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A Clinical Evaluation of Chairside Lithium Disilicate CAD/CAM Crowns: A Two-Year Report Dennis J. Fasbinder, Joseph B. Dennison, Donald Heys and Gisele Neiva JADA 2010;141(suppl 2):10S-14S 10.14219/jada.archive.2010.0355 The following resources related to this article are available online at jada.ada.org (this information is current as of December 21, 2014): Updated information and services including high-resolution figures, can be found in the online version of this article at: http://jada.ada.org/content/141/suppl_2/10S
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A clinical evaluation of chairside lithium disilicate CAD/CAM crowns A two-year report Dennis J. Fasbinder, DDS; Joseph B. Dennison, DDS, MS; Donald Heys, DDS, MS; Gisele Neiva, DDS, MS
here has been a growing interest in the use of all-ceramic restorations as replacements for traditional porcelain-fused-to-metal restorations because of their improved esthetic appearance. Developments in ceramic material science have resulted in improvements in the physical properties of modern ceramics, leading to a substantial increase in the clinical use of all-ceramic restorations. Ivoclar Vivadent (Amherst, N.Y.) introduced a lithium disilicate glass ceramic material for use in allceramic restorations. It is available as an ingot that can be press-fit (IPS e.max Press, Ivoclar Vivadent) and as a block that can be milled with computer-aided design/computer-aided manufacturing (CAD/CAM) technology (IPS e.max CAD, Ivoclar Vivadent).1 The manufacturer recommends its use for anterior or posterior crowns, implant crowns, inlays, onlays or veneers. The CAD/CAM material initially was available as a substructure material that afforded greater translucency than did other high-strength ceramic core materials. Although initially indicated for substructures, the CAD/CAM block has been used more recently for full-contour restorations of a single ceramic material (monolithic restorations). The milled lithium disilicate block must undergo a two-stage crystallization process before cementation. Lithium metasilicate crystals are precipitated during the first stage. The resulting glass ceramic has a crystal size range of 0.2 to 1.0 micrometers, with approximately 40 percent lithium metasilicate crystals by volume. This creates a blue-violet color in the block, thus accounting for the commonly used “blue block” description. This precrystallized state allows the block to be milled easily without excessive diamond bur wear or damage to the material. The final crystallization occurs after the crown has been milled to the desired form by means of CAD/ CAM technology. The crystallization process occurs at 850˚C in a vacuum. The metasilicate crystal phase is dissolved completely, and the lithium disilicate crystallizes. This process also converts the blue shade of the precrystallized block to the selected tooth shade and results in a glass ceramic with a fine-grained size of approximately 1.5 µm and a 70 percent crystal volume incorporated in a glass matrix.2 Clinicians can use the CEREC Acquisition Center system (Sirona Dental Systems, Charlotte, N.C.) or the
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ABSTRACT Background. Developments in ceramic material science have led to improvements in the physical properties of modern ceramics, leading to a substantial increase in the clinical use of all-ceramic restorations. The authors evaluated the clinical performance of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent, Amherst, N.Y.) all-ceramic crowns. Methods. The authors fabricated 62 lithium disilicate crowns with a chairside computer-aided design/ computer-aided manufacturing (CAD/CAM) system (CEREC 3, Sirona Dental Systems, Charlotte, N.C.) and cemented them with two types of adhesive resin cements. Two examiners used modified U.S. Public Health Service criteria to evaluate the crowns at baseline, six months, one year and two years. Results. There were no clinically identified cases of crown fracture or surface chipping. There was no reported sensitivity at one or two years with either cement. For margin discoloration, the percentage Alfa score was 86.9 percent for crowns cemented with a self-etching, dual-curing cement. All other percentage Alfa scores were greater than 92.0 percent, indicating no appreciable change in the crowns during the two-year study. Conclusions. The results show that lithium disilicate crowns performed well after two years of clinical service. Clinical Implications. Early results indicate that monolithic lithium disilicate CAD/CAM crowns may be an effective option for all-ceramic crowns. Key Words. CAD/CAM; crowns; cementation; dental porcelain; dental restoration. JADA 2010;141(6 suppl):10S-14S.
Dr. Fasbinder is a clinical professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, 1011 N. University, Ann Arbor, Mich. 48109-1078, e-mail “[email protected]”. Address reprint requests to Dr. Fasbinder. Dr. Dennison is a professor emeritus, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor. Dr. Heys is a professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor. Dr. Neiva is a clinical associate professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor.
June 2010
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E4D Dentist system (D4D Technologies, Richardson, Texas) to fabricate full-contour lithium disilicate crowns chairside. The CAD/CAM process gives clinicians the opportunity to mill the crown from monolithic blocks of lithium disilicate rather than the traditional laboratory process of fabricating a strong substructure veneered with weaker veneering porcelain. The IPS e.max CAD glass ceramic has a flexural strength of 360 to 400 megapascals, which is approximately two-and-one-half times greater than that of other monolithic ceramic blocks available for CAD/CAM chairside restoration fabrication.2,3 The enhanced strength of lithium disilicate allows for either adhesive or conventional cementation techniques. We conducted a nonrandomized longitudinal clinical trial to evaluate the clinical performance of the IPS e.max CAD glass ceramic material for chairside CAD/CAM-generated crowns cemented with two different cements. PARTICIPANTS, METHODS AND MATERIALS
The Health Sciences Institutional Review Board of the University of Michigan reviewed and approved the investigation protocol before the study began. We selected the participants from among current patients receiving clinical treatment at the School of Dentistry, University of Michigan, Ann Arbor. All of the participants signed a written informed consent form before enrolling in the study. All teeth were asymptomatic at the beginning of treatment. Participants received a maximum of two crowns, and all restorations had opposing functional occlusion and at least one proximal contact with an adjacent tooth. We did not exclude patients with specific occlusal schemes or parafunctional habits. Preparation. The clinician prepared, fabricated and placed all of the crowns in one treatment appointment. The clinician prepared the tooth by following the manufacturer’s guidelines for all-ceramic crowns with at least 2.0 millimeters of occlusal reduction over functional cusps, at least 1.5 mm of reduction over nonfunctional cusps and in the central fossa at least 1.2 mm of axial reduction, rounded shoulder margins and no sharp internal angles. For teeth with substantial loss of tooth structure resulting from caries or fracture, the clinician used composite cores (ExciTE F DSC and MultiCore, Ivoclar Vivadent) to create the required retention and resistance form. We used a dryfield illuminator (Isolite i2, Isolite Systems, Santa Barbara, Calif.) to isolate the quadrant during all clinical procedures.
Restoration fabrication. We fabricated all crowns with a CEREC 3 system (Sirona Dental Systems). The clinician used software (CEREC 3D, Version 2.8, Sirona Dental Systems) to design the desired crown contours and occlusal relationships. The clinician milled the crown from prefabricated block of IPS e.max CAD at standard milling speed. After recovering the crown from the milling chamber, the clinician trial fitted it to the preparation with a silicone material (Fit Checker, GC America, Alsip, Ill.) to stabilize the crown and adjusted it to ensure complete seating. After finalizing adjustments, the clinician thoroughly cleaned and dried the crown and then applied e.max CAD Crystall./Glaze paste (Ivoclar Vivadent) with shade tints to customize the crown’s shade relative to the existing dentition. The crown was fired in a porcelain oven under vacuum, according to the manufacturer’s instructions, to complete the crystallization process. The firing cycle consisted of two stages that required 35 minutes (however, it since has been reduced with the development of a spray glaze). Restoration cementation. When the crown was ready for cementation, the internal surface was etched for 20 seconds with 4.9 percent hydrofluoric acid, rinsed with water and air-dried with oil-free air. The dental assistant applied a prehydrolyzed silane coupling agent (Monobond-S, Ivoclar Vivadent) to the etched surface for 60 seconds and ensured evaporation of the solvent before adhesive cementation. The first group of 23 crowns (control) was cemented with a self-etching, dual-curing cement (Multilink Automix [MA], Ivoclar Vivadent) with a self-etching primer and adhesive. The second group of 39 crowns was cemented with an experimental self-adhesive, dual-curing cement (EC) developed by Ivoclar Vivadent. For the crowns cemented with MA, the clinician cleaned the isolated preparation with flour of pumice, rinsed it with water spray and lightly air dried it. The clinician treated the preparation for 15 seconds with Multilink Primer A and B (Ivoclar Vivadent) and lightly air dried it with the air-water syringe. An automix syringe was used to inject a 1:1 ratio of MA base and catalyst ABBREVIATION KEY. CAD/CAM: Computer-aided design/computer-aided manufacturing. EC: Experimental cement. FPD: Fixed partial denture. MA: Multilink Automix (Ivoclar Vivadent, Amherst, N.Y.). USPHS: U.S. Public Health Service. JADA, Vol. 141
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Figure 1. Preoperative occlusal view of teeth nos. 19 and 20.
Figure 2. Placement of the lithium disilicate crowns on teeth nos. 19 and 20 at baseline evaluation.
Postoperative sensitivity. To evaluate the postoperative sensitivity, the study coordinator contacted participants by telephone once per week after the initial appointment and for as long as four weeks or until the participant reported that the crown was asymptomatic. During the telephone interview, the participants reported a criterion-referenced rating of functional tooth sensitivity. Participants returned for evaluation only if they were having continued discomfort or any indication of premature occlusal contact. Restoration evaluation. Two independent evaluators conducted clinical evaluations at baseline (immediately after the crowns were cemented), six months, one year and two years by using modified U.S. Public Health Service (USPHS) criteria4 for color match, margin discoloration, margin adaptation, caries and crown fracture. The two evaluators discussed disagreements in evaluations to reach a consensus judgment for each criterion evaluated. The evaluators obtained intraoral digital color images at a 1:1 magnification at baseline and at the six-month, one-year and two-year recall visits to document preoperative status and postoperative conditions (Figures 1-5). Bitewing and periapical radiographs of each crown were obtained preoperatively and at the two-year recall visit. RESULTS
Figure 3. Crowns for teeth nos. 19 and 20 at the two-year recall visit.
directly into the crown. The clinician inserted the crown and removed the excess cement after two minutes. The crown was light cured for 20 seconds each from the facial, occlusal and lingual aspects, for a total of 60 seconds. For the crowns cemented with EC, the clinician cleaned the isolated preparation with flour of pumice, rinsed it and lightly air dried it. An automix syringe was used to inject a 1:1 ratio of EC base and catalyst directly into the crown. The clinician inserted the crown and removed the excess cement after two minutes. The crown was light cured for 20 seconds each from the facial, occlusal and lingual aspects, for a total of 60 seconds. The clinician finished and polished all the crowns by using a series of diamond finishing burs, rubber abrasive points and cups, finishing strips and diamond polishing paste. 12S
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Forty-three participants enrolled in the study. They received 62 crowns, including 20 on premolars and 42 on molars. The six-month and oneyear recall rates were 100.0 percent. The two-year recall rate was 98.4 percent because one participant had moved out of the area. One week postoperatively, the participants described 13.0 percent (three of 23) of the crowns cemented with MA and 10.3 percent (four of 39) of the crowns cemented with EC as slightly sensitive. However, all participants reported not having symptoms by the third week after treatment. At six months, the participants reported that 8.7 percent (two of 23) of the crowns cemented with MA and 7.7 percent (three of 39) of the crowns cemented with EC were slightly sensitive. No participants required treatment for sensitivity. There was no reported sensitivity at one year or two years. The table shows the percentage Alfa scores for each of the modified USPHS criteria. Margin discoloration was 86.9 percent Alfa for crowns cemented with MA because three crowns had localized margin discoloration. All other scores were greater
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Figure 4. Preoperative occlusal views of teeth nos. 3 and 4.
Figure 5. Lithium disilicate crowns for teeth nos. 3 and 4 at the two-year recall visit.
than 92.0 percent Alfa, indicating no appreciable change in the crowns during the two years of the study. All of the crowns cemented with MA were clinically acceptable at two years. Two crowns cemented with EC debonded: one at one year and the other at two years. Both of the debonded crowns were intact, and the treating clinician used MA to recement them.
with surface porcelain. There was no significant difference between the two crown types for any of the USPHS scores. One of the monolithic ceramic crowns fractured at 12.0 months, and one of the layered ceramic crowns fractured at 42.5 months. The Kaplan-Meier probability for survival was 91.7 percent for the layered ceramic crowns and 94.4 percent for the monolithic ceramic crowns after a mean ± standard deviation of 44.7 ± 10.3 months. Bindl and colleagues11 compared 208 monolithic posterior ceramic crowns on the basis of the tooth type and three types of crown preparation designs: reduced, classic or “endo.” Only two crowns in the reduced preparation group fractured after two years, with no fractures in the classic or endo preparation groups. By 55 months, two crowns in the classic preparation group fractured, and three more from the reduced preparation group fractured. After 55 ± 15 months, the investigators reported a Kaplan-Meier probability of survival for premolars of 97.0 percent for those in the classic preparation group, 92.9 percent for those in the reduced preparation group and 68.8 percent for those in the endo preparation group. For molars, they reported a Kaplan-Meier probability of survival of 94.6 percent for those in the classic preparation group, 92.1 percent for those in the reduced preparation group and 87.1 percent for those in the endo preparation group. These study results support the assertion that monolithic ceramic crowns have good success across five years of clinical service. The results from comprehensive and systematic reviews indicated that the five-year survival rate of all-ceramic crowns was greater than 93 percent.12-14 The most common mode of failure for all-ceramic restorations reported in the comprehensive and systematic reviews was complete fracture of the substructure, the veneer porcelain or both, requiring the layered all-ceramic crown to be remade.12-14 The most common minor problem was chipping or cracking limited to the veneer porce-
DISCUSSION
There are limited clinical studies of an early version of lithium disilicate glass ceramic. IPS Empress 2 (Ivoclar Vivadent) was a lithium disilicate glass ceramic fabricated by means of a lost-wax and heatpressed technique. The substructure was veneered with fluorapatite-based porcelain. Marquardt and Strub7 evaluated 58 IPS Empress 2 restorations (27 posterior crowns and 31 three-unit fixed partial dentures [FPDs]) after five years of clinical service. Two of the crowns had repairable fractures in the veneering porcelain. Six complete failures occurred within the FPDs. Taskonak and Sertgöz8 evaluated 20 IPS Empress 2 crowns and 20 FPDs after two years. They reported no crown fractures and 10 failures with the FPDs. This early lithium disilicate is not the same material as IPS e.max CAD or IPS e.max Press ceramics. There is a substantial difference in the microstructure of the lithium disilicate crystals and the matrix, resulting in improved physical properties and translucency of the IPS e.max lithium disilicate.9 There are few published clinical studies of monolithic ceramic crowns. Bindl and Mörmann10 compared monolithic ceramic crowns (Vitablocs Mark II, Vident, Brea, Calif.) with layered ceramic crowns (Vita In-Ceram Spinell, Vident). The monolithic ceramic crowns were fabricated with a CEREC 2 (Sirona Dental Systems) unit. The substructures of the layered ceramic crowns were milled with a CEREC 2 unit and then veneered
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TABLE
Percentage Alfa scores for CAD/CAM lithium disilicate all-ceramic crowns, according to recall visit. CRITERION
SIX-MONTH ONE-YEAR TWO-YEAR RECALL VISIT RECALL VISIT RECALL VISIT (ALFA SCORE %) (ALFA SCORE %) (ALFA SCORE %)
Color Match Margin Discoloration
MA * 95.6
EC † 92.3
MA 95.6
EC 94.9
MA 100.0
95.6
97.4
86.9
97.4
87.0
Margin Adaptation
100.0
100.0
100.0
100.0
100.0
Caries
100.0
100.0
100.0
100.0
100.0
Crown Fracture
100.0
100.0
100.0
100.0
100.0
* MA: Multilink Automix, Ivoclar Vivadent, Amherst, N.Y. † EC: Experimental cement.
lain.12-14 In contrast, in our study, there were no identified cases of fracture or surface chipping of the lithium disilicate crowns through the two-year period. Although two years is early in the desired clinical life span of a crown, this is a potentially clinically significant finding. Bilayered ceramic crowns consisting of a strong ceramic core veneered with a weaker surface porcelain generally experience chipping, fracture or delamination of the veneering porcelain on between 3 and 5 percent of the surface during the first five years of the clinical life span of the crown.12-14 Although a monolithic crown design might help clinicians avoid any potential problems inherent in a bilayered system, additional long-term clinical study is required to further document this finding from our study. The bond of self-adhesive resin cements to dentin is similar to that of self-etching systems; however, they do not have the same bond strength to enamel.5,6 Eight of the 39 crowns (20.5 percent) cemented with EC exhibited graying of the cervical one-half of the crown on the facial and lingual surfaces. This discoloration did not manifest as the typical dark linear stain commonly seen with marginal leakage and was not evaluated using the modified USPHS criterion for margin discoloration. None of the crowns with this discoloration exhibited any sensitivity. Two of the 39 crowns (5.1 percent) cemented with EC debonded, revealing that the discoloration was between the cement and tooth preparation. In both cases of debonding, there was no evidence of cement retained on the tooth surface—it was retained on the crown—and there was no damage to the lithium disilicate crowns. The clinician cleaned the cement from the internal aspect of the crowns, re-etched them with a hydrofluoric acid, applied a silane coupler and recemented them with MA. Although the evaluators classified these cases 14S
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as cement failures, we will continue to recall the participants so we can evaluate long-term survival of the ceramic material. CONCLUSIONS
We evaluated the clinical performance of the IPS e.max CAD ceramic crowns EC cemented with two different adhesive 97.2 97.2 resin cements. There were no clinically 100.0 identified cases of crown fracture or 100.0 surface chipping. There were no reports 100.0 of postoperative sensitivity for any of the crowns at the one- and two-year recall visits. The results show that lithium disilicate crowns perform well after two years of clinical service. ■
Disclosure. Dr. Fasbinder has received honoraria for educational programs and research funding for projects with the CEREC system from Sirona Dental Systems, Charlotte, N.C.; and Ivoclar Vivadent, Amherst, N.Y. This study was funded through a research grant from Ivoclar Vivadent, Amherst, N.Y. 1. Tysowsky G. The science behind lithium disilicate: today’s surprisingly versatile, esthetic & durable metal-free alternative. Oral Health J 2009;March:93-97. 2. Ivoclar Vivadent. IPS e.max Lithium Disilicate: The Future of AllCeramic Dentistry—Material Science, Practical Applications, Keys to Success. Amherst, N.Y.: Ivoclar Vivadent; 2009:1-15. 3. Giordano R. Materials for chairside CAD/CAM-produced restorations. JADA 2006;137(9 suppl):14S-21S. 4. Cvar JF, Ryge G. Criteria for the clinical evaluation of dental restorative materials. San Francisco: U.S. Department of Health, Education and Welfare, Public Health Service, National Institutes of Health; 1971. USPHS publication 790-244. 5. Hikita K, Van Meerbeek B, De Munck J, et al. Bonding effectiveness of adhesive luting agents to enamel and dentin. Dent Mater 2007;23(1):71-80. 6. Walter R, Miguez PA, Pereira PN. Microtensile bond strength of luting materials to coronal and root dentin. J Esthet Restor Dent 2005;17(3):165-171; discussion 171. 7. Marquardt P, Strub JR. Survival rates of IPS empress 2 all-ceramic crowns and fixed partial dentures: results of a 5-year prospective clinical study. Quintessence Int 2006;37(4):253-259. 8. Taskonak B, Sertgöz A. Two-year clinical evaluation of lithiadisilicate-based all-ceramic crowns and fixed partial dentures. Dent Mater 2006;22(11):1008-1013. 9. Stappert CF, Att W, Gerds T, Strub JR. Fracture resistance of different partial-coverage ceramic molar restorations: an in vitro investigation. JADA 2006;137(4):514-522. 10. Bindl A, Mörmann WH. Survival rate of mono-ceramic and ceramic-core CAD/CAM-generated anterior crowns over 2-5 years. Eur J Oral Sci 2004;112(2):197-204. 11. Bindl A, Richter B, Mörmann WH. Survival of ceramic computeraided design/manufacturing crowns bonded to preparations with reduced macroretention geometry. Int J Prosthodont 2005;18(3):219-224. 12. Conrad HJ, Seong WJ, Pesun IJ. Current ceramic materials and systems with clinical recommendations: a systematic review. J Prosthet Dent 2007;98(5):389-404. 13. Della Bona A, Kelly JR. The clinical success of all-ceramic restorations. JADA 2008;139(9 suppl):8S-13S. 14. Pjetursson B, Sailer I, Zwahlen M, Hämmerle C. A systematic review of the survival and complication rates of all-ceramic and metalceramic reconstructions after an observation period of at least three years, part I: single crowns (published correction appears in Clin Oral Implants Res 2008;19[3]:326-328). Clin Oral Implants Res 2007;18(suppl 3):73-85.
June 2010
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A Clinical Evaluation of Chairside Lithium Disilicate CAD/CAM Crowns: A Two-Year Report Dennis J. Fasbinder, Joseph B. Dennison, Donald Heys and Gisele Neiva JADA 2010;141(suppl 2):10S-14S 10.14219/jada.archive.2010.0355 The following resources related to this article are available online at jada.ada.org (this information is current as of December 21, 2014): Updated information and services including high-resolution figures, can be found in the online version of this article at: http://jada.ada.org/content/141/suppl_2/10S
This article cites 11 articles, 3 of which can be accessed free: http://jada.ada.org/content/141/suppl_2/10S/#BIBL Information about obtaining reprints of this article or about permission to reproduce this article in whole or in part can be found at: http://www.ada.org/990.aspx
Copyright © 2014 American Dental Association. All rights reserved. Reproduction or republication strictly prohibited without prior written permission of the American Dental Association.
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A clinical evaluation of chairside lithium disilicate CAD/CAM crowns A two-year report Dennis J. Fasbinder, DDS; Joseph B. Dennison, DDS, MS; Donald Heys, DDS, MS; Gisele Neiva, DDS, MS
here has been a growing interest in the use of all-ceramic restorations as replacements for traditional porcelain-fused-to-metal restorations because of their improved esthetic appearance. Developments in ceramic material science have resulted in improvements in the physical properties of modern ceramics, leading to a substantial increase in the clinical use of all-ceramic restorations. Ivoclar Vivadent (Amherst, N.Y.) introduced a lithium disilicate glass ceramic material for use in allceramic restorations. It is available as an ingot that can be press-fit (IPS e.max Press, Ivoclar Vivadent) and as a block that can be milled with computer-aided design/computer-aided manufacturing (CAD/CAM) technology (IPS e.max CAD, Ivoclar Vivadent).1 The manufacturer recommends its use for anterior or posterior crowns, implant crowns, inlays, onlays or veneers. The CAD/CAM material initially was available as a substructure material that afforded greater translucency than did other high-strength ceramic core materials. Although initially indicated for substructures, the CAD/CAM block has been used more recently for full-contour restorations of a single ceramic material (monolithic restorations). The milled lithium disilicate block must undergo a two-stage crystallization process before cementation. Lithium metasilicate crystals are precipitated during the first stage. The resulting glass ceramic has a crystal size range of 0.2 to 1.0 micrometers, with approximately 40 percent lithium metasilicate crystals by volume. This creates a blue-violet color in the block, thus accounting for the commonly used “blue block” description. This precrystallized state allows the block to be milled easily without excessive diamond bur wear or damage to the material. The final crystallization occurs after the crown has been milled to the desired form by means of CAD/ CAM technology. The crystallization process occurs at 850˚C in a vacuum. The metasilicate crystal phase is dissolved completely, and the lithium disilicate crystallizes. This process also converts the blue shade of the precrystallized block to the selected tooth shade and results in a glass ceramic with a fine-grained size of approximately 1.5 µm and a 70 percent crystal volume incorporated in a glass matrix.2 Clinicians can use the CEREC Acquisition Center system (Sirona Dental Systems, Charlotte, N.C.) or the
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ABSTRACT Background. Developments in ceramic material science have led to improvements in the physical properties of modern ceramics, leading to a substantial increase in the clinical use of all-ceramic restorations. The authors evaluated the clinical performance of lithium disilicate (IPS e.max CAD, Ivoclar Vivadent, Amherst, N.Y.) all-ceramic crowns. Methods. The authors fabricated 62 lithium disilicate crowns with a chairside computer-aided design/ computer-aided manufacturing (CAD/CAM) system (CEREC 3, Sirona Dental Systems, Charlotte, N.C.) and cemented them with two types of adhesive resin cements. Two examiners used modified U.S. Public Health Service criteria to evaluate the crowns at baseline, six months, one year and two years. Results. There were no clinically identified cases of crown fracture or surface chipping. There was no reported sensitivity at one or two years with either cement. For margin discoloration, the percentage Alfa score was 86.9 percent for crowns cemented with a self-etching, dual-curing cement. All other percentage Alfa scores were greater than 92.0 percent, indicating no appreciable change in the crowns during the two-year study. Conclusions. The results show that lithium disilicate crowns performed well after two years of clinical service. Clinical Implications. Early results indicate that monolithic lithium disilicate CAD/CAM crowns may be an effective option for all-ceramic crowns. Key Words. CAD/CAM; crowns; cementation; dental porcelain; dental restoration. JADA 2010;141(6 suppl):10S-14S.
Dr. Fasbinder is a clinical professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, 1011 N. University, Ann Arbor, Mich. 48109-1078, e-mail “[email protected]”. Address reprint requests to Dr. Fasbinder. Dr. Dennison is a professor emeritus, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor. Dr. Heys is a professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor. Dr. Neiva is a clinical associate professor, Cariology, Restorative Sciences, and Endodontics, School of Dentistry, University of Michigan, Ann Arbor.
June 2010
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E4D Dentist system (D4D Technologies, Richardson, Texas) to fabricate full-contour lithium disilicate crowns chairside. The CAD/CAM process gives clinicians the opportunity to mill the crown from monolithic blocks of lithium disilicate rather than the traditional laboratory process of fabricating a strong substructure veneered with weaker veneering porcelain. The IPS e.max CAD glass ceramic has a flexural strength of 360 to 400 megapascals, which is approximately two-and-one-half times greater than that of other monolithic ceramic blocks available for CAD/CAM chairside restoration fabrication.2,3 The enhanced strength of lithium disilicate allows for either adhesive or conventional cementation techniques. We conducted a nonrandomized longitudinal clinical trial to evaluate the clinical performance of the IPS e.max CAD glass ceramic material for chairside CAD/CAM-generated crowns cemented with two different cements. PARTICIPANTS, METHODS AND MATERIALS
The Health Sciences Institutional Review Board of the University of Michigan reviewed and approved the investigation protocol before the study began. We selected the participants from among current patients receiving clinical treatment at the School of Dentistry, University of Michigan, Ann Arbor. All of the participants signed a written informed consent form before enrolling in the study. All teeth were asymptomatic at the beginning of treatment. Participants received a maximum of two crowns, and all restorations had opposing functional occlusion and at least one proximal contact with an adjacent tooth. We did not exclude patients with specific occlusal schemes or parafunctional habits. Preparation. The clinician prepared, fabricated and placed all of the crowns in one treatment appointment. The clinician prepared the tooth by following the manufacturer’s guidelines for all-ceramic crowns with at least 2.0 millimeters of occlusal reduction over functional cusps, at least 1.5 mm of reduction over nonfunctional cusps and in the central fossa at least 1.2 mm of axial reduction, rounded shoulder margins and no sharp internal angles. For teeth with substantial loss of tooth structure resulting from caries or fracture, the clinician used composite cores (ExciTE F DSC and MultiCore, Ivoclar Vivadent) to create the required retention and resistance form. We used a dryfield illuminator (Isolite i2, Isolite Systems, Santa Barbara, Calif.) to isolate the quadrant during all clinical procedures.
Restoration fabrication. We fabricated all crowns with a CEREC 3 system (Sirona Dental Systems). The clinician used software (CEREC 3D, Version 2.8, Sirona Dental Systems) to design the desired crown contours and occlusal relationships. The clinician milled the crown from prefabricated block of IPS e.max CAD at standard milling speed. After recovering the crown from the milling chamber, the clinician trial fitted it to the preparation with a silicone material (Fit Checker, GC America, Alsip, Ill.) to stabilize the crown and adjusted it to ensure complete seating. After finalizing adjustments, the clinician thoroughly cleaned and dried the crown and then applied e.max CAD Crystall./Glaze paste (Ivoclar Vivadent) with shade tints to customize the crown’s shade relative to the existing dentition. The crown was fired in a porcelain oven under vacuum, according to the manufacturer’s instructions, to complete the crystallization process. The firing cycle consisted of two stages that required 35 minutes (however, it since has been reduced with the development of a spray glaze). Restoration cementation. When the crown was ready for cementation, the internal surface was etched for 20 seconds with 4.9 percent hydrofluoric acid, rinsed with water and air-dried with oil-free air. The dental assistant applied a prehydrolyzed silane coupling agent (Monobond-S, Ivoclar Vivadent) to the etched surface for 60 seconds and ensured evaporation of the solvent before adhesive cementation. The first group of 23 crowns (control) was cemented with a self-etching, dual-curing cement (Multilink Automix [MA], Ivoclar Vivadent) with a self-etching primer and adhesive. The second group of 39 crowns was cemented with an experimental self-adhesive, dual-curing cement (EC) developed by Ivoclar Vivadent. For the crowns cemented with MA, the clinician cleaned the isolated preparation with flour of pumice, rinsed it with water spray and lightly air dried it. The clinician treated the preparation for 15 seconds with Multilink Primer A and B (Ivoclar Vivadent) and lightly air dried it with the air-water syringe. An automix syringe was used to inject a 1:1 ratio of MA base and catalyst ABBREVIATION KEY. CAD/CAM: Computer-aided design/computer-aided manufacturing. EC: Experimental cement. FPD: Fixed partial denture. MA: Multilink Automix (Ivoclar Vivadent, Amherst, N.Y.). USPHS: U.S. Public Health Service. JADA, Vol. 141
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Figure 1. Preoperative occlusal view of teeth nos. 19 and 20.
Figure 2. Placement of the lithium disilicate crowns on teeth nos. 19 and 20 at baseline evaluation.
Postoperative sensitivity. To evaluate the postoperative sensitivity, the study coordinator contacted participants by telephone once per week after the initial appointment and for as long as four weeks or until the participant reported that the crown was asymptomatic. During the telephone interview, the participants reported a criterion-referenced rating of functional tooth sensitivity. Participants returned for evaluation only if they were having continued discomfort or any indication of premature occlusal contact. Restoration evaluation. Two independent evaluators conducted clinical evaluations at baseline (immediately after the crowns were cemented), six months, one year and two years by using modified U.S. Public Health Service (USPHS) criteria4 for color match, margin discoloration, margin adaptation, caries and crown fracture. The two evaluators discussed disagreements in evaluations to reach a consensus judgment for each criterion evaluated. The evaluators obtained intraoral digital color images at a 1:1 magnification at baseline and at the six-month, one-year and two-year recall visits to document preoperative status and postoperative conditions (Figures 1-5). Bitewing and periapical radiographs of each crown were obtained preoperatively and at the two-year recall visit. RESULTS
Figure 3. Crowns for teeth nos. 19 and 20 at the two-year recall visit.
directly into the crown. The clinician inserted the crown and removed the excess cement after two minutes. The crown was light cured for 20 seconds each from the facial, occlusal and lingual aspects, for a total of 60 seconds. For the crowns cemented with EC, the clinician cleaned the isolated preparation with flour of pumice, rinsed it and lightly air dried it. An automix syringe was used to inject a 1:1 ratio of EC base and catalyst directly into the crown. The clinician inserted the crown and removed the excess cement after two minutes. The crown was light cured for 20 seconds each from the facial, occlusal and lingual aspects, for a total of 60 seconds. The clinician finished and polished all the crowns by using a series of diamond finishing burs, rubber abrasive points and cups, finishing strips and diamond polishing paste. 12S
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Forty-three participants enrolled in the study. They received 62 crowns, including 20 on premolars and 42 on molars. The six-month and oneyear recall rates were 100.0 percent. The two-year recall rate was 98.4 percent because one participant had moved out of the area. One week postoperatively, the participants described 13.0 percent (three of 23) of the crowns cemented with MA and 10.3 percent (four of 39) of the crowns cemented with EC as slightly sensitive. However, all participants reported not having symptoms by the third week after treatment. At six months, the participants reported that 8.7 percent (two of 23) of the crowns cemented with MA and 7.7 percent (three of 39) of the crowns cemented with EC were slightly sensitive. No participants required treatment for sensitivity. There was no reported sensitivity at one year or two years. The table shows the percentage Alfa scores for each of the modified USPHS criteria. Margin discoloration was 86.9 percent Alfa for crowns cemented with MA because three crowns had localized margin discoloration. All other scores were greater
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Figure 4. Preoperative occlusal views of teeth nos. 3 and 4.
Figure 5. Lithium disilicate crowns for teeth nos. 3 and 4 at the two-year recall visit.
than 92.0 percent Alfa, indicating no appreciable change in the crowns during the two years of the study. All of the crowns cemented with MA were clinically acceptable at two years. Two crowns cemented with EC debonded: one at one year and the other at two years. Both of the debonded crowns were intact, and the treating clinician used MA to recement them.
with surface porcelain. There was no significant difference between the two crown types for any of the USPHS scores. One of the monolithic ceramic crowns fractured at 12.0 months, and one of the layered ceramic crowns fractured at 42.5 months. The Kaplan-Meier probability for survival was 91.7 percent for the layered ceramic crowns and 94.4 percent for the monolithic ceramic crowns after a mean ± standard deviation of 44.7 ± 10.3 months. Bindl and colleagues11 compared 208 monolithic posterior ceramic crowns on the basis of the tooth type and three types of crown preparation designs: reduced, classic or “endo.” Only two crowns in the reduced preparation group fractured after two years, with no fractures in the classic or endo preparation groups. By 55 months, two crowns in the classic preparation group fractured, and three more from the reduced preparation group fractured. After 55 ± 15 months, the investigators reported a Kaplan-Meier probability of survival for premolars of 97.0 percent for those in the classic preparation group, 92.9 percent for those in the reduced preparation group and 68.8 percent for those in the endo preparation group. For molars, they reported a Kaplan-Meier probability of survival of 94.6 percent for those in the classic preparation group, 92.1 percent for those in the reduced preparation group and 87.1 percent for those in the endo preparation group. These study results support the assertion that monolithic ceramic crowns have good success across five years of clinical service. The results from comprehensive and systematic reviews indicated that the five-year survival rate of all-ceramic crowns was greater than 93 percent.12-14 The most common mode of failure for all-ceramic restorations reported in the comprehensive and systematic reviews was complete fracture of the substructure, the veneer porcelain or both, requiring the layered all-ceramic crown to be remade.12-14 The most common minor problem was chipping or cracking limited to the veneer porce-
DISCUSSION
There are limited clinical studies of an early version of lithium disilicate glass ceramic. IPS Empress 2 (Ivoclar Vivadent) was a lithium disilicate glass ceramic fabricated by means of a lost-wax and heatpressed technique. The substructure was veneered with fluorapatite-based porcelain. Marquardt and Strub7 evaluated 58 IPS Empress 2 restorations (27 posterior crowns and 31 three-unit fixed partial dentures [FPDs]) after five years of clinical service. Two of the crowns had repairable fractures in the veneering porcelain. Six complete failures occurred within the FPDs. Taskonak and Sertgöz8 evaluated 20 IPS Empress 2 crowns and 20 FPDs after two years. They reported no crown fractures and 10 failures with the FPDs. This early lithium disilicate is not the same material as IPS e.max CAD or IPS e.max Press ceramics. There is a substantial difference in the microstructure of the lithium disilicate crystals and the matrix, resulting in improved physical properties and translucency of the IPS e.max lithium disilicate.9 There are few published clinical studies of monolithic ceramic crowns. Bindl and Mörmann10 compared monolithic ceramic crowns (Vitablocs Mark II, Vident, Brea, Calif.) with layered ceramic crowns (Vita In-Ceram Spinell, Vident). The monolithic ceramic crowns were fabricated with a CEREC 2 (Sirona Dental Systems) unit. The substructures of the layered ceramic crowns were milled with a CEREC 2 unit and then veneered
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TABLE
Percentage Alfa scores for CAD/CAM lithium disilicate all-ceramic crowns, according to recall visit. CRITERION
SIX-MONTH ONE-YEAR TWO-YEAR RECALL VISIT RECALL VISIT RECALL VISIT (ALFA SCORE %) (ALFA SCORE %) (ALFA SCORE %)
Color Match Margin Discoloration
MA * 95.6
EC † 92.3
MA 95.6
EC 94.9
MA 100.0
95.6
97.4
86.9
97.4
87.0
Margin Adaptation
100.0
100.0
100.0
100.0
100.0
Caries
100.0
100.0
100.0
100.0
100.0
Crown Fracture
100.0
100.0
100.0
100.0
100.0
* MA: Multilink Automix, Ivoclar Vivadent, Amherst, N.Y. † EC: Experimental cement.
lain.12-14 In contrast, in our study, there were no identified cases of fracture or surface chipping of the lithium disilicate crowns through the two-year period. Although two years is early in the desired clinical life span of a crown, this is a potentially clinically significant finding. Bilayered ceramic crowns consisting of a strong ceramic core veneered with a weaker surface porcelain generally experience chipping, fracture or delamination of the veneering porcelain on between 3 and 5 percent of the surface during the first five years of the clinical life span of the crown.12-14 Although a monolithic crown design might help clinicians avoid any potential problems inherent in a bilayered system, additional long-term clinical study is required to further document this finding from our study. The bond of self-adhesive resin cements to dentin is similar to that of self-etching systems; however, they do not have the same bond strength to enamel.5,6 Eight of the 39 crowns (20.5 percent) cemented with EC exhibited graying of the cervical one-half of the crown on the facial and lingual surfaces. This discoloration did not manifest as the typical dark linear stain commonly seen with marginal leakage and was not evaluated using the modified USPHS criterion for margin discoloration. None of the crowns with this discoloration exhibited any sensitivity. Two of the 39 crowns (5.1 percent) cemented with EC debonded, revealing that the discoloration was between the cement and tooth preparation. In both cases of debonding, there was no evidence of cement retained on the tooth surface—it was retained on the crown—and there was no damage to the lithium disilicate crowns. The clinician cleaned the cement from the internal aspect of the crowns, re-etched them with a hydrofluoric acid, applied a silane coupler and recemented them with MA. Although the evaluators classified these cases 14S
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as cement failures, we will continue to recall the participants so we can evaluate long-term survival of the ceramic material. CONCLUSIONS
We evaluated the clinical performance of the IPS e.max CAD ceramic crowns EC cemented with two different adhesive 97.2 97.2 resin cements. There were no clinically 100.0 identified cases of crown fracture or 100.0 surface chipping. There were no reports 100.0 of postoperative sensitivity for any of the crowns at the one- and two-year recall visits. The results show that lithium disilicate crowns perform well after two years of clinical service. ■
Disclosure. Dr. Fasbinder has received honoraria for educational programs and research funding for projects with the CEREC system from Sirona Dental Systems, Charlotte, N.C.; and Ivoclar Vivadent, Amherst, N.Y. This study was funded through a research grant from Ivoclar Vivadent, Amherst, N.Y. 1. Tysowsky G. The science behind lithium disilicate: today’s surprisingly versatile, esthetic & durable metal-free alternative. Oral Health J 2009;March:93-97. 2. Ivoclar Vivadent. IPS e.max Lithium Disilicate: The Future of AllCeramic Dentistry—Material Science, Practical Applications, Keys to Success. Amherst, N.Y.: Ivoclar Vivadent; 2009:1-15. 3. Giordano R. Materials for chairside CAD/CAM-produced restorations. JADA 2006;137(9 suppl):14S-21S. 4. Cvar JF, Ryge G. Criteria for the clinical evaluation of dental restorative materials. San Francisco: U.S. Department of Health, Education and Welfare, Public Health Service, National Institutes of Health; 1971. USPHS publication 790-244. 5. Hikita K, Van Meerbeek B, De Munck J, et al. Bonding effectiveness of adhesive luting agents to enamel and dentin. Dent Mater 2007;23(1):71-80. 6. Walter R, Miguez PA, Pereira PN. Microtensile bond strength of luting materials to coronal and root dentin. J Esthet Restor Dent 2005;17(3):165-171; discussion 171. 7. Marquardt P, Strub JR. Survival rates of IPS empress 2 all-ceramic crowns and fixed partial dentures: results of a 5-year prospective clinical study. Quintessence Int 2006;37(4):253-259. 8. Taskonak B, Sertgöz A. Two-year clinical evaluation of lithiadisilicate-based all-ceramic crowns and fixed partial dentures. Dent Mater 2006;22(11):1008-1013. 9. Stappert CF, Att W, Gerds T, Strub JR. Fracture resistance of different partial-coverage ceramic molar restorations: an in vitro investigation. JADA 2006;137(4):514-522. 10. Bindl A, Mörmann WH. Survival rate of mono-ceramic and ceramic-core CAD/CAM-generated anterior crowns over 2-5 years. Eur J Oral Sci 2004;112(2):197-204. 11. Bindl A, Richter B, Mörmann WH. Survival of ceramic computeraided design/manufacturing crowns bonded to preparations with reduced macroretention geometry. Int J Prosthodont 2005;18(3):219-224. 12. Conrad HJ, Seong WJ, Pesun IJ. Current ceramic materials and systems with clinical recommendations: a systematic review. J Prosthet Dent 2007;98(5):389-404. 13. Della Bona A, Kelly JR. The clinical success of all-ceramic restorations. JADA 2008;139(9 suppl):8S-13S. 14. Pjetursson B, Sailer I, Zwahlen M, Hämmerle C. A systematic review of the survival and complication rates of all-ceramic and metalceramic reconstructions after an observation period of at least three years, part I: single crowns (published correction appears in Clin Oral Implants Res 2008;19[3]:326-328). Clin Oral Implants Res 2007;18(suppl 3):73-85.
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