Fracture-Associated Dentine Sclerosis Patterns in Single-Canal Premolars with Natural Vertical Root Fractures: A Scanning Electron Microscopy Study.

OBJECTIVE

This study aimed to characterise the topographic distribution of naturally occurring vertical root fracture (VRF) lines in single-canal premolars and to evaluate whether these patterns are associated with regional differences in dentine sclerosis assessed by scanning electron microscopy (SEM).

METHODS

Twenty-four extracted root-filled single-canal premolars with clinically confirmed natural VRFs were examined. Fracture line localisation was mapped according to the root third and surface direction. In 10 specimens, longitudinal sections were analysed by SEM in the buccolingual and mesiodistal planes across the coronal, middle and apical thirds. Dentine sclerosis was quantified using the sclerosis coefficient (Ks), based on the proportion of dentinal tubule area within standardised SEM images.

RESULTS

Fracture sites were most frequently observed in the middle third of the root, particularly on the buccal surface. Scanning electron microscopy analysis showed pronounced directional heterogeneity of dentine sclerosis in the middle third, where Ks values were lower in the buccolingual plane than in the mesiodistal plane, especially near the canal wall. In contrast, apical and external regions showed more uniformly high sclerosis values.

CONCLUSION

This study's findings showed that in single-canal premolars with naturally occurring VRFs, fracture lines were most frequently observed on the buccal surface and in the middle third of the root. Scanning electron microscopy analysis showed that this region was characterised by the greatest directional heterogeneity in dentine sclerosis, with lower Ks values in the buccolingual than in the mesiodistal plane near the canal wall. Further biomechanical studies, including direct mechanical testing and finite element modelling, are required to determine whether the observed microstructural patterns may contribute to VRF initiation or propagation.