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ePaper created 2018-03-23, 14:21:22 | version 1.38.0
lab tribuneDental Tribune Middle East & Africa Edition | January-February 2015 3C < Page 2C More information is available from the publisher. Editorial Note individual patient anatomy. The cross-sectional slice is important for the assessment of the facial and lingual cortical bone plates, the intramedullary bone, and the positioning of teeth within the alveoli. The axial view al- lows inspection of the entire up- per or lower jaw, the maxillary sinus volume, the position of the incisive canal in the maxil- lae, and the mental foramina in the mandible. The panoramic view is an overall scout image, and can be helpful in tracing the mandibular nerve, and as- sessment of the maxillary si- nus floor near the nose region. The 3-D reconstructed volumes are invaluable in the planning process and in communicating information to the members of the implant team, including the patient and the dental laboratory technician who will fabricate the final prosthesis. These images are especially useful, as they are most readily understood and ap- preciated. As represented in the flow chart, a patient may be sent to a radi- ology centre for a CBCT scan of the mandibular arch without a scanning appliance. The 3-D re- constructed volumes are easily understood and interpreted for the mandible (Figs. 2a–c). In the case demonstrated, there were several hopeless anterior teeth that were planned for extraction. The extent of the bone loss can be appreciated by the clinician and demonstrated to the patient as an excellent educational and communication tool. The vir- tual mandible can be rotated to reveal all views of the patient’s individual anatomical presenta- tion (Figs. 3a & b). With innova- tive software tools, the teeth can be virtually extracted in the 3-D reconstructed volume, aiding the clinician in understanding the local anatomy to identify potential implant recipient sites (Figs. 4a & b). In this example, the alveolar ridge narrowed considerably at the crest. In or- der to facilitate implant place- ment, the ridge required an al- veolectomy, reducing the ridge by approximately 8–10 mm. Advanced software applications allow for the bone to be sec- tioned based upon the desired plan. A bone reduction template pioneered by the author can be simulated by the software and then fabricated to assist in the bone removal (Figs. 5a & b). The reduction template fits over the ridge, allowing complete visu- alisation of the residual bone to be sectioned from the alveolar ridge. The flattened ridge can also be simulated, greatly en- hancing the clinician’s appre- ciation of the remaining bone topography (Figs. 6a & b). The amount of bone to be removed can be visualised as shown in Figure 7a and then assessed with realistic manufacturer- specific implant placement in the bone (Fig. 7b). The occlusal and facial views reveal the new width of available crestal bone for implant placement (Figs. 8a & b). The visualisation of the bone crest can aid in the deter- mination of ideal implant recipi- ent sites. However, it must be noted that all other views must be considered to appreciate ad- jacent vital anatomical struc- tures and the remaining topog- raphy of the anterior mandible before any plan can be finalised. Several different options can be quickly simulated and then dis- cussed with the patient and all members of the implant team. The use of a bone reduction template can facilitate the accu- rate removal of bone and the im- mediate placement of implants, eliminating the need for two separate surgical interventions and thus mini mising patient morbidity. The initial plan in the case dem- onstrated was for the patient to receive an implant-retained overdenture. Therefore, recipi- ent sites were determined based upon the available bone in the mandibular symphysis between the right and left mental foram- ina, which were assessed in the axial and cross-sectional views. While it is possible to fabricate an overdenture design with im- plants in the posterior region of the mandible, the usual position of implants is within the sym- physis region. The choices were to place two implants, three im- plants, or four implants between the two mental foramina (Figs. 9a–d). The symphysis area is not free from risk. A cross-sectional view is necessary for an appre- ciation of the thickness of the facial and lingual cortical bone plates, and for assessment of the trajectory and topography of the anterior mandible. In addition, there are important vessels in the region that have been shown to cause severe haemorrhaging if perforated. These vessels may differ from patient to patient and underscore the importance of a 3-D diagnosis. In this case, two such vessels were found in the midline area of the symphy- sis (red arrows) as seen in the cross-sectional view, which also revealed the extensive bone loss surrounding the hopeless teeth (yellow areas; Fig. 10). Virtual realistic implants were simulated in the residual al- veolar bone (Figs. 11a–d). A simulated surgical template was fabricated for the desired implant positions and rested on the reduced bone both facially and lingually. At the midline, where the vital vessels resided, it was elected not to place an implant to avoid potential surgi- cal complications (Fig. 12). The simulated bone-borne surgical template was visualised in vari- ous 3-D reconstructed volumes (Figs. 13a–c). The first two re- vealed a midline horizontal sta- bilisation screw (Figs. 13a & b) and the last showed a standard bone-borne template without fixation (Fig. 13c). Had addition- al implants been required for improved stability or had a fixed detachable hybrid restoration been indicated, supplementary recipient sites could have been located based upon the available anatomy. In order to demonstrate the ca- pabilities of the new digital para- digms,fivevirtualimplantswere placed into the initial anterior al- veolar ridge after the teeth had been extracted virtually (Fig. 14a). The positions of implants canbefurtherenhancedbyplac- ing yellow abutment projections that extend above the occlusal plane. Using selective transpar- ency, the various structures can be adjusted in opacity and trans- lucency. Using advanced soft- ware simulation, horizontal os- teotomies to allow the implants to be placed in the same vertical position in the newly reduced ridge were illustrated (Fig. 14b). Implant-to-implant relation- ships can be evaluated in all dimensions (Figs. 15a & b). In addition, it is important to pro- vide ample clearance between the most posterior implants and the inferior alveolar nerve and mental foramen. Once the posi- tions of the implants have been finalised, a surgical guide can be simulated (Figs. 16a & b). Note that the implants were all paral- lel, which can aid in laboratory fabrication for overdentures and in achieving passive fit for fixed frameworks (Fig. 16c). The re- lationship between the original tooth position and the simulated implants can be appreciated in Figure 16d. If a fixed detach- able hybrid, full-arch CAD/CAM zirconia restoration, or an im- mediate restorative protocol is desired, the ability to simulate implant position with an accu- rate consideration of the desired tooth position will enhance the surgical, restorative and labora- tory phases of treatment. Conclusion The advent of complete den- ture fabrication has evolved into the adoption of overdenture concepts for both natural and implant-retained restorations. Conventional prosthodontic protocols have been developed to aid in the diagnosis, treatment planning and laboratory phases of the reconstruction. These include conventional periapi- cal radiographs, panoramic ra- diographs, oral examination, and mounted, articulated study casts. Using these, the clinician can assess several important as- pects of the patient’s anatomical presentation, including vertical dimension of occlusion, lip sup- port, phonetics, smile line, over- jet, overbite, and ridge contours, and can obtain a basic under- standing of the underlying bone structures. The accumulation of preliminary data afforded by conventional diagnostics pro- vides the foundation for prepar- ing a course of treatment for the patient. However, the review of findings is based upon a 2-D as- sessment of the patient’s bone anatomy. In order to understand each patient’s presentation fully, ad- vanced 3-D imaging modalities are essential. This article has illustrated the use of various in- novative virtual 3-D tools. The application of CT or lower radiation dosage CBCT provides clinicians with an accurate un- derstanding of the 3-D anatomi- cal reality of our patients as an aid in providing state-of-the- art treatment. Implants will be better positioned, with fewer surgical and restorative com- plications, and reduced labora- tory remakes based upon these diagnostic tools. The benefits will enable clinicians to better understand the relationship be- tween patient anatomy and the desired restorative outcomes in the process of achieving true restoratively driven implant reconstruction. The ability to utilise digital imaging and treat- ment planning technology is now within the reach of many clinicians through the various software products on the mar- ket. In addition, there are many thirdparty outlets online that en- able clinicians to upload their DICOM data for evaluation, processing, treatment planning, and even surgical template fab- rication. In many case presentations, a reduction of the alveolar crest is an essential part of the surgical phase to achieve adequate width of the bone for implant place- ment. It is now possible to plan for accurate bone reduction with the full knowledge of the impact on the inter-arch space and oc- clusal requirements. The advent of the bone reduction template provides one additional digital solution that can also result in reduced patient morbidity, espe- cially when the process can be completed in one surgical pro- cedure. New paradigms have been established that, in the author’s opinion, will continue to redefine the process of diag- nosis and treatment planning for dental implant procedures, both removable and fixed implant- retained alternatives, for years to come. Fig. 10 Fig. 11a-d Fig. 12 Fig. 13a-c Fig. 14a-b Fig. 16a-d Fig. 15a-b