Effect of root curvature on post length in the restoration of endodontically treated premolars

– Two hundred and eighteen bi-rooted maxillary premolars were examined radio graphically to determine the length from the apex at which root curvature occurred. The information may serve as a guide in determining post preparation length. The results of the study indicated that the lingual root was slightly straighter than the buccal root. The curvature of the root was on the average 6.47 mm from the apex on the buccal root and 5.18 mm from the apex on the lingual root.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75753/1/j.1600-9657.1985.tb00577.x.pd

Comparison of the fracture resistance of endodontically treated teeth restored with prefabricated posts and composite resin cores with different post lenghts

OBJECTIVE: This study evaluated the fracture strengths of endodontically treated teeth restored with prefabricated posts with different post lengths. MATERIAL AND METHODS: Thirty freshly extracted canines were endodontically treated. They were randomly divided into groups of 10 teeth and prepared according to 3 experimental protocols, as follows; Group 1/3 PP: teeth restored with prefabricated post and composite resin core (Z250) with post length of 5.0mm; Group 1/2 PP and Group 2/3 PP: teeth restored with prefabricated post and composite resin core (Z250) with different combinations of post length of 7.5mm and 10mm, respectively. All teeth were restored with full metal crowns. The fracture resistance (N) was measured in a universal testing machine (crosshead speed 0.5mm/min) at 45 degrees to the tooth long axis until failure. Data were analyzed by one-way analysis of variance (alpha=.05). RESULTS: The one-way analysis of variance demonstrated no significant difference among the different post lengths (P>;.05) (Groups 1/3 PP = 405.4 N, 1/2 PP = 395.6 N, 2/3 PP = 393.8 N). Failures occurred mainly due to core fracture. CONCLUSIONS: The results of this study showed that an increased post length in teeth restored with prefabricated posts did not significantly increase the fracture resistance of endodontically treated teeth

Clonal replacement and heterogeneity in breast tumors treated with neoadjuvant HER2-targeted therapy.

Genomic changes observed across treatment may result from either clonal evolution or geographically disparate sampling of heterogeneous tumors. Here we use computational modeling based on analysis of fifteen primary breast tumors and find that apparent clonal change between two tumor samples can frequently be explained by pre-treatment heterogeneity, such that at least two regions are necessary to detect treatment-induced clonal shifts. To assess for clonal replacement, we devise a summary statistic based on whole-exome sequencing of a pre-treatment biopsy and multi-region sampling of the post-treatment surgical specimen and apply this measure to five breast tumors treated with neoadjuvant HER2-targeted therapy. Two tumors underwent clonal replacement with treatment, and mathematical modeling indicates these two tumors had resistant subclones prior to treatment and rates of resistance-related genomic changes that were substantially larger than previous estimates. Our results provide a needed framework to incorporate primary tumor heterogeneity in investigating the evolution of resistance

Addition of Bromine to Ketenes and Bisketenes: Electrophilic Attack at Carbonyl Carbon and Neighboring Group Participation

Addition of bromine to bisketene (Me3SiCCO)2 (1) gave the fumaryl dibromide E-7, whose stereochemistry was proven by X-ray structure determination. Upon warming, E-7 rearranged to the furanone 8, and this process was faster in the more polar CD3CN compared to CDCl3, consistent with an ionization pathway for the rearrangement. The bromination of 1 in CH2ClCH2Cl followed second-order kinetics with a rate constant (2.1 ± 0.1) × 104 M-1 s-1 at 25 °C. The first-order dependence of bromine addition to 1 on [Br2] is attributed to intramolecular nucleophilic assistance by the second ketenyl moiety in an initial complex of 1 and Br2 to give E-7. A transition structure for this process has been calculated by ab initio methods. By contrast PhMe2SiCHCO 11 and γ-oxoketene 16 underwent bromination by third-order kinetics, second order in [Br2], indicating the absence of neighboring group participation in the rate-limiting step. The bisketene Me2Si(CHCO)2 (13) underwent bromination by mixed kinetics with both first- and second-order terms in [Br2]

Publisher Correction: Clonal replacement and heterogeneity in breast tumors treated with neoadjuvant HER2-targeted therapy

The original version of this Article omitted from the Author Contributions statement that ‘R.S. and J.G.R contributed equally to this work.’ This has been corrected in both the PDF and HTML versions of the Article.</jats:p