Simplifying Posterior Zirconia Crown Placement: Introducing a Self-Repairing Bioceramic Cement

Dr. Sam Simos
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INTRODUCTION
The success of indirect restorations is predicated on a number of factors, including treatment planning, material selection, preparation, and impression taking. However, cementation using strong and reliable materials is also of paramount importance to ensure marginal integrity and, consequentially, long-term functionality. Selecting the most appropriate cementation material for a specific case requires consideration of patient characteristics (caries risk, parafunctional habits), restorative material requirements, location in the mouth (anterior or posterior), and indications and handling characteristics of available options.1

Over the years, dental product manufacturers have introduced a wide array of materials that can be used to definitively seat indirect restorations fabricated from various materials. Adhesive bonding agents and light-cured, resin-based cements have been invaluable when placing glass-ceramic and aesthetic restorations, despite their often technique-sensitive protocol. On the other hand, dual-cure resins or conventional glass ionomer and zinc phosphate options are favorable when seating high-strength ceramic, metal-based, and/or posterior restorations.2

Glass ionomer cements, in particular, have been beneficial for high-caries-risk patients based upon their ability to promote remineralization and prevent secondary caries. Unfortunately, as traditional glass ionomer materials cure, imperfections can be left in the dentin/cement interface. Such imperfections can lead to the formation of marginal gaps and discrepancies when glass ionomer cements are used to secure zirconium oxide-based all-ceramic restorations.3 However, research has shown that using an adhesive bonding agent and composite resin cement when seating zirconia restorations might not ensure higher predictability, particularly in terms of retention.4

In response to demands for easier-to-use cements that demonstrate greater biocompatibility and enhanced physical properties, dental manufacturers have increasingly shifted the focus of their research and development to more retentive, biocompatible, and biorestorative options. As a result, bonding agents and composite resin cements that demonstrate remineralizing and antibacterial properties to combat recurrent caries have been introduced.5 Although these typically calcium silicate-based materials have been shown to be highly biocompatible, they have also demonstrated low strength characteristics.6 Simultaneously, regardless of the enhanced characteristics of many available cementation materials, 27.8% of full-coverage crown procedures involve replacement of existing restorations (according to the The Key Group’s 2015 Omnibus Dental Survey, Quarter 3), which often fail when marginal integrity is compromised due to microleakage.

Fortunately, manufacturers have developed a new class of bioactive dental cement that combines calcium aluminate and glass ionomer components. In clinical studies evaluating its 2-year and 3-year performance when full-coverage crowns and 3-unit bridges were placed, the material performed well in terms of retention, marginal seal, and handling (ie, working time, setting time, and ease of excess removal).7,8 Additionally, restorations seated with the bioactive cement showed no secondary caries and no marginal discolorations, and patients reported no sensitivity.8

Contributing to the performance of this cement was its ability to promote natural formation of hydroxyapatite at the cement/saliva interface, which can help minimize microleakage, in addition to increasing restoration stability.9 These properties of the calcium aluminate-based cement were shown to contribute less microleakage than other available cementation materials.10

Benefits of a Self-Repairing Bioceramic Cement
A new bioceramic cement has been recently introduced that features the combined chemistry of calcium aluminate and glass ionomers, which enables the creation of a self-repairing hydroxyapatite layer that minimizes microleakage and protects the restoration’s long-term marginal integrity (Calibra Bio Bioceramic Luting Cement [Dentsply Sirona]). Demonstrating good flowability and consistency, with low expansion and no shrinkage, this bioactive cement resolves the issues associated with imperfections at the dentin-cement interface.

Figure 1. Following root canal therapy, tooth No. 19 was prepared for a retentive full-coverage zirconia restoration. Figure 2. Tooth No. 19 was provisionalized using a temporary bis-acrylic crown and bridge material (Integrity [Dentsply Sirona]).
Figure 3. The zirconia restoration was tried in to confirm fit, contacts, occlusion, and aesthetics. Figure 4. After try-in and adjustment, the intaglio surface of the restoration was cleaned with bleach and thoroughly rinsed.
Figure 5. View of the Calibra Bio Bioceramic Luting Cement (Dentsply Sirona) capsule and dispensing gun. Figure 6. The capsule of bioceramic cement was activated and mixed for 8 to 10 seconds.

In the oral environment, calcium aluminate particles in the cement interact with phosphate ions found in saliva and dissolve to release calcium and hydroxyl ions that interact with phosphate ions in saliva to form hydroxyapatite along the preparation’s margins. Additionally, if future damage occurs, the ongoing interaction between the cement and saliva continuously repairs the hydroxyapatite layer, thereby enhancing and protecting the overall marginal integrity of the restoration. This bioceramic luting cement has calcium aluminate ionomer (CAIO) chemistry that delivers seamless adaptation toward tooth structure. In fact, a 3-year study has determined that this bioactive cement demonstrates excellent long-term marginal integrity, no marginal discolorations, no subject sensitivity, no secondary caries, and no loss of retention over time.7 The cement also has demonstrated a capability for filling artificial microscopic gaps up to 110 µm in height.

Containing no hema or BPA, Calibra Bio Bio­ceramic Luting Cement is indicated for use wherever glass ionomer cement would be used. Due to its bioactivity, it reportedly produces no adverse effects on vital oral tissues. And, because this bio­ceramic cement performs well within the moist oral environment, no primers, bonding, or conditioning is required, thereby reducing procedure time and simplifying cementation protocol. Yet, the bioactive cement still demonstrates retentive strength comparable to self-adhesive resin cements and is ideal for retentive tooth preparations. In addition to enabling less technique-sensitive restoration placements (which are beneficial when seating zirconia restorations), the cleanup of any excess cement can be easily done.

The following case presentation illustrates the simple placement techniques involved with definitively seating a full-coverage zirconia restoration.

CASE REPORT
A female patient presented for a full-coverage zirconia crown restoration on tooth No. 19 following root canal therapy. After a thorough examination, impressions were taken for laboratory communication and to use in creating a chairside provisional restoration.

A retentive crown preparation was completed (Figure 1), and final impressions were taken and sent to the dental laboratory. Tooth No. 19 was then provisionalized using a bis-acrylic temporary crown and bridge material (Integrity [Dentsply Sirona]) (Figure 2).

Cementation Protocol
The completed crown was delivered to the dental office. The intaglio surface of the zirconia restoration had been prepared by the lab team for cementation by sandblasting with 50 µm alumina according to the manufacturer’s instructions. Had the restoration been fabricated from a high-strength glass-ceramic material, the intaglio surface would have been etched with hydrofluoric acid according to the manufacturer’s instructions. No pretreatment (eg, silanes, primers, or bonding agents) was required; such pretreatments are contraindicated because they destroy the bond between the cement and restoration.

The provisional restoration was removed, and the preparation was cleaned and dried. The restoration was then tried in to confirm fit, contacts, occlusion, and aesthetics, as well as to determine if any minor adjustments were required prior to cementation (Figure 3). After try-in, the preparation was cleaned, rinsed, and dried, with care taken not to desiccate the tooth structure. Additionally, after try-in and adjustment, the intaglio surface of the restoration was cleaned with a sodium hypochlorite solution and thoroughly rinsed (Figure 4).

Figure 7. View of the activated capsule of the cement in the triturator. Figure 8. The activated capsule of the cement was inserted into the dispensing gun.
Figure 9. The restoration was completely filled with the bioceramic cement. Figure 10. After the restoration was seated, the bioceramic cement flowed around the entire circumference of the crown margin.
Figure 11. Once the restoration achieved an initial set, excess cement was easily peeled away from the gingival margins and interproximally. Figure 12. View of the definitive full-coverage zirconia (OTZ Zirconia [Ottawa Dental Laboratory]) crown restoration following complete setting.

The bioceramic cement was then activated and mixed for 8 seconds (Figures 5 to 7), after which the capsule was inserted into the extruder (Figure 8). The restoration was then completely filled with cement by first clicking the extruder trigger until the cement was visible in the clear nozzle, then gently squeezing the level 2 more times to extrude the cement (Figure 9). Ample working time (ie, a minimum of 2 minutes) allowed the restoration to be seated and stabilized under pressure, which helped to avoid any movement until the cement reached a rubber-like consistency. Note that the cement flowed around the entire circumference of the crown margin (Figure 10).

The seated restoration was allowed to set for approximately 2 minutes, after which excess cement was easily removed from the gingival margins and the interproximal areas (Figure 11). The restoration was allowed to stabilize for an additional 4 minutes to achieve a final set (ie, 6 minutes from insertion) (Figure 12).

CLOSING COMMENTS
Clinicians have multiple options for definitively cementing indirect restorations, regardless of the material from which they are fabricated. Selection of the most appropriate cement must be based on the requirements of the particular clinical situation, which may include location of the restoration in the mouth, type of restorative material, and patient characteristics. In this case, Calibra Bio Bioceramic Luting Cement was selected based on its ease-of-use; demonstrated retention; moisture tolerance; and ideal indications for use, which include the permanent cementation of zirconia full-coverage crowns to retentive preparations. Based upon its unique self-repairing, hydroxyapatite-layer-forming properties, the decision to seat the patient’s posterior restoration using this bioceramic cement ensured confidence that the restoration delivered will function predictably for years to come.


References

  1. Wassell RW, Barker D, Steele JG. Crowns and other extra-coronal restorations: try-in and cementation of crowns. Br Dent J. 2002;193:17-28.
  2. Pegoraro TA, da Silva NR, Carvalho RM. Cements for use in esthetic dentistry. Dent Clin North Am. 2007;51:453-471.
  3. Martínez-Rus F, Suárez MJ, Rivera B, et al. Influence of CAD/CAM systems and cement selection on marginal discrepancy of zirconia-based ceramic crowns. Am J Dent. 2012;25:67-72.
  4. Palacios RP, Johnson GH, Phillips KM, et al. Retention of zirconium oxide ceramic crowns with three types of cement. J Prosthet Dent. 2006;96:104-114.
  5. Zhang K, Zhang N, Weir MD, et al. Bioactive dental composites and bonding agents having remineralizing and antibacterial characteristics. Dent Clin North Am. 2017;61:669-687.
  6. Jefferies SR. Bioactive and biomimetic restorative materials: a comprehensive review. Part I. J Esthet Restor Dent. 2014;26:14-26.
  7. Jefferies SR, Pameijer CH, Appleby DC, et al. A bioactive dental luting cement—its retentive properties and 3-year clinical findings. Compend Contin Educ Dent. 2013;34(special issue 1):2-9.
  8. Jefferies SR, Pameijer CH, Appleby DC, et al. Prospective observation of a new bioactive luting cement: 2-year follow-up. J Prosthodont. 2012;21:33-41.
  9. Engstrand J, Unosson E, Engqvist H. Hydroxyapatite formation on a novel dental cement in human saliva. ISRN Dent. 2012;2012:624056.
  10. Pameijer CH, Zmener O, Alvarez Serrano S, et al. Sealing properties of a calcium aluminate luting agent. Am J Dent. 2010;23:121-124.

Dr. Simos received his DDS degree from Loyola University in Chicago and maintains a private practice, Allstar Smiles, in Bolingbrook and Ottawa, Ill. Dr. Simos teaches postgraduate courses in cosmetic, implant and restorative dentistry. In addition, he is a global speaker and author on the use of today’s innovative techniques and materials in dentistry. He can be reached via email at sam.s@allstarsmiles.com and on Instagram @drsamsimos.

Disclosure: The author reports no disclosures.

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