Precision of cephalometric analysis via fully and semiautomatic evaluation of digital lateral cephalographs.

OBJECTIVES: The aim of this study was to evaluate the precision of the cephalometric analysis using the orthodontic software Orthometric((R)) in two modes: fully automatic without any help by the user and semiautomatic with manual determination of all cephalometric landmarks. METHODS: From 100 indirectly digitally produced cephalographs, 72 were chosen randomly. On each one of these, three methods were applied on 12 decision-relevant cephalometric angles according to Hasund/Segner: (1) hand drawing on a transparent sheet over the cephalographic film; (2) software semiautomatically with manual correction on the screen; and (3) fully automatically. The hand-based method (1) is well established as a quality standard and reference. The angle measurement results of this method were compared with those of the semiautomatic and the fully automatic method by calculation of the mean absolute differences. Additionally, five randomly chosen cephalographs were evaluated ten times using all three methods for statistical evaluation of reproducibility. RESULTS: At tenfold evaluation of five cephalographs, the standard deviations of the angles were between 0.05 degrees and 0.8 degrees . These results were similar using all three methods. All three methods had similar reproducibility. At evaluation of 72 cephalographs, the mean absolute angle differences between the hand-based (1) and semiautomatic (2) methods were below 2 degrees and so within the allowed tolerance limit, except for the nasolabial angle. In contrast to this, all mean absolute angle differences between the (1) hand-based and (3) fully automatic methods exceeded 2 degrees , and with this the tolerance limit allowed by literature. CONCLUSIONS: The fully automatic determination of the cephalometric landmarks has led to relevant errors up to now, so that it is mandatory to check all automatically set landmarks and to correct them if required. In the case of the semiautomatic method, all relevant angles can be determined with the same reliability as hand drawing.

[A whole new development from the Bending Art System]. / Les toutes nouvelles évolutions du Bending Art System.

The system SureSmile (from Orametrix) has been developed on the basis of the Bending Art System (BAS) introduced in 1994 of which it is a manifold important evolution. It is a well considered combination of three-dimensional image processing, computer-assisted diagnosis, planning and realization of the treatment, which permits high quality orthodontia nevertheless capable of being reproduced in an objective manner. This article presents the system SureSmile.

Torque transmission between square wire and bracket as a function of measurement, form and hardness parameters.

The aim of the study was to investigate the influence of cross section, edge geometry and structural hardness on torque transmission between square wire and bracket. For this purpose, 5 different brands of stainless steel square wire in 3 dimensions (0.016" x 0.016", 0.016" x 0.022" and 0.017" x 0.025") were inserted into edgewise brackets with a slot size of 0.018" and loaded with different torques (1 and 3 Ncm). The slot and wire geometries were analyzed by computer on ground specimens before and after loading. In addition, the Vickers hardness and micro-hardness of the unstressed and stressed metal surfaces were determined. While the slot size was very accurately maintained, the wire dimensions deviated downwards by an average of 10%. Torque transmission led to notching and bending-up phenomena on the bracket slot flanks. A torque loading of 3 Ncm increased the torque play of 0.016" x 0.022" wires by 3.6 degrees, and of 0.017" x 0.025" wires by 3.7 degrees. In the case of 0.016" x 0.016" wires, an effective torque transmission was no longer possible. The average Vickers hardness of the wires was 533 kp/mm2, and that of the brackets 145 kp/mm2. The micro-hardness in the deformation area of stressed internal slot walls increased with increasing load transmission from 204 to 338 kp/mm2. As a result of excessively small wire dimensions and plastic deformation of the brackets, a relatively large torque play occurs. Deformation and notching in the area of the internal slot walls are inconsistent with demands for recycling brackets. A standardization of bracket wire systems stating the actual torque play would be desirable.

The force module for the bending art system. Preliminary results.

The force module for the bending art system (BAS) is used to calculate the initial forces and moments expected to act on a tooth after changing arch wires. The present study analyses the accuracy of the force module on the basis of 10 patients treated with the BAS (with an average observation period of 10 months). An average of 6 arch wires (0.16" x 0.016" steel) were used on each jaw. The approximate pressure in the periodontium was determined and statistically evaluated from the force module readings. The resulting average pressure values for the molars ranged between 0.26 N/cm2 and 0.54 N/cm2. The value in the area of the incisors, cuspids and bicuspids ranged between 1.03 N/cm2 and 2.83 N/cm2. Maximum pressure was 8.02 N/cm2. The results are discussed from a clinical point of view on a case-to-case basis. They are plausible in and for themselves. The more severe the initial state of misalignment, the higher the pressure values. These forces can be reduced by increasing the number of arch wires or by altering the form of the archwire correspondingly. The computer-generated values should be confirmed by taking a direct measurement on the tooth. The force module is just the first step in providing a reproducible estimation of the forces acting on a tooth. Even if the calculated absolute values should still be judged with reservation, they are nevertheless suitable for providing a comparative evaluation of various treatment concepts with reference to the forces acting on the periodontium and can serve clinicians as a rapidly available decision-making aid.

Continuous arch wire technique using the bending art system.

The bending art system (BAS) enables computerized production of individual arch wires for the multiband technique. Treatment planning using the continuous arch technique as part of the bending art system has been described. Planning of the arch wires follows an initial camera picture taken in the patient's mouth, and is divided into the following steps: ideal arch, target arch and course of treatment. The ideal arch establishes the individual shape of the arch wires in the horizontal plane. Based on the input of various small adjustments, the ideal arch is transformed into the target arch which represents the final arch of the treatment. Finally, the sequence of the various arches is established. The geometry of the intermediate arches is calculated on the assumption that each tooth is moved the shortest possible distance during transformation from the initial arch to the target arch. This procedure, called the direct method, is compared with the newly developed indirect method. With the indirect method, the camera picture is taken of the initial cast and the target arch is produced in accordance with a setup model in ideal occlusion. In contrast to the straight-wire technique, treatment with the BAS is not finalized with a straight arch wire since the occlusion of the individual patient rarely complies with the straight-wire norm.

Bending and torquing accuracy of the bending art system (BAS).

With the bending art system (BAS) the computerized production of individual arch wires has become possible. The BAS consists of an intraoral camera, a computer program and a bending machine producing the archwire by consecutive bending and twisting procedures. This study examines the accuracy of the bending machine when using 0.016" x 0.016" and 0.016" x 0.022" steel wire of rectangular cross-section. Bending angles ranging from 6 degrees to 54 degrees, and torsion angles ranging from 2 degrees to 35 degrees were tested; also the minimum distance between these individual operations was determined. The bent pieces of wire were analysed in a 3D-coordinate gauging system. The 0.016" x 0.016" steel wire showed a mean measuring error of 0.62 degree in bending procedures and of 0.72 degree in torsion procedures, whereas the 0.016" x 0.022" steel wire showed an error of 0.87 degree with edgewise bendings and of 0.86 degree with torsions. To ensure this accuracy a minimum distance of 0.5 mm to 0.7 mm, depending on which kind of bending combination is used, between bending and torsion is required. The error could be reduced even further if a more constant wire material and a more accurate calibration of the bending machine were used. All in all the precision of the bending machine meets the clinical requirements.