Navigational precision of drilling tools preventing damage to the mandibular canal

Purpose: The use of CT-based intraoperative navigation has greatly improved surgical control in many specialities. In this study the precision of the SMN(R) system (Zeiss, Oberkochen, Germany) for navigated drilling before implant insertion is evaluated. Material and Method: One hundred test drillings were carried out on 10 standardized acrylic lower jaw models with the aid of the navigation system after CT scanning. The CT scans were taken using a slice thickness of I min. Then the CT data were transferred to the workstation of the SMN(R) system and referentiation with the help of reference points (fiducials) of the mandibular models for superposition of the acrylic and the CT models were carried out. Referentiation of the model and the drilling were performed by a drilling tool. The limit of drilling was the upper border of the mandibular canal. The aim was to come as near as possible without perforation of the canal roof. Results: An average drilling depth of 6.23 mm. and a mean distance to the mandibular canal of 0.14 mm (s=0.05) was found. In 11 cases the upper border of the canal was perforated. The average penetration of the mandibular canal measured 0.19 mm. Eighty-nine drill holes were accomplished without perforation. The average distance to the alveolar canal measured 0.13 mm. Conclusion: A high precision of CT-based navigation for controlled drilling of mandibles for dental implants was seen. (C) 2001 European Association for Cranio-Maxillofacial Surgery.