This search for the ideal restorative has also influenced the options available for anterior implant restoration. The replacement of an anterior tooth using an implant has been a challenging obstacle for most clinicians. While a metal abutment provides long-term predictability and strength, it can compromise the esthetic value of the final restoration and limit the restorative options.
This is of particular concern if the implant crown is to be matched to metal-free adjacent restorations such as ceramic veneers or all-ceramic crowns, which provide translucency that allows the underlying tooth structure to be seen through the restoration,thus providing a more realistic and natural appearance. When a metallic abutment is used on an implant, the restoration must provide the opacity necessary to cover up the dark color of the abutment, thereby diminishing vitality.
The use of a metal-free abutment such as one made of monolithic zirconium oxide offers clinicians an improved platform for an overlying esthetic restoration4 (Figure 1 and Figure 2) in that the abutment can be dentin-shaded, thus allowing for placement of a more translucent overlying restoration. Moreover, compromised esthetics due to any dark grey color emanating from the metal abutment—which can shine through the gingival tissue, especially in a thin biotype—is eliminated. However, there has been concern about the fracture load capacity of these abutments as well as the differences among abutments available from varying manufacturers.
Also, there have been reports from clinicians who have seen fracture of the monolithic zirconium-oxide abutment at the interface between the titanium implant itself and the abutment during torquing of the abutment screw. Others have reported a high incidence of horizontal and vertical fractures either during placement of the screw or during function of the implant body itself due to the thin zirconium-oxide walls of the abutment (Figure 3).
Using a cast gold UCLA-style abutment over a titanium base has been done successfully for many years.14 The stock abutment is made up of two separate components—the titanium base with the internal or external hex and the coronal nylon sleeve, which can be modified and then cast in gold (Figure 4). One advantage of this type of abutment is the flexibility it affords the laboratory to custom design an ideal implant abutment. However, although abutment shape and margin placement are controllable, the cast gold itself used for the abutment does not allow for the use of a translucent overlying definitive restoration thereby yielding less-than-optimal esthetics.
Fig 1 Monolithic zirconium abutment replacing the maxillary left central incisor.
Fig 2 Use of an all-ceramic crown over the abutment to provide excellent esthetics and match adjacent all-ceramic restorations.