In Vitro Evaluation of a Three-Dimensional-Printed Handpiece-Guide for Fiber-Posts Removal

Objectives: Removal of root-posts for endodontic retreatment of devitalized teeth restored with fiber-posts is challenging. Three-dimensional endodontic guide has been suggested to improve safety and efficiency. However, limitations still exist, such as the requirement of specific drill and side effect of impeded irrigation. To overcome these problems, a novel handpiece-guide was proposed which guides the head of handpiece instead of drill with the aid of an adapter. This study was to evaluate the accuracy of three-dimensional-printed handpiece-guide through in vitro approach.
Methods: The right first molar, the right central incisor, the left first premolar and the left second molar of a digitalized standard maxillary dentition were virtually crown-amputated. Four cylinders (diameter×height: 6×12mm) were positioned along the directions of main root canals of corresponding teeth to form the virtual test model，which was printed with light-polymerizing-resin for ten copies. Four handpiece-guides targeting the cylindrical axes were designed and printed with titanium-alloy. One senor prosthodontist performed the drilling toward each cylindrical axis with handpiece-guide or freehand (n=5 in each). The drilled models were scanned. The coordinates of centers of all perforations and circle bases on top/bottom surfaces were collected. The top/bottom distance deviation, and the angle deviation between the actual drilling axis and cylindrical axis for each tooth were calculated and analyzed (Two-way ANOVA, Sidak's, P<0.05).
Results: No difference of the top distance deviation was detected between guided and freehand group (0.19±0.09mm vs 0.35±0.18mm). For the bottom distance deviation and angle deviation, the results of guided group were significantly smaller than freehand group (0.54±0.19mm vs 1.71±0.51mm；2.67±1.07° vs 8.48±2.86°). The effect of tooth position appears not obvious.
Conclusions: With limits of in vitro design, the accuracy of three-dimensional-printed handpiece-guide is clinically acceptable.