Comparative analysis of slot dimension in lingual bracket systems

BACKGROUND Orthodontic treatment with fixed appliances requires - among others - the correct clinical expression of torque, which depends on the precise fitting of archwire and slot. Especially in the lingual technique torque problems become clinically more evident than in labial appliances also with respect to the vertical alignment of teeth due to different distances from the center of resistance. The purpose of the present study was to compare the preciseness of slot dimensions of different lingual bracket systems. METHODS Three lingual bracket systems were included in the study (7th Generation and STb, Ormco, Glendora, CA, USA; Incognito, TOP-Service/3 M Unitek, Monrovia, CA, USA). Non destructive analysis of vertical slot dimensions was performed using precision pin gauges (Azurea, Belprahon, Switzerland) that were tapered in increments of 0.002 mm (0.00008 inch). The sizes of 240 incisor and canine brackets were measured per system (total: 720). Data were compared using one-way ANOVA. A p-value < 0.05 was considered statistically significant. RESULTS Average slot dimensions were 0.467 mm +/- 0.007 mm (0.0184 inch +/- 0.0003 inch) for the 7th Generation bracket system, 0.466 mm +/- 0.004 mm (0.0183 inch +/- 0.0001) inch for the STb bracket system and 0.459 mm +/- 0.004 mm (0.0181 inch +/- 0.0001) inch for the Incognito bracket system. Differences between systems were statistically significant (p < 0.05). CONCLUSIONS The analyzed bracket systems for lingual treatment exhibited significant differences in slot dimension that will clinically result in torque play. These aspects must be considered in lingual orthodontic treatment.