Biomechanical considerations for uprighting impacted mandibular molars

Abstract

This case report demonstrates two different uprighting mechanics separately applied to mesially tipped mandibular first and second molars. The biomechanical considerations for application of these mechanisms are also discussed. For repositioning of the first molar, which was severely tipped and deeply impacted, a novel cantilever mechanics was used. The molar tube was bonded in the buccolingual direction to facilitate insertion of a cantilever from the buccal side. By twisting the distal end of the cantilever, sufficient uprighting moment was generated. The mesial end of the cantilever was hooked over the miniscrew placed between the canine and first premolar, which could prevent exertion of an intrusive force to the anterior portion of the dentition as a side effect. For repositioning of the second molar, an uprighting mechanics using a compression force with two step bends incorporated into a nickel-titanium archwire was employed. This generated an uprighting moment as well as a distal force acting on the tipped second molar to regain the lost space for the first molar and bring it into its normal position. This epoch-making uprighting mechanics could also minimize the extrusion of the molar, thereby preventing occlusal interference by increasing interocclusal clearance between the inferiorly placed two step bends and the antagonist tooth. Consequently, the two step bends could help prevent occlusal interference. After 2 years and 11 months of active treatment, a desirable Class I occlusion was successfully achieved without permanent tooth extraction.

Review in the Treatment Decision of Modalities for Impacted Second Molar

“…Thus, an occlusal interference with the opposing tooth may occur. Morita et al suggested utilizing a compression force with a two-step bend incorporated into a NiTi archwire for cases in which the molar was slightly tipped and extruded [34].…”

Die kieferorthopädische Aufrichtung gekippter Molaren

“…Das Verhältnis von Extrusion und Aufrichtung kann dabei durch die Modifikation des Teilbogens gesteuert werden, da die Länge des Hebelarms direkt proportional zu der Größe des erzeugten Drehmoments ist 22 . Eine Erhöhung des Drehmoments kann folglich beispielsweise durch eine Extension des Hebels nach mesial, mit Anbindung mesial oder distal des Eckzahns statt zwischen den Prämolaren, erzielt werden 8 .…”

“…Dabei stellen ausgedehnte kariöse Läsionen oder Restaurationen, die Molaren-Inzisiven-Hypomineralisation (MIH), apikale Pathologien und endodontische Probleme die Hauptursachen für den Verlust erster Molaren dar 3 4 5 . In Folge neigen Oberkiefermolaren eher zu Rotation und Elongation 6 7 8 , während bei Unterkiefermolaren meist eine mesiale Kippung festzustellen ist 7 9 . Aber auch Lückensituationen bei Nichtanlagen, Zahnwanderungen und Zahnverlust in Folge von Parodontitis können eine Kippung von Molaren bedingen.…”

Force Systems Produced by Different Cantilever Configurations during Deactivation

“…Besides vertical activation, cantilevers can also be activated to produce a palatal as well as a buccal force [ 2 , 3 , 4 ]. They may serve as a simple system to solve multiple orthodontic problems [ 2 , 5 ], including frontal segment intrusion in deep bite correction [ 5 , 6 ] uprighting of tipped molars [ 7 , 8 ], intrusion of a single tooth [ 9 , 10 ], treatment of impacted teeth [ 11 , 12 , 13 , 14 , 15 ], correction of dental transposition [ 16 , 17 , 18 , 19 ], space closure [ 20 ], correction of occlusal plane cant [ 21 ] and dental asymmetries [ 22 ]. The commonly used material to manufacture cantilevers is titanium molybdenum alloy (TMA).…”