Fabricating an occlusally screw-retained bridge from monolithic Prettau® Zirconia.
Designed for use in full-contour situations, highly translucent Prettau® Zirconia can be used in conjunction with a specialized coloring system to create esthetic, implant-supported bridges.
The material is kind to opposing dentition and while its flexural strength is less than that of some other zirconias, when used in full-contour bridge cases it provides a stronger restoration when compared to a traditional bridge framework that must be covered with a veneering porcelain. Instead, Prettau® zirconia is designed and milled in full anatomical contour, and then prior to sintering, special Prettau® Liquids are applied with a technique similar to layering ceramic to add color and shade effects.
The color liquids are individually painted on the restoration using a small, metal-free brush. This step is similar to coloring a restoration before glaze firing. Final color intensity is defined by the number of brush strokes applied. While this technique does require a bit of practice, it makes the restorations highly customizable as the end result depends entirely on the way the brush is worked.
When the technique is mastered, it is possible to create highly esthetic full-contour, implant-retained bridges with optimal physical properties.
01 Beginning with a model made from the impression with the four screw-retained abutments in place, a wax mock-up is created and tooth position is checked against the abutments (Fig. A).
02 The gingiva is modeled precisely in wax with all denture teeth in place. If the final prosthesis is going to be copymilled, this full-arch model is then duplicated to create a silicone impression of the mock-up and this is processed for copymilling (Fig. B). If the case is going to be scanned and milled, the final wax-up is scanned.
03 The full-arch restoration is then milled from a solid block of Prettau Zirconia. Note: for full-arch bridges, it must remain connected to the base until sintered (Fig. C).
04 The milled restoration is given detailed shape with burs, stones and diamond rubbers to provide accurate anatomy (Fig. D).
05 A water-cooled handpiece is then used to slightly reinforce fissures (Fig. E), and a bur is used to reduce buccal surfaces if ceramic veneering is to be applied. The bur also is used to grind the connectors thinner without separating the restoration from the block (Fig. F).
06 A non-metallic brush is used to apply Prettau Colour Liquids for shading the teeth, and violet color liquid is used to shade the gingiva (Figs. G, H).
07 The connectors are thoroughly soaked and then the entire restoration is dried for at least 1 hour under an infrared drying lamp (Fig. I).
08 The restoration is placed under the firing porter and sintered until it reaches approximately 30ºC (86ºF). It is now ready to be disconnected from the base (Fig. J).
09 The bridge is now checked against the model and adjusted as necessary to fit before being cleaned with a sandblaster (Fig. K).
10 An opaque layer of the ceramic dentin and tissue staining is applied and the restoration is wash-baked at 920ºC (1688°F) for 2 minutes (Fig. L).
11 The dentin layer is applied and baked for 2 minutes at 820ºC (1,508°F). Then the first gingiva layer is applied and baked for 2 minutes at 815ºC (1,499°F) (Fig. M).
12 Stains are applied and the restoration is baked again for 1 minute at 700ºC (1,292ºF) (Fig. N).
13 Glaze powder is applied and the restoration is given a final 1 minute firing at 780-800ºC (1,436ºF – 1,472ºF) (Fig. O).
14 The final restoration ready for seating as seen from the palatal, buccal and full-arch views. (Figs. P, Q & R).