Accuracy of a CAD/CAM-guided template for locating abutment screws for cement-retained implant-supported restorations

Statement of problem The accuracy of computer-assisted design and computer-assisted manufacturing (CAD/CAM) screw channel drilling guide for locating the abutment screw has not been demonstrated. Purpose The purpose of this in vitro study was to evaluate the accuracy of a CAD/CAM guide for drilling the screw access channel in angled implants. Material and methods Eighteen students prepared screw access channels through the crowns and abutments of implants placed at 0-, 15-, and 30-degree angulations in the mandibular second molar on dental casts. Experimental and control groups differed in the use of a CAD/CAM screw channel drilling guide, and each group was subdivided according to implant angulation. The accuracy of the screw channel was evaluated with regard to position and angle. Surface and volume losses of crowns and abutments were used to evaluate damage to the implanted prostheses. Statistical significance was assessed using 2-way analysis of variance (ANOVA), followed by the Tukey honestly significant difference (HSD) test (α=.05). Results The implant angulation significantly influenced the effect of the drilling guide with regard to the accuracy of the screw channel (F=8.319, P<.001) and crown volume loss (F=4.474, P=.014). For the 30-degree angulation, the guided drilling group exhibited smaller screw access holes than the freehand drilling group (P<.001), whereas no statistical differences were found between the groups for the 0- or 15-degree angulation. Guided drilling groups showed smaller standard lateral deviations than the freehand drilling groups. No significant differences were found in abutment volume loss among the groups. Conclusions A CAD/CAM guide significantly enhanced the accuracy of drilling the screw channel and reduced damage to the crown and abutment, particularly at an implant angulation of 30 degrees.