The Drill on Implants: Implants 360: Can Screw-Retained Implants Solve Peri-Implantitis?

Debate over cement could bring implants full circle

By Pam Johnson

From the revolutionary introduction of Brånemark’s screw-retained style implants in the late 1960s to the advent of pre-fabricated abutments and the clinical simplicity of cement-retained implants in the early 1980s, today pressure is building to revert back to screw-retained implant restorations. The culprit? Growing concern over increased prevalence of peri-implantitis. Although the long-term bone integration success rate of dental implants is a reported 98%¹, the alarm has recently sounded for an increased percentage of implants in function for more than five years that demonstrate bone loss due to remnant cement being left in the sulcus.

“We are beginning to see repercussions of cement-retained implants now that these implants have been in place for 10 to 20 years,” says Joseph Apap, CDT, MDT, General Manager of Town & Country Dental Studios, based in Long Island, New York. “This is particularly true for implants with solid abutments that are 2- to 4-mm subgingival.” Residual cement left in the sulcus, he explains, invites an invasion of bacteria, leading to the formation of a periodontal lesion, the loss of bone and even implant failure if left untreated. Although most causes of peri-implant bone loss are biologic in nature and point to patient risk factors, recent reports and studies on the topic of peri-cementitis being presented by key opinion leaders and written in journals have caused concern and confusion among dental professionals restoring the implant site. The simple and safe solution perceived by many has been to revert back to the screw-retained technique.

Georgios E. Romanos, DDS, PhD, professor at the School of Dental Medicine Department of Periodontology at Stony Brook University in Stony Brook, New York, is upset over the overreaction and thinks the issue is more complex. “For more than 25 years I have used the same cementation-technique concept to restore implant sites with no incidence of implant failure due to peri-cementitis,” Romanos says. “If peri-implantitis were the sole culprit, then we would be seeing high incidences of implant failures in Europe, where very often implant-supported restorations for esthetic purposes are cement retained. But we are just not seeing that happen. Peri-implantitis is a more complex disease.”

Leon Hermanides, CDT, owner of Protea Dental Studio Inc. in Redmond, Washington, and clinical instructor at the Kois Center in Seattle, agrees that the reported prevalence of 10% to 20% of peri-implantitis in implants that have been in function for 5 to 10 years² may have a more complex etiology. “There is the complexity of the biologic system and patient-specific issues to be considered. There are so many complex facets to implant dentistry that, if all are not in line, the result can be implant failure.” And reverting back to screw-retained is not necessarily the answer. “The outcome-based studies I have seen indicate that there is either a very slight difference or the same difference in crestal bone loss rates between cement- and screw-retained implants,” Hermanides says. Indeed, Romanos points to an eight-year clinical evaluation published in 2014 in the International Journal of Oral and Maxillofacial Implants by Roberto Crespi, DDS, PhD, and his colleagues from Milano, Italy, that confirms the lack of statistical difference in bone loss between the two retention types. “So there must be other factors playing into the significant failure rates within the first nine years of implant placement,” Romanos says. Purported causes for implant failure rates range from poor implant placement, implant overload, and rough implant surfaces geared to help bone adhere for implant retention to the use of wide body implants or the failure of bone grafting materials applied to the exposed threads of the implant. Even at the impression stage in a conventionally delayed loaded case, Romanos suggests that the risk of introducing contaminated agents that compromise the site may occur when the dentist removes the healing cap and inserts a non-sterile impression coping for impression-taking and then replaces that same healing cap.

Regardless of the causes, in the end, all agree that there are indications and contra-indications as well as advantages and disadvantages for both implant retention types so no one system is applicable to every implant situation.

For dentists who want to stay in their cement-retained comfort zone but minimize the risk of implant complications down the road, several techniques exist to reduce the chance of leaving behind excess cement. Romanos suggests that when placing the restoration, the clinician dry the area with air, isolate with cotton, and inject liquid Vaseline into the sulcus. As the cemented crown is setting, the Vaseline protects the sulcus from cement penetration. After the cement sets, he sprays the area with water to wash away any excess cement that may have been extruded. “I use Temp Bond cement and have never had a restoration fail due to residual cement left around the crown.” (Go to insidedentaltech.com/idt874 to view images and a detailed description of the Romanos technique.)

Another technique that Apap suggests his clients use even when the crown is subgingival with a deep margin where cement removal is difficult is to replicate the abutment with bite material. “Before the clinician places the crown, he or she can squirt bite material into the restoration prepared by the laboratory and let it set. This becomes a replica of the abutment that can be used to express and remove excess cement out of the crown before it is placed in the mouth. The amount of cement left inside the crown is enough to retain the restoration to the abutment.”

Hermanides, who is an a proponent of cement-retained implants, is careful to ensure that the margins of his cement-retained restorations are no more than 1-½ mm under the gum on the facial, at the gingival margin on the lingual, and ½ to 1 mm below the gum on the proximal to allow access by an explorer for cement removal.

Helpful techniques aside, the reality for many laboratories is that they are seeing failed implants with cement still on the threads. For those laboratories, advising clients to use a CAD/CAM designed and milled screw-retained monolithic restoration cemented to a titanium abutment in the laboratory and delivered as a complete restoration helps simplify the procedure for their clients and alleviates any concerns of leaving behind residual cement in the subgingiva.

In conclusion, it may take many more years of research and clinical studies to resolve all the issues that may be impacting the long-term success rate of dental implants and the incidence of peri-implantitis.