Accuracy of CAD/CAM-guided template to locate abutment screw access hole in cement-retained implant crowns

Abstract

Purpose: The formation of screw-access hole for cement-retained implant restorations can be aided by using a computer-assisted design and computer-assisted manufacturing (CAD/CAM) drilling guide. The purpose of this study was to evaluate the accuracy of the CAD/CAM- guided template for drilling the screw-access hole in malpositioned implants.

Materials & Methods: Experimental factors were implant angulation and position. Eighteen students prepared screw-access holes through the crowns of implants placed at 0-, 15-, and 30-degree angulations in the mandibular second molar on dental casts. Another twenty students prepared the holes through the crowns of implant placed lingually on premolar and molar. Experimental and control groups differed in the use of a CAD/CAM screw-hole drilling guide, and each group was subdivided according to implant angulation and position. The preparation accuracy was evaluated in terms of the volume losses of crowns and abutments, the angular deviation of hole, and drilling entry point. An independent t test and two-way analysis of variance (ANOVA) with the Tukey honestly significant difference (HSD) test were performed to analyze intergroup differences and interactions (α=0.05).

Results: The implant angulation and position significantly influenced the effect of the drilling guide with regard to the accuracy of the screw-hole (F=8.319, P<0.05) and crown volume loss (F=4.474, P<0.05). For the 30-degree angulation, the guided drilling group exhibited smaller screw-access holes than the freehand drilling group (P<0.05), whereas no statistical differences were found between the groups for the 0- or 15-degree angulations. The accuracy of drilling entry point significantly correlated with prosthesis position and guide use (F = 51.281, P<0.05). The overall standard deviation was smaller in the guided drilling group than in the freehand drilling group.

Conclusion: A CAD/CAM guide template significantly enhances the accuracy of drilling the screw-hole and reduces damage to the crown and abutment, particularly at 30-degree angled and lingually placed implants.