The RPI bar clasping system devised by Kratochvil and Krol has been highly evaluated as a typical retainer of a lower extensional partial denture. However, since part of the approach arm, ranging from the junction with the skeleton to the distal end of an abutment tooth, is impacted at the denture base upon completion of the denture, the fulcrum of stress that is intended upon setting of the framework is removed to around the denture base and its vicinity, from which it is deduced that elasticity of the approach arm varies with the form of the denture base. To prevent changes in the elasticity, the Tubing method was devised and its effects were studied in experimental models. The clinical procedure was found to be very easy to handle, to be a practical method for improvement and to reduce markedly the physical effect of the denture base upon the clasp, having the following advantages as compared with the usual method:(1) it maintains reset of the arm to the designed position without any effect of the form of the denture base;(2) it induces a reduction in the lateral load to an abutment tooth;(3) it is partly helpful for reduction of metal fatigue of the clasp;(4) the feeling of the setting of denture is soft (according to a patient's impression).
