IPS Empress Crown
System: Three-Year
Clinical Trial Results

The IPS Empress system is a highly esthetic hot pressed glass ceramic material for fabrication of single crowns. Adhesive cementation of the system not only contributes to the esthetics but is necessary for increased strength of the crown. The purpose of this prospective clinical trial was to evaluate the longevity of 75 adhesively cemented Empress full crowns. An additional aim was to assess the adhesive cementation methodology and potential side effects. At the three-year point, one molar crown fractured for a 1.3 percent failure rate. The resin cementation technique that was employed exhibited a low incidence of microleakage with few clinical side effects. There was a 5.6 percent incidence of postcementation sensitivity, with all symptoms subsiding by eight weeks. None of the crowns in the study required endodontic therapy.

Article copyright 1998 Journal of the California Dental Association.
Photographs copyright of the authors.

The IPS Empress system (Ivoclar North America, Amherst, N.Y.) was offered in the early 1990s as a new standard of excellence in esthetic fixed prosthodontic materials. The fabrication methodology involves a lost-wax investment technology for the hot pressed ceramic system that dental technicians are familiar with. ^1,2

Figure 1. Disappearing margin achievable because of translucent ceramics and resin cementation. Margin located only 0.5 mm subgingival. Figure 2. Because of the high translucency of ceramic, the shade of the tooth preparation can be recorded with the Stumpmaterial Shade Guide.

The Empress system combines a highly translucent dentin shaded glass ceramic with a translucent adhesive resin composite cement. The high translucency of the system facilitates placement of margins less intrusive to the sulcus for a harmonious tissue-restoration interface and nearly invisible margins (Figure 1). This combination offers excellent esthetics and less invasive tooth preparation for more predictable achievement of high quality esthetic fixed prosthodontics. The system is so translucent that a shade selection and die material were developed to match the shade of the underlying tooth structure (Figures 2 and 3).

Figure 3. Cemented Empress crown illustrating translucency achieved with a low value shade.

The Empress all-ceramic system achieves its strength by means of several factors. Leucite crystal reinforcement provides a flexural strength of the parent pressed ceramic of about 125 MPa. ³ An approximate 45 percent increase in strength by compression bonding is created by a slight difference in coefficient of thermal expansion between parent ceramic and either veneering or stain and glaze ceramics. ⁴ The adhesive cementation technique further increases the overall restoration strength by a clinically unknown factor. ^5-7 Still, the strength values of this all-ceramic system are one-tenth that of metal-ceramic systems and one-third that of high strength core ceramics such as In-Ceram (Vident, Brea, Calif.). ⁴ The question arises: Does the adhesive cementation system sufficiently increase the strength of the cemented crown to provide predictable long-term clinical longevity? Although the principal reason for using these all-ceramic systems is esthetics, the system must have adequate strength to insure clinical longevity. The authors believe that although esthetics may not demand it, an all-ceramic system should be strong enough for predictable use for restoration of posterior teeth.

Literature Review

Since metal-ceramic restorations are the standard of care for esthetic fixed prosthodontic restorations, they should be the criterion for comparison with the new all-ceramic systems. Metal-ceramic restorations made up 70 percent to 80 percent of all fixed prostheses placed in the 1980s. ⁸ Few clinical studies have been performed on metal-ceramics. Leempoel and colleagues ⁹ studied the survival rate of crowns in Dutch general practices. For 1,323 anterior metal-ceramic crowns, survival rates at five years were 95 percent and at 10 years were 82 percent. For 2,011 premolar metal-ceramic crowns, survival rates at five years were 98 percent and at 10 years were 97 percent. Coornaert and colleagues ¹⁰ followed 2,181 metal-ceramic units over seven years and observed a 2.4 percent failure rate. The follow-up rate was 85 percent during the seven-year study, with most failures occurring within one year after cementation. A failure rate of 2.8 percent for metal-ceramic crowns was observed over seven years at the University of Zurich. ¹¹ At the five-year point, these clinical studies on metal-ceramic full-coverage restorations suggest a maximum failure rate of 2.8 percent to 5 percent. This 5 percent failure rate is, therefore, the maximum allowable failure rate criterion in evaluating all-ceramic systems.

Clinicians have been skeptical of new all-ceramic systems for good reason. In private practice, the clinical performance of many of the ceramic systems have fallen far short of manufacturers' claims about their products. The following is a summary of results on earlier all-ceramic systems.

Linkowski12 evaluated 224 Cerestore (Ceramco, Johnson & Johnson) crowns cemented with zinc phosphate and glass ionomer. At two years, they observed a failure rate of 3 percent for anteriors and 21 percent for posteriors. When 106 Dicor (Dentsply, York, Pa.) crowns cemented with zinc phosphate were evaluated at the three-year point by Moffa and colleagues,13 the incidence of fracture was 35 percent for molars, 12 percent for premolars and 3.5 percent for anteriors. Erpenstein14 evaluated a total of 159 Dicor crowns cemented with zinc phosphate. At two years, they found failure rates of 3 percent for anteriors, 13 percent for premolars and about 36 percent for molars. In spite of the excitement generated by advertising, these new all-ceramic systems were no better than McLean's Platinum foil porcelain jacket crown. ¹⁵ In 1983, he recorded failure rates of 2.1 percent for incisors, 6.4 percent for premolars and 15.2 percent for molars at the seven-year follow up. Even for the original feldspathic porcelain jacket crowns, Leempoel and colleagues ⁹ estimated that 25 percent would fail over 11 years.

For a more recently developed all-ceramic crown material, Jeneric/Pentron ¹⁶ claimed that metal-ceramics were on the endangered list and would become an outdated "dinosaur" because of the tremendous strength of Optec material. This could ostensibly not only be used for single crowns but also for fixed partial dentures with veneer abutment preparations. Christensen and Christensen ¹⁷ tested 40 FPDs with a variety of retainer designs and at two years found an 80 percent failure rate for posterior FPDs and a 22 percent failure rate with full crown retainers on anterior FPDs. It does not appear at this time that metal-ceramic technology can be relegated to the category of "dinosaur."

On a positive note, Hankinson and Cappetta studied 158 Optec crowns (Jeneric/Pentron) that were adhesively cemented. ¹⁸ At up to five years they observed a failure rate of 0 percent for anteriors, 2.3 percent premolars and 24 percent for molars.

While the resin cementation system offers some great clinical advantages such as outstanding esthetics, reduced microleakage by sealing of margins19,20 and strengthening of the ceramic crown, it does have some disadvantages. First, margins can be placed only minimally subgingival otherwise sulcular fluids will contaminate the bonding surfaces. Second, the technical procedures and moisture control are much more demanding than conventional procedures. Atraumatic tissue-tooth preparation and noniatrogenic periodontal principles must be followed for provisional restorations to prevent bleeding gingival tissues at the time of cementation. Third, the dental assistant must be highly organized in passing the brushes with the correct adhesives in the correct order for delivery by the dentist.

The Empress system must be adhesively cemented for maximum strength. Failure to comply with the above listed factors in adhesive cementation may seriously compromise the longevity of the Empress restoration. It is not suggested that conventional cements can withstand gingival bleeding, sulcular fluids or saliva during cementation, however, because of the larger number of steps for adhesive cementation and extended period of time that it must be maintained contamination free. Resin cementation is considered a technique-sensitive procedure. Adhesive cementation includes:

• Phosphoric acid etching of enamel, rinsing and drying;
  
  
• Application of Syntac Primer for 15 seconds and drying;
  
  
• Application of Syntac Adhesive for 15 seconds and drying;
  
  
• Application of Heliobond unfilled resin and air thinning;
  
  
• Mixing of the dual-curing resin cement, placement in the crown and seating onto the tooth; and
  
  
• Removal of excess cement prior to polymerization.

A drawback frequently cited by clinicians but nearly undocumented by clinical studies is the reported high incidence of postcementation sensitivity accompanying resin cementation. Therefore, evaluation of the adhesive cementation and potential side effect such as tooth sensitivity, microleakage, cement discoloration and pulpal problems are a critical part of a clinical study on adhesively cemented ceramic crown systems.
The purpose of this prospective clinical trial was to evaluate the longevity of 75 adhesively cemented Empress full crowns. An additional aim was to assess the adhesive cementation methodology and potential side effects.

Materials and Methods

Patients were recruited from the greater Los Angeles area and treated at the School of Dentistry Clinical Research Center at the University of California at Los Angeles. All of the Human Subject Protection Committee guidelines were followed. To be accepted into the study, patients had to have teeth adjacent to those to be restored and opposing teeth or fixed prosthodontics. Second molars were not tested in this study, following the ceramic system restoration protocol (Ivoclar North America, Amherst, N.Y.). Due to the moisture sensitivity of the resin cementation technique, teeth to be restored were rejected if the margins were located greater than 1 mm subgingivally.

Tooth Preparation

Figure 4. Tooth No. 12 has large amalgam filling, breakdown of tooth, recession exposing dentin. Potential problems if margins established subgingivally. Figure 5. Circumferential shoulder with all margins placed supragingivally especially facially and distally where recession was more pronounced.

All teeth were prepared with a flat-ended diamond, aiming for 1.3 mm of axial reduction and 1.5 mm to 2.0 mm for incisal or occlusal reduction. This preparation requirement is similar to that for metal-ceramic full-coverage restorations. The margin design was a shoulder configuration with a rounded axial-gingival line angle (Figures 4 and 5). The shoulder margin design provides the strength and most accurate marginal fit. When a round-ended diamond is used, if the tooth is penetrated more than half the diameter of the bur, lipping results. A flat-ended diamond can penetrate the tooth to varying degrees and still produce a shoulder configuration that is free of lipping. The bulk reduction was performed with a flat-ended diamond followed by refinement of the margin with tissue-protecting, end-cutting burs. The margins were finalized with hand instruments to achieve a smooth, clean and linear finish line.

Figure 6. Pressed ceramic core with veneer ceramic applied.

Fabrication Techniques

The full-ceramic crown restorations were pressed in the appropriate shade of colored ingots and veneered with 0.4 mm to 0.8 mm of ceramic material (Figure 6). In the more critical esthetic cases, the composite resin stump material was placed in the coping to represent the dentin shade.

Delivery and Adjustment Protocol

The provisional crown restorations were removed, the temporary cement was debrided, and the teeth were cleaned with cleaning paste (Syntac Cleaning Paste, Ivoclar Vivadent, Amherst, N.Y.). Proximal contacts were evaluated and adjusted when it was necessary. The internal adaptation and marginal integrity were evaluated (Fitchecker, GC America, Chicago, Ill.), and any areas of binding were adjusted until the fit was determined to be excellent. Lastly, the occlusion and the contours were adjusted. If any adjustment were made, the crowns then were glazed. The dimensions of the crown restorations were measured at eight points using a digital micrometer.

Cementation Procedure

The internal surfaces of the full-coverage crown restorations were etched with hydrofluoric acid gel (IPS Ceramic Etching Gel, Ivoclar Williams, Amherst, N.Y.) thoroughly rinsed and dried (Figure 7). Silane coupling agent (Monobond-S, Vivadent, Amherst, N.Y.) was applied to the etched ceramic and gently dried after 60 seconds. Unfilled resin (Heliobond, Ivoclar Vivadent) was applied and air thinned.

Prior to cementation, the areas of enamel were mapped in the patient record, etched for 30 seconds with 37 percent phosphoric acid, rinsed thoroughly and then dried. Dentin Primer and Adhesive (Syntac, Vivadent) were applied for 15 seconds each and air dried

Figure 7. Crown etched at chairside following external and internal crown adjustments. Figure 8. Two stages of Syntac dentin adhesive applied: Syntac Primer applied for 15 seconds and dried; Syntac Adhesive applied for 15 seconds and dried.

(Figure 8) . For Dual Cement (Vivadent), equal amounts of base and catalyst were mixed and applied in a thin layer in the crown. For Variolink (Vivadent), the appropriate shade of the luting cement base was determined and an equivalent amount of thick viscosity catalyst was mixed and applied in a thin layer on the walls of the crown. The full crown was then seated onto the preparation with sustained finger pressure and held in place while excess cement was wiped away. Dental floss was passed between the teeth to remove excess cement interproximally (Figure 9).

Figure 9. As much excess cement as possible removed prior to polymerization. Waxed dental floss pulled through proximals to remove excess cement at gingival embrasures. Figure 10. With as much excess cement as possible removed, the cement is light-cured. Figure 11. Completed Empress crown No. 12. Translucent ceramics and adhesive cementation allow margins to be placed supragingivally.

The resin cement was light polymerized from all aspects (Figure 10). After 10 minutes of setting time, the excess cement was removed with a No. 12 scalpel blade followed by unwaxed dental floss. The occlusion and the proximal contacts were verified (Figure 11).

Recall Evaluations

Measurements were made at baseline and recall visits scheduled annually. Evaluation appointments consisted of intraoral photographs, polyvinylsiloxane impressions of restored teeth and antagonist teeth and direct clinical measurements. Parameters measured included:

• General oral hygiene;
  
  
• Plaque index of tooth, cement and crown;
  
  
• Staining/discoloration of crown and cement;
  
  
• Interfacial staining;
  
  
• Secondary caries;
  
  
• Marginal integrity;
  
  
• Condition of crown; and
  
  
• Patient comfort with all teeth and crowns.

Results

A total of 75 all-ceramic crown restorations were placed in 33 subjects. Subjects ranged in age from 17 to 69. Of the crown restorations placed, 47 were on anterior teeth, 15 on premolars and 13 on first molars. Dual Cement was used for luting the first 19 crown restorations; Variolink was used for the remaining 56 crown restorations.

At the three-year point, one molar crown fractured after 27 months of service. The failed crown exhibited minimal microleakage ruling out failure of the adhesive cementation. Unfortunately, the failed crown could not be retrieved.

Of the crowned teeth, 53 were vital with patients reporting postcementation sensitivity to cold liquid in three crowns. This calculates to a 5.6 percent incidence of sensitivity. All symptoms, which subsided in three to eight weeks, began within 24 hours of cementation. None of the patients reported any other pain. Symptoms occurred in one molar restoration cemented with Dual Cement and one molar and one premolar cemented with Variolink. None of the restored teeth required root canal therapy through the period of the study. Two restorations (2.7 percent) exhibited slight microleakage at the dentin-cement interface. No secondary caries was detected. No staining or discoloration of the cement was observed.

No staining or discoloration of the ceramic was noted. No change in the surface finish of the crowns was noted.

Discussion

The high translucency of this ceramic material in conjunction with the resin cementation technique facilitates improved esthetic margin fabrication. This results in significantly less intrusion into the sulcus and improved long-term gingival health. Fixed prosthodontic procedures can be more easily performed when the margins are only slightly subgingival. The inherent esthetic properties of this resin-cemented, full-coverage crown system facilitates more predictable and easily achievable natural esthetics than metal-ceramic crowns.

While excellent esthetic results are attainable with these ceramic restorations, there is no question that the adhesive cementation procedure is complicated and extremely technique-sensitive. Two restorations (2.7 percent) exhibited slight microleakage at the dentin-cement interface. No secondary caries were noted. Therefore, the adhesive cementation techniques seem to be reliable. In terms of side effects, three abutment teeth experienced crown postcementation sensitivity. These symptoms were experienced as sensitivity to cold and subsided within eight weeks. None of the abutment teeth required endodontic treatment through the period of the study.

This postcementation sensitivity was found in 5.6 percent of the crowned teeth. Clinicians have anecdotally reported high rates of postoperative pain associated with resin-cemented ceramic restorations. Johnson and colleagues21 reported postcementation pain of approximately 29 percent for zinc phosphate cements. Therefore, the results of this study reflect favorably on the resin cementation technique.

Finishing of the margins with rotary instruments is difficult and will likely result in damage to the ceramic margin or gouging of the tooth structure apical to the margin. In gaining access for rotary instruments, damage to the soft tissue is also likely. In a well-fitting all-ceramic crown restoration, it is nearly impossible to polish a 60 m resin cement.22 An efficient method for removal of polymerized excess cement is required. In the authors' experience, a No. 12 scalpel blade is a highly effective tool for removing this material. The sharp blade easily shears off the excess material even in concave areas that a straight rotary instrument cannot effectively access. Clinicians do not attempt to polish zinc phosphate, glass-ionomer or polycarboxylate cemented crown restorations; therefore, the authors question why finishing should be attempted with resin cements. Removal of excess cement prior to light polymerization minimize the need for finishing resin-cemented ceramic crown margins.

Hankinson and Cappetta studied 158 Optec crowns (Jeneric/Pentron) that were adhesively cemented.18 At up to five years, a failure rate of 2.3 percent for premolars and 24 percent for molars was observed. This system is adhesively cemented and has a significantly higher leucite content than Empress.23 What may account for the high failure rate exhibited in that study is the fact the ceramic crowns are fabricated by a traditional powdered buildup of the entire crown on a refractory die material. This probably introduces many more voids and defects that may act as the origin of failure for crack propagation.

Lehner and colleagues24 reported a failure rate of 5 percent at two years for 78 Empress crowns. They did not always follow the adhesive cementation protocol. The present study followed the adhesive cementation protocol recommended by the ceramic manufacturer (Ivoclar North America) for every crown. Following the manufacturer's directions yielded a failure rate of only 1.3 percent for the Empress crowns. Relative to clinical studies on other all-ceramic crown systems, the results at three years for the Empress system are very favorable. In the present study, the protocol precluded full-coverage crown restorations on second molars. The one restoration that did fail was a first molar, indicating some caution be exercised in restoring molars.

Conclusions

The study protocol called for crown placement on first molars, premolars and anterior teeth. At the three-year point in this clinical study on the Empress all-ceramic crown system, the following conclusions can be made:

• Of the 75 Empress crowns cemented, only one crown failed, for a 1.3 percent failure rate.
  
  
• The failed crown was a molar that fractured at 27 months.
  
  
• The resin cementation technique that was employed exhibited a low incidence of microleakage with few clinical side effects.
  
  
• Three crowns experienced postcementation sensitivity to cold, the symptoms of which resolved at a maximum of 8 weeks.
  
  
• This was a 5.6 percent incidence of postcementation sensitivity.
  
  
• None of the crowns in the study required endodontic therapy.
  
  
• The placement criteria of margins no greater than 1 mm subgingival facilitated achievement of a positive clinical outcome.

---

Authors

John A. Sorensen, DMD, PhD, is the ODA Centennial Professor of Restorative Dentistry and director of the Clinical Research Center at Oregon Health Sciences University, Portland. He was formerly and associate professor and director of advanced prosthodontics at the University of California at Los Angeles.

Creighton Choi, DDS, is an adjunct assistant professor at UCLA. He also maintains a private practice in Beverly Hills, Calif.

Mete I. Fanuscu, DDS, maintains a practice limited to prosthodontics, in Istanbul, Turkey. He is formerly a research assistant at UCLA.

Wayne T. Mito, CDT, is a senior research associate at Oregon Health Sciences University. He is formerly a staff research associate in the advanced prosthodontics program at UCLA.

---

References

1. Wohlwend A, Swiss patent (CH-Pat. Anmeldung), No 668699-1986.

2. Wohlwend A, Verfahren und Ofen zur Herstellung von Zahnersatzteilen. European Patent (EU-Patentanmeldung) No 0231773 A, 1987.

3. Seghi R and Sorensen JA, Relative flexural strength of six new ceramic materials. Int J Prosthodont 1995;8:239.

4. Sorensen JA, Avera SP and Fanuscu MI, Effect of veneer porcelain on all-ceramic crown strength. J Dent Res 71:320, 1992. Abstract No. 1718.

5. Doering J, Jensen ME et al, Fracture resistance of resin-bonded etched porcelain full veneer crowns. J Dent Res 66:207, 1987. Abstract No. 803.

6. Eden GT and Kacicz JM. Dicor crown strength improvement due to bonding. J Dent Res 66:207, 1987. Abstract 801.

7. Malament KA and Grossman DG, Bonded vs. nonbonded Dicor crowns. Four-year report. J Dent Res 71:320, 1992 Abstract No 1720.

8. Anusavice KJ, Criteria for selection of restorative materials: Properties vs. technique sensitivity. In Anusavice KJ, ed, Quality Evaluation of Dental Restorations. Criteria for Placement and Replacement. Quintessence Publishing, Chicago, Ill, 1989, p 45.

9.Leempoel PJD, Eschen S et al, An evaluation of crowns and bridges in general dental practice. J Oral Rehabil 12:515-28, 1985.

10. Coornaert J, Adriaens P and DeBoever J, Long-term clinical study of porcelain-fused-to-metal restorations. J Prosthet Dent 51:338, 1984.

11. Strub JR, Stiffler S and Scharer P, Causes of failure following oral rehabilitation. Biological vs. technical factors. Quintessence Inter 3:215, 1988.

12. Linkowsky G, Klinische nachuntersuchung von schrumpfungsfreien porzellankronen (doctoral thesis). Zurich University, 18-23, 1988.

13. Moffa JP, Lugassy AA and Ellison JA, Clinical evaluation of a castable ceramic material. Three-year study. J Dent Res 67:118, 1988, Abstract No 43.

14. Erpenstein H and Kerschbaum T, Frakturrate von Dicor-Kronen unter klinischen bedingungen. Dtsch Zahnärztl Z 46:124-8, 1991.

15. McLean JW, The future of dental porcelain. In, John W. McLean, ed, Dental Ceramics. Proceedings of the First International Symposium on Dental Ceramics, Quintessence Publishing, Chicago, Ill, 26-8, 1983.

16. Optec HSP advertisement, Jeneric/Pentron. J Esthet Dent 1:20A, 1989.

17. Christensen RP and Christensen GJ: Service potential of all-ceramic fixed prostheses in areas of varying risk. J Dent Res 71:320, 1992, Abstract No 1716.

18. Hankinson J and Cappetta EG, Five years' clinical experience with a leucite-reinforce porcelain crown system. Int J Periodont Res Dent 14:138-53, 1994.

19. White SN, Sorensen JA et al, Microleakage of new crown and fixed partial denture luting agents. J Prosthet Dent 67:156-61, 1992.

20. Sorensen JA, Cruz M et al, Microleakage and marginal fidelity of gold inlays using new cements. J Dent Res 73:118, 1994, Abstract No 136.

21. Johnson G, Powell V and De Rouen T, Evaluation and control of postcementation pulpal sensitivity: Zinc phosphate and glass ionomer luting cements. J Am Dent Assoc 124:39, 1993.

22. Fanuscu MI and Sorensen JA, Pre- and postcementation fit of ceramic crown systems. J Dent Res 71:320, 1992, Abstract No 1717.

23. Denry IL, Rosenstiel SF and Hollaway JA, Characterization of crystalline leucite in feldspathic dental porcelain. J Dent Res 73:369, 1994, Abstract No 2139.

24. Lehner C, Studer S et al, Short-term results of IPS-Empress full-porcelain crowns. J Prosthod 6:20-30, 1997.

To request a printed copy of this article, please contact John A. Sorensen, DMD, PhD, Oregon Health Sciences University, School of Dentistry, 611 S.W. Campus Drive, Portland, OR 97201-3097.

---