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Clinical Brief

Nov 2009 — Vol. 3, Iss. 5

Full-arch Zirconium Oxide Bridge Fabricated with the Press-on Technique

Marlies Moser, Dr med dent; Christoph Zobler, CDT

Abstract
Because of their excellent mechanical and esthetic properties, zirconium oxide ceramic frameworks present an interesting alternative to conventional metal-reinforced restorations in modern dentistry. The fact that ZrO2 cannot be etched represents a certain drawback. However, this can be surmounted by pressing a glass-ceramic to the prepared margins. Subsequently, a dual-curing adhesive cement is applied to the glass-ceramic to enhance the marginal seal. This method complies with the standards of the adhesive technique. At present, this procedure is considerably superior to that offered by CAD/CAM techniques in terms of esthetics and accuracy of fit. The case described below shows how an 11-unit ZrO2 bridge was created with this press-on method and cemented with the adhesive technique to produce a strong solution which also completely satisfied the patient.

The conditioning of zirconium oxide has been a topic of controversy for many years. In discussions on the possibility of conventional and adhesive cementation of this material, dental professionals always end up deliberating about how long restorations of this kind can be expected to last. Currently, it is very difficult to properly condition the surface of ZrO2 for the adhesive cementation of restorations, as the material lacks the necessary glass content for etching purposes.1 Reliable results on the long-term bonding values between luting composites and ZrO2 ceramics are not yet available, in contrast to the plentiful information on bonding that has been gained for glass-ceramics.1-3 Ongoing scientific studies are focused on optimizing ZrO2 for the adhesive technique and therefore on achieving improved bonding values.4-7 The authors’ intention, therefore, was to achieve an adhesive bond at the preparation margin—that is, the shoulders—by reducing the margins and pressing a glass-ceramic on the circular shoulder preparation (IPS e.max ZirPress, Ivoclar Vivadent, http://www.ivoclarvivadent.com). This approach is explored in detail in the following case description.

The conditioning of zirconium oxide has been a topic of controversy for many years. In discussions on the possibility of conventional and adhesive cementation of this material, dental professionals always end up deliberating about how long restorations of this kind can be expected to last. Currently, it is very difficult to properly condition the surface of ZrO2 for the adhesive cementation of restorations, as the material lacks the necessary glass content for etching purposes.1 Reliable results on the long-term bonding values between luting composites and ZrO2 ceramics are not yet available, in contrast to the plentiful information on bonding that has been gained for glass-ceramics.1-3 Ongoing scientific studies are focused on optimizing ZrO2 for the adhesive technique and therefore on achieving improved bonding values.4-7 The authors’ intention, therefore, was to achieve an adhesive bond at the preparation margin—that is, the shoulders—by reducing the margins and pressing a glass-ceramic on the circular shoulder preparation (IPS e.max ZirPress, Ivoclar Vivadent, http://www.ivoclarvivadent.com). This approach is explored in detail in the following case description.

History and Findings

The 39-year-old patient presented with removable dentures, carious lesions in the residual dentition, pronounced bone resorption in the edentulous areas, and malocclusion (Figure 1 View Figure, Figure 2 View Figure, Figure 3 View Figure, Figure 4 View Figure). The patient wished to receive fixed restorations. The clinical examination revealed gaps in the dentition in both the upper and lower jaw, several carious lesions, and considerably reduced vertical height.

Alveolar bone loss, especially in the buccal region, was established in the gaps left by teeth Nos. 21 and 22 (Figure 1 View Figure). Because of the missing antagonist, tooth No. 16 had been substantially displaced and was located 3 mm to 4 mm below the physiological occlusal plain. Teeth Nos. 38 and 48 had tipped approximately 45 degrees toward the mesial aspect (Figure 4 View Figure). All the existing teeth were vital, the fillings were damaged and the periodontal findings were not pathological. The radiological examination confirmed these findings (Figure 5 View Figure).

Extraoral Diagnosis

To ensure the success of the treatment in cases of this kind involving multiple problems, a thorough dental case analysis is indispensable. Study models were fabricated and duplicated by means of a wax-up8 for the computer-aided model analysis (CMDT, computer-aided model analysis, Innsbruck) (Figure 6 View Figure, Figure 7 View Figure, Figure 8 View Figure). The wax-up was fabricated from the distal to the mesial aspect according to the previously calculated inclination of the guiding planes and the occlusal concept of sequential anterior canine guidance. In the process, the vertical height was raised as planned and the occlusal plane was adjusted. Provisional restorations were subsequently produced incorporating the desired situation. This method offered the patient the possibility of obtaining a preview of the results and the changes that were to take place. Furthermore, the patient was given the opportunity to express her own wishes, which at this stage could be satisfied with little effort, as long as they were consistent with the dental requirements.

Treatment Procedure

Preparation of the Abutment Teeth
At this stage of the treatment, the information on how to reconstruct and optimize the masticatory system, which had been gained from the dental cast analysis, was transferred to the patient’s mouth as completely as possible.

After the old fillings and carious lesions had been removed, the existing abutment teeth were ground according to the preparation guidelines for all-ceramics. Any undercut areas were blocked out with composite resin.

All full-arch bridge systems require absolutely parallel abutment preparation. Failure to observe these guidelines will result in difficulties in the placement of the restorations. To achieve this parallelism, it is advisable to systematically prepare the abutments located diagonally from each other, one after the other, taking the tooth axis into account. Primary preparation was carried out with an 80-µm grit diamond. The teeth were finished with 30- to 40-µm grit diamonds of the same shape (Figure 9 View Figure). In anterior areas, shoulders should be preferred over chamfers, as they produce more esthetic results.9 Moreover, in the fabrication of full-arch bridges, conical diamonds angled at 6 degrees can be very useful.

Soft Tissue Management
Because of the extraction of teeth Nos. 21 and 22 a number of years earlier, the starting situation for the placement of the bridge was not optimal. The bone resorption and lost interdental papillae presented an esthetic problem in the front part of the upper jaw. As a result, the places on which the pontics would come to rest were contoured with a large ball-shaped diamond. These pontic rests were taken into account in the finishing and insertion of the provisional.

Checking of the Preparation, Impression-taking, and Provisional Fabrication
A transparent matrix fabricated on the basis of the wax-up is suitable for checking the required thickness of the restorations. In the present case, it was important to take into consideration that the occlusal part of tooth No. 16 in the upper jaw needed to be reduced, as excentric interferences would otherwise occur, especially in mediotrusion, which would result in malocclusion and chipping of the restoration.

To check parallelism, it is advisable to take an intermediate impression, which can be measured in the parallelometer. Any necessary corrective preparation can be carried out at this stage. In the case at hand, the resin provisional was finally fabricated with the help of a vacuum-formed acrylic resin matrix. After finishing, stress-free placement ensued with a eugenol-free provisional cement.

Because of the missing teeth in the chewing center (Nos. 6 and 7), the fracture risk of the framework, the minimally retentive conditions, and the deep subgingival preparation margins of the distal abutment teeth (No. 8), the lower jaw was restored with porcelain-fused-to-metal (PFM) bridges. The abutments for these bridges were prepared in another appointment according to the conventional preparation guidelines for PFM ceramics. In the process, it was important to ensure that interference-free reconstruction could take place.

Mounting in the Articulator
The transfer of the joint-related situation in the articulator is important in all restorative procedures and of immense significance in raising the vertical height, as in-compatibility reactions in the form of a wide range of complaints may occur if this is not done correctly. To keep sources of error to a minimum in this case, the transfer of the skull-related information was carried out with a suitable anatomical transfer bow. Closed centric bite registration was requisite to prevent a forced bite. In addition, the elevated bite established with the provisional had to be transferred with utmost accuracy.

Technical Fabrication

In the fabrication of conventional metal-reinforced full-arch bridges, two physically different materials (framework and veneering material) are fired and cooled in several thermal cycles. In the cooling phase, stress builds up in the materials, which could cause distortion of the framework.

However, the authors reasoned that a stress-free framework could be milled with ZrO2 using CAD/CAM equipment.10-12 Recent scientific studies and analyses involv-ing ZrO2 have provided a great deal of information about the properties of this material. The ZrO2 framework was constructed with a reduced shoulder to ensure the exact fit of the restoration and enable etching of the ceramic.

Due to the excellent translucency of the IPS e.max ZirPress nano-fluorapatite glass-ceramic, the transition between the tooth structure and the restoration after adhesive bonding is difficult to distinguish. As the ZrO2 framework is completely covered with the pressed-on ceramic, it is prevented from absorbing moisture. Therefore, the strength values are affected only by the dynamic factors in the mouth.

Fabrication Procedure
Several silicone matrices of the full-contour wax-up were created to ensure the even reduction of the framework (Figure 6 View Figure, Figure 7 View Figure, Figure 8 View Figure). Next, the wax-up was used as the construction pattern in the dual-scan technique and the 11-unit zirconium oxide framework was produced (Figure 10 View Figure).

The CAD/CAM method allows long-span bridges to be constructed without stress build-up within the material. The authors have found the following fabrication guidelines to be of utmost importance:

  • Adjustments should be ground in carefully under water cooling.
  • Only the inner surfaces of crowns should be blasted for cleaning purposes at maximum 1 bar pressure.
  • The veneering surface of the framework must not be blasted, as this would change the CTE (coefficient of thermal expansion) value, which could cause cracking of the veneering ceramic at a later stage.
  • The connectors between the pontic or coping must not be reworked.
  • In the lower posterior jaw, the span length of two bridge units should not be exceeded if ZrO2 frameworks are used.
  • A shape and cusp supporting technique should be used, best with dual-scan.
  • All excentric interferences in the posterior region should be avoided, especially in mediotrusion, to prevent functional delamination.
  • The ZrO2 framework should be completely covered with ceramic, and the adhesive placement technique should be used to prevent exposure to moisture.

A thin layer of IPS e.max Ceram ZirLiner (Ivoclar Vivadent) was fired on the framework (Figure 11 View Figure). DeltaForm light-curing modelling composite (DeltaMed, http://www.deltamed.de), which fires out without leaving residue, was used to produce clean and accurate margins. This composite resin was applied only in marginal areas (Figure 12 View Figure and Figure 13 View Figure). With the help of the silicone matrix, the restoration was waxed-up to full contour in the next few steps (Figure 13 View Figure and Figure 14 View Figure). The advantage of using this procedure is obvious: because shrinkage no longer occurs, ample time is available for creating even the smallest functional details.

Large bridges involving several abutment teeth, which are fabricated using the press-on technique, demand a suitable investment system and a dedicated ceramic press furnace (Figure 15 View Figure). The authors used a prototype investment system to satisfy these requirements.

The next working steps corresponded to the conventional procedure used in pressing ceramics. Therefore, it was unnecessary to become accustomed to a new technique (Figure 16 View Figure and Figure 17 View Figure).

In this particular case, an IPS e.max ZirPress LT ingot in shade A2, which does not require veneering, was used (Figure 18 View Figure).

The decision about the level of esthetics must be made, taking into account the issue of cost. However, the staining technique produces entirely acceptable results in many cases (Figure 19 View Figure and Figure 20 View Figure). Should layering be desired after all, the IPS e.max Ceram veneering ceramic is available for this step. Due to the long span width of the restoration, the authors decided to use the staining technique in order to benefit from the higher strength of the pressed ceramic (110 MPa) compared to that of the layering ceramic (90 MPa). In the lower jaw, the frameworks for the posterior bridges on both sides were cast using an high-noble gold PFM alloy (Callisto Implant 78, Ivoclar Vivadent). Subsequently, these frameworks were veneered with IPS InLine according to functional criteria. From today‘s perspective, the authors would prefer to have used the press-on-metal technique (IPS InLine PoM) over the veneering technique to solve this case, as it offers the same advantages as the previously described press-on technique.

Placement

After the provisionals had been removed and the prepared teeth cleaned, the accuracy of fit and the occlusion of the restoration were checked.

The adhesive cementation of a multi-unit bridge requires some experience with the adhesive technique. The conditioning step and the application of the luting composite in particular do not have any allowance for mistakes. The removal of excess, particularly in the interdental spaces, must be done expediently. Excess adhesive must be removed in these areas before it hardens. Removing excess cured cement can damage the restoration or injure the tooth or gingiva.

The teeth and the restorations were conditioned at the same time:

Restorations

  • The pressed-on margins were etched with IPS Ceramic Etching Gel (5% hydrofluoric acid) (Ivoclar Vivadent) for 20 seconds.
  • The etching gel was rinsed off and the restorations were dried.
  • The restorations were silanized with Monobond S (Ivoclar Vivadent) for at least 60 seconds.
  • The dual-curing luting cement Variolink II (Ivoclar Vivadent) was mixed and applied.

Abutment teeth

  • The prepared shoulders were etched for 15 seconds with Ultra-etch (Ultradent, http://www.ultradent.com); etching of dentin is optional (5 to 10 seconds).
  • The etching gel was rinsed off and the teeth were dried.
  • The teeth were conditioned with Syntac Primer and Heliobond (Ivoclar Vivadent) was applied.

At this point, the full-arch bridge was quickly inserted in the patient’s mouth. Excess adhesive was removed before the adhesive was cured with a polymerization light (eg, bluephase, Ivoclar Vivadent). All the bonding surfaces of every abutment tooth had to be cured for 40 seconds. It is advisable to use several light sources to speed up this procedure. An added advantage of this approach is that the restoration does not have to be held in place for such a long time, because it stabilizes more rapidly. The authors usually place zirconium-reinforced restorations with Multilink Automix (Ivoclar Vivadent) in conjunction with the metal-zirconia primer. In the case at hand, however, Variolink II was used to cement the all-ceramic restoration, as all the abutment teeth were surrounded by a pressed-on margin that provided an etchable silicate ceramic surface. As a result, significantly better shear bond strength values were obtained, at least in the marginal areas.5,7,13 Furthermore, Variolink II offers the added advantage of a long working time, which in this case considerably reduced the risk of bonding errors (Figure 21 View Figure).

The conventional PFM bridges were placed in the lower jaw according to the customary cementation method.

Discussion

The results of the described treatment still looked very promising at the one-year recall examination. The problematic situation encountered in the upper anterior soft tissue represented a real challenge. The photos of the gingiva before and one year after the treatment show the excellent gingival compatibility of the IPS e.max ZirPress press-on ceramic (Figure 22 View Figure). This result may be attributed to the material’s outstanding biocompatibility (inert material) and low plaque affinity (highly compacted surface).

Moreover, the seal of the cement joints remained unchanged. The cement had neither cracked nor formed gaps. The pressed cervical margins together with adhesive cementation ensure smooth color transitions for enhanced esthetics. The press-on technique offers the added benefit of protecting the zirconium oxide framework from moisture. Adhesive cementation with a dual-curing luting composite achieves strength values that are comparable to those of other silicate ceramics. Furthermore, the stability of the framework is not affected by moisture.14,15

Light is diffusely scattered within glass-ceramic restorations. Therefore, the play of light within these restorations helps to mimic the effects observed in natural teeth. As a result, crowns have a natural appearance under all types of light.

Another important issue that should be taken into account is the danger of chipping or delamination of the ceramic from the framework material. Various studies16-19 have shown that in up to 15 percent of the cases examined, the veneering ceramic delaminated from ZrO2 frameworks. Therefore, in these cases, it is important to properly match the veneering ceramic to the framework material.

Another important aspect that needs to be addressed to ensure the longevity of all-ceramic restorations is the occlusal concept. This has been confirmed by the authors’ experience. Veneering ceramics are more susceptible to chipping under shearing loads than under axial loads. Consequently, interferences in the excentric position must be avoided at all cost. This phenomenon affects not only ceramic restorations, but also natural teeth. The occlusal concept of anterior canine guidance was used in this case. At the one-year recall there was no evidence of chipping or abrasion facets (Figure 23 View Figure and Figure 24 View Figure).

Conclusion

Full-arch bridges reinforced with an yttrium-stabilized zirconium oxide framework onto whose gingival preparation margins a ceramic has been pressed present an interesting esthetic alternative to metal-ceramic restorations. Even though the authors have used this approach only in the case described, the one-year recall results are promising and allow hope that the restoration will last a long time. The results of clinical studies involving a number of cases with bridge spans of this length are not yet available and are not expected in the near future. Time constraints place limitations on cementation with dual or chemically-curing luting composites. However, using conventional cementation would call into question the purpose of this approach.

This method of restoring a partially edentulous jaw produces successful long-term results only if all the requirements are fulfilled. The fabrication of such large restorations involves numerous potentials for error. Therefore, the indication must be exactly established, the procedure planned in detail, and the sources of error reduced to a minimum during the successive working steps.

Disclosure

The preceding material was provided by the manufacturer. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Dentistry India. The preceding is not a warranty, endorsement, or approval for the aforementioned products or services or their effectiveness, quality, or safety on the part of Dentistry India or AEGIS Communications. The publisher disclaims responsibility for any injury to persons or property resulting from any ideas or products referred to in the preceding material.

References

1. Rosentritt M, Behr M, Rinke S, et al. Zirkondioxidkeramik in der Kronen- und Brückenprothetik. Die Quintessenz. 2006;57(7):723-729.

2. Guazzato M, Quach L, Albakry M, Swain MV. Influence of surface and heat treatments on the flexural strength of Y-TZP dental ceramic. J Dent. 2005;33(1):9-18.

3. Kosmac T, Oblak C, Jevnikar P, et al. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater. 1999;15(6):426-433.

4. Lüthy H, Löffel O, Hämmerle C. Effect of thermocycling on bond strength of luting cements to zirconia ceramic. Dent Mater. 2006;22(2):195-200.

5. Piwowarczyk A, Lauer HC, Sorensen JA. The shear bond strength between luting cements and zirconia ceramics after two pre-treatments. Oper Dent. 2005;30(3): 382-388.

6. Wolfart M, Lehmann F, Wolfart S, Kern M. Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods. Dent Mater. 2007;23(1):45-50.

7. Palacios RP,Johnson GH, Phillips KM, Raigrodski AJ. Retention of zirconium oxide ceramic crowns with three types of cement. J Prosthet Dent. 2006;96(2):104-114.

8. Niederwanger A. Berechnung der Inzisaltischinklination für definierte Führungswinkel [dissertation]. Innsbruck, Austria: Leopold Franzens Universitat; 2001.

9. Baltzer A, Kaufmann V. http://www.dental-cam.com.

10. Roulet JF, Jand R. Keramiksysteme der Zukunft. Quintessenz Zahntech. 2004;30(9):989-1006.

11. Witkowsky S. Computer integrated manufacturing (CIM) als Konzept für das zahntechnische Labor. Quintessenz Zahntech. 2002;28(4): 374-386.

12. dos Santos J Jr, Blackman RB, Nelson SJ. Vectorial analysis of the static equilibrium of forces generated in the mandible in centric occlusion, group function, and balanced occlusion relationships. J Prosthet Dent. 1991;65(4):557-567.

13. Physikalische Eigenschaften und Haftwerte von Variolink II. http://www.ivoclarvivadent.de.

14. Falkensammer F. Vollkeramik- und Adhäsivtechnik. http://www.medunigraz.at/zahnklinik/download/adhaesivskriptendfassung.pdf. Accessed November 13, 2009.

15. Everts JE, Meng J, Gratton DG. Flexural strength of zirconia frameworks fatiqued under simulated oral conditions. J Dent Res. 2005;84(spec issue A):0425.

16. Pospiech PR, Nothdurft FP, Long-term behavior of Zirconia-based bridges: Three years result. J Dent Res. 2004. http://iadr.confex.com/iadr/eur04/techprogram/abstract_51366.htm. Accessed November 13, 2009.

17. Sailer I, Lüthy H, Feher A, et al. 3-year clinical results of zirconia posterior fixed partial dentures made by direct ceramic maching (DMC). J Dent Res. 2003;82(spec issue B):074.

18. Vult von Steyern P, Carlson P, Ninler K. All-ceramic fixed partial dentures designed according to the DC-Zirkon technique. A 2 year clinical study. J Oral Rehabil. 2005;32(3):180-187.

19. Sailer I, Feher A, Filser F, et al. Klinische 5-Jahres-Ergebnisse für Seitenzahnbrücken mit Zirkoniumdioxidgerüst, hergestellt mit einem Prototyp-CAM Verfahren. Quintessenz Tech. 2008;34(1):86-95.

Figure 1 Pre-operative view of the upper jaw. Figure 2 Pre-operative view of the lower jaw.
Figure 3 Posterior teeth in the right side of the jaw. Figure 4 Posterior teeth in the left side of the jaw.
Figure 5 Radiograph of the pre-operative situation. Figure 6 Wax-up.
Figure 7 and Figure 8 Wax-up in the centric and the excentric position.
Figure 9 Prepared abutment teeth.
Figure 10 Zirconium oxide framework. Figure 11 Application of IPS e.max Ceram ZirLiner.
Figure 12 Reduced shoulder design. Figure 13 Shoulders modelled with light-curing composite resin that fires out without leaving residue.
Figure 14 Restoration waxed-up to full anatomical contour. Figure 15 Preparation for pressing.
Figure 16 Divestment of the ZrO2 framework onto which the ceramic has been pressed. Figure 17 Pressed restoration with press sprues and sprue button.
Figure 18 Creation of the detailed anatomical features. Figure 19 Full-arch bridge with cervical margins onto which a ceramic has been pressed.
Figure 20 Stained and glazed full-arch bridge. Figure 21 Radiograph of the placed restorations.
Figure 22 Gingiva after one year.
Figure 23 and Figure 24 Occlusal view of the upper jaw after one year. The situation is stable, without chipping or abrasion facets. Conventional PFM bridges on both sides of the lower jaw.