Korean J Orthod.  2021 Mar;51(2):135-141. 10.4041/kjod.2021.51.2.135.

Micro-computed tomography evaluation of general trends in aligner thickness and gap width after thermoforming procedures involving six commercial clear aligners: An in vitro study

• Palone M
• Longo M
• Arveda N
• Nacucchi M
• Pascalis FD
• Spedicato GA
• Siciliani G
• Lombardo L

• KMID: 2513582
• DOI: http://doi.org/10.4041/kjod.2021.51.2.135

Abstract

Objective
To assess the effects of thermoforming on aligner thickness and gap width in six aligner systems with the same nominal thickness.
Methods
Six passive upper aligners of different brands were adapted to a single printed cast. Each sample was evaluated with high-resolution micro-computed tomography. To investigate aligner thickness and gap width, two-dimensional (2D) analysis was conducted assessing the effects of the following variables: tooth type (central incisor, canine, and first molar), 2D reference points, and aligner type. Data were analyzed and compared using analysis of variance and Tukey’s post-hoc tests (p < 0.05).
Results
Tooth type, dental region, and aligner type affected both the gap width and aligner thickness. The aligner thickness remained moderately stable across the arch only in the F22.
Conclusions
All thermoformed samples displayed smaller aligner thickness and gap width at anterior teeth and both gingival and coronal centers than at posterior teeth and occlusal surfaces.

Keyword

Gap width; Aligner thickness; Thermoforming procedure; Clear aligner therapy

Figure

• 

  Figure 1 Identification of slice planes and two-dimensional reference points on the construction grid for the incisor (A), canine (B), and first molar (C). Eight points were identified: 1, palatal gingival edge; 2, palatal surface center; 3, incisal edge; 4, vestibular surface center; 5, vestibular gingival edge; 6, vestibular cusp; 7, palatal cusp; and 8, central groove.

Reference

1. Lombardo L, Arreghini A, Maccarrone R, Bianchi A, Scalia S, Siciliani G. 2015; Optical properties of orthodontic aligners--spectrophotometry analysis of three types before and after aging. Prog Orthod. 16:41. DOI: 10.1186/s40510-015-0111-z. PMID: 26582007. PMCID: PMC4651973.

2. Ryu JH, Kwon JS, Jiang HB, Cha JY, Kim KM. 2018; Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners. Korean J Orthod. 48:316–25. DOI: 10.4041/kjod.2018.48.5.316. PMID: 30206530. PMCID: PMC6123073.

3. Gao L, Wichelhaus A. 2017; Forces and moments delivered by the PET-G aligner to a maxillary central incisor for palatal tipping and intrusion. Angle Orthod. 87:534–41. DOI: 10.2319/090216-666.1. PMID: 28165289.

4. Elkholy F, Schmidt F, Jäger R, Lapatki BG. 2017; Forces and moments applied during derotation of a maxillary central incisor with thinner aligners: an in-vitro study. Am J Orthod Dentofacial Orthop. 151:407–15. DOI: 10.1016/j.ajodo.2016.08.020. PMID: 28153171.

5. Cowley DP, Mah J, O'Toole B. 2012; The effect of gingival-margin design on the retention of thermoformed aligners. J Clin Orthod. 46:697–702. quiz 705PMID: 23395874.

6. Lombardo L, Arreghini A, Ramina F, Huanca Ghislanzoni LT, Siciliani G. 2017; Predictability of orthodontic movement with orthodontic aligners: a retrospective study. Prog Orthod. 18:35. DOI: 10.1186/s40510-017-0190-0. PMID: 29130127. PMCID: PMC5682257.

7. Lombardo L, Toni G, Stefanoni F, Mollica F, Guarneri MP, Siciliani G. 2013; The effect of temperature on the mechanical behavior of nickel-titanium orthodontic initial archwires. Angle Orthod. 83:298–305. DOI: 10.2319/040612-287.1. PMID: 22908946.

8. Martina S, Rongo R, Bucci R, Razionale AV, Valletta R, D'Antò V. 2019; In vitro cytotoxicity of different thermoplastic materials for clear aligners. Angle Orthod. 89:942–5. DOI: 10.2319/091718-674.1. PMID: 30945933.

9. Alexandropoulos A, Al Jabbari YS, Zinelis S, Eliades T. 2015; Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials. Aust Orthod J. 31:165–70. PMID: 26999889.

10. Jindal P, Juneja M, Siena FL, Bajaj D, Breedon P. 2019; Mechanical and geometric properties of thermoformed and 3D printed clear dental aligners. Am J Orthod Dentofacial Orthop. 156:694–701. DOI: 10.1016/j.ajodo.2019.05.012. PMID: 31677678.

11. Bucci R, Rongo R, Levatè C, Michelotti A, Barone S, Razionale AV, et al. 2019; Thickness of orthodontic clear aligners after thermoforming and after 10 days of intraoral exposure: a prospective clinical study. Prog Orthod. 20:36. DOI: 10.1186/s40510-019-0289-6. PMID: 31495908. PMCID: PMC6732265.

12. Mantovani E, Castroflorio E, Rossini G, Garino F, Cugliari G, Deregibus A, et al. 2018; Scanning electron microscopy evaluation of aligner fit on teeth. Angle Orthod. 88:596–601. DOI: 10.2319/120417-827.1. PMID: 29911907.

13. Mantovani E, Castroflorio E, Rossini G, Garino F, Cugliari G, Deregibus A, et al. 2019; Scanning electron microscopy analysis of aligner fitting on anchorage attachments. J Orofac Orthop. 80:79–87. DOI: 10.1007/s00056-018-00167-1. PMID: 30673806.

14. Ryokawa H, Miyazaki Y, Fujishima A, Miyazaki T, Maki K. 2006; The mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Orthod Waves. 65:64–72. DOI: 10.1016/j.odw.2006.03.003.

15. Lombardo L, Palone M, Longo M, Arveda N, Nacucchi M, De Pascalis F, et al. 2020; MicroCT X-ray comparison of aligner gap and thickness of six brands of aligners: an in-vitro study. Prog Orthod. 21:12. DOI: 10.1186/s40510-020-00312-w. PMID: 32390068. PMCID: PMC7211786.

16. Gierie WV. 2018; Clear aligner therapy: an overview. J Clin Orthod. 52:665–74. PMID: 30576290.

17. Dahlberg G. 1940. Statistical methods for medical and biological students. Interscience Publishers Inc.;London:

18. R Development Core Team RR. 2011. A language and environment for statistical computing [Internet]. R Development Core Team RR;Available from: http://www.r-project.org. cited 2020 Feb 29.

19. Dorow C, Krtsin N, Sander FG. 2002; In vivo experimental investigation of tooth mobility in humans. Biomed Tech. 47:20–5. DOI: 10.1515/bmte.2002.47.1-2.20. PMID: 11921633.

20. Moshiri S, Araújo EA, McCray JF, Thiesen G, Kim KB. 2017; Cephalometric evaluation of adult anterior open bite non-extraction treatment with Invisalign. Dental Press J Orthod. 22:30–8. DOI: 10.1590/2177-6709.22.5.030-038.oar. PMID: 29160342. PMCID: PMC5730134.

21. Ojima K, Dan C, Watanabe H, Kumagai Y, Nanda R. 2019; The biomechanics of aligner orthodontics in open-bite cases. J Clin Orthod. 53:699–712. PMID: 32059222.