Biomechanical preparation in primary molars using manual and three NiTi instruments: a cone-beam-computed tomographic in vitro study.

PURPOSE: To evaluate nickel-titanium rotary systems, ProTaper Universal (PTU), ProTaper Next (PTN), self-adjusting file (SAF), and stainless steel hand K files in deciduous root canals in longitudinal and horizontal sections by three-dimensional reconstruction. Whether there was any difference in shaping ability, transportation, dentine removal, untouched canal surface area, and preparation time among the different groups when used in primary root canals. METHODS: Shaping and cleaning of canals in primary molars were done using the four systems, and CBCT and specialized software were used for scanning, image processing, three-dimensional reconstruction, and analysis of pre-operative and post-operative to evaluate the groups for their shaping properties, transportation, amount of dentine removal, untouched canal surface area, and preparation time in primary root canals. RESULTS: None of the groups reported stripping of canals or instrument failure. SAF demonstrated less removal of dentine as compared to other groups. Hand K files presented with high untouched canal surface area, while it was least with SAF. In addition, rotary files provided faster preparation than hand files, and among the rotary systems, PTN took least time for cleaning and shaping of canals. All the groups were similar in transportation at cervical and apical third. CONCLUSION: Under the conditions of this study, SAF seemed to result in more conservative and meticulous removal of dentine. This is desirable to preserve the integrity of thin-walled primary root canals. SAF also showed less untouched canal areas suggesting better contact with the primary canal walls. The rotary file groups required less clinical time which is important in paediatric treatments.

Real-time optical imaging of naturally evoked electrical activity in intact frog brain.

A major obstacle to understanding the function and development of the vertebrate brain is the difficulty in monitoring dynamic patterns of electrical activity in the millesecond time domain; this has limited investigations of such phenomena as modular organization of functional units, seizure activities and spreading depression. The use of voltage-sensitive dyes and the recent development of the use of an array of photodiodes has provided a unique technique for monitoring the dynamic patterns of electrical activity in real time from a variety of invertebrate or vertebrate neuronal preparations including the rat cortex. In the present study, this technique has been used to investigate the intact optic tectum of the frog. We demonstrate that optical measurements can be used for real-time imaging of spatio-temporal patterns of neuronal responses and for identification of functional units evoked by natural visual stimuli. We report also the structure of the new voltage-sensitive probe that facilitates the in vivo applications of this technique.

Visualization of the spread of electrical activity in rat hippocampal slices by voltage-sensitive optical probes.

1. Voltage-sensitive membrane-bound dyes and a matrix of 100 photodetectors were used to detect the spread of evoked electrical activity at the CA1 region of rat hippocampus slices. A display processor was designed in order to visualize the spread of electrical activity in slow motion.2. The stimulation of the Schaffer collateral-commissural path in the stratum radiatum evoked short latency (2-4 msec) fast optical signals, followed by longer latency (4-15 msec) slow signals which decayed within 20-50 msec. Multiple fast signals were frequently detected at the stratum pyramidale; they propagated toward the stratum oriens with an approximate conduction velocity of 0.1 m/sec.3. The fast signals were unaltered in a low Ca(2+) high Mg(2+) medium but were blocked by tetrodotoxin. These signals probably represent action potentials in the Schaffer collateral axons. Their conduction velocity was about 0.2 m/sec and their refractory period about 3-4 msec.4. The slow signals were absent in a low Ca(2+) medium and probably represent excitatory post-synaptic potentials (e.p.s.p.s) generated in the apical dendrites of the pyramidal cells. They were generated in the stratum radiatum, where the presynaptic signals were seen, and spread into somata and basal dendrites (the stratum pyramidale and oriens, respectively).5. The timing of the signals with fast rise-time, which were detected at the statum pyramidale, approximately coincided with the timing of the extracellularly recorded field potentials. These multiple discharges probably represent action potentials of the pyramidal cells. They spread back into the apical dendrites but with significant attenuation of the amplitudes of the high frequency components of the pyramidal action potentials.6. Hyperpolarizing potentials could be detected when strong stimuli were applied to the stratum radiatum or alveus. The net hyperpolarizations were detected only in the stratum pyramidale and the border region between the stratum pyramidale and radiatum. Frequently the inhibition was masked by the large e.p.s.p.s. However, its existence could be demonstrated by treatment of the slice with picrotoxin or a low Cl(-) medium. Under these conditions a long-lasting depolarization of the apical dedrites was evoked by the stimulation. This was associated with an increase of the multiple discharges in the stratum pyramidale and oriens.7. These studies illustrate the usefulness of voltage-sensitive dyes in the analysis of passive and active electrical properties, pharmacological properties and synaptic connexions in mammalian brain slices, at the level both of small neuronal elements (dendrites, axons) and of synchronously active neuronal populations.