ABSTRACT
INTRODUCTION: This study evaluated the shaping characteristics of the ProTaper Gold system (PTG; Dentsply Maillefer, Ballaigues, Switzerland) and compared it with that of the ProTaper Next (PTN, Dentsply Maillefer) and ProTaper Universal (PTU, Dentsply Maillefer) systems using micro-computed tomographic imaging. METHODS: Twenty-four mandibular first molars with 2 separate mesial canals were matched anatomically using micro-computed tomographic scanning (SkyScan1174v2; Bruker-microCT, Kontich, Belgium) with a voxel size of 19.6 µm. Canals were prepared with PTG, PTU, or PTN rotary systems to F2 or X2 instruments, respectively, and scanned again. Coregistered images were evaluated for 2- and 3-dimensional morphometric measurements of canal transportation, centering ability, untouched canal walls, and remaining dentin thickness. Data were statistically compared using Kruskal-Wallis and 1-way analysis of variance tests (α = 5%). RESULTS: Overall, PTN showed significantly higher percentage values of static voxels than PTG and PTU systems (P < .05). Surface area, perimeter, and minor diameter were higher in the PTG and PTU groups than in the PTN group (P < .05). No difference was observed in form factor, roundness, major diameter, aspect ratio, or structure model index (P > .05). PTG (0.11 ± 0.05 mm) and PTN (0.09 ± 0.05 mm) produced significantly less transportation than PTU (0.14 ± 0.07 mm) (P < .05), and the percentage decrease in dentin thickness was significantly lower for PTG (22.67 ± 2.96) and PTN (17.71 ± 5.93%) (P ≥ .05) than PTU (29.93 ± 6.24%) (P < .05). CONCLUSIONS: PTG and PTN produced less transportation and maintained more dentin than PTU. PTN had less canal wall contact than PTG and PTU, but all file systems were able to instrument moderately curved mesial root canals of mandibular molars without clinically significant errors.
Subject(s)
Dental Pulp Cavity/anatomy & histology , Dental Pulp Cavity/diagnostic imaging , Root Canal Preparation/instrumentation , X-Ray Microtomography , Dental Alloys , Humans , Image Processing, Computer-Assisted , Mandible , Molar/anatomy & histology , Molar/diagnostic imaging , Nickel , Titanium , X-Ray Microtomography/methodsABSTRACT
Previous studies have demonstrated that the base excision repair enzyme thymine DNA glycosylase (TDG) mediates recruitment of histone acetyltransferases CREB-binding protein (CBP) and p300 to DNA, suggesting a plausible role for these factors in TDG-mediated repair. Furthermore, TDG was found to potentiate CBP/p300-dependent transcription and serve as a substrate for CBP/p300 acetylation. Here, we show that the small ubiquitin-like modifier 1 (SUMO-1) protein binding activity of TDG is essential for activation of CBP and localization to promyelocytic leukemia protein oncogenic domains (PODs). SUMO-1 binding is mediated by two distinct amino- and carboxy-terminal motifs (residues 144 to 148 and 319 to 322) that are negatively regulated by DNA binding via an amino-terminal hydrophilic region (residues 1 to 121). TDG is also posttranslationally modified by covalent conjugation of SUMO-1 (sumoylation) to lysine 341. Interestingly, we found that sumoylation of TDG blocks interaction with CBP and prevents TDG acetylation in vitro. Furthermore, sumoylation effectively abrogates intermolecular SUMO-1 binding and a sumoylation-deficient mutant accumulates in PODs, suggesting that sumoylation negatively regulates translocation to these nuclear structures. These findings suggest that TDG sumoylation promotes intramolecular interactions with amino- and carboxy-terminal SUMO-1 binding motifs that dramatically alter the biochemical properties and subcellular localization of TDG.
