Bruce S. Haskell

Auxiliary springs in continuous arch treatment: Part 1. An analytical study employing the finite-element method

This report describes the results of a finite-element analysis with ANSYS (Version 4.3) from Swanson Analysis Systems and 1 mm-long, 2-D elastic beam elements to modify and refine the designs of maxillary and mandibular springs for space-closure management. This system permitted static analysis by means of modern software systems instead of expensive and cumbersome mechanical bench studies. Our examination of anterior and posterior reactions led to what we believe are optimal designs with clinically manageable moment/force ratios and new canine brackets that accommodate these springs within the framework of conventional and straight-wire appliance systems. Three degrees of freedom were used at each node for translations in the x and y directions and a rotation about the z axis, producing 182 elements with 183 nodes for the mandibular model and 146 elements with 147 nodes for the maxillary model. Elgiloy retraction spring models (0.1650 inch x 0.02150 inch) in the edgewise mode were developed so that the effects of three different preactivation bends could be refined by computer analysis. Sixty-four analyses were performed for each spring, with each of three angle bends (theta 1, theta 2, and theta 3) varied from 0 degrees to 45 degrees in 15 degrees increments. The employment of this computer method promises to simplify the design and development of complex interacting orthodontic systems. Clinical cases are presented in Part 2 of this series, which illustrates the application of auxiliary springs.

Diagnostic Accuracy of Film-Based, TIFF, and Wavelet Compressed Digital Temporomandibular Joint Images

The purpose of this research was to determine if digitization and the application of various compression routines to digital images of temporomandibular joint (TMJ) radiographs would diminish observer accuracy in the detection of specific osseous characteristics associated with TMJ degenerative joint disease (DJD). Nine observers viewed 6 cropped hard-copy radiographic films each of 34 TMJs (17 radiographic series). Regions of interest measuring 2 in × 2 in were digitized using an 8-bit scanner with transparency adapter at 300 dpi. The images were placed into a montage of 6 images and stored as tagged image file format (TIFF), compressed at 4 levels (25∶1, 50∶1, 75∶1, and 100∶1) using a wavelet algorithm, and displayed to the observers on a computer monitor. Their observations regarding condylar faceting, sclerosis, osteophyte formation, erosion, and abnormal shape were analyzed using ROC. Kappa values were determined for relative condylar size and condylar position within the glenoid fossa. Indices were compared using ANOVA at a significance level ofP<.05. Although significant and substantial observer variability was demonstrated, there were no statistically significant differences between image modalities, except for condylar position, in which TIFF and wavelet (at all compression ratios) performed better than the original image. For faceting, wavelet 100∶1 performed better than radiographic film images. Little actual image file reduction was achieved at compression ratios above 25∶1.

Auxiliary springs in continuous arch treatment: Part 2. Appliance use and case reports

In the second part of this series, three clinical examples are presented to illustrate the use of auxiliary space-closure springs with clinically manageable moment-to-force ratios and new canine brackets to accommodate these springs within the framework of conventional and straight-wire 0.018-inch appliance systems. Eligiloy retraction spring models (0.1650 inch x 0.02150 inch) in the edgewise mode were developed for translational movements along a main archwire. The effects of different preactivation bends for influencing intraarch anchorage are shown for the conditions of reciprocal closure, posterior protraction, and anterior retraction.

Submentovertex Radiology: Cephalometric Considerations in Temporomandibular Dysfunction

Controversy exists in the literature concerning the association between the radiographic and the clinical features of the temporomandibular dysfunction (TMD). Hence, this study reinvestigated possible correlations between radiographically detected asymmetries and the clinical signs and symptoms of TMD. Complete clinical and radiographic records were gathered from 52 patients sequentially referred for corrected angle tomographs of the temporomandibular joint (TMJ). Measurements from submentovertex (SMV), lateral and posterior-anterior (PA) cephalographs and corrected angle parasagittal tomographs and recorded clinical signs and symptoms of TMD were the data inputs. Significant findings were as follows: a) as the discrepancy in the posterior condyle to pogonion measurement increased, the pogonion and both maxillary and mandibular incisors shifted laterally towards the shorter side; b) as the ANB angle increased, so did the difference in condylar angle measurements between the two condyles; c) the side with the larger condylar angle was positioned forward on the SMV; and d) a perpendicular bisector (Marmarys Centerline) of the line drawn between the right and left foramen spinosum was found to be a reliable baseline reference for SMV analyses. No statistically significant relation was found linking specific signs and symptoms of TMD to maxillofacial asymmetries recorded on SMV, lateral or PA cephalographs. None of the radiographic signs studied were found to be good predictors of specific signs and symptoms in TMD.

A removable appliance for alignment of second molars

On occasion active orthodontic treatment may be terminated before complete eruption of the second molars. A standard Hawley removable appliance used for retention after active orthodontic treatment can be modified to improve alignment of buccally positioned second molars (Fig. 1). Fig. 2 demonstrates the results of full-time appliance wear for a 3-month period. The appliance is fabricated by adding a 0.030-inch spring to a standard Hawley removable appliance. The spring may be soldered to an Adams clasp on the first molar. Two horizontal helices are incorporated into the spring to ensure that a desirable force and rate are obtained. Acrylic must be relieved from the lingual surface of the teeth to be moved. If mesiopalatal rotation is also desired, a recurve extension can be incorporated into the spring (Fig. 3).