Treatment Practices Strengthened with the Use of CAD/CAM

A female patient in her early 60s presented at a dental clinic concerned that her anterior teeth would soon break. Over many years, her failing bite, along with some parafunctional habits such as clenching, bruxing, and nail biting produced a destructive abrasion pattern on her maxillary lingual surfaces and ultimately led to chipping of the remaining labial surfaces (Figure 1 and Figure 2). In order to complete a comprehensive evaluation and functional assessment, the dentist completed preliminary impressions, full-mouth radiographic series, a clinical and periodontal examination, a TMJ evaluation, centric relation records, and face bow registration. The case was mounted on a semi-adjustable articulator in the patient’s habitual centric occlusion, so the dental team could evaluate her occlusion and develop a treatment plan to restore her esthetics with the conventional philosophy of “form follows function.” It was determined that the patient’s vertical dimension of occlusion (VDO) would need to be increased by 2 mm or 3 mm posteriorly, resulting in an approximately 4-mm opening of the maxillary anterior dentition. To ensure that the patient could tolerate this vertical dimension of occlusion, an appliance was fabricated using an iNterra INoffice Nightguard (DENTSPLY, dentsply.com) (Figure 3) for the patient to wear for one month. The patient wore the appliance all day, except when eating, and minimal occlusal adjustments were made.

In order to assess the necessary change of VDO, a preliminary diagnostic wax-up was performed only on the lingual and incisal surfaces of the abraded anterior teeth, approximating what had been abraded. The semi-adjustable articulator was then closed to occlude the lower anterior teeth with the maxillary lingual surface. The anterior guide pin was dropped to engage properly with the guide table. A wax bite registration was then made from the articulation and returned to the patient’s mouth to confirm that she would be able to tolerate this new vertical dimension and when closed into the bite that she did not experience any muscle tension. The newly corrected wax bite was then used to rearticulate the lower model and the occlusal appliance was fabricated indirectly on the articulator using iNterra, which was chosen for its semi-rigid structure and easy chairside adjustability.

After wearing the occlusal appliance for a month, the patient reported that there was no discomfort and that she felt significantly more comfortable with the appliance in place compared with how she felt when not wearing it. This was exactly what the dental team was hoping for and consequently allowed the case to commence with the 3-mm increased vertical dimension of occlusion.

The appliance was used to rearticulate the maxillary and mandibular models to the new maxillo-mandibular relationship. It was determined that in order to achieve the level of function and esthetic outcome for the patient, the maxillary arch would need to be restored to ideal function, in the newly established vertical dimension of occlusion. Using the rearticulated case, a diagnostic wax-up was initiated and proper gnathological concepts were observed. These preliminary steps in the restorative workup were critical, due to considerations of the patient’s parafunctional habits that had previously destroyed her dentition and her newly established vertical dimension of occlusion. The vertical dimension of occlusion had been opened extensively to achieve best results; avoiding or not obeying these fundamental gnatholoical concepts and laws would have resulted in a potentially catastrophic outcome.

The diagnostic wax-up was designed to re-engage the new bite, while maintaining and being careful not to violate the biological space in the oral environment. The biological space is the natural dimensional parameters, which the patient had become accustomed to, and therefore wax was applied directly over the unprepared tooth structures to maintain the same dimensional space (Figure 4). These measures will result in an elevated and positive post-operative experience and will promote a rapid restorative acceptance. The completed diagnostic wax-up was subsequently sent to the dental office and utilized for two functions. First, it served as a communication instrument and conveyed to the patient the desired restorative outcome, so that all parties involved harbored the same expectations. Second, the wax-up was used to fabricate an immediate provisional for the patient upon preparing the natural teeth to accept the crowns. The teeth were prepared with shoulder margin, packed with cord, and impressed with polyvinyl siloxane using conventional impression methodologies (Figure 5). The wax-up was duplicated and poured, followed by the creation of a silicone matrix used to translate the wax-up information to the oral environment and fabricate acrylic provisionals intraorally after the tooth structure was reduced (Figure 6 and Figure 7). A three-part bite procedure was administered to capture the appropriate vertical dimension and maintain the newly established vertical dimension of occlusion. This was done in sections, where the provisionals had been sectioned, separating the anterior teeth and two posterior sections. While two of the three sections were in place intraorally, the remaining section’s bite was captured and repeated for all three sections respectively (Figure 8).

Once all the information was captured through impressions, bite registration, and shade selection, the case was sent to the dental laboratory to begin the fabrication process. The impressions were poured and sectioned, and the dies were trimmed and ditched. The study cast and the final impression of the preparations were cross-articulated to the counter model. The use of CAD/CAM in fabricating the case was deemed optimal because it provides a vast array of benefits when tackling a case of this nature. It supports the dental technologist with instruments and tools, and coupled with a high level of dental intelligence, it can produce a very accurate, precise, repeatable, and consistent restorative process. To fabricate this case through digital means, a D900 scanner (3Shape, 3shape.com) and CAD software were used.

To begin the case, the models and dies were scanned digitally to obtain all critical information. To capture the gingival topography—which is very important for many large and complex cases—when entering the order form, the neighborhood scan was selected as sectioned, and because the software called for a full-arch scan, a solid/uncut model was scanned. With this technique, the solid model provided all the pertinent gingival topography, while the individual trimmed and ditched die scans fit neatly within the full arch.

An additional feature and added benefit for digitizing a complex case is the ability to overlay the temporaries over the prepared model. In this case, in the preliminary stages—performing the above steps and then following up with scanning provisionals—this provided a template for designing the final prosthesis and a visual alert to a potential articulation failure. Because the case was digitized, the dental technologist was able to recognize malocclusion and resolve it prior to committing to the expense in time and labor involved with fabricating the crowns incorrectly (Figure 9 and Figure 10). This not only saved time and money for the dental laboratory, but also prevented frustration and an overall negative experience for the dentist and patient.

After scanning the case into the Dental System™ software (3Shape), the design module commenced and the preliminary preparation steps were followed, including annotating, establishing path of insertion and proper margin line, and cement and drill parameters. These steps are immensely critical to the fit of the final restoration. The key advantage of digital technology in dentistry is that the computer is an extension of the dental technologist’s tool box, and CAD/CAM is just another tool. These digital tools provide a seamless workflow with a heightened level of precision; however, the dental technologist needs to use dental intelligence to make the case viable. The software cannot determine whether a case will hold up and remain successful once inserted; rather, the dental technologist’s years of experience, education, training, and knowledge, in collaboration with the software, will yield the greatest viable results.

The digital design software proposes an initial tooth shape and size from the tooth library, which can be changed at the discretion of the dental technologist in order to best fit in the patient’s oral environment. The teeth then can be manipulated, either as a group or individually, to achieve the desired function (Figure 11). The software provides a series of tools, which are standardized in all 3Shape modules and therefore reduce learning curves among differing modules. Furthermore, similar to conventional dental technology, the process advances with what is known as coarse to fine adjustments, whereas the tools allow you to engage with larger surfaces and progressively smaller surfaces, resulting in the final design. Here, the provisional double scan was used to align the newly designed teeth to have similar shape, size, and orientation to that of the temporaries, which were worn by the patient (Figure 12), leading to a more predictable result.

The 3Shape software makes attaining good and accurate occlusion easier than dental laboratory technology’s conventional methodologies. The software deploys a virtual articulator that the dental technologist can benefit from in several ways (Figure 13). It can be used as a marking tool, similar to articulating paper, marking areas that are high in occlusion and leaving a mark in red where the dental technologist can remove material as necessary in order to be in proper occlusion. The dental technologist may also choose the adaptive occlusion feature, in which the software automatically reduces any premature occlusal contact while going through protrusive and lateral movements. The dental technologist can select an alternative method and leave everything out of occlusion by deploying the parameter tool and inputting the distance desired away from the antagonist. Finally, the dental technologist can select to free-form handle the bite and function, and remove or add as is most necessary. Whatever means needed can be used to achieve appropriate occlusal functions; again, it is the dental intelligence possessed by the dental technologist that will validate and accept the restored bite (Figure 14).

Keeping esthetics in mind while designing provides an easier means to attain lifelike final restorations. Knowing the restorative materials well will dictate the level of design required to achieve success with esthetic results. IPS e.max CAD (Ivoclar Vivadent, ivoclarvivadent.com) was chosen to complete the aforementioned case, and therefore the anterior incisals were cut back in the software and prepared to receive micro-layering with IPS e.max overlay porcelain (Figure 15). The posteriors, however, were left to be stained and glazed, because the desired shade was A3/A2 and with the history of the patient’s paranormal function, it was determined that a full-contour IPS e.max CAD crown would be better able to appropriately handle the masticatory forces.

Upon the successful completion of the design functions of the case, manufacturing files needed to be generated and sent for milling. In this case, STL files were produced and assessed for proper integration. By simply going to the manufacturing file folder, the desired files in STL format can be viewed and assessed prior to sending for milling (Figure 16). A quick visual assessment of every file is recommended to be sure that margins and proper surfaces have been translated accurately. Thereafter, the STL files were sent to Wieland Precision Technology (Ivoclar Vivadent) for milling IPS e.max CAD and returned in the purple/pre-crystallized form (Figure 17); fit on the model and contacts were then adjusted as necessary. Minimal adjustments were needed, because the majority of the work was completed in the design. Once satisfied with the fit, margins, contacts, bite, etc, the restorative units were subsequently crystallized using a Programat oven (Ivoclar Vivadent) with a preprogrammed crystallization program (Figure 18). As soon as the restorations were crystallized, stains were fired onto the restorations prior to layering porcelain, resulting in esthetic and lifelike restorative outcomes. A combination of staggering enamel and translucency was incorporated and layered on the anterior teeth and provided the appearance of vitality with the multilayered ceramic restorations (Figure 19).

Because the IPS e.max CAD units are milled in the appropriate shade, very little cutback in the software is necessary to achieve the desired appropriate shade. Often, depending on targeted shade, as little as 0.3 mm to 0.5 mm of cutback is required to truly achieve the appropriate shade. As a corollary of this, the less overlaid material and more solid material used in the restoration, the stronger the inherited crown, producing a higher level of success and longevity for the restoration.

The completed case was returned to the dentist for final insertion and calibration. Because the case was completed using digital technology, the precision and consistency were remarkable. Furthermore, the understanding of what is required for the case to be viable through adequate dental intelligence was valuable, looking at the distribution of the occlusal forces and making sure that the gingival topography was respected and used to help with the esthetic final outcome. A series of phonetic tests were performed to be certain that the biological space was maintained and phonetics were not changed from the previous oral situation of the provisionals. The restorations were then tried-in to verify the fit, contacts, and occlusion, and once all parties were satisfied, the restorations were etched and bonded to the patient’s dentition. The outcomes were truly remarkable and the patient was extremely pleased (Figure 20). Considering the parafunctional habits that the patient possessed, a nightguard was fabricated and the patient was instructed to wear it nightly to protect the restorations. She was amazed at how comfortable and beautiful her smile had become and asked if she could eat some of the things that she hadn’t in a very long time because of the state of her teeth prior to the restorative process. A month after insertion, the patient returned for post-op assessment and stated that she forgot that her teeth were not her own, because they felt and looked like her own.

The dental restorative landscape is rapidly transforming, with emerging technologies and new materials providing both the dental professionals and patients with better options while achieving the best results. Technological advancements allow the dental professional to achieve more consistent, more precise assessments and manufacturing practices, while elevating the treatment protocols and overall dental experience. The most important factor in the dental treatment practice is the breadth of knowledge and dental intelligence needed for restoring the oral environment. The restorative dental team of the dentist and dental technologist contributed expertise for the betterment and attainment of the best restorative outcomes for the patient. To be sure one is ahead of the curve, it is advisable to become a true lifetime learner, trying to aggregate as much knowledge in vast modalities, disciplines, technologies, and materials as possible. Only then can you truly ensure that you are providing the best restorative outcome for the patient and all involved.

The authors had no disclosures to report.

This article was double-blind peer reviewed by members of IDT’s Editorial Advisory Board

Daniel Alter, MSc, MDT, CDT
Professor
New York City College of Technology
New York, NY

Richard Sousa, DDS, MDT
Owner
East Hills Dental Associates
Roslyn Heights, NY

Irene Lai, DDS
Associate Dentist
Queens, NY