Dr Kleanthis Manolakis, Thessaloniki, Greece
Partial or total loss of teeth is associated with a loss of quality of life and in most cases consequent psychosocial problems [1, 2]. In patients treated with conventional dental prostheses to replace missing teeth, the gain in quality of life does not appear to be possible to the desired extent . The replacement of missing teeth with implant-supported restorations is therefore a preferred treatment option, since the attachment of prosthodontic restorations on implants leads to a higher treatment satisfaction than conventional mucosa-supported dentures [4-9].
Looking at the specific situation of the patient, the primary question is which type of connection between implant and the intermediate implant structures and which type of restoration (fixed vs. removable, or conditionally removable) is suitable for a - from a dental perspective - predictable treatment outcome and to achieve long-term treatment success. Success of the treatment is defined not only from the point of view of the dentist. The satisfaction of the patient, the manageability or ability to take care of the new dental prosthesis and the economic aspects must also be taken into account in the desired treatment result . The success of a treatment obviously depends to a greater extent on how the patient perceives the treatment outcome from his point of view and not how the success of the therapy is defined and perceived by the practitioner .
In this context, a minimally invasive approach without extensive augmentation is a treatment option favoured by the majority of patients [4, 12]. It is of interest to know to what extent an implant restoration is actually possible in patients with a resorption of the bony alveolar process without bone augmentation and how many implants are necessary to achieve a satisfactory rehabilitation of the patients.
Implant treatment therefore focuses on the objective functional parameters such as the long-term rehabilitation of chewing and / or speaking ability, as well as patient-specific psychosocial factors such as a better quality of life and improved aesthetics . In order to take the patient's preferences into consideration and at the same time not jeopardize the success of the treatment, a functional communication between the dentist and the patient is essential [14, 15].
Despite good communication between the patient and the practitioner, it cannot always be ruled out that the patient's expectations regarding his prosthodontic rehabilitation cannot be fulfilled [16-18]. Therefore, it is appropriate to use implant systems that simultaneously allow multiple treatment options and are thus independent of the final decision on the design of the superstructure and the type of fixation and which allow redesigning of the prosthodontic restoration during the course of treatment . In the case of a reduced budget, patients can initially be given removable dentures which is more cost-effective. If the patient's economic situation permits, the removable denture can be easily converted into a higher-quality, fixed prosthodontic option. Conversely, this approach also has the advantage that of being able to patients with increasing age and with a potential for increasing loss of hygiene can again be treated with a removable implant-supported prosthesis.
This fact has already been recognized by the manufacturer. Thus, for example, the company BEGO Implant Systems (Bremen, Germany) offers implant systems that can be equipped flexibly with different prosthodontic abutment and connection systems.
Flexibility is especially important in light of the fact that no generally valid recommendations can be made from the statements currently available in the literature as to which treatment option for restoration with implant-supported dentures is the treatment of choice.
As a retrospective comparative clinical study has shown, the number of implants or the nature of the connection between the implant and the superstructure do not appear to have any impact on oral quality of life .
However, the results of another clinical study showed that this result is not universal with respect to the type of prosthodontic connection. There, interforaminal implants placed in the lower jaw by means of bars led to an oral quality of life that was perceived to be significantly better than in case of implants without bar connectors .
In turn, the number of implants and the type of prosthodontic attachments had no influence on patient satisfaction.
The finding that objective parameters, such as the success or survival rates of implants and prosthodontic intermediate implant structures also do not seem to depend on the number of implants, but in most cases, the fixation of implant-supported intermediate implant structures in the lower jaw over a minimum of two  or maximum of four to six implants is considered as a suitable and foreseeable treatment option [22-25].
In implant-prosthetic and laboratory terms, having fewer implants has the advantage of facilitating parallel insertion on the patient and parallelization in the laboratory as well as fabrication of the intermediate implant structure.
The principle of using a reduced number of implants was implemented in the All-on-4 ® concept, which was already developed by Paolo Maló in the late 1990s. This procedure allows a minimally invasive approach to immediate restoration with fixed provisional or final dental prostheses on a reduced number of implants. In this type of restoration in the lower jaw, the interforaminal area can be considered as an insertion site, as that is where the supply of bone is usually the largest and there is no risk of injury to the inferior alveolar nerve when placing the implants. The two proximal implants are inserted straight while the distal implants are inserted at an angle, in order to obtain the largest possible support polygon for the prosthodontic intermediate implant structure. The inclination of the distal implants is then balanced with specially designed abutments.
The apparently low impact of the number of implants and the nature of the connection to the intermediate implant structure on functional and psychosocial parameters has also been shown in two randomized clinical investigations by Krennmair et al. There, an improvement in patient satisfaction was also achieved in the stabilization of mandibular prostheses on only two implants. After functioning for one or five years no implant loss was observed [26, 27]. The same studies also showed that the type of connection between implant and the prosthodontic intermediate implant structure (ball-and-socket joint vs. locator) had no impact on the subjective perception-guided patient preference or on the objective implant-related clinical and radiographic parameters .
The objective of the present case report was to test different prosthodontic restoration concepts for implant placement without any augmentation measures on a patient. On the basis of this procedure, it was to be determined to what extent attachment systems are actually interchangeable without much effort. Locator ® like abutments (PS Easy-Con, BEGO Implant Systems, Bremen, Germany) and ball-headed anchors (PS BA, BEGO Implant Systems) were used for a removable prosthodontic restoration. As a conditionally removable option, a composite-veneered bridge was fabricated and fixed on abutments of the MultiPlus system (BEGO Implant Systems) on a cobalt-chromium framework produced by means of laser melting.
The 69-year-old male patient presented in our clinic with the desire to be provided with an implantsupported dental prosthesis in the lower jaw. He had no systemic diseases, was a non-smoker and did not take any medications. The oral hygiene of the patient was average. He wanted a dental prosthesis that is minimally invasive, and would be fixed on a reduced number of implants without any augmentative measures. The patient had previously been provided with a removable mucosal partial denture with a plastic base fixed to the only remaining tooth 33 by means of curved retaining elements for a period of eight years. Due to massive periodontal problems, the tooth was no longer worth preserving (Fig. 1 and 2). In the opposite jaw, the patient was provided with fixed crowns / bridges, which were also inadequate and would need to be replaced at a later date.
Basically, it is assumed that in the case of a residual bone smaller than 5.0 mm in width bone augmentation measures must be carried out in connection with implant treatment, so as to obtain a sufficiently large bone bed for the implants .
In the present case, the alveolar process in the area of the insertion sites of the implants barely met the requirements for implantation without additional augmentation measures. After consultation with the patient we decided to extract the tooth 33 and a subsequent implant-supported prosthodontic restoration of the lower jaw on four implants in the canine and molar area on both sides without any additional augmentation measures.
According to the Misch classification, the quality of mandibular alveolar bone was classified as D3 [29-31]. Bones of grade D3 in addition to the second highest grade D2 are among the most frequently observed bone densities. In the literature it is described that in D1 and D4 bones the risk of early implant losses is higher compared to the other two bone quality classes . Nevertheless, in view of the relatively low bone supply, a two-step procedure with a delayed loading protocol and covered healing was chosen to ensure a sufficient stability of the implants in the alveolar bone over a healing period of several weeks. Implant treatment was carried out about three months after extraction of the tooth 33. Within this period, enough bone was formed in the area of the bony defect in tooth 33, for implantation to be performed in this region (Fig. 3).
The implant placement was performed under local anaesthesia and under direct vision with the formation of a mucoperiosteal flap. The open procedure was chosen as there was an advanced resorption of the bony alveolar process in the oro-vestibular direction, thus allowing a very good assessment of bone contours and bone quality and implant positioning under direct vision [33-35].
BEGO Semados® RSX Implants (BEGO Implant Systems) with the standard diameters 3.75 mm (region 036 and 043) and 4.10 mm (region 046 and 033) were used. The implantation was performed without support according to the manufacturer's standard protocol. All implants were placed epicrestally at the buccal point, except for the implant in region 043 (Figure 4). Since the alveolar ridge was saddle-shaped, the implant neck was approximately 1.0 mm subcrestal for all implants. The implant in region 043 was inserted approximately 2.0 mm subcrestally in the lingual direction.
Due to the good vertical bone supply, implants with a length of 11.5 mm could be used in the canine area and implants with a length of 10 mm in the posterior region. In this case, it was not necessary to bend the implants in the posterior region – as is usual with the classic All-on-4® method (Fig. 5).
The mucosa was sutured tight over the implants and the patient was instructed not to wear the prosthesis for a week. The one-week prosthesis course was prescribed to reduce the risk of mucosal perforation in the region of the implants and subsequent infection . One week after implantation, the patient presented again for suture removal. The mucosa in the surgical area had no inflammation and showed no signs of infection (Fig. 6).
After another 7-week healing period, the implants were exposed and restored with platform switch and gingival formers (PS HP, BEGO Implant Systems) (Fig. 7).
Two weeks later, impressions for the implants were taken. After another two weeks, the patient's final prosthodontic restoration was performed.
To fix removable, total prosthodontic reconstructions, our case report uses ball attachment anchor (PS BA, BEGO Implant Systems) and Locator® -like Easy-Con abutments (PS Easy-Con, BEGO Implant Systems). Ball attachments consist of a spherical metallic male part (Fig. 8). The female part is incorporated into the prosthesis and could be made of metal or plastic (Figure 9). The advantages of the ball attachment include the good hygienic ability, the low costs and the reduced treatment time .
A relatively high frequency of repairs owing to retention losses is also compensated by the fact that repairs in this system can be carried out very quickly and easily.
However, due to their height, ball attachment anchors require a sufficient inter-maxillary distance, which can complicate the design of the prosthodontic restoration because the anchor requires a correspondingly large vertical space and the attachment extends far into the oral cavity. Another disadvantage is that ball attachment anchors can be used only on implants that are inserted axially or in parallel. The retention is significantly reduced on implants that are not inserted in parallel beyond an angulation > 15 degrees .
In our case, the implants were positioned approximately parallel so that there were no major deviations of the implant axes (Fig. 10). There was ample inter-maxillary space and we were able to provide the patient with a mandibular overdenture prosthesis fixed to ball attachments. The clinical outcome was equally satisfactory for clinicians and patients in terms of aesthetics and function (Fig. 11 and 12).
The Easy-Con system (PS Easy-Con) is also susceptible to repair, as the replacement of the polyamide inserts must take place following retention losses . Since the restoration height is significantly lower than with the ball attachment anchors, the Easy-Con abutments can be used very well as attachments with a small inter-maxillary distance. Easy-Con abutments consist of a metallic female part integrated in the abutment. This consists of a raised, annular edge. The polyamide (nylon) male part is placed on the annular abutment and maintains its retention over the outer surfaces and the inner surfaces of the metallic ring (Fig. 13). The base of the prosthesis is also made of polyamide inserts (Fig. 14). Due to the material-related elasticity of the Easy-Con components, the system has a good elasticity / resilience (self-aligning) and is able to adapt well to the movements of the intermediate implant structure during functional loading . In contrast to the ball attachment system, differently designed male parts can allow axial non-parallelisms between implants to be compensated up to a deviation angle of 40 degrees without loss of retention . The patient was also supplied with a functional and visually appealing overdenture prosthesis using the Easy-Con system (Fig. 15).
No significant differences in clinical or radiographic parameters could be identified between a Locator® like abutments and ball attachment anchors in a clinical study conducted after a five-year period under functional loading . In the case of ball attachment anchors, more frequent prosthodontic aftercare was initially required compared to Locator like abutments, but this decreased with increasing observation time and in terms of frequency this no longer differed from self-aligning systems.
In a more recent in vitro study, statistically significant differences were noticed in the retention behaviour and stability of a cobalt-chromium denture framework fixed on two implants depending on the respective prosthodontic attachment system, the force applied and the distribution of implants / implant positioning. The highest retention and stability values were measured with ball attachment anchors, followed by self-aligning systems . The more distal the implants were placed, the higher were the retention and stability values found in the anterior-posterior direction. When Locator® -like abutments are joined on four implants in the lower jaw using bars, lower crestal bone loss rates and less follow-up were found compared to simple Locator ® system joints on two implants . The different effects on crestal bone resorption in this study were attributed to the stabilization effect through the bars rather than the type of prosthodontic connection. In contrast, an older in vitro examination showed that ball attachment anchors on implants lead to a better distribution of force in the posterior region of the lower jaw than the bar connectors . In a comparative clinical study on the restoration of edentulous patients in the mandible using two implants and locators as against magnetic attachments significantly higher peri-implant bone loss was seen in locator attachments .
On the basis of the available evidence, it is not yet possible to make definitive statements with regard to the influence of various prosthodontic connections in implant-supported, removable dentures on the remodelling behaviour of the crestal bone.
The third treatment option selected was a conditionally removable reconstruction fixed to the native PS MultiPlus abutment (Fig. 16 and 17). A cobaltchromium framework (EOS, Electro Optical Systems Munich, Germany) produced by means of selective laser melting, formed the base of the conditionally removable bridge. In our patient’s case, a very good, accurate fit of the metal framework could be achieved (Fig. 18). The framework was veneered using composite (anaxblend big block dentin and big block enamel, anaxdent GmbH, Stuttgart, Germany) (Fig. 19a and b). The screw channels were sealed with composites (EcuSphere-Carat, DMG Chemisch-Pharmazeutische Fabrik GmbH, Hamburg, Germany) after the insertion of the intermediate implant structure (Fig. 20). The final clinical outcome was very satisfactory for the patient as the reconstruction was very natural and aesthetic (Fig. 21) It is important that the patient is intensively instructed about oral hygiene and cleaning of the dentures so as not to jeopardize the longterm success of the reconstruction. This is of great importance because patients are often unaware that implants require more care than natural teeth .
If it turns out that adequate oral care is not possible, other attachments can be used after discussing with the patient and the dentures can again be made removable.
Removable, fully prosthodontic overdenture restorations on implants are of course less well accepted by patients than fixed implant-supported restorations [11, 43, 44]. The increased acceptance of fixed implant-supported intermediate implant structures can be attributed to the changed design of the prosthodontic replacement, as this is designed in the form of a bridge with veneers of ceramic or composite and without the plastic barrier required in the cover denture solution. The improved aesthetics and wearing comfort of bridges compared to cover denture prostheses obviously also lead to increased patient satisfaction [11, 43, 44]. However, oral hygiene procedures in fixed reconstructions are more difficult for the patient to perform than is the case with removable prostheses. However, removable reconstructions appear to be more susceptible to repair than fixed dentures . With respect to implant survival rates, in both fixed and removable intermediate implant structures, in contrast to the results of the examinations listed in the previous sections, the dependence on the number of implants appears to be a significant. A recent systematic review, including a meta-analysis, found that fixation of fixed reconstructions on four implants and removable dentures on two implants in the lower jaw lead to higher implant loss rates than if more implants were used to stabilize the intermediate implant structures .
Fixed dentures can either be cemented to the implants or screwed to the implants as conditionally removable dentures. While the cemented dentures can no longer be removed, the conditionally removable prosthodontic intermediate implant structures can be removed by the dentist. Both principles of fixation are controversially debated and are part of many clinical studies and systematic reviews, the results of which are not consistent. In a systematic review, no differences could be identified in the crestal bone remodelling rates, depending on the type of fixation . Even in terms of implant survival rates and prosthodontic loss rates, no differences were found in a recent review . The results of an earlier review demonstrate the superiority of cemented intermediate implant structures in biological and clinical terms . In contrast, in a recent systematic review, biological and / or technical complications were more commonly observed in cemented total restorations than in screwed total reconstructions . However, screwed ceramic intermediate implant structures had higher chipping rates of the veneers. In other systematic reviews, no differences were determined in the survival rates of the implants and the intermediate implant structures depending on the type of fixation [48, 51]. It is important to note that because the study designs are at times very different and in particular the definitions of success parameters vary, it is currently not possible to make a direct comparison of the two fixation types and evidence-based statements .
Ball attachment anchors (PS BA), Locator® -like abutments (PS Easy-Con) and MultiPlus attachments enable a good and predictable prosthodontic restoration on four implants. The fact that a minimally invasive approach to implant placement was chosen in this patient’s case increased the patient's acceptance of the proposed implant treatment. The ability to target different prosthodontic solutions with a reduced number of implants, depending on patient-specific factors, facilitates fulfilling patient desires and allows the prosthodontic solution to be redesigned even during the course of treatment.