Hybrid Screw-Cementable Implant Restorations
Deliver the clinical benefits of screw-retained restorations in less time
Jonathan Esquivel, DDS
Restoring teeth with dental implants requires delicate planning, proper clinical execution, and extensive follow-up. Implant-supported restorations can either be cement-retained or screw-retained. When cement is used, any excess cement allowed to remain in the peri-implant tissues can be a cause of failure for dental implants. Research has indicated that the incidence of peri-implant disease among implants with excess cement is approximately 80%.1 With natural teeth, the orientation of the connective tissue fibers is perpendicular and they have insertions, but with an implant, they run in a parallel orientation around the implant components.2 This lack of a seal and the anatomical form of abutments makes it easier for excess cement to flow into deeper areas and cause damage. Although proper cement selection, improved abutment designs, and updated placement techniques have reduced the potential for excess cement,3 the use of screw-retained implant restorations is preferable to eliminate the possibility of cement-induced peri-implant disease.
Screw-Retained Implant Restorations
Beyond eliminating the problems associated with excess cement, other benefits of screw-retained implant restorations include that they require less restorative space and can be more easily retrieved should re-treatment become necessary. However, their delivery can be more time-consuming, and poorly designed access channel openings can result in patient dissatisfaction. For an anterior, screw-retained implant restoration to achieve proper esthetics, the implant needs to be placed in a specific 3-dimensional position that will allow the screw access hole of the implant restoration to be lingual to the incisal edge. There are many fabrication methods for screw-retained restorations, but the most classic approach involves using a universal clearance-limited abutment (UCLA). With the evolution of materials and the demand for esthetic restorations, titanium bases have been developed to accommodate custom-made ceramic abutments and crowns that can then be delivered in a screw-retained fashion. These abutments have ceramics either pressed or layered directly onto them, and then the crowns are cemented to them extraorally prior to delivery. This design is sometimes referred to as a screw-cementable restoration.
The Screw-Cementable Solution
Adjusting interproximal contacts on a cement-retained crown is a very simple process because the abutment is connected to the implant. This permits the crown's contacts to be adjusted in the same manner as a tooth-supported restoration. However, with a screw-retained crown, adjusting the interproximal contacts is more complex because the clinician will have to screw and unscrew the restoration each time until the abutment is fully seated. Screw-cementable restorations solve this problem because the abutment can remain connected to the implant while the contact points of the crown are adjusted like a cement-retained restoration. Once the contact points are allowing the crown to adequately seat, the abutment is unscrewed, and the crown is cemented to it extraorally (Figure 1 and Figure 2). The bonding protocol required will vary depending on the materials used for the abutment and the crown.
If the abutment or the crown is made of zirconia, following the "APC" bonding protocol described by Blatz and colleagues is recommended.4 If the abutment or the crown is made of lithium disilicate, the protocol for that specific material needs to be followed. If a titanium abutment with no mechanical retention is used, air abrading and priming the metal before bonding the restoration is recommended. After the crown has been seated on the abutment and light cured (Figure 3), the clinician can carefully clean away the excess cement (Figure 4) and polish the crown/abutment interface before torqueing the completed restoration into place (Figure 5).
Due to anatomical limitations, it is sometimes impossible to place an implant in the correct position to accommodate a screw-retained crown. If the screw access hole of the provisional restoration is located at the incisal edge or on the facial aspect (Figure 6), the clinician will have to consider a cement-retained restoration or a restoration/abutment design with an angled screw access channel.5 These types of abutments can be used to correct the degree of angulation of implants, which presents an advantage in the esthetic zone because the screw access hole can be shifted from a facial position to one lingual to the incisal edge (Figure 7). These abutments require a CAD/CAM-fabricated restoration in order to achieve a proper relationship with the titanium base.
A 54-year-old male patient presented to the clinic to have implant-supported restorations placed at the sites of teeth Nos. 14 and 15 (Figure 8). Custom-made titanium CAD/CAM abutments and porcelain-fused-to-metal (PFM) restorations (Noritake Super Porcelain EX 3, Kuraray Noritake) were fabricated, which were designed in a manner to be cement retained. However, after the restorations were adjusted and seated in the mouth, access holes were created to convert them into screw-cementable designs.
In this clinical scenario, the titanium abutments offered no mechanical retention; therefore, air abrasion was performed, and then the metal was primed with a single-component adhesive primer (CLEARFIL™ CERAMIC Primer Plus, Kuraray Noritake). Once the abutments were prepared, a resin cement (PANAVIA™ V5, Kuraray Noritake) was used to cement the restorations to them extraorally. After light curing, cement cleanup, and finishing, the crowns were delivered as screw-retained restorations (Figure 9), preventing excess cement problems in the peri-implant tissues and offering easier retrievability if needed in the future (Figure 10).
When compared with cement-retained implant restorations, screw-retained implant restorations offer clinical and biological advantages. Screw-cementable restorations can provide an even better option because they require less chair time during the delivery appointment. An appropriate bonding protocol must be followed when bonding ceramic restorations to zirconia or titanium abutments to create screw-cementable restorations. In situations where implants cannot be ideally placed, abutments with angulated screw access channels can facilitate screw access holes that are more lingually located, permitting screw retention with excellent esthetics.
About the Author
Jonathan Esquivel, DDS
Department of Prosthodontics
Louisiana State University
School of Dentistry
New Orleans, Louisiana
For more information, contact:
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