Placing Anterior Lithium-Disilicate Restorations Using a Dual-Cure Resin Cement

Stephen D. Poss, DDS

Seating today’s esthetic indirect restorations in a predictable manner can present clinicians with many challenges depending on the case. The shade of the selected cement may adversely affect the anticipated esthetics of the definitive crowns or veneers, and, most importantly, the materials chosen could yield less-than-desirable bond strengths that compromise treatment integrity.^1,2 Moreover, multiple adhesive and cementation steps could be required. The restoration could be placed far enough posteriorly that light-curing becomes difficult, and ensuring complete and proper removal of excess cement from the restoration and gingival margins could be troublesome. Ultimately, the cementation and adhesive materials selected, combined with the techniques used for their placement, can significantly impact the quality and efficient delivery of laboratory-fabricated restorations.³

In recent years, a variety of new adhesive bonding and cementation materials have been introduced that, according to the manufacturers and as discussed in the literature, have the potential to simplify the delivery of indirect restorations while simultaneously reducing and/or eliminating many of the challenges clinicians face during placement. Eighth-generation universal adhesive bonding systems are indicated for use as either a self-etch bonding agent or an etch-and-rinse bonding agent with phosphoric acid, thereby simplifying this aspect of the adhesive protocol. Because they are compatible with all etching techniques (ie, self-etch, selective enamel-etch, total-etch), universal adhesives enable an efficient, effective, and convenient approach to adhesive bonding. They also have been shown to demonstrate enhanced material characteristics for adhesively bonding both enamel and dentin to a variety of restorations (eg, ceramic veneers, direct composites, indirect composites).^4-6

Among the other materials that can influence the overall predictability and success of adhesively luting indirect restorations are resin cements. Increasingly available dual- and light-cure adhesive cements represent convenient and easy-to-handle alternatives for establishing the requisite micromechanical and chemical bond between tooth structure and restorations, particularly today’s in-demand high-strength ceramics (eg, lithium disilicate).^3,7 Whether the tooth substrate is enamel or dentin, dual-cured materials have demonstrated better performance than single-step resin cements.^8,9

While these characteristics are advantageous, bond strength and micromechanical properties,¹⁰ color stability, and atraumatic removal of excess material from gingival and interproximal areas remain essential elements for long-term treatment functionality. Research has shown that using adhesives and dual-cure resin cements from different manufacturers and/or those that require different curing methods may be deleterious and may lead to low shear bond strengths.¹¹ In addition, when bonding to dentin, dual-cured resin cements used in combination with an adhesive bonding agent have demonstrated reduced bond strengths when not light activated.¹²

Further, studies have indicated that all resin cements (eg, light-cure, dual-cure) demonstrate varying levels of discoloration, and dual-cure resin cements may influence the esthetics of restorations—particularly along the margins.¹³ When excess cement has been left adjacent to gingival tissues, inflammation and high levels of bacteria have been reported.^14,15

Therefore, clinicians need to select carefully from among the universal adhesive and dual-cure cement options available to ensure clinical efficacy, long-term restorative stability, predictable esthetics, and procedural efficiency.^16,17 In the author’s experience, a visible light-cured, dual-cured, or self-cured high-strength resin cement containing fluoride that is designed for use following application of a compatible dentin/enamel adhesive can help to achieve high retentive strength, color stability, a simplified cementation process, and easy excess cleanup when seating highly esthetic all-ceramic restorations. The following case presentation demonstrates the manner in which anterior lithium-disilicate restorations were definitively cemented using a dual-cure resin cement and a universal adhesive bonding agent.

Case Presentation

A 38-year-old man presented with the chief complaint being the appearance of his smile (Figure 1). A media industry professional, he was self-conscious about the spaces between his teeth, and his failing restorations were discolored (Figure 2). He requested closure of the tooth spacing and a uniform, lighter tooth color.

A thorough examination was performed that included intraoral, photographic, and radiographic evaluations, along with a full periodontal and temporomandibular joint (TMJ) examination. He had no signs or symptoms of any TMJ disorders, and no periodontal disease was evident. Failing composite restorations were observed on teeth Nos. 7 through 11, and his mandibular teeth Nos. 23 through 27 were chipped and also had large discolored composite restorations (Figure 3).

After discussing these findings with the patient—and in consideration of his limited time schedule and esthetic concerns—laboratory-fabricated indirect lithium-disilicate restorations were recommended. Those teeth that presented with large decaying composite restorations would require more of a ¾ crown, while the other teeth could be more conservatively prepared for veneers. The patient accepted this treatment plan.

Photographs, preoperative shades, and preoperative impressions were obtained for use in fabricating an esthetically enhanced wax-up to illustrate the ideal smile design (Figure 4). After patient review and acceptance of the proposed wax-up, it was used as the basis for fabricating reduction matrices to guide tooth preparation and reduction. The wax-up was also used to create a matrix for fabricating provisional restorations that would be similar to the shape reflected in the wax-up (Figure 5).

Preparation and Provisionalization

The patient was given anesthesia. Using depth cutters that would enable conservative ceramic preparations, the minimal amount of tooth reduction required (ie, 0.3 mm to 0.5 mm) was achieved, with the reduction matrix serving as a guide (Figure 6).⁷ As much of the preparations remained in enamel as possible to enhance restoration longevity.⁷

The preparations were then rinsed and dried, and shade-tab photographs were taken. Preparation impressions and opposing arch and interocclusal records were then taken. These records were forwarded to the laboratory for use in fabricating the definitive lithium-disilicate veneer, crown, and/or ¾ crown restorations.

To create and place the provisional restorations, the preparations were first cleaned with chlorhexidine and dried. A provisional material (Integrity®, Dentsply Sirona, www.dentsplysirona.com) was then placed in the matrix made from the wax-up, and the matrix was placed over the prepared teeth. The matrix was then removed, and the provisionals carefully trimmed intraorally.

When the patient returned 1 week later, esthetics, phonetics, and shape/length were evaluated, and adjustments were made. Final shades were selected, impressions and photographs of the provisionals were done, and a stick bite was also taken. These records were also forwarded to the laboratory.

Final Cementation

The definitive restorations were received from the laboratory. During the delivery appointment, the patient was given anesthesia and the provisionals were removed. The lithium-disilicate restorations were tried in to verify fit, and then removed.

The preparations were cleaned with chlorhexidine (Figure 7), rinsed, and isolated. They were then etched according to a total-etch protocol by applying a 34% phosphoric-acid conditioning gel. Care was taken to ensure the etchant did not remain on the dentin for more than 15 seconds (Figure 8).

The etchant was rinsed off, after which a universal adhesive (Prime&Bond Elect®, Dentsply Sirona) was applied to all prepared surfaces for 20 seconds (Figure 9).^8,9 The solvent in the adhesive was evaporated, and the teeth were then light-cured for 10 seconds each.

A dual-cure esthetic cement (Calibra® Ceram, Dentsply Sirona) was placed in each veneer, crown, and/or ¾ crown as the restoration was seated (Figure 10). Among the reasons for choosing this cement were its compatibility with the selected adhesive, long-term strength and high immediate bond strengths, and shade-stabilizing technologies to prevent color shifts over time in light-transmissible restorations.¹⁸

Beginning with the central incisors and proceeding to the laterals and posteriorly, the restorations were individually seated. Excess cement was carefully cleaned from the restorations (Figure 11), after which each veneer was tack cured into place for 3 seconds at the gingival apex of the restoration (Figure 12). However, if needed, this cement enables a wider timeframe for tack-curing of up to 10 seconds, and an extended 45-second gel phase for thorough cement cleanup. This allowed easy and effective removal of excess cement from the restorations, gingival margins, and interproximally.

A final light-cure was then performed from the buccal and lingual aspects for 30 seconds for each tooth, and any remaining excess cement was easily peeled off with a scaler (Figure 13). The occlusion was then verified, and any necessary adjustments were made and polishing performed.

Conclusion

When placing esthetic all-ceramic restorations (Figure 14 through Figure 16), the materials used for their adhesive cementation should be selected on a case-by-case basis and with an understanding of the products’ capabilities and limitations. Not all bonding agents and dual-cure cements perform ideally in all clinical situations, or with all other restorative substrates. When used to place the lithium-disilicate restorations presented in this case, the universal adhesive and the dual-cure cement contributed to reliable seating, efficient and thorough cleanup of excess, and high immediate and long-term strength.

About the Author

Stephen D. Poss, DDS
Private Practice
Brentwood, Tennessee

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