Mode of Retention of Fixed Implant Prosthesis
Fixed dental implant-supported prostheses may be either cement-retained or screw-retained. Screw-retained prostheses (Figure 6) are retrievable and require lesser vertical restorative space compared to cement-retained prostheses.58,59 Retrievability enables better hygiene maintenance of the prosthesis, the implants, and the surrounding mucosa60 and easier management of the restorations in case of complications. Screw loosening, the requirement of sectioning and soldering procedures, increased costs, greater complexity of components and laboratory procedures, increased chairside time, and compromised esthetics, occlusion and porcelain strength are the major disadvantages associated with screw-retained prostheses.58-61 It is also difficult to place a screw-retained restoration in a patient’s mouth with a limited oral opening as it may be challenging to insert the screwdriver in the oral cavity.62
Cement-retained implant prostheses (Figure 7) offer superior stability,63 occlusion, esthetics, stronger implant prosthetic connection, and improved force transmission compared to screw-retained implant prostheses.58,59 Extrusion of the excess cement into the peri-implant sulcus (which may be difficult to recognize and remove) is one of the major drawbacks of a cement-retained prosthesis.58,64 Several techniques have been reported that aid in preventing/decreasing the flow of cement into the subgingival sulcus.64-67
Picture courtesy of Dr. Wicks
The Locator F-Tx attachment system (attachment system for fixed implant-supported prostheses) (Figure 8) has been recently introduced by Zest Dental Solutions as a solution to the disadvantages of both screw and cement retention.68 F-Tx system eliminates the use of screw access holes, cement, and several difficult intraoral procedures.23,68 Unique spherical abutment geometry allows denture attachment housings (DAHs) of the F-Tx system to pivot in any direction (angle correction) up to 20 degrees. The F-Tx Denture Attachment Housings (DAHs) are picked up in the prosthesis via a chairside pick-up procedure similar to that used for the conventional locator attachment system.68
Picture courtesy of Dr. Massad
Locator F-Tx attachment system.
Fixation by revolutionary “snap-in” feature; angulation correction up to 20°from the vertical; stress-free passive fit; decreased requirement of vertical restorative space (9-12mm); improved esthetics; and higher patient comfort and satisfaction are the listed advantages of the F-Tx attachment system.68 The F-Tx attachment is contraindicated for single-tooth restorations, unilateral partial fixed implant prostheses, implants with divergence greater than 20° or where a resilient connection is required.68