Distribution and size of scallop patterns at the human dentin enamel junction revealed with micro tomography

• High-resolution micro-CT and 3D reconstruction revealed, for the first time, a topographic mapping of scallop patterns at the human dentin–enamel junction (DEJ). • Scallop size varies widely by location on the tooth as well as tooth type, with the largest scallops concentrated on mesial and distal faces of incisors and at interproximal contact points. • RMS roughness measurements quantified the surface heterogeneity of the DEJ, confirming significant topographic differences across tooth regions. • Multiphoton microscopy with second harmonic generation demonstrated a high concentration of collagen fibers, particularly at scallop peaks. • Findings support the hypothesis that scallop patterns enhance mechanical resistance at the DEJ, potentially contributing to crack deflection and tooth resilience. The dentin–enamel junction (DEJ) plays a critical role in tooth biomechanics, acting as a tough, crack-deflecting interface between the brittle enamel and the more resilient dentin. Although previous studies have described the DEJ using histology and electron microscopy techniques, the three-dimensional (3D) distribution and structural heterogeneity of scallop patterns along the DEJ remain poorly understood. Here, we combined high-resolution X-ray microcomputed tomography (µCT) with multiphoton microscopy (MPM) to investigate scallop morphology, spatial distribution, and collagen fiber organization across human teeth. Non-carious human teeth (n = 35) were scanned at 5 µm resolution, allowing 3D reconstruction of the DEJ surface. Scallop size, distribution, and root mean square (RMS) roughness were quantified across mesial, distal, buccal, and lingual faces of incisors, canines, premolars, and molars. MPM with second harmonic generation (SHG) provided complementary imaging of collagen fiber presence within scallop structures. Scallop size depended primarily on location but also on tooth type: the largest scallops (>150 µm) were concentrated on mesial and distal faces at interproximal contact areas, while molars lacked large scallops entirely. RMS roughness confirmed significant topographic heterogeneity between regions. SHG imaging showed high collagen density at scallop peaks. These findings provide the first whole-tooth 3D mapping of scallop patterns, supporting the hypothesis that scalloped DEJ structures enhance crack resistance and mechanical resilience. Further studies using higher-resolution imaging and comparative models across species may clarify the developmental and functional origins of these unique microstructures.