Intermaxillary forces during activator treatment

The mode of action of the activator appliance is still unclear. Apart from a possible mandibular growth enhancing effect, some investigators believe that orthopedic forces may be applied to the maxilla, contributing to Class II correction by inhibition of maxillary growth. In addition, orthodontic forces may arise that produce dentoalveolar changes. The purpose of this study was to measure the magnitude of anteroposterior intermaxillary forces during wear of the activator appliance. Ten consecutive patients with Class II dental and skeletal relationships were treated with a modified activator appliance. The appliance had maxillary and mandibular segments that could be detached from each other during the measuring session. A force transducer was placed at the anterior part of the maxillary segment, and the anteroposterior force exerted by the mandibular segment was measured. Measurements were taken in the upright and reclined position at every patient visit for a period of 6 months. Results indicated that intermaxillary forces were generally in the orthodontic range (median values of 100 gf at the upright position and 123 gf at the reclined position). A wide variation in force levels was noted, both between patients and for the same patient during the experimental period. No statistically significant change in force levels was observed during the 6 month period and no difference was noted between upright and reclined posture.     

Scar traction appliance for a patient with microstomia: a clinical report

This clinical report illustrates how an active traction appliance was made for a patient with severe microstomia by attaching custom-made lip retractors to an orthodontic headgear. A steady, light tensile force was imparted to the lips with the elastic bands between the retractors and the headgear.     

Reliability of isometric wrist extension torque using the LIDO WorkSET for late follow-up of postoperative wrist patients

Instrumentation was developed to apply controlled biaxial (normal and shear) forces to the skin of a human or animal subject. The instrument mimicked any reference waveform within the constraints of a bandwidth of 15 Hz, a maximum force of 20 N, and displacement ranges of 15 mm for the normal direction and 18 mm for the shear direction. Two shaker motors, positioned with their axes parallel, were used with a low effective mass linkage and small-angle rotational joints to deliver the force. A digital feedback controller independently controlled the instantaneous normal and shear forces and recorded the resultant displacements. Evaluations on human and animal (pig) subjects demonstrated mean absolute errors between the applied and reference waveforms of less than 1.2% full-scale output for both the normal and shear directions. No degradation in performance was apparent over the course of a 1-h loading session. The instrument is to be used for the investigation of skin adaptation to mechanical stress, information that could be used to design new therapeutic methods to encourage skin load-tolerance.     

Modelling biological gel contraction by cells: mechanocellular formulation and cell traction force quantification

Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However, due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving holder. We formulate here a mathematical model describing the dynamic behaviour of the cell-gel medium in such devices. This model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the system under various conditions for cells and gel concentrations. This model is then used as the theoretical basis of an experimental device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported for various kind of cells with the use of similar or different experimental devices.     

Lateral force-displacement behaviour of the human patella and its variation with knee flexion--a biomechanical study in vitro

This study measured the patellar lateral force-displacement behaviour at a range of knee flexion angles in normal human cadaver specimens. The knee extensor muscles were loaded in proportion to their physiological cross-sectional areas, the tensions being applied in physiological directions along the separate quadriceps muscles. Knee extension was blocked at a range of knee flexion angles from 0 to 90 degrees, and patellar lateral displacement versus force characteristics were measured. This experiment was repeated with three total muscle forces, 20, 175 and 350 N, which were held constant at all flexion angles. It was shown that similar stability variation was obtained with the different total muscle loads, and also the forces required to produce a range of patellar displacements (1.5, 9 mm) were examined. A 5 mm lateral patellar displacement required a constant displacing force (i.e. the patella had constant lateral stability) up to 60 degrees knee flexion, and then a significant increase at 90 degrees. The results were related to surgical and anatomical observations.     

Representational momentum, centripetal force, and curvilinear impetus

In 3 experiments, observers witnessed a target moving along a circular orbit and indicated the location at which the target vanished. The judged vanishing point was displaced forward in the direction of implied momentum and inward in the direction of implied centripetal force. In general, increases in either the angular velocity of the target or the radius length of the orbit increased the magnitude of forward displacement. If both angular velocity and radius length were varied, then increases in either angular velocity or radius length also increased the magnitude of inward displacement. The displacement patterns were consistent with hypotheses that analogues of momentum and centripetal force were incorporated into the representational system. A framework is proposed that accounts for (a) the forward and inward displacements and (b) naive-physics data on the spiral tube problem previously interpreted as suggesting a belief in a naive curvilinear-impetus principle.     

Control of the vertical dimension in Class II correction using a cervical headgear and lower utility arch in growing patients. Part I

A retrospective cephalometric study was performed comparing three groups of 30 growing patients with Class II, Division 1 malocclusions. Group 1 was treated with a cervical headgear/lower utility arch combination (CHG/LUA), group 2 was treated with a cervical headgear alone (CHG), and the third group was untreated. The average treatment time was 1 year, 6 months. No other appliances were used during this period. Maxillary and mandibular dental and skeletal treatment responses were compared with an analysis of variance (ANOVA) and a Scheffe's test. In addition, a multiple stepwise regression was performed to determine whether pretreatment measures of facial pattern were accurate predictors of mandibular rotational response. Both treatment groups demonstrated significant reduction in maxillary protrusion. The CHG-only group showed significantly greater anterior descent of the palatal plane as compared with the untreated group. The maxillary molars showed significant distal movement in both treatment groups without any extrusion beyond that seen with normal growth. The maxillary incisor demonstrated significant retroclination in the CHG-only group. There was no statistical difference among the groups for variables commonly used for measuring mandibular rotation or protrusion. The change in vertical position of the lower molar was not significantly different among the groups. A CHG as used in this study produced maxillary orthopedic and orthodontic changes without upper molar extrusion beyond that seen with normal eruption and in the absence of an opening rotation of the mandible, even in subjects with dolicocephalic facial patterns. The LUA did not appear to influence lower molar eruption or mandibular rotational response. None of the commonly used predictors of facial pattern, such as the Y-axis, XY-axis, or MP angle, accurately predicted mandibular rotational response. Further study would be necessary to ascertain whether this was a result of their invalidation as predictors, or a result of the treatment strategy employed.     

Shedding of syncytiotrophoblast microvilli into the maternal circulation in pre-eclamptic pregnancies

A new formula, expressing the local angular displacement of an orthodontic beam when subjected to a second-order couple applied at midspan, has been developed and analyzed. The computed displacements were compared with the results of ex vivo testing. There was good agreement between the results from the theoretical evaluation and the bench testing. Second-order activation of an orthodontic beam can be described in four sequential phases. The initial displacement is influenced by the second-order clearance between bracket-slot and wire as well as the relationship between the bracket-slot width and interbracket distance. During phase II there is a nonlinear relationship between applied couple and rotational displacement. Within phases three and four displacement is linearly related to the interbracket distance, provided the relationship between the bracket-slot width and interbracket distance remains constant. For a given tooth size, the second-order beam stiffness is exponentially related to bracket width. The experiments also show that even small deflections of thin stainless steel wires can lead to second-order couples of large magnitudes when using a clinically relevant interbracket distance. Consequently, it is important that the orthodontist evaluates his or her choice of bracket width and arch wire stiffness in each clinical case in order to avoid supra-physiologic force levels.     

Effects of dopamine on postural control in parkinsonian subjects: scaling, set, and tone

1. This study investigates the effects of parkinsonism and of dopamine replacement therapy (levodopa) on scaling the magnitude of automatic postural responses based on sensory feedback and on predictive central set. Surface reactive torques and electromyographic (EMG) activity in response to backward surface translations were compared in patients with parkinsonism ON and OFF levodopa and in elderly control subjects. Correlations between the earliest postural responses [initial rate of change of torque and integrated EMG (IEMG)] and translation velocity provided a measure of postural magnitude scaling using somatosensory feedback. Correlations of responses with expected translation amplitude provided a measure of scaling dependent on predictive central set because the responses preceded amplitude completion. 2. Parkinsonian EMG responses in six leg and trunk muscles were not later than in elderly control subjects. In fact, quadriceps antagonist latencies were earlier than normal, resulting in coactivation at the knee not present in control subjects. EMG activation was fragmented, with short burst durations and high tonic levels that often returned to baseline with multiple bursts. In addition, parkinsonian responses showed smaller-than-normal agonist extensor bursts and larger-than-normal activation in tibialis and rectus femorus antagonist flexors. 3. Although parkinsonian subjects scaled postural responses to both displacement velocities and amplitudes, their torque response were smaller than those of elderly controls, especially in response to the largest displacement amplitudes. The gain (slope) of postural response magnitude scaling to displacement velocity was similar for parkinsonian and control subjects, although parkinsonian subjects had smaller torques. Parkinsonian subjects were also able to use prediction to scale responses to small expected displacement amplitudes, but many patients did not generate the larger plantarflexion torques required at larger displacement amplitudes. Reduced torque at large amplitudes was associated with less agonist gastrocnemius IEMG, increased tibialis antagonist burst responses, and increased tibialis tonic background activity. 4. Levodopa further reduced the already low magnitude of initial torque and IEMG responses to displacement velocities and amplitudes in parkinsonian patients. The ability to scale postural responses to velocity feedback was not affected by levodopa, but the ability to scale responses to large displacement amplitudes based on central set was worsened by levodopa. Levodopa also significantly reduced the tonic, background levels of EMG, particularly the distal gastrocnemius and tibialis activity. 5. High baseline muscle tone was apparent in parkinsonian subjects from their high background EMG activity in quiet stance, especially in tibialis and quadriceps, and the slow initial velocity of center of mass falling in response to displacements. By reducing tone, levodopa reduced passive stiffness to perturbations without increasing EMG burst magnitudes, resulting in less resistance to external displacements and thus faster center of body mass (COM) displacements. 6. The biggest postural deficit in parkinsonian subjects was not in response latency, pattern, or reactive or predictive scaling of response magnitude, but in quickly generating an adequate level of postural force. Dopamine improved tonic background postural tone but further weakened automatic postural responses to external displacements. Thus the basal ganglia may participate in postural control by regulating appropriate levels of background postural tone and by enabling adequate force generation for resisting external displacements.     

Outcomes of the surgical exposure, bonding and eruption of 82 impacted maxillary canines

BACKGROUND: Advances in bonding techniques and materials allow for reliable bracket placement on ectopically positioned teeth. This prospective study evaluates the outcome of forced orthodontic eruption of impacted canine teeth in both palatal and labial positions. METHODS: Eighty-two impacted maxillary canines in 54 patients were included in the study and were observed for 18 to 30 months after exposure. Following exposure by means of a palatal flap or an apically repositioned buccal flap, an orthodontic traction hook, with a ligation chain attached, was bonded to each impacted tooth using a light cured orthodontic resin cement. A periodontal dressing was placed over the surgical site for a period of time. RESULTS: All teeth were successfully erupted. Complications consisted of: failure of initial bond, at the time of surgery, which required rebonding; premature debonding at the time of pack removal and; debonding of brackets during orthodontic eruption. There was no infection, eruption failure, ankylosis, resorption or periodontal defect (pocket greater than 3 mm) associated with any of the exposed teeth. Attached gingiva of less than 3 mm was seen in only two of the buccally positioned canines (9%). CONCLUSION: Forced orthodontic eruption of impacted maxillary canines with a well bonded orthodontic traction hook and ligation chain, used in conjunction with a palatal flap or an apically repositioned labial flap, results in predictable orthodontic eruption with few complications.     

Intramedullary versus extramedullary fixation of subtrochanteric fractures. A biomechanical study

We compared two different subtrochanteric fracture fixation techniques, an intramedullary hip screw system (IMHS) and an extramedullary, dual sliding screw-plate system (MSP), to determine relative fixation stability. 6 matched pairs of osteosynthesized osteopenic cadaver femurs were axially loaded to 1000 N with concurrent, simulated abductor forces of 0%, 50%, or 86% of the applied head force. The initial loading sequence was made with uniaxial dynamization--the lag screw of the MSP locked and distal locking of the IMHS nail. Femoral head displacement and medial femoral strain were measured for intact femur controls, after fixation of a 2-part reverse oblique subtrochanteric fracture and finally a 3-part reverse oblique subtrochanteric fracture with a lateral wedge defect. The samples were then loaded at 750 N for 10(4) cycles with both devices uniaxially locked, followed by 10(4) cycles with both devices fully biaxially dynamized (unlocked). For the 2-part subtrochanteric fracture pattern, both devices exhibited similar inferior displacements of the femoral head (average 2.0 mm) and medial femoral strain (approximately 70% of intact). Increasing abductor forces decreased medial compressive strain but did not significantly affect head displacement. For the 3-part fracture model, the MSP demonstrated significantly less inferior displacement of the head (1.6 mm vs. 2.1 mm) and both devices demonstrated significantly decreased medial strain. After cycling, head displacement increased approximately 50% in both devices and medial strain increased slightly. After unlocking and cycling, the MSP group showed significant lateral displacement of the proximal fragment. The IMHS and MSP devices provide similar stability for fixation of 2-part and 3-part reverse oblique subtrochanteric fractures. In a biaxially dynamized, 3-part reverse oblique fracture, displacement of the proximal fragment can occur with the MSP.     

Guiding occlusal development with functional appliances

Functional appliances have been used in orthodontics since their introduction by Pierre Robin almost one hundred years ago, however, our understanding of how they bring about orthodontic correction is still limited. This article is a brief overview of their history, mode of action, advantages and disadvantages, and includes the results of a study of attempts to control and minimise their side-effects using a recent development in functional appliances: the 'Teuscher Appliance'. This appliance combines a high-pull headgear with the activator, and is designed to reduce the often reported side-effects of functional appliances. The skeletal and dentoalveolar effects of treatment with the Teuscher Appliance on 40 consecutively-treated patients are reported and illustrated with four individual case reports. The results showed that the skeletal effect on the maxilla was a retardation of the normal forward and downward growth in 80 per cent of the cases, and that mandibular growth in 70 per cent of cases was forward. In patients whose mandibular growth was primarily in a vertical direction, such growth could be ascribed mainly to posterior rotation of the maxilla and/or the fact that the acrylic covering the lower posterior teeth to correct a deep bite was removed, promoting the eruption of these teeth and increasing the anterior vertical development. The dentoalveolar changes were characterised by retroclination of the maxillary incisors in 90 per cent of the patients, and were due to insufficient torque control by the built-in torque springs, which need further development. The mandibular incisors were well controlled by capping. The statistical analysis showed an inverse correlation between the initial incisor inclination and the change during treatment. This suggests that proclination of the lower incisors, as previously reported, is not a contra-indication to functional appliance treatment, provided the appliance is correctly designed. Overall, this study showed considerable individual response to treatment, and that the occlusal correction occurred through a combination of skeletal and dentoalveolar changes.     

A case of bilateral optic neuropathy and recurrent transverse myelopathy associated with perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA)

The purpose of this study was to evaluate skeletal and dental effects of bionator headgear combination appliances on patients in development period with Class II, division 1 malocclusion. The comparison of computerized X-ray cephalometric measurements between the 26 treated children and 26 untreated children was made. The results showed that ANB angle was significantly reduced and horizontal mandibular growth development tended to be normal in the treated group. It was suggested that the bionator headgear combination appliance can restrain the maxillary growth early and promote the forward mandibular growth which contribute the functional jaws correction.     

Intraoperative measurement of suture forces in Shouldice repair of primary inguinal hernias

A special instrument was developed in order to quantify intraoperatively the traction forces which are employed during Shouldice repair of a primary inguinal hernia while adapting the lateral edge of the rectus sheath and the iliopubic tract. Further investigations were performed under the Valsalva manoeuvre and simultaneous measurement of the intra-abdominal pressure. In 25 patients an average increase in traction forces of 3.62 +/- 0.60 N was registered when the hernial gap was decreased to 0.3 cm. By applying the Valsalva manoeuvre with an average increase of 32 mm Hg in intra-abdominal pressure, traction was increased by a further 1.67 +/- 0.20 N on average. Hernia repair, tensing of the abdominal muscles and increasing the intra-abdominal pressure, however, have a small effect on the traction forces affecting the edges of the hernial gap. It may therefore be concluded that these factors, frequently believed causal for early hernia recurrence, are actually less influential as the force vector stressing the repair zone points in a different direction.     

The current status of psychoanalysis

When a perturbation displaces the human hand from equilibrium, arm muscles respond by producing restoring forces. When a set of displacements are given at various directions from the same equilibrium position, the resulting restoring forces form a "postural force field." It is not known whether these postural forces are related to those generated when a reaching movement is executed. However, if a movement is a consequence of a shift of the equilibrium position of the hand toward the target, then, from the postural force field, predictions can be made regarding the nature of the elastic forces acting on the hand during the movement. We have taken the first steps in testing this hypothesis by measuring the postural force field of a subject's arm over relatively large distances, and comparing these forces with the static forces generated at the hand while the subject attempted a reaching movement. Using a robot manipulandum, the hand was displaced at various directions from an equilibrium position. The measured restoring forces were fitted to a nonlinear model to define a postural force field for that equilibrium position. This field was used to predict elastic forces generated when the subject attempted to move the manipulandum from a point on the circumference of a circle to a target at its center--the center corresponded to the equilibrium position at which the postural field was measured. In some of the movement trials, the manipulandum was locked during approximately the first 120 msec of the program for motion and the resulting static "evoked" forces measured. We found that (1) the evoked forces did not point to the target, but were a function of the configuration of the arm and rotated with the shoulder joint, and (2) the magnitude of the evoked forces varied systematically, even though the movements were of the same magnitude. These patterns were remarkably similar to those observed in the postural forces. Our results provide experimental evidence linking maintenance of posture in a multijoint system to that of generating a movement. The evidence is consistent with the hypothesis that the CNS programs a reaching movement by shifting the equilibrium position of the hand toward the target.     

The prevalence of epilepsy follows the distribution of onchocerciasis in a west Ugandan focus

A study was made to determine whether skeletal alterations usually produced by rapid maxillary expansion may be compensated for in time by growth and/or comprehensive orthodontic treatment. In 30 patients, orthodontic treatment was started with rapid maxillary expansion, followed by fixed appliances, not combined with any other form of orthopedic device. Mean treatment time was 3.1 years. Nine measurements from the Ricketts analysis were studied, based on lateral cephalometric radiographs. Records were taken before orthodontic treatment and after completion of active therapy. A statistical analysis was made of the nine variables used, reflecting the vertical and anteroposterior skeletal proportions of the face, contrasting the changes before and after treatment. Of all the variables studied, the four that change with age according to the Ricketts analysis (mandibular plane angle, maxillary height, facial depth and facial convexity), yielded statistically significant differences after treatment, indicative of normal growth. The five remaining variables that remain constant with age according to the Ricketts analysis (facial axis, lower facial height, total facial height, palatal plane inclination and maxillary depth) showed no significant changes after treatment, also indicative of normal growth.     

UDP-GlcNAc:Galbeta1-->3GalNAc (GlcNAc to GalNAc) beta1-->6N-acetylglucosaminyltransferase holds a key role on the control of CD15s expression in human pre-B lymphoid cell lines

Distraction osteogenesis has become an important technique to treat craniofacial skeletal dysplasia. In this study, the technique of maxillary distraction with a rigid external distraction device is presented. Cephalometric results in the first 14 consecutive patients are analyzed. The study sample consisted of 14 patients with various cleft types and maxillary hypoplasia treated with the rigid external distraction technique. Analysis of the predistraction and postdistraction cephalometric radiographs revealed significant skeletal maxillary advancement. All patients had correction of the maxillary hypoplasia with positive skeletal convexity and dental overjet after maxillary distraction. The morbidity for the procedure was minimal. Surgical and orthodontic procedures are thoroughly described.     

Treatment of an ankylosed central incisor by single-tooth dento-osseous osteotomy

This article presents a case of an ankylosed upper central incisor that did not respond to orthodontic mechanics alone or to surgical luxation followed by orthodontic traction. We performed an osteotomy involving the dento-osseous segment in one surgical stage to allow its inferior displacement. The patient was followed for 18 months and the result was considered satisfactory from both the occlusal and periodontal standpoints.     

Individual finger forces acting on a grasped object during shaking actions

Individual finger grip forces acting on a hand-held object were examined during shaking tasks with a five-finger precision grip. The subjects (n = 13) shook a force transducer-equipped grip object (mass = 400 g) in vertical, horizontal, and mediolateral directions at an average movement speed of 33 cm/s (moderate) and 66 cm/s (fast). In addition, grip forces were examined while the subjects (n = 10) held the object in front of the body and walked or ran in place. It was found that the grip forces for all the fingers changed temporally and spatially coupling with the acceleration of the object resulting from shaking. The results suggest that grip force control is accomplished in an active and anticipatory fashion. Regardless of the shaking direction and speed, among the four fingers the absolute grip force in the index finger was largest, followed by the middle, ring, and little finger forces. The index finger therefore plays a primary role in grip force control during shaking. The percent force contribution by each finger varied depending on the direction of shaking. Contributions of the ring and little fingers were larger when shaken in the horizontal and mediolateral directions than they were in the vertical direction. The results suggest that different finger co-ordination is required in relation to shaking direction. Changes in shaking speed from moderate to fast changed the grip forces for all the fingers. During walking and running, grip force control similar to that during active vertical shaking was required to hold the object safely in the hand.     

Structural Control by Temporal Finite Elements

The shape control of structural systems using the temporal finite element method (TFEM) is addressed in this work. In particular, the standard time marching TFEM is used to predict the displacements of each degree of freedom (DOF) at the end of a given time interval. If these displacements do not exceed the limits imposed on the structure for serviceability, safety, etc., then the displacements for the next time step are computed. If, however, any of the displacements exceed their limit, a control velocity is computed and applied at the beginning of the time interval for each DOF exceeding its limit. The magnitude and direction of this velocity are such as to render the displacement at the end of the time interval equal to the limit value. An example of a two-degree-of-freedom system serves to illustrate this methodology.