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Forces and moments delivered by PET-G aligners to an upper central incisor for labial and palatal translation

Kraft- und Drehmomentübertragung von Alignern aus PET-G bei labialen und palatinalen Bewegungen eines mittleren oberen Schneidezahnes

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Abstract

Objectives

Aligners made of polyethylene terephthalate glycol (PET-G) were tested in an experimental study for labial and palatal translation of an upper central incisor to quantify the forces and moments thus delivered and to biomechanically evaluate the capability of bodily movement.

Materials and methods

Using a resin model of the upper dentition, tooth 21 was separated and connected to a 3D force/moment (F/M) sensor to record the forces and moments delivered by aligners for labial and palatal displacement. An impression was taken with tooth 21 in its neutral position to obtain casts for standardized thermoplastic fabrication of aligners varying in make and foil thickness (Duran® 0.5/0.625/0.75 mm; Erkodur® 0.5/0.6/0.8 mm; Track-A® 0.5/0.63/0.8 mm). Upon placing each aligner over the teeth of the resin model, the separated tooth was subjected to 0.01 mm increments of labial and palatal translation by 0.25 mm in either direction.

Results

The mean forces delivered by the thinnest (0.5 mm) aligners for 0.25 mm of palatal displacement of tooth 21 were 3.01 ± 0.07 N (Duran®), 5.31 ± 0.89 N (Erkodur®), and 3.69 ± 0.81 N (Track-A®). The thickest (0.75 or 0.8 mm) aligners delivered 4.49 ± 0.16 N (Duran®), 7.22 ± 0.45 N (Erkodur®), and 5.20 ± 0.68 N (Track-A®). The mean forces for palatal as compared to labial displacement were higher by a mean of 48 % with the Erkodur® and by 23 % with the Track-A® aligners but were smaller by 37 % with the Duran® aligners. The moment-to-force (M/F) ratios, calculated in relation to the center of resistance of the separated measurement tooth, ranged from − 9.91 to − 12.22 mm, thus, approaching the value of − 8.80 mm for uncontrolled tipping of this tooth.

Conclusion

Manufacturers of PET-G aligners have recommended setup increments of 0.5–1 mm, which appears excessive based on our results. PET-G aligners not featuring modifications (e.g., reinforcing ribs or composite attachments bonded to the teeth) are unsuitable for bodily movement of upper central incisors in labial or palatal directions.

Zusammenfassung

Ziele

Ziele der vorliegenden Studie waren die Messung der von Alignern aus PET-G (Polyethylenterephthalat-Glycol) bei labialen bzw. palatinalen Bewegungen eines mittleren oberen Inzisivi ausgeübten Kräfte und Drehmomente und die biomechanische Evaluierung ihres Potenzials für körperliche Zahnbewegungen.

Material und Methode

Von einem OK(Oberkiefer)-Kunststoffmodell wurde Zahn 21 separiert und auf einen 3-D-Kraft-/Drehmoment(F/M)-Sensor an einer Positionierungseinheit montiert. In Neutralposition dieses Messzahnes wurde eine Abformung durchgeführt und auf entsprechenden Gipsmodellen standardisierte Aligner verschiedener Fabrikate und Dicken (Duran® 0.5/0.625/0.75 mm; Erkodur® 0.5/0.6/0.8 mm; Track-A® 0.5/0.63/0.8 mm) hergestellt. Bei applizierten Alignern erfolgten labiale und palatinale Translationen des Zahnes 21 im Ausmaß von mindestens 0,25 mm.

Ergebnisse

Die bei palatinaler Auslenkung des Messzahnes um 0,25 mm ermittelten Kräfte betrugen bei den Alignern mit 0,5 mm Ausgangsdicke 3,01 ± 0,07 N (Duran®, Scheu Dental), 5,31 ± 0,89 N (Erkodur®, Erkodent) bzw. 3,69 ± 0,81 N (Track-A®, Forestadent). Die entsprechenden Werte für die 0,75–bzw. 0,8–mm-Schienen betrugen 4,49 ± 0,16 N (Duran®), 7,22 ± 0,45 N (Erkodur®) bzw. 5,20 ± 0,68 N (Track-A®). Die bei Palatinalbewegung auftretenden Kraftwerte waren bei den Erkodur®- bzw. Track-A®-Schienen um durchschnittlich 48 bzw. 23 % größer als bei Labialbewegung, und bei den Duran®-Schienen waren sie um 37 % kleiner. Die bei Translation des Messzahnes berechneten Drehmoment-Kraft(M/F)-Ratios lagen, bezogen auf das Widerstandszentrum, zwischen − 9,91 und − 12,22 mm, was annähernd dem Wert für eine unkontrollierte Kippung dieses Zahnes entspricht.

Schlussfolgerungen

Die bisher von Herstellern empfohlenen Setupschritte für PET-G-Aligner von 0,5−1 mm erscheinen in Anbetracht dieser Ergebnisse zu groß. PET-G-Aligner ohne Versteifungen oder adhäsiv auf den Zahnkronen befestigte Komposit-Attachments sind für körperliche Bewegungen von mittleren OK-Inzisivi in labiopalatinaler Richtung ungeeignet.

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Compliance with ethical guidelines

Conflict of interest. Fayez Elkholy, Thanapon Panchaphongsaphak, Fatih Kilic, Falko Schmidt, and Bernd G. Lapatki state that there are no conflicts of interest.

The accompanying manuscript does not include studies on humans or animals.

Einhaltung ethischer Richtlinien

Interessenkonflikt. Fayez Elkholy, Thanapon Panchaphongsaphak, Fatih Kilic, Falko Schmidt und Bernd G. Lapatki geben an, dass kein Interessenkonflikt besteht.

Dieser Beitrag beinhaltet keine Studien an Menschen oder Tieren.

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Authors and Affiliations

  1. Department of Orofacial Orthopedics and Orthodontics, University of Ulm Dental School, Albert-Einstein-Allee 11, 89081, Ulm, Germany

    F. Elkholy, T. Panchaphongsaphak, F. Kilic, F. Schmidt & B.G. Lapatki

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  1. F. Elkholy
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Elkholy, F., Panchaphongsaphak, T., Kilic, F. et al. Forces and moments delivered by PET-G aligners to an upper central incisor for labial and palatal translation. J Orofac Orthop 76, 460–475 (2015). https://doi.org/10.1007/s00056-015-0307-3

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