RESUMEN
<p><b>OBJECTIVE</b>To compare the mechanical properties of different dental optimal material selection for orthodontic appliance.</p><p><b>METHODS</b>Four commercialized thermoplastic products under different test conditions, and provide the suggestion of thermoplastic products were tested. The tear strength, elongation at break and stress relaxation of these materials were measured under different test conditions.</p><p><b>RESULTS</b>The tear strength declined after thermoforming, and rose again after 2 weeks of distilled water immersion. The elongation at break rose after thermoforming, and declined after 2 weeks of distilled water immersion. No significant changes were observed for brand A under different test conditions. Brand A showed the slowest stress relaxation of 0.0148 N/s.</p><p><b>CONCLUSIONS</b>The mechanical properties of thermoplastic materials were influenced by environmental factors. Brand A exhibited optimal comprehensive properties.</p>