A comparison of three methods for preparing centered platforms around separated instruments in curved canals.

This study compared three methods for creating the most centered staging platform (SP) around separated instruments (SI) in curved canals. Green .04 ProFiles, notched at D(3), were separated in the apical third of 42 mesiobuccal canals of maxillary and mandibular molars. Teeth were divided into three groups. SPs were prepared in group 1 with Gates Gliddens (GG) to a size #3; group 2 with LightSpeed to a size 90; and group 3 with incrementally cut rotary .06 ProFiles to size 82. Pre- and postoperative digital radiographs were imported into AutoCAD to measure the deviation of SP from the head of the separated instrument. Pearson's correlation showed a positive relationship between deviation of the SP and the distance of the SI from the elbow of the canal. ANOVA showed that LightSpeed instruments were significantly more effective in preparing a centered staging platform around separated instruments in curved canals when compared to GG drills and ProFiles (p < 0.05).

Investigating structural changes induced by nucleotide binding to RecA using difference FTIR.

Nucleotide binding to RecA results in either the high-DNA affinity form (Adenosine 5'-triphosphate (ATP)-bound) or the more inactive protein conformation associated with a lower affinity for DNA (Adenosine 5'-diphosphate (ADP)-bound). Many of the key structural differences between the RecA-ATP and RecA-ADP bound forms have yet to be elucidated. We have used caged-nucleotides and difference FTIR in efforts to obtain a comprehensive understanding of the molecular changes induced by nucleotide binding to RecA. The photochemical release of nucleotides (ADP and ATP) from biologically inactive precursors was used to initiate nucleotide binding to RecA. Here we present ATP hydrolysis assays and fluorescence studies suggesting that the caged nucleotides do not interact with RecA before photochemical release. Furthermore, we now compare difference spectra obtained in H2O and D2O as our first attempt at identifying the origin of the vibrations influenced by nucleotide binding. The infrared data suggest that unique alpha-helical, beta structures, and side chain rearrangements are associated with the high- and low-DNA affinity forms of RecA. Difference spectra obtained over time isolate contributions arising from perturbations in the nucleotide phosphates and have provided further information about the protein structural changes involved in nucleotide binding and the allosteric regulation of RecA.