The world of restoration placement can be a confusing one. When is the tooth too dry or too wet, when do we total-etch or not etch, when can we cement, when do we use light or chemical or dual-cure materials? We can choose from self-adhesive resin cements or those with separate bonding steps. These variations can be confusing, sometimes leading to compromised results.1 A goal for efficient clinical success is to use a protocol that offers exceptional clinical performance, consistent application, and ease of use.
So Many Cements, So Little Time
Newer crown and bridge materials like lithium disilicate (such as IPS e.max [Ivoclar Vivadent]) have gained widespread use throughout dentistry because of their overall strength, esthetics, and versatility. A clinical advantage of lithium disilicate is that it can be either traditionally (or conventionally) cemented or resin bonded into place.2 This material has the strength to be conventionally cemented, but there are potential advantages to using a luting resin, including increased esthetics, higher bond strengths to the tooth and ceramic, less microleakage, strengthening of the ceramic, and the ability to lessen the effects of a less-than-perfect preparation.3,4
The cementation of any restoration is either adhesive or nonadhesive.5 Traditional cementation is often preferred by clinicians because of ease of use, simple cleanup, and dependable results. When preparations are short or over-tapered, or if occlusal forces are heavy, bonding with resin cement is indicated. In these situations, dual-cure resin cements with a separate or “built-in” dentin-bonding agent (DBA) provide maximum restoration retention, microleakage prevention, and increased fracture/fatigue resistance of the restorative material itself.6
Traditional cementation is a viable option with lithium disilicate if the amount of surface area and degree of divergence of the prepared walls can provide sufficient micromechanical retention.7 Bioactive cements (such as Ceramir Crown & Bridge [Doxa]) and resin-reinforced glass ionomer cements (such as RelyX Luting [3M ESPE] or GC Fuji PLUS [GC America]) have been popular choices due to ease of use and less technique sensitivity, low reported postoperative sensitivity, and long-term clinical success on retentive preparations. No etching, primers, or bonding agents are used with these materials, but there is some compromise in both esthetics and retention.3
Self-adhesive resin cements (such as RelyX Unicem [3M ESPE], SmartCem [DENTSPLY Caulk], SpeedCEM [Ivoclar Vivadent], and Maxcem Elite [Kerr]) have been popular choices for all-ceramic cementation because of their simplicity, good esthetics, and ability to bond to dentin without a primer.8 These cements have a high level of success if the preparations are highly retentive; however, they do not give bond strengths nearly as high as those dual-cure resin cements with a separate dentin bonding agent which could lead to restoration displacement and failure.9,10 Their simplicity is desirable in a busy practice and their restoration retention is higher than traditional cementation, particularly when the prepared tooth has adequate surface area, 4° to 8° of taper, and axial wall heights of at least 4.0 mm. However, it is not possible to have “ideal” preparations in every case.11
Adhesive resin cements provide the maximum in esthetics and in restoration retention but require the application of a separate DBA. Despite its proven long-term high bond strengths, the total-etch technique where the entire preparation is etched with phosphoric acid is often avoided by clinicians, particularly for full crowns, because of the removal of the smear layer and the potential sensitivity associated with it.12 This etch-and-rinse protocol can be the most technique sensitive method as moisture control, desiccation, bacterial contamination, curing, and other variables help determine clinical success or failure.13
Instead, self-adhesive dentin bonding agents have been introduced that give high bond strengths to the preparation without a separate etching step, particularly on dentin.11 ALL-BOND UNIVERSAL (BISCO Dental Products) and RelyX Scotchbond Universal (3M ESPE) are examples of 2 newer “universal” DBAs that claim less technique sensitivity and more clinical tolerance than previous self-etch bonding agents. Each has a compatible dual-cure adhesive resin: DUO-LINK UNIVERSAL (BISCO Dental Products) and RelyX Ultimate (3M ESPE). Each is dual-cure so that in areas where curing light penetration is doubtful, they have the ability to chemically cure themselves. Both have versatility in that they can be used with almost any indirect material used in dentistry today and in almost any bonding situation except for thin, transparent anterior veneers.
Diagnosis and Treatment Planning
A patient reported with compromised esthetics having older porcelain restorations and failing composites on anterior teeth (Figure 1). A plan was made to include gingival recontouring and the placement of 8 lithium disilicate (IPS e.max) restorations from teeth Nos. 5 through 12.
A mock-up was done before anesthesia, phonetics and incisal edge position checked, and an impression for temporary fabrication and for assisting the dental laboratory team for incisal edge position.
|Figure 1. The treatment plan included replacing anterior crowns and composites with lithium disilicate restorations to make the smile more ideal.||Figure 2. After biologic width determination, a diode laser was used to contour soft tissues; 2.0 mm depth cuts were made with a 330 bur.|
The 2.0-mm incisal depth grooves were placed with a 330 bur, and then the old restorations and decay were removed (Figure 2). Buildups were done, using a self-etch dentin bonding agent (ALL-BOND UNIVERSAL) and a dual-cure buildup resin (CORE-FLO [BISCO Dental Products]), to replace missing tooth structure and failing restorations. Preparations were done with an intended taper of 4° to 8°, a uniform one-mm to 1.5-mm chamfer margin, and 1.5 mm to 2 mm clearance in all excursive movements according to the manufacturer’s preparation guide14,15 (Figure 3).
Preparation shade photos were taken to help the lab determine the degree of opacity needed for the definitive lithium disilicate restorations (Figure 4). Our goal was to use a ceramic ingot with the least amount of translucency needed to cover the preparation shade so that the final result would be as lifelike as possible. Two vinyl polysiloxane impressions (Panasil [Kettenbach LP]) were taken and sent to the lab along with a bite registration and alignment guide, lower model, written case description, and a full series of photos (Figure 5).
Provisional restorations were made using a matrix from a mock-up, composite temporary material (Luxatemp Ultra [DMG America]), and covered with a composite glaze (BisCover [BISCO Dental Products]). They were cemented with a zinc oxide (noneugenol) translucent temporary cement (ZONEfree [DUX Dental]).16 This cement reduces the potential interference that a eugenol containing cement could have on the final bonding to the tooth.17
The patient returned 4 days after placement when an examination of esthetics, function, and patient experience was performed. After minor adjustments, photos and an impression were taken of the transitional restorations and forwarded to the lab team.
|Figure 3. Decay was removed and buildups were done with a dual-cure composite; preps were finished with tapered end-cutting diamonds.||Figure 4. A full series of pre-op, mock-up, and preparation shade photos were taken and sent to our lab team.|
|Figure 5. Final vinyl polysiloxane impressions were taken of the preps along with alignment guides and models of the opposing arch.||Figure 6. A moderate translucent lithium disilicate ingot (IPS e.max [Ivoclar Vivadent]) was pressed, cutback, and characterization porcelain added in the incisal.|
|Figure 7. At the insertion appointment, a single central temporary was removed. Note the clean surface after using a noneugenol zinc oxide temporary cement.||Figure 8. Try-in of a single central allows midline, cant, and incisal edge position to be verified particularly when the lab uses the temps and mock-up when determining incisal edge position.|
|Figure 9. The other incisor temps were removed. Note that excess room is made on the mesial of the cuspid temps to make sure there are no interferences during |
|Figure 10. After try-in, the preps were cleaned with oil-free pumice.|
|Figure 11. The interproximal areas were cleaned with an unfilled gauze, water, and pumice.||Figure 12. Cleaning of the contaminated lithium disilicate was done with a cleaning paste for 20 seconds and then rinsed.|
|Figure 13. Silane was applied because thorough cleaning would lessen its effects.||Figure 14. After 30 seconds, the crowns were thoroughly dried, leaving a frosty but not chalky surface that was ideal for bonding.|
Upon return of the restorations from the dental laboratory, the full contour pressed lithium disilicate crowns were inspected on the model (Figure 6). Note that the high level of translucency allowed a hint of yellow die spacer to show through the final restorations while on the model. Because of this, the preparation shade of the teeth and the luting material would influence the final appearance that must be taken into account when choosing the final resin color.
The temporary of a single central incisor was removed and the crown for tooth No. 8 tried-in to verify the length and contour with respect to the temporaries (Figure 7). Since our lab team was instructed to follow incisal edge position of the temporaries and the mock-up, it was prudent to check before removing all of the temporaries (Figure 8). After verification of the midline, cant, and incisal edge position of the central, the other incisor temporaries were removed and the definitive restorations tried-in place with water to check the coloration (Figure 9).
Preparation of the teeth for cementation—Isolation and minimizing the chance for salivary and blood contamination cannot be overemphasized. Retractors were placed and the teeth cleaned with oil-free pumice (Figure 10). Interproximal surfaces could not be reached with a prophy cup completely, so a damp 2-x-2 unfilled gauze was used to “shoe-shine” those surfaces.18 The noneugenol cement cleans off very easily and combined with oil-free pumice cleaning allows for very effective resin cement bonding19 (Figure 11).
Preparation of the crowns for cementation—After try-in, any contaminates were removed by using a universal cleaning paste (Ivoclean [Ivoclar Vivadent]). This material is placed with a microbrush to the entire bondable surface of the restorations, allowed to sit for 20 seconds, and rinsed thoroughly (Figure 12). This material provides a thorough cleaning and removal of proteins, phosphates, and other contaminates that may interfere with bond strengths.20 A silane-based porcelain primer was placed on the internal porcelain surfaces for 30 seconds (Figure 13). It should be noted that even if the lab team places silane on the restorations, thorough cleaning may remove the silanization and should therefore be applied again and then dried thoroughly (Figure 14). Several coats of a universal bonding agent, ALL-BOND UNIVERSAL, are then applied to the porcelain and air-thinned (Figures 15 and 16). ALL-BOND UNIVERSAL is an adhesive for any direct or indirect bonding scenario from total-etch to nonetch to selective-etch. Its high level of clinical tolerance makes it an ideal product for most any bonding situation. In this situation where the entire preparation is on dentin or composite, high bond strengths are achieved without the use of a separate phosphoric acid etching. Several coats are applied to the teeth with a microbrush and agitated onto the surface (Figure 17). The ethanol carrier must be evaporated to reduce chances of sensitivity, increase bond strengths, and lower the film thickness to less than 10 µm (Figure 18).
|Figure 15. A universal dentin-bonding agent (DBA) (ALL-BOND UNIVERSAL [BISCO Dental Products]) was applied in several layers.||Figure 16. Air-thinning was done to remove the solvent and to decrease the film thickness to under 10 µm. Light-curing was not done.|
|Figure 17. After retraction of the soft tissues, the same universal DBA was applied to the tooth in several layers.||Figure 18. Air-thinning was done to remove the solvent, increasing bond strengths to dentin and decreasing chances for sensitivity associated with this chemical carrier.|
|Figure 19. The dual-cure resin cement (universal shade) (DUO-LINK UNIVERSAL [BISCO Dental Products]) was applied to the crowns, seated, and then flash-cured for 2 to 3 seconds.||Figure 20. The material, due to its rubbery consistency, was easily peeled off.|
|Figure 21. Cleanup was then done with floss, a composite knife, and scaler.||Figure 22. The remaining temporaries were then removed and the definitive restorations cemented with the same method.|
|Figure 23. All restorations were then light-cured a minimum of 60 seconds (30 seconds from both the lingual and facial) to increase the rate of conversion and |
polymerization of the materials.
|Figure 24. Lithium disilicate (IPS e.max), along with a universal bonding agent and dual-cure resin cement, gave us strength and predictability and long-term success.|
For cementation onto preparations with significant enamel present, a 15-second etch with phosphoric acid only on the enamel yields higher bond strengths than relying on self-adhesion from a self-etching adhesive or a self-adhesive resin cement.9,3,21 This selective-etch technique allows for maximum bonding to enamel and dentin while minimizing dentin smear layer removal that may lead to sensitivity.
Cement placement—DUO-LINK UNIVERSAL is a dual-cure resin cement that provides great long-term retention with any indirect restoration. The dual-cure material is a paste-paste material and is placed into the crowns via an automix tube. The crowns were then seated in place and a “flash-cure” was done for 2 seconds from about 2 inches away (Figure 19).
A very important characteristic is that it has a consistent rubbery phase after brief curing that makes for a very easy cleanup (Figure 20). The restorations were then flossed and cleanup was finished with a composite knife and scaler (Figure 21). The restorations were each cured for 30 seconds from the facial, followed by 30 seconds from the lingual. The temporaries were then removed from the cuspids and bicuspids and the restorations placed in the same manner (Figure 22).
Despite being a dual-cure cement, the light-curing increases the boding strength by increasing the rate of polymerization and percentage of resin conversion.3,10 The curing light cures resin at the margins easily and penetrates more translucent porcelain particularly in the anterior (Figure 23). This transmission of light also decreases the chance of shade shifting of any dual- cure material that may occur with time.
Clinical efficiency comes from using materials that have a nearly universal application, high success rate, and minimal staff effort. The use of a dentin bonding agent that gives predictably high bond strengths in the total-, non-, or selective-etch protocols takes much of the decision making out of choosing a bonding agent. Similarly, the use of a dual-cure resin provides the maximum in bond strengths while using a technique that is nearly universal for all silica-based ceramics. Lithium disilicate has garnered great popularity for many of the same reasons. It has a high level of strength and esthetics that makes it nearly as universal of an indirect material that we have seen in dentistry. These nearly universal materials and techniques have simplified office procedures and have given us predictable, patient-pleasing results that bring us to the top of our game (Figure 24).
Dr. Griffin is a clinical director for the Pacific Aesthetic Continuum (PAC) and would like to thank the PAC lab for their excellent work.
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Disclosure: Dr. Griffin reports no disclosures.