Full-Contour Productivity

June 26, 2012
Shannon Davidson, CDT
Shannon Davidson, CDT

Issue 4

Staying competitive in the current economy has increased the need for an alternative to gold-based restorations. I am constantly thinking of ways to use my CAD/CAM system to streamline and improve productivity while maintaining and ensuring quality.

Staying competitive in the current economy has increased the need for an alternative to gold-based restorations. I am constantly thinking of ways to use my CAD/CAM system to streamline and improve productivity while maintaining and ensuring quality.

The recent development of Crystal Diamond Zirconia has made milling full-contour zirconia restorations more appealing. This presentation focuses on a technique that combines traditional waxing, full-contour milling, and custom acid-based pre-sinter infiltrating. This process is an efficient way to produce a high-quality restoration consistently.

Case Presentation

The patient presented with a gold crown that was in need of replacement. Options were discussed and a full-contour zirconia crown was agreed upon for the following reasons: lifetime guarantee, natural tooth color, and cost-effectiveness compared with that of a gold crown.

A digital impression was taken chairside with the Cadent iTero intraoral digitizer and CAM milled models produced by Cadent received by the laboratory.

Laboratory Procedure

01 A waxup is produced using a Gnathoflex Premium Silicone (XPdent) occlusal form (Fig. A). Note: This technique is extremely fast and consistent. The contact and axial walls are completed in wax. It is not necessary to perfect the margin area as the scan of the die is responsible for the intimacy of the fit and margins.

02 Using a 3Shape scanner, the waxup on the die is first scanned (Fig. B), then the waxup is removed and the die scanned. Note: It is critical that when removing the waxup the die is not moved.

03 Full-contour zirconia crowns are milled out of a Crystal Diamond milling blank using Turning Solutions’ Dental Mill CAM milling unit (Fig. C). A five-tool routine is used to achieve the detailed anatomy. Note: Crystal Diamond is more translucent than conventional zirconia used for copings and bridges and this maximizes the esthetic result.

04 Once the milling is complete, the green-state crown is removed from the milling blank by cutting the sprues with a highspeed carbide (Fig. D). Milling dust is then removed using a compressed gas duster.

05 Using a plastic microbrush, Prettau liquids (ZirkonZahn) are applied to the crown in a systematic way to enhance esthetics (Figs. E, F). Note: Do not use a conventional brush with a metal ferrule as this will contaminate the liquid and the crown.

06 The crown is sintered and seated on the model to refine the margins using a ceramic polisher.

07 The contacts and occlusion are checked and any necessary adjustments made. The model is mounted on Denar articulators using the Denar iTero Mounting System (Whip Mix).

08 The surface of the crown is lightly sandblasted to accept the glaze. Once glazed, the crown is fired to stabilize it at 1025°C for 2 minutes. Note the variation in color from the custom infiltration liquids.

09 Conventional stains are used to highlight and adjust value and chroma if necessary.

10 A slight tabac stain is placed in deepest fossae. White or cream is placed on ridges, then a light blue/violet stain is washed around the circumference of the occlusion. The stain is then fired and set at 900°C. Glaze is applied in the same fashion as a conventional ceramic crown and fired at 900°C.

11 The completed crown on the model. Note the natural appearance without the additional labor of layering porcelain.