Purpose - The purpose of this paper is to propose an imperfect symmetry transform framework for orbital prosthesis modelling. Design/methodology/approach - Current models of patients with orbital defects have imperfect symmetries. Commonly used methods, such as principal component analysis (PCA) or iterative closest points algorithm (ICP), do not detect perfect symmetries and therefore produce poor results. The authors propose an improved ICP algorithm based on the M-estimator, which can remove outliers from the optimization and detect incorrect symmetry. Using this algorithm, the mid-facial plane of a patient's facial model can be precisely obtained despite perturbation of the facial shape due to the defect. Findings - The results showed that the orbital prosthesis fitted well to the patient's appearance. Clinical applications confirmed that this framework is attractive and has the potential for use in creating desired orbital prostheses or other bilateral maxillofacial prostheses in daily clinical practice. Practical implications - The method described in this report will improve the fabrication accuracy of orbital prostheses or other bilateral maxillofacial prostheses. Originality/value - This imperfect symmetry transform framework has great potential for use in clinical applications because of its advantages over other existing methods in terms of accuracy.
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