Implants are not teeth. Techniques and materials routinely used on the natural dentition are not always suitable for implant restoration.
Recently, a new issue with implants has come to light the association of peri-implant disease and residual excess cement (REC). Understanding why and how REC impacts the peri-implant site may help eliminate some of the problem.
If you’re not planning for a screw-retained restoration, take the following rules into account.
Biology: Cementing restorations on natural teeth has occurred for over 100 years, with few if any real problems when the tooth and surrounding tissues are healthy. However, implants are not teeth, and using techniques and materials used on the natural dentition may be detrimental to the implant as well as the implant supporting tissues.
Biologically, a tooth has a highly sophisticated network of fiber bundles (Sharpey type), attaching the soft tissues to living cementum, producing compartments that slow down and limit the progression of disease.
An implant has a weaker hemidesmosomal attachment that is more susceptible to trauma and stripping, and only one compartment exists, which is formed by circumferential fibers that surround the implant like an “o-ring.”
Restoration depth: Tooth preparations for crowns and bridges are far more superficially related to the gingival margin.
Rarely are they deeper than 1 mm, and most often the preparation finish line is supra-gingival. The flat top head of an implant is often placed deeper into the tissues to enable emergence profiles. It is known that 3mm deep on the facial aspect can easily become 6mm deep if a papilla is present inter proximally, so the cement finish line must be carefully controlled by the abutment placed on the implant.
A recent study demonstrated that the deeper the cement finish line, the greater the depth of the soft tissues and the greater the amount of REC (Linkevicius 2013).
Cements designed to be protective of teeth may damage implant surfaces. Some cements contain fluoride — known to protect the natural tooth. However, under the acidic conditions found in some cements, the fluoride has been shown to corrode titanium, and the manufacturers’ instructions often clearly state that they are not suitable for titanium structures.
With teeth, highly radio-opaque cements may hide decay and thus may be detrimental to successful longterm results. Not so with implants, where radio-opacity is crucial for finding REC around implants.
Conventional dental cements are often tooth-colored to hide a visible cement line. Implant cements should never be shaded to blend with the gingiva, since it makes finding and cleaning out REC more difficult.
Consider the environment that these cements are placed into. Teeth suffer from caries, so antimicrobial activity against the causative organisms is desirable in most cases. These bacteria are not problematic for implants, however. Anti-microbial activity against potentially harmful gram-negative bacteria — such as Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatumor Porphyromonas gingivalis — may be more appropriate when considering cemented implant restorations. Recent research at the University of Washington suggests that some cements promote the growth of these disease producing bacteria, others limit it (in press 2013).
Understand how much cement is actually required with an implant restoration. A definite amount of space has been built into the design of the crown to allow for the cement. Use too much cement and the excess will have to be extruded from the abutment-crown system. A recent survey concluded that most dentists have no idea how much cement to use, or where to apply it (Wadhwani 2012).
Clean up is made much easier if the cement you use does not bond to the abutment or the implant itself. Most implants have rough surfaces to promote healing. These rough surfaces make clean up potentially more difficult. A non–adhesive cement is much more likely to be removed in unwanted areas. Use a softer cement, but utilize abutment modifications such as air-abrasion, less taper, increased height or internal venting to promote better retention. We do this with teeth all the time —consider retention and resistance form!
Isolation of the implant cement site may be difficult, if not impossible. Use of retraction cord is not recommended as placement may strip the hemidesmosomal attachment. Some cements in their unset stages have chemicals that can cause allergic responses. These can leach into the surrounding tissues and result in inflammation.
There is no ideal cement, but understanding why the techniques used on teeth and implants are very different may make this process less of a problem for you and your patient.