Clinical and radiographic outcomes of non-axial implants in partial rehabilitation of the atrophic posterior maxilla: a retrospective case series and narrative review

1. Introduction

Population ageing has increased the clinical relevance of partial and complete edentulism. Loss of posterior occlusal support is associated with deterioration in masticatory performance [1], while extensive tooth loss in older adults has been linked to nutritional and functional disadvantages [31]. Recent Global Burden of Disease analyses indicate that edentulism remains highly prevalent and that absolute case numbers are expected to increase as populations age [6,24]. Posterior tooth loss is particularly relevant because it reduces the number of functional occlusal units, impairs food comminution and may increase the mechanical demand on the remaining dentition. Restoring posterior support is therefore an important objective in patients with progressive tooth loss and in those requiring rehabilitation of the atrophic maxilla.

The posterior maxilla is anatomically challenging because post-extraction ridge resorption, reduced trabecular density and progressive maxillary sinus pneumatization may substantially reduce the bone volume available for implant placement [4,17]. Maxillary sinus floor elevation, through lateral or transcrestal approaches, is an established method for increasing the available bone volume [2,10,12]. Nevertheless, augmentation procedures may increase surgical complexity, healing time, cost and postoperative morbidity. Evidence summarised in the Cochrane review by Esposito et al. suggests that, in selected patients with sufficient residual bone to obtain primary stability, shorter implants without sinus augmentation may provide outcomes comparable to longer implants placed with augmentation, with fewer surgical complications [10].

Sinus augmentation is predictable when appropriately indicated, but complications can occur. Infection of a sinus graft is a recognised adverse event that may require prolonged medical and surgical management [11], and postoperative infection is associated with a higher risk of implant failure [13]. In addition, biofilm formation on implant surfaces contributes to peri-implant inflammation and may compromise long-term maintenance [21]. These considerations support a proportional approach to treatment planning: regenerative procedures should be used when their expected benefit outweighs their additional invasiveness, rather than being regarded as mandatory in every atrophic posterior maxilla.

Graftless implant strategies aim to optimise the use of residual native bone. Depending on the anatomy, these strategies may include short implants, implants tilted anterior or tangential to the maxillary sinus, trans-sinus implants and implants engaging posterior anchorage sites. Such approaches do not replace sinus augmentation in all patients; rather, they broaden the range of treatment options available when primary stability, prosthetically driven positioning and adequate hygiene access can be achieved without grafting [2,10].

Non-axial implants are of particular interest in partial posterior rehabilitation. Tilting an implant can permit engagement of available bone anterior to or alongside the maxillary sinus, increase the anteroposterior spread of implant support and reduce distal cantilevering [22]. The concept was initially developed mainly in full-arch protocols [16,26,30] and has subsequently been applied to segmental posterior rehabilitations, including configurations combining one axial and one trans-sinus tilted implant [23]. The primary aim of the present study was to describe implant survival and complications in a consecutive clinical cohort treated with graftless partial rehabilitation of the atrophic posterior maxilla. The secondary aim was to contextualise the findings through a narrative review of contemporary graftless implant strategies.

2. Materials and Methods

Surgical and prosthetic procedures

All surgical procedures were performed under local anaesthesia according to the clinical protocols adopted by the Department of Dentistry of the IRCCS San Raffaele Hospital. Implant osteotomies and fixture placement were performed in accordance with the relevant manufacturers’ instructions.

The implant strategy was selected according to residual bone anatomy, maxillary sinus pneumatization, prosthetic requirements and patient-specific clinical factors. The objective was to obtain prosthetically acceptable implant positioning and adequate primary stability using native bone. Immediate or early loading was adopted only when the surgical and prosthetic conditions were considered suitable.

All rehabilitations supported fixed implant-supported prostheses. Definitive restorations were delivered after the planned healing or loading phase. Patients were enrolled in a maintenance programme including professional oral hygiene and scheduled clinical and radiographic follow-up.

Radiographic evaluation

Radiographic assessment was performed using panoramic radiographs and cone-beam computed tomography (CBCT), when available. Images were reviewed for implant position, peri-implant radiolucency and evident changes in peri-implant bone levels.

Available postoperative and follow-up images were compared qualitatively. Because imaging modality, projection and follow-up intervals were not standardised, no quantitative marginal bone-level measurement was performed. Findings consistent with progressive pathological bone loss or implant failure were recorded.

Radiographic examinations were reviewed by an experienced investigator using the available image-analysis software.

3. Results

4. Discussion

This retrospective case series found an implant survival rate of 95.45% after a mean follow-up of 4.7 years in graftless partial rehabilitation of the atrophic posterior maxilla. All implants were functional at 12 months, and the two losses occurred later. The findings indicate clinical feasibility in selected patients, but they do not establish equivalence or superiority over sinus augmentation because the study had no control group and included a small, heterogeneous cohort.

Developments in three-dimensional assessment, implant design and prosthetically driven planning have expanded the possibility of using residual native bone in the posterior maxilla [2,4,17]. In selected cases, the Cochrane evidence suggests that less invasive alternatives may achieve acceptable outcomes while reducing treatment-related complications [10]. Graftless rehabilitation should therefore be regarded as one option within an anatomy- and patient-specific treatment pathway, not as a universal replacement for augmentation.

The survival observed in this cohort is broadly compatible with reports on short and tilted implants [10,19,22,30] and with the clinical report on an axial/trans-sinus configuration for partial posterior rehabilitation [23]. Direct comparison is limited by differences in study design, loading protocol, implant system, prosthetic configuration and follow-up duration. In addition, much of the tilted-implant evidence concerns complete-arch rehabilitation rather than partial posterior prostheses.

The absence of early failure suggests that primary stability and initial osseointegration were achieved in the included cases. One late loss followed peri-implantitis three years after loading, and the other followed an irretrievable fracture of a Multi-Unit Abutment screw. These events underline the importance of long-term plaque control, maintenance and prosthetic surveillance. Biofilm-related complications and prosthetic design factors remain relevant regardless of whether grafting is performed [19,21].

Neither failure can be attributed directly to the absence of a regenerative procedure. However, the retrospective design does not permit causal inference. The results instead support the practical importance of case selection, implant positioning, passively fitting prostheses, controlled occlusal loading and structured maintenance.

Graftless strategies encompass different techniques with distinct anatomical indications and levels of complexity. Short implants use the available vertical bone; tilted implants redirect the osteotomy to engage residual bone; and trans-sinus implants use a long oblique trajectory to reach remote anchorage. These approaches share the objective of achieving stable implant support while avoiding augmentation when a prosthetically acceptable result can be obtained.

Short implants have the strongest comparative evidence among these options. In selected posterior maxillary sites, they may provide survival comparable to longer implants placed with sinus augmentation while reducing surgical morbidity [10,19]. Tilted implants can increase anteroposterior spread and reduce cantilever length, with systematic-review data showing high survival in full-arch applications [22,30].

For partial posterior maxillary rehabilitation, the axial/trans-sinus tilted configuration described by Agliardi et al. is directly relevant to the present treatment concept [23]. Nevertheless, evidence remains largely observational and operator-dependent. The current reference list does not contain a dedicated pterygoid-implant systematic review or a directly relevant subperiosteal-implant study; quantitative conclusions for those techniques would therefore be unsupported.

These techniques should be considered complementary rather than competing. Selection depends on residual bone height and width, sinus anatomy, prosthetic space, hygiene access, systemic and behavioural risk factors, and the clinician’s experience. A less invasive approach is justified only when it can meet the same biological and prosthetic objectives as the more invasive alternative.

The concept of biological cost is relevant to shared decision-making. Sinus augmentation is an established and often necessary treatment [10,12], but it adds a surgical site, healing time and potential morbidity. Decision-tree approaches therefore recommend matching the procedure to residual anatomy and the expected benefit [2].

The present findings should not be interpreted as evidence against regenerative procedures. Sinus floor elevation remains predictable and well supported [10,12]. At the same time, sinus-graft infection and postoperative implant infection are clinically important complications [11,13], and biofilm control remains central to long-term implant health [21]. The appropriate conclusion is therapeutic proportionality rather than routine avoidance of biomaterials.

In patients with sufficient native bone for primary stability and prosthetically acceptable implant placement, graftless strategies may reduce surgical burden. In patients without adequate native anchorage, augmentation or alternative remote-anchorage techniques may remain necessary.

This study has substantial limitations: its retrospective single-centre design; small sample size; absence of a comparator; inclusion of different implant strategies and loading protocols; incomplete reporting of patient demographics, periodontal and smoking risk, implant dimensions and site-specific outcomes; non-standardised radiographic examinations; qualitative rather than quantitative bone-level assessment; and absence of patient-reported outcomes. The literature component was narrative, without a reproducible search strategy, study-selection flow, risk-of-bias assessment or meta-analysis. Prospective multicentre studies should use standardised clinical, radiographic and prosthesis-level outcomes and should account for clustering of multiple implants within patients.

5. Conclusions

Within the limitations of this retrospective case series, graftless fixed rehabilitation of the atrophic posterior maxilla using implants placed in native bone was clinically feasible in selected patients.

At a mean follow-up of 4.7 years, implant survival was 95.45%, with no implant loss during the first year and no prosthesis-level failure. These results cannot establish equivalence to sinus augmentation, but they support further evaluation of non-axial and trans-sinus strategies for partial posterior rehabilitation.

Careful patient selection, three-dimensional prosthetically driven planning, adequate primary stability and structured maintenance remain essential. Comparative prospective studies with quantitative marginal bone-level assessment are required before broader conclusions can be drawn.