September 2011, Volume 7, Issue 8
Published by AEGIS Communications
Seating Anterior All-Ceramic Crowns
This case presentation demonstrates the placement of highly esthetic all-ceramic indirect restorations with an innovative universal adhesive luting cement and the wave technique.
By John Schwartz, DDS
Indicated as a leading cause of fracture, debonding, and restorative failure, the seating of all-ceramic indirect restorations requires proper consideration of the case, material, and technique to ensure a long-lasting, stable, and esthetic result.1 Because it is a technique-sensitive process, improper preparation, occlusal positioning, curing, and excess material near the margins and interproximal areas are common causes of clinical failures.2-4 Providing little assistance to the dentist, conventional luting cements offer limited esthetic potential and lack the strength necessary to withstand the forces of mastication, while demonstrating low bond strengths, high solubility, and the need for multiple bonding steps before placement.3,4 Although many conventional materials are still in use today, the demand for highly esthetic all-ceramic restorations has led to the need for more efficient seating protocols and materials.5
Through better understanding of the chemical and mechanical aspects of adhesion, techniques for adhesive luting have improved.2-4 Advanced all-ceramic restorative materials that offer high strength, enhanced esthetics, and simpler fabrication through advanced laboratory/chairside computer-aided manufacture/computer-aided design (CAD/CAM) technologies have contributed to the evolution of indirect all-ceramic restorations.6,7 Because adhesive material science had yet to reach its full potential, bonding indirect all-ceramic restorations has remained a challenge.1
To resolve these clinical challenges, new generations of adhesive luting cements have been developed.5 Through the incorporation of resin fillers, adhesive luting cements now offer greater stability, durability, and longevity.7 Various shade options are also now available to enhance even the most esthetically challenging indirect all-ceramic restorations.7
Because they are available from a variety of manufacturers and indicated for use with many different materials, the chemical, physical, and optical qualities of these materials may differ, along with their effect on stability, longevity, and esthetics.8,9 Therefore, it remains critical that the dentist carefully consider the requirements of the case to ensure the materials used will provide the best in function and esthetics.8,9
Composed of 70% needlelike crystals in a glassy matrix and demonstrating high monolithic strength, IPS e.max® (Ivoclar Vivadent, Inc., www.ivoclarvivadent.com) lithium-disilicate glass-ceramic is indicated for use in the fabrication of single-tooth restorations, partial and full crowns, thin crowns, inlays and onlays, implant superstructures, and three-unit anterior bridges.10,11 Available for two processing techniques, indirect restorations can be pressed using the lost hot-wax technique (IPS e.max® Press, Ivoclar Vivadent) or fabricated in the laboratory or chairside using CAD/CAM processes (IPS e.max® CAD, Ivoclar Vivadent).10,11 Although all material characteristics are similar, differences in strength between IPS e.max CAD (360 MPa) and IPS e.max Press (400 MPa) relate to the length and size of the crystals comprising the matrix.10-12
Enhancing the esthetics of all-ceramic restorations, the IPS e.max system incorporates true-to-nature shades and a relatively low refractive index to provide excellent optical characteristics such as optimal light transmission.10,11 To create restorations that are truly indistinguishable from nature, IPS e.max can be further characterized through cutback-and-layer or stain-and-glaze techniques.10,11
When seating indirect lithium-disilicate restorations, the compressive strength of IPS e.max substructures provides flexibility in cementation.10-12 Conventional cementation protocols can be followed when moisture control is questionable or sclerotic dentin is present, using cement that demonstrates very low expansion set properties to avoid excessively stressing the internal surfaces of the restoration.11 Although conventional cementation may be required in rare cases, an ideal bond between IPS e.max lithium-disilicate restorations and prepared dentition is achieved with a universal, dual-curing adhesive luting cement.10,11
Developed for adhesive cementation of both posterior and anterior indirect all-ceramic restorations, Multilink® Automix (Ivoclar Vivadent) is a universal, dual-curing luting cement indicated for inlays, onlays, crowns, bridges, and posts fabricated from a broad range of restorative materials, including metal and metal-ceramics, oxide-ceramics, fiber-reinforced composites, precious alloys, and all-ceramics.13,14
Used in conjunction with self-curing and self-etching one-step primer (Multilink® A&B, Ivoclar Vivadent), Multilink Automix seals the dentin in 15 seconds, provides excellent marginal adaptation, and high immediate bond strengths.13,14 With this, the patented hydrolytically stable acidic monomers ensure durable adhesion and long-term bonds within 10 minutes of placement.13
Minimizing waste and providing a consistent mix with each use, the Automix Delivery System (Ivoclar Vivadent) does not require activation capsules or application tools or devices.13 In addition, Multilink Automix is available in an “easy clean-up” formula, which allows excess cement to be pre-cured into a gel-like consistency for simple and efficient removal with a scaler, probe, or floss.13
Regardless of indication, dentists can expect high immediate bond strengths, stability, longevity, good marginal adaptation, and minimal postoperative sensitivity when seating with Multilink Automix.13,14
The Wave Technique
The wave technique maximizes the plasticity change that resin-filled cements undergo on initial curing with halogen-based curing lights.15 By placing the curing tip near the margin of the restoration, the cement changes to a gel state after only 3 seconds and begins to “peel” away. Remaining excess cement can then be easily removed with a probe or scaler and the restoration can then be “tacked” into place by curing the margin for 5 seconds.15 The same process is completed on the lingual, and once tacked on both the buccal and lingual, dental floss can be passed through the interproximal area to remove excess cement. The total curing time for the facial, cervical, interproximal, buccal, lingual , and incisal will take 60 seconds (10 seconds on each area).
Simplifying cementation and clean-up, the wave technique allows all excess cement to be removed before final curing, reducing the risk of damaging the restoration, bond, and/or the soft tissues.15 By providing ideal stability and longevity, the wave technique allows the dentist to be sure the luting agent has fully cured and properly adhered to the prepared dentition and all-ceramic restorations.
A 55-year-old woman presented with the desire for functional and esthetic restorations in the anterior as well as a bruxism habit. Teeth Nos. 7 through 10 had been previously restored with feldspathic porcelain crowns. However, the restorations demonstrated wear from bruxing and had become unnatural in appearance because of shade issues. After a comprehensive esthetic and functional examination, all diagnostic information was gathered and a definitive treatment plan was developed.
To provide resistance from wear and improve esthetics, all-ceramic lithium disilicate (IPS e.max CAD) was chosen to be CAD/CAM-fabricated chairside into anterior laminate crowns. To ensure long-term stability and adhesion to the prepared anterior dentition, the crowns would be cemented using adhesive resin cement (Multilink Automix) and cured using the wave technique.
Preparation of Dentition
The anterior dentition was prepared for adhesive cementation of CAD/CAM-fabricated anterior lithium-disilicate laminate crowns, which would eliminate discolorations, improve overjet function, and prevent additional lingual wear. Following the manufacturer’s guide and the specific considerations for this case, depth cuts of 0.6 mm to 0.8 mm were first completed. A medium-grit round-ended diamond bur was then used to remove a uniform thickness of facial enamel and to join the depth-cut grooves. Using a diamond bur on an angle, the incisal edges of the preparations were beveled back and reduced by 1 mm to 1.5 mm. The shouldered margins were then prepared with a 1.2-mm TPE diamond to provide room for the required bulk of lithium disilicate.
Preparation for Cementation
Before seating, the crowns were milled chairside (The E4D Milling Center, D4D Technologies LLC, www.e4d.com) from BL4 shade blocks (IPS e.max CAD) and finished on the model to ensure proper fit, function, and esthetics (Figure 1). A latex-free lip and cheek retractor (such as OptraGate®, Ivoclar Vivadent) was placed to provide isolation and improve access. The preparations were then manually cleaned with a microtip brush and water/pumice slurry.
Preparation of IPS e.max Crowns for Cementation
The internal surface of the lithium-disilicate crowns were cleaned according to the manufacturer’s instructions to remove the smear layer, and air-dried to ensure clean inner surfaces and maximum bond strength. A 5% hydrofluoric etching gel (IPS Ceramic Etching Gel, Ivoclar Vivadent) was then applied to the internal surfaces of the crowns for 20 seconds to achieve the proper etch pattern and remove contaminants (Figure 2). After etching, the restorations were thoroughly rinsed with water and air-dried.
The internal surfaces of the crowns were then coated with a silane coupler (Monobond Plus, Ivoclar Vivadent) and allowed to sit for 1 minute (Figure 3). Air was used to remove excess material and the restorations were ready to be seated with adhesive resin cement (Multilink Automix).
To seal the dentin, achieve ideal marginal adaptation, and facilitate immediate high bond strength, self-etching and self-curing primer (Multilink A&B) was applied to the preparations. Three drops of Multilink A were mixed with three drops of Multilink B in the tray (Figure 4). To ensure sufficient coverage, five coats of the primer solution were applied to each preparation with a microtip brush (Figure 5). After primer application, air was used to remove excess solution that had pooled on the surface. The primer was allowed to sit on the preparations for 30 seconds until the surrounding gingival tissues became pale from the etchant.
The dual-cure adhesive cement (Multilink Automix) was then extruded from the automix tip into the crowns one at a time (Figure 6). The crowns for teeth Nos. 7 through 10 were then seated individually while applying firm pressure (Figure 7).
To facilitate a proper cure, the wave technique was used. Holding the curing light 2 mm from the crowns, the light was slightly waved in a single direction, from one interproximal area to the next for 3 seconds to cure the buccal-cervical surfaces of each crown (Figure 8). A hygiene scaler was then used to remove excess cement from the buccal and interproximal areas (Figure 9). After removing all excess material, wave curing continued for 5 seconds on the cervical aspect of the buccal surfaces of each crown.
The lingual surfaces of the crowns were then cured for 3 seconds each and the scaler was used to remove excess lingual cement (Figure 10). The lingual was then “tacked” for 5 seconds and the interproximal areas were cleaned with dental floss (Figure 11). After ensuring all excess material had been removed, the seated anterior lithium-disilicate crowns were cured for 1 minute each on both the buccal and lingual surfaces (Figure 12).
Upon completion of the case, the patient was very pleased with the lithium-disilicate CAD-fabricated crowns (IPS e.max CAD) seated with the specially formulated universal dual-cure adhesive cement (Multilink Automix). The restorations offered the best in fit and function, while meeting the patient’s ultimate goal of improved esthetics and a naturally appearing smile (Figure 13 and Figure 14).
This case presentation demonstrates the placement of highly esthetic all-ceramic indirect restorations using an efficient and reliable adhesive cementation technique and material. Providing a stable, durable, and long-lasting bond, the material reduced the risk of future clinical challenges, such as fracture, debonding, and failure. Through careful consideration of all aspects of the case, including proper material and technique selection, the patient was provided with restorations that met her demands and demonstrated the ideal fit, function, and esthetics.
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About the Author
John Schwartz, DDS
Center for Advanced Dental Learning