The method involves completing initial intra-oral three-dimensional optical measurements of a section in a dental arch to determine an individual data. References (36, 38) are positioned in relation to an area. Subsequent intra-oral three-dimensional optical measurements of a dental arch area are completed to determine an additional individual data. The initial individual data is combined with the additional individual data and the references to calculate an overall data. The measurement of the section in the dental arch is combined with the reference and the overall data.