September 13, 2016
by Bobby Chagger, BSc, DDS
Digital dentistry has been embraced in our daily practice from the use of digital radiography to the fabrication of CAD/CAM restorations. The transformation in office economics, treatment philosophy, staff productivity and case presentation which accompany this shift in practice are issues worthy of serious attention, but space does not permit further exploration here.
Orthodontics has been less rapid in acceptance of the digital transformation in dentistry. Part of the issue with adoption across the profession was the lack of inter-operability between systems, forcing practitioners to make economics part of what would preferably have been purely clinical evaluations of a particular product. The inability to connect how digital impressions were created and then provided to different suppliers was a significant issue among others. For example, in the past, optical scanners such as CEREC (Dentsply Sirona) (Fig. 1) or the True Definition Scanner (3M) did not communicate with Invisalign.
This connectivity now exists as equipment manufacturers and the manufacturers of Orthodontic solutions now communicate. This article will discuss adoption of digital technology to facilitate orthodontics with reference to the clinician experience in digital transformation of other dental disciplines, with specific focus on optical impressions.
Optical impressions reduce the perceived treatment barrier associated with the need for full mouth PVS impressions. PVS impressions were required for traditional Aligner Therapy. Instead, a digital scanner utilizes a small camera, and eliminates this issue. Scans can be taken quickly and the patient does not suffer from gagging or repeated impressions to achieve a perfection. A virtual model of the patient is produced and allows for treatment simulations and outcomes – giving the clinician an ability to predict how treatment will progress and how long it might take. This increased predictability allows for confidence to the clinician and allows for better communication with the patient. The simulation can be demonstrated to the patient and the patient can make a better-informed decision on their treatment plan. Treatment planning and treatment philosophy have moved forward with the advent of digitization in orthodontics.
Considerations – Optical Impressions
From a manufacturer perspective, systems such as CEREC Ortho, iTero or 3M’s True Definition Scanner provide choices for the user. To select an optical scanner, consider the ability of the chosen device to integrate with our other digital modalities and capacity to export to third party manufacturers. In simpler terms, can I use my optical scanner to fabricate a CAD/CAM restoration? Can I integrate with a CBCT scan? Scan export considerations include the ability to send the digital scan to companies such as Align, 3M Incognito or Sirona Connect – third party manufacturers who may be relevant to the treatment process.
From an execution perspective, it is critical to perform full mouth scanning and obtain correct bite registration to achieve success in any proposed treatment. There has been a movement away from the previously accepted form of free form scanning. Instead, guided scanning is the preferred modality for the capture of the full arch and a bite registration.
Guided scanning is a form of scanning with an optical scanner whereby a protocol is followed to predictably image an arch. This protocol, once utilized effectively, allows for an extremely accurate representation of the arches in as little time as five minutes or less. The advantage of an optical impression is that one is able to assess the quality of the scan on screen while scanning. In this fashion, the quality of the scan is quickly approved and this leads to less error propagation and eventually better treatment. Traditionally, when one takes an alginate or PVS impression, inspection of the impression is done so as to accept its quality. However, in the traditional model, the true acceptance only occurs once one has physically poured the model from the impression. This unnecessary step with optical impressions creates a valuable savings of time, as inspection of the model may not occur until the next day.
CEREC Ortho Example
An example of guided scanning can be demonstrated with the use of CEREC Ortho. CEREC Ortho utilizes a protocol whereby the starting point of the scanning of an arch is always defined as the occlusal of the distal most tooth of the patient’s right side. From this starting point, the camera is moved lingually along the quadrant to approximately the contralateral canine. Following this portion, one would return to the original starting point and image from the occlusal of the distal most part of the patient’s right side to the incisal portion of the contralateral canine. The third pass would involve going back to the starting point, rotating the camera to the buccal and moving the camera to image the facial aspect up to the contralateral canine. The final step for this quadrant would be a transverse image from the lingual of the canine in that quadrant to its facial surface. Following this side of the arch, one would repeat the scanning in exactly the same fashion to the opposite side of the arch. Naturally, the only change would be the new starting point. This time, the starting point would be the occlusal portion of the distal most teeth on the patient’s left side.
Following the guided scanning of the mandibular arch, the protocol would be repeated in the maxillary arch. With our only change being the starting point being either the occlusal portion of the distal most tooth of the patient’s left or right side of their arch. With optical scanning, one is also able to image the gingival portion of the patient’s oral cavity. In the maxillary arch, one can also image the palatal area. The imaging of the palatal area may be necessary if one is fabricating a removable appliance such as a Rapid Palatal Expander.
Following imaging of the maxillary and mandibular arches, the next step is to define the correct occlusal relationship between the arches. This “bite registration” is facilitated by utilizing something called a “double buccal bite”. To facilitate this virtual bite registration, the patient is asked to put their teeth together in Centric Occlusion. Or, in any position that the clinician feels is their desired occlusal relation. At this point, the patient must be informed not to slide or move the position of their teeth. First, one side of the buccal aspect of the teeth will be imaged from the gingival portion of the upper premolars down to the gingival portion of the lower premolars. Following this rapid imaging, the clinician will move to the opposite side and repeat the process where they will image the gingival portion of the upper premolars down to the gingival portion of the lower premolars. Once imaged, the imaging software will verify the double buccal bite and determine if the patient’s teeth moved while the virtual bite registration was being registered. With the verification of the double buccal bite, guided scanning for the patient has been completed (Fig. 2).
With the goal of achieving a perfectly represented virtual model, an approval process must be performed. The completed maxillary and mandibular virtual models must be inspected for any discrepancies (Figs. 3, 4). If any discrepancies exist, they can be quickly corrected by filling in the missing or incorrect data points with a quick scan. One does not need to image the entire arch again. In addition, the virtual bite registration must be verified. Inspection of the occlusal relationship via graphic visualization of the occlusal contact points is warranted (Fig. 4a). With this final approval of the occlusal relationship, imaging is complete and the clinician can move towards the export stage.
Fig. 3 Fig. 4a
Storage and Export of Models
In orthodontics, a record of a patient’s pre-treatment records need to retained. Traditionally, physical models would be created and then they would be stored either in the office or at an off-site storage site. In the digital world, the virtual impressions can be utilized as the pre-treatment records and stored digitally. Digital solutions for storage range from an external hard drive or encrypted online storage. With the progression of technology, other storage mediums will become available and utilized. When a physical model of the virtual impression is required, the file can be utilized to physically print the models. Printing of these models can be accomplished at any company such as Stratasys or a commercial laboratory. With the progression of 3D printing, solutions for printing in the office can also be utilized. When the models are printed, the software physically prints onto the models the patient’s name and date of the scan (Figs. 5, 6).
Fig. 5 Fig. 6
In the export stage, the clinician has the option to send their scan for fabrication of their appliances to a variety of companies (Figs. 7, 8). The clinician can utilize aligner therapy and send their scan to Invisalign, Clear Correct or MTM. For example, if one were to export their case to Invisalign, after upload, Invsialign would review the optical impression to ascertain if it is acceptable. The scan would then be merged with the prescription that is completed at the Invisalign Doctor Site. This process would allow for creation of the ClinCheck that would assist the clinician in creation of the aligners for the patient.
Fig. 7a Fig. 7b
Currently other orthodontic export solutions that are available to the clinician are OnyxCeph, 3M Incognito, CA Digital or Dolphin 3D. Non-aligner therapy can be facilitated with 3M Incognito. 3M Incognito allows for lingual appliances with custom CAD/CAM manufactured brackets and wires. The clinician would create their own treatment plan in the 3M software and 3M would deliver the bonding jigs, brackets and wires. OnyxCeph allows for virtual bracket placement with the creation of indirect bonding trays. Virtual setups are also an option so as to create models for aligners and other appliances.
The true advantage of guided scanning and the double buccal bite is the creation of an extremely accurate virtual impression and an accurate occlusal relationship. In prosthodontics, these scans can be sent to any commercial laboratory with the use of a communication network such as Sirona Connect which allow for the transfer of the virtual impressions to the commercial laboratory in a secure and efficient manner. With the almost instantaneous delivery of the virtual models to the laboratory, the RDT at the laboratory could discuss the case with the clinician while the patient is still chairside. This high level of communication will allow for better quality treatment and better prosthetic results.
Guided scanning has become the gold standard protocol for optical impressions. This gold standard has allowed for digital orthodontics to be utilized at a clinical level in a predictable and efficient manner.
There are numerous aspects to incorporating digital technology effectively in any dental discipline, but the merits of successful adoption are compelling for patient, clinician and the profession. OH
Dr. Bobby Chagger is a graduate of the University of Toronto and has a strong interest in dental implantology utilizing ConeBeam and CEREC. He has successfully integrated CEREC and ConeBeam into his seven ChaggerDental Offices in Southern Ontario. His passion and insight have brought him international recognition as a Speaker and Educator. Join him at Canada’s Largest Digital Dentistry Summit this October in Toronto. Go to www.europeaninvasion.ca for information.
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