The effect of irrigation time, root morphology and dentine thickness on tooth surface strain when using 5% sodium hypochlorite and 17% EDTA.
OBJECTIVE
To evaluate the effect of irrigation with 5% sodium hypochlorite (NaOCl) alone and in conjunction with 17% ethylenediaminetetraacetic acid (EDTA) on tooth surface strain (TSS) and to analyse the influence of irrigation time, root morphology and dentine thickness.


METHODS
Thirty-six single-rooted pre-molars with single canals had their crown and enamel reduced and root canals prepared using a standardized protocol. Teeth were grouped according to anatomical criteria and randomly distributed to experimental irrigation groups: (A) saline (negative control); (B) 5% NaOCl (positive control); (C) 5% NaOCl alternated with 17% EDTA. TSS was measured using electrical strain gauges bonded to the cervico-proximal part of the tooth. Teeth, mounted in clear acrylic resin placed in a universal testing machine, were subjected to nine consecutive 10-min irrigation periods followed by non-destructive occlusal loading to record TSS. Statistical analysis was carried out using two-way hierarchical anova and post hoc multiple comparisons.


RESULTS
Two groups showed an increase in TSS from the baseline (initial 10-min irrigation with saline). Group A showed a negligible reduction of 1.2% (343-339 muepsilon), which was not statistically significant (P = 0.7). Group B showed a highly significant (P = 0.001) increase in TSS by 53.7% (178-253 muepsilon), and group C showed a significant (P = 0.02) increase in TSS by 17.4% (163-192 muepsilon). The rate of change in TSS was significantly different between test groups. The length of the tooth (P = 0.04) as well as the mesio-distal (P = 0.05) width had significant effects on TSS.


CONCLUSIONS
Irrigation with 5% with or without 17% EDTA increased TSS. The increase was significantly greater with 5% NaOCl alone than with 5% NaOCl alternated with 17% EDTA in contrast to previous findings with longer duration of irrigant exposure. Tooth length and mesio-distal root width significantly contributed to the increase in TSS.
Unit of Endodontology, Divisions of Restorative Dental Sciences, UCL Eastman Dental Institute, University College London, London, UK.
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Sobhani
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Gulabivala
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D000704:Analysis of Variance; D016001:Confidence Intervals; D003799:Dental Stress Analysis; D003804:Dentin / Q000033:anatomy & histology; D004492:Edetic Acid / Q000008:administration & dosage; D006801:Humans; D016014:Linear Models; D012388:Root Canal Irrigants / Q000008:administration & dosage*; D018915:Root Canal Preparation / Q000379:methods*; D012973:Sodium Hypochlorite / Q000008:administration & dosage; D018709:Statistics, Nonparametric; D013499:Surface Properties; D007507:Therapeutic Irrigation / Q000379:methods; D013997:Time Factors; D014092:Tooth Root / Q000033:anatomy & histology
D012388:Root Canal Irrigants; D004492:Edetic Acid; D012973:Sodium Hypochlorite