Surgical guidance for zygomatic implants: what accuracy for which type of guide?

The placement of zygomatic implants (ZI) represents one of the most complex surgical challenges in oral rehabilitation, primarily due to restricted accessibility and limited visibility within the atrophic maxilla. In this critical context, precise positioning is imperative to avoid major anatomical complications. This randomised prospective study (NCT06227351) specifically addresses this issue by evaluating the contribution of computer-aided design and computer-aided manufacturing (CAD/CAM) in securing the surgical procedure.

The central objective of this study was to clinically compare two computerised 3D guidance protocols: the so-called "completely limiting" guides (Group I) and the "partially limiting" guides (Group II). The authors sought to determine the impact of the guide design on the accuracy of implant positioning, evaluated by linear deviations (at the coronal and apical points) and angular deviations.

The study tests the hypothesis that a partially limiting guide could constitute an effective and less invasive treatment modality. The aim is to verify whether this type of device significantly reduces operative time — the study's secondary endpoint — while maintaining clinical accuracy comparable to full guidance, the latter being theoretically more restrictive but potentially more accurate at the implant apex.

Methodology: Comparison of 3D surgical guides

This prospective randomised controlled clinical trial was conducted on a cohort of 6 patients (mean age: 56.9 ± 7.57 years) presenting with posterior maxillary atrophy. A total of 12 zygomatic implants (ZI) were placed and analysed, equally divided into two study groups:

• Group I (n = 6 implants): Use of 3D computer-aided surgical guides referred to as "completely limiting".
• Group II (n = 6 implants): Use of 3D computer surgical guides referred to as "partially limiting".

The experimental protocol aimed to compare the accuracy of the final positioning relative to the initial digital planning. The primary outcome variables included linear deviations measured at the coronal and apical points of the implant, as well as angular deviations. The mean operative time was recorded as a secondary endpoint.

The accuracy evaluation was based on the analysis of specific anatomical planes, including the midsagittal plane (MSP), the Frankfort horizontal plane (FHP) and the coronal plane (CP), using CBCT imaging and the integration of DICOM and STL data. The data underwent statistical analysis to identify significant differences (p < 0.05) between the two types of guidance.

Surgical precision and efficacy: results of the comparative study

The study involved a sample of 12 zygomatic implants (ZI) evenly distributed between the two groups (n=6 per group) in 6 patients presenting with maxillary atrophy. The mean age of the participants was 56.9 ± 7.57 years, with a homogeneous demographic and clinical distribution between the groups at baseline.

Analysis of positioning accuracy

The results show that the overall accuracy of implant positioning is comparable between fully restrictive guides (Group I) and partially restrictive guides (Group II). No statistically significant difference was observed regarding coronal linear deviations or angular deviations.

However, a notable difference was identified at the apical level:

• Apical deviation (midsagittal plane): Group II showed a significantly higher deviation than Group I (p = 0.015).
• The fully restrictive guide thus demonstrated superior control over the position of the implant apex, a critical zone during ZI placement.

Operative efficiency and clinical safety

Time saving constitutes the most marked result in favour of partial guidance. Analysis of the operative time reveals a statistically significant difference between the two protocols:

Qualitatively and observationally, the postoperative follow-up revealed no major complications. The authors report:

• Zero complications: Absence of infection, peri-implantitis or associated sinus pathology.
• Cohort stability: No dropouts were recorded during the study.

In summary, while the fully restrictive guide offers better control of the apical trajectory, the partially restrictive guide significantly reduces the procedure time (average saving of 5.83 minutes) while maintaining clinically acceptable overall accuracy.

Trade-off between control and efficiency

The results of this study highlight a tangible clinical dilemma: saving time versus apical control. The use of a partially restrictive guide reduces the procedure time by nearly 22%. This speed is an asset in limiting practitioner fatigue and exposure of the surgical site. However, the loss of apical precision observed in Group II (p = 0.015) is not insignificant. In zygomatic surgery, the apex is often located in high-risk anatomical areas; full guidance offers superior safety here, where every millimetre counts.

Limitations and perspective

It is crucial to note that this study is based on a limited sample of 12 implants. While this low statistical power limits the generalisation of the results, the total absence of post-operative complications in both groups suggests that both guidance modalities are clinically acceptable. Unlike some more invasive approaches, these 3D guides enable satisfactory precision to be maintained even under restricted visibility conditions.

Implications for practice

For the clinician, the choice of guide must depend on the complexity of the local anatomy. In cases where the apical margin of error is extremely small, the fully limiting guide stands out as the 'gold standard' of safety, despite a longer implementation time. The partial guide, smoother to handle, seems relevant for less critical cases where optimising operative time is a priority.

Summary of results

This prospective randomised study involving 12 zygomatic implants demonstrates that partially limiting guides significantly reduce operative time (21.17 ± 2.14 min versus 27 ± 2.37 min, p=0.01). While overall accuracy is comparable between the two systems, the fully limiting guide provides superior control of the apical position in the median sagittal plane (p=0.015).

In practical terms, for the practitioner:

• Efficiency gain: Favour the partially limiting guide to reduce the procedure time and improve surgical accessibility without compromising coronal precision.
• Apical safety: Opt for a completely limiting guide in complex anatomical situations where the trajectory of the implant apex is critical.
• Technical reliability: Both guided approaches allow for secure placement with no sinus or infectious complications in the short term.

Technical glossary of the study

Zygomatic Implants (ZI): Long anchorage devices inserted into the zygomatic bone, indicated for prosthetic rehabilitation in patients with severe maxillary atrophy where conventional implants cannot be stabilised.

Completely limiting 3D surgical guide: Computer-generated positioning template fully restricting the drill path and implant insertion, aimed at reducing manual directional errors at the expense of reduced accessibility.

Partially limiting 3D surgical guide: Guiding device providing selective restriction of the surgical trajectory, allowing for improved intraoperative visibility and, according to this study, a significant reduction in operative time.

Apical deviation: Measurement of the linear deviation between the planned position of the implant apex in the digital planning and its actual position after insertion. The study shows a significantly more pronounced deviation in the midsagittal plane for partial guides.

Midsagittal Plane (MSP): Vertical anatomical reference plane dividing the body into two equal parts (right and left), used in the study to precisely quantify the spatial accuracy of the placed implants.

ZAGA (Zygoma Anatomy Guided Approach): Specific surgical approach mentioned in the study protocols, adapting the trajectory of the zygomatic implant according to the patient's individual bone and sinus anatomy.

Maxillary atrophy: Clinical condition characterised by significant bone resorption of the maxilla, constituting the primary indication here for the use of zygomatic implants under 3D guidance.

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