Covering the Implant Prosthesis Screw Access Hole: A Biological Approach to Material Selection and Technique.

Abstract

W ith implant treatment in the esthetic zone, it is a constant endeavor to maintain and increase the volume of peri-implant tissues. Many recent developments in implant and abutment design have this as the primary goal. Thus we have seen the evolution and creation of ‘‘platform switch’’ abutments, narrowed abutment diameters, and conical implant connections—all in an effort to maximize the volume of the peri-implant bone and soft tissues. The conical connection in particular was developed with the aim of maximizing the integrity of the abutment– implant connection and thus reducing movement, decreasing peri-implant bone stress, and minimizing leakage of the contents inside the abutment into the delicate zone where bone, connective tissue, implant, and abutment all merge (Figure 1). This concept is sound and it does appear to reduce leakage into the peri-implant tissues, but it does not eliminate leakage. This is a problem that worsens over time with repeated loading. The ‘‘platform switch’’ design has mostly (but not entirely), proven to better maintain bone levels than abutments that flare directly from the head of the implant. Multiple finite element analyses have shown that the conical connection may serve to significantly reduce the stresses on the peri-implant crestal bone. It appears that the mechanical integrity of the conical connection provides a biologic benefit even outside the implant itself. The reason for the success seen with platform switch implants appears to be twofold: First, the nonintegrating abutment components are more narrow and thus further away from the bone allowing more space for the necessary biologic width. When nonintegrating components encroach upon this space, the bone remodels laterally and apically to create the necessary biologic space. Secondly, the platform switch design moves the implant–abutment junction (IAJ) away from the bone, and thus moves the inflammatory cell infiltrate coming from inside the implant / abutment and exiting at the IAJ further away from the crestal bone. Much histological study has been made into the biologic environment adjacent to the IAJ, and it has been well established that bone is maintained at a more coronal position when leakage is minimized by use of conical connections, and when the leakage that does occur is moved further away from the bone by use of platform switch abutments. Recent short-term data suggest that the conical connection and minimizing leakage at the IAJ is the more important factor in limiting bone loss. Based on these concepts, it is evident that the contents inside the implant/ abutment directly, and negatively, affect the peri-implant bone position. Leakage from the IAJ cannot be eliminated, but efforts should be made by the clinician to minimize it. It is clear that the contents of the implant/abutment negatively affect the peri-implant bone, and that they will leak from the IAJ. Thus, what is put into the abutment to cover the screw can have a significant effect. According to a 2008 survey, 59% of prosthodontic residency directors and 77% of restorative department chairpersons in the United States use cotton pellets to cover the screw access opening under the definitive restoration. The use of cotton is an adaptation of the method used to temporarily fill the access for endodontically treated teeth, though it appears to be falling out of vogue for this purpose as well. It should be noted that cotton was never intended for use under a definitive restoration. The problem with the use of cotton is that the internal aspect of most implants and implant abutments are hollow, whereas the connection at the IAJ between them is prone to leakage. This creates a 358C, mostly oxygen-free, hollow tube filled with saliva, oral flora, and nutrients—an environment ripe for the proliferation of anaerobic bacteria. As the patient functions on the implant, the IAJ continues to flex and wear, pumping saliva, nutrients and oral flora into the implant chamber from the peri-implant area (not the screw access hole). As the anaerobic bacteria proliferate and the IAJ continues to flex and leak, the anaerobic byproducts are pumped out of the implant at the IAJ and directly into the peri-implant tissues. Covering the screw with cotton, in particular, appears to be problematic because it is an open, organic, scaffold-like structure (Figure 2). These properties provide pathogenic oral flora an ideal substrate upon which to flourish and which likely increases the volume and potency of the inflammatory cell infiltrate. Additionally, cotton has been shown to allow the most leakage into the implant, when compared in vitro to gutta-percha, silicone plugs, and polyvinyl siloxane (PVS) impression materials. The seal created by polytetrafluoroethylene (PTFE) tape has been shown to be effective in sealing endodontically treated teeth and in implant abutments when compared with cotton. Ultimately, it appears that the 1 Section of Restorative Dentistry, University of California-Los Angeles School of Dentistry, Los Angeles, CA, USA. 2 Department of Restorative Dentistry, Loma Linda University School of Dentistry, Loma Linda, CA, USA. 3 Private practice limited to prosthodontics, Bellevue, WA, USA. * Corresponding author, e-mail: tschoenbaum@dentistry.ucla.edu DOI: 10.1563/aaid-joi-D-16-00119