Frictional evaluations of dental typodont models using four self-ligating designs and a conventional design.

Abstract: After a previous study using typodonts and three standardized archwire (AW) sizes, the frictional evaluations of four self-ligating brackets were directed toward the optimal AW-bracket system. Four participating manufacturers suggested three AWs, which were a representation of the three stages of orthodontic treatment, to be coupled with their respective self-ligating design. Four replicated typodont models were mounted with a self-ligating design, and a fifth model was mounted with a conventional design that served as a control. The first experiment evaluated the manufacturer-suggested AWs against the respective self-ligating design. Because no third-stage AWs could engage their respective designs, a second experiment was implemented to gain more detailed analyses of the designs. This experiment included any successful manufacturer-suggested AWs from the first experiment against the four self-ligating designs and the control design. All self-ligating designs performed with the efficiency and reproducibility associated with expectations. Specifically, self-ligation outperformed the conventional brackets when coupled with up to 0.020- x 0.020-inch wires. The clearance of the various AW sizes and alloys changed with malocclusion. Furthermore, the parameter that best correlated with drawing forces was the bending stiffness of the AW, which was directly associated with the nominal dimension of each wire. The best AW-bracket system can be selected, when taking into account the stiffness (elastic modulus and size of the AW) along with the amount of malocclusion present, once the treatment plan is determined.

Evaluation of the frictional resistance of conventional and self-ligating bracket designs using standardized archwires and dental typodonts.

The frictional behavior of four conventional and four self-ligating brackets were simulated using a mechanical testing machine. Analyses of the two-bracket types were completed by drawing samples of three standardized archwires through quadrants of typodont models in the dry/wet states. Pretreatment typodonts of an oral cavity featured progressively malocclused quadrants. As nominal dimensions of the archwires were increased, the drawing forces of all brackets increased at different rates. When coupled with a small wire, the self-ligating brackets performed better than the conventional brackets. For the 0.014-inch wires in the upper right quadrant, the maximum drawing forces averaged 125 and 810 cN for self-ligating and conventional brackets, respectively. When coupled with larger wires, various designs interchangeably displayed superior performance. For the 0.019- x 0.025-inch wires in the upper left quadrant, the maximum drawing forces averaged 1635 and 2080 cN for self-ligating and conventional brackets, respectively. As the malocclusion increased, the drawing forces increased. For example, in the least malocclused quadrant and with the smallest wire, maximum drawing forces for self-ligating and conventional brackets averaged 80 and 810 cN, respectively, whereas in the most malocclused quadrant tested with the same wire size, maximum drawing forces for self-ligating and conventional brackets averaged 870 and 1345 cN, respectively. For maximum values between the dry and wet states, significant differences between ambient states existed only for the In-Ovation brackets in the lower left quadrant. These test outcomes illustrated how bracket design, wire size, malocclusion, and ambient state influenced drawing forces.