Zusammenfassung: Ziel: Überprüfung, ob durch eine bestimmte operative Technik die Rate der Krossenrezidive signifikant gesenkt werden kann. Methode: In eine prospektiv-randomisierte, farbduplex-kontrollierte Studie wurden 1389 Krossen (1054 Patienten) eingeschlossen, davon wurden 631 Patienten (766 Krossen) in den folgenden fünf Jahren nachuntersucht. Die Patienten wurden in drei Gruppen randomisiert. In der Kontrollgruppe (G1) wurden 607 radikale Krossektomien durchgeführt. In der Gruppe G2 wurde in 292 Fällen zusätzlich die Fascia cribrosa übernäht. In der Gruppe G3 (490 Krossen) wurde nach radikaler Krossektomie das Endothel des Stumpfes invertierend übernäht. Ergebnisse: Bei der Nachuntersuchung wurden vier Gruppen unterschieden: regelrechte postoperative Verhältnisse, Krossenrezidiv mit oder ohne klinischer Relevanz, verbliebener Stumpf. In G1 wurden 30/311 (9,6%), in G2 10/176 (5,7%) und in G3 26/279 (9,3%) Neovaskularisationen mit und ohne klinische Relevanz gefunden Schlussfolgerung: Die Studie zeigt, dass die Krossenrezidivrate durch Neoangiogenese nach korrekter Krossektomie durch die Einrichtung einer Barriere über dem Stumpfendothel nicht signifikant gesenkt wird.

This study aimed to investigate the dynamic behavior of different torque archwires for fixed orthodontic treatment using an automated, force-controlled biomechanical simulation system. A novel biomechanical simulation system (HOSEA) was used to simulate dynamic tooth movements and measure torque expression of four different archwire groups: 0.017″ x 0.025″ torque segmented archwires (TSA) with 30° torque bending, 0.018″ x 0.025″ TSA with 45° torque bending, 0.017″ x 0.025″ stainless steel (SS) archwires with 30° torque bending and 0.018″ x 0.025″ SS with 30° torque bending (n = 10/group) used with 0.022″ self-ligating brackets. The Kruskal–Wallis test was used for statistical analysis (p < 0.050). The 0.018″ x 0.025″ SS archwires produced the highest initial rotational torque moment (M_y) of −9.835 Nmm. The reduction in rotational moment per degree (M_y/R_y) was significantly lower for TSA compared to SS archwires (p < 0.001). TSA 0.018″ x 0.025″ was the only group in which all archwires induced a min. 10° rotation in the simulation. Collateral forces and moments, especially F_x, F_z and M_x, occurred during torque application. The measured forces and moments were within a suitable range for the application of palatal root torque to incisors for the 0.018″ x 0.025″ archwires. The 0.018″ x 0.025″ TSA reliably achieved at least 10° incisal rotation without reactivation.

En-bloc retraction is a common procedure in orthodontic therapy. The application of palatal root torque moments is required to control incisor inclination during retraction, yet studies comparing forces and moments with respect to different mechanics are lacking. This study aimed to investigate the forces and moments during orthodontic en-bloc retraction using a robotic biomechanical simulation system, comparing two distinct approaches: (I) compound technique [stainless steel (SS) combined with nickel-titanium (NiTi)] using industrially pretorqued retraction-torque-archwires (RTA) in combination with NiTi closed coil springs; (II) conventional sliding mechanics using SS archwires with manually applied anterior twist bends in combination with elastic chains. Two dimensions (0.017” × 0.025” and 0.018” × 0.025”) and ten archwires per group were investigated using 0.022” slot self-ligating brackets. Kruskal–Wallis tests with a significance level of α = 0.05 were conducted. The biomechanical simulation showed that en-bloc retraction was characterized by a series of tipping and uprighting movements, differing significantly regarding the examined mechanics. Collateral forces and moments occurred in all groups. Notably, RTA exhibited fewer extrusive forces. The most bodily movement was achieved with the compound technique and the 0.018” × 0.025” RTA. Sliding mechanics exhibited maximum palatal root torque moments of more than 20 Nmm, exceeding recommended values.