Digital Smile Design and Fabrication of CAD/CAM Restorations in a Complex Esthetic Case

In recent decades, smile design has progressively shifted from analog to digital workflows, which have further evolved from 2-dimensional (2D) to 3D tools.⁸ The implementation of digital tools and online interaction has improved communication among clinicians, dental technicians, and patients.⁹ Merging 2D photographs with 3D digital files allows the transition to a full digital workflow and facilitates facially driven digital smile design.

Newer digital smile design tools can be used to design and modify smiles of patients digitally and visualize the projected outcome before any irreversible procedures are done. Such tools also permit meticulous analysis of the patient's facial and dental characteristics to facilitate the digital design. Typically, a STL file of the digital smile design is 3D-printed, and that model is used for producing a chairside mock-up.¹⁰ Verification of all esthetic parameters is crucial, as the same or a respectively modified 3D smile design is used to fabricate the definitive restorations. In fact, all of the subsequent steps, including restorative treatment type, material, and preparation design, are directly dependent on the accuracy of this initial design.

Computer-aided design/computer-aided manufacturing (CAD/CAM) technologies continue to increase in popularity due to their clinical performance, patient acceptance, and cost efficiency.¹¹ When patients present with existing dental implants, the handling of different kinds of dental restorations in the anterior esthetic zone can be especially challenging. Digital design software can be used to simplify this task and enable the clinician to achieve desired outcomes more efficiently than with analog methods while maintaining adequate quality for the definitive restorations.¹²

This article describes an efficient digital workflow that combines the use of newly released digital smile design software with standard dental CAD/CAM software to enhance digital design and predictably achieve an esthetic outcome in a complex case.

Case Report

A 33-year-old female patient presented with a defective anterior direct resin restoration, an existing implant restoration with chipped porcelain at the incisal edge, and abnormally sized teeth (Figure 1 through Figure 3). Her medical history revealed no contraindication for dental treatment. In 2015 a dental implant had been placed to restore tooth No. 8, and radiographic examination revealed that the implant was well osseointegrated. Periodontal and peri-implant probing depths ranged from 3 mm to 4 mm, with no indication of active inflammation. The patient had adequate oral hygiene.

Various treatment options were presented to the patient, who elected to proceed with ceramic restorations for the anterior teeth to improve their shape and color. Although orthodontic treatment and soft-tissue augmentation surgery were suggested to the patient as the preferred treatment in this case, the patient refused that option.

Intraoral scans (CEREC^® Primescan^®, Dentsply Sirona, dentsply
sirona.com) were made and a 3D smile analysis was performed with digital smile design software (SmileFy, smilefy.com) (Figure 4 through Figure 6). A 3D-printed model was made from the digital design in the software and used to create silicone indexes to make an intraoral mock-up for patient approval (Figure 7 and Figure 8). The same mock-up would also serve as a guide for the tooth preparations and reduction as well as for the provisional restorations.

Clinical Steps

The conservative treatment approach included minimally invasive tooth preparations of the maxillary premolar teeth Nos. 4, 5, and 12 for partial-coverage restorations, facial laminate veneers for teeth Nos. 6 and 7, and full-coverage restorations for endodontically treated teeth Nos. 9 and 10 (Figure 9). Subsequently, a digital intraoral scan was made using a powder-free scanner (CEREC Primescan) after insertion of scan bodies for the dental implant (Dentium SuperLine, DentiumUSA, dentiumusa.com) in the area of tooth No. 8 using a triple scanning technique to capture the emergence profile (Figure 10). The digital files were exported to the laboratory through a software-specific connection portal.

In the dental CAD software (DentalCAD, exocad, exocad.com), a new case was created and the elements that needed to be designed were selected. The implant was selected and matched from the implant library to be compatible with the scan bodies. The previously designed mock-up smile was imported as an additional file in STL format to serve as a guide for the design of the definitive restorations. A tooth with natural texture was selected from the proposed library within the dental CAD software, and a custom abutment design was performed for the implant restoration. Once the design was completed, a STL file was created and exported for fabrication of the definitive restorations (Figure 11).

Laboratory Steps

After the intraoral scans were received by the dental technology laboratory, all files were imported into the laboratory software (exocad). Based on the imported SmileFy files, a digital mold was selected and positioned as a digital wax-up. This was used to communicate all of the subsequent steps with the clinician and to evaluate and confirm the restorative design.

Based on the digital design and to maximize the esthetic outcome, lithium-disilicate ceramic was selected as the restorative material. The patient expressed her desire for "vital" and "young-looking" teeth.

A custom hybrid abutment was designed with assistance from the digital implant library. All the crowns were designed based on the abutment design and milled. After milling the custom hybrid abutment from zirconia (Ceramill^® Zolid HT+, Amann Girrbach, amanngirrbach.us) in the desired shade, which was similar to the adjacent prepared teeth, it was sintered overnight. The crowns were milled in a pressable wax to fabricate the lithium-disilicate restorations (GC Initial^® LiSi Press, GC America, gcamerica.com).

The zirconia abutment was adjusted, and the emergence profile in contact with the soft tissues was polished to ensure ideal tissue integration. The abutment was then bonded to an authentic titanium base with a dual-cure bonding material (G-CEM LinkForce^®, GC America) following manufacturer's instructions.

The crowns were fitted on 3D-printed model dies and the abutment. A digital analog was seated into the 3D model. It should be noted that the digital analogs must be virtually aligned with a digital library in the CAD/CAM software. The digital analogs must be the same brand as the digital implant library, because  intraoral scan bodies are always virtually connected with the digital implant library. Switching to a different brand would require switching to a different library.

After the wax crowns were fitted, they were sprued with tunnel wax and waxed onto the ring to press the lithium-disilicate ingots into the molds. Selection of the proper ingots in terms of shade and translucency is key to maximizing the esthetic appearance of the restorations.

In this case, GC Initial Press MT (GC America) was selected (MT stands for "medium translucency"). With this level of translucency, the technician is able to on one hand mask certain underlying shade discrepancies but on the other hand absorb some of the underlying color to achieve a highly vital and natural-looking outcome. All crowns were designed in a facial-cutback design. Porcelain was layered to simulate the 3-dimensional appearance of a natural tooth and match the vitality of the remaining unprepared teeth. Glazing and polishing with a diamond polishing paste completed the laboratory steps (Figure 12 and Figure 13).

Final Insertion

After try-in, the internal surfaces of the restorations were etched with hydrofluoric acid for 20 seconds and silanated, as per manufacturer's instructions, and zirconia abutment surfaces were treated with air-particle abrasion and a special ceramic primer, following the APC (air-abrasion, primer with MDP, composite resin cement) zirconia bonding technique.^13,14 Adhesive cementation was performed for a dual-cure, color-stable resin cement with a clear shade (Figure 14 through Figure 18).

Conclusion

Analog design protocols through the use of wax-ups are highly variable, technique sensitive, and operator dependent. Digital smile design and treatment planning tools facilitate simplified processes through the use of natural tooth libraries, based on the specific esthetic and functional needs of the individual patient. The treatment roadmap consolidated in the initial smile design facilitates a straightforward treatment plan and execution, even in complex esthetic situations where a variety of restorations are needed. Current CAD/CAM technologies provide opportunities to challenge traditional workflows for increased efficiency, precision, predictability, and, ultimately, better patient care. As demonstrated in this case report, these tools are able to provide esthetic outcomes in harmony with the patient's face.

Disclosure

The authors had no conflicts of interest to report associated with this article.

About the Authors

Abdulrahman Almalki, BDS, MSOB
Postgraduate Resident, Advanced Education Program in Prosthodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania

Julian Conejo, DDS, MSc
Assistant Professor, Clinical Restorative Dentistry, and Director, Chairside CAD/CAM Dentistry, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania

Alexander Wünsche, CDT, ZT
President, Zahntechnique Dental Laboratory, Miami, Florida

Evantha Anadioti, DMD, MS
Assistant Professor, Clinical Restorative Dentistry, and Founding Director, Advanced Education Program in Prosthodontics, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania; Fellow, American College of Prosthodontists

Markus B. Blatz, DMD, PhD
Professor of Restorative Dentistry, Chair, Department of Preventive and Restorative Sciences, and Assistant Dean, Digital Innovation and Professional Development, University of Pennsylvania School of Dental Medicine, Philadelphia Pennsylvania; Editor-in-Chief, Compendium of Continuing Education in Dentistry