Nikolaos Pandis

Forces exerted by conventional and self-ligating brackets during simulated first- and second-order corrections.

INTRODUCTION Our aim in this study was to comparatively assess the forces generated from conventional and self-ligating bracket systems during the late leveling and alignment stage, specifically for first- and second-order movement. METHODS Three types of brackets were selected: Orthos2 (Ormco, Glendora, Calif), Damon2 (Ormco), and In Ovation-R (GAC, Bohemia, NY). The brackets were bonded on resin replicas constructed from a model of an aligned mandibular arch, and a 0.014 x 0.025-in copper-nickel-titanium wire (Ormco) was placed. First- and second-order corrections-buccolingual and intrusion-extrusion movements-were simulated on the orthodontic measurement and simulation system. A 2-mm displacement was applied on the x-axis and a 1-mm displacement on the z-axis, both in 0.1-mm intervals; 5 repetitions were performed for each wire-bracket-interval combination, and new brackets and archwires were used for each trial. The forces generated by manipulation of the bracket in the 2 directions were recorded directly with the orthodontic measurement and simulation system software and were statistically analyzed with 2-way ANOVA, with bracket and displacement as the discriminating variables. Group differences were further analyzed with the Tukey post-hoc comparisons test with the family error rate set at the 0.05 level. RESULTS In the first-order correction, the direction showed a significant effect on force magnitude, with inward (lingual) movement having lower force levels for the In Ovation-R. No significant difference was found between the Damon2 and the conventional appliance for this movement. In the second-order model, no difference was noted between the 2 self-ligating brackets in magnitude of force, but the conventional bracket showed higher force levels, which accounted for 20%, or 1 N, of the increase in magnitude. The effect of the direction of displacement (intrusion vs extrusion) on force variation did not produce a significant effect. CONCLUSIONS The forces generated by first- and second-order corrections in self-ligating appliances do not show a consistent pattern and depend on the wire, the direction of movement, and the design of the ligating component.

Comparative assessment of forces generated during simulated alignment with self-ligating and conventional brackets

The objectives of this study were to comparatively assess the magnitude and direction of forces and moments generated from different bracket systems, during the initial levelling and alignment stage of orthodontic treatment. Three types of brackets were used: Orthos2 (Ormco), Damon2 (Ormco), and In-Ovation R (GAC). The brackets were bonded on resin replicas models of a patients crowded mandibular arch, and a 0.014 inch Damon archform CuNiTi (Ormco) wire was inserted. The model was mounted on the Orthodontic Measurement and Simulation System (OMSS) and six static measurements were taken at the initial crowded state per bracket for the lateral incisor, canine, and first premolar. A total of 10 repetitions were performed for each measurement, with new brackets and archwires used for each trial. The forces and moments generated were registered directly on the OMSS software and were statistically analyzed using a one-way analysis of variance separately for each dental arch location and force component. Group differences were further analyzed with Tukeys post hoc comparisons test at the 0.05 significance level. The lingually inclined, crowded lateral incisor presented an extrusive and buccal movement and showed the lowest force in the vertical direction, whereas the self-ligating group of brackets generated the highest force in the buccolingual direction. The moments applied by the three bracket systems followed the general trend shown for forces; in the vertical axis, the self-ligating brackets exerted lower forces than their conventional counterpart. This was modified in the buccolingual direction where, in most instances, the self-ligating appliances applied higher moments compared with the conventional bracket. In most cases, the magnitude of forces and moments ranged between 30-70 cN and 2-6 N mm, respectively. However, maximum forces and moments developed at the lateral incisor were almost four times higher than the average.

A comparative assessment of the forces and moments generated with various maxillary incisor intrusion biomechanics

The aim of this study was to comparatively evaluate the intrusive forces and buccolingual torquing moments generated during anterior maxillary intrusion using different maxillary incisor intrusion mechanics. Five wire specimens were used for each of the following intrusive arches: blue Elgiloy utility arch 0.016 x 0.016 inch, TMA utility arch 0.017 x 0.025 inch, Burstone TMA intrusion arch 0.017 x 0.025 inch, and reverse curve of Spee NiTi 0.016 x 0.022 inch. The wires were inserted on bracketed dental arches constructed on maxillary Frasaco models, segmented mesially to the maxillary canines. Simulated intrusion from 0.0 to 3 mm was performed using the orthodontic measurement and simulation system (OMSS), and forces and moments were recorded in the sagittal plane at 0.1 mm vertical displacement increments. All measurements were repeated five times for each specimen and values recorded at 1.5 mm for all wires were used for statistical evaluations. The results were analysed with one-way analysis of variance with forces and moments serving as the dependent variables and wire type as the independent variable. Post hoc multiple comparisons were performed using the Tukey test (0.05 error rate). Comparison of the two major intrusion techniques for the maxillary anterior teeth, segmented and bioprogressive, revealed that the Burstone TMA 0.017 x 0.025 inch intrusion arch exerted the lowest force on the incisors (0.99 N), followed by the TMA utility 0.017 x 0.025 inch (1.33 N) and the blue Elgiloy 0.016 x 0.016 inch utility (1.43 N). The highest force was recorded for the reverse curve of Spee NiTi and exceeded the value of 9 N. The lowest buccolingual moments were recorded with the Burstone intrusion arch (2.47 Nmm), whereas the highest was registered for the utility arch constructed with a 0.017 x 0.025 inch TMA wire (7.31 Nmm).