Screw-retained design
The choice of whether to screw or cement retain an implant restoration remains one considerable debate amongst dental professionals. The literature is consistent that the success of both options are very high. Complication rates of both are essentially identical (3-5%).
The traditional rationale for screw retention is the retrievability of the restoration. This is a luxury that does not exist in conventional fixed prosthodontics on teeth. As a result, any complication with the restoration can be more easily addressed. The screw retained restoration is easily removed which allows for repair or examination of soft tissue and direct visualization of the implant. This also negates the need to remake the restoration if an abutment screw or prosthetic screw loosens. A more recent argument in favor of screw retention is to eliminate the potential complications associated with excess residual cement – often difficult to completely remove with a cement retained crown. With the development of the Angulated Screw Channel (ASC) the ability to utilize the screw retained option has been expanded. With angulations of up to 25° from the long axis of the implant it is still possible to fabricate a screw retained restoration. One perceived disadvantage to the screw retained option has been the concern over the visibility of the access channel. With the improved esthetic materials, ability to angulate the screw channel and various other approaches this is easily dealt with. The argument that the patient is responsible as the driving factor for not accepting the appearance of screw access channel is not supported in the literature.Cement-retained Design
The cement retained option provides the assurance of maximum esthetics. The concern with cement retention is two fold. The first being the restoration is cemented to an abutment that is screw retained. The abutment screw becomes loose and the final restoration cannot be removed without destroying it, in many instances. This results in a remake and increased cost. Additionally the recent literature reports cases of late implant failure. It is well known that implants lack any transeptal fibers that would limit the progression of cement along the implant surface during seating of the crown and associated expression of excess cement. This extrusion along the implant surface potentially acts as medium for colonization by bacteria and can jeopardize the osseointegrated attachment. This will ultimately result in implant failure. With the advent of new cements that are essentially invisible to the eye and radiolucent, excess cement may be left behind. There have been proposed clinical approaches to limit this scenario. In addition if custom abutments are utilized in this approach the fabrication costs may be higher than a screw retained option. In certain instances cement retention is the only option (whether it be space or esthetic) it is highly recommended that the insertion process be carried out in a meticulous manner, with first seating the restoration on a refractory die wiping away the excess, then proceeding to the oral cavity. It is also advisable to utilize a radio opaque luting agent, and be certain all excess material has been removed as portrayed in the sequence above.
