Reinforced Lithium Silicate Ceramic: A Case Report

INTRODUCTION
All-ceramic restorations have recently supplanted PFM restorations as the material of choice for fixed prosthetics. The early all-ceramic materials were aesthetic but lacked strengths high enough for posterior applications in certain clinical situations. This ultimately resulted in the development and introduction of layered zirconia and then later, monolithic zirconia as higher-strength restorative alternatives. However, the move to highest-strength monolithic zirconia restorations was accompanied by a decrease in aesthetics. More translucent zirconia ceramics have recently entered the marketplace, but these, while much improved, still do not compare equally to the aesthetic quality and characteristics of lithium disilicate, such as IPS e.max (Ivoclar Vivadent). Lithium disilicate is a very aesthetic, high-strength polycrystalline ceramic that, unlike its predecessors (feldspathic porcelain and leucite-reinforced porcelain), can be either conventionally cemented or adhesively bonded, depending upon the design of the preparation and other factors.1

CAD/CAM Reinforced Lithium Disilicate
An alternative all-ceramic material, zirconia-reinforced lithium silicate (ZLS) (Celtra Duo [Dentsply Sirona]), was introduced several years ago as a CAD/CAM (millable) block. This all-ceramic material is indicated for single anterior and posterior units as well as veneers and inlay/onlays.

The CAD/CAM version (Celtra Duo) also provided the dentist or dental technician the option to mill and polish the material (210 MPa) or, alternatively, to mill and fire the material to improve the strength (> 420 MPa),2,3 with similar aesthetics resulting from both methods. By comparison with lithium disilicate (IPS e.max CAD [Ivoclar Vivadent]), firing yields a strength of 408.3 MPa in one study done by Kang et al.4 Recently, in 2017, the manufacturer has been reporting an average flexural strength of 500 MPa for IPS e.max.

Figure 1. The patient presented with stained vertical cracks in both maxillary central incisors, with pain on percussion and isolated probing indicative of a vertical root fracture on the left central incisor (No. 9).

The benefits of the ZLS ceramics when milled include enhanced aesthetics, excellent flexural strength, and faster restoration milling. The increased glass content of the ZLS ceramic improves translucency, facilitating noticeable visibility in opalescence and fluorescence with natural appearing aesthetics. The dissolved zirconia (10% by volume) reinforces the glass matrix without the clouding that is typical of zirconia ceramics. The ultrafine microstructure of the glass ceramic crystals (< 1.0 μm) allow for faster and easier milling of the ZLS material. Additionally, the material can be finished and polished in its final crystallized tooth-colored state or fired to achieve higher strength, depending upon the clinical situation encountered. Yet, because Celtra Duo is only available in the small single-unit blocks and not in the larger pucks for large scale CAD/CAM milling at this time, its use has been limited to single units.

Pressed Reinforced Lithium Disilicate Now Available
Most recently, a pressable ZLS material (Celtra Press [Dentsply Sirona]) has been introduced, allowing dental laboratory technicians who do not own CAD/CAM milling systems to offer ZLS restorations to their doctors. As an alternative, the pressable version (Celtra Press) allows for bridges to be fabricated in addition to single-unit anterior and posterior crowns, inlays/onlays, and veneers. Celtra Press also provides higher strengths (> 500 MPa) than Celtra Duo (210 MPa to > 420 MPa), which is essentially equal to the most recently reported strength for lithium disilicate (IPS e.max), but lower than the traditional formulations of monolithic zirconia (> 1,000 MPa).5 In recent years, zirconia formulations have been created and introduced with higher translucency formulations to improve aesthetics when used for anterior restorations. However, these materials present with lower (and varying) flexural strengths (range of ~650 to 800+ MPa) and fracture toughness values when compared to the original (higher opacity) zirconia materials (depending upon the material formulations), but higher strength values than pressed ZLS ceramic. To the practicing dentist, the clinically relevant question is, how much strength is required? And, when would we chose a zirconia over a ZLS material? In the authors’ opinion and clinical experience, traditional monolithic zirconia (versus ZLS materials with lower strength) would be indicated for posterior bridges in patients who present with evidence of bruxism when higher strength is a primary concern and when aesthetics may not be so critical.

This article will present a case report describing the use of a recently introduced ZLS material (Celtra Press) for a patient who required the placement an aesthetic anterior fixed partial denture (bridge).

CASE REPORT
Diagnosis and Treatment Planning

A 62-year-old patient presented with sensitivity on the left maxillary central incisor. Upon examination, stained vertical cracks on the facial of both central incisors, with the crack continuing over the incisal edge and down the lingual on the left central incisor (tooth No. 9) were noted. There was an absence of any mobility of the teeth, with the left central incisor presenting with percussion sensitivity and recurrent decay associated with a previously placed composite resin restoration (Figure 1).

Figure 2. Buccal view following removal of the provisional bridge demonstrating the bullet-shaped pontic area developed with the provisional after 4 weeks of healing. Figure 3. Occlusal view following removal of the provisional bridge showing the bullet-shaped pontic area developed by the provisional bridge following several weeks of healing.
Figure 4. Master cast of the maxillary arch, demonstrating bullet-shaped pontic area to provide a natural emergence of the pontic that would be fabricated for the 3-unit anterior bridge. Figure 5. Master casts mounted, demonstrating the patient’s occlusal arrangement.
Figure 6. Dies have been sectioned on the master cast and abutment margins outlined in red pencil. Figure 7. A full contour wax-up of the 3-unit bridge to be fabricated.
Figure 8. An incisal view of the full-contour wax-up of the 3-unit bridge to be pressed. Figure 9. An incisal view of a second wax-up with cutback on the facial where ceramic will be placed on the Celtra Press (Dentsply Sirona) frame of the 3-unit bridge.
Figure 10. The full-contour wax-up was sprued and ready to be invested for pressing the Celtra Press ceramic. Figure 11. The Celtra Press full-contour bridge following pressing and removal of investment.

Endodontics was attempted on tooth No. 9, but a vertical root fracture was identified and confirmed by isolated probing where the fracture line met the lingual gingiva at mid-tooth. The treatment recommended to the patient was extraction of the left central incisor, socket grafting, and preparation of the right and left lateral incisors (teeth Nos. 8 and 9) with placement of a provisional bridge. Then, following a healing period to accommodate any soft-tissue shrinkage at the pontic site, an impression would be taken and a Celtra Press bridge would be fabricated and delivered.

Clinical Protocol
Local anesthetic (4% Septocaine with 1:200,000 epi [Septodont]) was administered with The Wand (Milestone Scientific) by infiltrating the area to be treated. An impression was taken with a fast-set monophase vinyl polysilxoane (VPS) (Aquasil Ultra [Dentsply Sirona]) in an anterior dual-arch tray. A power periotome (Luxator LX [Directa Dental]) was utilized to atraumatically luxate the tooth, and it was then extracted using a ronguer. Next, the socket was curetted (Molt 4L/2R [Zoll Dental Instruments]) to remove any remaining tissue in the socket. The abutment teeth were then prepared for full-coverage restorations using carbide burs (Great White Ultra [SS White Burs]). The previously taken impression was filled with a bis-acryl provisional material (Integrity Temporary Crown & Bridge Material [Dentsply Sirona]) and the temporary bridge was fabricated with material extending into the extraction socket. Upon setting, the impression was removed intraorally and the bridge was contoured and polished. The pontic area was shaped to provide a bullet-shaped pontic that extended 4.0 mm into the socket from the gingival margin. Osseous grafting putty (NovaBone) was placed into the socket to within 5.0 mm of the gingival margins of the socket. Lastly, the provisional bridge was luted into place with Integrity TempGrip Temporary Cement (Dentsply Sirona), any excess cement cleaned up, and the patient dismissed.

The patient returned one month later, and the marginal areas and pontic soft tissue showed no signs of inflammation. It was therefore determined that the final restorative impression could be taken. The provisional bridge was removed and the pontic area was evaluated (Figure 2). A cupped area had been formed in the gingiva by training the soft tissue with the provisional bridge to allow a more natural emergence that could be accomplished by a ridge-lap pontic (Figure 3). A final impression was taken in a full-arch tray using a heavy-body VPS (Aquasil Ultra) in the tray and a light-body VPS (Aquasil Ultra Xtra [Dentsply Sirona]) injected around the teeth intraorally and then the tray was seated. After the impression materials were set, the tray was removed and an opposing impression was taken using a monophase VPS (Aquasil Ultra), and a VPS (Regisil 2X [Dentsply Sirona]) bite registration was taken. The shade was recorded (VITA Easyshade [VITA North America]) with cervical of A3 and the body and incisal A2. Photographs were taken to assist the lab in communications. The provisional was once again luted back into the mouth, excess cement cleaned up, and the patient was dismissed.

Final Prosthesis Fabrication by the Laboratory Team
The case was shipped to the laboratory team (Aesthetic Restorations [AR] Lab in Hattiesburg, Miss) and the impressions were poured in resin die stone (Resin Rock [Whip Mix]) (Figure 4) and mounted with the enclosed bite registration (Figure 5). Dies were sectioned and trimmed, and the margins were marked using a red pencil (Figure 6). The model was scanned using a 3Shape lab scanner and a virtual wax-up was digitally created. The wax-up was then CAD/CAM milled of wax from a disk (Dentsply Sirona) (Figure 7).

Figure 12. Celtra Press bridge following polishing and glazing on the master model. Figure 13. The monolithic Celtra Press bridge (first option) at try-in.
Figure 14. The Celtra Press bridge (second option) with cutback and overlay of ceramic to provide more translucency in the incisal edges at try-in. Figure 15. The Celtra Press layered bridge was selected by the patient and doctor. Shown here after luting into place using Calibra Ceram (Dentsply Sirona) adhesive resin cement.
Figure 16. Lingual view of the luted layered Celtra Press bridge. Only Celtra Press material (no layering ceramic) on the lingual surfaces to provide a stronger surface during function. Figure 17. Retracted view of the Celtra Press layered bridge and adjacent bonded composites that improved our patient’s aesthetics and eliminated all recurrent caries.

After communication with Mr. Chess Moore at AR Lab, it was decided that 2 different bridges would be fabricated—one would be a monolithic Celtra Press bridge (Figure 8), and the other would be a Celtra Press frame with a facial cutback to be layered with Celtra Ceram porcelain (Figure 9). To maintain the highest strength in the bridge, the lingual surface of the abutments and pontic were not cut back to eliminate any potential for chipping of the overlaying ceramic that would be applied during function. The cutback was limited to the facial aspects, the only area that would be visible once the bridge was inserted. The decision to make these 2 different bridge designs (a monolithic bridge with surface stain, or a bridge with intrinsic staining and more translucent incisal possible) would allow us and the patient to choose which aesthetic option blended better into his smile.

The CAD/CAM milled wax bridges were sprued (Figure 10) and invested in Celtra Press investment (Dentsply Sirona) and the bridges were pressed in shade A3 Celtra Press ceramic. Following pressing, the investment was removed from the sprued ceramic bridge (Figure 11) and the sprue was cut off the pressed bridges.

The monolithic bridge was stained with Celtra stain (Dentsply Sirona) to warm the gingival (cervical) portion; and violet and white stain were applied in the incisal area. Glaze was applied to the restoration and fired according to the manufacturer’s instructions. The cut-back bridge had Celtra stain applied in an A4 at the cervical, with off-white at the line angles. Other characterizations were also applied to the Celtra Press bridge frame and fired per manufacturer’s instructions (Figure 12). Celtra Ceram in a shade E2 (enamel) was applied over the internal staining on the Celtra Press ceramic to achieve the desired final contours, and then the restoration was fired per manufacturer’s instructions.

Delivery Appointment
When patient presented for insertion of the restoration, the provisional bridge was removed and any residual cement was removed from the preparations/margins. The monolithic Celtra Press bridge was tried in, and the patient was given a mirror to view this prosthesis and the alternative bridge option (Figure 13). Next, the layered Celtra Press bridge was tried in, and the patient gave his input as to which bridge he preferred (Figure 14). The patient indicated that he liked the layered bridge better due to the slight incisal translucency and the author agreed with his decision.

The teeth were isolated with cotton rolls, and the abutments were dried with cotton pellets. Then, an appropriate resin cement kit (Calibra Ceram [Dentsply Sirona]) was prepared for use. Prime&Bond Elect adhesive (Dentsply Sirona) was applied to the abutments with a microbrush to thoroughly wet all the tooth surfaces, then agitated for 20 seconds. Next, the adhesive on the preparations was air-thinned and then light-cured (Demi Ultra Cordless [Kerr]) for 10 seconds per abutment from the facial and lingual directions. The interior of the abutments on the bridge was air-dried, and then Calibra Ceram resin cement from the automix syringe was dispensed into the bridge and then seated. The margins were tack-cured with the curing light for 5 seconds, then excess cement was removed using an explorer. The abutments were then light-cured for 20 seconds from the facial and lingual of each abutment and then left alone for 4 minutes to complete the self-curing polymerization process. (This was done because there can be certain areas where the curing light may not have been able to penetrate.) After the cement was polymerized, the margins were finished using an extra-fine finishing diamond (No. 859 [Dentsply Sirona]). Lastly, the occlusion was checked and adjusted as needed (Figures 15 and 16).

Final Clinical Treatment
The patient returned at a subsequent visit to have caries removed from the cervical of the right first premolar, canine, lateral incisor, and left canine and first and second premolars, under local anesthetic. The teeth were isolated, acid-etched for 20 seconds, and then rinsed and dried. A strip of polytetrafluoroethylene tape was placed interproximally. Prime&Bond Elect was applied to the prepared surfaces and air-thinned, then light-cured for 20 seconds. A flowable composite (Esthet•X Flow (Dentsply Sirona) in shade A2 was placed into the cervical preparation area and light-cured. This was then overlaid with an aesthetic light-cured composite (Esthet•X HD Micro Matrix Restorative [Dentsply Sirona]) in shade A2 to cover the entire facial of the teeth being treated. This was done to correct the tooth’s shape and to optimize the facial aesthetics. The interproximal matrix was removed, and restorations were polished using a diamond polishing paste (Couture [Centrix Dental]) in a prophy cup.

The final bridge and direct composite restorations provided a natural aesthetic that improved our patient’s smile (Figure 17).

CLOSING COMMENTS
The ZLS ceramic described herein offers comparable aesthetics to the lithium disilicate and, per the authors’ clinical experience, is a reliable high-strength restoration that can be adhesively bonded. The option of using this material for monolithic or layered restorations is a plus for (thin) veneers, inlays/onlays, anterior or posterior single-unit full-coverage restorations, anterior 3-unit bridges, or certain posterior 3-unit bridges (per manufacturer’s indications), and as an all-ceramic implant abutment option.


References

  1. Rinke S, Rödiger M, Ziebolz D, et al. Fabrication of zirconia-reinforced lithium silicate ceramic restorations using a complete digital workflow. Case Rep Dent. 2015;2015:162178.
  2. Elsaka SE, Elnaghy AM. Mechanical properties of zirconia reinforced lithium silicate glass-ceramic. Dent Mater. 2016;32:908-914.
  3. Fabianelli A, Goracci C, Bertelli E, et al. A clinical trial of Empress II porcelain inlays luted to vital teeth with a dual-curing adhesive system and a self-curing resin cement. J Adhes Dent. 2006;8:427-431.
  4. Kang SH, Chang J, Son HH. Flexural strength and microstructure of two lithium disilicate glass ceramics for CAD/CAM restoration in the dental clinic. Restor Dent Endod. 2013;38:134-140.
  5. Matsuzaki F, Sekine H, Honma S, et al. Translucency and flexural strength of monolithic translucent zirconia and porcelain-layered zirconia. Dent Mater J. 2015;34:910-917.

Dr. Kurtzman is in private general practice in Silver Spring, Md. A former assistant clinical professor at University of Maryland, he has earned Fellowships in the AGD, American Academy of Implant Prosthodontics, American College of Dentists, International Congress of Oral Implantologists (ICOI), Pierre Fauchard Academy, and Association of Dental Implantology; Masterships in the AGD and ICOI; and Diplomate status in the ICOI and American Dental Implant Association. He has lectured internationally on the topics of restorative dentistry, endodontics, implant surgery and prosthetics, removable and fixed prosthetics, and periodontics, and he has published more than 540 articles. He has been included in Dentistry Today’s Leaders in Continuing Education directory since 2006. He can be reached via email at This email address is being protected from spambots. You need JavaScript enabled to view it..

Disclosure: Dr. Kurtzman reports no disclosures.

Mr. Moore is a certified dental technician with more than 39 years of experience. He owns and operates Aesthetic Restorations (AR) Lab in Hattiesburg, Miss, and collaborates with talented US doctors and clinicians to fabricate all aspects of permanent dental restorations, which routinely includes the production of large implant or full-mouth restorations. He also worked in-office, which allowed him the opportunity to be present chairside with patients and sharpen skills such as shade matching and communication. Mr. Moore’s current memberships include the following: American Academy of Cosmetic Dentistry, International Congress of Oral Implantologists, and various dental study clubs. He has worked closely with several dental schools, including University of North Carolina, Louisiana State University, School of Dentistry, University of Mississippi Medical Center, and the University of Florida (Apopka). He has taught or hosted small, informal hands-on clinics within his laboratory and enjoys sharing tips and insights with other technicians. He can be reached by calling (601) 261-9438.

Disclosure: Mr. Moore maintains a position as paid consultant for Dentsply Sirona.

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