CD0412

I CE article _ mastering occlusal function Fig. 11_The prior crowns are removed and teeth prepared. The computer proposal will morph into various shapes as it is going through the calculation. It also looksforratiosoftoothsizeandpositionwithinthe arch. This is a great advantage, because these digi- tal dental anatomies are not limited by size, but can fit within any range of tooth dimensions. The final- ized digital anatomy is a reflection of what the computer discovered through its analysis of the re- ference tooth. It also places the three-dimensional shape in contact with the opposing teeth (Fig. 3). If the clinician would like to see variations of the Biogeneric calculation, a slider allows that to hap- pen.Thistoolisreferredtoas“BiogenericVariation.” Ifimageshavetobere-taken,“BiogenericVariation” is the new name (Fig. 4). The slider travels through anatomies within the Biogeneric database and re- veals them through morphing of the proposal. This allows for a truly customized shape for the clinical situation, and within function. _Digital scanning During the course of treatment, the upper and lower arches or quadrants are scanned into the computer using the CEREC Bluecam digital scan- ning camera. The CEREC system can have multiple preparations within the same arch or in opposing arches. Each arch is saved in its corresponding li- brary of images within the software and evaluated for quality of margin integrity, path of draw, pre- parationgeometry,etc.(Fig.5).Themajoradvantage ofdigitalimpressionsisthatthephysicalimpression is eliminated from the process. This allows for im- mediate feedback to the clinician if the information is correct, rather than waiting to evaluate the in- verseofthephysicalimpressionmanyminuteslater. There are never any tears or bubbles with digital impressions. They also never distort. Therefore, they have tremendous value to the doctor and the patient, especially because the images are taken so easily and within a minute. After the upper and lower arches are captured, they are articulated by images taken from the buccal direction. The articulation for the upper and lower jaws is done in a static maximum intercuspation position utilizing what is referred to as the “buccal bite.” This would be similar to a triple tray type using physical impression material, but by doing it digitally, the position never changes. Articulation of the models iscompletedwithinthesoftware,andthemaximum intercuspation position is always repeatable. There isneverflexorvariationwiththearticulatorbecause ofitsdigitalnature.Therefore,iftakencorrectly,the buccal bite can place the maxillary and mandibular teethinaveryspecificpositionthatcanbedesigned to within microns of space.5 Another major advan- tage of an optical buccal jaw registration is that the position can be seen in the computer as the scan is taking place, much like when preparation images are being taken. How many times does a patient try and help the procedure by biting toward the area of work during an impression? Or, can you even find their centric occlusion through impression material and while anesthetized? The relation is hidden under physical impression material, and may not be realized until physical stone models are mounted on an articu- lator. However, with digitally scanned articulation, it can easily be seen that it may be incorrect, or the jaws are not stable, during the imaging (Fig. 6). The clinician simply stops the scan, coaches the pa- tient into the proper position, and then scans again (Fig. 7). This greatly enhances the predictability of occlusion of the final restoration. The operator takes control of the articulation of the three models: upper, lower and buccal bite. The buccalbiteisdraggedtothecorrespondingportions of the upper and lower models. The software then recognizes similar surfaces and “shrink wraps” the buccalbitedown.Thesameisdonefortheopposing arch. This establishes the digital maximum inter- cuspation position within the software (Figs. 8–10). The repeatable digital maximum intercuspation position also allows for multiple units to be de- signed in a highly predictable manner. Whether the restorations are being designed side by side or from one arch to another, the occlusal morphology and pinpoint placement of occlusal stops can be confi- dently placed knowing the arches are stable within the digital world. 08 I cosmeticdentistry 4_2012 Fig. 11