Achieving Functional and Esthetic Success Using All-Ceramic CAD/CAM Restorations and Advanced Material and Equipment Technologies

Alex Touchstone, DDS

At a time when manufacturers are introducing new innovations on a seemingly daily basis, it may become burdensome—even daunting—for clinicians to interpret the relevancy of new products, materials, and equipment to the routine clinical treatments they provide their patients. Within the last decade alone, multiple new forms of composites, bonding agents, and adhesive cements have been introduced that may simplify direct and indirect restorative protocol. Digital technologies are also changing the manner in which clinicians can diagnose, treat, and manage patients. Even the most fundamental of dental tools, such as rotary instrumentation, are evolving to enable more predictable, convenient, and efficacious patient care. There are other examples, but those should suffice to illustrate the point.

Two such innovations in dentistry that are gaining greater acceptance from members of the profession include soft-tissue lasers and computer aided design/ computer aided machining (CAD/CAM) restorative systems. The former afford clinicians in general and specialty practice an opportunity to perform a variety of procedures more conservatively, conveniently, and comfortably for patients.¹ These include aphthous ulcer treatment, gingivectomy and gingivoplasty, frenectomy, sulcular debridement, and others. The latter, in a similar fashion, has introduced avenues by which clinicians can fabricate esthetic and strong metal-free restorations chairside that can be cemented either conventionally or according to adhesive protocols, depending on the material used.² Such CAD/CAM technologies are also used by laboratories.

This article will briefly summarize these 2 innovations and their relevancy to daily practice. A case is presented to demonstrate their combined use in addressing the functional, esthetic, restorative, and clinical issues with which the patient presented. The objective is to illustrate the manner in which they can be integrated into routine restorative planning and protocol to deliver convenient, efficacious, and comfortable treatments to patients.

Soft-tissue Lasers

It is beyond the scope of this article to address all of the characteristics, features, and benefits of all available types of soft-tissue lasers, but there is a variety available, including CO₂, Nd:YAG, and diode versions, all of which enable the delivery of minimally invasive treatments.³ All lasers are bactericidal and demonstrate an advantage over traditional surgical and non-surgical procedures in creating a disinfected field.² The advantages associated with the use of soft-tissue lasers include virtually bloodless procedures and excellent field visibility; enhanced infection control and elimination of bacteremia; lack of mechanical tissue trauma; quicker healing; reduced postoperative pain and edema; and reduced scarring and tissue shrinkage.¹

Because they’re hemostatic and transmitted through an optical fiber, Nd:YAG and diode soft-tissue lasers, in particular, have been considered a substitute for the scalpel in periodontal surgery.¹ The literature reports that the optical fiber facilitates tactile sensitivity, thereby creating a familiar setting for insertion into the depth of the periodontal pocket.¹

Because of the attributes previously mentioned, soft-tissue lasers have found their way into esthetic dentistry.⁴ Critical to achieving esthetic results is manipulating the gingival tissue in the most atraumatic manner possible, as well as respecting biologic width considerations. When soft-tissue lasers are used in conjunction with proper treatment planning, they enable the realization of smile designs and esthetic treatments that do not compromise the health or function of patients.⁴

CAD/CAM Metal-free Restorative Materials

Since chairside CAD/CAM systems were introduced nearly 20 years ago (CEREC®, Sirona Dental Systems, Charlotte, NC), they have garnered a steadily increasing following of loyal users.⁵ Despite the proven strength, durability, and recently improved esthetics of ceramometal restorations, clinicians have still demanded a means to consistently reproduce natural dentition in the most lifelike and esthetic manner possible.⁶ To this end, CAD/CAM enables the rapid chairside creation of tooth-colored restorations using an optical impression-taking technique, simple computerized designing, and precise machining.⁵ Recent updates to the technology now make handling of all of its components sufficiently user-friendly.⁷

The technology has been used successfully for a variety of clinical situations. The preliminary results of a 1-year prospective clinical study indicate that when CEREC-produced crowns were placed on either reduced stump preparations or as endodontic crowns, no fractures or loss of retention were observed.⁸ Considering that time is a dentist’s and patient’s most valuable commodity, chairside CAD/CAM metal-free restorations can be used to definitively restore form, function, and esthetics in a single visit, regardless of the specific treatment indication.⁹

A variety of materials is available for use with CAD/CAM fabrication technologies, including zirconia, aluminum oxide, feldspathic ceramic, and others. Among them is a leucite-reinforced dental ceramic material that is distinguished by its range of indications for all CEREC 3D applications, including inlays, onlays, veneers, and anterior and posterior crowns. In this material, thermally produced leucite crystals are homogeneously dispersed within the glassy matrix and are present at a concentration of up to 40%. As a result of this higher concentration of leucite crystals, restorations fabricated with this material demonstrate enhanced physical properties, including greater strength, a lower probability of failure, and a better resistance to cyclic loading and fractures than other materials tested.¹⁰

Case Presentation

A 35-year-old female presented with a chief complaint of an unattractive smile and headaches (Figure 1). She requested that the porcelain-fused-to-metal (PFM) crowns on teeth #7 through #10 be replaced with all-ceramic crowns, and she desired veneers for all teeth that showed when smiling. A thorough examination was performed that included full-mouth radiographs, intraoral photographs, and impressions for study models that were mounted on an articulator via a facebow transfer (Figure 2).

The examination and occlusal analysis revealed several non-working lateral interferences to be addressed in the all-ceramic treatment plan. Occlusal interferences place adverse stress on restorations and can result in premature failures, while lateral stresses can produce cement failures and porcelain fractures.¹¹ Addressing these interferences would help ensure the long-term functional success of the esthetic restorations, as well as possibly relieve her headaches by maintaining occlusal harmony in all excursive pathways. Therefore, the noted interferences were removed from the casts and marked for reference for future intraoral adjustments (Figure 3).

Treatment Plan

The treatment plan included a complete occlusal adjustment, fabrication, and placement of machined all-ceramic crowns on teeth #7 through #10, and similarly created veneers on teeth #4 through #6, #11 through #13, and #20 through #29 (e.g., CEREC 3D; ProCAD®, Ivoclar Vivadent, Amherst, NY). Although these machinable, leucite-reinforced glass ceramic blocks can be used to fabricate immediately gratifying all-ceramic restorations in a single visit, there are times when they should be fabricated in a delayed, indirect manner. In this case, because occlusal adjustments were required, anterior provisionalization of the patient’s 4 maxillary incisors was essential to ensure comfort with her new occlusal scheme, as well as to provide additional time for the cut-back and characterization of the crown restorations necessary to achieve her anticipated esthetic effects. In order to reproduce in the machined all-ceramic restorations the natural internal characterization of the patient’s maxillary incisors, the indirect technique for her crown restorations would incorporate the cut-back and layering of the incisal one-third using a creative layering porcelain.

Treatment Protocol

During each treatment appointment, the patient was made comfortable with a combination of nitrous oxide analgesia at 40% concentration and 4% Septocaine with 1:100,000 Epinephrine (Septodont).

The first treatment appointment involved preparation of the 4 maxillary incisors, which was completed according to conservative preparation guidelines. Specifically, the labial and gingival margins were reduced by 1 mm; the facial and lingual aspects by 1.5 mm; and the incisal aspects by 2 mm.

Impressions for use in the indirect CAD/CAM fabrication technique were obtained using a vinyl polysiloxane material. The patient was fitted with provisional restorations for teeth #7 through #10 and re-appointed for 2 weeks later.

Indirect CAD/CAM Fabrication

In the interim, master casts were fabricated and mounted against the articulated mandibular cast, and a diagnostic wax-up of the desired form of the maxillary incisors was created (Figure 4). Care was taken to adjust the wax-up in order to maintain occlusal harmony throughout all excursive pathways (Figure 5). Using this wax-up as a basis, an optical impression was obtained and a correlation design method for CAD/CAM restorations was employed for fabricating the crown restorations. This process enabled the duplication of the exact contours of the wax-up.

To mill the restorations, the selected all-ceramic blocks were placed into the CEREC 3D milling unit, and the cover was closed to initiate the milling process. Adequate lubricant to cool the milling bur and all-ceramic block—150 ml—was used. Once the milled restorations were seated on their corresponding dies (Figure 6), an incisal matrix was made with silicone putty (Figure 7). This was used as a guide during the cut-back (Figure 8) and layering of creative materials on the incisal one-third of the crown restorations (Figure 9), techniques that were employed to achieve the patient’s desired characterization (Figure 10). Afterwards, the crowns were glazed. The load to fracture for glazed crown restorations has been shown to be higher than for those that are polished.¹

Cementation & Direct Correlation Techniques

The patient returned 2 weeks later for the second appointment, during which the maxillary incisor crowns were delivered and the veneers for teeth #4 through #6 and #11 through #13 were also fabricated and delivered. Patient comfort was maintained in the manner previously described.

The patient’s occlusion was first evaluated and adjusted to reflect the changes made to the diagnostic casts (Figure 11 and Figure 12), after which the provisional crown restorations were removed and the preparations suitably cleansed. At that time, gingival in-growth was noticed over the crown preparation margins, potentially complicating the delivery of the crowns (Figure 13). This problem was quickly and efficaciously addressed with the use of a soft-tissue diode laser (Odyssey™ 2.4G, Ivoclar Vivadent) to trough around the margins (Figure 14). The use of soft-tissue lasers for troughing prior to placing an indirect restoration—as opposed to using a retraction cord technique—has been reported as resulting in little or no postoperative discomfort for the patient, in addition to reducing intraoperative complications related to tissue recession.^3,12,13

Gingival Troughing Using a Soft-tissue Diode Laser

The preparations were again cleansed with water, rinsed with a light water spray, and air-dried with low volume. With the soft-tissue laser tip initiated and at a setting of 0.4 to 0.7 watts in the continuous wave mode, the laser fiber contacted the sulcus lining, just inside the crest of the gingiva while resting against the tooth. Very light pressure was applied, and lasing began with small, paintbrush strokes around the circumference of each tooth, creating a small trough between the tooth and gingival tissue.

Adhesive Bonding

The selected all-ceramic restorations require placement using adhesive bonding protocol that include a total etch technique with either a light-cure or dual-cure cement. For this case, a light-cure microfill resin cement with a value shade arrangement was selected. The correct cement shade was first determined by trying the restorations in with the try-in paste. Then, proper isolation, which is critical for adhesive bonding, was achieved using cotton rolls and a rubber dam. A total etch technique was used on the enamel for 15 seconds and the dentin for 10 seconds, after which a single-component dentin bonding agent was scrubbed onto the preparations for 10 seconds, air-dried, and light-cured for 10 seconds with a high output curing light.

The internal aspects of the 4 crown restorations were etched with hydrofluoric acid for 60 seconds and then silanated for 60 seconds and air-dried. Next, the bonding agent was applied to the restorations, but not cured. The selected low-value light-cured cement was dispensed into the restorations, and they were seated onto the preparations. Excess cement was removed, and the restorations were cured from all surfaces for 60 seconds per surface to ensure a complete depth of cure.

Subsequently, teeth #4 through #6 and #11 through #13 were prepared for the aforementioned veneer restorations, which would be immediately fabricated using the CAD/CAM technique. An incisal reduction of 1 mm, facial reduction of 0.7 mm, and reduction at the gingival margins of 0.6 mm was accomplished. For the direct correlation method, impressions were obtained digitally using an infrared camera, the process for which requires coating of the affected dentition with a bonding medium and then dusting with a contrast powder (Figure 15). The veneer restorations were then designed and milled in the manner previously described, glazed, and adhesively bonded into place according to the same adhesive protocol (Figure 16).

The patient returned the next day for delivery of the mandibular all-ceramic CAD/CAM veneers that would be fabricated using the same direct method employed for the maxillary veneers. The teeth were prepared accordingly, but would accommodate an adequate ceramic thickness in the occlusal areas (Figure 17). The veneers were adhesively bonded into place using the same materials and protocol previously described.

Conclusion

This article has demonstrated the manner in which CAD/CAM fabricated all-ceramic restorations can be incorporated into the treatment plan to achieve a patient’s esthetic goals and simultaneously restore proper occlusal harmony throughout the envelope of function (Figure 18; Figure 19; Figure 20). What facilitated esthetic control of the restorations, as well as their timely and efficacious placement, was the use of integrated material and equipment technologies that have been supported in the literature for their applications in adhesive, esthetic, and soft-tissue procedures. Combined, such integration enabled this case to be completed quickly, esthetically, and in a functionally sound manner. During monthly re-evaluations and as a result of nightly wear of an occlusal orthotic device, the patient reports cessation of her headaches, complete comfort while chewing, and complete satisfaction with the appearance of her smile.

References

1. Stabholtz A, Zeltser R, Sela M, et al. The use of lasers in dentistry: principles of operation and clinical applications. Compend Contin Educ Dent. 2003; 24(12):935-48.

2. Kurbad A. Clinical aspects of all-ceramic CAD/ CAM restorations. Int J Comput Dent. 2002; 5(2-3):183-97.

3. Kotlow LA. Lasers in pediatric dentistry. Dent Clin North Am. 2004;48(4):889-922.

4. Adams TC, Pang PK. Lasers in aesthetic dentistry. Dent Clin North Am. 2004;48(4): 833-60.

5. Hehn S. The evolution of a chairside CAD/ CAM system for dental restorations. Compend Contin Educ Dent. 2001;22(6 Suppl):4-6.

6. Kugel G, Perry RD, Aboushala A. Restoring anterior maxillary dentition using alumina- and zirconia-based CAD/CAM restorations. Compend Contin Educ Dent. 2003;24(8): 569-76.

7. Mormann WH, Bindl A. All-ceramic, chair-side computer-aided design/computer-aided machining restorations. Dent Clin North Am. 2002;46(2):405-26.

8. Otto T. Computer-aided direct all-ceramic crowns: preliminary 1-year results of a prospective clinical study. Int J Periodontics Restorative Dent. 2004;24(5):446-55.

9. Gaglio MA. Esthetic restorations designed with confidence and predictability. Compend Contin Educ Dent. 2001;22(6 Suppl):30-4.

10. Chen HY, Hickel R, Setcos JC, et al. Effects of surface finish and fatigue testing on the fracture strength of CAD-CAM and pressed ceramic crowns. J Prosthet Dent. 1999; 82(4):468-75.

11. Clayton JA. Occlusion and prosthodontics. Dent Clin North Am. 1995;39(2):313-33.

12. Scott A. Use of an erbium laser in lieu of retraction cord: a modern technique. Gen Dent. 2005;53(2):116-9.

13. Passes H, Furman M, Rosenfeld D, et al. A case study of lasers in cosmetic dentistry. Curr Opin Cosmet Dent. 1995;92-9.