Objectives: Endodontic instruments tend to diverge from the long axis of root canal during preparation. This tendency increases with increasing canal curvature and retreatment cases. The purpose of this study was to assess and compare the apical transportation induced by different reciprocating single file systems in curved canals obturated with GuttaCore and single-cone obturation techniques using microcomputed tomography. Materials and methods: Sixty-four mandibular molar teeth with root canal systems that have two independent severely curved canals in the mesial root have been chosen for the current study. The root canals have been instrumented with WaveOne Gold primary file and obturated by Single-cone and GuttaCore obturation techniques. First micro-CT scan has been taken and the samples have been subdivided into 4 groups for each obturation technique (n=16 canals each group) according to the retreatment system: Group R: Reciproc (R25 file), group RB: Reciproc Blue (R25 file), group WO: WaveOne (Primary file 25) and group WOG: WaveOne Gold (Primary file 25). After the retreatment procedures, the second micro-CT scan has been taken and then the apical transportation at 2, 3 and 4 mm from the apex were calculated. Results: Apical transportation caused by Reciproc and WaveOne groups was significantly higher than the Reciproc Blue and WaveOne Gold groups. Conclusion: Under the circumstances of the current study, Reciproc and WaveOne files caused higher apical transportation than the Reciporc Blue and WaveOne Gold files. The lowest apical transportation occurred at 2 mm from the apex. Clinically relevant: The use of Reciproc blue and WaveOne Gold files can be considered safer in the removal of GuttaCore and single-cone obturation materials

The shear bond measurement of two self-adhesive composite resins to both enamel and dentin (An in vitro study) Abdulkareem Ramadhan Ibrahim (1) Background and objectives: The aim of this study is to measure the shear bond strength of two self-adhesive composite resins (Vertise Flow, Kerr and Constic, DMG) to both enamel and dentin and compared it to that of conventional flowable composite (used with self-etching bonding system).Methods: Sixty freshly extracted human third molar teeth were chosen for this study (thirty for enamel samples and thirty for dentin samples). The teeth were mounted horizontally, in blocks of self-cured acrylic resin to leave only buccal surfaces exposed. Then 0.5 and 2mm were cut from the buccal surface to obtain flat enamel and dentin surfaces successively. Thirty enamel samples were divided into three groups; group E1: Vertise Flow, group E2: Constic and group E3: conventional composite with self-etching bonding. Also the thirty dentin groups were divided into three groups, group D1, D2 and D3 with the same corresponding composites as in enamel groups. For all the specimens composite cylinders (4mm height and 4 mm in diameter) were built of the flat surface of the sample then subjected to shear bond testing in a universal testing machine. Results: Group E3 (conventional flowable composite bonded to enamel) had the highest bond strength while group D1 ( Vertise Flow bonded to dentin) had the lowest bond. Conclusion:Both self-adhesive composites provided insufficient shear bond strength less than that required for using in most clinical conditions.