This retrospective study suggested that the rehabilitation of edentulous patients or patients with a failing dentition through full-arch immediate loading by means of the Flat-on-Bridge technique is a reliable and successful solution, even in the case of post-extractive implant placement. The present approach was focused on the passive fit of the prosthetic framework over the surface of flat abutments, thus correcting the emergence of the - eventually uneven - implant axis. The use of such abutments helps the clinician to exploit the residual bone whenever there is a lack of volume at post-extractive sites. Almost all rehabilitations successfully survived at a 7-year follow up visit, with only 3 prosthesis out of 75 presenting a complication related to a single implant failure: in each case, the prosthesis survival was ensured anyway.
The comparison of present data with those available in literature describes very similar success rates [19,20].
In 2018, Gallucci and colleagues reviewed the evidence regarding oral rehabilitations with different combinations of implant placement and loading protocols: immediate implant placement and loading; immediate implant placement with early loading; immediate implant placement with delayed loading; late implant placement and late loading . The analysis reported highest survival and success score for the combination of immediate implant placement with early loading, 98.2% and 98.7%-100% respectively. The authors suggested the importance of considering placement and loading time as a single denominator in the overall success analysis.
The few studies assessing the outcome of full-arch restorations supported by post-extractive implants and/or immediate and non-immediate implants are not homogenous.
In the present study, most of the implants had been placed in post-extractive sites, and no difference could be recorded between immediate implants and implants placed in healed ridge in terms of survival and success outcomes. This result is in line with previous literature on the same topic. Altintas and colleagues found that the success rate was the same for non-immediate and immediate implants (97.8%) supporting full-arch fixed prosthesis . More recently, Lerner and colleagues presented a retrospective clinical study on 110 implants (65 of them being post-extractive) supporting complete-arch fixed prosthesis with a very high success rate (98.2%) .
Most of the studies included a digital planned template to guide surgery whenever there were failing teeth to be extracted and, thus, immediate implants to be placed. That was not the case of the present study, where implants have been placed without the aid of a digital-manufactured surgical template. Still, the cumulative implant survival rate at 7 years was 99%, with only one failure occurring among immediate implants. It must be highlighted that immediate implants might represent a challenge to the ordinary surgeon and it has been suggested that skillfulness might influence the clinical outcome of post-extractive implants . That is even truer in the case of multi-implant positioning which requires careful pre-operatory diagnostic planning but also intra-operatory adaptability. In fact, primary stability is achieved simply where there is sufficient bone available: therefore, longer implants should be used as well as the maximum number of implants.
The environment around immediate post-extractive implants is unique: from a biological perspective, it contains periodontal ligament remnants; from a mechanical perspective, peri-implant compressive strains arouse during the implant insertion; this phenomenon, coupled with heat transfer during drilling, creates a zone of apoptosis circumscribing the implant . The same happens around some regions of an immediate implant, but the implant area facing the bone is less extensive. The osteogenesis in the alveolar fosse is primarily caused by blood clots around the implant, therefore, extensive blood lacunae around the implant surface will represent the initial chamber of osteogenesis .
The combination of the FOB procedure with crestal thickening obtained using graft of different biomaterials with Growth Factors and Fibrin Rich in Leukocytes and Platelet deriving from L-PRF led to optimal stabilization of final soft tissues. This aspect represents a huge difference with respect to other implant systematics: the reduced size of the Flat Abutment grants the maintaining of a close contact with the marginal periodontium.
The positive success rate of immediate implants in the preset study might be justified by the macroscopic mechanical passivation of the supra-structure mediated by the flat-to-flat connection. In fact, micro-movements, prosthetic unfitting, and unfavorable loading are among the factors that impair the healing process of immediate implants.
Furthermore, implant micro design contributes to the success of immediate implant placement and loading. The patented Ossean surface comes with particular hydrophilic properties that enhance the osteointegration in the firs 4 weeks after surgery: the fractal, nano-rough Ossean surface, in fact, has been reported to influence cellular genetic expression - or the fate of stem cells -at the nano-level, which in turn induces faster implants osteointegration .
The present was a retrospective study without a control group, therefore, its results may not be generalized. A further limitation of the study was represented by the lack of peri-implant mucosal inflammation data analysis. However, the long follow-up of the present study makes the outcome more reliable than other short-term studies on the same topic.
Long-term function of implant- supported full-arch immediate prosthesis usually leads to a high prosthetic complication prevalence, featuring the prosthesis fracture as the most common complication one during the first year of loading. In the present study, no prosthetic fracture was reported, confirming that the framework reinforcement (metallic or event glass-fibers reinforcement) could be the most important success key during the osseointegration period. Glass fiber-reinforced acrylic immediate prosthesis may function better in cases of removable denture in the opposing jaw. More comparative studies are need to demonstrate this postulate.
Even if the flat abutment protocol can be provided also with a lower number of supporting implants, the optimal number of implants was always considered a minimum of 6 and 8 implants in the lower and upper arch, respectively. Only future studies will be helpful to ascertain the minimum number of implants to be required for prosthetic support with this type of protocol.