Korean J Orthod.  2024 Jul;54(4):199-209. 10.4041/kjod24.085.

Intraoral ageing of aligners and attachments: Adverse effects on clinical efficiency and release of biologically-active compounds

• Eliades T
• Eliades G

• KMID: 2558290
• DOI: http://doi.org/10.4041/kjod24.085

Abstract

The clinical application of aligners is accompanied by the ageing of the polymer appliances and the attachments used, which may result in inefficiency in reaching the predicted range of tooth movement, and release of compounds and microplastics in the oral cavity as a result of the friction, wear and attrition of the aligner and composite attachment. The purpose of this review is to present the mechanism and effects of in vivo ageing; describe the hydrolytic degradation of aligners and enzymatic degradation of composite attachments; examine the ageing pattern of aligners in vivo, under actual clinical scenarios; and identify a link to the discrepancy between predicted and actual clinical outcome. Lastly, strategies to deal with three potentially critical issues associated with the use of aligners, namely the necessity of weekly renewal, the dissimilar mechanical properties of aligner and attachment resulting in wear and plastic deformation of the aligner, and the development of integuments and biofilms with microbial colonization of the appliance, are discussed.

Keyword

Removable; Resin; Aligners; Physical property

Figure

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  Figure 1 Schematic representation of the possible interactions occurring at the biomaterial surfaces exposed to a biological environment. Adapted from the article of Eliades et al. (2003)6 with original copyright holder’s permission.

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  Figure 2 Dark- (A) and bright-field (B) reflected light microscopic images of 1 hr-pellicle developed intraorally on ultra-smooth Ge crystal surface. The integument formed is composed of amorphous proteinaceous material with dendritic arrangement of microbial aggregates. Arrows show early evidence of crystalline development onto the adsorbed species.

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  Figure 3 Secondary (SE) and atomic number contrast backscattered electron images (BE) of 1 hr-pellicle developed intraorally on ultra-smooth Ge crystal surface. Crystalline structures are identified onto the adsorbed biofilm (black areas of low mean atomic number) mainly composed of K and Cl. The X-ray elemental mapping of the area in the insert of the BE image demonstrated that K and Cl have similar distribution even on small dendritic arrangements with low atomic number, indicating KCl formation, whereas P and S are uniformly distributed. No Ca was traced.

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  Figure 4 Reflected light stereomicroscopic image of a retrieved polyethylene terephthalate glycol aligner with evidence of cracking.

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  Figure 5 Polarized light microscopic image of a polyester-urethan aligner with a birefringence pattern indicating residual stresses.

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  Figure 6 Attenuated total reflection Fourier-transform infrared spectroscopy (FTIR) spectra of a polyester-urethane aligner (InvisalignTM, Tempe, Arizona, USA), before (A) and after 1-week intraoral exposure (B, C), with the corresponding reflected light images. The original aligner structure is covered to various extents by proteinaceous material, which creates an amorphous film adsorbed on the aligner surface, as illustrated in the corresponding images.

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  Figure 7 Attenuated total reflection Fourier-transform infrared spectroscopy (FTIR) spectra of a 3D-printed acrylate/urethane dimethacrylate aligner (GraphyTM, Seoul, Korea), before (A) and after 1-week intraoral exposure (B, C), with the corresponding reflected light images. The original aligner structure (A) is covered to various extents by an amorphous proteinaceous material, which clearly demonstrates evidence of mineralization, as illustrated in the spectra and the corresponding images.

Reference

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