The biomechanical challenge of the maxillary overdenture

Unlike the mandible, where clinical consensus is firmly established, the stabilization of implant-supported removable prostheses in the maxilla remains a predictability challenge. The lower trabecular bone quality, unfavorable force distribution, and increased sensitivity to non-axial loads complicate the choice of the ideal attachment. Until now, practitioners have largely relied on retrospective data, laboratory tests, or extrapolations from mandibular models.

The randomized study conducted by Ibrahim et al. (2026) addresses some of these uncertainties by directly comparing two systems over a two-year period: telescopic attachments and LOCATOR attachments. The specific objective was to evaluate whether these two types of anchors differ significantly in terms of retention and vertical and horizontal marginal bone loss (MBL). The protocol was standardized on patients receiving four maxillary implants with delayed loading.

The central hypothesis of this work is based on the trade-off between mechanical performance and biological integrity. The authors tested whether the superior retention, classically attributed to the telescopic friction system, influences stress distribution and, by extension, the stability of the peri-implant bone level compared to the resilience offered by the LOCATOR system.

Methodology: A 24-month randomized clinical trial

Ibrahim et al. designed this randomized clinical trial (RCT) to compare two attachment systems on maxillary implant-retained overdentures. The study is based on a 24-month follow-up, specifically targeting the edentulous maxilla, a critical area for prosthetic stability due to often lower bone quality.

• Implant configuration: Each patient received 4 parallel implants. The protocol uses guided surgery to limit positioning variations and requires standardized delayed loading.
• Study groups: The trial compares telescopic attachments (friction system) to LOCATOR-type attachments (low-profile abutments with resilient inserts).
• Prosthetic design: To isolate the effect of the attachments, all prostheses include full palatal coverage and oppose a mandibular overdenture.
• Analysis and measurements: Researchers evaluated retention as well as marginal bone loss (MBL). The latter was measured radiographically along two distinct axes: vertical bone loss and horizontal loss.

The sample sizing was primarily aimed at detecting retention differences. The authors then interpreted the bone loss data in light of conventional implant success thresholds to determine the clinical relevance of the results.

Results: A trade-off between retention and bone preservation

The randomized clinical trial (RCT) comparing telescopic attachments to LOCATOR systems on four maxillary implants reveals significant mechanical and biological discrepancies after a 24-month follow-up.

Retention and marginal bone loss (MBL)

The results indicate that telescopic attachments provide superior retention. However, this mechanical performance is correlated with more pronounced marginal bone loss compared to the LOCATOR system. Although statistically significant, the magnitudes of these differences remain moderate on a millimetric scale.

Clinical and biomechanical observations

• Retention dynamics: The mechanical superiority of the telescopic group is explained by the friction and the wedge effect between the primary and secondary copings. However, this rigidity limits the rotational freedom of the prosthesis during function.
• Load management: LOCATOR attachments allow for limited vertical and rotational movement thanks to the resilience of the nylon inserts. This flexibility appears to promote better distribution of non-axial loads, which are particularly critical in the maxilla.
• Peri-implant stability: Despite the disparities between the two groups, the overall bone loss for both systems remained consistent with the conventional implant success thresholds accepted in the literature.

In summary, the data from this trial suggest that maximum prosthetic retention may induce increased mechanical stress on the maxillary peri-implant bone, resulting in greater bone remodeling than that observed with more resilient attachments.

The retention paradox: stability vs peri-implant health

The results of this randomized clinical trial challenge the common perception that maximum retention is always preferable. While telescopic attachments offer superior hold, they are associated with more pronounced marginal bone loss (MBL) compared to the LOCATOR system after two years. Clinically, this discrepancy of 0.44 mm vertically and 0.24 mm horizontally, although statistically significant, remains within the acceptable thresholds for implant success. However, this trend suggests that the rigidity of the friction coupling in telescopic crowns transfers more non-axial stress to the peri-implant bone, in contrast to the resilience of the LOCATOR system which allows for limited freedom of movement.

A scope limited by an ideal protocol

The study presents methodological limitations that require caution: a modest sample size, a follow-up of only 24 months, and the use of radiographic substitutes. Above all, the standardized protocol with parallel implants and complete palatal coverage limits the generalization of the results. In configurations without a palate or with divergent implants, where the management of lateral forces is critical, the biomechanical behavior of these attachments could differ radically.

Conclusion: In concrete terms, for the practitioner:

• Do not systematically prioritize maximum mechanical retention: a certain resilience (LOCATOR type) seems to better preserve the maxillary crestal bone in the medium term.
• Reserve telescopic attachments for patients requiring strict prosthetic stability and a precise insertion axis, while anticipating rigorous radiographic follow-up.
• Consider that force management in the maxilla depends as much on the prosthesis design (palatal support) as on the choice of the attachment itself.

Summary of results

The study by Ibrahim et al. shows that telescopic attachments offer superior retention compared to the LOCATOR system, but at the cost of more pronounced marginal bone loss: +0.44 mm vertically and +0.24 mm horizontally at 24 months. Although statistically significant, these differences remain within the physiological limits of implant success, suggesting that the rigidity of the telescopic system transmits more stress to the maxilla.

In concrete terms, for the practitioner:

• Prioritize resilience: In the maxilla, where trabecular bone is less dense, opt for LOCATOR-type attachments that allow for slight functional play and reduce non-axial loads.
• Target retention with caution: High mechanical retention (telescopic) is not synonymous with durability; evaluate the risk of increased bone loss related to rigid friction before choosing this system.
• Optimize prosthetic support: Maintain full palatal coverage to ensure complementary mucosal support, thereby limiting direct overload on implants in maxillary overdenture designs.

Technical lexicon of the study

Telescopic attachments: Prosthetic connection systems based on friction and the wedge effect between a primary coping (abutment) and a secondary coping integrated into the prosthesis, offering a rigid connection.

LOCATOR attachments: Low-profile "stud" type attachment systems, characterized by the use of nylon inserts for retention and a design allowing for prosthetic resilience.

Marginal Bone Loss (MBL): Physiological or pathological resorption of the crestal bone surrounding the implant neck, evaluated here by vertical and horizontal radiographic measurements over a 24-month period.

Non-axial loading: Mechanical forces applied to the implant at a divergent angle relative to its longitudinal axis, frequent in the maxilla due to prosthetic rotation movements.

Peri-implant strain: Level of mechanical deformation transferred to the supporting bone during function, varying according to the rigidity of the attachment and the extent of palatal coverage.

Resilient nylon inserts: Interchangeable components of the LOCATOR system allowing limited vertical and rotational movement of the prosthesis, thereby reducing stress concentration on the implants.

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