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Rules of engagement

by: Chandur Wadhwani

If you’re not planning for a screw-retained restoration, take the following rules into account.

Rules of Engagement

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.

Rule number 1

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.”

Rule number 2

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 et al 2013).

Rule number 3

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.

Rule number 4

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.

Rule number 5

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.

Rule number 6

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).

Rule number 7

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, Hess, Piñeyro, Opler & Chung 2012).

Rule number 8

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!

Rule number 9

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.

Rule number 10

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.

References

Wilson TG. The positive relationship between excess cement and peri-implant disease: A prospective clinical endoscopic study. J Periodontol 2009;80:1388-1392.

Wadhwani CP, Piñeyro AF. Implant cementation: clinical problems and solutions. Dent Today. 2012 Jan;31(1):56, 58, 60-2.

Wadhwani C, Rapoport D, La Rosa S, Hess T, Kretschmar S.Radiographic detection and characteristic patterns of residual excess cement associated with cement-retained implant restorations: A clinical report. J Prosthet Dent. 2012 Mar;107(3):151-7.

Wadhwani C, Piñeyro A, Hess T, Zhang H, Chung KH.Effect of implant abutment modification on the extrusion of excess cement at the crown-abutment margin for cement-retained implant restorations. Int J Oral Maxillofac Implants. 2011 Nov-Dec;26(6):1241-6.

Tarica DY, Alvarado VM, Truong ST. Survey of United States dental schools on cementation protocols for implant crown restorations. 2010 J Prosthet Dent. Feb;103(2):68-79.

Agar JR, Cameron SM, Hughbanks JC, Parker MH. Cement removal from restorations luted to titanium abutments with simulated subgingival margins. J Prosthet Dent 1997;78:43-7.

Linkevicius T et al. The influence of the cementation margin position on the amount of undetected cement. A prospective clinical study. Clin Oral Implants Res. 2013 Jan;24(1):71-6

Sadan A, Blatz MB, Bellerino M, et al. Prosthetic de- sign considerations for anterior single-implant restorations. J Esthet Restor Dent . 2004;16:165-175.

Bennani V, Schwass D, Chandler N. Gingival retraction techniques for implants versus teeth: current status. J Am Dent Assoc. 2008 Oct; 139(10):1354-63.

Wadhwani C, Hess T, Piñeyro A, Opler R, Chung KH. Cement application techniques in luting implant-supported crowns: a quantitative and qualitative survey. Int J Oral Maxillofac Implants. 2012 Jul-Aug;27(4):859-64

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