The "Butterfly Effect" and Its Correlation to the Direction of the Fracture Line in Root Dentin

The butterfly effect is an optical phenomenon and is related to the presence of sclerotic dentin in the roots. The unique pattern of sclerotic dentin formation produces a characteristic butterfly shape in transverse sections of the roots. The objective of this study was to evaluate the direction of the fracture line in roots that exhibit the butterfly effect.

Thirty single-rooted premolars with oval-shaped roots were decoronated and embedded in acrylic blocks and subjected to vertical force under a universal testing machine (HPBSD; Tec-Sol India, Chennai, India). Fractured roots were examined under a stereomicroscope (Model no. 080772; Lawrence and Mayo, Mumbai, India) at ×10 magnification to determine the location and direction of the fracture line. To evaluate the correlation between the direction of sclerotic dentin and the direction of the fracture line, teeth were sectioned and observed under a stereomicroscope at ×20 and ×40 magnification. The correlation was analyzed using the Fisher exact test (P < .05 for the coronal and apical thirds and P > .05 for the middle third).

Sclerotic dentin was observed more in the apical area and less in the coronal third of the root. The correlation between the direction of sclerotic dentin and the direction of the fracture line was statistically significant in the coronal and apical thirds of the root.

The vertical root fracture that runs buccolingually is correlated to the harder sclerotic dentin present in the mesiodistal direction.