Frames of reference for the measurement of occlusal change and the integration of data from orthodontic models and cephalometric radiographs

Orthodontic movement of a canine into an adjoining extraction site

The orthodontic movement of a canine tooth into an adjoining extraction site using a removable appliance is calculated using the finite element method (FEM). The calculated movements are compared, using a reflex plotter, with actual clinical measurements made on several patients. In both cases, wide variations in tooth displacement and hence rotation are found. The most important variable indicated by FEM appears to be the angle at which the load acts on the tooth. The position and magnitude of load have only a minor influence.

Initial tooth movement: force application and pain--a relationship?

Initial dental casts of 24 patients, who had previously completed a discomfort index card for the first 16 days following placement of a fixed appliance, were examined. A method is described whereby the anterior and overall crowding in the relevant dental arch was measured as a tooth/arch discrepancy index using the reflex metrograph. The crowding was measured in three dimensions as the discrepancy between the sum of the anatomic mesiodistal widths of the teeth and the actual mean arch shape canine to canine (3 to 3) and first molar to first molar (6 to 6) inclusive. An additional two-dimensional method using the best "goodness of fit" (least variance) of a parabolic arch shape for the mean arch length in the 6 to 6 crowding measurement is also described. The measurement accuracy of the reflex plotter was less than 0.12 mm. The method error for the crowding measurements expressed as root mean square (RMS) values was 0.97 mm for the anterior tooth/arch, 1.45 mm for the overall tooth/arch discrepancies, and 1.35 mm for the tooth/arch discrepancy based on the best fit of a parabolic curve. It is proposed that since the same bracket width and fully engaged arch wire type were used in every case, some relationship between the initial crowding that reflected the forces applied and the discomfort experienced by the patients might be expected. This was not found to be true. There was no correlation between the total discomfort experienced and the crowding measurements 3 to 3 or 6 to 6.(ABSTRACT TRUNCATED AT 250 WORDS)

Operational performance of the Reflex Metrograph and its applicability to the three-dimensional analysis of dental casts

The purpose of the present study was to investigate the applicability of a new instrument (the Reflex Metrograph) to the three-dimensional analysis of dental casts. In this system, a dental cast, placed in front of a semireflecting mirror, creates an identical image behind the mirror. The measurement of a point is made by aligning a light source behind the mirror in coincidence with the image of a specific point on the object. The light source is carried on a three-dimensional slide system, and coordinates are digitized for sampling by the computer. Measurement accuracy of the instrument was evaluated for three measuring points determined on a maxillary dental cast placed in six different locations. In addition, differences in the performance skills of ten operators were evaluated. The results indicate that digitization of a point in three planes of space can be undertaken without direct contact of the object and that a consistent measurement accuracy can be obtained, regardless of differences in the location of the cast relative to the mirror or in the anatomic shape of the measured areas. In addition, operators with no previous experience can determine specific points to an accuracy of +/- 0.1 mm, with a minimal amount of training. Finally, measurement by the same operator for a pooled sample is recommended in order to avoid interoperator measurement error when determining linear distances.