Tooth intrusion in implant-assisted prostheses Cherilyn G. Sheets, DDS, a and James C. Earthman, PhD b School of Dentistry, University of Southern California, Los Angeles, and University of California, Irvine, Calif. Statement of problem. Numerous reports and surveys have been published on natural tooth abutment intrusion with implant-connected fbxed partial dentures. The consensus of these publications was that the cause of intrusion was multifactorial, with causative factors such as disuse atrophy, debris impaction, impaired rebound memou, and mechanical binding. It was also believed that the process was irreversible. Purpose. In this article, the limitations with these theories are discussed, and nvo patient reports of tooth intrusion reversal are reviewed. A review of the current literature is discussed, as well as the current theory of tooth movement in response to dynamic mechanical stimulus, a brief discussion of current experimental procedures and results, and the current recommendations for reversal of intrusion. (J Prosthet Dent 1997;77:39-45.) A decade ago, P. I. BrSnemark, MD, gave the profession a protocol for restoring the dentition ofeden- tulous patients. On the basis of 20 years of research, Dr. Br~nemark recommended isolation of the implants from the natural abutments for partially edentulous situ- ations, the use of resilient restorative materials for the occlusal surfaces of the restorations, and a retrievable design to the prosthesis. The recommendations were a compensation for the potential difference in the way natural teeth and implants would react to static and dynamic loading. Since then, clinicians began to modify Br~qemark's original recommendations. Porcelain fused to metal re- placed acrylic resin on restorations because of its increased strength and the long-term esthetics provided by the porcelain. I Screw access holes were often eliminated be- cause of the improvements that were desired in occlu- sion, esthetics, and patient comfort. 2 Implants became part of restorative treatment plans that not only included Presented at the Academyof Prosthodonticsannual meeting, New- port Beach, Calif.,May 1996. %ssociate Clinical Professor, Department of Prosthodontics, School of Dentistry,University of Southern California,and Private prac- tice, Newport Beach. UAssociate Professor, Materials Science and Engineering,University of California, Irvine. implants but other trcatmcnt modalities, such as porce- lain-fused-to-metal restorations, porcelain veneers, in- lays, and onlays. Ultimately, even natural teeth and im- plants were joined in implant-assisted prostheses as part of comprehensive occlusal restorations, a These changes from the original Br~nemark proto- cols have brought some interesting complications. One of the most surprising problems was the occurrence of tooth intrusion in implant-assisted prostheses. The purpose of this article is to explore the subject of tooth intrusion in implant-assisted prostheses. This article examines the current theories for the occurrence of tooth intrusion, two pertinent patient studies, the ap- plicable literature from several disciplines, a hypoth- esis to explain the intrusion phenomenon, current re- search to quantify the effects of energy dissipation in dental implant structures, and current recommendations for the treatment of intrusion. EXISTING THEORIES In an international survey of natural tooth abutment intrusion with implant-connected fixed partial dentures (FPDs), Rieder and PareP reported that the respondents felt the cause of intrusion was multifactorial and the re- sult of causative factors such as disuse atrophy, debris impaction, impaired rebound memory;, and mechanical ~ANUARY 1997 THE JOURNAL OF PROSTHETIC DENTISTRY 39