Twelve years of clinical experience with the ITI® dental implant system at the university of Geneva

Introduction

At the University of Geneva, as at most universities worldwide, the use of dental implants had been progressively abandoned due to the high frequency of failures and complications observed for different implant systems that had been developed in the early sixties (^{Held and Fiore Donno, 1976}). It was only after the favourable reports published in the seventies and the eighties in relation with implants utilized according to the principles of osseointegration (^{Brånemark et al., 1969} ; ^{Schroeder et al., 1976}, ¹⁹⁷⁸, ¹⁹⁸¹ ; ^{Brånemark et al., 1985}) that the use of dental implants had been reconsidered. At that time the Swedish teams that had developed the Brånemark^® system were fabricating essentially implant borne fixed-detachable prosthetic suprastructures in edentulous patients. This approach represented a relatively complex and expensive treatment modality (^{Albrektsson et al., 1981} ; ^{Brånemark et al., 1977}) for which we did not have many indications. We were convinced, however, that the highly favourable results obtained with osseointegration should allow to enhance our treatment options for numerous other clinical situations. Consequently, we evaluated other implant systems available at that time in the search for a more simple approach that would be better adapted to the demands of many of our patients. We finally chose an implant system (^{fig. 1}) which had been developed in Switzerland by The International Team for Implantology (ITI), an international group of independent researchers and clinicians gathered by Professor André Schroeder of the University of Bern, in conjunction with an industrial partner. This original system comprised implants made of titanium, featuring a rough surface to better promote osseointegration, and designed to be used according to a one-step non-submerged surgical protocol (^{Schroeder, 1991} ; ^{Scacchi, 2000}). The system also offered an extremely simplified prosthetic approach, similar to that applied in conventional fixed prosthodontics (^{Sutter et al., 1988}, ¹⁹⁹³ ; ^{Scacchi, 2000}). These specific characteristics appeared to be optimally suited with respect to the philosophy we intended to implement in the utilization of dental implants. In our opinion, the use of implants should not represent a specific self sufficient discipline, but rather one of the different techniques available when it comes to the prosthetic rehabilitation of various kinds of edentulism, and the potential and quality of outcomes of it should allow any clinician to propose it to his patients (^{Bernard et al., 1996a}). Clearly, the characteristics of a given implant system also strongly influence the concept of its clinical application. The original principles which had motivated our choice in the late eighties, have been in the meantime repeatedly confirmed and validated by numerous experimental and clinical studies. In fact, they have been the decisive elements of evolution observed in the course of the last ten years in the field of dental implants.

Evolution of concepts in implantology

The results reported for osseointegrated implants in the treatment of different types of edentulism (^{Albrektsson and Sennerby, 1991} ; ^{Bert and Missika, 1991} ; ^{Noack et al., 1999} ; ^{van Steenberghe et al., 1999}) permit nowadays to consider the use of dental implants as one of the different therapeutic modalities during the establishment of any prosthetic treatment plan. In numerous clinical situations the use of implants allows to simplify the treatment, to keep it less invasive with respect to tooth structure or to render the treatment more reliable (^{Belser et al., 1996b} and ^c). The use of implants should therefore be considered as an alternative modality to conventional prosthetic rehabilitations, including those located in the esthetic zone (^{Belser et al., 1993} ; ^{Bernard et al., 1993}). In particular, the evolution of implant systems and procedures, aiming at simplifications as well as at time and cost effectiveness, should ultimately permit that implants are used by a larger number of clinicians and hence become accessible for an increasing number of patients. In recent years, many evolutions have taken place, all contributing to the simplification of implant therapy, but without jeopardizing the overall quality of the results.

Utilization of a non-submerged single-step surgical technique

The utilization of a submerged, two-stage surgical technique, as originally recommended to achieve osseointegration, allows to avoid contamination of the implant from the oral cavity during the initial phase of healing (^{Brånemark et al., 1977} ; ^{Albrektsson et al., 1981}). This approach, however, requires an incision at the level of the alveolar mucosa, which in turn quite frequently leads to swelling and post-surgical hematoma (^{Worthington et al., 1987} ; ^{Langer and Langer, 1990} ; ^{Cranin et al., 1998} ; ^{Scharf and Tarnow, 1993b}). It also requires a second surgical intervention once osseointegration has been achieved, in order to expose the implant shoulder and to insert a transmucosal element that will serve as support for the prosthetic suprastructure. Again, a period for mucosal healing has to be included prior to the prosthetic rehabilitation (^{Adell et al., 1985}). Such a procedure is quite constraining as it imposes two surgical interventions to the patient and thus lengthens the duration of treatment. The possibility to predictably achieve osseointegration for implants exposed to the oral cavity from the moment of insertion has also been documented for now more than 20 years (^{Schroeder et al., 1981} ; ^{Babbush, 1986}). The first histological studies which have demonstrated osseointegration under such conditions have been performed with hollow cylinder implants covered with a titanium plasma spray, inserted in monkeys according to a one-step non-submerged surgical protocol (^{Schroeder et al., 1976}, ¹⁹⁷⁸, ¹⁹⁸¹). In fact, ITI^® implants have always been designed to be used according to a one-step non-submerged surgical procedure (^{Schroeder et al., 1983} ; ^{Schroeder, 1991} ; ^{Buser et al., 1998a}). The technique of placing implants in a non-submerged fashion is more simple when compared with the classical submerged approach. The utilization of a mid-crestal incision within the keratinised attached mucosa permits to limit post-surgical sequelae at a maximum (^{Langer and Langer, 1990} ; ^{Bernard et al., 1992a} ; ^{Ouhayoun et al., 1993}). Furthermore, healing of the peri-implant soft tissues occurs simultaneously with osseointegration (^{fig. 2}). Neither a second surgical intervention, which would cause an additional discomfort to the patient, nor another healing time, which would delay the prosthetic rehabilitation, are necessary (^{fig. 3}). One of the primary advantages of a non-submerged approach consists in the location of the junction between the implant shoulder and the secondary components. In fact, this junction is located at the level of the bone crest for the submerged two-stage systems, whereas it is positioned somewhere close to the mucosal surface for a non-submerged one-stage system. This particularity permits to ultimately obtain a histological situation quite similar to that observed around a natural tooth (^{Bernard et al., 1992a}), as well as biological and mechanical conditions that are favourable in terms of long-term stability of the results (^{Buser et al., 1997}, ^1999b). The principle advantage of this non-submerged technique lies in the fact that the use of a transmucosal secondary component leading to a to a « micro-gap » (^{Binon et al., 1992}) which in turn creates a submucosal ecological niche (^{Quirynen and van Steenberghe, 1993}). This space can be colonized by microorganisms (^{Quirynen et al., 1994}) and could ultimately serve as reservoir for potentially pathogenic bacteria transmitted from periodontal lesions (^{Papaioannou et al., 1995} ; ^{Quirynen et al., 1996} ; ^{Ellen, 1998}). Additionally, the non-submerged techniques also permit to locate the transition between implant shoulder and suprastructure in the juxta-mucosal region, i.e. accessible for oral hygiene measures (^{Leon, 1977}), which in turn decreases the risk for peri-implant inflammation and infection. In order to achieve a similar situation, and to reduce the risk for bacterial contamination, it has been recommended to diminish the mucosal thickness at the moment of placement of the secondary components for the two-stage submerged systems (^{Papaioannou et al., 1996}). Positioning of the transition between implant shoulder and secondary components at the level of the mucosa rather than at the crestal bone also represents a biomechanical advantage as it reduces the lever effect and the associated stress on the junction between implant and suprastructure (^{Sutter et al., 1988}, ¹⁹⁹³ ; ^{Sutter, 1996} ; ^{Buser et al., 1999b} ; ^{Merz et al., 2000}). As for implants of two-stage systems, the positioning of the prosthetic junction at the level of the bone crest favors the incidence of mechanical complications (^{Jemt et al., 1991}, ¹⁹⁹² ; ^{Kallus and Bessing, 1994} ; ^{Wie, 1995} ; ^{Henry et al., 1996} ; ^{Brägger, 1999}), the prevention of which requires specific conceptional rules for the suprastructures (^{Skalak, 1983} ; ^{Rangert et al., 1989}, ¹⁹⁹⁷).

The different radiographic evaluations of the osseous evolution around non-submerged ITI^® implants (^{Buser et al., 1992}, ^1999b ; ^{Weber et al., 1992b}, ²⁰⁰⁰) revealed comparable values to those observed for implants inserted according to a two-stage surgical protocol (^{Albrektsson et al., 1986}). Furthermore, under identical experimental conditions, a greater amount of bone loss has been observed around submerged implants when compared with implants placed following a one-stage surgical protocol. This additional crestal bone loss in case of submerged implants occurs after the second stage surgery (^{Fiorellini et al., 1992} ; ^{Hermann et al., 1997}). Under experimental conditions reproducing the different steps of fabrication of a prosthetic suprastructure on a submerged implant, it could be shown that the amount of crestal bone loss after exposure of the implant depends on the depth of the junction between implant and secondary components, and that a distance of approximately 2 mm will ultimately separate the junction from the crestal bone (^{Hermann et al., 1997}). These observations are in accordance with the notion of a peri-implant biologic width (^{Cochran et al., 1997} ; ^{Lindhe and Berglundh, 1998}). The position of the junction between implant and secondary components conditions the epithelial downgrowth apically to that junction (^{Donley and Gillette 1991} ; ^{Abrahamson et al., 1997}), and the osseous remodelling depends on the reestablishment of that biologic width : the deeper the junction is located, the more pronounced will be the crestal bone loss (^{Hermann et al., 1997}). Furthermore, it has been observed that the dimension of the biologic width is smaller and more close to that associated with natural teeth, for one-part implants when compared with two-part implants, regardless if they were placed according to a one-stage or two-stage surgical protocol (^{Hermann et al., 2001}) (^{fig. 4}). This observation supports the use of a non-submerged approach in various clinical situations, comprising edentulous areas in the esthetic zone (^{Belser et al., 1993}, ^1996a, ¹⁹⁹⁸ ; ^{Belser and Bernard, 1999} ; ^{Bernard et al., 1993}), and still maintaining highly favourable success rates (^{Buser et al., 1997}, ^1999b).

In a pilot study, utilizing Brånemark^® implants with a non-submerged surgical protocol, we could demonstrate that it was possible to predictably achieve osseointegration also following a one-stage procedure with implants originally designed for a submerged two-stage surgical protocol (^{Bernard et al., 1995b}). Other studies have confirmed this possibility (^{Ericsson et al., 1994}, 1997 ; ^{Henry and Rosenberg, 1994} ; ^{Becker et al., 1997} ; ^{Collaert and de Bruyn, 1998} ; ^{Kohal et al., 1999} ; ^{Roynesdal et al., 1999}). This approach offers numerous advantages as it permits to simplify the procedure and to diminish the inconvenience for the patient, as well to reduce the duration of treatment. The utilization, however, of implants originally designed for a two-stage procedure, according to a one-stage protocol, does not modify neither the peri-implant osseous remodelling nor the soft tissue adaptation, as the junction between implant and secondary components will remain at the crestal bone level. And it is the position of this junction which determines the apical migration of the epithelium and the crestal bone level once the biologic width has been established (^{Abrahamsson et al., 1997} ; ^{Cochran et al., 1997} ; ^{Lindhe and Berglundh, 1998} ; ^{Davarpanah et al., 2000} ; ^{Hermann et al., 1997}, ²⁰⁰⁰, ²⁰⁰¹). In order to benefit from a favourable peri-implant bone and soft tissue adaptation, it is mandatory to utilize one-part implants, specifically designed for a non-submerged procedure, which permit to position the junction between implant and secondary components at soft tissue level rather than at bone crest level (^{Bernard et al., 1995b}).

Utilization of implants with a rough surface

Since the first publications describing the principle of osseointegration (^{Brånemark et al., 1969} ; ^{Brånemark et al., 1985}), numerous clinical studies have shown that screw-form titanium implants with a machined surface like the one of the Brånemark^® system allowed to obtain favourable long term results in the treatment of different situations of edentulism (^{Albrektsson and Sennerby, 1991} ; ^{van Steenberghe and Naert, 1998}). These studies have also consistently demonstrated, however, that a significant increase of failures could be observed in case of reduced bone density or limited bone height, where implants of less than 13 mm length had to be used (^{Friberg et al., 1991} ; ^{Jaffin and Berman, 1991} ; ^{Bahat, 1993} ; ^{Henry et al., 1993} ; ^{Bahat and Handelsman, 1996} ; ^{Sennerby and Roos, 1998} ; ^{Esposito et al., 1998} ; ^{Schwartz-Arad and Dolev, 2000}). Consequently, different solutions have been searched for in an attempt to improve treatment outcomes with screw-type titanium implants featuring a machined surface, in situations with unfavourable bony conditions, as they are frequently encountered in the posterior regions of the jaws. To insert as many implants as possible, to use implants of maximum length, to aim for bicortical anchorage or to adopt surgical techniques offering a optimal primary stability of the implants, has therefore been proposed (^{Bahat, 1993} ; ^{Bahat and Handelsman, 1996} ; ^{Schwartz-Arad and Dolev, 2000}). Such recommendations, while improving the results, are also increasing the complexity and the related expenses of the treatment.

Modifications of the implant surface permit also to improve the conditions for osseointegration (^{Wennerberg and Albrektsson, 2000} ; ^{Wong et al., 1995}).

Removal torque measurements, carried out on titanium screws of identical form but with three different surfaces during the first six months after placement, clearly demonstrated the influence of the surface status on bone anchorage (^{fig. 5}). As for the machined titanium screw (L), the related removal torque values stayed stable at the same level as the applied insertion torque values. With respect to the titanium screws with a rough surface, in form of a titanium plasma spray (TPS) or created by means of sandblasting and acid etching (SLA), the removal torque values significantly increased after the second week post-surgically, reaching values five time higher than those measured for smooth titanium after 24 weeks (^{Wilke et al., 1990}). These results have been confirmed by a study conducted on miniature pigs, using three different surfaces of full-body titanium screws (^{Buser et al., 1999b}) : the removal torque values of implants with a machined surface stayed similar to those used for insertion, while the values associated with rough surfaces were 5-6 times higher after only a few weeks post-operatively. The maximum values were higher and reached more rapidly for SLA surfaces when compared with TPS.

In an experimental study on dogs, comparing removal torque values of 7 and 10 mm long Brånemark^® implants, inserted according to a submerged protocol, with non-submerged 6 and 10 mm long ITI^® implants, we could confirm on the one hand osseointegration of one-stage ITI^® implants and on the other hand significant differences of removal torque values between the two types of implants investigated. The removal torque values associated with ITI^® implants were consistently higher than those measured for Brånemark^® implants and the removal torque values of 6 mm ITI^® implants were superior to those measured for 10 mm Brånemark^® implants. As far as Brånemark^® implants are concerned, there was no difference between 7 and 10 mm implants, whereas 10 mm ITI^® implants revealed significantly higher removal torque values than 6 mm implants (^{Bernard et al., 2000c}).

The described fundamental differences regarding kinetics and the nature of osseointegration between titanium implants with a machined or a rough surface, leads to conceptual differences when it comes to the recommendations of their respective clinical use.

Utilization of a limited number of implants

It has been recommended for the use of titanium implants featuring a machined surface, in particular in the posterior segments of the jaws, to insert one implant for each missing occlusal unit, to avoid cantilever units and - if possible - to place the implants according to the principle of tripodization in order to prevent potential mechanical complications (^{Rangert et al., 1989}, ¹⁹⁹⁷).

These recommendations, however, do not apply to the ITI^® implant system due to the bony anchorage reported for specific rough surfaces (^{Buser et al., 1998a}) on the one hand and due to the mechanical resistance of the morse taper connection between implant and abutment on the other hand (^{Sutter et al., 1988}, ¹⁹⁹³ ; ^{Sutter, 1996} ; ^{Merz et al., 2000}). In fact, the replacement of each missing occlusal unit by one ITI^® implant is restricted to clinical situations requiring either the use of diameter-reduced or 6 mm long implants. In case of three missing occlusal units, the standard solution consists in the placement of two implants to support a three unit fixed partial denture (FPD) with a central pontic. If for anatomical reasons a mesial implant can not be inserted, a three unit FPD with a mesial cantilever extension appears to be an acceptable solution. More exceptionally, the fabrication of a FPD featuring a distal extension can also be carried out (^{Belser et al., 2000}, ²⁰⁰¹) (^{fig. 6}, ⁷, ⁸, ⁹, ¹⁰ and ¹¹).

Such an approach makes it possible to use fewer implants than prosthetic units, which in turn facilitates to adapt the implant borne prosthesis to the dimensions of a given edentulous segment, simplifies the treatment and reduces the related overall expenses.

Utilization of shorter implants

It has been recommended for screw-type titanium implants with a machined surface, to use the greatest possible length and to achieve a bicortical anchorage (^{Brånemark et al., 1977} ; ^{Brånemark, 1985} ; ^{Adell et al., 1985} ; ^{Bahat, 1993}). In view of the improved osseous anchorage observed for titanium implants featuring a rough surface, it appears possible to use successfully shorter implants. The utilization of implants of reduced length permits to simplify the therapeutic procedure (^{Bernard et al., 1995b}). As it is not necessary to aim for maximum osseous height, the evaluation of the vertical dimension of the bone can be accomplished by simple radiographic means (^{Belser et al., 1996c} ; ^{Bernard et al., 1996a} and ^b ; ^{Gröndal, 1997} ; ^{Bernard and Samson, 2000} ; ^{Dula et al., 2001}). The subsequent surgical procedure is more simple as well (^{Bernard et al., 1992b}), as the implants are not placed as a function of the bone situation, but as a function of the future prosthetic rehabilitation (^{Bernard et al., 1996a}). It is in fact the prosthetic treatment plan which will lead to the decision of the precise position and axis of the implants rather than the available bone mass itself. Under such conditions, the subsequent prosthetic steps will be simplified as well (^{Belser et al., 1996b}, ²⁰⁰⁰, ²⁰⁰¹).

From April 1989 until November 2001, 3 309 one-stage non-submerged ITI^® implants of 6 to 12 mm length (^{fig. 12}) have been inserted in 1 327 patients presenting with different types of edentulism (^{fig. 13}).

The choice to use implants has to be made in the context of a comprehensive treatment plan, after having determined the existence of eventual general or local risk factors and after having evaluated the other prosthetic treatment options. This approach, which is carried out in collaboration with the patient, allows to transmit the relevant informations necessary to obtain his informed consent (^{Belser et al., 1996c} ; ^{Bernard et al., 1996a}). A simple clinical and radiographic examination only, as in our opinion the use of tomodensitometric techniques should be restricted to a small number of particular clinical indications (^{Bernard et al., 1996b} ; ^{Bernard and Samson, 2000} ; ^{Dula et al., 2001}), is carried out prior to the installation of ITI^® dental implants according to a one-stage non-submerged surgical protocol (^{Bernard et al., 1992a} ; ^{Buser and von Arx, 2000a} ; ^{Buser et al., 2000b} ; ^{Weingart et ten Bruggenkate, 2000}).

The results obtained with these 3 309 rather short implants, most of them placed in the posterior segments of the jaws (^{fig. 14}), are extremely favourable since we did only observe 23 early failures (7 %) and 29 secondary failures (0.9 %) for a follow-up period of more than 12 years for the first implants inserted.

The same favourable success rates are observed in situations that are commonly considered difficult (^{Bahat, 1993} ; ^{Esposito et al., 1998} ; ^{Schwartz-Arad and Dolev, 2000}), as implant placement in posterior regions, in particular in the maxilla (^{Bernard et al., 2000b}), or in bone of low density (^{Bernard et al., 2001}).

These extremely favourable results observed for non-submerged ITI^® dental implants with a maximum length of 12 mm, including sites of low bone density, are in accordance with data reported in numerous other clinical studies (^{ten Bruggenkate et al., 1990}, ¹⁹⁹¹, ¹⁹⁹⁸ ; ^{Buser et al., 1990}, ¹⁹⁹⁷ ; ^{van Gool et al., 1992} ; ^{Weber et al., 1992b}, ²⁰⁰⁰ ; ^{Wedgwood et al., 1992} ; ^{Wismeijer et al., 1992}, ¹⁹⁹⁹ ; ^{Pham et al., 1994} ; ^{Mericske-Stern et al., 1994}, ²⁰⁰¹ ; ^{Bernard et al., 1995a} ; ^{Astrand et al., 1996} ; ^{Donastsky and Hillerup, 1996} ; ^{Behneke et al., 1997} ; ^{Levine et al., 1997}) and in studies carried out in private dental practice (^{Bischof et al., 2001}). In particular, they confirm the low percentage of mechanical and biological complications observed for this type of implants (^{Lang et al., 2000} ; ^{Schwarz, 2000} ; ^{Mericske-Stern et al., 2001}).

The possibility to use shorter implants represents one of the major advantages of ITI^® dental implants. This permits to utilize implants in a larger number of clinical situations and to limit the necessity to apply bone augmentation procedures that are often troublesome for the patient and that significantly increase the cost and length of treatment.

Reduction of osseointegration delays

The different experimental studies that have evaluated the bony anchorage of implants have shown a rapid increase of removal torque values that correspond to a high percentage of direct bone contact to rough titanium surfaces (^{Buser, 1999a}), which allows to propose shorter healing periods for implants featuring rough surface. For ITI^® implants with a TPS surface, healing periods of 3 months for both the mandible and the maxilla are used since many years (^{Buser et al., 1998a}). More recently, the favourable results observed for a new type of roughened surface produced by selective subtraction techniques, i.e. sandblasting and acid attack (^{Klokkevold et al., 1997} ; ^{Buser et al., 1998b}, ^1999b ; ^{Lazzara et al., 1999}), have led to the proposition to further reduce the healing periods (^{Lazzara et al., 1998}). As far as ITI^® dental implants are concerned, featuring the SLA surface which has demonstrated highly favourable results in animal experiments (^{Cochran et al., 1996}, ¹⁹⁹⁸), clinical studies have confirmed these results with a successful osseointegration rate of 99 % after only 6 weeks of healing in standard bony conditions (^{Cochran et al., 2002}).

This evolution with respect to healing periods represents a significant change of image of implant dentistry which frequently appeared in the past to both patients and clinicians as a complex and highly surgical procedure. In fact, the association of a single step surgical protocol with a shortened healing period of only six weeks, permits to perform an implant supported prosthetic rehabilitation under similar time conditions as conventional techniques and by this token to give implant dentistry a comparable image as habitual dentistry. A selection of simple prosthetic components allows, for the majority of clinical indications, to produce cemented suprastructures and thus contributes to the overall simplification of the procedures on the one hand and to the approaching of conventional tooth-borne and implant-borne techniques in the perception of the clinicians on the other hand. More sophisticated implant-borne restorations being reserved for complex clinical situations and rehabilitations located in the esthetic zone (^{Belser et al., 2000}, ²⁰⁰¹ ; ^{Mericske-Sternet al., 2000} ; ^{Scacchi et al., 2000}, ^{Taylor et al., 2000}).

Furthermore, the utilization of implants designed for a single-step procedure and featuring a rough surface, appears also perfectly adapted for immediate loading protocols (^{Jaffi, 2000}), an approach which has recently received a lot of attention (^{Tarnow et al., 1997} ; ^{Ericsson et al., 2000} ; ^{Szmukler-Moncler et al., 2000}).

Simplification of the conditions of surgical sterility

Among the criteria considered mandatory for achieving osseointegration, conditions of surgical sterility close to those commonly applied in the field of orthopaedic surgery, have been classically recommended when it comes to the insertion of dental implants (^{Adell et al., 1985} ; ^{van Steenberghe and Naert, 1998}). These conditions of sterility, however, are quite difficult to implement and respect outside a surgical operative theatre and are very troublesome for both the patient and the surgical team. Furthermore, it implies a respective specific training and significantly contributes to the overall expenses. Due to the impossibility to render the oral cavity sterile, and due to the fact that frequently the installation of dental implants takes place in the dental practice (^{Lambrecht et al., 1999}), the necessity to respect sterile conditions similar to those requested for orthopaedic surgery, clearly needs revision (^{Scharf and Tarnow, 1993a}). In order to determine the eventual influence of strict sterile conditions on the rate of successful osseointegration, we have carried out a prospective clinical study, comparing the early failure rate following implant surgery performed under either strict sterile conditions or under more simple aseptic conditions, as commonly applied in the field of oral surgery. Additionally, we have evaluated the long-term results associated to implants inserted under habitual aseptic conditions.

The two studies have confirmed that strict sterile surgical conditions were not mandatory for achieving osseointegration of dental implants (^{Bernard et al., 2000a} ), and that the use of a non-submerged surgical protocol under habitual aseptic dental conditions permitted to obtain high success rates (^{Bernard et al., 2000d}). The rate of early failures was - under these conditions - even slightly inferior to those published by groups using strict sterile surgical conditions (^{van Steenberghe et al., 1999} ; ^{Zarb and Schmitt, 1990} ; ^{Friberg et al., 1991} ; ^{Esposito et al., 1998}). These data support the implementation of a significant simplification of the implant-surgical protocol, which in turn facilitates the practice of implant dentistry in a dental operatory.

Evolution of prosthetic concepts

During recent years, the prosthetic concepts have significantly evolved, simultaneously with the evolution of indications for dental implants. Different models of implants, adapted for the replacement of different groups of teeth have been developed. With recent innovations as for example narrow neck implants (NNI) (^{fig. 1}), or, to the contrary, wide neck implants (WNI), and the variety of associated secondary components (^{fig. 15} and ¹⁶), the ITI^® dental implant system permits to treat the entire spectrum of indications (^{Belser et al., 2000}, ²⁰⁰¹ ; ^{Scacchi et al., 2000}).

Complete fixed prosthetic rehabilitations, essentially screw-retained, originally utilized for the treatment of edentulous patients, have been progressively supplemented by fixed partial dentures (FPD's) of limited length and by single-tooth restorations (^{fig. 17}), administered in partially edentulous patients (^{Bernard et al., 1996a} ; ^{Belser et al., 2000}, ²⁰⁰¹).

For these indication, the implementation of cemented suprastructures considerably simplifies the prosthetic procedures of the treatment. The utilization of non-submerged implants with a supra-mucosally located margin, combined with a cemented suprastructure of traditional design, is particularly well adapted to the posterior segments of the jaws (^{Bernard et al., 1992} ; ^{Bernard et al., 1992} ; ^{Belser et al., 1996} ; ^{Belser et al., 1996}). Positioning and axis of the implants during surgery are determined by the planned prosthetic rehabilitation (« prosthetically-driven implant placement ») which subsequently permits the use of conical solid abutments, ensuring on the one hand a solid connexion to the implant based on the morsecone principle, and being optimally designed for cemented suprastructures on the other hand (^{Bernard et al., 1992a} et ^b ; ^{Sutter et al., 1993} ; ^{Belser et al., 1996c} ; ^{Sutter, 1996} ; ^{Merz et al., 2000}). The use of prefabricated auxiliary parts for impression taking, as well as the implementation of analogues and burn-out patterns during the laboratory procedures, considerably facilitates the fabrication of the prosthesis which in fact become more simple when compared with traditional tooth-borne prosthetic rehabilitations (^{Belser et al., 2000}, ²⁰⁰¹ ; ^{Scacchi, 2000} ; ^{Taylor et al., 2000}) (^{fig. 18}, ¹⁹, ²⁰ and ²¹⁾ .

When it comes to implants located within the esthetic zone, a deeper placement of the shoulder of implants specifically designed for this indication, permits to hide the margin below the mucosa, but still without placing the implant shoulder at the level of the bone crest which in turn would lead to a secondary bone loss due to the reorganisation of a biologic width (^{Hermann et al., 1997}, ²⁰⁰¹). Under these particular circumstances, screw-retained restorations, based on prefabricated machined components, will permit to assure a maximum marginal adaptation favouring to maintain the long-term stability of the esthetic result (^{Belser et al., 1993}, ^1996a, ¹⁹⁹⁸, ²⁰⁰⁰, ²⁰⁰¹ ; ^{Belser et Bernard, 1999} ; ^{Bernard et al., 1993}) (^{fig. 22}, ²³, ²⁴, ²⁵, ²⁶, ²⁷, ²⁸, ²⁹, ³⁰, ³¹, ³², ³³, ³⁴, ³⁵ and ³⁶).

The combination of these different concepts allows to optimally address any individual clinical situation (^{fig. 37}, ³⁸, ³⁹ and ⁴⁰).

Conclusion

During the last twelve years, numerous evolutions could be observed in the field of dental implants which is increasingly occupying a preponderant place in dental medicine. Modern implant dentistry has been developed from the principle of osseointegration which has allowed to obtain extremely favourable long-term success rates. The initial recommendations, that had originally given to the field of implantology an image of a rather complex technique, have been progressively simplified, benefiting from the increasing knowledge, but maintaining the standard of quality of the results. The association of a non-submerged technique with implants featuring a rough surface, permitting a diminution of the healing time, initiated by the ITI^® implant system, has completely modified the patient's perception of this type of treatment. Classical implant dentistry left the impression of a complex treatment with a heavy surgical component, followed by a waiting period prior to a second surgical intervention, which in turn was followed by a by another period of healing. To the contrary, the utilization of a one-step procedure, featuring a simple surgical intervention and a prosthetic treatment only a few weeks later, resembles more and more to a traditional dental therapy. There are other advantages associated to these evolutions, as the implants designed for a single-step procedure foster a rapid and favourable peri-implant soft tissue adaptation. The same is true for the roughened implant surfaces which enhance the quality of the bony anchorage and allow to obtain high success rates also for short implants placed in difficult bone situations. These simplifications of the procedures go in parallel with the constant increase of indications as a consequence of the obtained results and should allow, as we had envisioned from the very beginning of our implant activity, to render these techniques accessible to the largest number of patients and clinicians possible.

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