Summary: Studies on how the body senses the need to correct extracellular and intracellular volumes and ionic concentration changes is relatively scanty. The present studies were designed to determine the effect of oral distilled water (DW) and saline loads, gargling with DW and DW preload on thirst perception (TP) and drinking in euhydrate and dehydrated subjects. The subjects were healthy male volunteers between the ages of 17 and 35 years. Group A subjects were given DW or various concentrations of sodium chloride (NaCl) orally. Subjects in groups B, C and D were dehydrated for 18 hours before the experiment. Group B gargled 500ml of DW in divided volume of 50ml at five minutes interval over a period of 50 minutes. Group C gargled with DW and different concentrations of NaCl. Group D were preloaded with four volumes of DW before ad libitum DW intake. TP was rated using the Visual Analogue Scale. Results showed that in Group A, drinking DW reduced TP, suggesting that baseline TP in normal euhydrate subjects is slightly elevated. Drinking DW reduced TP more than drinking NaCl solutions. Gargling resulted in a gradual fall in TP. The decrease in TP was statistically significant after 30 minutes of gargling. Gargling with different concentrations of NaCl solutions resulted in significant reductions in TP in all the groups. There was a significant decrease in TP in the group preloaded with 1000ml of distilled water at 5 minutes of rehydration. At 20 minutes TP was abolished suggesting that approximately 1000ml of water was needed for the rehydration. These results show that baseline TP in euhydrates is elevated and that TP increases in dehydrated subjects. Gargling reduces TP, but did not abolish thirst. It is suggested that a fall in plasma osmolality due to drinking may be responsible for abolishing thirst.

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BACKGROUND Advances in root canal instruments have led to lesser frequency of dentinal crack formation. Not many studies have been reported in literature that compare crack formation using instruments based on control memory (CM) and M wire technology. The study intended to evaluate and compare the prevalence of dentinal cracks formed by ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland), HyFlex CM (Coltene, Whaldent) and Wave One (Dentsply, Maillefer) reciprocating file systems at the apical and middle third of the mesiobuccal root canal of mandibular molars under scanning electron microscope (SEM). METHODS Forty-five extracted sound human mandibular molars were decoronated and mesial roots were retained followed by root canal instrumentation using ProTaper Next, HyFlex CM and WaveOne reciprocating files. Roots were then sectioned perpendicular to the long axis of teeth and viewed under scanning electron microscope to detect the presence of cracks. RESULTS ProTaper Next system produced more cracks compared with HyFlex and Wave One (P < 0.05) but there was no statistically significant difference between all the three groups. All the file systems showed more incidences of cracks in the apical third compared to middle third. CONCLUSIONS All the NiTi instruments produced cracks and the highest incidence of cracks was seen in the apical third compared to middle third region. KEY WORDS Dentinal Cracks, HyFlex CM, ProTaper Next, Root Canal, Wave One

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