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The effect of sodium hypochlorite and ethylenediaminetetraacetic acid irrigation, individually and in alternation, on tooth surface strain.

AIM
To evaluate the effect of irrigation regimens on tooth surface strain using saline, sodium hypochlorite (3% and 5% NaOCl) and ethylenediaminetetraacetic acid (17% EDTA), individually and in alternating combinations.


METHODOLOGY
Single-rooted premolar teeth with single canals prepared to standardized dimensions were grouped by anatomical features and randomly distributed amongst six experimental groups (n = 12 each). The six groups were: (1) saline; (2) 5% NaOCl; (3) 3% NaOCl; (4) 17% EDTA; (5) 3% NaOCl and 17% EDTA; (6) 5% NaOCl and 17% EDTA. All groups underwent four (group 1) or five (groups 2, 3, 4, 5, 6) sequential 30-min irrigation periods following each of which the tooth was subjected to a standard regime of cyclic, nondestructive, occlusal loading. Tooth surface strain was measured during each loading cycle using electrical strain gauges mounted cervico-proximally. The data were analysed by Hierarchical anova and post hoc multiple comparisons.


RESULTS
Irrigation with 5% NaOCl alone or alternating with 17% EDTA significantly (P < 0.001) increased the peak strain values for each of the irrigation periods compared with that of saline (group 1). The data for the other groups revealed no significant differences compared with those of saline. The strain increase after the fourth irrigation cycle was significantly higher for group 6 than for group 2. The measured canal morphology and dentine thickness parameters did not prove to have a significant effect on tooth surface strain.


CONCLUSIONS
Irrigation with 5% NaOCl acting alone or alternated with 17% EDTA (used in 30 min cycles), significantly increased tooth surface strain. The alternated regimen showed significantly greater changes in tooth surface strain than NaOCl alone. Irrigation with 3% NaOCl and 17% EDTA individually or in combination did not significantly alter the tooth surface strain.