Morphological investigation of various orthodontic lingual bracket slots using scanning electron microscopy and atomic force microscopy

Various labial and lingual orthodontic appliances with aesthetic materials have been developed due to an increased demand in aesthetic orthodontic treatment. However, there are few reports regarding the morphology of lingual orthodontic appliances. Therefore, this study evaluates the roughness of slot surfaces of various orthodontic lingual brackets using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Three types of stainless steel lingual brackets (Stealth (R), 7th Generation (R), and Clippy L (R)) and one gold lingual bracket (Incognito (TM)) with a slot size of 0.018 inches x 0.025 inches (0.457 x 0.635 mm(2)) were selected as representative lingual materials. Both FE-SEM and AFM examinations showed that the Stealth (R) and Clippy L (R) brackets had the lowest surface roughness, while the 7th Generation (R) bracket had the highest surface roughness. There was a significant difference in surface morphology between the types of lingual brackets, even when composed of the same material. The surface roughness of the bracket slot was dependent on the manufacturing process or surface polishing process rather than the fundamental properties of the bracket materials. There was no significant difference in the mean surface roughness of the slot floor between gold and stainless steel lingual brackets. These findings suggest that, although the gold lingual bracket is very expensive, it has great potential for use in patients with nickel allergy.