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Evaluation of effectiveness and stability of aligner treatments using the Peer Assessment Rating Index

Evaluation der Effektivität und Stabilität von Aligner-Behandlungen mittels Peer-Assessment-Rating-Index

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Journal of Orofacial Orthopedics / Fortschritte der Kieferorthopädie Aims and scope Submit manuscript



The aims of this study were to measure treatment effects of aligner treatments in adult patients directly after treatment and the stability of these effects after a short-term retention period using the Peer Assessment Rating (PAR) Index.


This double-center trial consecutively screened 98 adult patients of whom 33 patients were treated according to predefined inclusion and exclusion criteria. The study sample was shown to be representative for adult orthodontic reality with regard to gender, age, and distribution of malocclusion type. Malocclusion severity was rated by using the PAR Index measured at baseline (T0), after finishing orthodontic treatment with Invisalign® (T1; Align Technology Inc., Santa Clara, CA, USA) and after a mean retention period of 10 months (T2). Furthermore, to better understand the observed treatment modality, specific treatment characteristics were recorded and analyzed.


The average PAR score at T0 was 22.18 (standard deviation [SD] ± 8.68). Posttreatment PAR score was 4.64 (SD ± 4.23) at T1 and was stable after a retention period of 10.07 months at T2 (SD ± 126.80 days; PAR 4.36, SD ± 3.93). All of the study cases showed a significant reduction of the total PAR score between T0 and T1 (p < 0.001), but no further difference between T1 and T2 (PAR 4.64 vs. 4.36). Cases were either classified ‘improved’ (n = 23) or ‘greatly improved’ (n = 10); no case was classified into the third PAR Index category ‘worse or no different’. On average, 72 aligners (SD ± 22) with 12 attachments per treatment (SD ± 4) were used to align teeth. Six patients needed a case refinement with a mean of 23 (SD ± 8) further aligners. The maximum number of needed ClinCheck® (Align Technology Inc., Santa Clara, CA, USA) treatment plan revisions was 18 (mean 7, SD ± 4).


The detected improvement rate indicated a good standard of orthodontic treatment using aligners. Treatment effects were stable throughout a short-term retention period using a specific retention protocol. Effectiveness and stability were equally achieved in mild, moderate, and rather severe cases within this consecutive sample. A critical focus should be placed on accurate treatment planning in order to make tooth movements predictable, realistic, and stable.



Ziele dieser Studie waren zum einen die Behandlungseffektivität von Aligner-Behandlungen erwachsener Patienten mittels PAR(Peer-Assessment-Rating)-Index zu evaluieren und zum anderen die Stabilität dieser Behandlungseffekte zu untersuchen.


Im Rahmen des Forschungsprojektes wurden 98 Patienten aus zwei Studienzentren konsekutiv gescreent, von denen 33 Patienten gemäß Ein- und Ausschlusskriterien rekrutiert werden konnten. Zahnfehlstellungen und Okklusionsabweichungen wurden mittels PAR-Index vor der entsprechenden Behandlung mit Invisalign® (Align Technology Inc., Santa Clara/CA, USA; T0), nach der aktiven kieferorthopädischen Behandlung (T1) und nach einer durchschnittlichen Retentionszeit von 10 Monaten (T2) ermittelt. Darüber hinaus wurden behandlungsspezifische Details vor Bestätigung erfasst und analysiert.


Der durchschnittliche PAR-Summenwert zu T0 betrug 22,18 (Standardabweichung [SD] ± 8.68). Durch die kieferorthopädische Behandlung konnte dieser auf 4,64 (SD ± 4,23) zu T1 reduziert werden und blieb nach 10,07 Monaten zu T2 mit 4,36 stabil (SD ± 3,93). Bei allen Patienten wurde eine signifikante PAR-Index-Reduktion zwischen T0 und T1 (p < 0,001) ermittelt. Zwischen T1 und T2 stellten sich keine signifikanten Veränderungen ein (PAR 4,64 vs. 4,36). Alle Patientenfälle wurden entweder als „improved“ (n = 23) oder „greatly improved“ (n = 10) eingestuft; keine Behandlung fiel in die dritte PAR-Index-Kategorie „worse or no different“. Durchschnittlich 72 Aligner (SD ± 22) mit 12 Attachments (SD ± 4) pro Behandlung wurden zur Begradigung der Zahnfehlstellungen und zur Einstellung der Okklusion genutzt. Sechs Patienten benötigten ein „case refinement“ mit durchschnittlich 23 (SD ± 8) Alignern. Sieben Revisionen des ClinCheck®-Behandlungsplans waren im Mittel vor entsprechender Bestätigung nötig (SD ± 4).


Die vorliegende Studie zeigt, dass ein guter kieferorthopädischer Standard zusammen mit einer hohen Behandlungseffektivität durch Aligner-Behandlungen erzielbar ist. Die Behandlungseffekte waren innerhalb des untersuchten Zeitraums stabil. Ein besonderer Fokus sollte auf einer genauen digitalen Behandlungsplanung liegen, damit entsprechende Zahnbewegungen durch Aligner realistisch erzielbar und stabil sein können.

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Correspondence to Isabelle Graf.

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Conflict of interest

I. Graf was award recipient of the International Align Research Award by Align Technology, Inc. (Santa Clara, CA, USA). There has been no interfering by Align Technology at any point—not regarding the study planning and study procedures, nor regarding the analyses and presentation of study results. C. Puppe, J. Schwarze, K. Höfer, H. Christ and B. Braumann declare that they have no competing interests.

Ethical standards

The study was approved by the ethics commission of Cologne University’s Faculty of Medicine (NO 15-103).

Additional information

Authors I. Graf and C. Puppe contributed equally to the manuscript.

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Graf, I., Puppe, C., Schwarze, J. et al. Evaluation of effectiveness and stability of aligner treatments using the Peer Assessment Rating Index. J Orofac Orthop 82, 23–31 (2021).

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