The Butterfly Effect: An investigation of sealer penetration, adaptation and apical crack formation in filled root canals.

Abstract

Background The butterfly effect is an optical phenomenon seen in some root cross-sections and is related to density and direction of dentinal tubules.

Aim The aim of the present study was three-fold. (i) To investigate the quality of adaptation and depth of penetration of root canal sealers (AH Plus®, EndoREZ®, Kerr Pulp Canal Sealer®, MTA Fillapex®) and obturation material (ProRoot® MTA) into the bucco-lingual and mesio-distal aspects of roots with and without the butterfly effect. (ii) To investigate apical cracks in roots which exhibit the butterfly effect and undergo apical resection and ultrasonic root-end cavity preparation. Finally, (iii) the effect of obturation material on crack formation was also studied.

Methodology 120 extracted single-rooted teeth were decoronated at the cemento-enamel junction. Roots were viewed under a light microscope (x10) and coded according to the presence or absence of the butterfly effect. Canals were prepared using ProTaper Next files to size X3. Debris was removed using 15% EDTA and 5.25% NaOCl. 100 roots randomly assigned to five obturation groups (gutta-percha (GP) with AH Plus®, GP with EndoREZ®, GP with Kerr Pulp Canal Sealer®, GP with MTA Fillapex®, and ProRoot® MTA alone). Each group contained 10 butterfly, and 10 non-butterfly roots. Control groups of (10 butterfly and 10 non-butterfly) prepared roots were used to confirm smear layer removal. Roots were embedded in resin such that the apical third was exposed. Forty roots (20 GP with AH Plus® and 20 ProRoot® MTA) were resected perpendicular to their long axis, 3 mm from the apex and cavities cut using ultrasonic retrotips. Resin replicas were used for crack imaging with scanning electron microscopy (SEM). 100 roots were then cut horizontally to yield coronal and middle sections. Sections were observed with confocal laser scanning microscope (CLSM) (x10) and “bird’s eye-view” images taken. Depth of penetration was measured using Image J software (National Institute of Health, Bethesda, MD, USA). Sections were then observed with SEM (x400) and images taken from the dentine-sealer or ProRoot® MTA interface. Adaptation was scored as good, reasonable, poor or absent. Statistical analyses were completed with Stata 13.1 (StataCorp, College Station, TX, USA).

Results Teeth with the butterfly effect had greater mean penetration bucco-lingually (766.25 µm) compared with mesio-distally (184.09 µm), a significant difference (P = 0.003). In contrast, teeth without the butterfly effect had no significant difference between bucco-lingual (385.78 µm) and mesio-distal (387.03 µm) penetrations (P = 0.98). Teeth with the butterfly effect had significantly greater penetration bucco-lingually compared to teeth without the effect (P = 0.01) and significantly less penetration mesio-distally (P = 0.008).

Coronal sections had the greatest mean penetration (430.79 µm) compared with middle sections (247.25 µm), a significant difference (P = 0.006). Adaptation was also significantly more favourable in coronal sections (78% good or reasonable) than middle sections (57% good or reasonable) (P = 0.0012). Depth of penetration and quality of adaptation varied between the sealer groups and ProRoot® MTA, however these did not reach significance.

Following root-end resection and cavity preparation, cracks occurred more frequently in teeth with the butterfly effect (80%) compared to those without (20%), a significant difference (P = 0.001). Most cracks (73%) ran bucco-lingually. Teeth obturated with MTA developed fewer cracks (40%) compared to those obturated with GP and AH Plus® (60%), but this was not significant.

Conclusion The butterfly effect influences sealer penetration and adaptation inside root canals. Roots with the butterfly effect have greater penetration bucco-lingually. This may enhance entombment of bacteria, which could lead to improved treatment outcomes. Root-ends with the butterfly effect have a significantly higher number of bucco-lingual cracks following resection and ultrasonic root-end preparation. This might explain the development of some vertical root fractures, which usually run bucco-lingually. Canal obturation with MTA may be protective.