Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials

Abstract

The aim of the present study was to characterise the chemical and mechanical properties of contemporary thermoplastic orthodontic materials. Materials and methods: Four thermoplastic materials were tested: Clear Aligner (Scheu-Dental), ACE and A+ (Dentsply), and Invisalign (Align Technology). Eight appliances were fabricated from each material and a small portion from each was analysed by ATR-FTIR spectroscopy. The appliances were cut and, following metallographic grinding and polishing, were subjected to instrumented indentation testing (IIT) employing a Vickers indenter. Martens Hardness (HM), Indentation Modulus (E IT ), Elastic to Total Work Ratio (elastic index (η IT )) and Indentation Creep (C IT ) were determined according to ISO 14577-1. The mean values of the mechanical properties were statistically analysed by one way ANOVA and Tukey Kramer multiple comparison test at a = 0.05. Results: ATR-FTIR analysis identified that Invisalign was a polyurethane-based material, whereas the others were based on polyester, polyethylene glycol terephthalate (PETG). Invisalign showed higher hardness and modulus values, a slightly higher brittleness and lesser creep resistance compared with the PETG-based products. Conclusions: The materials tested showed significant differences in their chemical structure and mechanical properties and therefore differences in their clinical behaviour are anticipated.

Comparative analysis of mechanical properties of orthodontic aligners produced by different contemporary 3D printers

“…The range of HM of 3D-printed groups was found similar to values of clear aligners made of PETG polymer (92 ~ 101 N/mm 2 ) 18 by thermoforming and lower than Invisalign (118 ~ 122 N/mm 2 ). [18][19][20] This means that 3D-printed aligners are more susceptible to intraoral wear compared to Invisalign ones.…”

“…The range of HM of 3D-printed groups was found similar to values of clear aligners made of PETG polymer (92 ~ 101 N/mm 2 ) 18 by thermoforming and lower than Invisalign (118 ~ 122 N/mm 2 ). [18][19][20] This means that 3D-printed aligners are more susceptible to intraoral wear compared to Invisalign ones. Modulus of elasticity of 3D-printed groups matches to Invisalign (2467 ~ 2616 MPa), [18][19][20] but is higher than the clear aligner made by thermoforming (2212 ~ 2374 MPa), 18 a finding which is in accordance with recently published results.…”

“…This means that 3D‐printed aligners along with Invisalign appliances may provide higher counter forces under the same strain than the thermoformed ones. Invisalign (40.0 ~ 40.8%) and clear aligner appliances (34.0 ~ 35.9) 18‐20 showed a higher elastic index than 3D‐printed appliances implying a more brittle behaviour.…”

“…[18][19][20] This means that 3D-printed aligners are more susceptible to intraoral wear compared to Invisalign ones. Modulus of elasticity of 3D-printed groups matches to Invisalign (2467 ~ 2616 MPa), [18][19][20] but is higher than the clear aligner made by thermoforming (2212 ~ 2374 MPa), 18 a finding which is in accordance with recently published results. 10 This means that 3D-printed aligners along with Invisalign appliances may provide higher counter forces under the same strain than the thermoformed ones.…”

“…Invisalign (40.0 ~ 40.8%) and clear aligner appliances (34.0 ~ 35.9)[18][19][20] showed a higher elastic index than 3D-printed appliances implying a more brittle behaviour.TA B L E 2 Results of the 3D printers tested for all outcomes…”