Dental Tribune United Kingdom Edition

versity of Milan, 44 skeletal Class I normodivergent patients were selected from an archive of 500 CBCT scans. The cephalomet- ric diagnosis of a skeletal Class I normodivergent relationship is based on the School of Milan. The same patients were then analysed with 3-D cephalometry. The re- sults allowed the identification of a normal range of values for each measurement (Table II). The 3-D technique goes beyond the limitations of 2-D analysis in many ways: • effective representation of true 3-D morphology of the cranial structures without distortion, avoiding projection and identifi cation errors • reduced operator bias because the measurements are pe formed automatically • simplicity and repeatability in the identification of landmarks, using true anatomic structures without superimposition or the problems of geometric construc tion • ability to obtain CA using the three dimension • dento-skeletal alterations can be analysed in 3-D in order to determine appropriate treat ment. Combined orthodontic and surgical planning The introduction of 3-D imaging techniques has revolutionised the planning phase of combined or- thodontic and surgical treatment. The use of the computer, together with dedicated software, allows for a fast, precise and standard- ised procedure. 3-D virtual plan- ning entails the following: • CBCT scan • high-definition impression • reference aligner • digital scan cast • CBCT digital cast interface Using virtual planning, it is possible to obtain the virtual vis- ual surgical treatment objective and the virtual orthodontic model. High-definition impressions are obtained using polyvinyl siloxane, which guarantees well-defined details while allowing for the dou- ble-pour method. Double-poured casts are necessary to obtain an adequate scan and require the use of both a full cast and indi- vidual dental elements selected from a second cast. Single dental element scans allow for proper analysis of contact points. An op- tical cast scan is performed using structured-light scanners, which produce a 3-D image captured by a camera. In this manner, a group of points is determined by the soft- ware, which then determines the coordinates of the acquired points and finally creates the 3-D image (Fig 3).5 Moreover, the digital dental cast is then combined with the CBCT scan, which allows for a very detailed analysis of both the bone (through the CBCT scan) and the dental structure (through the cast scan). CBCT does not pro- vide enough data regarding all the dental details necessary to pro- duce the orthodontic model (Fig. 4).6 In order to superimpose the two records properly, a specific three-contact point bite registra- tion wax, known as the reference aligner, has been introduced. The reference aligner needs to be ap- plied to the teeth when the high- definition impressions are taken. It is made of Moyco (an extra-hard wax) and consists of a supporting Fig 1 Fig 2 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. Table I_Effective radiation dose (background radiation 8 μSv/day). Table II_Normal values range. ‘The introduction of 3-D imaging techniques has revolutionised the planning phase of combined ortho- dontic and surgical treatment’ Fig. 3_Digital cast. Fig 3 Fig. 4_CBCT digital cast interface. Fig 4 October 29 - November 4, 201222 Clinical United Kingdom Edition page 21DTß