difficult to visualize from the standard arthroscopy portals. This study was designed to measure changes in knee laxity and graft forces resulting from mal-position of the tibial tunnel medial and lateral to the center of the PCL's tibial insertion. Bone,patellar tendon,bone allografts were inserted into three separate tibial tunnels drilled into each of 10 fresh-frozen knee specimens. Drilling the tibial tunnel 5 mm medial or lateral to the center of the PCL's tibial footprint had no significant effect on knee laxities: the graft pretension necessary to restore normal laxity at 90 of knee flexion (laxity match pretension) with the medial tunnel was 13.8 N (29%) greater than with the central tunnel. During passive knee flexion,extension, graft forces with the medial tibial tunnel were significantly higher than those with the central tunnel for flexion angles greater than 65 while graft forces with the central tibial tunnel were not significantly different than those with the lateral tibial tunnel. Graft forces with medial and lateral tunnels were not significantly different from those with a central tunnel for 100 N applied posterior tibial force, 5 N m applied varus and valgus moment, and 5 N m applied internal and external tibial torque. With the exception of slightly higher graft forces recorded with the medial tunnel beyond 65 of passive knee flexion, errors in medial,lateral placement of the tibial tunnel would not appear to have important effects on the biomechanical characteristics of the reconstructed knee. 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source]

Effects of 6 elevation of the heels on 3D kinematics of the distal portion of the forelimb in the walking horse

Summary Reasons for performing study: Understanding of the biomechanical effects of heel elevation remains incomplete because in vivo studies performed with skin markers do not measure the actual movements of the 3 digital joints. Objective: To quantify the effects of 6 heel wedge on the 3-dimensional movements of the 4 distal segments of the forelimb in the walking horse. Methods: Four healthy horses were used. Kinematics of the distal segments was measured invasively with a system based on ultrasonic triangulation. Three-dimensional rotations of the digital joints were calculated by use of a ,joint coordinate system' (JCS). Data obtained with heel wedges were compared to those obtained with standard shoes during the stance phase of the stride. Results: Heel wedges significantly increased maximal flexion of the proximal (PIPJ) and distal (DIPJ) interphalangeal joints and maximal extension (mean s.d. +0.8 0.3) of the metacarpophalangeal joint (MPJ). Extension of the PIPJ and DIPJ was decreased at heel-off. Few effects were observed in extrasagittal planes of movement. Conclusions: Heel wedges affect the sagittal plane kinematics of the 3 digital joints. Potential relevance: Controversial effects previously observed on the MPJ may be explained by the substantial involvement of the PIPJ, which was wrongly neglected in previous studies performed on the moving horse. [source]

Effectiveness of maternity support belts in reducing low back pain during pregnancy: a review

Simone SM Ho
Aims., This article aims to review the literature published to date on the types, current use, the biomechanical effects and adverse effects of maternity support belts for low back pain during pregnancy, to identify future research directions. Background., Lumbar/pelvic support belts are frequently recommended for the prevention and treatment of low back pain during pregnancy. Design., Systematic review. Methods., MEDLINE, CINAHL, the Cochrane Library and patents databases were electronically searched. Results., Maternity support belts belong to one of the four main types of maternity support garments, which are widely commercially-available. Current research showed limited evidence in support of the commercial maternity products regarding the effectiveness in the prevention and/or treatment of low back pain during pregnancy, other than that from the manufacturers. However, potential stabilisation effect of maternity support belt was demonstrated in some studies. Adverse effects reported include increased pain, fetal heart rate changes, skin irritation and discomfort. Conclusions., There is insufficient scientific evidence to conclude that wearing maternity support belts reduces pregnancy-related low back pain and/or pelvic girdle pain. Future research directions in the area of biomechanics and physiology are recommended. Relevance to clinical practice., This review provides comprehensive understanding of the effectiveness of maternity support belts for the relief of low back pain during pregnancy which will facilitate healthcare professionals in providing evidence-based advice to their patients. [source]

The effect of retainer thickness on posterior resin-banded prostheses: a finite element study

T.-S. Lin
summary, According to its design concept, a resin-bonded prosthesis, compared with the conventional fixed partial denture, is a weak and unstable structure. Therefore, a resin-bonded prosthesis induces a higher failure rate, especially in the posterior region. Recently, adhesion agents have been profoundly improved. However, the design guidelines of posterior resin-bonded prostheses (RBP) have seldom been evaluated from a biomechanical perspective. The objective of this study was to investigate the biomechanical effects of the retainer thickness on posterior RBP using the finite element method. A solid model of a posterior mandibular resin-bonded prosthesis, which employed the second molar and second premolar as the abutment teeth, was constructed and meshed with various retainer thickness (ranging from 02 to 10 mm). Horizontal and vertical loadings of 200 N were applied respectively at the central fossa of the pontic to examine the stress level at the interface between the retainer and abutment teeth. All exterior nodes in the root, below the cementoenamel junction were fixed as the boundary condition. The results showed that horizontal loading would induce higher interfacial stresses than the vertical loading which indicated that the horizontal component of the occlusal force plays a more important role in evaluating the debonding phenomenon. Further, the peak interfacial stresses increased as the retainer thickness decreased and, based on the fitted relation between retainer thickness and interfacial stresses, a 04 mm retainer thickness was suggested as the minimum required to prevent severe interfacial stresses increasing. [source]

Effects of alternative instrumentation strategies in adolescent idiopathic scoliosis: A biomechanical analysis

Martin Robitaille
Abstract The recent advent of modern instrumentation systems has improved the correction of scoliosis, but complicated the surgical decision-making process, especially with the introduction of diverse spinal fixation devices, new preoperative corrective maneuvers, and the reevaluation of many rules concerning the selection of fusion levels and other guidelines for surgical correction. Our objective was to assess the biomechanical effects of different instrumentation strategies for the same scoliotic cases. Several instrumentation strategies suggested by a group of 32 experienced senior surgeons for five cases were individually simulated using a validated computer model implemented in a spine surgery simulator. The resulting geometric indices varied among the five cases (e.g., range of main thoracic Cobb angles: 5,17, 16,29, 25,44, 15,34, 16,32; kyphosis: 22,33, 20,54, 33,55, 24,49, 29,46; and lordosis: 10,52, 24,38, 26,54, 8,28, 34,53). The average correction was better with pedicle screws (71%) than with hooks (51%) and hybrid constructs (67%). For the first time, to our knowledge, the effect of different instrumentation strategies was compared on the same patients, which is possible only with a surgery simulator. A large variability of instrumentation strategies existed among experienced surgeons and produced rather different results. This study questions the criteria for optimal configuration and standards to design the best surgical construct. 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:104,113, 2009 [source]

Long-term biomechanical properties of rabbit cornea after photodynamic collagen crosslinking

Gregor Wollensak
Abstract. Purpose:, Photodynamic riboflavin/ultraviolet-A (UVA)-induced collagen cross-linking, which increases the biomechanical stiffness of the human cornea by about 300%, has been introduced recently as a possible treatment for progressive keratoconus. The present study was undertaken to evaluate the longterm biomechanical effects of this new cross-linking treatment as a necessary prerequisite to its clinical success. Methods:, The corneas of the left eyes of nine male rabbits were cross-linked. The contralateral eyes served as controls. After removal of the central 7 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 mins with an irradiance of 3 mW/cm2 using a 370-nm UVA double diode. Groups of three animals were killed immediately after treatment and at 3 and 8 months, respectively. Biomechanical stress,strain measurements were performed using a microcomputer-controlled biomaterial tester on 4 10-mm corneal strips. Results:, Corneal thickness in the treated rabbit cornea was 408 20 ,m. A constant and significant increase in ultimate stress (of 69.7,106.0%), Young's modulus of elasticity (of 78.4,87.4%) and a decrease in ultimate strain (of 0.57,78.4%) were found over a time period of up to 8 months after cross-linking treatment. Conclusions:, Riboflavin/UVA-induced collagen cross-linking leads to a longterm increase in biomechanical rigidity which remains stable over time. These data support our previous longterm clinical observations and give hope that this new treatment will halt progressive keratoconus definitively. [source]