Digital Restorative Dentistry:

Can You Throw Your Impression Material Away?

Lee Culp, CDT | Frank Higginbottom, DDS | Chuck Sargent

It is not really necessary to understand the intricacies of how digital impression systems work to reap their benefits. It is, however, necessary to ensure that dentists and laboratories are on the same page in order to maximize use of the technology by working collaboratively with compatible equipment and products and an understanding of who does what.

Analog vs Digital Impressions

Whether digital or analog, impressions are negatives of the hard or soft tissue in the oral environment from which a positive reproduction or cast is made. Materials from plaster to hydrocolloid to polysulfide and, now, polyethers were always subject to issues related to the materials and processes involved—distortion and inaccuracies that occur when materials go from a liquid to a solid, the model preparation, waxing of the restoration, investing, and casting.

There are also challenges when the teeth in restorations—single units, multiple units, splinted units, and implants—are not in a straight line; when implants, in particular, are placed on a curve, there are problems with accuracy and passive fit. Therefore, it makes sense that scanned implant positions would be more accurate than polyvinyl impressions.

Going Digital for the First Time

Making the leap into digital impressioning can be challenging, with bumps along the way in terms of adjustment. For example, a given implant-scan body—a one-piece component—is not necessarily compatible with all scanners, but care must be taken to ensure that it is, because it is the implant body that enables the scanner to precisely locate an implant to create pertinent data and images.

However, the equipment companies offer training to those who purchase their technology, which opens a whole world of options to the dentist, including the choice between sending the digital scans to a laboratory for traditional fabrication or, using a CAD/CAM system, milling them out chairside.

Beyond the Impression

Dentists who take digital impressions have more to gain than having a cleaner way to create a model. They have a better ability to diagnose due to the ability to enlarge and otherwise manipulate and evaluate data and images; and they can communicate better with their laboratory and other dental team members with whom they wish to collaborate.

Dentists can also visually show patients problems that they may experience now or in the future, thus improving their ability to understand and accept the need for treatment. This is especially helpful with asymptomatic patients for whom it can be difficult to recognize the need for recommended preventive treatment. However, even those who “do not feel anything” are better able to understand an existing or potential problem when they are able to view photographs generated by the technology—as 80% of learning occurs visually—and the doctor can present the case as never before with images combining slices of the cone beam, creating a mash-up of the tissue data, as well as the cone beam data.¹

Much can be learned about blood flow by electronically viewing the condition of the tissue. Dentists can also gain insight into airway issues with images of the upper and lower jaws. In short, images generated via intraoral scanning devices provide the means for the dental team to interpret all the data together and decide how to proceed.

In terms of implant planning, the clinician can use the scan and cone beam data to virtually remove teeth and decide where the implant should go, establishing the correct curve. Then, too, there is the ability to design and print a surgical guide using a 3D printer either at a local laboratory or right in the dentist’s own office.

Using analysis tools, dentists can click on “clearance” for a color map of the occlusion and then “switch view” for a closer look at where that occlusion is. Then, by hitting the “send” button, this information can be received by the laboratory in minutes. Furthermore, because the laboratory can receive and review the scan while the patient is still in the chair, adjustments can be made without the need to call the patient back.

Clinical Cases

The cases below—which were all model-less—resolved issues both simple and complex.

Case 1

Early Digital Impression

A case believed to be the first digital impression received in a laboratory disproves beliefs about scanned impressions and milled restorations. This case, based on a digital impression of the preparation, is from nearly 13 years ago. After the doctor adjusted the contact as requested based on the scan, the restoration was designed, milled, stained, and glazed (Figure 1 through Figure 4). It was sent to the doctor, who placed it the next morning.

Case 2

Broken Teeth Repaired in 3 Hours

Another case involved a 22-year-old woman who had presented with broken teeth but no pulpal involvement (Figure 5 and Figure 6). The area was first scanned without preparing; it was then decided to leave the break and do a modified preparation without an impression or the use of anesthesia. The laboratory used a multilayered block, moving it up and down in the software to choose how much enamel to show (Figure 7 and Figure 8). The restorations were removed from the mill and placed on the teeth before bonding (Figure 9 through Figure 12). In about 3 hours, it was possible to send the patient home with her smile restored painlessly.

Case 3

Simplified Smile Change in 2 Hours

A third case involved a 23-year-old man who had requested veneers Figure 13 through Figure 15). However, the dental team determined that the smile improvement he desired could be achieved more easily by enlarging his laterals to fill out his smile. Again, there was no preparation, no impression, and no anesthesia, and the laboratory was able to very quickly restore those teeth by designing and milling out IPS Empress® lucite-reinforced ceramic teeth (Ivoclar Vivadent) using a prelayered block (Figure 16). This required only milling, glazing, and bonding the restoration—all of which was completed to change the patient’s smile in about 2 hours (Figure 17).

Case 4

Anterior Restoration

A more complicated case with a young boy required a full-mouth rehabilitation. With larger digital cases, the laboratory creates three digital designs—one in wax, one in plastic, and one in glass. The temporary phase begins after completing the diagnostics. Many temporaries are now completed in the laboratory because, using an industrial PMMA material that is double cross-linked, it is possible to fabricate long-lasting provisionals with no residual monomer, which is essentially the same chemistry as a high-quality denture tooth.²

The only work done by hand now in laboratories is finishing the restoration. Here, the restorations were stained and glazed with light pure stains to replicate the patient’s teeth to verify the desired function and esthetics—eg, shape and color. This patient’s teeth were modified because of severe discoloration.

Using the final design for the maxillary and mandibular teeth, the restorations were then milled from IPS e.max® lithium disilicate (Ivoclar Vivadent) in a porcelain oven, where they were taken from the “blue stage” to the crystalized, more translucent stage, which shows that it is possible to achieve beautiful esthetics without very complex layering. In this case, blending to the natural posterior teeth from the bicuspids to the premolars involved bleaching and surface microabrasion (Figure 18 through Figure 32).

Again, everything was done digitally—the restorations were created on a screen and milled with a milling machine.

Case 5

Overdenture for a Young Patient

In a case with Lyndon Cooper, DDS, PhD, who is a professor of prosthodontics at the University of North Carolina, the primary author [Culp] was asked to create an overdenture for a young boy who was largely edentulous (Figure 33 through Figure 36). Dr. Cooper had provided information on the patient’s correct vertical dimension and overbite, and requested a software-designed overdenture for the patient, who—because of his age—was not ready for a final restoration (Figure 36).

After a wax-up of the teeth based on that information was completed, it was scanned into the computer to begin the process of digitally designing and fabricating an overdenture (Figure 37 and Figure 38).

The denture that was created was a monolithic, milled PMMA denture. The only thing layered was a thin layer of light-cured, tissue-shaded composite material ((Figure 39 through Figure 42). Because there was sufficient vertical room, it was possible to build in extra retention with the use of a precision attachment, bonded onto the existing posterior teeth. This provided the extra retention needed to retain the restoration as the child grew and a final restorative solution could be determined.

The monolithic overdenture made it possible to give this young patient an attractive smile until he was old enough for permanent restorations.

Case 6

Teeth for Implants

In a case done with Jonathon Ferencz, DDS, who is a clinical associate professor of prosthodontics and occlusion at New York University College of Medicine, a screw-retained zirconia restoration was done with no model (Figure 43).

After the implants were placed, the dentist sent the laboratory a trio scan of the existing dentition with scanning flags.³ After receiving that information, it was loaded into the computer to verify that the flagged implants were those for which the teeth would be placed digitally. The scan flags, which indicate the implant type, angulation, and depth, enable the technician to design the teeth suspended over the implant locations prior to abutment placement. Once the teeth were virtually placed in the desired location, the computer generated a proposed abutment based on the information entered. From there, the technician would modify the abutment to tissue contours and tooth contours, and then the teeth would attach to the abutments (Figure 44 through Figure 48).

In this case, the restoration was screw-retained. Once it was completed, the file of the abutments was sent to the milling center for fabrication. However, as the file of the bridge was sent to the laboratory’s mill, the zirconia bridge was ready before the abutments (Figure 49). After verifying that the abutments fit, they were returned to the doctor, who seated the restoration (Figure 50 and Figure 51).

Case 7

Complex Maxillofacial Implant Case with Cancer Patient

This restorative case was done with Dr. Larry Brech, who is currently a clinical associate professor of prosthodontics and occlusion in the Division of Prosthodontics and Restorative Dentistry at New York University College of Dentistry. He also serves as the director of maxillofacial prosthetics in the advanced education program in prosthodontics at NYU.

This case could have potentially taken 2 years to complete. The restorative team included a medical and orofacial dental surgical team, a digital medical modeling team, and a dental laboratory prosthetic team.

Using computed tomography and intraoral scanning, along with digital planning and design software, this case was accomplished in 1 day (Figure 52 through Figure 65). A patient with a cancerous bone lesion had bone from a fibula placed into the defect after removal of the lesion. This case, which required separate surgeries—one in the leg and one in the mandible—to repair the defect and place a restoration, required careful planning and collaboration by numerous dental team members.

First, the team met using TeamViewer to plan and design the surgery and prosthetic steps. The cancerous lesion in the bone was digitally removed. After determining the exact part of the fibula that was needed for the bone replacement procedure in the mouth, cut guides were created to be able to remove the portion of fibula from the leg and place it exactly back in the lower jaw; the same was done to the mandible.

With this information, the technician was able to design new teeth to replace the old teeth and to place the implants digitally. Even before meeting the patient or the surgery, the restoration was created digitally by the laboratory technician.

On the day of the surgery, the medical/dental surgical team removed the diseased area of the mandible, as the second surgical team removed the part of the fibula that would fit into the defect. During the fibula surgery, several things were accomplished at the same time. The tissue was flapped, the bone was exposed, the cut guides were placed on the leg, the cut guides were placed in the mandible, the surgical guide was placed on the bone of the leg, the implants were placed, and the actual prosthetic was placed. When everything was ready, the surgical team removed the bone from the leg, the other surgical team removed the lesion from the mandible, and the leg surgeons handed the replacement bone from the leg to the surgeons on the head. Then everything was placed together. The prosthetic that was fabricated by the laboratory was a milled PMMA restoration, which would be screw-retained to the implants during healing.

Discussion

As these cases demonstrate, intraoral scanning enables the dentist to make a data acquisition and to see exactly he or she is sending to the laboratory, and to see it 100 times larger.⁴ If it shows that the preparation or data are incorrect, it can be corrected immediately. Once this data is received, it enters the laboratory workflow to start the restorations.

Beyond Restoration to Prevention

To date, the focus of digital technology has been on using it to diagnose and treat existing problems. However, this same technology can be used perhaps far more effectively to anticipate problems and render early treatment, or perhaps prevent dental problems entirely. Using what might be called “predictive technology” in the periodontal or operative realm, it may be possible to intervene far sooner by spotting problems sooner. By scanning patients, including children, more frequently—eg, every 6 months—the computer can indicate if tissue is moving, if bone is eroding, or whether teeth are moving or wearing too much.

About the Authors

Lee Culp, CDT
CEO of Sculpture Studios

Frank Higginbottom, DDS
Associate Clinical Professor
Department of Oral and Maxillofacial Surgery and Pharmacology
Baylor College of Dentistry
Dallas, Texas
Clinical Associate Professor
Department of Periodontics
The University of Texas
San Antonio, Texas
Private Practice
Dallas, Texas

Chuck Sargent
Sales Manager
3Shape Dental Systems

Disclosure

Lee Culp, CDT, is a consultant for Ivoclar Vivadent and 3Shape.

References

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2. Li RW, Chow TW, Matinlinna JP. Ceramic dental biomaterials and CAD/CAM technology: state of the art. J Prosthodont Res. 2014;58(4):208-216.

3. Joda T, Wittneben JG, Brägger U. Digital implant impressions with the “Individualized Scanbody Technique” for emergence profile support. Clin Oral Implants Res. 2014;25(3):395-397.

4. Ender A, Mehl A. Full arch scans: conventional versus digital impressions—an in-vitro study. Int J Comput Dent. 2011;14(1):11-21.