Exact component combination
Verify the implant system, platform, Ti-base/abutment reference and fixation-screw reference. If the manufacturer's instructions specify single use of the screw, perform the control test with a new screw.
TROUBLESHOOTING
TORQUE · PRELOAD · SEATING
CLINIC + LABORATORY
Mechanical stability of the implant-prosthetic connection
Why does a fixation screw or Ti-base loosen?
Loosening is rarely caused by a single fault. It reflects the balance between preload, complete seating, connection geometry, the tightening instrument, soft tissues and functional loading.
This page links clinical and laboratory checkpoints with published evidence. Particular attention is given to posterior restorations and to situations in which a standard healing abutment is followed directly by the definitive crown without prior shaping of the emergence profile.
Torque → preloadCorrect component reference, torque and controlled preload
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Complete passive seatingImplant connection, proximal contacts, soft tissues
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Connection geometryContact surfaces, implant axis, Ti-base and crown height
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Functional loadingMolar region, occlusion, eccentric forces and parafunction
First, define the problem correctly
Screw loosening is an outcome, not a single diagnosis
A screw joint remains stable when sufficient preload is generated and functional separating forces do not overcome it. When loosening recurs, the entire chain should therefore be assessed rather than focusing only on the Ncm value.
Direct evidence
Preload, torque, geometry and loading
These mechanisms are directly addressed in experimental, FEM and clinical studies of screw loosening.
Indirect evidence
Soft tissues and emergence profile
The literature documents rapid dimensional changes, tissue collapse and the need to transfer the emergence profile accurately to the definitive restoration.
Clinical inference
Unstable soft-tissue profile → inaccurate transfer → secondary risk
The literature supports the dynamic behaviour of peri-implant mucosa and the difficulty of transferring the emergence profile accurately. However, a direct study linking oedema to screw loosening is still lacking.
Controlled retest
Reduce uncontrolled variables first
When loosening recurs, the goal is not to change several variables at once. It is more useful to create clearly defined conditions for the next check. If the problem recurs under a standardized protocol, that observation carries greater diagnostic value.
Principle: standardization does not identify the fault by itself. It reduces noise. The same logic is used in the literature to reduce uncertainty in digital workflows and clinical protocols.
System-compatible driver
Using the driver specified for the relevant geometry removes the tolerance or wear of a different instrument as one possible variable. Full engagement and stable contact between the working surfaces are essential.
Verified torque output
It is not appropriate to assume automatically that the torque wrench is inaccurate. When investigating a recurrent problem, however, its actual output should be verified according to the manufacturer's instructions or a validated control procedure.
Passive seating before torque
The implant connection must be clean and the Ti-base should already be in its final position before definitive tightening. Soft-tissue pressure, proximal contact or any other obstruction should not be overcome by the screw itself.
1 · Fixation
Torque creates preload. They are not the same thing.
Tightening torque is the input. The objective is to create controlled elastic preload in the screw so that the joint remains clamped. The resulting preload is influenced by friction, the condition of the thread and seating surfaces, screw geometry and the tightening procedure itself.
Specified tightening torque
Use the value specified for the exact component reference. The current label, blister and instructions for use take precedence over a general table.
Settling effect and retorque
Microscopic irregularities of the contacting surfaces settle after the first tightening. Retorque may increase residual preload in some systems, but it is not a universal rule for every component.
The driver must engage fully
Verify compatible geometry, full insertion, absence of play and wear of the working tip. A similar shape does not automatically mean identical tolerances.
Verifying the torque instrument
Mechanical torque-limiting devices can be relatively accurate, but their actual output should not simply be assumed during diagnostics. Verify the instrument according to the manufacturer's IFU or a validated control procedure.
2 · Seating and soft tissues
Before tightening, verify that the Ti-base is fully seated
The screw should not act as a press that pulls the crown into place against resistance from surrounding structures. Before final preload is generated, the definitive component should seat as passively as possible and the implant connection must be clean.
Check separately
implant connection · blood and debris · proximal contacts · soft-tissue pressure · correct index orientation · complete seating; for a subgingival connection, consider radiographic verification when in doubt.
Important distinction
Resistance during crown insertion is not proof of the cause of loosening. It is a diagnostic signal: before final torque, determine whether the resistance comes from soft tissue, a proximal contact, debris, incorrect orientation or the restoration itself.
Indirect evidence Clinical inference
When soft-tissue conditions change between scanning and delivery
A possible relationship between marked peri-implant soft-tissue swelling, the working model and subsequent seating of the definitive restoration was brought to our attention by an implantologist from a practice in Prague 1. The same issue was highlighted from the laboratory perspective by his dental technician while working with a soft-tissue model. Published literature does not support the claim that oedema itself 'loosens the screw', but it does support the individual intermediate steps in this clinical reasoning.
Supported by evidence
Soft tissues change shape rapidly after support is removed
Clinical studies show rapid collapse of peri-implant mucosa after removal of a provisional restoration. The interval between removing support and scanning can therefore alter the recorded emergence profile.
Li et al., 2019 → Supported by evidence
The emergence profile must be actively transferred into the digital model
The individualized scan body technique was described specifically to stabilize the already shaped supra-implant mucosa and transfer its contour together with the implant position into the 3D data.
Joda et al., 2014 → Supported in the posterior region
Standard and anatomically shaped healing abutments do not create the same profile
A randomized clinical study in premolar and molar sites found different peri-implant soft-tissue profile outcomes with CAD/CAM socket-sealing abutments compared with standard titanium healing abutments.
Elgendi et al., 2025 → Important nuance · 2026
A customized healing abutment is not automatically 'better' in every parameter
An RCT in mandibular first molars found some linear differences between a prefabricated convex and a custom concave healing abutment, but no significant difference in overall buccal volumetric change. Profile selection should therefore be driven by the clinical objective rather than by a universal hierarchy.
Ramadan et al., 2026 →Clinic → laboratory → clinic
Where can a discrepancy arise between the mouth and the working model?
The definitive restoration may be technically accurate relative to the model yet encounter different soft-tissue geometry at delivery. The critical issue is not 'swelling as a mechanical force on the screw', but agreement between the clinical situation, its recorded representation and the resulting emergence profile.
1. Healing with a standard healing abutment onlyIn a molar site, the transmucosal profile may remain substantially simpler and narrower than the cervical geometry of the definitive crown. This is not inherently an error, but it means a larger change in shape at definitive delivery.
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2. Bulky, swollen or otherwise unstable peri-implant mucosaThe actual soft-tissue contour can change over time. The literature also shows that mucosa can collapse very quickly after the supporting restoration is removed.
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3. An impression or intraoral scan captures only one moment in timeIf a transient, compressed or already collapsing profile is recorded, the digital data or soft-tissue mask may represent a different geometry from the tissue present at later delivery.
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4. The laboratory fabricates accurately to the supplied modelThe dental technician may create a cervical contour that is accurate relative to the model, but the model is always a reproduction of the recorded situation. A soft-tissue change that was not transferred may therefore become apparent only in the mouth.
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5. The definitive molar crown enters a different profileA broad anatomical emergence profile may compress the tissue, while tight proximal contacts may act at the same time. The clinical impression that 'the crown is down' is therefore not equivalent to verified complete passive seating of the Ti-base.
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6. Secondary mechanical risk arises only if seating is incompleteIf the component was not fully seated at final torque and settles further later, the clamping conditions of the screw joint may change. This final step is clinical inference, not a directly proven pathway from oedema to screw loosening.
≈ 500 µmA 2025 systematic review reports that one included study observed approximately half a millimetre of peri-implant mucosal collapse within the first tens of seconds after removal of a provisional restoration.
Stabilize the profileThe Individualized Scanbody Technique was developed specifically to stabilize the shaped supra-implant mucosa during digital impression taking and transfer its contour into the 3D data.
Posterior RCTA 2025 randomized study in premolar and molar sites confirmed that an anatomically CAD/CAM-shaped healing abutment and a standard healing abutment do not produce the same resulting soft-tissue profile.
Practical workflow
What this means before definitive tightening
This section is not an argument for routine provisionalization of every implant. It is a control framework for situations involving a pronounced soft-tissue profile, a more deeply positioned implant or unexpected resistance during restoration insertion.
- 01Assess tissue stability at the time of impression taking or scanning.
With marked swelling, bleeding or an unstable profile, consider whether the record reflects the situation on which the definitive cervical geometry should be based. - 02For a thick tissue phenotype, consider controlled emergence-profile shaping.
Depending on the clinical situation, a provisional crown or an anatomically customized healing abutment may be used, not as a screw-loosening prevention measure in itself, but to create more controlled soft-tissue geometry. - 03Transfer the established profile into the laboratory data.
In a digital workflow, minimize mucosal collapse and use a method that stabilizes or reproduces the shaped contour. - 04At delivery, distinguish soft-tissue resistance from proximal-contact resistance.
Assess each source of resistance separately. The screw should not be used to overcome an unidentified obstruction. - 05Verify complete passive seating of the Ti-base before final torque.
For a deep or subgingival connection, or whenever seating is uncertain, consider radiographic verification when clinically indicated. - 06Only then assess preload and functional loading.
Correct tightening torque, a compatible driver, the condition of the torque wrench, occlusion and posterior leverage remain direct mechanical factors in joint stability.
A justified conclusion
An unstable or substantially altered soft-tissue profile can complicate accurate capture, transfer to the working model and clinical verification of passive seating of the definitive restoration. The individual steps of this mechanism are supported by the literature.
What would be too strong a claim
‘Gingival swelling causes fixation-screw loosening.’ A direct causal study supporting that statement is currently lacking. We therefore do not present oedema as an independently proven mechanical cause, but as a possible factor affecting transfer accuracy and complete seating.
3 · Functional environment
Why the problem often appears in first and second molars
It is not a property of the tooth number itself. The molar region, however, often combines high cyclic forces, non-axial loading components, a broad occlusal table and sometimes an unfavourable lever arm between the implant axis and the point of contact.
Molar location
In a six-year retrospective study of 1,928 implants, loosening was most frequent in the molar region, reaching 8.5%.
Crown height
Increased crown-height space under non-axial loading alters stress distribution and may contribute to fatigue-related mechanical complications.
Axis and horizontal offset
The farther the occlusal force acts from the implant axis, the greater the bending moment that the connection must withstand.
Occlusion and parafunction
Check MIP, excursive interferences, local premature contacts and historical or clinical signs of bruxism.
Posterior access is a variable in its own right
In a laboratory model of limited intraoral access, general dentists generated insufficient torque with a hand screwdriver. The authors therefore emphasized the importance of a mechanical torque wrench in posterior regions. The study did not evaluate a specific IPD driver, but it clearly illustrates why, in molar sites, simply reaching the screw head must be distinguished from genuinely controlled tightening.
Hill et al., 2007 →Driver angle: do not transfer numerical limits between systems
An in-vitro study of an off-axis hexalobular system found similar output at 0–15°, with a reduction at 25–28°. That system was designed for angulation and does not establish an allowable deviation for a straight HEX driver. With a straight screw channel, full engagement and alignment with the screw axis therefore remain the objective.
Opler et al., 2020 →4 · System geometry
The implant, Ti-base and screw function as one mechanical assembly
Stability cannot be attributed to the screw alone. Implant-abutment contact surfaces, anti-rotational geometry, tolerances, transmucosal height, restoration accuracy and the direction of functional loading all matter.
Contact surfaces and micromovement
Different connection geometries alter stress distribution and the system's ability to resist separating forces. When a problem recurs, assess the entire interface rather than the screw alone.
Ti-base gingival height is not merely an aesthetic parameter
FEM data show that gingival height affects the biomechanics of the assembly. They do not, however, justify a simple rule such as 'a taller Ti-base means a higher risk of loosening'.
5 · Practical workflow
The screw keeps loosening. What should be checked?
Work from the simplest and most readily verifiable variables towards the biomechanics of the entire restoration. Each step should either support or rule out one group of causes.
01
Component identification
Implant system, platform, exact Ti-base/abutment reference, screw, thread, screw seat and recommended tightening torque.
02
Instrument
Correct driver profile, full engagement, tip condition, a compatible torque instrument and verification of its output according to the manufacturer's instructions or a validated control procedure.
03
Passive seating
Clean the implant connection and verify orientation, proximal contacts and soft-tissue pressure. The screw should not compensate for inadequate passive seating.
04
Definitive fixation
Use an undamaged screw and the specified tightening torque. Retorque only when it is part of the protocol for the specific system.
05
Occlusion and leverage
Check MIP, lateral and protrusive movements, crown-height space, implant axis, horizontal offset and parafunctional loading.
06
If the problem recurs
Assess connection geometry, the condition of the seating surfaces and thread, restoration accuracy, any possible manufacturing issue and the complete component history.
6 · Thirteen checkpoints
Quick checklist for the clinic and laboratory
1. Specified tightening torque
Is the torque value specified for the exact component reference being used?
2. Settling / retorque
Does the procedure follow the system-specific protocol?
3. Driver
Is the geometry compatible, the tip unworn and the driver fully engaged?
4. Torque instrument
Is it functioning correctly and checked according to the manufacturer's instructions for use?
5. Soft tissues
Is the emergence profile stable, with no pronounced tissue pressure during insertion?
6. Gingival height
Does the Ti-base match the clinical geometry and restorative design?
7. Proximal contacts
Do they interfere with complete crown seating?
8. Implant connection
Is it clean and free of blood or foreign material?
9. Molar location
What cyclic and non-axial forces act at this site?
10. Crown height and axis
Is there an excessive lever arm or horizontal offset?
11. Occlusion / bruxism
Are premature or excursive contacts present?
12. Connection geometry
Is the Ti-base fully seated and the connection free of signs of damage?
13. Recurrence
When the problem recurs, do not assess one isolated factor. Review the entire system, from the soft-tissue record and laboratory model through the component, screw, instrument and functional loading.
Published evidence
What the studies support and where clinical inference remains
The sources below support the individual links in this chain. None of them alone demonstrates that post-infectious or other oedema directly causes screw loosening. Together, however, they support three important points: peri-implant mucosa is dimensionally dynamic, a shaped emergence profile must be transferred accurately into the working data, and a stable screw joint requires complete passive seating. We therefore describe the transition from an altered soft-tissue profile to secondary mechanical instability as a clinical inference.
Mikulás et al., 2025 · systematic review of digital methods for capturing the peri-implant emergence profile; highlights significant soft-tissue collapse during direct scanning.
Li et al., 2019 · dynamic changes in peri-implant soft tissues after removal of an interim restoration.
Joda, Wittneben & Brägger, 2014 · Individualized Scanbody Technique; stabilization of the shaped supra-implant mucosa and transfer of its contour together with the implant position into 3D data.
Duran et al., 2018 · pilot digital study; an immediate digital impression after removal of an implant restoration did not accurately capture the desired soft-tissue dimensions.
Elian et al., 2007 · accurate transfer of a shaped peri-implant emergence profile from the provisional restoration to the definitive restoration and working model.
Wittneben et al., 2016 · volumetric changes in the emergence profile after soft-tissue conditioning with a fixed provisional restoration.
Chokaree et al., 2024 · randomized clinical study of customized versus prefabricated healing abutments.
Elgendi et al., 2025 · randomized clinical study of anatomically CAD/CAM-shaped versus standard healing abutments in the posterior region.
Lee et al., 2020 · clinical study of screw loosening in 1,928 implants; the highest incidence was found in the molar region.
Bulaqi et al., 2015 · FEM analysis of the effect of increased crown height under non-axial loading.
Wang et al., 2024 · systematic review and meta-analysis of the accuracy of mechanical torque-limiting devices; both principal types can be relatively accurate, although substantial heterogeneity exists across studies.
Cehreli et al., 2020 · practical technique for validating and calibrating dental torque-limiting devices.
Hill et al., 2007 · limited posterior access and inadequate torque when using a hand driver alone under model conditions.
Opler et al., 2020 · effect of driver angle in an off-axis hexalobular system; the numerical results cannot be transferred directly to straight HEX systems.
Ramadan et al., 2026 · RCT in mandibular first molars; different healing-abutment emergence designs produced some linear differences but no significant difference in overall buccal volumetric change.
Srivastava, 2025 · review of mechanical causes of screw loosening: settling effect, preload, torque and geometric factors.
Related technical library
Continue from the clinical problem to the underlying technical principle
Detailed technical abstracts, FEM studies and original source articles are available in the IPD library. A separate scientific library is available for clinical studies of Galimplant implants.
Clinical safety framework
This text is intended as a technical and educational overview, not as a substitute for clinical judgement or the instructions for use of a specific implant system. Always verify the recommended tightening torque, sterilization requirements and compatibility against the current label, blister and manufacturer's documentation. In cases of recurrent loosening, the implant, connection, prosthetic restoration and occlusion must be assessed individually.
