Individual Arch Research Articles

Prediction of Early Palatal Growth and Development in Children with Cleft Lip and Palate

With the use of multilevel modeling of longitudinal data, the relationship between the developmental status of the palate at 4 years of age and early palatal growth and development from birth to 1.5 years of age was studied. A model to predict palatal depths and widths at 4 years of age was developed and tested. The sample consisted of 130 children with cleft lip and/or palate. They were divided into three groups according to surgical treatment; (1) no palatal surgery, (2) soft palatal surgery, and (3) soft and hard palatal surgery. Results showed that in groups 1 and 2, the total arch depth at 4 years of age is strongly related to the initial arch depth at birth. No or low correlations were found between palatal depth at 4 years of age and the growth velocity at birth. The anterior arch width in groups 2 and 3 at 4 years of age appeared to be strongly related to the early growth velocity. In group 1, a moderate correlation with the palatal width and growth velocity at birth was observed. The results of the individual predictions of arch depths and arch widths were reasonable to fair. It was concluded that prediction of individual arch variables at 4 years of age is possible, although within limits. Clinically this means that extreme development can be discriminated from more average development.

Bite-opening Mechanics as Applied in the Begg Technique

In the Begg Technique, factors controlling the anterior intrusive force provided by the archwire have yet to be fully clarified. The rationale for bite opening with very light forces, the effect of Class II elastics on intrusive force magnitude and the intrinsic quality of 'Australian' wire in bite opening are examined in this paper. A formula is presented which allows the intrusive force that archwires exert in different individuals to be predicted. The values derived from the formula were compared with case model measurements. It was found that the intrusive force of the archwire was affected by the length of the individual dental arch. The magnitude of this intrusive force was seen to increase gradually during the period of bite opening and appeared to be related to the use of Class II elastics. The study revealed factors which affected the magnitude of the intrusive force.

Evolution of an active region and associated H? arch structures

We have studied the early stages of development of two adjacent active regions observed at the center and the wings of Hα for six days. From the growth of spots and arch structures we found that periods of slow flux emergence were followed by periods of vigorous flux emergence. We observed arch filaments covering an appreciable range of sizes (from a length of about 27 000 km and a height of 2000–3000 km to a length of 45 000 km and a height of about 15 000 km). Individual arch filaments within the same arcade sometimes have different inclinations of their planes with respect to the vertical. We observed isolated cases of arches crossing each other at an angle of ∼45°. During their early stages arch filament systems are short and they expand at a rate of about 0.8 km s−1. The rate of growth of arch filament systems is faster when the orientation of the flux tubes is nearly parallel to the equator. Our observations suggest that the early part of the evolution of individual arch filaments in a grown system is not visible; however, in a few cases we observed arch filaments appearing as dark features near one footpoint and expanding towards the other, with a mean velocity of about 30 km s−1.

An explanation for fast downflows on the Sun

The discovery of coronal loops has provoked major revisions in the theory of solar and stellar atmospheres. The solar corona is now recognized as a highly structured plasma, organized by bundles of intense magnetic field into individual arch- and loop-like structures along which gas can flow1. Each arch, rooted in the solar interior, extends through the chromosphere (T 106Κ) in its upper reaches. Early attempts at explaining the temperature and density structure of isolated static loops met with considerable success, despite the simplicity of the theory2,3; however, attempts to generalize the theory to describe loops with mass flows have remained singularly unsuccessful4–9. Here we point out that the puzzling observational properties of loop mass flows10–15 can be naturally explained if the loop is sufficiently cool (T ≲ 106 K)—that is, if it contains no coronal plasma.

Optimal design of arch-networks

Optimality criteria for minimum volume design are derived for a class of arch-networks comprising of pin-supported arches contained in vertical planes. The supports lie in a horizontal plane and the loads are applied vertically. It is assumed that the arches transmit loads by axial compression and the interaction among arches at intersections is by vertical reactions. It is shown that in the optimal arch-network, the centroids of all arches lie on a single surface and each individual arch is of an optimal form. An iterative numerical procedure to obtain the optimal solution for a given layout plan of arches and the loading on it is presented. Two examples are provided for the purpose of illustration.

Comparison study between three tooth positioners

Maintenance of arch dimensions during treatment and retention is essential for the stability of orthodontic results. This study compared ten essential measurements between posttreatment models and three different tooth positioners. Two custom-made positioners and one prefabricated positioner were evaluated. The material for this study consisted of models of twelve patients who were treated orthodontically to a Class I occlusion. Three sets of models were made at the debanding appointment. One set was kept as the original control model. The other two sets were sent to two different laboratories for construction of custom-made positioners. Identical instructions were included. A fourth set of models was made from the prefinisher positioner that was selected for each patient. The original control model, the returned individualized setups, and the prefinisher models were compared. Changes in maxillary and mandibular intercanine and intermolar widths were recorded, along with arch length, molar classification, rotations, spaces, curve of Spee, overjet, overbite, midline discrepancies, and teeth positioned out of arch symmetry. This study showed that there was a significant difference in the mandibular intercanine and maxillary intermolar width between the control model and the prefinisher model. No significant difference in arch length, maxillary intercanine width, and mandibular intermolar width was found between the control model and the other three models. All studied models had a Class I molar relationship. Open contact points and a slight curve of Spee were found in a high percentage of cases. Rotations, midline discrepancies, overjet, and overbite were within normal limits. Arch symmetry was acceptable in all but one case. Positioners, although they appear in most cases to respect individual arch dimensions, should be checked carefully before delivery to the patient.

Are coronal loops stable?

The solar corona is now recognized as a highly inhomogeneous plasma that comprises a complex network of individual arch and loop-like structures1. This has led to the recent idea that the isolated ‘coronal loop’ may form a basic building block of quiescent solar and stellar atmospheres2,3. Theoretical studies4,5, however, suggest that isolated loops are violently unstable and hence should collapse on the radiative time scale of the plasma. The simple fact that loops exist stably over long periods demonstrates the inadequacy of the current theory. We point out here that a crucial ingredient is missing from the theory and hence reconcile the existence of coronal loops with the disruptive effect of the radiative instability.

OUT-OF-PLANE BEHAVIOR OF CIRCULAR ARCHES UNDER SIDE LOADINGS

This paper presents out-of-plane behavior of circular arches subjected to lateral loads. The arches are analysed by dividing it in three components (two arch ribs and a lateral bracing system) and by solving the elastic differential equations for them with the aid of the Laplace transformation method. In relation to interaction of flexural rigidity of cross beam, torsional rigidity of arch ribs and warping rigidity as a whole cross section of the arch, the effect of biaxial flexural rigidity of individual arch ribs on their out-of-plane behavior is chiefly investigated. The effect of end-supporting conditions of the arches is also discussed.

Threshold levels for displacement of human teeth in response to laterally directed forces.

Threshold levels for the relationship of force magnitude to force duration to tooth displacement were recorded. It is apparent that the forces produced by the buccolingual muscles at "rest" could cause tooth displacement and may thereby influence individual tooth location and dental arch form.