CAD/CAM - international magazine of digital dentistry

26 I I opinion _ CBCT _3-D cephalometry The aim of orthodontic diagnosis is to identify dento-alveolar, skeletal and functional alterations in the maxillo-facial complex. Diagnosis and treat- mentplanningarebasedonacombinationofstudy models, intra-oral and extra-oral images, and radi- ographs, traditionally consisting of panoramic and cephalometric radiographs. Cephalometric analysis (CA) plays an important role in diagnosis and treatment planning. Tradi- tional CA is based on three different X-ray projec- tions: latero-lateral teleradiography, postero-an- terior teleradiography and axial projection. How- ever,conventionalradiographsarelimitedbecause they provide a 2-D representation of 3-D struc- tures. The traditional system, analysing the three dimensions separately, is insufficient because dento-facial alterations often take place in 3-D space. Thus, the limits of traditional CA are: _errors in radiographic projection, resulting in en- hancements and distortions; _operator errors in the measurement systems; _errors in the identification of the cephalometric landmarks owing to superimposition of anatomic structures; and _inability to evaluate the three dimensions of the craniofacial complex.1 The recent introduction of CBCT in combination with computer software allows the application of this new methodology to different fields of den- tistry, including its successful use in orthodontics (Fig. 1).2 Owing to CBCT, the 3-D morphology of the cranialskeletalstructurescanberepresentedprop- erly.WithCBCT,thepatientisexposedtosimilarlev- elsofradiationasduringconventionalCAandupto 20 times less than during multi-slice-CT exams (Table I).3 AttheOrthodonticDepartmentattheUniversity of Milan, CA is performed with a new 3-D method- ology that allows for an easy, effective and repeat- able way to decrease operator-driven errors.4 It is based on the identification of 18 points (10 median and 8 lateral), all of which are identified on a hard- tissue CT section and verified on the two remaining CT sections. Further verification is then performed on the volume rendering generated by SimPlant OMS (Materialise). The 18 points determine 36 measurements on the sagittal, vertical and transversal dimensions (Fig.2).AttheUniversityofMilan,44skeletalClassI normodivergent patients were selected from an archive of 500 CBCT scans. The cephalometric diagnosis of a skeletal Class I normodivergentrelationshipisbasedontheSchool of Milan. The same patients were then analysed with 3-D cephalometry. The results allowed the identification of a normal range of values for each measurement (Table II). The3-Dtechniquegoesbeyondthelimitationsof 2-D analysis in many ways: CAD/CAM 2_2012 Fig. 1_The i-CAT Classic, a cone beam 3-D dental imaging system (Imaging Sciences International). Fig. 2_3-D rendering and cephalometric landmarks. CBCTin orthodontics Authors_ Prof Giampietro Farronato, Dr Francesca Bellincioni, Dr Margherita Colombo, Dr Daniela Falzone, Dr Salvadori Sara, Dr Gaia Passaler & Dr Gianfranco Santamaria, Italy Method Scan parameters in kV Dose in µSv Cephalometric analysis 69 / 15 mA / 14.1 s 50 Latero-lateral teleradiography 80 30 Postero-anterior teleradiography 80 40 Multi-slice CT 120 / 400 mA / 0.5 s 2370 CBCT 120 / 5 mA / 20 s 110 CBCT 120 / 5 mA / 10 s 60 Table I_Effective radiation dose (background radiation 8 µSv/day). Fig. 1 Fig. 2