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A Protocol for Screw-Retrievable, Cement-Retained, Implant-Supported Fixed Partial Dentures Abdulaziz AlHelal, BDS, MS1/Mathew T. Kattadiyil, BDS, MDS, MS2/ Bader AlBader, BDS3/Jefferson L. Clark, DDS4

Longevity of implant-supported fixed partial dentures (ISFPDs) may be associated with multiple clinical complications, irrespective of whether retention is achieved via screws or cement. While use of screws ensures ease of prosthesis retrievability and elimination of the inherently risky cementation process, more mechanical strains are induced in this design. A combined screw-retrievable and cement-retained ISFPD is designed to achieve the best passive fit and strain reduction while allowing complete excess cement removal and maintaining ease of retrievability. Moreover, this approach suggests better protection of the cement layer from oral environment degradation and offers scope for an alternative retention protocol. This paper outlines aspects of the clinical indications and fabrication of a screw-retrievable, cementretained ISFPD. A diagnostic assessment method that provides tactile resistance guidance for selection is also proposed. Int J Prosthodont 2017;30:577–580. doi: 10.11607/ijp.5321

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raditionally, implant-supported fixed partial denture (ISFPD) designs have included either cementor screw-retained prostheses. Cement-retained ISFPDs have increased in popularity over the past two decades with reports of favorable stress distribution,1 while screw-retained designs have the primary advantage of easy retrievability. A prosthesis that utilizes advantages from both designs could prove beneficial.2 This paper offers a prosthetic guideline discussing the parameters of design and fabrication principles of the screw-retrievable, cement-retained (SRCR) ISFPD.

Prosthesis The SRCR ISFPD is defined as an ISFPD that includes a cement-retained fixed partial denture (FPD) superstructure with screw access channels designed to correspond to the screw access channels of the custom abutments to which it is cemented (Fig 1).

1Faculty,

Department of Prosthetic Dental Sciences, College of Dentistry, King Saud University, Riyadh, Saudi Arabia. 2Professor and Director, Advanced Specialty Education Program in Prosthodontics, Loma Linda University School of Dentistry, Loma Linda, California, USA. 3Faculty, College of Dentistry, Imam Abdulrhman Alfaisal University, Dammam, Saudi Arabia. 4Graduate Student, Advanced Specialty Education Program in Prosthodontics, Loma Linda University School of Dentistry, Loma Linda, California, USA. Correspondence to: Dr Abdulaziz AlHelal, Loma Linda University, School of Dentistry, 11092 Anderson Street, Suite # 3313, Loma Linda, CA 92350, USA. Email: [email protected] ©2017 by Quintessence Publishing Co Inc.

Diagnosis and Decision-Making There are multiple diagnostic methods based on the classification for ISFPDs by AlHelal et al3 to determine the type of ISFPD to be used. A simplified and objective diagnostic assessment procedure can be done during one of the following stages: Impression-Making Stage. Impressions are made with the use of engaging impression copings. Following the fitting and intraoral splinting of impression copings and prior to definitive impression making, the splinted impression copings are unscrewed. Friction-free removal indicates the ability to use an ABC-I ISFPD.3 If removal encounters slight resistance, one engaging abutment should be used along with nonengaging abutments (ABC-II ISFPD).3 Custom Abutments Trial Placement Stage. Once custom abutments are verified for fit and design, they are splinted with a rigid material to assess its removal. A prefabricated verification jig can be used and cemented over the custom abutment at this stage as a trial cementation technique (Fig 2a). Custom abutments at this stage can be unscrewed and checked for prosthesis removal. The disadvantages of this technique include the limited modifications that can be made to the custom abutments. Also, modifying an engaging into a nonengaging custom abutment must be done carefully to avoid damage. Definitive Cast Stage. Either impression copings or custom abutments can be used at this stage, as previously described (Figs 2b, 2c, and 2d). The advantage of making a diagnostic assessment at this stage is that it allows complete control in the decision-making

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Protocol for Screw-Retrievable, Cement-Retained, Implant-Supported Fixed Partial Dentures

Fig 1   Sketch of the proposed SRCR ISFPD guideline showing design concept. Blue line indicates the die spacer application being only on the axial sandblasted surface, which will be occupied with future definitive cement. A dual cement seal was achieved by painting the die spacer short of the cervical part of custom abutments (primary/cervical cement seal) and by avoiding occlusal surface application of the die spacer near screw access channels of custom abutments (secondary/occlusal cement seal with a margin of 0.5–1 mm). Screw access channels for both ISFPD and custom abutments are correspondent to each other.

Fig 2  (a) Prefabricated trial cementation jig in place for diagnosis of implant angulation classification and to determine type of ISFPD that can be used at custom abutments try-in stage. (b) Two splinted impression copings on master cast prior to removal. (c) Successful removal of splinted impression copings, indicating parallel implants at master cast stage (ABC-I/PBC-I classification).3 (d) Example of unsuccessful impression coping removal, indicating the necessity for one engaging and one nonengaging implant abutment (ABC-II/PBC-II classification).3

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process for the type of ISFPD prosthesis. Impression copings can be easily replaced from an engaging impression to a nonengaging impression coping.

Fabrication Steps and Guideline 1. Fabricate the custom abutments either conventionally or digitally from a complete contoured wax pattern of the proposed ISFPD. 2. Once the custom abutments are fabricated, die spacer application should be designed with a dual seal design. The die space is applied in a conventional manner on the axial surfaces and short of the cervical finish line (primary/cervical cement seal), as shown in Fig 3a. Additionally, the die spacer is applied on the occlusal surface short of the screw access channels by approximately 0.5 mm to 1 mm. This allows for a secondary tight seal contact between the retainer’s intaglio surfaces and the

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occlusal surfaces of the custom abutments closest to the screw access channels (secondary/occlusal cement seal) (Fig 3b). 3. Fabricate a cementable ISFPD framework (conventional or virtual design) over the custom abutments with occlusal screw access channels parallel and correspondent to the screw access channels of the custom abutments. 4. Complete the fabrication of the ISFPD with the choice of restorative material (Fig 3c). 5. Sandblast both custom abutments and intaglio surfaces of ISFPD retainers (Figs 3d and 3e). 6. At the placement appointment, place the custom abutments and hand tighten the screw up to threefourths the recommended manufacturer instruction torque value. Cover the screw access channel with polytetrafluoroethylene tape. 7. Cement the ISFPD superstructure intraorally with definitive resin cement.

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AlHelal et al

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Fig 3  (a) Showing die spacer painted on custom abutments, avoiding conventional cervical finish line (primary/cervical cement seal). This is aimed to prevent the cement from leakage degradation at the cervical prosthesis aspect. (b) 0.5–1 mm around custom abutment screw access channel was left free from the die spacer. The secondary/occlusal cement seal is aimed to prevent cement film degradation at the coronal aspect of the prosthesis, especially when the sealing restorative material is compromised. (c) Showing final porcelain fused to metal SRCR ISFPD parts, including two engaging abutments (ABC-Ia/PBC-I classification).3 (d) Titanium milled custom abutments sandblasted (avoiding finish line) and placed intraorally during intraoral cementation. (e) Intaglio view of sandblasted ISFPD before cementation procedure.

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Fig 4  (a) Lateral clinical view of final SRCR ISFPD. (b) Occlusal clinical view of final placement of SRCR ISFPD (SAC-II classification).3 (c) Final radiograph of prosthesis in place.

8. Following complete polymerization of the resin cement, remove excess cement from the access channels and retrieve the prosthesis. 9. Inspect and assure complete removal of remaining excess cement found at the mating area between the ISFPD, custom abutments, and on the implant platforms. 10. Polish the intaglio surfaces of the custom abutments and the ISFPD to assure the elimination of residual cement layer and scratches. 11. Place the prosthesis over the supporting implants and torque the ISFPD screws following manufacturer instructions. Seal the access holes with preferred choice of material, followed with composite or porcelain plug (Fig 4).

Discussion The suggested technique uniquely combines advantages of both screw- and cement-retained methods of retention. The SRCR ISFPD with chairside cementation protocol reduces the amount of strain on the prosthetic components and the stress on the supporting implants compared to a conventional screw-retained ISFPD. This modality also provides ease of retrievability similar to that of a conventional screw-retained ISFPD. This allows convenient accessibility to and direct visualization of the implant platform for easy and complete excess cement removal (Figs 5 and 6). Proper diagnosis of ISFPD type based on the diagnostic and prosthetic classifications for ISFPD is

Volume 30, Number 6, 2017 © 2017 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

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Protocol for Screw-Retrievable, Cement-Retained, Implant-Supported Fixed Partial Dentures

Fig 5  (a) Example of milled titanium custom abutments with monolithic zirconia SRCR ISFPD (ABC-Ib/PBC-I with SAC-I classification).3 (b) Prosthesis clinical try-in. (c) Sealing abutment screw access channel prior to clinical cementation. (d) Clinical cementation of SRCR ISFPD. Note excess cement at the labial prosthesis margin. a

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Fig 6  (a) Extraoral view of retrieved SRCR ISFPD following intraoral cementation. Note the amount of excess cement at lingual aspect of the prosthesis. (b) Prosthesis view following complete removal of excess cement and polishing. (c) Occlusal prosthesis view following completion of SRCR ISFPD guideline protocol. (d) Clinical view of final placed SRCR ISFPD. a

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critical.3 An objective diagnostic assessment using tactile resistance was utilized to decide the type of ISFPD indicated. This assisted in preventing complications associated with potential unintentional locking of the SRCR ISFPD.

Conclusions The SRCR ISFPD, when applicable, provides easy retrievability and less stress/strain to supporting implants/prosthetic components for partially edentulous patients. The application of a double seal design to the prosthesis provides a more superior long-term seal to the cement retention mechanism with SRCR ISFPDs.

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References  1. Heckmann SM, Karl M, Wichmann MG, Winter W, Graef F, Taylor TD. Loading of bone surrounding implants through three-unit fixed partial denture fixation: A finite-element analysis based on in vitro and in vivo strain measurements. Clin Oral Implants Res 2006;17:345–350.   2. Rajan M, Gunaseelan R. Fabrication of a cement- and screwretained implant prosthesis. J Prosthet Dent 2004;92:578–580.   3. AlHelal A, Kattadiyil MT, Clark JL, AlBader B. Diagnostic classification and design considerations for implant-supported fixed partial dentures and screw access channel: The ABC/PBC and SAC Classifications. Int J Prosthodont (in press).

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