Newly described treatment concepts to avoid extensive grafting procedures are showing encouraging results, in particular those using tilted implants Back

Steffen Kistler, Frank Kistler, Georg Bayer and Joerg Neugebauer

Introduction

The expectations of patients considering the replacement of lost oral structures or missing teeth focus primarily on the treatment outcome. The objective is to restore function at a high level and to rebuild the cosmetic impression. Even though the general population is increasingly being made aware of the potential benefits of implant-supported therapy by the media and the dental industry, the information they disseminate is often incomplete or even misleading.1,2 Patients initially tend to be less interested in the finer details of the underlying treatment concepts aimed at achieving the desired objective. When the time comes for the planning phase, and the patient learns more about the various treatment options, additional factors will affect their decision against or in favour of a specific treatment. Important criteria that influence the acceptance of the proposed path of rehabilitation, in addition to the expected overall cost, include the number of surgical interventions required and the concomitant risks.3,4 Especially invasive procedures, such as those often required in severely atrophied jaws, may trigger anxiety in patients who are afraid of pain and complications, not only during the surgical procedure but also postoperatively.3,5,6

Rehabilitation of the atrophied jaw

The range of indications for implant dentistry has expanded significantly in recent years. Combining implant treatment with state-ofthe-art computer-guided technologies has made this treatment modality more precise and ultimately more patient-friendly.7–11

It is especially beneficial in patients afflicted by edentulism and the related consequences such as atrophy of the jaws over an extended period when implants can often only be placed following additional grafting procedures.12,13This is particularly true in the maxilla which is often characterised by a less favourable bone quality and where the available implant site is additionally compromised by the extension of the maxillary sinus.14 Various techniques and concepts have been discussed over the past few years to improve the initial clinical situation and thus facilitate the use of implants even in these cases. These include less common procedures such as zygomatic implants or distraction osteogenesis.15,16 Another procedure that has been discussed with regard to an improvement of the implant site is the Le Fort I steotomy.17,18

Numerous techniques for sinus floor elevation have been established in clinical treatment methodology. Consideration for patients’ expectations and their desire to minimise the extent of surgical interventions, plus the need for cost-effective rehabilitation, has led to techniques that avoid extensive grafting procedures gaining ground. In particular, the use of short and tilted implants is receiving increasing attention in dental literature.

Sinus floor elevation
In addition to the classical sinus floor elevation procedure with lateral fenestration, osteotomes used in a so-called internal sinus floor elevation as described by Summers19 has yielded good long-term results.20,21Patients have reported that the tapping of the hand instruments was very unpleasant, but there are clear advantages in that no additional surgical field is opened, nor is any additional invasive procedure required.22 However, this technique can only be applied in the presence of sufficient residual bone. Different minimal height requirements have been put forward in the literature but, from a conservative point of view, a bone height of 6 to 8mm appears to be adequate.23 If the residual bone height is sufficient, the sinus grafting can be performed simultaneously to the implant insertio n, although there is no consensus in the literature regarding the success rate of this approach.24

On the other hand, a broad range of complications have been reported in the context of sinus floor elevation, from rupture of the Schneiderian membrane, swelling and hematoma, through to sinusitis.25 There have even been reports of cases where the grafting material was partially or even completely lost, and the question remains as to which grafting material is preferred.26,12 Many authors still recommend autogenous bone as the gold standard; however, it is not always readily available in the quantities necessary to fill the augmentation space. Moreover, extensive resorption may occur at or around the grafting material, not to mention increased morbidity at the donor site.27,12 Good results have been reported for combinations of autogenous bone and bone substitutes. But here, too, practitioners have to make a choice. There are synthetic materials such as beta-tri-calcium phosphate, which can be produced in batches of a standard quality, but whose use in sinus floor elevation has sometimes been advised against owing to the fast resorption that takes place.28 On the other hand, xenogeneic materials produce good results, although there have been recent reports about lost bovine grafting material on the cranial aspect over the years, as no endogenic bone tissue can develop without the body’s own remodeling processes, which are tantamount to an inflammatory reaction. As a consequence, implants will be exposed on their apical aspects.29

Finally, many patients are skeptical about this type of invasive procedures, so alternatives should be explored.

Short implants
One option might be short implants that, with their reduced overall length, make maximum use of the residual bone. But these implants also require an adequate bone volume for proper positioning. Often an adequate position cannot be found thus compromising the prosthetic result. Interestingly, recent studies have shown that it determines long-term success but their diameter.30 This would be an argument in favour of using shorter and thicker implants. However, reports on the success of short implants do not reach any consensus, nor any agreement on the definition of this type of implant.31 While some authors regard 8 to 10mm as short, others wouldn’t consider using anything over 6mm.32,33 Long-term results have been less favourable in the posterior maxilla than in the mandible, which has been explained by differences in bone quality and the higher masticatory forces occurring in this area.31,33 With the introduction of modern implant systems with microrough surfaces, a positive trend for the use of short implants is emerging.34

Tilted implants
Another way to avoid the conventional removable denture, which often covers the palate, is the use of tilted implants. The original concept, described by Dr Paulo Maló et al under the name ‘all-on-four’, has been intensively studied and yielded good results in a number of applications.35–41 Today, this concept may be applied both in the maxilla and in the mandible; it may be combined with fixed or removable restorations and with a single-stage or twostage surgical technique (Figure 1).

One advantage is that this technique, when used in the maxilla, may help avoid sinus floor elevation. In addition, use of the available bone is maximised without sacrificing proper anchorage to the bone. The angulation of the distal implants allows them to be placed in a more posterior direction, which reduces leverage and facilitates the implant stability to be supported by the cortical bone wall of the maxillary and nasal sinuses.40 It has been shown that distal implants are subject to the greatest loads, regardless of the degree of angulation and the number of implants.42

Combined with proper treatment planning, this concept can help to achieve satisfactory restorative results. Computerguided three-dimensional treatment planning, based on CT and CBCT images, seems to be very useful in identifying the most suitable implant positions.43,44

The implant type chosen should be characterised by an ideal surface topography that, under the right circumstances, positively influences bone healing. This applies, for example, to the DENTSPLY Friadent plus surface. This gritblasted and thermally-etched surface type has been shown to promote initial osseointegration in numerous studies.45,46 is not so much the length of the implant that Furthermore, the DENTSPLY Friadent implant system portfolio offers several abutment types that enable the user to place the ANKYLOS® and XiVE®implants in terms of tilted implants. Using the example of the ANKYLOS® system, the utilisation of the so-called SmartFixTM concept is explained in Figures 1 to 20.

For the ANYKLOS® SmartFixTM concept the already existing Balance Base portfolio has been expanded by new abutment types with the angulation of 15° and 30°. These are capable of compensating an actual inclination of the implants up to 45°.

The special seating instrument is a smart and user-friendly solution (Figures 3 to 7). Whereas other systems operate with rigid auxiliary components, these sometimes present intractable problems if used in the distal areas or where mouth opening is limited, the flexible application device design of the SmartFixTM seating instrument offers considerably more user convenience. In addition, the angled abutments are available for two different gingival heights. 

Due to its keyed and friction-locked TissueCare taper connection, ANKYLOS® can be placed subcrestally without irritating the peri-implant tissue. This benefits the placement of tilted implants as the distal implant shoulder is always below the bone level. Thanks to SmartFixTM, the ANKYLOS® system, which has been on the market in almost unmodified form for 25 years, can combine the advantages of taper connections with the advantages of tilted implants, which offer freedom of position and thereby greatly increase system flexibility. Moreover, the extremely narrow and platform-switched abutments avoid the collision with the distal
bone crest.

The positive results reported in the literature should be reason enough to include this treatment concept into the clinical routine and to present it as an option to eligible patients.47,48 However, the reaction of the angled transition area between the implant and the abutment with regard to tissue stability and establishment of periimplantitis over the years remains to be seen.