Evaluation of Abutment Parallelism and Path of Withdrawal Using Three Intra- and One Extra-Oral Methods: A Survey and In vitro Study

Abstract

A dental student or a future dental practitioner needs to be trained to visualize their teeth preparations to detect any amount of undercuts present so as to minimize further clinical and laboratory problems such as over taper and open margins. introduCtionDuring teeth preparation, our main aim is always to develop a common path of placement/insertion to achieve passive and complete seating of the prosthesis. [1] Path of placement or withdrawal according to GPT is defined as: "the specific direction in which prosthesis is placed on the residual alveolar ridge, abutment teeth, dental implant abutment(s), or attachments." [2] Fixed partial denture (FPD) with unparalleled abutments will necessitate excessive seating force that often results in fractures in the veneering ceramic. In order to avoid these side effects, clinicians tend to over taper the preparation. The excessive reduction of the prepared abutments can compromise restoration retention and resistance and jeopardize the biological health of the dentin-pulp complex in vital abutment teeth. [3,4] el-Ebrashi et al. [5] and Jogerson [6] suggested an optimum convergence angle (CA) of 2.5º-6.5º to decrease stress concentrations. Jadhav et al. [7] suggested 2º-7º of taper or 4º-14º of CA to obtain maximum retention and stated some