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Full Restoration with Zolid FX
A successful concept for sophisticated prosthetics.
Tue. 27 April 2021, 8:00 AM
The patient case outlined here describes the challenges that prosthetics have to face under high stress. The patient presented in the practice with pronounced tooth abrasion and asked to have his natural dental appearance restored.
Full restorations have their very own challenges. Particularly when the patient tends to relieve his daytime stress by grinding his teeth at night. After completion of pre-treatment and splint therapy, the patient presented to us with the status shown in Figures 1+2.
Fig. 1 - Pronounced abrasion due to bruxism, resulting in significant loss of the vertical dimension
Fig. 2 - Pronounced abrasion due to bruxism, resulting in significant loss of the vertical dimension
Our task was to fabricate prosthetics which, in addition to their natural esthetics, can also withstand the high mechanical stress and offer corresponding durability. Patient and clinician wanted a complete ceramic restoration consisting of single crowns in the maxillary and mandibular region, except for a 3-unit bridge in the 4th quadrant. The restoration was to be fabricated at the bite height specified during splint therapy. This is specified to us via a corresponding construction bite.
Choice of materials and design
We always attempt to use only a single material for each case or restoration. Different ceramics have different light properties, which can be an optical disadvantage. For restorations consisting exclusively of single crowns, we usually choose veneered zirconia, in exceptional cases also lithium disilicate. The bond between lithium disilicate and veneer ceramics demonstrates higher bond strengths than between zirconia and corresponding veneer ceramic. However, we appreciate the concentration of zirconia as a universally applicable material for frames. With a limited choice of materials, we can gain maximum experience and thus achieve a very high level of production reliability and predictability of the results. Depending on the mechanical stress, we select a different thickness of the veneer ceramic on zirconia. In the case of extreme stress, we also dispense with a glaze in the functional area of the contact relationships (Lit.1). For bruxism patients, however, we choose unveneered lithium disilicate for individual crowns in the posterior region, as the natural abrasion and associated loss of height observed for this material were similar to that of natural teeth. Unveneered, smooth polished zirconia would exhibit less loss of height over the years and would result in uneven abrasion of the teeth with unforeseeable consequences. Our standard solution is thinly veneered zirconia if only a few teeth are to be restored, e.g. in case of isolated gaps.
In this case, we decided to partially veneer the crowns and the bridge due to the exceptional mechanical stress on the prosthetics.
The visible, vestibular parts were to be veneered with the Creation CT veneer ceramics. We wished to place the transition to the unveneered area outside the heavily stressed functional paths and static contact zones. At the time of fabrication we had ZI, Zolid and Zolid FX at our disposal. Due to the small bridge span, we selected the super high translucency material Zolid FX Multilayer for the full restoration, including the bridge from 45-47. The tooth stumps are not significantly discolored. This allows us to make full use of the optical advantages of the translucent material. To achieve maximum individuality, the Zolid FX multilayer crowns were partially stained with liquids before sintering. It is recommended to use a pre-stained blank that is slightly lighter than the tooth shade to be achieved in order to avoid a restoration that is too dark.
Design of the functional areas
In virtual design, we try to make with as few occlusal contact points as possible. We consider this to be sufficient if the tooth can be loaded axially. A reduced number of occlusion contacts helps us to keep the dynamic function under control. This is absolutely necessary in the case of extremely hard zirconia, as defects in this area can lead to unforeseeable consequences for the softer components of the masticatory organ. Our occlusal design can be viewed as an example in Figures 3+4. The veneering areas are defined with some distance to the contact paths and surfaces. Normally we extend the cutback to such an extent that small optical optimizations of the incisal cutting edge are possible through the individual layering technique of the veneer, particularly in the anterior region. The anterior teeth are therefore often given a cutback that runs approximately in the middle of the incisal edge in a mesial-distal direction. However, in patients where extreme functional loading can be expected, this boundary line runs all the way along the outer buccal edge of the abrasive surface to prevent chipping under these special conditions.
Fig. 3 - The occlusal design is created and the contacts are placed on unveneered zirconia. These should not be positioned directly on the veneering interface.
Fig. 4 - The occlusal design is created and the contacts are placed on unveneered zirconia. These should not be positioned directly on the veneering interface.
The surface quality of zirconia
In this case, the unveneered areas of zirconia were provided with a surface structure prior to sintering. Figures 5-9 show the tools, work steps and results of surface characterization prior to sintering. The powerful characterizations can, for example, only be performed by hand with a coarse stone, without the use of a motor. These structures are subsequently smoothed again slightly at the raised areas with mostly smoother surfaces. It is important that these structures are not applied to bridges in tensile stress areas to prevent any possible initial formation of cracks. Finally, the fissures are reworked if necessary. Figures 10+11 demonstrate this final processing step before cleaning, infiltration and sintering.
The small contact and guide surfaces on zirconia must be polished to a high gloss after sintering and grinding to prevent mutual abrasion and early failure of the restoration. The analysis of an internal study by our laboratory shows that polishing with a diamond polisher or the finest diamond grinder largely removes the deep surface damage caused by a Rotring diamond. The success of this approach is confirmed in the study by Coldea et. al. (Lit. 2): If final sintered Y-TZP zirconia is processed with coarse abrasives, subsequent polishing is absolutely necessary. It is recommended to grind or polish gradually with increasingly finer grinders or polishers. The surfaces are smoothed with suitable diamond silicone polishers, i.e. the spikes are removed without causing any further surface damage. This can be facilitated quite easily, for example, with the polishing sets in Figures 12+13.
In contrast to veneer ceramics or lithium disilicate, our polished zirconia samples convince with very low roughness depths.
The smooth surface of final sintered zirconia that can be achieved by polishing also has advantages in abrasion behavior when compared to veneer ceramics. Preis et. al. have come to this conclusion in a comparison of the abrasion behavior of zirconia and veneer ceramics on natural enamel. Abrasion caused by zirconia was considerably less than that of veneer ceramics. Due to the veneer ceramics, the antagonist exhibited a roughened surface and partially also cracks and fractures in the enamel. The contact surfaces with zirconia were polished. (Lit. 3) An in vitro study by Sripetchdanond J et. Al. showed that monolithic zirconia had a lower wear depth than glass-ceramic when compared to human enamel. (Lit. 4) The best result of our laboratory test with the lowest roughness depth was obtained by working with an epoxy resin- bonded, diamond-containing stone. The remaining surface structures were efficiently polished with two-stage diamond polishers as shown in Figure 13. The surface quality can be further increased with a subsequent glaze layer. However, one must allow for abrasion of the glazing material in the functional area. A meticulously smoothed surface is therefore a prerequisite for long-term success. Nevertheless, we now avoid the use of glazing material as far as possible, as the solubility and a surface that tends to roughness in an acidic environment in the long term has been observed and discussed critically in the literature.
After sintering, the surface is again smoothed with diamond silicone polishers in wheel and brush form (Fig. 14-16). High-gloss polished zirconia tends to have a mother-of-pearl-like shine, which does not really resemble a natural tooth. We therefore try to polish only those parts which are in direct contact to a high gloss. All other areas receive a rather matt finish, well visible at the crowns of this patient case as shown in Figure 17. The nature-like translucency of Zolid FX (Fig. 18) makes it possible to manage with a reduced veneer thickness. The Zolid FX frame material with its dentine-colored shade hereby assumes parts of the optical dentine core. The fluorescence is applied with a fluorescent liner before veneering.
Fig. 5 - Tools for surface characterization before sintering
Fig. 6 - Stones and sandpaper cones are drawn over the surface by hand without rotation
Fig. 7 - Stones and sandpaper cones are drawn over the surface by hand without rotation
Fig. 8 - Stones and sandpaper cones are drawn over the surface by hand without rotation
Fig. 9 - Interim status of surface treatment before partial smoothing
Fig. 10 - If required, the fissures can be re-contoured with a pointed carbide cutter
Fig. 11 - If required, the fissures can be re-contoured with a pointed carbide cutter
Fig. 12 - After sintering, diamond silicone polishers are recommended for refining the zirconia surface. For example, the Zolid Sinter State Polishing Kit from Amman Girrbach is well suited here
Fig. 13 - EVE DYPg stone and diamond polisher EVE Diacera
Fig. 14 - Silicone brushes with diamonds do not change the shape of the surface, but smooth it without changing the anatomy. Contact with the workpiece should be made at a slight angle so that the bristles can deflect better and do not kink
Fig. 15 - Silicone brushes with diamonds do not change the shape of the surface, but smooth it without changing the anatomy. Contact with the workpiece should be made at a slight angle so that the bristles can deflect better and do not kink
Fig. 16 - Low-structure, more smooth areas, such as those found at the exposed tooth equator, are partially polished with silicone wheels.
Fig. 17 - The objective is a high-quality surface with a matt finish. Only the small occlusal contact or functional surfaces are polished to a high gloss.
Fig. 18 - The nature-like translucency of Zolid FX makes it possible to dispense with part of the dentine layering with veneer ceramics
The work is tried in as an intermediate step in the mouth. The color shade and natural appearance with incisal facets and enamel cracks both suit and please the patient. The occlusal contacts are checked by the dentist with Shimstock foil and, where necessary, discreetly optimized with the Rotring diamond and subsequent polishing in analogy to the laboratory procedure. Back in the laboratory we finish the work with glaze firing without glazing material (Fig. 19).
The cemented restoration looks authentic and inconspicuous in the mouth (Fig. 20-23).
The patient and our dental partner are both very satisfied with the restoration. The nearnatural appearance exceeded the expectations of the patient. He considers the reconstructed bite height and function to be very comfortable. Our thanks go to Dr. Cornell Lischka for the excellent cooperation.
Fig. 19 - The combination of areas with monolithic zirconia and areas with buccal veneering combines the entirely different advantages of two ceramics
Fig. 20 - The combination of areas with monolithic zirconia and areas with buccal veneering combines the entirely different advantages of two ceramics
Fig. 21 - New teeth with abrasion facets and cracks that suit bruxism patients. Stability, function and inconspicuous integration of the restoration were the objective of our work
Fig. 22 - New teeth with abrasion facets and cracks that suit bruxism patients. Stability, function and inconspicuous integration of the restoration were the objective of our work
Fig. 23 - The patient’s smile speaks a clear language.
- Maier J. The optical and functional integration of monolithic zirconia restorations based on a case study. Quintessenz Zahntechnik (4):474-487
- Andrea Coldea, Marc Stephan, Michael Tholey, Norbert Thiel; Investigation of the influence of different ceramic grinding systems on zirconia; Quintessenz Zahntech 2009;35(4).
- Preis V, Behr M, Kolbeck C, Hahnel S, Handel G, Rosentritt M. ;Wear performance of substructure ceramics and veneering porcelains; Dent Mater. 2011 Aug;27(8):796-804. epub 2011 Apr 27.
- Sripetchdanond J, Leevailoj C.; Wear of human enamel opposing monolithic zirconia, glass ceramic, and composite resin: an in vitro study; J Prosthet Dent. 2014 Nov;112(5):1141-50. doi: 10.1016/j.prosdent.2014.05.006. Epub 2014 Jun 28.