Effect of thickness of the clear aligners on retentive force of the appliances

Objective To investigate the retentive force of China-made removable clear aligners of different thickness.Methods Four models of lower arch and their removable clear orthodontic appliances were produced.The appliance designs were divided into 4 groups:(1) 1.00 mm thickness without attachment; (2) 0.75 mm thickness without attachment; (3) 1.00 mm thickness with attachment; (4) 0.75 mm thickness with attachment.Repeated placement and removal were tested on 7 different points of appliances and retentive force was evaluated using a universal testing machine.Results Significant statistics difference were found among the 4 groups.The attachment could increase retentive force of the appliances.The group of 1.00 mm thickness has greater retentive force than 0.75 mm group.The retentive forces at removing-points on buccal surface of second molar and lingual surface of first molar were smaller than that at other points.Conclusions China-made clear removable orthodontic appliances of 1.00 mm thickness apply greater retentive force than 0.75 mm thickness appliances.The attachments increase significantly the retentive force of the clear aligners.Removing the appliances from buccal or lingual surface of molar should be easier. Key words: Clear aligners; Attachment; Thickness; Retentive force