Date of Award

Summer 2015

Document Type


Degree Name

Master of Science (MS)



First Advisor

Bradley, Gerard T.

Second Advisor

Berzins, David

Third Advisor

Liu, Dawei


Background/Objectives: This study aimed to investigate the viscoelastic properties of two clear aligner systems, Invisalign (Align Technology, Inc, Santa Clara, CA, USA) and Simpli5 (Allesee Orthodontic Appliances, Sturtevant, WI, USA), and determine if there was a difference after use. A survey assessed patients’ perceptions of the aligner material and post-treatment satisfaction. Materials/Methods: Mandibular aligners were collected from two patients after 2-3 weeks of use (n=6). Duplicate, unused aligners were obtained for each patient (n=6). Dynamic mechanical analysis (DMA) characterized the viscoelastic properties of the materials. Three tests were done on separate specimens: frequency scan (0.1-10 Hz under 25 μm displacement at 37oC), creep-recovery (1 N, 2 N and 3 N at 37oC) and temperature ramp (28o-120oC at 5oC/min under 1 Hz and 25 μm displacement). The survey was given to sequential patients (n=7) after completing aligner therapy. Repeated measures of multivariate analysis of variance were performed. Results: No statistically significant difference in storage modulus, loss modulus, tan δ, creep compliance, or strain recovery was found comparing the materials in as-received and after-use states, and no significant difference was found between Invisalign and Simpli5 (p>0.05). The tan δ (loss modulus/storage modulus) values for as-received Invisalign and Simpli5 at 1 Hz were 0.056±0.01 and 0.093±0.03. The creep compliance (μm2/N) for as-received Invisalign and Simpli5 were 300±50 and 155±36. Strain recoveries were >94%. Patients’ survey responses were predominately positive, as all were pleased with the esthetics, comfort, and performance of the aligners. Conclusions: While there was no significant difference between the materials before or after use, both Invisalign and Simpli5 demonstrated favorable qualities, including low tan δ values and positive patient perception of the material.