Screw‐Retention vs Cement Retention of Restorations
Stability of the connections between the different parts of the overall implant system is a significant factor in the clinical success of the reconstruction. This is especially true for single‐tooth restorations, where there is a need for a strong interlock between abutment and implant. The implant‐abutment connection stability is influenced by factors such as component fit, machining accuracy, saliva contamination and screw preload.
Attaching the final restoration to the abutment by a screw or dental cement was addressed briefly in Chapters 3, 6, and 11. Which approach is “better” is still a matter of debate. Some clinicians prefer screw‐retention and others choose to use a resin‐based or adhesive resin “cement” to retain the restoration, Fig. 13.1.
Cement Retention of Restorations
The present international consensus is that cement retention may be recommended for the following situations:
- For short‐span prostheses with margins at or above the tissue level
- To enhance esthetics when the screw access passes through the buccal aspect of a restoration
- In cases of malpositioned implants
- To reduce initial treatment costs
- Situations in which access is severely restricted or the patient has limited ability to maximize opening of the jaws.
Using cement retention will often simplify laboratory fabrication procedures for the restoration. Resorting to cement retention of the restoration to the abutment may be the only approach to satisfactorily join restoration and implant, particularly if access to the implant is restricted. Finally, in some instances, there is an esthetic benefit in having intact restorative surfaces, for example, screw access traversing the buccal aspect on an anterior tooth.
However, there can be problems associated with cement‐retained restorations, notably if the restoration should fail or need to be replaced. In such cases, removing the cemented restoration from the abutment can present a far greater challenge than simply unscrewing it. Another and important factor regarding cement‐retained restorations is that there is always a finite thickness of cement film between restoration and abutment. One consequence of this is that if a viscous cement was used or there is a thick cement film, the restoration may not seat completely down on the abutment. Consequently, there can be a gap between the margins of the restoration and the abutment collar, (Fig. 13.2). Inability to completely seat restorations is well‐known in prosthodontics, and the gap at the external line angle can be quite large [1, 2].
The presence of such a gap can result in a multitude of issues, including leaching out of the cement. The latter will permit ingress of fluids and bacteria which may lead to quite significant problems, namely peri‐implant bone loss.