Appearing in the August and September issues, the first two articles in this three-part series on cemented implant restorations explored factors that influence restoration success, including the impact of cement selection and radiolucency. This concluding installment will cover cement application techniques and abutment modifications designed to ensure successful implant outcomes.
HABIT 5: CEMENTATION TECHNIQUE
Residual cement from implant restoration contributes to peri-implant disease and implant failure, which makes correct cementation technique essential to clinical success. Naturally, the easiest way to avoid excess cement extrusion is to limit the volume of cement used to fill the luting space provided during crown fabrication.1,2 One of the most useful techniques is to fabricate a secondary copy abutment that is used to extrude excess cement extraorally prior to seating the crown. A “throw-away” copy abutment that is slightly smaller than the implant abutment is made from a material such as polyvinyl siloxane.2,3 The crown is loaded with cement and quickly seated over the copy abutment, which helps eliminate any excess cement. Once the outside of the prosthesis is cleaned up, the intaglio surface now has closer to the ideal layer of cement. The crown is then seated on the abutment and the copy abutment is discarded.
HABIT 6: CEMENT FLOW CHARACTERISTICS
An interesting aspect of dental cements relates to their flow characteristics. All fluids can be categorized as either Newtonian or non-Newtonian, depending on how they act when force is applied.4 Historically, Newton recognized that when a bucket of water is rapidly stirred, its viscosity does not change. However, when a pale of cream is rapidly stirred, it thickens and eventually forms butter. Water is an example of a Newtonian fluid, whereas cream, ketchup and cornstarch mix are examples of non-Newtonian fluids. Most dental cements are non-Newtonian and shear thin, although some — such as zinc phosphate — do the opposite by shear thickening and flowing less as force is applied.
Studies using super-computers have shown that with shear-thinning acrylic resins, the most appropriate way to load an implant crown is to place a cement layer in a half-toroid (or half doughnut) shape in the lower 1 mm of the crown (near its margin) and seat the crown in 0.5 seconds.5 If this is done too quickly, the cement will thin, which results in more cement than anticipated being extruded. Conversely, if this is done too slowly, air voids are introduced — again resulting in unwanted cement extrusion. This is further discussed in the next section on abutment design and modifications.
HABIT 7: ABUTMENT MODIFICATIONS
When metal abutments are used, increasing the surface area of the abutment by air-particle abrasion with 50 micron alumina can enhance the retentive strength of cemented implants. Titanium can also be etched with 5% hydrofluoric acid for 30 seconds, providing a similar increase in surface area.6
More sophisticated ways to alter the flow of cement exist and are available to industry if manufacturers choose to pursue such designs. Two examples would be providing a “golf ball” textured surface or adding venting channels and holes within the abutment itself that would result in internalization of the cement, thereby minimizing or eliminating excess cement extrusion.
Dentistry has been slow to recognize that seating a crown on an implant is similar to a piston entering a combustion chamber in an engine, and that this is an engineering process governed by conforming shapes and surfaces, as well as liquid flow characteristics. Ongoing research on cement flow characteristics can be used to develop future abutment designs in which form follows function. Such designs might appear quite distinct from current abutments that simply follow conventional tooth preparation shapes.
Ultimately, a thorough understanding of implant components and dental cement characteristics can help clinicians achieve excellent outcomes in implant therapy. This three-part series, which incorporates scientific principles of biology, chemistry and physics, is intended to aid clinical decision-making when cementing implant restorations.
- Wiskott HW, Belser UC, Scherrer SS. The effect of film thickness and surface texture on the resistance of cemented extracoronal restorations to lateral fatigue loading. Int J Prosthodont. 1999;12:255–262.
- Bukhari SA, AlHelal A, Kattadiyil MT, Wadhwani CPK, Taleb A, Dehom S. An in vitro investigation comparing methods of minimizing excess luting agent for cement-retained implant-supported fixed partial dentures. J Prosthet Dent. 2020;124:706–715.
- Wadhwani CPK. Cementation in Dental Implantology, An Evidence-Based Guide. Heidelberg, Germany: Springer-Verlag; 2015:140–144.
- Newtonian and Non-Newtonian Fluids — Newton’s Law of Viscosity. Available at: https://www.apsed.in/post/newtonian-and-non-newtonian-fluids-newton-s-law-of-viscosity. Accessed September 9, 2022.
- Wadhwani C, Sabine Goodwin S, Chung KH. Cementing an implant crown: A novel measurement system using computational fluid dynamics approach. Clin Implant Dent Relat Res. 2016;18:97–106.
- Wadhwani C, Chung KH. In-office technique for selectively etching titanium abutments to improve bonding for interim implant prostheses. J Prosthet Dent. 2016;115:271–273.
From Decisions in Dentistry. October 2022;8(10)24.