24 is superimposed in a step g to an external surface of a normative shape of the target tissue 16 i e without the defect 18 preferably the template is superimposed via warping however a best fit process is also contemplated the template specifics a u201c seated u201d edge which is fixed to the subject patient and the remaining surface shape which is not affixed to the subject it is to be understood that the normative shape represents a desired or average shape of the target tissue preferably the normative shape is determined in a bilateral structure from a substantially mirror image of the target tissue e g a defect is present in a left side of a skull and complete data is available for a right control side of a skull however if too much of the target tissue is missing on the affected side or the defect crosses the midline in a way that prevents establishing the midline appropriate normative average surfaces which as described below are already homology mapped are used in this case the normative average data is brought in and registered to the homology mapped normative surface surrounding the defect once the template is warped points on the template are mapped in a step h to points on the external surface of the normative shape of the hone of interest 16 a shape of an implant 26 to be u201c dropped in u201d the defect 18 is determined in a step i as a function of a difference between the mapped points on the external surface of the target tissue and the external surface of the template the implant 26 is seated fit in the defect 18 of the target tissue 16 in a step.