No abstract

The aim of this investigation was to evaluate the use of resonance frequency measurements in the clinical measurement of implant stability. Resonance frequency measurements are undertaken by measuring the response of a small transducer attached to an implant fixture or abutment. Two groups of patients were selected for study. Group A comprised 9 patients who had a total of 56 implants placed. Resonance frequency measurements were made at fixture installation and repeated 8 months later at abutment connection. The resonance frequency of the implant/transducer system increased for 50 out of the 56 implants from a mean value of 7473 Hz +/- 127 Hz (P < 0.05) to a mean of 7915 Hz +/- 112 Hz (P < 0.05). Two implants had failed to integrate and the resonance frequency of these had fallen. Group B comprised 9 patients who had been provided with fixed prostheses and had a total of 52 implants placed. They were examined 5 years after fixture placement and the prostheses removed. All implants were judged clinically to be osseointegrated. The level of the marginal bone around each implant was calculated by measuring the number of exposed threads on intraoral periapical radiographs and added to the length of each abutment to give a value termed the effective implant length (EIL). Measurements indicated a correlation (R = -0.78, P < 0.01) between EIL and resonance frequency. The results support the hypothesis that the resonance frequency of an implant/transducer system is related to the height of the implant not surrounded by bone and the stability of the implant/tissue interface as determined by the absence of clinical mobility.

In the 1960s and 1970s, implant-supported prostheses based on subperiosteal or blade implants had a poor reputation because of questionable clinical outcomes and lack of scientific documentation. The change to a scientifically sound discipline was initiated by the two scientific pioneers of modern implant dentistry, Professor P. I. Brånemark from the University of Gothenburg in Sweden and Professor André Schroeder from the University of Bern in Switzerland. Together with their teams, and independently of each other, they laid the foundation for the most significant development and paradigm shift in dental medicine. The present volume of Periodontology 2000 celebrates 50 years of osseointegration. It reviews the progress of implant therapy over the past 50 years, including the basics of implant surgery required to achieve osseointegration on a predictable basis and evolving innovations. The development of bone-augmentation techniques, such as guided bone regeneration and sinus floor elevation, to correct local bone defects at potential implant sites has increased the indications for implant therapy. The paradigm shift to moderately rough implant surfaces resulted in faster and enhanced bone integration and led to improvements in various treatment protocols, such as immediate and early implant placement in postextraction sites, and made various loading protocols possible, including immediate and early implant loading. In the past 15 years, preoperative analysis and presurgical planning improved as a result of the introduction of three-dimensional imaging techniques. Hereby, cone-beam computed tomography offers better image quality with reduced radiation exposure, when compared with dental computed tomography. This opened the door for digital planning and surgical modifications. Over the last 50 years this evolution has facilitated tremendous progress in esthetic outcomes with implant-supported prostheses and improved patient-centered outcomes. This volume of Periodontology 2000 also discusses the current trends and open questions of implant dentistry, such as the potential of digital implant dentistry in the surgical and prosthetic field, the trend for an increasing average age of implant patients and the related adaptations of treatment protocols, and the second attempt to establish ceramic implants using, this time, zirconia as the implant material. Finally, some of the hottest controversies are discussed, such as recent suggestions on bone integration being a potential foreign-body reaction and the evidence-based appraisal of the peri-implantitis debate.

Within the limitations of this study, it is concluded that failing implants show a continuous decrease of stability until failure. Low RFA levels after 1 and 2 months seem to indicate an increased risk for future failure. This information may be used to avoid implant failure in the future by unloading implants with decreasing degree of stability with time as diagnosed with the RFA technique.

When looking across all bone qualities, the Mark IV implant develops a significantly higher insertion torque than the Standard, Mark II, and Osseotite implant types, and a significantly higher resonance frequency value than the Standard implant, indicating a higher interfacial stiffness at the implant-bone interface.

The study showed that there is great potential for healing and bone formation in the maxillary sinus without the use of additional bone grafts or bone substitutes. The secluded compartment created by the elevated sinus membrane, implants, and replaceable bone window allowed bone formation according to the principle of guided tissue regeneration. The precise mechanisms are not known, and further histologic studies are needed. Sinus membrane elevation without the use of additional graft material was found to be a predictable technique for bone augmentation of the maxillary sinus floor.

The aim of this investigation was to measure the resonance frequency of a number of implants placed in the rabbit tibia at insertion and at predetermined periods thereafter and to correlate the results with histomorphometric measurements made when the animals were sacrificed. Ten mature New Zealand White rabbits were used in the study. Two c.p. threaded titanium implants were placed in the right tibia of each animal. Resonance frequency measurements were made by screwing a small transducer onto a standard abutment mounted on each fixture. Measurements were repeated with the transducer oriented perpendicular and parallel to the long axis of the tibia for all proximal implants 14 and 28 days after placement and in 6 implants additionally at 42, 56, 93, 122 and 168 days after which all animals were sacrificed. Histomorphometric analysis comprised 2 parts; measurement of bone-implant contact area and height. A significant increase in resonance frequency was observed after 14 (405 Hz, +/- 234 Hz) and 28 (658 Hz, +/- 332 Hz) days. The increase in resonance frequency levelled after approximately 40 days and little further change was observed. The variation in bone-implant contact area was relatively small (1.8-4.9 mm2) and the range of bone-implant contact heights was also narrow (-1.5 (-)+ 1.5 mm). Values for resonance frequencies plotted against contact area and height were grouped around 10 kHz. In conclusion, it was shown that resonance frequency measurements can be made at placement and during healing in vivo and changes may be related to the increase in stiffness of an implant in the surrounding tissues.

The present study showed a strong bone tissue response to surface-modified zirconia implants after 6 weeks of healing in rabbit bone. The modified zirconia implants showed a resistance to torque forces similar to that of oxidized implants and a four- to fivefold increase compared with machined zirconia implants. The findings suggest that surface-modified zirconia implants can reach firm stability in bone.