Load Application Duration of Bilaminate Aligner Material

Objective: Invisible removable orthodontic aligners have increased in popularity due to poor esthetics associated with traditional fixed orthodontic appliances. Inclusion of a soft layer in the aligner, which contacts the teeth, may alleviate potential patient discomfort and difficulty during insertion and removal. Questions arise as to how this soft liner may affect the duration of force application. The purpose of this study was to assess the duration of force application of orthodontic aligner material with and without a soft inner lining.

Methods: An adult human molar was cleaned and horizontally mounted in die stone with the facial aspect exposed for testing. Two types of orthodontic aligner materials were vacuum adapted over the tooth. One aligner from a polycarbonate sheet and a second from polycarbonate laminated with a lower modulus polyurethane. Simulated orthodontic forces of 100gm were applied to the aligner materials on the tooth using a calibrated load cell with a digital readout. The change in load as a function of time was monitored for both aligner materials. Five replications were performed for each material. The data was analyzed using AVOVA.

 Results: Under the condition of this study, there was a statistically different time of force decay between the two materials. The decay time for the polycarbonate laminated with the lower modulus polyurethane was significantly longer than that of unlaminated polycarbonate.

Conclusion: The results indicate the potential for longer term force application with aligners having a lowered modulus inner layer.