Rehabilitation of the jaws with a reduced number of implants: 9-year follow-up and correlation between operator expertise and implant-prosthetic issues

1. Introduction

Edentulism remains an important clinical and public-health problem, particularly in ageing populations. Although tooth retention has improved, demographic ageing means that the need for complete prosthetic rehabilitation persists, with consequences for mastication, quality of life, and oral function [1,3–4,18–19,36].

Following tooth loss, the alveolar process undergoes progressive remodelling. Bone quantity and quality, cortical anatomy, and the relationship with anatomical structures influence implant planning and may complicate treatment in advanced atrophy [5– 6,8,21,26]. Reconstructive approaches, including sinus augmentation, may be indicated in selected cases, but they increase surgical complexity and treatment burden [14,32].

Modern implant therapy is based on predictable osseointegration and standardized criteria for success, survival, and failure. Long-term outcome is influenced by biological, prosthetic, patient-related, and treatment-related risk factors, while implant surface characteristics and peri-implant tissue conditions may also affect maintenance and complication profiles [2,10–13,20,28].

Immediate-loading and immediate-restoration concepts have progressively expanded treatment options. Evidence on immediate loading, soft-tissue response, and implant timing supports carefully selected accelerated protocols, provided that surgical and prosthetic conditions are appropriate [11,15–16]. Patient-centred considerations are also relevant because avoidance of extensive grafting and reduction in treatment duration may improve acceptability [14].

For complete-arch rehabilitation, a reduced number of implants can be used to support a fixed prosthesis. Distal implants may be intentionally tilted to exploit residual bone, avoid anatomical limitations, increase anteroposterior spread, and reduce distal cantilever length. Systematic reviews and meta-analyses have reported clinically comparable outcomes between tilted and axial implants when appropriate protocols are followed [22–23,25,34]. Digital planning and guided or navigated implant placement may further support full-arch workflows and positioning accuracy [7,29–30,35].

Long-term clinical series have documented high survival for full-arch implant-prosthetic rehabilitation, including in elderly patients and in medically complex populations, while highlighting the need for careful risk assessment and maintenance [18,20,24,31,33,38]. Functional rehabilitation should also be considered within the broader biomechanics of the stomatognathic system [17].

Operator-related factors are another potential determinant of outcome. Surgical experience has been associated with implant survival, and technical skill has been linked to complication rates in other surgical settings [27,37]. However, operator expertise is multidimensional and is not adequately represented by elapsed time alone. The present retrospective study therefore evaluates outcomes across three consecutive treatment periods performed by the same surgeon, focusing on implant failures and prosthetic complications as descriptive clinical endpoints.

2. Materials and methods

This retrospective observational study was conducted at the Department of Dentistry, IRCCS San Raffaele Hospital, Milan, Italy. Clinical records of patients treated from 2013 through 2021 were reviewed. Eligible patients presented with a completely edentulous maxilla and/or mandible, or severely compromised residual dentition requiring extraction, and received a fixed full-arch implant-supported prosthesis using a reduced number of implants with immediate loading.

Inclusion criteria were:

• edentulism of one or both arches, or severe compromise of the residual dentition;
• indication for fixed implant-supported prosthetic rehabilitation;
• absence of uncontrolled systemic disease.

Exclusion criteria were:

• ongoing or previous bisphosphonate therapy;
• head and neck radiotherapy in progress or completed less than 12 months previously;
• inability or unwillingness to adhere to long-term professional and home-care maintenance protocols.

For descriptive analysis, cases were categorized into three consecutive treatment cohorts according to year of surgery: 2013–2015, 2016–2018, and 2019–2021.

All fixtures were described as two-stage, self-tapping, internal-connection implants and were placed by the same surgeon. The surgical concept combined axial and, where anatomically indicated, tilted distal implants in order to maximize use of residual bone. Immediate provisional fixed prostheses were delivered after surgery when adequate primary stability had been achieved. Definitive prosthetic rehabilitation was subsequently completed after the initial healing phase, as illustrated by the representative clinical sequences.

The primary outcomes were implant failure and prosthetic complications affecting provisional or definitive prostheses. Implant outcome was evaluated according to clinical function, mobility, symptoms, and radiographic findings, in keeping with established distinctions among implant success, survival, and failure [12–13].

An implant was considered clinically functional as a prosthetic support when all of the following conditions were present:

• adequate function as a prosthetic support;
• absence of mobility during prosthesis removal and re-tightening;
• absence of pain or other clinical symptoms;
• absence of peri-implant radiolucency on radiographic examination.

Implant removal, or failure to fulfil one or more of these clinical conditions, was classified as implant failure. Prosthetic complications included clinically recorded problems affecting either provisional or definitive prostheses during the study period. Counts and crude percentages were calculated for the entire sample and for each treatment cohort. Percentages of implant failure used the number of implants as denominator; percentages of prosthetic complications used the number of rehabilitated arches as denominator.

2.1 Clinical cases

Representative maxillary and mandibular treatment sequences are shown in Figures 1 and 2. The images illustrate the surgical and prosthetic workflow used in the clinical series.

2.1.1 Maxillary fixed implant rehabilitation

2.1.2 Mandibular fixed implant rehabilitation

3. Results

A total of 159 patients met the stated inclusion and exclusion criteria and received full-arch immediate-loading rehabilitation during the 2013–2021 study period. The sample included 79 men and 80 women, aged 40–90 years, with a mean age of 65.04 years.

A total of 192 arches were rehabilitated: 89 mandibular and 103 maxillary arches. Overall, 852 implants were reported as placed. Fourteen implants failed and were removed, corresponding to a crude implant failure proportion of 1.64% (14/852). Thirty-one prosthetic complications were reported among the 192 rehabilitated arches, corresponding to a crude complication proportion of 16.14% (31/192).

For temporal analysis, the sample was divided into three cohorts according to the year of surgery: 2013–2015, 2016–2018, and 2019–2021. Cohort-level results are summarized in Table 1.

In the first period, 140 implants were placed and 3 failed (2.14%); 31 arches were rehabilitated and 7 prosthetic complications were recorded (22.6%). In the second period, 100 implants were placed and 8 failed (8.00%); 21 arches were rehabilitated and 11 prosthetic complications were recorded (52.4%). In the third period, 612 implants were placed and 3 failed (0.49%); 140 arches were rehabilitated and 13 prosthetic complications were recorded (9.3%).

4. Discussion

The present retrospective series showed an overall implant failure proportion of 1.64% and a prosthetic complication proportion of 16.14% across 192 full-arch rehabilitations. These findings are consistent with the broader literature showing that implant-supported rehabilitation can achieve high long-term survival while still being associated with biological and technical complications that require maintenance [10–13,20,31,38].

The use of a reduced number of implants, including tilted distal implants, is supported by evidence showing clinically favourable outcomes and no clear survival disadvantage compared with axial placement in appropriately selected cases [22–23,25,34]. The biomechanical rationale includes avoidance of anatomical constraints, increased anteroposterior spread, and reduction of distal cantilever extension. Cantilever design remains an important prosthetic consideration in fixed restorations [9].

Contemporary full-arch treatment is increasingly integrated with digital planning, guided surgery, navigated placement, and digital impression workflows [7,29,30,35]. These technologies can improve standardization and planning, but they do not eliminate the importance of clinical judgement, anatomical knowledge, surgical execution, and prosthetic design.

The most notable result of the present analysis was the non-linear variation across the three periods. The 2016–2018 cohort showed the highest implant failure and prosthetic complication proportions, whereas the 2019–2021 cohort showed the lowest. A simple assumption that outcomes improve in a strictly linear manner with elapsed professional time is therefore not supported by these descriptive data.

Published evidence nevertheless supports an effect of operator experience on implant outcomes. Lambert et al. reported improved implant survival with increasing surgical experience [27]. Pomares emphasized the relevance of operator experience in complex computer-guided full-arch rehabilitation [30], while long-term All-on-4 series demonstrate the importance of standardized protocols and cumulative clinical expertise [31,38]. Evidence from other surgical disciplines similarly shows that technical skill can influence complication rates [37].

The clinical interpretation proposed by this series is that experience is beneficial only when accompanied by sustained attention, careful case selection, and consistent adherence to protocol. The higher event proportions observed in the middle period may reflect a combination of operator-related and case-related factors rather than experience alone. In retrospective practice-based data, possible contributors include case complexity, bone quality, systemic risk factors, prosthetic design, maintenance adherence, and evolving surgical or restorative workflows [2,5,11,24,33].

Bone anatomy and quality remain central to full-arch planning. Advanced resorption, sinus anatomy, and proximity to the inferior alveolar nerve may constrain implant positioning and increase treatment complexity [5,21,26]. Tilted placement and alternative reconstructive strategies can reduce or modify the need for grafting in selected cases [22–23,25,32,34].

The study should be interpreted in light of its retrospective, single-centre and single-operator design. The analysis is descriptive and does not include multivariable adjustment or time-to-event modelling. Accordingly, differences among treatment periods cannot establish a causal relationship between operator experience and outcome. The value of the series lies in documenting real-world temporal variation and emphasizing the need for continuous audit of implant and prosthetic complications.

5. Conclusions

Within the limitations of this retrospective single-operator series, full-arch immediate-loading rehabilitation supported by a reduced number of implants showed a low overall crude implant failure proportion. Prosthetic complications remained clinically relevant and varied substantially across treatment periods.

The highest implant failure and prosthetic complication proportions occurred in the 2016–2018 period, followed by a marked reduction in 2019–2021. These findings indicate that cumulative experience alone should not be regarded as a sufficient surrogate for treatment quality. Standardized protocols, careful case selection, continuous clinical attention, maintenance, and systematic outcome monitoring remain essential throughout professional practice.

The observed temporal pattern is compatible with the broader evidence that operator experience and technical skill can influence clinical outcomes, but the retrospective design does not permit a causal attribution. Future studies should incorporate standardized follow-up, explicit complication definitions, patient- and implant-level covariates, and appropriate inferential or survival analyses.