Surface alterations and compound release from aligner attachments in vitro.

AIM: The aim of the present study was to assess the alterations in morphology, roughness, and composition of the surfaces of a conventional and a flowable composite attachment engaged with aligners, and to evaluate the release of resin monomers and their derivatives in an aqueous environment. METHODS: Zirconia tooth-arch frames (n = 20) and corresponding thermoformed PET-G aligners with bonded attachments comprising two composite materials (universal-C and flowable-F) were fabricated. The morphological features (stereomicroscopy), roughness (optical profilometry), and surface composition (ATR-FTIR) of the attachments were examined before and after immersion in water. To simulate intraoral use, the aligners were removed and re-seated to the frames four times per day for a 7-day immersion period. After testing, the eluents were analyzed by LC-MS/MS targeting the compounds Bis-GMA, UDMA, 2-HEMA, TEGDMA and BPA and by LC-HRMS for suspect screening of the leached dental material compounds and their degradation products. RESULTS: After testing, abrasion-induced defects were found on attachment surfaces such as scratches, marginal cracks, loss of surface texturing, and fractures. The morphological changes and debonding rate were greater in F. Comparisons (before-after testing) revealed a significantly lower Sc roughness parameter in F. The surface composition of the aligners after testing showed minor changes from the control, with insignificant differences in the degree of C = C conversion, except for few cases with strong evidence of hydrolytic degradation. Targeted analysis results revealed a significant difference in the compounds released between Days 1 and 7 in both materials. Insignificant differences were found when C was compared with F in both timeframes. Several degradation products were detected on Day 7, with a strong reduction in the concentration of the targeted compounds. CONCLUSIONS: The use of aligners affects the surface characteristics and degradation rate of composite attachments in an aqueous environment, releasing monomers, and monomer hydrolysates within 1-week simulated use.

Leaching from a 3D-printed aligner resin.

AIM: To quantitatively assess the degree of conversion and the water-leaching targeted compound from 3D-printed aligners. MATERIALS AND METHODS: 3D-printed aligners were made of photopolymerized resin (Tera Harz TC85A). The molecular structure and degree of conversion of the set resin were investigated by ATR-FTIR spectroscopy (n = 5). The aligners (n = 10) were immersed in double distilled water for 1 week at 37°C and the eluents were analysed using liquid chromatography/mass spectrometry methods (LC-ESI-MS/MS for urethane dimethacrylate [UDMA] and LC-APCI-MS/MS for bispenol-A [BPA]). RESULTS: The resin was composed of aliphatic vinyl ester-urethane monomers, with acrylate and/or methacrylate functionalization. The degree of conversion was estimated as to 83%. There was no detection of BPA in any of the assessed samples (0.25 µg/l). Quantifiable amounts of UDMA were detected in all the exposed samples, ranging from 29 to 96 µg/l. CONCLUSIONS: Although efficiently polymerized and BPA free, the great variability in the amount of UDMA monomer leached from the examined samples may raise concerns on potential health hazards after repeated intraoral exposure, which is indicated for this class of materials.

Salivary levels of eluents during Invisalign™ treatment with attachments: an in vivo investigation.

BACKGROUND: The aim of the present study was to investigate qualitatively and quantitatively the elution of substances from polyester-urethane (Invisalign™) aligners and resin composite attachments (Tetric EvoFlow) in vivo. METHODS: Patients (n = 11) treated with the aligners and attachments (16 per patient, without other composite restorations) for an average of 20 months, who were planned for attachment removed were enrolled in the study. Patients were instructed to rinse with 50 mL of distilled water upon entry and the rinsing solution was collected (before removal). Then, the attachments were removed with low-speed tungsten carbide burs for adhesive residue removal, a thorough water rinsing was performed immediately after the grinding process to discard grinding particle residues, and subsequently, after a second water-rinsing the solution was collected for analysis (after removal). The rinsing solutions were analyzed for targeted (LC-MS/MS: Bis-GMA, DCDMA, UDMA, BPA) and untargeted (LC-HRMS: screening of leached species and their degradation products) compounds. RESULTS: Targeted analysis revealed a significant reduction in BPA after attachment removal (4 times lower). Bis-GMA, DCDMA, UDMA were below the detection limit before removal but were all detectable after removal with Bis-GMA and UDMA at quantifiable levels. Untargeted analysis reviled the presence of mono-methacrylate transformation products of Bis-GMA (Bis-GMA-M1) and UDMA (UDMA-M1), UDMA without methacrylate moieties (UDMA-M2), and 4-(dimethylamino) benzoic acid (DMAB), the degradation product of the photo-initiator ethyl-4-(dimethylamino) benzoate (EDMAB), all after attachment removal. Several amino acids and endogenous metabolites were also found both before and after removal. CONCLUSIONS: Elevated levels of BPA were traced instantaneously in patients treated with Invisalign™ and flowable resin composite attachments for the testing period. BPA was reduced after attachment removal, but residual monomers and resin degradation products were found after removal. Alternative resin formulations and attachment materials may be utilized to reduce eluents.