| Objectives. The aim of this study was to investigate the thickness of root canal walls and the dimensions of maxillary premolar roots, and to provide some clinical reco mmendations for post space preparation of maxillary premolar roots.Materials and Methods. CBCT data recorded in Department of Radiology, Stomatology Hospital Zhejiang Province from December2012to January2014were used for this study. The CBCT data included130subjects with246maxillary premolars,129first and117second premolars. The root cross-sections at4,5,6,7,8,9mm distant from the radiologic root apex were analyzed by CBCT built-in software NNT for the thickness of root canal walls, root lengths and the mesio-distal and bucco-lingual diameters of maxillary premolar roots. The probability of thickness of residual root canal walls being less than1mm was theoretically calculated after post space preparation of maxillary premolars with single canal in single root by1#～3#Peeso reamers.Results. The mesial and distal root canal walls of maxillary premolars were very thin, with P25being less than1mm from apex up to6mm. Mesio-distal diameters of maxillary premolars with single root were narrow, and their P25were less than2.7mm from apex up to7mm in maxillary first premolar and from apex up to6mm in maxillary second premolar. The probability of residual thickness being less than1mm after post preparation with Peeso reamer was over80%at9mm distant from apex of maxillary first, second premolars after post space preparation by1#or2#Peeso reamer respectively, and at8mm distant from apex of maxillary second premolar after post space preparation by1#Peeso reamer. The mesio-distal diameters of single root with double canals were narrower than those of single root with single canal, with median being2.5-2.6mm from apex up to9mm. Theoretically, the thickness of mesial or distal root canal walls after post space preparation should be less than1mm. The furcation of maxillary first premolar was found under7mm distant from apex. The thickness of palatal wall of buccal root and the mesial/distal walls of lingual root were thin, with P25being less than1mm from apex up to7mm. The lengths of root of maxillary first, second premolar were12.9±1.7mm and12.8±2.0mm respectively.Conclusions. The maxillary premolars have thin root canal walls in mesial and distal aspects, and narrow diameter in mesio-distal direction, and thin root canal walls in the palatal aspect of buccal root and mesial/distal aspects of lingual root from the root furcation to apex. It is recommended that (1) post space preparation be avoided under6mm distant from the apex, the post length be reduced as much as possible, and the root canal walls in mesial and distal aspects be removed as little as possible,(2) the root canal at9mm distant from apex could be prepared by1#Peeso reamer in maxillary first premolar, and at8mm from apex by1#Peeso reamer, at9mm from apex by2#Peeso reamer in maxillary second premolar,(3) two root canals of single-root premolars not be prepared into an oval canal,(4) post space preparation be avoided under the root furcation. |
