Preparation Junctions for All-Ceramic CAD/CAM Crown and Bridge Restorations

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Background: The preparation junction type is determined by a number of factors that need to be taken in consideration with CAD/CAM Fixed Prosthodontics: the used material; the condition of the retainer teeth, their periodontium and the occlusion; the design software and the type of drills; the working protocol; the cement and the method of cementation.

The aim: of this article is to describe the optimal preparation junctions for CAD/CAM crown and bridge restorations made by ceramics based on zirconium dioxide and the basic factors that affect them.

Materials and methods: Chamfer and radial shoulder preparation junctions are suitable (width 1 - 1, 5 mm). Trimming of 1, 5-2 mm dental tissues is necessary on the occlusal surface. The homothetic tooth reduction is optimal. The surface has to be smooth and the edges rounded.

Results: The preparation width depends on the size and vitality of the tooth. In stained teeth the removal of more tissues provides a greater volume needed for masking the dark color. Vestibular preparation under the level of the gingiva is preferable to ensure optimal aesthetics. The preparation junction is determined also by the CAD/CAM software abilities, the type of drills and protocol of impression taking (classical or digital). The creation of a working model with an intraoral scanner is greatly facilitated by preparations above the gingival margin.

Conclusions: Knowledge about the criteria for selection of preparation junctions is essential for fabrication of accurate and aesthetic CAD/CAM restorations.

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