Remineralization ability of sodium fluoride on the microhardness of enamel, dentin, and dentinoenamel junction: An in vitro study.

AIM: Dental tissues such as enamel, dentinoenamel junction (DEJ), dentin, and root dentin can react differently to demineralization and remineralization. The aim of this study was to evaluate the remineralization ability of sodium fluoride on the microhardness of enamel, dentin, and dentinoenamel junction. MATERIALS AND METHODS: Ten extracted third molar teeth were sectioned mesiodistally to form control and test groups. For the test group, initial demineralization was done with acetic acid for 24 h followed by remineralization for 28 days by application of sodium fluoride (226 ppm) for 2 min twice a day. Vickers microhardness test was done to control and test groups at different sites after initial demineralization and on the 3rd, 5th, 7th, 14th, and 28th day of remineralization. STATISTICAL ANALYSIS USED: Data were analyzed with one-way analysis of variance and post hoc test with a significance level of P < 0.001 with SPSS (21) software. RESULTS: Microhardness values in the demineralization group were significantly lower than controls (P < 0.001). Evaluation of remineralization samples showed that microhardness similar to control values were achieved at the 3rd day in root predentin and on the 5th day in coronal dentin and coronal predentin. On the 7th day, remineralization coronal predentin was significantly higher than the control (P < 0.001). On the 14th day, DEJ axial zone and root dentin were similar to control and coronal dentin was significantly higher than the control (P < 0.001). Enamel was similar to control on the 28th day. Microhardness of DEJ-cusp tip and DEJ-center of the fissure was significantly lower than control even at the 28th day (P < 0.001). CONCLUSION: Long-term repeated application of sodium fluoride (226 ppm) can improve the microhardness of demineralized dental tissues on enamel, dentin, and DEJ-axial zone, except in the DEJ-cusp tip and DEJ-center of fissure.

Influence of irrigating needle-tip designs in removing bacteria inoculated into instrumented root canals measured using single-tube luminometer.

This study tested the mechanical efficacy of various irrigating needle tip designs on bacteria inoculated into instrumented root canals. Root canals of 30 extracted permanent canines were prepared to size 60 at working length (WL) using ProFile 0.04 taper rotary nickel-titanium files. Root canals were autoclaved and inoculated with a 20-microl suspension (1.4 x 10(7) cells) of genetically engineered Escherichia coli pYUB556. Bioluminescence was measured before inoculation (baseline), after inoculation and after irrigation with 6 ml of saline using luminometer. Safety-ended needles with single (group 1) and double (group 2) side-port and hypodermic needles (group 3) were used upto 1 mm short of WL. The percentage of bacteria remaining after irrigation was 67.9 +/- 9.5, 75.3 +/- 12.9 and 77.7 +/- 11.8 respectively (p < 0.05; Kruskal-Wallis) with no difference between group II and group III (p > 0.05; Mann-Whitney). Irrigation using safety needles with single side port was significantly effective.