BackgroundThe research aimed to evaluate the optimal Single-Photon Emission Computed Tomography (SPECT) cut-off value in differentiating condylar growth activeness, to observe 3-dimensional (3D) mandibular growth pattern, and to explore the potential correlation between 3D measurement parameters and SPECT uptake ratios in Chinese unilateral condylar hyperplasia (UCH) patients.MethodsData of fifty-four Chinese UCH patients were analyzed retrospectively. All patients underwent SPECT within 1 month before or after the first CT examination (CT1); and received a second CT examination at least 12 months later (CT2). Data from CT scans were analyzed by comparing bilateral differences between CT1 and CT2. The sensitivity and specificity of SPECT were calculated by the receiver operating characteristic (ROC) curve. Pearson’s correlation analysis was performed to investigate whether the mandibular growth was correlated with SPECT value.ResultsSPECT had a sensitivity of 68.00% and a specificity of 72.41%, with an area under the ROC curve being 0.709. The optimal SPECT cut-off value for evaluating condylar activity has been determined to be 13%. In patients with an active growing condyle, there was a significant increase in Co-Gn and Co-Go, but not in Go-Gn, Go-MF, or MF-Gn. Pearson’s correlation analysis revealed no correlation between 3D measurement parameters and differences in relative condylar uptake ratios.ConclusionSPECT showed good diagnostic performance in UCH with the cut-off value of 13%. For those with an active growing condyle, the mandible grows diagonally and vertically, while the relative condylar uptake ratio was not directly related to mandibular growth.