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.
1
,2
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.3
,4
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.5
,6
There is also the benefit of using high-strength materials that have a lower risk of fracture or chipping than ceramic veneered prostheses,7
and because of the extraoral cementation, cement remnants around the implant-abutment interface are avoided.3
,4
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.
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Moreover, because airborne-particle abrasion with aluminum oxide (particle size 50 μm, 0.25 MPa pressure, for 10 seconds, and at 10 mm)9
on the titanium base4
,9
or in the intaglio of translucent zirconia10
,11
(particle size 50 μm, 0.2 MPa pressure, for 15 seconds, and at 10 mm)11
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.12
Additionally, pressure higher than 0.3 MPa may negatively affect the flexural strength of translucent zirconia.11
To perform corrective firing cycles on the ceramic, the prosthesis must be removed from the base
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; the only nondestructive way to achieve this is to soften the cement, whereas the bond strength between the titanium base and crown is high.4
,13
This softening can be performed with an Er,Cr:YSGG laser14
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.Technique
- 1.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.
- 2.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.
![Figure thumbnail gr1]()
Figure 1Monolithic zirconia screw-retained implant-supported crown adhesively cemented onto titanium base placed in pin in ceramic furnace. - 3.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).
![Figure thumbnail gr2]()
Figure 2After firing cycle, screwdriver firmly pushed against screw. Note displacement of titanium base from crown. - 4.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.
![Figure thumbnail gr3]()
Figure 3After airborne-particle abrasion with aluminum oxide (particle size 50 μm, 0.25 MPa pressure, for 10 seconds, at 10 mm) base clean and ready for adhesive recementation. Note nonoxidized connection of base. Intaglio surface of translucent zirconia also airborne-particle abraded with aluminum oxide (particle size 50 μm, 0.2 MPa pressure, for 15 seconds, at 10 mm).
References
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- Bonding of composite cements to zirconia: A systematic review and meta-analysis of in vitro studies.J Mech Behav Biomed Mater. 2018; 80: 258-268
- Effects of air-abrasion pressure on mechanical and bonding properties of translucent zirconia.Clin Oral Investig. 2021; 25: 1979-1988
- Effect of different airborne-particle abrasion/bonding agent combinations on the bond strength of a resin cement to a base metal alloy.J Prosthet Dent. 2012; 108: 316-323
- Retention of zirconia copings over smooth and airborne-particle-abraded titanium bases with different resin cements.J Prosthet Dent. 2019; 121: 949-954
- Resin cement removal from titanium dental implant surface using a novel side-firing laser fiber and Er,Cr:YSGG irradiation.Am J Dent. 2020; 33: 178-182
Article info
Publication history
Published online: June 05, 2021
Footnotes
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Identification
Copyright
© 2021 by the Editorial Council for the Journal of Prosthetic Dentistry.
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