The patient was a woman over 70 years of age who had undergone several implantological treatments in the previous 18 years. Because of complications with her implants, she had never got beyond the provisional stage. Many of the previously inserted implants in the upper jaw had been lost due to the qualitatively and quantitatively inadequate bone supply. The patient also suffered from osteoporosis and had taken Fosamax (alendronic acid) for a short time a few years earlier. The original temporary bridge restoration was still in function, and there were unused covered implants in the lower jaw. The original implants were 3i external hex implants. The patient did not accept removable dentures. As a result, she was referred to the oral surgeon, who transplanted autologous hipbones into the upper jaw and subsequently inserted seven Zimmer implants into this bone. He also exposed the covered implants in the lower jaw. All implants were stable, so that the definitive prosthetic restoration could finally be started (Fig. 1) . Due to the complex situation and the patient's history, the dentures should be fixed and removable (Fig. 2) .
The patient decided on the very light white color tone OM1 of the Vita 3D Master color ring. OM1 is a challenge for every dental technician because the material has no internal color shading and it is difficult to achieve a naturally warm appearance. In addition, when a metal framework is used, the required opaque makes the finished dental prosthesis less translucent. The best material for this type of denture today is therefore zirconium oxide, which, in addition to its strength, stability and precise processing options, is particularly characterized by its natural white tone and translucency. The simplest fixed-removable prosthetic
The solution would be a bridge that is screwed directly to the implant heads. However, after carefully studying the space, a dimensional problem became apparent. The occlusogingival height was 25.4 mm in the upper jaw and 22.6 mm in the lower jaw. The largest available zirconium oxide blank for manual milling allows for an occlusal-gingival height of 17.6 mm or less. Therefore, both bridges had to be made from two components: the sub-construction should be screwed to the implant and the superstructure with the sub-construction.
First, the existing temporary restoration (which the patient found good with the exception of the color) was duplicated in order to plan the definitive restoration (Fig. 3) . Minor modifications were then made to this construction in order to improve the chewing function. A silicone duplicate was made from the final construction. In the next step, the final position of the connecting screws of the two components was determined (Fig. 3a to 3d). This work was done with the precision milling device F3. This step had to be done before the cut back to ensure that the access openings match the occlusion. At the same time, the direction of insertion for the sub-construction to be attached to the implants was determined. After the screw positions had been determined, the plastic for the bar was cut back, again with the precision parallel milling device F3 according to the angle determined when the screws were positioned (Fig. 4a and 4b) .
The bars were modeled in plastic, then segmented and reconnected with a light-curing adhesive to achieve a tension-free passive fit. Plastic models must always be tried in before milling the zirconia in the mouth. In the next work step, the bars of the sub-construction were inserted into the templates and milled manually as usual with the zirconium milling device. The milled bars were then tinted slightly pink on the underside and placed in the sintering furnace, with the unused part of the blank being placed upright to prevent deformation of the zirconium oxide during the sintering process (Figs. 5a and 5b) .
After sintering, both bars were finished in a precision milling device with special milling diamonds for zirconium oxide with water cooling (Fig. 6a and b) . In the shaded area of the bars, mechanical retentions were attached to which the artificial gingiva would later be attached. The retentions consisted of glaze paste mixed with aluminum oxide, which was fired on in a ceramic oven.
Next, the bars were polished to a mirror finish and the screw housings were inserted and fixed with composite cement (Fig. 7 a and b) . The models including the bars were then brought into the correct position according to the original silicone key, and the framework for the superstructure was poured with liquid denture resin.
The fully contoured framework was cut back slightly in the anterior region (from premolar to premolar) to make room for the ceramic veneer. Since the occlusion was already correctly specified by the temporary, the posterior teeth and the occlusal surfaces were retained in their full anatomical contour, so that they can later be milled out of the zirconium oxide blank in their entirety (Figs. 8a and 8b) .
Both parts of the framework were segmented again and again adhesively attached to the bars to ensure a precise fit (Figs. 9a and 9b) . The frameworks were then milled manually with the zirconium oxide milling device and sintered like the bars - but without coloring (Fig. 10 a and b).
After sintering, the frameworks were veneered with ceramic in shade OM1 and the occlusal area was slightly colored. Uncolored zirconium oxide frameworks are the perfect sub-construction when a patient wants a brilliant white restoration. The natural translucency and white color of the zirconium oxide enable a highly aesthetic result, even with posterior teeth made entirely of zirconium oxide (Figs. 11a and 11b) .
Gingival Resin Was Polymerized Onto The Bars And Matched To The Ceramic Gingiva Of The Framework. No Gingival Ceramic Could Be Burned Onto The Sub-Construction Because The Screw Housings Were Attached To The Zirconium Oxide With Composite Cement And This Cement Could Not Withstand The Temperatures During Firing (Fig. 12) . The result was a very white, fixed, removable, ceramic-veneered zirconium oxide dental prosthesis, the shape of which corresponded exactly to the temporary dental prosthesis that the patient valued. The patient was extremely satisfied with the results (Figs. 13 to 18) .
Zirconium oxide is the perfect material for all types of dentures. It has all the properties we could want: strength and stability as well as excellent biocompatibility and aesthetics. Restorations of any complexity can be made from zirconium oxide - as long as we have the right tools to exploit the impressive potential of this material.
Doctor of Dental Surgery `85, McGill University, Montreal, Quebec
Diploma in Prosthodontics `89, University of Toronto, Toronto, Ontario
Specialist in Prosthodontics `89, Ordre des Dentistes du Quebec
Fellow Pierre Fauchard Academy `05
Dr. A. W. Thornton Gold Medal ’85, McGill University
Association of Prosthodontists of Canada
Association of Prosthodontists of Quebc
Assistant Professor ‘91, McGill University, Montreal, Quebec.
Section Head ‘92, Dept. of Prosthodontics, Jewish General Hospital, Montreal.
Dr. Caro presently has private practice in Prosthodontics in Westmount, Quebec. He is as well teaching Prosthodontics and Implant Dentistry, McGill University and training residents in Prosthodontics and Implants in Jewish General Hospital. He is living in Montreal, Canada.
Owner of KerenOr Dental Studio in Montreal, Canada. He is a second generation dental technician and been in the profession for 20 years. He was graduated in Israel as a Certified Dental Technician in 1988. After graduating, he received further two year training and education in Germany. During his professional carrier, Haim took many courses and seminars in order to stay current with all the innovations in dental industry. In 2006 he took training at ZirkonZahn, Italy with manual milling system and at the same year his lab became North America first full service all Zirconia laboratory.