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ePaper created 2015-03-07, 18:13:20 | version 1.33.01
technique _ CBCT diagnostic I _and the anatomy of the nasal cavity above the alve- olus _Foranedentulousorpartiallyedentatepatientpres- entation, the application of a radiopaque scanning template is an invaluable part of the diagnostic phase. When teeth are to be extracted and implants placed, it is difficult to fabricate a radiopaque scan- ningtemplateunlesstheteethhavebeenpreparedto acceptanacrylictransitionalrestoration.Theappear- ance of the cross-sectional slice of a maxillary ante- rior incisor tooth can be seen in Fig. 2. The position of the tooth appears to be facial to the alveolus, which the author has termed as the ‘reality of anatomy’. The apex of the root gives the impression that it dehis- cences through the facial cortical plate of bone (red arrow).Thefacialaspectoftherootappearstobeap- proximately 4mm above the alveolar crestal bone (pink arrow). The patient’s lip rests against the facial aspect of the alveolus and the tooth (yellow arrows). A maxillary canine tooth on another patient presents a similar pattern in the cross-sectional slice (Fig. 3). Thetoothrootdoesnotresidewithinthegreatestvol- ume of bone, at a different trajectory from the alveo- lus. This can lead to complications if an implant os- teotomy is prepared within the actual tooth socket, potentially perforating through the thin facial corti- calplate(pinkarrows).Again,theliprestsagainstthe alveolar-tooth-root complex, limiting the apprecia- tion of the thickness of the soft tissue, and aiding to define the facial cortical housing (yellow arrows). In eithercross-sectionalexample(Figs.2&3),theextent of the labial vestibule cannot be determined. The use of interactive treatment planning soft- ware adds advanced software tools to help remove scatter,improvethediagnosticcapabilities,whilecre- ating three dimensional reconstructed volumes that canbeseeninallplanesofview.Theabilitytonavigate and ‘slice through’ 3-D volumes, known as ‘clipping’, provides unprecedented visualisation of the max- illo-mandibular structures. A maxillary 3-D volume ‘clipped’ through the right canine (marked in red) is seen in Figs. 4a and b. The 3-D reconstructed volume helpstofurtherdefinethemaxillaryalveolaranatomy, tooth, and root position within the bone. An advanced software feature allows for manipulation of the grey- scale density of the scan data (thresholding). This tool knownas‘segmentation’ canbeusedtoreducescatter from metal artifacts, such as crowns or fillings, and to separate one object from another. Through software segmentation, the maxillary right canine can be vir- tually extracted from the alveolus, illustrating the socket anatomy, the thin facial cortical plate (yellow arrows),andthepalatalbonethickness(greenarrow) (Fig.5).Thesoftwareallowstheimagestobeenlarged for closer inspection (Fig. 6). Note the areas of good densityandwherethedensityispoorwithinthealve- olus, superior to the root socket. Thecapabilitytovirtuallyremoveatoothandroot from the bone can aid clinicians in making educated decisions regarding immediate extraction-to-implant placement,immediate-to-transitionalrestoration,and anappreciationofthepotential‘gapdistance’,which may be present after implant placement. A simulated implant of the appropriate diameter and length can be positioned within the virtual socket to gain initial stabilisationasrelatedtothedesiredrestorativeout- come (Fig. 7). The thin facial cortical bone can be clearly seen (yellow arrow), as can the thicker palatal bone (green arrow). The facial ‘gap’ between the im- plant and the facial cortical plate can be fully appre- ciated, and decisions made whether or not to fill the gap with bone (red arrows). ThediagnosticinformationfromCBCTdatacanbe significantlyimprovedbytakingonesimplestepprior to the scan, regardless of the software application, and without regard to advanced software tools. For almosttwodecades,theauthorhasadvocatedtheuse of a ‘lip-lift’ technique: moving the lip away from the teethwiththeuseofasimplecottonroll(Fig.8).Plac- Figs. 4a & b_A maxillary 3-D volume ‘clipped’ through the right canine tooth (marked in red) (a). The 3-D reconstructed volume helps to further define the maxillary alveolar anatomy, tooth, and root position within the bone (b). I 07cone beam1_2015 Fig. 4a Fig. 4b