A preform made of composite material designed to be formed on a laboratory model and to be integrated in a base plate of a dental prosthesis. The preform comprises a grid formed by a meshing of weft threads and warp threads coated in an impregnating resin, the space between the meshes being exempt of fibers and resin, and determining a surface of free spaces of more than 25% of the total surface of the grid. The weft threads are fixed onto the warp threads at the nodes of the meshing to enable the preform to be handled and to be formed on a laboratory model, without the impregnating resin creeping into the spaces of the meshes.