Controlling incisor torque with completely customized lingual appliances.

Ons Alouini,Moritz Blanck-Lubarsch,Hans-Joachim Helms,Dirk Wiechmann,Michael Knösel

doi:10.1007/s00056-020-00231-9

Abstract

PurposeTo test the null hypothesis of no significant deviation between the center of rotation (CROT) and the center of resistance (CRES) during space closure in Angle class II division 2 subjects achieved using a completely customized lingual appliance (CCLA) in combination with class II elastics and elastic chains.MethodsThis retrospective study included 29 patients (male/female 11/18; mean age 15.6 [13–27] years) with inclusion criteria of an Angle class II/2 occlusion of least of half of a cusp, maxillary dental arch spacing, completed CCLA treatment (WIN, DW Lingual Systems, Bad Essen, Germany) in one center with a standardized archwire sequence and use of class II elastics and elastic chains only. Maxillary incisor root inclination was assessed by X‑ray superimpositions of the maxilla at the beginning (T1) and the end (T3) of CCLA treatment. Using Keynote software (Apple®, Cupertino, CA, USA), the incisor’s CROT was assessed with the point of intersection of the incisor axes (T1; T3) following vertical correction of overbite changes. CRES was defined at 36% of the incisor’s apex–incisal edge distance.ResultsThe null hypothesis was rejected: the mean CROT − CRES difference was 52.6% (p < 0.001). The mean CROT was located at 88.6% (min–max 51–100%) of the incisor’s apex–incisal edge distance. Although 6.9% of CROT were located between the CRES and the alveolar crest, the vast majority (93.1%) were assessed between the alveolar crest and the incisal edge, or beyond.ConclusionCCLAs can create upper incisor palatal root torque even in cases in which lingually oriented forces applied incisally to the center of resistance of the upper incisors counteract these intended root movements.

Highlights

Occurrence of Angle class II division 2 (II/2) malocclusion varies between different populations [1]: While recent French, Swedish, and Turkish studies have reported lower prevalence rates, ranging from 1.8 to 5.4% [2,3,4], British and Croatian researchers have reported an incidence of 10% (British) or even 18% (Croatian population) [5, 6]
Orthodontic corrections are considered to be more difficult in those cases compared with Angle class II division 1 malocclusions, as incisor torque corrections are distinctively more difficult to implement, due to the increased and permanent labial resting pressure forces caused by the lips [7,8,9]
Despite these sophisticated approaches, the most common clinical approaches include space closure by either elastic chains or class I sliding mechanics, both of which are capable of achieving space closure, but have the immanent challenge of producing force vectors counteracting third-order incisor correction by palatal root torque required in Angle class II/2 treatments

Summary

Introduction

Occurrence of Angle class II division 2 (II/2) malocclusion varies between different populations [1]: While recent French, Swedish, and Turkish studies have reported lower prevalence rates, ranging from 1.8 to 5.4% [2,3,4], British and Croatian researchers have reported an incidence of 10% (British) or even 18% (Croatian population) [5, 6]. While the use of elastic chains and class II elastics is common for simultaneous space closure and occlusal adjustments, it complicates incisor torque control in Angle class II/2 subjects by producing forces that reduce incisor root inclination without providing additional counteracting moments. Closing-loop mechanics with nonsegmented labial archwires may be suitable for incisor retraction along with an adequate proclination, making use of appropriate gable bends mesially and distally of the retraction loops Despite these sophisticated approaches, the most common clinical approaches include space closure by either elastic chains or class I sliding mechanics, both of which are capable of achieving space closure, but have the immanent challenge of producing force vectors counteracting third-order incisor correction by palatal root torque required in Angle class II/2 treatments

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