system may include bending force in first and second orders and a torsional force in third order. Analytical and experimental studies on bending force have been introduced, but information about torsion is still lack. The purpose of this study was to estimate the torsional moment in the force system of rectangular arch wires through theoretical and experimental studies. Wires most frequently used for third order control were selected as study materials. Cross sections of 0.016X17.022, 0.0174.025, 0.0194.025 inch rectangular wires in four different materials such as stainless steel (O mco), TMA (Ormco), NiTi (Ormco), and braided stainless steel (DentaFlex, Dentaurum) were used. The torque/twist rate of each test material was calculated using the torsion fotiuula Torque/twist rate, yield torsional moment, and ultimate torsional moment were measured with a torque gauge. The torsion formula assesses that the torque,/twist rate (T/theta) is proportional to the characteristics of material(G) and cross section (J), and is inversely proportional to the length of wire (L). Most experimental results conesponded with the formula. The relative stiffness was calculated for reference to a logical sequence of wire changes.
Logic ; Orthodontic Wires* ; Stainless Steel ; Torque ; Torsion, Mechanical

OBJECTIVE: The purpose of this study was to estimate the fracture resistance of commercially available ceramic brackets to torsional force exerted from arch wires and to evaluate the characteristics of bracket fracture. METHODS: Lingual root torque was applied to maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 x0.027-inch stainless steel arch wire. A custom designed apparatus that attached to an Instron was used to test seven types of ceramic brackets (n = 15). The torque value and torque angle at fracture were measured. In order to evaluate the characteristics of failure, fracture sites and the failure patterns of brackets were examined with a Scanning Electron Microscope. RESULTS: Crystal structure and manufacturing process of ceramic brackets had a significant effect on fracture resistance. Monocrystalline alumina (Inspire) brackets showed significantly greater resistance to torsional force than polycrystalline alumina brackets except InVu. There was no significant difference in fracture resistance during arch wire torsional force between ceramic brackets with metal slots and those without metal slots (p > 0.05). All Clarity brackets partially fractured only at the incisal slot base and the others broke at various locations. CONCLUSION: The fracture resistance of all the ceramic brackets during arch wire torsion appears to be adequate for clinical use.
Aluminum Oxide ; Ceramics* ; Incisor ; Stainless Steel ; Torque ; Torsion, Mechanical*

PURPOSE: To examine the effects of change in the weight bearing on the growth plate metabolism, a simulated animal model of weightlessness was introduced and the chondrocytes' cellular kinetics were evaluated. MATERIALS AND METHODS: Unloading condition on the hind-limb of Sprague-Dawley rats was created by fixing a tail and lifting the hind-limb. Six rats aged 6 weeks old were assigned to each group of unloading, reloading, and control groups of unloading or reloading. Unloading was maintained for three weeks, and then reloading was applied for another one week thereafter. Histomorphometry for the assessment of vertical length of the growth plate, 5-bromo-2'-deoxyuridin (BrdU) immunohistochemistry for cellular kinetics, and biotin nick end labeling TUNEL assay for chondrocytes in the growth plate were performed. RESULTS: The vertical length of the growth plate and the proliferative potential of chondrocytes were decreased in the unloading group than those of control groups. Inter-group differences were more significant in the proliferative and hypertrophic zones. Reloading increased the length of growth plate and proliferative potential of chondrocytes as evidenced by increase of the ratio of positive BrdU stained cells. However, apoptotic changes in the growth plate were not affected by the alterations of weight bearing. CONCLUSION: Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plate and have no effects on the apoptosis occurred. This may suggest that deprived weight bearing due to various clinical situations hamper normal longitudinal bone growth, and further studies regarding the factors for reversibility of chontrocytic proliferation upon variable mechanical stresses are needed.
Animals ; Apoptosis ; Biotin ; Bone Development ; Bromodeoxyuridine ; Chondrocytes ; Growth Plate* ; Immunohistochemistry ; In Situ Nick-End Labeling ; Kinetics* ; Lifting ; Metabolism ; Models, Animal ; Rats ; Rats, Sprague-Dawley ; Stress, Mechanical ; Tail ; Weight-Bearing* ; Weightlessness

BACKGROUND: To examine the effects of changes in mechanical loading on endochondral bone formation, a simulated rat model of weightlessness was introduced and the changes in the growth plate were evaluated. METHODS: Unloading condition on the hindlimb of Sprague-Dawley rats was created by fixing a tail and lifting the hindlimb. Six rats aged 6 weeks old were assigned to each group of unloading and reloading with their control group. Unloading was maintained for three weeks, and then reloading was applied for another one week afterwards. Histomorphometry for the assessment of vertical length of the growth plate, 5-bromo-2'-deoxyuridin (BrdU) immunohistochemistry for cellular kinetics, and biotin nick end labeling TUNEL assay for chondrocytes in the growth plate were performed. RESULTS: The vertical length of the growth plate and the proliferative potential of chondrocytes were decreased in the unloading group than those of the control group. Inter-group differences were more significant in the proliferative and hypertrophic zones. Reloading increased the length of growth plate and proliferative potential of chondrocytes as evidenced by the increase of the ratio of positive BrdU stained cells. However, the apoptotic changes in the growth plate were not affected by the alterations of the weight bearing. CONCLUSION: Alterations in the weight bearing induced changes in the chondrocytic proliferative potential of the growth plates and had no effect on the apoptosis occurrence. This may suggest that deprived weight bearing due to various clinical situations hamper normal longitudinal bone growth. Further studies regarding the factors for reversibility of chondrocytic proliferation upon variable mechanical stresses are needed.
Animals ; Apoptosis ; Biotin ; Bone Development ; Bromodeoxyuridine ; Chondrocytes ; Growth Plate ; Hindlimb ; Immunohistochemistry ; In Situ Nick-End Labeling ; Kinetics ; Lifting ; Models, Animal ; Osteogenesis* ; Rats* ; Rats, Sprague-Dawley ; Stress, Mechanical ; Tail ; Weight-Bearing ; Weightlessness

A detailed three-dimensional nonlinear finite element model of lumbar segment L3-L5 was developed to investigate the influence of vibration on the components of human spine. The results show that the vibration effects of different spinal components are not exactly the same, and the stress near the posterior region of L4-L5 annulus is higher than that of its anterior region. The vibration exerts a great influence on the facet joint of L4-L5 segment. The changing amplitudes of stress and deformation of spine reduce by 50% on the condition that the damping ratio is 0.08.
Biomechanical Phenomena ; Cadaver ; Computer Simulation ; Finite Element Analysis ; Humans ; Lumbar Vertebrae ; physiology ; Models, Biological ; Nonlinear Dynamics ; Stress, Mechanical ; Vibration ; Weight-Bearing ; physiology

Distraction osteogenesis(DO) is defined as a gradual mechanical process of mechanical stretching two vascularized bone surface apart with a critical rate and rhythm such that new bone forms within the expanding gap, reliably bridges the gap, and ultimately remodels to normal structure. DO has become a mainstay in bone tissue engineering and has significantly improved our armamentarium for reconstructive craniomaxillofacial procedures. But the molecular and biological mechanisms that regulate the formation of new bone during distraction osteogenesis are not completely understood. BMPs are potent osteoinductive agents. Our hypothesis was that BMPs, especially BMP-2 and BMP-4, might play an importent role in the signaling pathways that link the mechanical forces created by distraction to biological responses and in promting new bone formation. Using a rabbit's mandible, we investigated the expression of BMP-2, -4 at different time points during distraction osteogenesis. The purpose of this study is to research the pattern of expression of BMP-2, -4 in new bone formation during distraction osteogenesis of the rabbit mandible. The experimental group was applied gradual distraction (0.7mm a day by twice a day, 4.9mm in total, for 7 days) and the control group was carried out osteotomy alone. They were examined clinically, histologically, and by RT-PCR analysis. On 3 days after osteotomy, the high level of expression of BMP-2, -4 was detected. But, the expression of BMP-4 was decreased during latency period. As distraction was started, its expression was increased and maintained till postoperative 28days. In control group, the expression of BMP-4was remarkably decreased till postoperative 14 days. On the other hand, the expression of BMP-2 was no difference between experimental group and control group. The expression of BMP-4 was maintanined at high level during the entire experimental period in both group. These findings suggested that excellent bone formation during distraction osteogenesis is associated with enhanced expression of BMP-4 genes by mechanical tension stress.
Bone and Bones ; Hand ; Latency Period (Psychology) ; Mandible* ; Mechanical Processes ; Osteogenesis ; Osteogenesis, Distraction* ; Osteotomy

OBJECTIVETo investigate the changes of stress distribution in the normal maxillary complex under different conditions and explore the feature of biomechanical reaction.

METHODSA three-dimensional finite element stress analysis has been used to investigate the characters of stress distribution at open-mouth position and in centric occlusion.

RESULTSUnder the same load, the stresses of the same region in the normal maxillary complex were distributed unequally. The limits of stress at open-mouth position (8.969 N) were wider than that in centric occlusion (6.497 N).

CONCLUSIONSThe stress of the whole maxillary complex in centric occlusion was lower than that at open-mouth position because of the different state of masticatory muscle. This indicated that the effect of muscles needed to be considered in the study of maxillary complex biomechanics.

PURPOSE: To report the difficulties in the process of locking head screw removal due to the stripping of the hexagonal recess of the screw head. MATERIALS AND METHODS: We have removed 113 5.0-self tapping locking head screws and 202 3.5-self tapping locking head screws from 34 patients with fracture healing and 5 patients complicated with infection. All of the operations were done by one surgeon. All the screws were placed with the use of torque limiting attachment or driver. RESULTS: All of 113 5.0-self tapping locking head screws were removed without difficulties with an usual manner. 21 out of 202 3.5-self tapping locking head screws were removed with many difficulties due to the stripping of the hexagonal recess. 3 screws were removed successfully with the use of conical extraction screw. 12 screws were taken out by further stripping and destruction of the screw head. In 6 situations where the only one screw was left stripped, the plate was bent around the stripped screw and then it was removed by turning the plate as a handle. One screw was removed with the partial breakage of the near cortex upon lifting the plate after failed attempt of using conical extraction screw. CONCLUSION: Although we have followed the guidelines at the time of insertion we have experienced difficulties in the removal of 3.5 locking head screws due to the stripping of the hexagonal recess. Care should be taken at the time of removal of the locking plate especially for the 3.5 locking screws.
Fracture Healing ; Head ; Humans ; Lifting ; Torque

The objective of this program is to investigate the biological effect of dynamic strain on human periosteal cells in vitro. Using a well-established model, the Flexercell unit, we placed mechanical stress (50,000 microstrain, 1 Hz and sine wave) on human periosteal cells grown in collagen coated flexible membrane. The time points of proliferative and differentiative properties were assessed by means of cell counting, thymidine incorporation, synthesis of alkaline phosphatase and osteocalcin, and long term of mechanical load induced calcium nodules formation was also demonstrated. The results showed that the application of highly controlled strains exerted a significant effect on human periosteal cells by up regulation of osteogenic properties rather than exercised an influence on proliferation. The results suggested that the promoting effects of dynamic strain on human periosteal cells probably contribute to the biological function of mechanical loading bearing.
Biomechanical Phenomena ; Cell Proliferation ; Cells, Cultured ; Humans ; Periosteum ; cytology ; Stress, Mechanical ; Ulna ; cytology ; Weight-Bearing

OBJECTIVETo investigate the stress distribution and fracture mechanism of proximal femur under impact loads.

METHODSThe image data of one male's femur were collected by the Lightspeed multi-lay spiral computed tomography. A 3D finite element model of the femur was established by employing the finite element software ANSYS, which mainly concentrated on the effects of the directions of the impact loads arising from intense movements and the parenchyma on the hip joint as well as those of the femur material properties on the distribution of the Mises equivalent stress in the femur after impact.

RESULTSThe numerical results about the effects of the angle sigma of the impact loads to the anterior direction and the angle gamma of the impact loads to the femur shaft on the bone fracture were given. The angle sigma had larger effect on the stress distribution than the angle gamma, which mainly represented the fracture of the upper femur including the femoral neck fracture when the posterolateral femur was impacted. This result was consistent with the clinical one. The parenchyma on the hip joint has relatively large relaxation effect on the impact loads.

CONCLUSIONSA 3D finite element analysis model of the femoral hip joint under dynamic loads is successfully established by using the impact dynamic theory.