Background: Together with diagnosis and treatment planning, a good knowledge of the root canal system and its\r\nfrequent variations is a necessity for successful root canal therapy. The selection of instrumentation techniques for\r\nvariants in internal anatomy of teeth has significant effects on the shaping ability and cleaning effectiveness. The\r\naim of this study was to reveal the differences made by including variations in the internal anatomy of premolars\r\ninto the study protocol for investigation of a single instrumentation technique (hand ProTaper instruments)\r\nassessed by microcomputed tomography and three-dimensional reconstruction.\r\nMethods: Five single-root premolars, whose root canal systems were classified into one of five types, were\r\nscanned with micro-CT before and after preparation with a hand ProTaper instrument. Instrumentation\r\ncharacteristics were measured quantitatively in 3-D using a customized application framework based on MeVisLab.\r\nNumeric values were obtained for canal surface area, volume, volume changes, percentage of untouched surface,\r\ndentin wall thickness, and the thickness of dentin removed. Preparation errors were also evaluated using a colorcoded\r\nreconstruction.\r\nResults: Canal volumes and surface areas were increased after instrumentation. Prepared canals of all five types\r\nwere straightened, with transportation toward the inner aspects of S-shaped or multiple curves. However, a ledge\r\nwas formed at the apical third curve of the type II canal system and a wide range in the percentage of unchanged\r\ncanal surfaces (27.4-83.0%) was recorded. The dentin walls were more than 0.3 mm thick except in a 1 mm zone\r\nfrom the apical surface and the hazardous area of the type II canal system after preparation with an F3 instrument.\r\nConclusions: The 3-D color-coded images showed different morphological changes in the five types of root canal\r\nsystems shaped with the same hand instrumentation technique. Premolars are among the most complex teeth for\r\nroot canal treatment and instrumentation techniques for the root canal systems of premolars should be selected\r\nindividually depending on the 3-D canal configuration of each tooth. Further study is needed to demonstrate the\r\ndifferences made by including variations in the internal anatomy of teeth into the study protocol of clinical RCT for\r\nidentifying the best preparation technique.
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