A method of producing a surgical template comprising the steps of: i) obtaining a set of 3D surface data, the 3D surface data representing a surface of a patient's oral situation, ii) obtaining a virtual support structure model describing a dental splint configured to fit to a portion of the surface of the patient's oral situation, iii) obtaining planned bore position data, the planned bore position data describing the longitudinal axes of a set of one or more planned implant bore holes relative to the 3D surface data, iv) automatically modifying the virtual support structure model to provide support material for guide holes in the virtual support structure model corresponding to the one or more planned implant bore holes, v) producing the surgical template in dependence on the modified virtual support structure model, wherein the method further comprises the steps of, for each bore hole: vi) generating a 3D distance map image of the support structure model, wherein the 3D distance map is a voxel image and wherein each voxel in the 3D distance map image has a value corresponding to the distance from said voxel to the closest point on the surface of the support structure model, vii) generating a 3D distance map image of a sleeve support shape for the guide hole, wherein the 3D distance map is a voxel image and wherein each voxel in the 3D distance map image has a value corresponding to the distance from said voxel to the closest point on the surface of the sleeve support shape, the sleeve support shape having a longitudinal axis corresponding to the bore hole, viii) combining the 3D distance map image of the sleeve support shape with the 3D distance map image of the support structure model, ix) modifying the support structure model to add support material where the combined voxel values at each point in the combined 3D distance map images correspond to a distance less than a minimum distance. i) obtaining a set of 3D surface data, the 3D surface data representing a surface of a patient's oral situation, ii) obtaining a virtual support structure model describing a dental splint configured to fit to a portion of the surface of the patient's oral situation, iii) obtaining planned bore position data, the planned bore position data describing the longitudinal axes of a set of one or more planned implant bore holes relative to the 3D surface data, iv) automatically modifying the virtual support structure model to provide support material for guide holes in the virtual support structure model corresponding to the one or more planned implant bore holes, v) producing the surgical template in dependence on the modified virtual support structure model, wherein the method further comprises the steps of, for each bore hole: vi) generating a 3D distance map image of the support structure model, wherein the 3D distance map is a voxel image and wherein each voxel in the 3D distance map image has a value corresponding to the distance from said voxel to the closest point on the surface of the support structure model, vii) generating a 3D distance map image of a sleeve support shape for the guide hole, wherein the 3D distance map is a voxel image and wherein each voxel in the 3D distance map image has a value corresponding to the distance from said voxel to the closest point on the surface of the sleeve support shape, the sleeve support shape having a longitudinal axis corresponding to the bore hole, viii) combining the 3D distance map image of the sleeve support shape with the 3D distance map image of the support structure model, ix) modifying the support structure model to add support material where the combined voxel values at each point in the combined 3D distance map images correspond to a distance less than a minimum distance.