In managing loose abutment screws, locating precisely the position of the screw access channel is difficult. This technique describes the use of cone-beam computed tomography (CBCT) and surgical guide planning software to locate the screw access channel with the intention of retrieving a loosened cement-retained implant-supported prosthesis. The method minimizes damage to the abutment crown assembly

Asiri, Waleed Nasir

Cho, Seok-Hwan

Domagala, Agnieszka

Thompson, Geoffrey A.

English

epublications@Marquette

Marquette Universitye-Publications@MarquetteSchool of Dentistry Faculty Research andPublications Dentistry, School of2-1-2018A Method of Locating the Abutment Screw AccessChannel with Cone-Beam ComputedTomography and a 3D-Printed Drilling GuideWaleed Nasir AsiriMarquette UniversityAgnieszka DomagalaMarquette University, agnieszka.domagala@marquette.eduSeok-Hwan ChoMarquette University, seokhwan.cho@marquette.eduGeoffrey A. ThompsonMarquette University, geoffrey.thompson@marquette.eduAccepted version. The Journal of Prosthetic Dentistry, Vol. 119, No. 2 (February 2018): 210-213. DOI.© 2018 Elsevier B.V. Used with permission.                                                       Marquette Universitye-Publications@MarquetteDentistry Faculty Research and Publications/School of DentistryThis paper is NOT THE PUBLISHED VERSION; but the author’s final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation below.The Journal of Prosthetic Dentistry, Vol. 119, No. 2 (February, 2018): 210-213. DOI. This article is ©Elsevier and permission has been granted for this version to appear in e-Publications@Marquette. Elsevier does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from Elsevier.ContentsAbstract......................................................................................................................................................... 2Technique...................................................................................................................................................... 2Discussion...................................................................................................................................................... 5Summary ....................................................................................................................................................... 6References .................................................................................................................................................... 6A method of locating the abutment screwaccess channel with cone-beam computed tomography and a 3D-printed drilling guideWaleed AsiriGraduate Prosthodontics, Marquette University School of Dentistry, Milwaukee, WIDaniel DomagalaGraduate Prosthodontics, Marquette University School of Dentistry, Milwaukee, WI                                                                                                                   Seok-Hwan ChoPredoctoral Prosthodontics and Biomaterials, Department of General Dental Sciences,Marquette University School of Dentistry, Milwaukee, WIGeoffrey A. ThompsonDepartment of General Dental Sciences, Graduate Prosthodontics, Marquette University School of Dentistry, Milwaukee, WIAbstractIn managing loose abutment screws, locating precisely the position of the screw access channel isdifficult. This technique describes the use of cone-beam computed tomography (CBCT) and surgicalguide planning software to locate the screw access channel with the intention of retrieving a loosenedcement-retained implant-supported prosthesis. The method minimizes damage to the abutment crownassembly.Screw loosening is one of the most frequent mechanical complications observed in implant-supported dental prostheses,1, 2, 3 especially with respect to cement-retained implant-supportedrestorations.4 To retrieve a loosened cement-retained implant prostheses, it may be necessary to create a screw access channel through an existing restoration. Several methods for locating the screw accesschannel have been described, including using ceramic stains,5 acrylic resin;6 fabricating a vacuum-formed template,7 forming a silicone putty matrix,8 using a handpiece sleeve,9 making extraoral andintraoral photographs,10 and designing and printing a drilling guide at the time the implant abutment isdesigned.11, 12 All these techniques require a definitive cast to fabricate a drilling guide. The precisionof the procedure is variable and depends on the chosen technique and the capabilities of theclinician.13 Other methods use intraoral radiographs14 or cone-beam computed tomography (CBCT).15 Inboth techniques, a definitive cast is not required for guide fabrication; however, these methods mayresult in inadvertent damage to a ceramic restoration or to the abutment because of freehand drilling.This report describes the fabrication of a 3-dimensional (3D) printed drilling guide that precisely locatesthe abutment screw access channel of cement-retained implant prostheses using CBCT and surgical guide planning software. Little or no damage to the cement-retained implant-supported prostheses orimplant abutment is possible, even when precementation diagnostic or definitive casts are missing. Thistechnique is particularly useful for retrieving multiple splinted units.Technique1. Determine clinically that the loose cement-retained implant prosthesis and abutment are still united by cement and that the loss of screw preload is the cause of the loose restoration.2. Make a CBCT (Scanora 3DX; Soredex) to create a Digital Imaging and Communications inMedicine (DICOM) format file.3. Make an irreversible hydrocolloid impression (Jeltrate; Dentsply Sirona) in order to fabricate a stone cast (Microstone; Whip Mix Corp).4. Scan the cast with a laboratory scanner (D900; 3Shape) to provide a standard tessellationlanguage (STL) file.                                                 A 5. Both the DICOM and STL files are loaded and aligned in the surgical planning software(Blueskyplan3; Blue Sky Bio LLC). An implant is selected and placed in the desired position withrespect to the in vivo implant position. This step will determine the direction of the screw accesschannel (Fig. 1A) and design of the drilling guide. The drilling guide is fabricated toaccommodate a round diamond rotary cutting instrument (BR6379.31.023; Brasseler USA)(Fig. 1B). The digitally planned guide is sent to a dental laboratory or a computer-aided designand computer-aided manufacturing (CAD-CAM) company (Blue Sky Bio LLC) for fabrication of a 3D printed drilling guide (Fig. 2).Figure 1. A, Determination of direction of screw access channel by combining CBCT Digital Imaging and Communications in Medicine (DICOM) file image and standard tessellation language (STL) file image. B, Design ofdrilling guide to accommodate round diamond rotary instrument.Figure 2. Three-dimensional (3D) printed drilling guide and round diamond rotary instrument.6. After receiving the 3D printed drilling guide, assess the fit clinically and then drill through its sleeve withthe round diamond rotary instrument (Fig. 3). During drilling, verify that the direction of the rotary cutting instrument is as planned by making an intraoral radiograph (Fig. 4).          Figure 3. A, Drilling procedure with 3-dimensional (3D) printed drilling guide. B, Close-up image of screw accesshole opening. C, Precisely drilled access hole with minimal damage.Figure 4. Radiographic verification.                                                                                      7. Remove the drilling guide, unscrew the abutment screw, and remove the crown abutmentassembly. Ensure that the crown abutment assembly is securely cemented and then clean theassembly with a 0.12% chlorhexidine gluconate solution (Peridex; 3M Oral Care).8. Place the crown abutment assembly in the mouth and tighten the new abutment screwaccording to the manufacturer’s torque recommendations.9. Fill most of the screw access opening with polytetrafluoroethylene tape. Then use a pinkcomposite resin (Pink opaque; Cosmedent, Inc) to mask the metal color. Finally, place a toothcolor composite resin (Revolution Formula 2; Kerr Corp) (Fig. 5). Adjust the occlusion asnecessary.Figure 5. Retrieved implant prosthesis with screw access hole filled with composite resin.DiscussionThis technique presents a method of retrieving a loosened cement-retained implant prosthesis usingCBCT and CAD-CAM. After successfully removing the loosened cement-retained implant prosthesis, it isconverted into a screw-retained implant prosthesis with a direct composite resin restoration coveringthe screw access channel.The advantages of this method are that it eliminates freehand drilling and reduces the possibility ofdamaging the existing crown and abutment. In addition, no precementation records are needed. Thecost of the CBCT and the 3D printed drilling guide may be less than fabricating a new crown. Moreover,the CBCT-driven drilling guide may produce a smaller access opening and result in less damage thantypical freehand drilling.13 Although the level of radiation received from a CBCT is less than that from conventional computedtomography, dosages are considerably higher than conventional dental radiography.16 The benefits ofCBCT in dentistry are undeniable; however, its use must be justifiable compared with conventional techniques.16 The retrieval of the loosened cement-retained implant prostheses and the integrity of the prosthesisand implant abutment depend on the drilling technique, the accuracy of the drilling guide, and theexisting access channel direction. If a drilling procedure is inaccurate, it may cause unnecessary damageto ceramic surfaces and compromise the removal of the existing restoration. If the screw access hole isoutside the occlusal table, such as on a cusp tip area or labial surface, then the retrieval and reuse of the                                                                                                                                                                                                loosened cement-retained implant prostheses may not be desirable. It may be better to fabricate a new restoration to eliminate possible fracture or for esthetic reasons. Therefore, the direction of the implant screw access hole should be carefully evaluated during the diagnostic phase.SummaryThe technique for fabricating a 3D printed drilling guide by using CAD-CAM and CBCT to retrieve a loosened cement-retained implant prosthesis will help dental clinicians deal with emergency situationswith abutment screw loosening of cement-retained implant-supported fixed prostheses. With thismethod, the screw access channel can be located precisely, and the existing crown can be retrievedwhen a patient presents to the practice with no treatment records and no definitive cast.References1 M.E. Kreissl, T. Gerds, R. Muche, G. Heydecke, J.R. Strub. Technical complications of implantsupported fixed partial dentures in partially edentulous cases after an average observation period of 5 years. Clin Oral Implants Res, 18 (2007), pp. 720-7262 B.E. Pjetursson, K. Tan, N.P. Lang, U. Brägger, M. Egger, M. Zwahlen. A systematic review of thesurvival and complication rates of fixed partial dentures (FPDs) after an observation period of atleast 5 years. Clin Oral Implants Res, 15 (2004), pp. 625-6423 U. Brägger, S. Aeschlimann, W. Bürgin, C.H. Hämmerle, N.P. Lang. Biological and technicalcomplications and failures with fixed partial dentures (FPD) on implants and teeth after four tofive years of function. Clin Oral Implants Res, 12 (2001), pp. 26-344 R.L. Simon. Single implant-supported molar and premolar crowns: a ten-year retrospective clinicalreport. J Prosthet Dent, 90 (2003), pp. 517-5215 E.R. Schwedhelm, A.J. Raigrodski. A technique for locating implant abutment screws of posteriorcement-retained metal-ceramic restorations with ceramic occlusal surfaces. J Prosthet Dent, 95 (2006), pp. 165-1676 A. Ahmed, G. Maroulakos, J. Garaicoa. Acrylic resin guide for locating the abutment screw accesschannel of cement-retained implant prostheses. J Prosthet Dent, 115 (2016), pp. 560-5637 J.L. Tarlow. A modified technique to locate the abutment screw access opening of a cemented implant-supported restoration. J Prosthet Dent, 108 (2012), pp. 58-598 E.E. Hill. A simple, permanent index for abutment screw access for cemented implant-supported crowns. J Prosthet Dent, 97 (2007), pp. 313-3149 H.W. Kang, D.H. Lee. Using a guide template with a handpiece sleeve to locate the abutment screwposition of a cement-retained implant restoration. J Prosthet Dent, 114 (2015), pp. 339-34210 O. Figueras-Alvarez, J. Cano-Batalla. An alternative method for registering the abutment screwposition of cement-retained implant restorations. J Prosthet Dent, 112 (2014), pp. 1304-130511 J.I. Park, T.H. Yoon. A three-dimensional image-superimposition CAD/CAM technique to record theposition and angulation of the implant abutment screw access channel. J Prosthet Dent, 109 (2013), pp. 57-6012 D.H. Lee. CAD/CAM-fabricated template for locating implant abutment screws in cement-retained anatomic zirconia restorations. J Prosthet Dent, 114 (2015), pp. 343-34513 D.H. Lee, H.N. Mai, L.J. Li, K.W. Lee. Accuracy of a CAD/CAM-guided template for locating abutmentscrews for cement-retained implant-supported restorations. J Prosthet Dent, 116 (2016), pp. 67-73                                     14 P.G. Patil. A technique for repairing a loosening abutment screw for a cement-retained implantprosthesis. J Prosthodont, 20 (2011), pp. 652-65515 R. Wicks, W.H. Shintaku, A. Johnson. Three-dimensional location of the retaining screw axis for acemented single tooth implant restoration. J Prosthodont, 21 (2012) 149-316 J.A. Roberts, N.A. Drage, J. Davies, D.W. Thomas. Effective dose from cone beam CT examinations in dentistry. Br J Radiol, 82 (2009), pp. 35-40

A Method of Locating the Abutment Screw Access Channel with Cone-Beam Computed Tomography and a 3D-Printed Drilling Guide

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A Method of Locating the Abutment Screw Access Channel with Cone-Beam Computed Tomography and a 3D-Printed Drilling Guide

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