Evaluation of dimensional accuracy and surface roughness of lingual bracket slot –An in vitro study

The paradigm shift with the increasing number of adults and teens seeking aesthetic options for orthodontic treatment led to the increased demand for lingual orthodontics. When it comes to size and slot dimensions, lingual brackets are very different from labial brackets.With the rise of lingual orthodontics in our everyday practice, it's more critical than ever for practitioners to understand these potential bracket size variations. The resistance to sliding mechanics can occur if the contact angle between the archwire and bracket increases, this creates the need for precise bracket slot dimension. The amount of friction varies proportionally to the accuracy of the dimensions and the roughness of the bracket slot. To evaluate the precision of commercially available orthodontic lingual bracket slots in inch dimensions with manufacturers’ published dimensions using a stereomicroscope and to compare the surface roughness of commercially available orthodontic lingual bracket slots using an atomic force microscope. Lingual brackets from four different manufacturers were taken for evaluation of slot dimensions. Twenty brackets of each manufacturer were randomly selected. Trinocular Stemi 2000 Stereo Zoom Microscope with Digital Camera (Carl Zeiss, Germany) was used for measurement of bracket slot dimensions. An atomic Force Microscope (AFM) (Nanoscope® IV Di digital instrument, California, USA) was used to evaluate the surface roughness of lingual bracket slots. Comparison of dimensions between mesial processes and comparison of dimensions between distal processes showed that the difference was only marginal with no significant statistic value. Statistically significant results proved that slot dimensions were not precise as per the manufacturer’s standards for given lingual brackets and were oversized for all bracket systems. Statistically insignificant results showed that the bracket systems were similar concerning the surface roughness of the bracket. The analyzed series of lingual bracket systems exhibited significant differences with manufacturers’ standards in slot dimension, which will clinically result in torque play. Lack of standardization of slot dimensions during the manufacturing process may be clinically associated with undesirable tooth positioning and movement; inferring that the bracket systems were similar concerning the surface roughness of the bracket slot.