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Dental Tribune Middle East & Africa Edition | 5/2017 IMPLANT TRIBUNE 4 The synthesis of aesthetics, health and structural stability The advantages of using the Angulated Screw Channel (ASC) abutment system By Dr Chandur Wadhwani, USA There are many reasons why ce- ment-retained implant restorations gained popularity over the last few years, which can be attributed to aesthetics, ease of use and familiar- ity with cementation techniques. However, Pauletto, Gapski and oth- ers reported that cement excess was problematic; then Wilson’s study established a positive relationship between excess residual cement and peri-implantitis. Surveys on cements used for im- plant restorations indicated a diver- sity in material selection, application technique and volume. This suggest- ed a lack of conformity and under- standing of cement usage within the dental profession. To overcome the cement problem, it became evident Fig. 1: Failed, removed im- plant, cement extrusion is noted on multiple threads. Figs. 2a & b: The anterior teeth present a challenge to the screw-retained restoration unless an Angulated Screw Chan- nel (ASC) abutment is used (a). In cases where the surgical placement is less than ideal, the ASC may help limit further compromise to the site (b). Fig. 3: The ASC shows the angle redirection of the screw access channel. Angulated Screw Channel saves the day An innovative solution to the off- axial implant is the Angulated Screw Channel (ASC) abutment system developed by Nobel Biocare (Fig. 3). angulations. CAD/CAM design ena- bles the restorations to be efficiently designed and quickly manufactured at Nobel Biocare’s production facili- ties (Fig. 5). Milled zirconia is highly aesthetic, thus especially useful at the soft tissue emergence site. abutment, with its well-designed circumferential wall strength, is held through the abutment screw, optimising the ceramic’s ability to withstand forces that have been seen to fracture non-titanium base abut- ments. in techniques Prosthet Dent. 2010 Feb;103(2):68-79 5. Wadhwani C, Hess T, Pineyro A, Opler R, Chung KH. Cement ap- plication luting implant-supported crowns: a quan- titative and qualitative survey. Int J Oral Maxillofac Implants. 2012 Jul- Aug;27(4):859-64. 6. Raval NC, Wadhwani CP, Jain S, Darveau RP.The Interaction of Im- plant Luting Cements and Oral Bac- teria Linked to Peri-Implant Disease: An In Vitro Analysis of Planktonic and Biofilm Growth--A Preliminary Study. Clin Implant Dent Relat Res. 2015 Dec;17(6):1029-35. 7. Wadhwani C, Hess T, Pineyro A, Chung KH. Effects of abutment and screw access channel modification on dislodgement of cement-retained implant-supported restorations. Int J Prosthodont. 2013 Jan-Feb;26(1):54-6. Figs. 4a & b: Even with shallow margins and minimal cement (a), the elimination of cement extrusion still presents a clinical challenge (b). Fig. 5: The Nobel Biocare CAD/CAM software allows ideal screw access site to be planned, then machine fabricated. Figs. 6a–c: The screw access from Figure 2a has been redirected using the ASC abutment and crown (a & b), producing a pleasing natural appearance thanks to a screw-retained implant restoration (c). that improved understanding was required for cement material selec- tion, abutment design and the deter- mination of cement margin depths. Even with the very best intentions, however, residual excess cement can lead o disease, affecting the health of the implant/tissue interface and re- mains a dominant risk factor. The association of residual excess cement and peri-implantitis has re- sulted in the need to re-examine al- ternatives such as the screw-retained implant crown. For many implant systems, the ability to use a screw-re- tained implant restoration is limited to regions where the screw access channel emerges in an aesthetically ‘safe’ site. Usually the anterior maxilla and mandible present the greatest chal- lenges, as the long axis of the implant often projects through the proposed incisal edge or even facial to the final restoration (Fig. 2a). Occasionally, when the surgeon places the implant in a compromised site—or the im- plant is inappropriately placed—the traditional screw-retained implant restoration may seem to provide more of a challenge than a solution (Fig. 2b). With the ability to alter the screw channel up to 25 degrees, it elimi- nates the need for cementation in the vast majority of cases like these. The ASC provides for an active syn- thesis of health, aesthetics, and ex- cellent structural and mechanical abutment joint stability. Health With use of the ASC abutment sys- tem, cement extrusion into the fragile peri-implant soft tissues is eliminated. The ASC puts an end to the onslaught of cement fluid pres- sure and unset chemicals from the cement material. It also gets rid of the potential for foreign bodies be- ing pushed around the implant site, which can jeopardise implant health (Fig. 4). In addition, the use of zirco- nia abutment superstructures in combination with titanium bases provides optimised materials for biocompatibility and health. Aesthetics With the ASC, the screw access chan- nel can be projected away from high- aesthetic-risk areas and placed ap- propriately at a variety of different Mechanical stability CAD/CAM utilisation (Fig. 6a–c) al- lows for optimised screw access site planning, and the machining of components provides a precise, dedicated connection, optimised for the implant-abutment joint. As with all implant-to-abutment connections, the optimised pas- sive fit results when these surfaces are in intimate contact and forces are distributed universally. Casting abutments cannot always provide an even connection with joint con- tact, as they are often inadvertently damaged through cleaning and pol- ishing, which alters the consequent fit (Fig. 7). When this occurs, the joint connection may fail, with screw loos- ening or even failure of the implants as a result. Structural components Titanium alloy abutment bases provide the most accurate fit with machining tolerances readily con- trolled. Abrasive wear, i.e. the release of titanium metal into the peri-im- plant tissues from the inside of the implant, is not an issue. The zirconia Conclusion The benefits of the ASC abutment system are numerous, reflecting a multiple symbiosis of engineering ingenuity and biocompatible mate- rials, and allowing for the combina- tion of good aesthetics and excellent health. References 1. Pauletto N, Lahiffe BJ, Walton JN. Complications associated with ex- cess cement around crowns on os- seointegrated implants: a clinical report. Int J Oral Maxillofac Implants. 1999 Nov-Dec;14(6):865-8. 2. Gapski R, Neugeboren N, Pomer- anz AZ, Reissner MW. Endosseous implant failure influenced by crown cementation: a clinical case report. Int J Oral Maxillofac Implants. 2008 Sep-Oct;23(5):943-6. 3. Wilson TG Jr. The positive relation- ship between excess cement and peri-implant disease: a prospective clinical endoscopic study. J Periodon- tol. 2009 Sep;80(9):1388-92 4. Tarica DY, Alvarado VM, Truong ST. Survey of United States dental schools on cementation protocols for implant crown restorations. J Fig. 7: An actual case: Note cast abutment has been damaged through routine labo- ratory procedures. 8. Wadhwani C, Goodwin S, Chung KH. Cementing an Implant Crown: A Novel Measurement System Using Computational Fluid Dynamics Ap- proach. Clin Implant Dent Relat Res. 2016 Feb;18(1):97-106. Editorial note: For the complete refer- ences to this article please visit: nobel- biocare.com/news Dr Chandur Wadhwani is a prosthodontist in private practice in Bellevue, Washington, USA. An adjunct assistant professor at Loma Linda Univer- sity’s School of Dentistry, he is also affili- ate faculty at the University of Washing- ton School of Dentistry in Seattle. He has written the first evidence-based textbook dedicated solely to implant cementation. Here, he describes some of the advantag- es of working with the NobelProcera ASC (Angulated Screw Channel) abutment system.