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Monolithic screw-retained computer-aided design and computer-aided manufacturer (CAD-CAM) ceramics are widely used for implant-supported prostheses because of their efficiency in terms of manufacturing time, cost, and predictability.
In this prosthetic design, a complete-contour prosthesis is typically milled in translucent zirconia or lithium disilicate and adhesively cemented under optimal conditions extraorally onto a titanium base, resulting in a screw-retained prosthesis.
This method has the advantage of using prefabricated machined titanium bases that will not be processed in a furnace as in conventional techniques for metal-ceramic restorations, ensuring their structural integrity, absence of oxidation, and optimum fit.
In the autho's practice, intraoral adjustments for these prostheses may be performed by cementing the crowns with an interim luting agent onto the bases, which facilitates removal in case ceramic modifications for color or proximal or occlusal contacts are needed. However, in some clinical situations, the crowns may become loose or displace from the base, so it may be preferable to perform intraoral adjustments with the prosthesis already definitively cemented to the base.
is an essential step for adequate retention, some dentists may request that their prostheses are definitively cemented by the dental laboratory technician, as chairside airborne-particle abrasion devices may not be as effective as laboratory ones.
or in a conventional ceramic furnace, but an improper temperature may oxidize the base or even expand the metal to the point of fracturing the ceramic. Therefore, the reported technique provides a straightforward, safe, and rapid way of removing the titanium base from the crown while preserving both.
Set the holding temperature of the furnace (Programat C2; Ivoclar AG) to 200 °C, closing time to 1 minute, temperature increase rate to 30 °C per minute until a maximum temperature of 400 °C, and a holding time of 1 minute are reached. Vacuum or slow cooling are not required.
Place the crown without the screw on a support pin or mantle and start the furnace firing cycle, which will last about 7 minutes (Fig. 1). In the presented setting, a slow and gradual rise in temperature prevented an abrupt linear thermal expansion of the metal that could crack or fracture the ceramic. The final temperature is sufficiently high to soften the cement without oxidizing the metal base or damaging the ceramic.
At the end of the cycle, allow the crown to cool at room temperature. Place the screw into the crown and firmly push in the screw with a screwdriver (SCS; Institut Straumann AG). The base will displace easily (Fig. 2).
Remove the cement residue from the base with a hand instrument and then use airborne-particle abrasion (Basic Eco; Renfert) with aluminum oxide (particle size 50 μm, 0.25 MPa pressure, for 10 seconds at 10 mm) (Fig. 3). Correct the crown with the necessary firing cycles and then adhesively recement the base to the crown.
Is the use of digital technologies for the fabrication of implant-supported reconstructions more efficient and/or more effective than conventional techniques: A systematic review.