state of the art in oral implants

Tomas Albrektsson and Lars Sennerby Biomaterials Group, Department of Handicap Research, Gothenburg University, Brunnsgatan 2, S-41312 Gothenburg, Sweden

Albrektsson T and Sennerby L: State of the art in oral implants. J Clin Periodontol 1991; 18: 474-481. Abstract. Uncontrolled oral implant devices are still being widely used. The documentation of most oral implant systems is poorly backed up or not followed up for an adequate time period. Success rates are being quoted without reference to any defined success criteria. Frequently used oral implant designs such as the Core-Vent, IMZ and Calcitek hydroxyapatite coated implants are in neither case supported by any adequate clinical reports from minimally 5-years of follow-up. Other implant systems such as the ITI, some subperiosteal designs and the Tiibingen implant demonstrate well-controlled and acceptable 5-year data but are not followed up in a sufficient number or have demonstrated less good results in the 10-year evaluation. The Small transosteal staple has been adequately reported for more than 10 years of follow-up, whereas the Branemark implant is the only endosseous design that has demonstrated acceptable 15-year success rates.

Oral implants have been used for a long time. Oral implants devices of the past, in some cases most unfortunately still used at present, were poorly controlled from a clinical standpoint. The backing up of oral implants in the scientific literature used to be mostly of the case history type. During the 1960s and 70s, dental implants "sub-communities" formed all over the world, albeit the oral implant treatment was not recognized by any major university and there were very few oral implant courses given at the university level. The use of a series of scientifically unproven devices has continued. It is surely an important task for the dental community at large to properly define what is a "lege artis" treatment and what procedures or oral implant designs that should be avoided at the present state of scientific knowledge. Recent NortAmerican attempts to improve the current situation such as the NIH Concensus Development Conference of 1988 failed in identifying some of the problems associated with certain types of oral implants. Nevertheless, the conference stated clearly that for the future, we need prospective studies of oral implants following standardized ways of reporting. All failures have to be reported irrespective of when they occurred. Criteria for patients selection as well as clear definitions of success and failure should also be reported. In fact, these basic demands which are well in line with our previous suggestions (Albrektsson et al. 1986)

have also been emphasized by the American FDA in their suggested new regulations for oral implants. These regulations are to be valid from 1992 and will ask for a 3-year prospective report of minimally 100 consecutively treated patients and then a 2-year follow-up resulting in 5-year clinical data before any market introduction of a new implant system or continued sales of previously introduced ones. Considering the fact that oral implants are inserted in human beings, this seems to be quite a logical approach that will help us to avoid a lot of unnecessary human suffering. To improve the state of art in oral implants, we feel it is most important that the dental profession will support a much stricter regulation on the sales of oral implants than is the case today. In the present paper, we will discuss current implant usage and try to differentiate between survival and success criteria. The importance of uniform success criteria for the evaluation of different implant systems will be stressed. In addition, the outcome of some currently used oral implant systems will be summarized, based on a literature review study with emphasis on papers published after 1986, when our previous survey was authored (Albrektsson et al. 1986). Survival and Success of Oral Implants

Implant survival is often misquoted to indicate implant success. However, in

Key words: oral implants; success criteria; clinical outcome. Accepted for publication 5 June 1990

reality, implant survival only relates to the devices remaining in the jaws of the patient. The quality of the survival as well as the function of the implant is irrelevant. Nevertheless, controlled survival figures also accounting for patient drop-out cases and patient death, such as in the elegant paper by Shulman et al. (1986) do provide valuable data. Another condition for the value of life time-table statistics is of course that we have an adequate and regular patient control. However, the present authors are of the opinion that success rates aremuch more valuable than survival figures in the determination of the actual outcome of an implantation procedure. If success rates are presented, these must relate to defined success criteria. The most frequently cited success criteria in the literature seem to be those presented by Schnitman & Shulman (1979) and those presented by Albrektsson et al. (1986). These success criteria are presented in Table 1. Other success criteria have been presented by Cranin et al. (1982) and McKinney et al. (1984). The latter differs mainly from the Schnitman & Shulman (1979) criteria in the addition of some subjective patient evaluation with respect to implant fucntion, absence of discomfort and patient attitude of an improved aesthetics, and psychological attitude. In addition. Smith & Zarb (1989) have recently suggested an addition to the previously suggested criteria of Albrektsson et al

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(1986). Smith & Zarb (1989) want to height measurements cannot be per- of loss of alveolar bone more than 0.2 stress that the implant design should formed in orthopantograms. Further- mm annually for some years, a bone not preclude placement of a crown or more, it is advantageous if the evalu- resorption that later ceased after bridge prosthesis with a material that is satis- ation is based on a minimum of 100 reconstruction. Of course, we could disfactory to the patient and the dentist. consecutively analysed implants, then cuss whether this bone loss is truly indicative of implant failure if the implant The consensus conference on clinical presented as an average with standard periodontics (Nevins et al. 1989) has deviations to compensate for the uncer- afterwards will function adequately for suggested very similar criteria for im- tainty in each individual measurement. several years. However, such cases are plant success, such as those previously We do not believe that there is any rea- rare and we would after all prefer to son to use specific success criteria to recommend a strict approach in all sucpublished by Albrektsson et al. (1986). The present authors believe it is evaluate soft tissue anchored and the cess evaluations even if there do exist "border-line cases". mandatory to evaluate implants follow- so-called osseointegrated oral implants, ing standardized success criteria. For in- with exception of the mobility parstance, a progressive saucerization of ameter. Here, it seems logical to accept the bone as well as poor function of the some mobility around soft tissue an- Soft Tissue Anchored Oral implants implant because of infection and pain chored devices, whereas the bone an- The Blade Vent implants have recently will be rated as "positive" with respect chored implants should be immobile so received a provisional acceptance by the to survival statistics until the very mo- as to be rated as scuccessful. As teeth American Dental Association, based on ment the implant is lifted out of the and implants differ from one another, it an analysis of the clinical data from Kabone bed. Implants giving rise to such is uncertain to what extent we can use pur et al. (1987, 1989). This study is a symptoms should, however, never be ra- conventional periodontal techniques to prospective investigation of the outted as "successful". Furthermore, we see indicate implant success or failure. come of a consecutive series of blade a need to continuously strengthen the Smith & Zarb (1989) pointed out that implants inserted at 5 different Veteran demands for a minimal % of success there is little information that sulcus Administration centers. Altogether, 114 with subsequent improvements in im- depth is related to implant success. Lek- patients received fixed partial prosplant technology and clinics. Whereas holm et al. (1986) have demonstrated theses and 118 patients removable parthe 1978 consensus conference (Schnit- that the presence of deep pockets is not tial prostheses. In the former case, a lifeman & Shulman 1978) only asked for a necessarily correlated to an accelerated table analysis indicated a 5-year survival minimum of 75% success over a follow marginal bone loss. Where the gingival rate of 84.2%, and in the latter case up of 5 years, this is an unacceptably state is concerned. Smith & Zarb (1989), there was a 74% survival rate. However, low figure in 1990 and would rather after having summarized the literature if success criteria involving bone deindicate a poor outcome than a good on the subject, concluded that "it apterioration are included in the evaluone. Not even the suggested 85% suc- pears that although increasing the deation, no less than 45% of the implants cess over a follow-up of 5 years sug- gree of gingival inflammation is not a showed an unacceptable degree of bone desirable response, it has not been gested by Albrektsson et al. (1986) and loss, as proposed by Albrektsson et al. Smith & Zarb (1989) seems to provide shown to be a factor in implant success(1986). The same unacceptable high dea very stringent criteria in the mandible ". Smith & Zarb (1989) further conbetween the mental foraminae. At least cluded that even if the gingival implan- gree of bone loss was demonstrated in in this region, more than a 95% 5-year tation an indicidual cases should pro- the controlled study by Smithloff & Fritz (1982, 1987). The latter study origsuccess rate could be expected with gress to bone loss, this would be much inally involved 32 patients and 49 immodern oral implant devices. In other better evaluated by testing implant molocations such as the posterior man- bility in combination with a standard- plants that have been meticulously followed up over a long time span. To our dible, poorer success rates are to be ex- ized radiographic technique. knowledge, none of the lately published pected. To include a limited maximal Having stressed the importance of controlled Blade Vent studies have demdegree of bone resorption in the success implant success criteria, we must also onstrated acceptable success rates (Kapcriteria seems logical, not the least since admit to the need of a constant updatur et al. 1989, Smithloff & Fritz 1987, this is one of the few objectively assessing, with increasing knowledge. The Schnitman et al. 1988). We do not find able parameters. However, it should be present authors are aware of the probthat the available data from these added that a controlled radiography lems associated for instance with bone studies could motivate any further rouwith evaluations in individual radioheight measurements where there have tine clinical use of blade implants (Fig. grams is necessary. Adequate bone been reports (Adell et al. 1981) of cases 1). Subperiosteal Implants Table 1. Success criteria proposed by Albrektsson et al. (1986) (1) That an individual, unattached implant is immobile when tested clinically (2) That a radiograph does not demonstrate any evidence of periimplant radiolucency (3) That vertical bone loss be less than 0,2 mm annually following the implant's 1st year of service 4) That individual implant performance be characterized by an absence of signs and symptoms such as pain, infections, neuropathies, paresthesia, or violation of the mandibular canal 5) That, in the context of the above, a success rate of 8 5 % at the end of a 5-year observation period and 80% at the end of a 10-year period be the minimum criteria for success

Recently published studies on subperiosteal implants indicate good initial success rates but a clear drop in outcome over 5 and 10 years of oral followup (James et al. 1988, Bodine & Yanase 1985). The data by James et al. (1988) refer to 14 inserted unilateral upper subperiosteal implants with a 5-year survival of 92% and 31 full upper sub-

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periosteals with a 5-year survival of 80%. A total of 147 full lower subperiosteals had been inserted and the 13-year survival rate of those was 78%, The material of Bodine & Yanase (1985) represents a meticulously controlled follow-up of 28 patients with a 5-year survival rate of the order of 90%, a 10year rate of about 60% and 15-year rate of about 50% survival. Using the success criteria suggested by Schnitman & Shulman (1979); Mercier et al. (1981) reported a subperiosteal success rate of 60% for a follow up of 3,3 years (average). Although the survival studies by James et al, (1988) and Bodine & Yana-

se (1985) are very well controlled and provide valuable data, we do not fmd that subperiosteal devices have survived the scrutiny of time and they cannot be recommended for routine clinical usage at the present stage. Single-crystal Sapphire Implants

This is a one-stage oral implant of aluminum oxide. Previously reported success rates by Sawa et al. (1980) should not be compared with other figures quoted in this study, as the authors have admitted that early failures were excluded from their material. A very

well-controlled study of this implant has been presented by Koth et al, (1988), This study involves the evaluation of various soft tissue parameters as well as assessment of implant mobility and radiographic indices. Of the originally 29 inserted implants in 18 patients, 1 was already aborted at the initial surgical procedure and 5 other implants were rated as failures at the time of prosthodontic treatment. The 5-year success rate of the single crystal aluminum implant seems to be between 70 and 78% (Steflik et al. 1988), depending on whether the outcome is based on 27, 28 or all originally inserted 29 implants. The Tubingen Aluminum Ceramic Implant

This implant has been well documented in the literature. Success rates of the order of 90% for a follow-up of 5 years or more (Schulte & d'Hoedt 1988) have been reported, albeit a complete 10-year evaluation has not been found in the literature, A Swedish study of 70 implants inserted in 45 patients with a follow-up of 0 to 5 years indicated a success rate of 88% (Nordenram et al, 1986), Cranin et al, (1987) have reported a success rate of 80% over an average of 19 months of follow-up. Verbal communication with participants of the Swedish team (Kondell 1989) has indicated that in the Swedish material, there has at least been a tendency of implant fracture in load-bearing constructions. The significance of this problem is, however, difficult to analyse at present. Nevertheless, it should be observed that the Tubingen implant success rate mainly is related to single replacements in contrast to some other implant systems, Transmandibular Staple Implant

Fig. I. Blade Vent implants may occasionally, as in this case, remain in the jaw bone of the patient for more than 10 years (a). Failure due to soft tissue inflammation and progressive saucerization of the bone seems inevitable with time in the case of the presently used softtissue anchored implants (b).

The staple implant is of course limited to the lower jaw and would generally imply extra-oral incision as well as general anaesthesia. Small & Misiek (1986) presented the outcome of a retrospective study carried out on 1516 patients treated between the years 1968 and 1984, They described a cumulative rate of success of 94.6% for 5 years and 90.9% for a follow up of more than 10 years. However, a relatively majoi degree of bone loss as well as implant mobihty was observed in about 10% ol the cases. Bosker & Van Dijk (1989) have presented an up to 12-year follow-

State of the art in oral implants up of a different type of transmandibular implant manufactured from a gold alloy. Their study included 368 patients that had mainly been treated with removable dentures. The authors reported some complications in the form of infection and gingival hyperplasia, but the overall survival rate was quite positive, as only 6 patients had had their implants removed. A prospective study of 13 consecutively treated patients (Powers et al. 1989) followed up for 2 years as well as a multicenter study of 190 patients (Maxson et al. 1989), have further verified the good function of the Bosker transmandibular implant at least over follow-up times of 2-5 years. Other authors (Davenport et al. 1985, Friedman & Vernon 1983) have described a couple of cases of osteomyelitis and cellular carcinoma with an assumed relation to transmandibular plates. However, the reports of such serious complications seem to be very few in comparison to the large number of treated patients. The Core-Vent Titanium Aiioy impiant

In a recent publication by Patrick et al. (1989), 1732 consecutively inserted Core-Vent implants were evaluated. The mean implantation time was 27 months. Success rates of the order of 96 to 98% were reported. However, these data are very difficult to compare to other success figures quoted in the present paper. In the first place, there is sparse information on the quality and frequency of patient control, e.g., the number of patients that actually appeared on scheduled recalls. Secondly, bridges were cemented and it is not clear whether any mobility checks were performed with bridges removed at patient recalls. The quality of their radiographical examinations did not make it possible to investigate possible bone loss around the implants. With the presently used Core-Vent design, other investigators (Moy 1987, Malmquist & Sennerby 1990) have reported a severe bone resorption around Core-Vent implants. Whereas Moy (1987) reported between 50 and 60% success based on 101 consecutively inserted Core-Vent implants followed for 2 yers, Malmquist & Senlerby (1990) in their 2-4 year report )n 47 consecutively inserted implants, bund only a 9.3% success. If the more iberal success criteria suggested by (chnitman & Shulman (1979) were !sed, Malmquist & Sennerby (1990) still

only found 37.2% of the implants which could be rated as successful (Fig. 2). The present authors therefore believe that the reported high success rate by Patrick et al. (1989) should be interpreted with caution, as uncertainty remains with respect to implant mobility as well as loss in bone height around their devices. The IMZ Implant

This implant system advocates the use of a stress breaking element, the so called IME. However, recent studies by Lill et al. (1988) and McGlumphy et al. (1989) present some conflicting data, considering the actual function of the IME component. The IMZ implant of commercially pure titanium has been used clinically for more than 10 years. However, Albrektsson et al. (1986) found it difficult to compare success rate reported by Kirsch & Ackermann (1983) with those of other dental implant systems, as there were no proper success rates presented. Finally, this criticism remains as illustrated in a recently published paper by Kirsch & Ackerman (1989). In this latter paper, a total of 3088 IMZ implants placed in 1401 consecutive cases were reported. 10.8% of the implants were lost to follow-up for various reasons, but it is unclear if every other patient participated in the annual control pro-

gram. Individual radiograms with estimations of the bone height were not presented. Therefore, the impressively high success rate of 97.8% seems rather to be a survival % with some remaining queries. For instance, Flemmig & Holtje (1988), reported an average marginal bone loss with 39 consecutively placed IMZ implants of 2.89±0.29 mm. The average time of follow-up was 5.5 years. 3 of the 39 implants were shown to be mobile. The present authors see a great need for more controlled studies such as that of Flemmig & Holtje (1988), to provide us with estimates of the accurate success rate of the IMZ implant system (Fig. 3). In addition, it should be added that there have been various designs as well as surface coatings of clinically used IMZ implants which make the data difficult to analyse in detail. The ITI Implant

In their comparative study, Albrektsson et al. (1986) found the ITI implant to be well documented in the literature from a scientific as well as from a clinical aspect. However, at the time, there were no proper long-term follow-up studies published. The notion that the ITI hollow cylinder implant is a well-documented system has been further confirmed in a recently published book

Fig. 2. The Core-Vent hollow basket implant, a design frequently used in North America, in many cases seems to induce a severe bone loss that extends down in the basket region (a). Irrespective of whether the implants in question have been initially stable and "osseointegrated", the gradual bone resorption has caused frequent implant failures within 5 years in many cases (b).

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(Schroder et al. 1988). ITI implants are allowed to immediately penetrate the mucosa from the time of placement. This does not seem to disturb the bone anchorage of the devices (Buser et al. 1988). Schroder & Krekeler (1988) reported success rates of the order of 85 to 92% for a follow-up of 0 to 8 years. Maeglin (1988) reported different complications that may occur with the ITI implant treatment. Implant fractures were regarded as improbable, a statement that is in some conflict with a recent report of the ITI implant typeF inserted in dogs. Here, 15% of the implants fractured (Liithy & Strub 1988). Liithy et al. (1987) have also demonstrated a significant decrease of the coating thickness of ITI hollow basket and IMZ plasma-flame-sprayed implants. However, these authors stated that the microhardness of the ITI hollow basket implant was significantly higher than that of the IMZ implant. In summary, the ITI implant must be regarded as one of the best documented systems of those currently available. However, it must be pointed out that there are several varieties in design of this implant that may lead to different success rates. The Branemark Implant

The threaded commercially pure titanium introduced by Branemark et al.

(1977) still seems to be the best controlled oral implant device from an experimental as well as a clinical standpoint (Branemark et al. 1985, Albrektsson & Zarb 1989). Albrektsson et al. (1988a, b) pubhshed a multicenter study ofthe outcome of 13091 consecutively inserted Nobelpharma implants. Success rate for follow-ups of more than 5 years were 85 to 100% in the maxilla and 93 to 99% in the mandible. Other follow-up studies have indicated similar results (Mito et al. 1989). These authors reported an average implant success in the mandible of 99% and in the maxilla of 89% for a follow-up of 0-36 months. The material consisted ofthe 145 maxillary and 247 mandibular implants. Most of the maxillary failures occurred in the posterior region. Kondell et al. (1988) reported the outcome of 350 maxillary and 440 mandibular implants that had all been consecutively inserted. There was an 88% success in the maxilla (average follow up time ~ 2 years, range 1-5 years) and a 99% mandibular (average follow up ^ 3 years, range 1-6 years) success. Albrektsson & Lekholm (1989) have reported the so-called routine group 1 Branemark implants inserted between 1971 and 1976. Altogether, 524 maxillary fixtures have been followed with a 5-year maxillary success rate of 84%, a 10-year success rate of 81 % and a 15-year success rate of 78% (73 to 83% in a 95% confidence inter-

val). 480 followed-up mandibular fixtures showed corresponding success rates of 91% (5 years) 89% (10 years) and 86% (15 years) (81-90% in a 95% confidence interval). The continuously registered bridge stability rate for 15 years was 93% in the maxilla (« = 80) and 99% in the mandible (« = 83). In the case of partial edentulous jaws, 43 fixtures had been followed from 6 to 20 years with an 86% implant success rate and a 100% bridge success rate. In what was referred to as the research group 1 in which 324 fixtures had been followed for 1 to 5 years, there was a fixture success rate of 96% and a bridge stability rate («= 124) of 98%. The success criteria in the study were those described by Albrektsson et al. (1986) (Fig. 4). In a retrospective multicenter study with partially edentulous patients by Van Steenberghe et al. (1989), the authors reported an 87% individual implant success in the maxilla (« = 40) and a 92% success in the mandible (77 = 93) for a follow-up of 6-36 months. Hydroxyapatite Coated Implants

HA-coated implants have so far only been followed up over a hmited time period. Kent etal. (1988) presented an abstract of 0 to 3 years outcome of 457 consecutively-inserted integral implants with a cumulative success rate of 97.4% and an interval success rate of 95.6%.

Fig. 3. Reported succes rates of the IMZ implant are slightly difficult to interpret. These photographs represent 1 of 4 IMZ implants tha: had to be removed from a patient in spite of an undisturbed anchorage after more than 1 year of clinical insertion (a). This implant also showed a mixture of bone and soft tissue anchorage (b, c). .,

State of the art in oral implants The exact success criteria as well as further details of the follow-up conditions were not revealed. Dennisen et al. (1989) reported 71 HA-coated "prestressed" implants of which 67 were connected to various types of superstructures. The titanium core was lost in no less than 16 of these cases and another implant suffered from a fractured post. Golec (1988) reported 514 hydroxyapatite-coated integral implants inserted in edentulous ridges. Only 7 of those were failures for a follow-up of 0-3 years. 255 hydroxyapatite-coated implants were placed in immediate extraction sockets and only 4 failures were reported. However, success criteria and patient follow-up data were not reported adequately and the conclusions that can be drawn from this paper are uncertain. The major risk associated with hydroxyapatite coated implants is that of coat failure. Such problems have been reported by Albrektsson & Sennerby (1990), Levandowsky & Johns (1989) as well as by Lemons et al. (1989). However, it must be regarded as unknown whether coat loosening will constitute a major problem with hydroxyapatite coated devices or not. Nevertheless, HA-coated implants have to our knowledge become clinical routine insertions far too rapidly (Fig. 5).

^. The Branemark implant represents the est-controlled deviee from a basic science as ell as clinical point of view. In this retrieved uman specimen, there is good bone anchor;e in the threads but an evident bone re)rption around the points of thread.

Concluding Remarks

As can be seen in this review, most currently marketed oral implants are poorly backed up from a scientific point of view. Either there is a lack of clinical documentation or the follow-up period of a new implant design is only a couple of years, which surely prevents any conclusions as to the long-term chnical results. Reported clinical results with various implant systems must be read with caution, as generally the frequency and quality of the patient control is poorly reported. Success rates are often quoted without referral to any success criteria. The so-called "5-year success rate" often represents a 0- to 5-year survival rate at best. In some cases, implant failures that have occurred during the incorporation period are not included in the statistics. Nevertheless, several implant systems seem to give quite acceptable 5-year results such as subperiosteal implants (at least the designs used by James et al. (1988) and Bodine & Yanase (1985)), the Small transmandibular staple implant (Small & Miziek 1986), the Tubingen frialit implants (Schulte & d'Hoedt 1988), the ITI-hollow cylinder implant (Schrdder et al. 1988) and the Branemark implant (Adell et al. 1981). However, if we look at 10-year figures, the most reasonable time of evaluation, the data for most of these implant systems are either lacking or unacceptably

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poor as defined by AlbreJctsson et al. (1986). Sufficient 10-year data on which to base a rehable statistics with success rates above those suggested by Albrektsson et al. (1986), seems to exist only with the Branemark implant and the Small transmandibular staple. This same conclusion was drawn in our earlier paper (Albrektsson et al. 1986). Whereas for instance the Tubingen statistics are mainly based on single replacements, the Branemark figures mainly relate to fully edentulous jaws. This could explain part of the difference seen in the reported statistics between these 2 implant systems, not withstanding that the first long-term data of the Branemark system used as single implants or in partially edentulous cases, seem to indicate a replication of Branemark data from fully edentulous Jaws. It seems mandatory to avoid a direct loading of oral implants to prevent interfacial soft tissue formation. However, at least the short-term outcome of various controlled implant systems such as the Tubingen, the ITI and the Branemark devices, where various regimes with respect to time for gingival penetration are recommended, seems to indicate that there is insufficient evidence to back up the necessity for a 2-stage surgical procedure. For instance, the ITI onestage implant procedure has resulted in a more than 90% 5-year success rate between the mental foraminae in the

Fig. 5. One type of currently used hydroxyapatite coated implants is the Integral® (a). Hydroxyapatite has been demonstrated as establishing a rapid and good bony contact as in this retrieved clinical case (b).

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mandible, in spite of the fact that this implant allows immediate penetration of the soft tissues. There is of course a possibility that even higher success %s could be achieved with the ITI implants, should a 2-stage principle be recommended. The Branemark implant, after all, shows between 95 and 99% success for a follow-up of 5 years between the mental foraminae in the mandible. The only way to investigate the exact importance of this parameter for implant success would be to arrange a controlled protocol with the same implant design that is alternatively subjected to a 1and 2-stage soft tissue penetration. It should be added that the ITI implant is presently being marketed in a two-stage version as well. In the future, success criteria will have to be up-dated continuously so that patients are guaranteed the most optimal treatment available. Furthermore, success rates presented should be related to location of the implant in either central portions of the mandible or maxilla, respectively, or posterior portions of the same bones. These 4 regions present 4 different bone sites with respect to healing capacity. In the 1990s, hopefully, we will see a more strict attitude to untested clinical products that are to be inserted in human beings, and that current types of "human experimentation" with oral implants will come to an end.

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Tubingen Implantat aus Frialit® - Weitere Ergebnisse, Z. Zahndrztliche Implantol IV, 167-173. Shulman, L, B., Rogoff, G, S., Savitt, E, D, & Kent, R, L, (1986) Evaluaton in reconstructive implantology. Dental Clinics of North America 30, 327-350, Small, I. A, & Miziek, D, (1986) 16-year evaluation of the mandibular staple bone plate, /, Oral Maxillofac, Surg, 44, 60-66, Smith, D, E. & Zarb, G, A, (1989) Criteria for success of osseointegrated endosseous implants, /, Prosth, Dent, 62, no, 5, 567-572. Smithloff, M, & Fritz, M, E. (1982) Use of blade implants in a selected population of partially edentulous patients, J, Periodontol, 53, 413-418, Smithloff, M, & Fritz, M, E. (1987) The use of blade implants in a selected population of partially edentulous adults, a 15-year report, /, Periodontol 58, 589-593, Steflik, D, E,, McKinney, R, V, Koth, D, L, & Howell, F, V, (1988) Morphological and clinical results of ceramic implants in patients. The Third World Biomaterials Congress, Kyoto, Japan, 21-25 April, Van Steenberghe, D,, Sulhvan, D,, Listrom, R,, Balshi, T,, Henry, R, Worthington, P, & Wahlstrom, U, (1989) A retrospective multicenter evaluation of the survival rate of osseointegrated fixtures supporting fixed partial prostheses in the treatment of partial edentulism, /, Prosth, Dent, 61, 217-223, Address: T, Albrektsson Biomaterials Group Department of Handicap Research Gothenburg University Brunnsgatan 2 S-413 12 Gothenburg Sweden