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 im
plant insertion is evaluated. Material and Method: One hundred test drillin
gs were carried out on 10 standardized acrylic lower jaw models with the ai
d 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 works
tation of the SMN(R) system and referentiation with the help of reference p
oints (fiducials) of the mandibular models for superposition of the acrylic
and the CT models were carried out. Referentiation of the model and the dr
illing were performed by a drilling tool. The limit of drilling was the upp
er 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 o
f 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 av
erage penetration of the mandibular canal measured 0.19 mm. Eighty-nine dri
ll 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 see
n. (C) 2001 European Association for Cranio-Maxillofacial Surgery.