RESUMEN
OBJECTIVE: Aim of this study was to investigate the forces and moments during segmented intrusion of a mandibular canine using Cantilever-Intrusion-Springs (CIS). METHODS: Three different CIS modifications were investigated using a robotic biomechanical simulation system: unmodified CIS (#1, control), CIS with a lingual directed 6° toe-in bend (#2), and CIS with an additional 20° twist bend (#3). Tooth movement was simulated by the apparative robotic stand, controlled by a force-control algorithm, recording the acting forces and moments with a force-torque sensor. Statistical analysis was performed using Shapiro-Wilk, Kolmogorov-Smirnov, Kruskal-Wallis ANOVA and post hoc tests with Bonferroni correction (α = 0.05). RESULTS: The initial intrusive force, which was uniformly generated by a 35° Tip-Back bend, decreased significantly (p < 0.05) from 0.31 N in group (#1) to 0.28 N in group (#3). Vestibular crown tipping reduced significantly (p < 0.05) from 2.11° in group (#1) and 1.72° in group (#2) to 0.05° in group (#3). Matching to that the direction of orovestibular force significantly (p < 0.05) shifted from 0.15 N to vestibular in group (#1) to 0.51 N to oral in group (#3) and the orovestibular tipping moment decreased also significantly (p < 0.05) from 4.63 Nmm to vestibular in group (#1) to 3.56 Nmm in group (#2) and reversed to 1.20 Nmm to oral in group (#3). Apart from that the orovestibular displacement changed significantly (p < 0.05) from 0.66 mm in buccal direction in group (#1) to 0.29 mm orally in group (#2) and 1.49 mm in oral direction as well in group (#3). SIGNIFICANCE: None of the modifications studied achieved pure mandibular canine intrusion without collateral effects. The significant lingual displacement caused by modification (#3) is, not least from an aesthetic perspective, considered much more severe than a slight tipping of the canine. Consequently, modification (#2) can be recommended for clinical application based on the biomechanical findings.
RESUMEN
This study was performed to locate the anteroposterior position of the center of resistance of upper anterior teeth when intrusive forces are acted on them by applying segmented arch mechanics. Three-dimensional finite elernent model of upper six anterior teeth, periodontal ligament and alveolar bone was constructed The locations of the center of resistance were compared according to the three variables, which are number of teeth contained in anterior segment, axial inclination of anterior teeth, and degree of alveolar bone loss. The following conclusions were drawn from this study; 1. When the axial inclination and alveolar bone height were normal, the locations of center of resistance of anterior segment according to the number of teeth contained were as follows; 1). In 2 teeth segment, the center of resistance was located in the distal area of lateral incisor bracket 2) In 4 teeth segment, the center of resistance was located in the distal 2/3 of the distance between the brackets of lateral incisor and canine. 3) In 6 teeth segment, the center of resistance was located in 3mm distal of canine bracket, which is interproxirnal area. between canine and 1st premolar. 4) As the number of teeth contained in anterior segment increased, the center of resistance shifted to the distal side. 2. As the labial inclination of incisors increased, the center of resistance shifted to the distal side. 3. As the alveolar bone loss increased, the center of resistance shifted to the distal side.