Date of Award

2016

Document Type

Thesis

Degree Name

Master of Science in Dentistry

College

College of Dental Medicine

First Advisor

Luis Leite

Second Advisor

Lawrence Littman

Third Advisor

Jompobe Vuthiganon

Abstract

Objective: It is the objective of this study to determine the dimensional accuracy and precision that is achievable by two manufacturing methods of stainless steel orthodontic brackets, CNC milling and metal-injection molding. To determine this, we propose the following specific aims: 1) to determine the actual dimensions of the slots in both milled and MIMed orthodontic bracket and standard deviations. 2) Using mathematical models to determine if the dimensional difference, if one exists, between milled and MIMed brackets will result in a difference in third order tooth movement (torque) realization (effective torque vs nominal torque). The actual bracket slot dimensions from both manufacturing techniques will be used in the mathematical model, which determines effective torque produced by a rectangular archwire within a rectangular slot. And 3) to determine if there is a statistical difference in the precision of the two different manufacturing methods. Materials and Methods: In this study ten brackets of two different types of 0.022 in (0.559 mm) slot maxillary right central incisor stainless steel conventional brackets were investigated: GAC OmniArch (GAC, Bohemia, NY, USA) and OPAL Avex (OPAL Orthodontics, South Jordan, UT, USA), both brackets with MBT prescription, which is 17° torque for the maxillary central incisors. The GAC stainless steel brackets are produced by the MIM process. The OPAL stainless steel brackets are produced by the CNC milling process. The mesial profiles of the brackets were imaged using ZEN imaging software through a Carl Zeiss Stemi508 microscope (Carl Zeiss MicroImaging GmbH, Jena, Germany), at 45x magnification. The brackets were carefully aligned so that the slots were photographed perpendicular to the slot. The images were calibrated and evaluated using the GNU Image Manipulation Program (GIMP) software. Using the software, points were selected and transferred for analysis into an Excel spreadsheet. In each photo 3 points were selected on the left (gingival) wall, the right (incisal) wall, and the floor. The points were all plotted on a 2-dimensional Cartesian (x,y) coordinate system, which was given by the GIMP software. Using Excel, a trend-line was generated for the walls and the floor, using linear regression. This analysis allowed for the determination of the bottom and top slot height as well as the angle between the slot walls. In addition to these measurements, the torque play for each bracket was determined for five different, commonly used rectangular wires. Nominal values for the archwires were used to determine torque play. The archwire dimensions used were: 0.016in × 0.022in, 0.017in × 0.025in, 0.018in × 0.025in, 0.019in × 0.025in, and 0.021in × 0.025in. The torque play is the more clinically applicable information. Furthermore, all of the brackets evaluated in the study were additionally imaged using scanning electron microscopy (SEM) allowing for more precise subjective evaluation of the bracket slots, in addition to the objective forms of evaluation previously mentioned. The SEM images revealed any surface inconsistencies within the bracket slots, that could affect bracket-wire interaction, and therefore tooth movement. Results: The bottom slot dimension for the OPAL sample had a mean of 0.0216in, with a standard deviation of 0.0002in, and a maximum of 0.0219in. The entire sample being below the nominal slot height of 0.022 in. The GAC bracket slots on the other hand had a mean of 0.0230in, with a standard deviation of 0.0003in, and a maximum of 0.0234in. The entire sample of GAC brackets evaluated had a bottom slot height above 0.022in. On average, the AVEX OPAL bracket slot heights were 2% below the nominal value, whereas the GAC OmniArch brackets were 4.5% oversized. All of the brackets in each sample were divergent, meaning that the top height of the bracket slot was greater than the bottom height, and there was no difference between the two groups when considering divergence angle. There was a statistical difference found for the deviation angles for wires of commonly used nominal sizes. Furthermore, comparison of the two groups was performed to test the deviation from the mean for each individual sample. This essentially would test the precision of the manufacturing techniques. It was determined that there was a statistical difference in the precision of the bracket slot heights between the two groups. The SEM images offer more insight into the shape of the bracket slot and surface appearance of the brackets. Conclusions: In conclusion, it was determined that there was a statistically significant difference between the two samples of brackets, GAC OmniArch and AVEX OPAL, in the outcome variables of bottom slot height, top slot height, and deviation angle for the five nominally sized archwires used in the mathematical model, which effects torque realization. In addition, it was determined that there is a statistically significant difference between the two samples, in terms of deviation from the mean, for those outcome variables. Therefore it can be concluded that there is a statistically significant difference between the two samples in terms of both accuracy and precision.

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