Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials.

AIM: 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.