| [Objectives]The aim of this in vivo study was to investigate the root lengths, the buccolingual (BL) and mesiodistal (MD) diameters of the roots, and the thicknesses of root walls of mandibular premolars. The probability that the residual thickness of root walls was not less than0.8,0.9, or1.0mm in BL and MD directions after post space preparation by1#,2#,3#peeso reamers (respective diameter:0.7mm,0.9mm,1.1mm) was analyzed.[Materials and Methods]CBCT (NewTom3G QR-DVT9000, Italy) data were obtained from Department of Radiology, Hospital of Stomatology Affiliated to Zhejiang University School of Medicine, including ninety patients, fifty-two male and forty-eight female, age from twenty to seventy-nine years old, the mean age thirty-six years old. Ninety first mandibular premolars and ninety second mandibular premolars from the CBCT data were selected for this study. The cross-sections at4,5,6,7,8,9mm distant from the radiologic apex were used to measure the BL and MD diameters of the root and the thicknesses of root walls, and the root lengths were measured from the apex to the cemento-enamel junction (CEJ). The diameter ratios and the mean tapers in BL and MD direcions were analyzed. The probability that the residual thickness of root walls being not less than0.8,0.9, or1.0mm in BL and MD directions after post space preparation by1#,2#,3#peeso reamers was analyzed. The data were analyzed by repeated, three-way analysis of variance (ANOVA) with statistical significance at P<0.05.[Results]P25of root walls thickness was less than1mm as following:the mesial and distal thickness of root walls at4-6mm distant from the apex in first mandibular premolars, the mesial thickness of root wall at4mm distant from the apex and the distal thickness of root wall at4-6mm distant from the apex in second mandibular premolars. The gender didn’t significantly influence root diameters (P>0.05), while different positions (from apex to CEJ) and different directions (BL/MD) significantly influenced root diameters (P＜0.05) with a significant interaction. The root lengths of first and second mandibular premolars were13.0±1.3mm and13.2±1.5mm, respectively. The diameter ratios of first and second mandibular premolars was1.5-1.7. The mean tapers of first and second mandibular premolars were9°～12°and8.8°～14.8°in BL direction,4.6°～8.1°and4.2°～8.3°in MD direction, while mean tapers gradually became larger apically. The inflection of the residual thickness of root walls after post space preparation was at6mm distant from the apex, and the probabilities that the residual thickness of root walls were not less than lmm were94%and97%after post space preparation in first and second madibular premolars by3#peeso reamer in BL direction, and they were only50%and69%by using1#peeso reamer in MD direction.[Conclusions]1) It is recommended to use CBCT scanning before post space preparation of mandibular premolars for measurement of the thickness of root walls to evaluate the prognosis of post placement.2) In order to preserve root canal walls in apical regions, it is suggested that the length of post space preparation should be reduced as possible, when the ratio of post length/crown height is larger than1.3) It is suggested not to prepare the root canal deeper than6mm distant from the apex, and avoid using3#peeso reamer or larger rotary instruments.4) The recommendation of post space preparation by peeso reamer is as following:at 7-8mm distant from apex by1peeso reamer, and at9mm from apex by2*peeso reamer in first mandibular premolar; at6-7mm from apex by1*peeso reamer, and at8-9mm from apex by2#peeso reamer in second mandibular premolar.5) The mesial and distal walls of root canals should be prepared as few as possible to maintain their original root canal shapes during post space preparation. |
