Attachments and IPR in clear aligner therapy: the gap between plan and result

Case selection and expectations

A 2025 systematic review of 21 randomised trials reported no significant difference between clear aligners and fixed appliances in ABO objective grading scores, Little's irregularity index or PAR scores; these primary outcomes were not pooled, as meta-analysis was possible only for secondary outcomes. In the meta-analysis, plaque, gingival and bleeding indices were lower with aligners. The overall quality of evidence was low, and both approaches worked well in simple, non-extraction cases. Finding no difference does not show that the two approaches are equivalent, and the authors call for more studies of complex malocclusions.¹ A 2025 meta-analysis of 15 randomised and non-randomised trials (1084 patients) found no significant difference in treatment quality or duration in non-extraction cases, whereas in extraction cases fixed appliances gave better treatment quality; evidence that post-treatment stability is similar was limited, and the authors note that heterogeneity and short follow-up limit the strength of the conclusions.²⁰

The picture changes with the type of movement. A 2015 systematic review of 11 studies found anterior intrusion and posterior buccolingual inclination effectively controlled; anterior extrusion was the hardest movement to control (30% accuracy), and rotation of rounded teeth was not controlled effectively.⁶ More recent reviews temper the intrusion finding: a 2026 review lists intrusion among the movements with reduced predictability,⁸ and in a 2025 review of eight clinical studies on lower incisor intrusion, predictability ranged from 35% to 65%, with a serious risk of bias in seven of the studies.¹⁹ A meta-analysis of rotational movement found the lowest accuracy for upper canines (47.9%) and the highest for lower incisors (70.7%); the software prediction was not met whether or not attachments or IPR were used.² A 2025 review of 12 studies reported rotational accuracy between 36% and 85%, with maxillary canines and premolars the least reliable; attachments and IPR were widely used, but their effectiveness was inconsistent, and the certainty of evidence was low to moderate.¹⁸

Additional aligners after the first series (refinement) should therefore be treated as an ordinary part of treatment. Systematic reviews report that most movements may not be completed predictably with a single set of aligners, and that the need for refinement may be associated with case complexity, extraction treatment, IPR strategy, severe spacing and large corrections.^{7, 8}

What do attachments add?

A systematic review of 26 studies concluded that attachments significantly improve the expression of orthodontic movement and aligner retention, and that the tooth sites and shapes where they work better can be identified.³ In another review of five clinical trials (medium risk of bias), attachments mostly improved anterior root torque, rotation and mesiodistal movement and increased posterior anchorage, although some studies showed contradictory or non-significant results. Attachments also seem to improve intrusion, but evidence for intrusion, as for extrusion, is lacking.⁹ The contribution of attachments therefore depends on the movement and the configuration.

A meta-analysis comparing software-proposed optimised attachments with conventional attachments within one commercial system found no significant difference in accuracy for most movements. Pooled accuracy for canine derotation was 61.2% with conventional and 71.5% with optimised attachments; for anterior extrusion it was 57.5% and 62.4%. No attachment type produced the full planned movement.¹⁰

Removing attachments at the end of treatment is a clinical step in its own right. In three laboratory studies, enamel loss ranged from about 15 µm to more than 50 µm, and residual composite covered about 20% to 40% of the surface. Multi-step protocols using a tungsten carbide bur followed by silicone polishers under magnification gave the most favourable balance between removing composite and preserving enamel under laboratory conditions, and magnification of 2.5 times or more improved precision. There are no clinical trials, and the authors state that these findings cannot be directly extrapolated to routine clinical practice; a preferred clinical protocol has not been established.¹¹

IPR: how safe, how accurate?

In a systematic review of 18 studies, four of which assessed caries, meta-analysis showed no difference in caries incidence between surfaces treated with interproximal enamel reduction (IPR) and untreated surfaces 1 to 7 years later; no reliable conclusion on enamel roughness after IPR could be drawn because the studies were too diverse.⁴ A more recent review of eight clinical studies reported no demineralisation, no increase in caries, no periodontal change and no sensitivity after IPR; the quality of evidence was low to very low.¹² Not detecting an increase does not show that there is no risk for every patient or technique.

Proximal enamel thickness is one of the limits on how much can be removed. According to a meta-analysis of 11 studies, distal enamel is on average 0.10 mm thicker than mesial enamel; enamel is thicker on premolars and molars and thinnest on lower central incisors (low level of evidence).¹³ These are population averages; they do not set the limit for an individual tooth.

The amount performed and the amount planned often differ. In a study of 40 patients treated with manual stripping, IPR performed was mostly less than planned, and accuracy was reported as 44.95% in the upper arch and 37.02% in the lower arch. The millimetre differences given in the abstract do not match the main results table, so they are not quoted here; the authors note that the differences in millimetres may not be clinically relevant.⁵ In another study of similar design with 40 patients, also with manual stripping, predictability of crowding resolution was high (87% upper, 81% lower), while IPR was the least accurate way of gaining space (49% and 42%).¹⁴ In a prospective study of 42 patients comparing hand-held strips with two motor-driven methods, the authors judged the motor-driven methods more accurate overall: with hand strips, the amount executed was significantly less than planned, especially on upper central incisors and lower canines. The abstract gives the mean planned-to-executed difference as 0.08, 0.09 and 0.10 mm for the three groups; no between-group comparison of these means is reported in the abstract. Anxiety and discomfort did not differ between methods.¹⁵

A review of aligner change intervals found no general difference in movement efficacy between 7-, 10- and 14-day protocols, while the 14-day protocol gave better results for some posterior movements. The level of evidence for efficacy was very low, and meta-analysis was not possible; for complex situations the authors suggest a protocol chosen by clinical judgement.¹⁶

Step-by-step protocol

1. Before reading the plan, confirm through examination that the case suits aligner treatment and record the patient's consent; in randomised comparisons with fixed appliances both worked well in simple, non-extraction cases, and in extraction cases a meta-analysis reported better treatment quality with fixed appliances.^{1, 20}
2. Read the digital plan movement by movement. Flag movements with low predictability, such as canine rotation, intrusion, anterior extrusion and rotation of rounded teeth.^{2, 6, 8}
3. At the start, tell the patient that additional aligners may be needed after the first series,^{7, 8} and discuss the retention plan. The Cochrane review of retention procedures excluded aligner studies, so this article does not recommend a specific retention method.¹⁷
4. Check the attachment plan for the flagged movements and for teeth that need anchorage; root torque, rotation and mesiodistal movement are the movements reported to benefit from attachments, although results vary, and a review of rotation found the effect of attachments inconsistent.^{3, 9, 18}
5. Review the IPR plan tooth by tooth and surface by surface and record the cumulative amount for each surface. Enamel is thinnest on lower central incisors and distal enamel is on average thicker than mesial; these averages do not set the limit for an individual tooth.¹³
6. Measure the amount of IPR performed as you go, whatever method you use, and record it alongside the planned amount. With hand strips, the amount executed fell short of plan especially on upper central incisors and lower canines; an advantage of motor-driven methods was not consistent across measures.^{5, 15}
7. Choose the change interval by clinical judgement, taking the movement into account; 7-, 10- and 14-day protocols gave similar results for most movements, and 14 days was better for some posterior movements (very low level of evidence).¹⁶
8. At reviews, compare planned and achieved positions. Where they differ, check attachments and the IPR record before revising the plan; the need for refinement has several contributing factors.^{7, 8}
9. At the end of treatment, consider using magnification for attachment removal. In laboratory studies magnification improved precision and a tungsten carbide bur followed by silicone polishers gave the most favourable balance; the authors state that these findings cannot be directly extrapolated to routine clinical practice, and a preferred clinical protocol has not been established.¹¹ After removal, put in place the retention plan discussed at the start.

Common errors and fixes

Level of evidence

What is known

Attachments are reported to improve the expression of planned movement and aligner retention, with results varying by movement; this comes from two systematic reviews, one based on clinical trials at medium risk of bias and the other not reporting a quality level in its abstract.^{3, 9} In the meta-analysis of a review that included four caries studies, caries incidence did not differ between surfaces treated with IPR and untreated surfaces over 1 to 7 years.⁴ Differences between planned and achieved movement, and between planned and performed IPR, have been reported.^{2, 5} Randomised trials found no significant difference in correction scores between aligners and fixed appliances, and both worked well in simple cases (low quality; these outcomes were not pooled).¹

What is not known

Further clinical trials are needed on how the number, size, shape and position of attachments affect each movement.⁹ Within the one commercial system studied, optimised attachments have not been shown to be superior overall.¹⁰ The predictability of intrusion and rotation varies widely between studies.^{18, 19} The clinical significance of enamel roughness after IPR is unclear.⁴ Evidence on attachment removal comes from laboratory studies only.¹¹ The Cochrane review of retention procedures excluded aligner studies, so it gives no direct comparison of retention strategies after aligner treatment.¹⁷

At the chair

• Have examination and consent confirmed that the case suits aligners?
• Are low-predictability movements flagged in the plan?
• Have refinement and the retention plan been discussed with the patient?
• Are attachments placed for torque, rotation, mesiodistal movement and anchorage needs?
• Is the IPR plan reviewed tooth by tooth and surface by surface, with the cumulative amount recorded?
• Is IPR measured as it is performed, whatever the method, and recorded alongside the planned amount?
• Was the change interval chosen by clinical judgement, taking the movement into account?
• When planned and achieved positions differ, were attachments and the IPR record checked before revising the plan?
• Has the use of magnification for attachment removal been considered, bearing in mind that the evidence comes from laboratory studies?
• After removal, has the retention plan discussed at the start been put in place?

References

1. Baneshi M, O'Malley L, El-Angbawi A, Thiruvenkatachari B. EFFECTIVENESS OF CLEAR ORTHODONTIC ALIGNERS IN CORRECTING MALOCCLUSIONS: A SYSTEMATIC REVIEW AND META-ANALYSIS. J Evid Based Dent Pract. 2025;25(1):102081. PMID: 39947778 · DOI: 10.1016/j.jebdp.2024.102081
2. Koletsi D, Iliadi A, Eliades T. Predictability of rotational tooth movement with orthodontic aligners comparing software-based and achieved data: A systematic review and meta-analysis of observational studies. J Orthod. 2021;48(3):277-287. PMID: 34176358 · DOI: 10.1177/14653125211027266
3. Jedliński M, Mazur M, Greco M, Belfus J, Grocholewicz K, Janiszewska-Olszowska J. Attachments for the Orthodontic Aligner Treatment-State of the Art-A Comprehensive Systematic Review. Int J Environ Res Public Health. 2023;20(5):4481. PMID: 36901488 · DOI: 10.3390/ijerph20054481
4. Koretsi V, Chatzigianni A, Sidiropoulou S. Enamel roughness and incidence of caries after interproximal enamel reduction: a systematic review. Orthod Craniofac Res. 2014;17(1):1-13. PMID: 24011354 · DOI: 10.1111/ocr.12030
5. De Felice ME, Nucci L, Fiori A, Flores-Mir C, Perillo L, Grassia V. Accuracy of interproximal enamel reduction during clear aligner treatment. Prog Orthod. 2020;21(1):28. PMID: 32719906 · DOI: 10.1186/s40510-020-00329-1
6. Rossini G, Parrini S, Castroflorio T, Deregibus A, Debernardi CL. Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod. 2015;85(5):881-9. PMID: 25412265 · DOI: 10.2319/061614-436.1
7. Robertson L, Kaur H, Fagundes NCF, Romanyk D, Major P, Flores Mir C. Effectiveness of clear aligner therapy for orthodontic treatment: A systematic review. Orthod Craniofac Res. 2020;23(2):133-142. PMID: 31651082 · DOI: 10.1111/ocr.12353
8. Nogueira Matos K, Belline da Silva T, Matos de Faria Almeida L, de Faria Almeida M, Dos Santos Dantas Guimarães HH. Clinical, biomechanical, and digital factors associated with refinement after the first series of clear aligners: A systematic review. Int Orthod. 2026;24(4):101211. PMID: 42442043 · DOI: 10.1016/j.ortho.2026.101211
9. Nucera R, Dolci C, Bellocchio AM, Costa S, Barbera S, Rustico L, et al. Effects of Composite Attachments on Orthodontic Clear Aligners Therapy: A Systematic Review. Materials (Basel). 2022;15(2):533. PMID: 35057250 · DOI: 10.3390/ma15020533
10. Muthuswamy Pandian S, Subramanian AK, Vaiid N. Comparison of efficacy and accuracy of tooth movements in optimized and conventional attachments of clear aligners - A systematic review and meta-analysis. J Oral Biol Craniofac Res. 2025;15(5):1123-1133. PMID: 40778386 · DOI: 10.1016/j.jobcr.2025.07.019
11. Nassar N, Corbani K, Bourgi R, Kmeid R, Cuevas-Suárez CE, A Holiel A. Enamel Integrity and Residual Composite Following Clear Aligner Attachment Removal: A Systematic Review. Clin Pract. 2026;16(3):51. PMID: 41892495 · DOI: 10.3390/clinpract16030051
12. Gómez-Aguirre JN, Argueta-Figueroa L, Castro-Gutiérrez MEM, Torres-Rosas R. Effects of interproximal enamel reduction techniques used for orthodontics: A systematic review. Orthod Craniofac Res. 2022;25(3):304-319. PMID: 34865310 · DOI: 10.1111/ocr.12555
13. Kailasam V, Rangarajan H, Easwaran HN, Muthu MS. Proximal enamel thickness of the permanent teeth: A systematic review and meta-analysis. Am J Orthod Dentofacial Orthop. 2021;160(6):793-804.e3. PMID: 34420845 · DOI: 10.1016/j.ajodo.2021.05.007
14. Fiori A, Minervini G, Nucci L, d'Apuzzo F, Perillo L, Grassia V. Predictability of crowding resolution in clear aligner treatment. Prog Orthod. 2022;23(1):43. PMID: 36437397 · DOI: 10.1186/s40510-022-00438-z
15. Güleç-Ergün P, Arman-Özçırpıcı A, Atakan-Kocabalkan A, Tunçer Nİ. Comparison of the accuracy of three interproximal reduction methods used in clear aligner treatment. Clin Oral Investig. 2024;28(1):95. PMID: 38221544 · DOI: 10.1007/s00784-024-05499-4
16. Monisha J, Peter E. Efficacy of clear aligner wear protocols in orthodontic tooth movement-a systematic review. Eur J Orthod. 2024;46(3):cjae020. PMID: 38666743 · DOI: 10.1093/ejo/cjae020
17. Martin C, Littlewood SJ, Millett DT, Doubleday B, Bearn D, Worthington HV, et al. Retention procedures for stabilising tooth position after treatment with orthodontic braces. Cochrane Database Syst Rev. 2023;5(5):CD002283. PMID: 37219527 · DOI: 10.1002/14651858.CD002283.pub5
18. Benedetti G, Sicca N, Lopponi G, Dettori C, Verdecchia A, Spinas E. Evaluating the Clinical Success of Clear Aligners for Rotational Tooth Movements in Adult Patients: A Systematic Review. Dent J (Basel). 2025;13(10):440. PMID: 41149087 · DOI: 10.3390/dj13100440
19. Fracchia DE, Bignotti D, Lai S, Battista E, Verdecchia A, Spinas E. Predictability of Lower Incisor Intrusion with Clear Aligners: A Systematic Review of Efficacy and Influencing Factors. J Clin Med. 2025;14(17):6339. PMID: 40944102 · DOI: 10.3390/jcm14176339
20. Alhafi ZM, Hajeer MY, Alam MK, Jaber ST. Quality and stability of orthodontic treatment outcomes with clear aligners versus fixed appliances: a systematic review and meta-analysis. Eur J Orthod. 2025;47(6):cjaf091. PMID: 41127933 · DOI: 10.1093/ejo/cjaf091

Methods note

Sources were searched in PubMed (NCBI E-utilities) on 5 November 2026. The search covered attachments in clear aligner therapy, interproximal enamel reduction, predictability of tooth movement, aligners compared with fixed appliances, refinement, change intervals and attachment removal. Systematic reviews and meta-analyses were given priority; because no review of IPR accuracy was found, three primary clinical studies were added. Three 2025 reviews (on rotation, on lower incisor intrusion and on aligners compared with fixed appliances in extraction and non-extraction cases) were added on 5 November 2026 after an external review of the text. Author, title, journal, year and DOI of every source were checked against its PubMed record; findings were taken from abstracts only, and full texts were not read, except that the main results table of one study was compared with its abstract to check a discrepancy.⁵ No product or brand names are given. This is not a systematic review; it was prepared from one database by one reader.

Author: Dr. Ferit Çiftçi · Dentist · Author page · Last updated: 5 November 2026

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