Comprehensive augmentation procedures are not necessary, which results in a very high patient acceptance, due to the reduced surgical efforts. The reduced surgical efforts result in high patient acceptance since comprehensive augmentation measures can be avoided. The theoretical backgrounds for the SKY fast & fixed-System are introduced and discussed.
The beginnings of modern implantology in the mid seventies of the last century mainly entailed implant placement in patients with sufficiently large bone site, mostly in the mandible, but also with an increase in placement in the maxilla. Especially in the maxilla, however, edentulous patients often exhibited considerable caudalization of the maxillary sinus so that implants could only be integrated in the intrasinusal region.
This implant position could normally not be used for a fixed restoration such as an extension bridge; as a consequence the use of removable restorations became established for the maxilla. As an option for posterior support, tuber implants were already integrated in the early years. Owing to the large distance (span) to the anterior implants, bar restorations were preferred for hygienic reasons (5).
An increase in early failure rates of the tuber implants, however, resulted in avoidance of this technique and at the beginning of the nineties sinus floor elevation and augmentation became the standard procedure for the preparation of the implant site in the maxilla. Today sinus floor elevation using bone replacement material or autologous bone is considered the standard or routine procedure for patient restorations in the maxilla, especially in cases of loss of posterior teeth.
Depending on the height of residual bone and on which augmentation material is available, this procedure, however, requires relatively long time until the implants can be integrated or exposed to masticatory stress. Moreover, today more and more patients refuse invasive surgical treatment so that the use of angulated implants for anchoring fixed restorations has become a new trend during the past few years.
To use the existing bone quantity without extensive augmentation measures, an implant body is required that features a surface suitable to withstand the high forces that are applied. The modern implant systems with a micro-porous, hydrophilic surface available in the market today fulfill this precondition; as a result these implants allow achieving good long-term stability even in sites with reduced bone quantity (13).
In the last few years the workgroup around Paulo Mal and the biomechanical expert Bob Rangert established the concept of angulated implants for fixed bridges in mandible and maxilla whilst avoiding sinus floor elevation or nerve lateralization in the mandible. The works of Malo show a high cumulative survival rate of 97.6 % (20), with a survival rate of prosthetic restorations of 100 %; 4 implants are sufficient for the integration of a fixed bridge in the mandible.
A large width of the restoration base from the anterior to the posterior region is required to ensure adequate posterior support. Angulated placement of the distal implants in the mandible is carried out via the foramen mentale so that the mucosa is not penetrated in region 03 04 but in region 05 06 (2, 16). This way the restoration provides a larger surface and wider support can be achieved. In the maxilla the implants are placed to the anterior wall of the sinus floor so that reverse angulation compared to the maxilla is obtained.
The inclination angles of these implants are between 30° und 45° and require the use of special prosthetic abutments to be able to prepare standard dental restorations on these implants (15). The first reports about placement of angulated implants showed a higher success rate for angulated implants after 5 years (3) but also stated that the abutment or retention screws needed to be refastened frequently since the fabrication of the prosthetic restoration was restricted owing to the use of standardized components.
Thanks to inclined insertion, a longer implant can be used and hence wide biomechanical support can be achieved (16). However, a very specific procedure is required and users must be familiar with the anatomical structures and detailed treatment planning (15, 32, 33).
The results of other studies showed (8) that bone resorption at implants with angulated placement was even lower than for implants placed axially.
This demonstrates that these implants offer high biomechanical stability thanks to the longer anchoring portion. The claim for tooth-like axial loading to achieve and retain osseointegration with long-term stability could be refuted in a retrospective study (17) in which the implants in the intraforaminary region had an inclination of 74.3 ± 9.3° depending on the respective skeletal class.
The angulation for this patient group correlated with the skeletal class; inclination did not have any influence on the survival rate and the peri-implant parameters such as bone resorption, depth of pocket and peri-implant health. Angulated abutments with up to 45° were also used by other authors for a high number of implants over a long observation period of more than 10 years (29). This application demonstrated that the angle of the abutment does not affect the survival rate.
Today data of long-term studies between 8 and 12 years are available which show the usual complication rates of the Branemark system; 2 patients lost three implants in the first year but later on the success rate of the implants amounted to 97 % (28). Bone resorption was observed for 10 % of the implants and the average was 1.2 mm.
These long-term data indicate that implant restorations with long-term stability can also be obtained without the necessity of performing augmentation procedures (28). Already 10 years ago other studies showed that the survival rates of implants with straight abutments were lower than those of implants with angulated abutments in the maxilla. Reverse results were found for the mandible. The authors, however, pointed out that angulated abutments would not necessarily cause reduced peri-implant stability (4).
In addition to the angulated implants placed in the region of the tooth-supporting alveolar process (ridge), these results could also be collected for the so-called zygoma implants (3, 26, 30). Due to the anatomical situation these implants are also placed at a large inclination angle to anchor the implant in the highly atrophied maxilla without the use of comprehensive augmentation measures.
These patients also produced promising success data and good long-term stability even though some authors reported increased risk of periimplantitis (1). The use of angulated implants to avoid augmentation (grafting) requires sound knowledge of the anatomical structures. The technique of digital volume tomography, which is widely used today, allows accurate evaluation of the existing bone quantity which can be perfectly made use of with three-dimensional implant planning (14, 23).
The available template techniques allow inserting the implants under correct prosthetic conditions. Simulation of abutment placement in these programs even enables the user to determine and adjust the path of insertion depending on the prefabricated abutment.
As a result, the prosthetic phase is simplified so that initial complication rates caused by inaccurate fit and loosening of screws can be further reduced. Using the corresponding technique (11) it is also possible to take a precise impression of several angulated implants.
This study showed that no different results were obtained for the closed and open impression techniques. However, it is recommended to use a relatively flexible material to avoid that forces resulting from undercuts or angulation may lead to tearing or destroying (damaging) the impression material (24).
Consequently, the material should have a relatively low Shore hardness and high tear resistance. For angulated placement of the implants, however, it must be ensured that, from the material-technical point of view, the implants fulfill the biomechanical requirements (6). In cases of failure of the implant for biomechanical reasons, the histomorphological preparation revealed considerable implant contact (27).
Well developed compact bone with small marrow cavities and without any symptoms of resorption resulted. Owing to the high mechanical stress of the implant geometry, fracture of the implant body occurred which, however, did not affect osseointegration.
Consequently, a stable implant-abutment connection must be used for angulated implants (27). Demands made on an implant system including the concept of angulated implants require the suitability of the system for immediate loading and a stable, if possible, internal abutment geometry with limited residual rotation and high mechanical stability.
Microporous implant surfaces allow optimal bone apposition thanks to early osseointegration and special abutments for the use of the angulated implants ensure simple impression taking or registration to prepare the prosthesis in a way to ensure immediate function. In several studies (19-22) the clinical works of Paulo Malo showed that especially implants with a microporous surface produce a very high success rate.
The peri-implant bone level after one year of prosthetic loading remains unchanged so that this treatment concept can be successfully applied in the maxilla and the mandible as well. 9
During the past few years the mechanical approach of osseointegration with the necessity of axial loading of the implants lacks confirmation. Various studies showed that angulated implants - even with angles of 45° - offered high long-term stability (29). Compared to the natural tooth, the periodontium is missing for the implant and mobilization of the implant will not occur in cases of extra-axial loading. Extensive implant-bone contact of damaged angulated implants could be proven after explantation (27).
The previous studies, however, demand a sufficient length when inserting angulated implants to ensure mechanical stabilization after achieving osseointegration or within the scope of immediate loading (9, 18). The sufficient implant length of more than 12 mm guarantees initial mechanical anchoring, which is required to eliminate micromovement and to achieve osseointegration. This principle of treatment with immediate restorations/immediate loading also applies to the placement of angulated implants (20-22). The results obtained for the use of immediate loading/immediate restorations during the past years showed that – in addition to high primary stability - surface conditioning of the implants is essential for successful use.
Hence implants with a microporous surface obtained by anode oxidation or sandblasting and high temperature etching exhibit a high success rate for immediate restorations (12, 13, 31). This approach can also be implemented for the use of angulated implants in the atrophied jaw (21). Compared to the early years of modern implantology, the tolerances for implant abutments and implants could be reduced further through advanced manufacturing technologies so that even high mechanical loads can be transferred to a stable implant body (10).
This way the risk of screw loosening, in particular in cases of extra-axial loading, is reduced. As far as screw loosening is concerned, it is obvious that the rate of complications for modern implant systems has clearly decreased compared to classical implant systems (7). Thanks to a special system, optimal use of the available bone based on detailed preoperative planning allows placement of implants without damaging anatomical structures so that no or only minor augmentation measures need to be performed. Consequently, morbidity of patients is reduced and higher acceptance of the implant therapy is achieved (24).
In addition to the surgical risks, the prolonged duration of treatment involving multiple surgical interventions is frequently unacceptable for patients since it would result in reduced quality of life. Since the use of the available bone and immediate restorations reduce invasive treatment to a single appointment, patient acceptance can be increased considerably.