T echniques for assembling dental splints and bridges require that the individual units be maintained in exact relationships during the manipulations necessary for joining them with solder. Some elements in these techniques can cause crown misalignment. I f the retainers of the completed assembly are even slightly malpositioned, the prosthesis cannot be correctly seated and failure of the appliance can be predicted. The first purpose of this study was to simulate in the laborato’ry a clinical technique for bridge assembly and to measure the influence each of the following procedures had upon changes in crown position: ( 1) transfer of the crowns from the model by an impression plaster index, (2) investment of the crowns in the soldering refractory material, and (3) connection of the crowns with solder. Also of interest were the effects upon the assembly of: (a) varying the symmetry or configuration of the soldering investment, (b) modifying the manner of heat application to the crowns and soldering investment, and (c) omitting or providing a solder space between the crowns. The second purpose of the study was to develop a test method suitable for measuring the minute changes that occur. A commercial optical comparator was selected for the primary measuring instrument. It was necessary to design accessories and develop a system for its use.