The philosophy of the year 2000 in oral rehabilitation by means of implants

Say oral rehabilitation by means of implants and never implantology

Implants are since decades a familiar part of the armentarium of many medical specialities : e.g. artificial valves in cardiac surgery, lenses in ophthalmology, synthetic ossicles in oto-rhino-laryngology, femoral implants to carry a hip prosthesis in orthopedics, etc. None of them uses the term implantology ! In oral health care, fillings, strictu sensu dental implants, have played a major role. No successful attempts were reported on oral implants, by which endosseous implants are meant, until P.-I. Brånemark reported at the end of the seventies, mostly unnoticed, his 10 years clinical follow-up study. It were endosseous implants installed in edentulous lower jaw patients to carry a fixed prosthesis. Results were good and properly documented (^{Brånemark et al., 1977}). When the 15 years report from the same group appeared in 1981 the attention of many was drawn on the osseointegration approach. Osseointegrated oral implants became lege artis worldwide, even if scepticism took some time to dissipate in some centres (^{Adell et al., 1981}).

At the end of this millennium some one and a half million patients worldwide have been treated by « osseointegrated » implants, which mostly means that an intimate bone-to-implant apposition has been achieved, which is a less stringent definition of the term, originally implying a longlasting stability. The market value of these oral implants is estimated at some 0.7 billion US dollars with an annual growth close to 10 %. Thus, the oral health care community and the government regulatory bodies must take their responsibility in this matter seriously, both from a health care and economical view-point.

Since hundreds of thousands of patients have their implants exposed to the oral environment, and several thousands have been monitored in more or less planned studies, an enormous amount of information has been gathered during two decades. Most of it has been reported in specialised journals of which one - Clinical Oral Implants Research - even reached number 2 for its impact factor among all « dental » journals. On the other hand because of the lack of scrutiny by some referees many papers in other journals cannot be used to draw firm conclusions, because of methodological flawlessness.

I thus seems appropriate to analyse in an evidence-based approach what has changed since the osseointegration technique was clinically introduced in 1965, to distil cautiously what the present day philosophy, mostly science, is.

Aseptic surgery

The sterile approach for surgery has been more or less respected since thirty years ; the integration of endosseous implant surgery in periodontology has even upgraded the awareness of surgical sterility measures which were common since a long time in other medical disciplines. Some have questioned the degree of sterility standards by comparing the incidence of postoperative infections in a classic dental office setting with an OR environment. It is impossible to draw conclusions from this sort of study, since the way of handling is much more influential than the symbolism of the OR. The use of antibiotics, still regularly practised, can also obscure the lack of asepsia during implant surgery. Since postoperative infectious complications occur rarely anyway, it will be difficult to prove with the present-day reports on small groups of patients, how much sterility matters for the immediate postoperative outcome. In orthopaedic surgery for example it appeared that for the placement of artificial hip prostheses the introduction of laminar air flow reduced the incidence of infectious complications from 1 to 0.5 % (^{Salvati et al., 1982}). There is no chance what-soever to observe this difference in the ambulatory surgery approach commonly used for oral implants. Although it appears only a half per cent, it means a reduction by half ! One should not conclude therefore that sterility is of no relevance in periodontal surgery, especially where implantable devices are involved as was beautifully pointed out by ^{Haanaes (1990)}. It was demonstrated that there is no need to obliterate the nasal air passage - which can also lead to hypercapnia especially in the elderly - to achieve a clean environment (^{van Steenberghe et al., 1997}). Indeed, the expired air does not contain more bacteria than the normal environment. On the other hand touching the nose, which is the most contaminated area of the face, can compromize all other efforts to achieve a sterile/clean environment (^{fig. 1a} and ^1b).

One cannot ignore the bacterial load of the oro-pharyngeal environment. The translocation of bacteria from pockets around teeth and the tongue dorsum to the surgical area is definitely possible. Therefore it has been advocated to control this before implants are installed. In a prospective multicentre study on partial edentulism rehabilitated by means of screw-shaped c.p. titanium implants, it appeared that immediate failures - i.e. before, at or shortly after abutment surgery - concentrated in patients with a high plaque index at the time of surgery (^{van Steenberghe et al., 1990}). Of course, one could argue that the accompanying gingivitis could also be responsible.

Meticulous surgery

The avoidance of heat trauma during osseous surgery has been another characteristic during implant placement. It was the great merit of Albrektsson's team to find that irreversible damage not only occurs above 80 °C, when alkaline phosphatase, an essential enzyme for osteoblasts is inhibited, but already at 47 °C if this is maintained for 1 minute (^{Eriksson et al., 1982} ; ^{Eriksson and Albrektsson, 1983}). This means a rise of temperature of only 10 °C above body temperature. All implants systems have adopted this approach either by internal or mostly external cooling. The latter approach offers the advantage not to flush away the marrow cells.

It was recently shown that for low speed drilling such as at implant installation itself or at tapping, no rise of bone temperature occurs, and cooling at this stage seems superfluous.

The impact of contamination of the implant surface itself by other metallic particles has also been questioned. At least in animals it seems that the purposely contamination of the titaniumxoyde layer by stainless steel pincettes does not lead to an increase of the incidence of non-integration. In vitro is has been shown many times that surface impurities of the oxide layer can compromize the cell adhesion to the implant surface (^{Ellingsen et al., 1995}).

The mode of incision is another matter of debate. While it is an old well-established tradition in general surgery and plastic surgery in particular, not to incise above the place where a foreign body has to be implanted, the need to do so for endosseous oral implants was questioned already in the early days. One of the reasons is that some general practitioners wanted to be involved in the surgical phase and were unfamiliar with the anatomical environment of more basal parts of the jaw bone. It is evident that when one-stage implants are placed or one-or two-stage implants in an extraction wound, crestal incisions are unquestioned. Both approaches have led to good post-operative results ; but the question whether paracrestal incisions (normally at about 1 cm) lead to less perforations, dehiscences etc. remains unanswered. It would be difficult to set up a comparative study to answer such a question, while the traditional approach has given excellent outcomes for decades.

The possibility to make a palatal rather than labial incision when esthetic demands exist, has been well documented (^{Langer and Langer, 1990}), even if some more mucosal dehiscences have been reported.

It was also documented that implants placed in fresh extraction wounds have a prognosis equal to those placed after proper healing (^{Gelb, 1993} ; ^{Haas et al., 1995} ; ^{Rosenquist and Grenthe, 1996}). This even applies to the concomitant use of expanded teflon membranes to cover the alveolar defects around the implants (^{Becker et al., 1994}). One can thus conclude that a faster oral rehabilitation can be assured in patients who have to become edentulous.

Bone volume and number of implants

When too limited bone height or volume is available, bone augmentation procedures have been widely used with more or less success. In general, autologous bone grafts remain the golden standard. The vast literature often consists of uncontrolled studies which has led to sometimes confusing perspectives, with worries about overtreatment. Some tentative review papers have been produced (e.g. ^{Tolman, 1995}).

The number of implants needed to carry a prosthesis remains unknown. Biomechanical models have been proposed (^{Rangert et al., 1989}) which seemed to apply to clinical reality. Although for lateral regions in partial edentulism the placement of 3 implants vs. 2 can be advocated (^{Rangert et al., 1997}), there is no argument to install otherwise as many implants as possible. Full bridges in both the upper or lower edentulous jaws survived after 10 years as well on 4 as on 6 implants (^{Brånemark et al., 1995}).

Delayed, early and immediate loading

An ongoing debate is whether it should be preferred to subject endosseous implants to important occlusal loads after some months of healing, or whether this can be done after some weeks. From experimental work on animals it was shown that micromovements during the early healing stage could lead to fibrous encapsulation instead of intimate bone apposition (^{Brunski et al., 1979}). At the clinical level one-stage implants like the ITI have shown that after some weeks of healing, a sufficient interface has built up to allow chewing loads (^{Schroeder et al., 1981} ; ^{Buser et al., 1997}). The early losses are no different of what has been observed for two-stage implants. Whether a very roughened surface or a particular implant configuration is needed to allow an early loading remains unknown. It has been documented at the animal level that the interfacial bone-implant strength can be increased by roughening, although the measurement methodology remains weak (^{Gotfredsen et al., 1992}). Whether a more prolonged healing, eventually unloaded by keeping the implant at or below the gingival level, may increase the success rate of one-stage implants, has not been documented. Two-stage screw-shaped implants like the Brånemark type, have been used as one-stage, but with less good clinical results (^{Balshi and Wolfinger, 1997} ; ^{Schnitman et al., 1997} ; ^{Tarnow et al., 1997} ; ^{Becker et al., 1997}). The few early failures tended to occur or to concentrate in the immediate loading group. In one multicenter study, where Brånemark implants were installed as one-stage in either the upper or lower jaw, no differences were observed. One should point out that the jaw bones had limited resorption and were of good bone quality. Thus presently, if there no special reasons, and if the bone quality is not sufficient to insure a proper rigid interface, the two-stage approach should be preferred for this type of implant.

That loading can be allowed after a few weeks, if the bone mineralisation is sufficient and if the patient adapts his chewing forces accordingly, is common knowledge derived from leg fracture healing. Depending on the degree of mineralisation especially at the fracture line, a more or less controlled activation/walking is allowed. Recently, for the edentulous lower jaw final fixed prostheses were installed the same day on three interconnected screw-shaped implants (^{Brånemark et al., 1999}). This concept of the same-day teeth is one step forward of the immediate loading concept not to be confused with early loading and this breakthrough opens new perspectives for several categories of patients. It also demonstrates that the borderlines of how osseointegration can be achieved are not finally set.

Relative contra-indications

The role of systemic factors on the success rate of endosseous oral implants has been well documented over the last twenty years. To summarize one can say that are evidently detrimental :

- smoking even if it has been suggested that quitting tobacco might improve results after a while (^{Bain and Moy, 1993}) ;

- local radiotherapy, even if the latter are reversed by hyperbaric oxygen sessions prior to and after irradiation (^{Arcuri et al., 1997}) ;

- bone demineralisation as illustrated by worse results for all types of implants in poor bone quality or a case-report on the dramatic effect of diphosphonates on already osseointegrated implants (^{Starck and Epker, 1995}).

Surprisingly, age (^{Jemt, 1993}), diabetes type I and II (^{Shernoff et al., 1994}), sclerodermia, lupus and other systemic factors are only (very) relative contra-indications.

Marginal bone loss

The cause of marginal bone loss around implants, often called periimplantitis in analogy with periodontitis will remain a matter of intense debate at the beginning of this new century. Data from experimentally induced marginal inflammation in animals (^{Lindhe et al., 1992}) cannot be extrapolated as such at the clinical level (^{van Steenberghe et al., 1999}). The picture is obscured by the fact that when pockets exist around abutments the subgingival environment, just as around teeth are becoming colonized after some time by periodontal pathogens (^{Lindhe and Berglundh, 1998}). It thus becomes difficult to distinguish between associated observations and etiological relationship. Since the lack of marginal bone loss often functions as the surrogate measurement for implant survival a lot of attention has focused on this aspect of oral implants.

Overload is capable of inducing marginal bone loss around abutments just as chronic plaque-related gingivitis is (in monkeys : ^{Isidor, 1997} ; in man : ^{Quirynen et al., 1992}). The resulting loss of « attachment » might later lead to subgingival bacterial colonisation, more intense inflammation. The interaction between overload and plaque-induced marginal inflammation is unknown (^{fig. 2}).

Since very roughened implant surfaces, but mostly with a cylindrical configuration have reported more often than others an ongoing marginal bone loss (for review see ^{van Steenberghe et al., 1999}), the debate became more inflamed (^{fig. 3a} and ^3b). The lack of long-term prospective split-mouth studies with marginal bone level observations around different implant surfaces leaves the question unanswered for some time. Meanwhile it is evident from the enormous contrast in medium-term survival of different implant types, even though the methodologies and assessments greatly vary, that endosseous implants cannot be considered generic.

The profession, and to a lesser extent the patients focus more and more on optimal esthetics (^{fig. 4}). Mucogingival surgery has been described to improve the outlook (^{Godet, 1991}). Preoperative planning involving drilling templates - custom-made on the basis of models or CT-scan data - or navigation (^{Jacobs et al., 1999}) allows a better interaction between periodontologist and restorative dentist (^{fig. 5a} and ^5b).

Conclusions and future perspectives

At the beginning of this new millennium, many more people will benefit from oral rehabilitation by means of osseointegrated implants. The reassuring outcome of implant surgery if not the survival of the implants in medically compromized patients will broaden the candidate population. Improved implant surfaces will allow dealing with limited bone heights. Augmentation techniques will allow dealing with reduced bone volumes. Smoking will be one of the few remaining challenges.

When needed, and when the bone quality allows, the healing time of implants before the prosthetic superstructure is installed can be shortened, eventually to a few hours. Implant installation can also be considered without hesitation in fresh extraction wounds.

Esthetics will in some professional circles be of paramount importance. There is a risk in a steep increase of marginal inflammatory reactions because esthetic endeavours lead to subgingival margins and difficult accessibility of interimplant spaces.

The communication from planning till prosthesis installation between the periodontologist or who is responsible for surgery, the restorative dentist and the technical laboratory will take place by means of interactive image transmission.

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