Complete implant rehabilitations: between longevity and mechanical challenges

The rehabilitation of complete edentulism with screw-retained fixed prostheses currently represents a benchmark therapeutic solution. However, in dental practice, we know that this approach remains an ongoing clinical challenge, exposing the practitioner to a complex array of biological and mechanical complications. This retrospective study, conducted between 2020 and 2024, delves into this issue by analysing the data of 58 patients who received 78 fixed complete prostheses supported by a total of 373 implants.

The specific objective of this work was to evaluate survival rates and identify risk factors correlated with complications, notably prosthetic fractures. The results immediately highlight a duality: while implant longevity is near-optimal with a survival rate of 99.8%, prosthetic stability proves more complex, showing a rate of 92.3%. The study specifically tests the hypothesis of a correlation between bimaxillary rehabilitation and the incidence of fractures, while recording frequent technical incidents such as screw loosening, which affects 24.1% of cases here.

Methodology: 4-year retrospective cohort analysis

This retrospective cohort study was designed to evaluate the clinical reliability and complication rates of complete implant-supported prosthetic rehabilitations. The investigation was conducted over a four-year period, spanning from 2020 to 2024, to collect longitudinal data on short- and medium-term therapeutic success.

The methodological protocol was structured around the following main areas:

• Population and sampling: The study included 58 patients presenting with complete edentulism, either unimaxillary or bimaxillary. In total, 78 screw-retained fixed complete prostheses were followed up, supported by a total of 373 osseointegrated implants.
• Evaluation criteria: The researchers analysed the survival rate of the implants and prosthetic structures. The reporting of complications was divided into two categories: biological (peri-implant mucositis and peri-implantitis) and mechanical (screw loosening and prosthetic fractures).
• Risk factor analysis: A specific evaluation was conducted to identify the variables associated with the risk of fracture of restorative materials, particularly comparing the impact of a single-arch rehabilitation versus a bimaxillary rehabilitation.
• Clinical follow-up: Data were collected retrospectively from patient records, documenting every mechanical incident or peri-implant pathology occurring between placement and the end of the observation period in 2024.

Results: High implant survival under real mechanical challenges

Analysis of the follow-up data reveals excellent durability of the primary anchorage, contrasting with a notable frequency of technical complications. The implant survival rate stands at 99.8%, while that of the prostheses reaches 92.3% over the study period.

Biological complications: a predominance of mucositis

Peri-implant health is characterised by a significant incidence of reversible inflammation, whereas severe infectious pathologies remain marginal:

• Peri-implant mucositis: identified on 10.46% of implants.
• Peri-implantitis: limited to 0.5% of cases, demonstrating satisfactory bone stability in the majority of rehabilitations.

Mechanical complications and risk factors

The technical aspect represents the main maintenance challenge in the practice. Screw loosening stands out as the most recurrent complication, affecting nearly a quarter of restorations. Prosthetic fractures, although less frequent, present a non-random distribution.

Risk factor analysis reveals a major clinical correlation: prosthetic fractures occur almost exclusively in patients who have undergone bimaxillary rehabilitation. This observation emphasises the critical impact of occlusal load and the lack of resilience when two full implant-supported arches oppose each other.

Clinical analysis of results and biomechanics

The data from this retrospective study highlight a remarkable surgical performance with an implant survival rate of 99.8%. However, the lower prosthetic survival rate (92.3%) underlines that the major challenge of complete screw-retained rehabilitation is not osseointegration, but the longevity of the prosthetic assembly. The high prevalence of screw loosening (24.1%) confirms that the management of occlusal forces and the stability of the connections remain the critical points of these complex restorations.

Identified complications and risk factors

The study reveals that the risk of prosthetic fracture (7.7%) is significantly correlated with bimaxillary rehabilitations. This result suggests that in the absence of the physiological shock absorption provided by the periodontal ligament on a natural opposing arch, mechanical stresses are entirely transmitted to the prosthetic framework. Biologically, although peri-implant mucositis affects 10.46% of implants, the very low rate of peri-implantitis (0.5%) demonstrates good short- and medium-term tissue tolerance of the global loading protocol.

Limitations and perspectives

Although the results align with classic literature reviews (such as Papaspyridakos et al.), the study is limited by its retrospective nature and a four-year follow-up period (2020-2024). This follow-up, although significant, does not yet allow for the evaluation of material fatigue over the very long term. Nevertheless, the robustness of the data on 373 implants helps to guide maintenance protocols in the practice.

Summary of the key study results

This study demonstrates excellent clinical reliability with an implant survival of 99.8% and prosthetic survival of 92.3%. However, maintenance remains demanding: screw loosening affects 24.1% of cases and peri-implant mucositis 10.46%, while prosthetic fractures (7.7%) occur predominantly during bimaxillary rehabilitations.

In practical terms, for the practitioner:

• Systematic mechanical maintenance: Given a screw loosening rate of 24.1%, it is imperative to check the tightening torque and the integrity of the hardware during each follow-up visit.
• Caution in bimaxillary cases: As the risk of fracture is correlated with double full-arch restorations, reinforce the prosthetic structure or drastically adjust the occlusal scheme for these high-stress configurations.
• Early detection of mucositis: With 10.46% of observed mucositis cases, longevity depends on a strict prophylactic hygiene protocol to neutralise inflammation before it progresses to peri-implantitis (0.5%).

Technical glossary of the study

Phục hình cố định toàn bộ bắt vít (Screw-retained complete fixed implant prosthesis): Full-arch implant-supported restoration, mechanically secured by retaining screws. This system allows for treatment reversibility for maintenance or complication management without damaging the framework.

Tỷ lệ sống sót (Survival rate) : Percentage of implants or prostheses remaining in place and functional at the end of the follow-up period (here 2020-2024), regardless of the existence of minor biological or mechanical complications.

Viêm niêm mạc quanh implant (Peri-implant mucositis): Reversible inflammatory reaction of the soft tissues surrounding an implant in function, without associated supporting bone loss. This is the most frequent biological complication recorded in this cohort (10.46%).

Viêm quanh implant (Peri-implantitis): Pathological condition of the peri-implant tissues characterised by inflammation of the mucosa and progressive bone loss. The study reports a low prevalence of 0.5% in this sample.

Lỏng vít (Screw loosening): Mechanical complication characterised by the loss of preload of the abutment screw or prosthetic screw, identified as the predominant technical problem (24.1%) in the patients followed.

Nứt gãy phục hình (Prosthetic fracture) : Structural rupture of the prosthesis (framework or veneering material). This complication was specifically correlated in the study with bimaxillary rehabilitations.

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