Early Osseointegration in a Sheep Tibia Model: Correlating Digital Periapical Radiograph Gray-Level and RGB-Derived Metrics with Histologic Tissue Composition

Objective: This study aimed to evaluate peri-implant tissue changes during early osseointegration using a combined approach of digital radiographic analysis, RGB pseudocolorization, and histomorphometry in a sheep tibia model. Materials and Methods: Thirty titanium implants were placed in the tibiae of six adult sheep and evaluated at 14 and 28 days post-implantation. Digital periapical radiographs were acquired, grayscale values and RGB channel intensities were measured using Fiji/ImageJ, and compared with histological parameters (bone tissue, collagen, and medullary spaces) quantified from picrosirius–hematoxylin-stained sections. Manual overlay of radiographic and histological images was performed to ensure spatial correspondence of regions of interest. Statistical analyses assessed differences over time and correlations between image data and histological composition. Results: Radiographic grayscale values and histologically measured bone and collagen increased significantly from 14 to 28 days (p < 0.01), while medullary spaces decreased (p < 0.001), indicating progressive bone formation and matrix maturation. RGB analysis revealed significant increases in green channel intensity and decreases in red channel intensity (p < 0.05), while the blue channel remained stable. At 14 days, strong correlations were observed between blue channel intensity and bone tissue (r = 0.81; p = 0.015), and between green channel intensity and collagen (r = 0.98; p < 0.001). Visual overlays demonstrated alignment between radiographic high-density zones and histologically dense bone regions. Conclusions: RGB pseudocolorized radiographic analysis, correlated with histological findings, offers a non-invasive and reproducible method for early detection of peri-implant tissue maturation. This feasibility correlation study provides a foundation for future investigations integrating imaging, histology, and biomechanical testing.