Most implant dentists are concerned with providing their patients with a long-lasting and reliable restoration. However, the long-term success of a crown can depend on a number of different biological components and material related factors. One of the main decisions a clinician will need to make is whether to use a screw-retained implant crown or to use a cement-retained restoration. Scientific studies have not produced conclusive data supporting one type of restoration over the other so the choice is largely down to personal preference and whether screw access is favorable.
Advantages of Using a Screw-Retained Implant Crown
Screw-retained restorations are popular due to the easy retrievability of the crown and, of course, there is no need to use dental cement. Using a cement-free restoration eliminates the risk of leaving cement sub-gingivally. It can often be difficult to ensure any excess cement is completely removed which could otherwise increase the risk of peri-implantitis. Additionally, it can be nice to have the option to easily re-tighten an implant screw or to remove an implant crown if problems occur. Retrievability could be particularly beneficial where hygiene is a concern as the implant crown can be easily removed and thoroughly cleaned before being replaced.
Generally, it can be advantageous to use a screw retained implant crown when restoring posterior teeth, especially upper posterior teeth. Screw retained implant crowns can also be useful when restoring more complex implant cases.
Planning Implant Placement for a Screw-Retained Implant Crown
If using a screw-retained implant crown is an option, then it is necessary to make this decision prior to placing the implant. This ensures the implant can be correctly oriented so that the implant screw will exit in the right location. Ideally, screw access should be available in the central fossa of a molar or bicuspid or on the palatal surface of an anterior crown. With posterior implants, this doesn’t usually cause a problem but it may be more of a concern with anterior implants and where the screw access hole must exit palatally. It is possible that the anatomy of the hard tissues may not allow this to happen.
Seating a Screw-Retained Implant Crown
There are various techniques that can be used to seat a screw-retained implant crown but most dentists choose to use composite resin. Prior to seating the crown, some dentists prefer to gently roughen the surface around the screw hole using light air abrasion or a diamond bur, before etching and cleaning the area. Ideally, a new screw will be provided for seating the restoration but if the lab screw is to be used then it must be thoroughly cleaned prior to fitting. Once the restoration has been seated and the screw is correctly torqued, it can be advisable to cover up the screw head to avoid getting composite directly on the screw. The access channel can then be covered with composite.
Possible Disadvantages of Using a Screw-Retained Implant Crown
One possible disadvantage of using this type of restoration is that the presence of occlusal access for the screw will interfere with the morphology of the crown. The screw access hole must be closed with composite resin and this could impair the final esthetic outcome especially where a metal-based framework is used. One way to get around this problem is to use an opaque composite to help mask the metal followed by body colored and enamel colored composite resins. However, choosing a zirconia crown eliminates this disadvantage, allowing an aesthetically pleasing closure of the screw access channel to easily be achieved with conventional composite resin.
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