What Happens After You Torque the Screw

Consider a screw-retained full-arch provisional at delivery. The restoration is seated, and its screws are tightened according to the applicable manufacturer instructions.

The torque has been applied. What does that tell us about the joint?

It tells us the turning moment used during tightening. It does not directly tell us the exact clamping force created, or how much of that force will remain over time. Friction is one reason the relationship between torque and preload is less straightforward than it appears.^[1]

For a printed provisional connected directly to multi-unit abutments, that distinction deserves attention. In a configuration where the screw bears directly against restorative polymer, the material supporting the screw head differs from the metallic bearing surface provided by a titanium base. Directly connected printed interim workflows have been described in the dental literature.^[8]

The useful question is what happens to that connection after tightening, while the patient is using the restoration.

What tightening actually creates

As a seated screw is tightened, it stretches slightly within its elastic range. That stretch produces tension in the screw and compression in the components being clamped together. The initial tension is the screw's preload.^[2]

A helpful way to picture the screw is as a very stiff spring. Its elastic stretch maintains the force holding the mating surfaces together. The screw and the compressed components then respond together when external loads act on the joint; their relative stiffness and the way those loads enter the assembly influence that response.^[2]

Torque is the input used to create this condition. Because friction at the threads and beneath the screw head influences the result, the same torque value does not necessarily produce the same preload under different surface conditions.^[1]

There are therefore two questions to distinguish: how much preload was generated during tightening, and how much remains afterward.

A screw can lose preload without unscrewing

Imagine the screw immediately after tightening, held in a slightly stretched condition.

Now suppose the contacting surfaces settle. Microscopic surface irregularities flatten or locally deform, reducing the effective thickness of the material being clamped. This type of embedment is an established mechanism of preload relaxation.^[7]

The screw can recover some of its elastic stretch without rotating backward. Less stretch means less tension and, consequently, less clamping force.

The threaded position may be unchanged. The mechanical condition of the joint is not. This follows from the relationship between screw extension and the compression of the joined components.^[2]

That is why a backed-out screw and a reduction in preload should not be treated as interchangeable observations.

Whether a particular reduction becomes clinically important is a separate question. Understanding the mechanism does not establish its magnitude in a particular restoration.

Explainer

Preload loss, step by step

Step 1

Tighten

The screw stretches slightly within its elastic range. That stretch is what clamps the parts together.

Step 2

The bearing surface

With no titanium base, the screw head can bear directly on printed polymer, which becomes part of the clamped joint.

Step 3

Surfaces settle

If the clamped surfaces flatten or deform slightly, the effective thickness under the screw head is reduced.

Step 4

Less stretch, less clamp

The screw has not turned backward, but it holds less stretch, so the joint is clamped less tightly.

The big idea

Torque turns the screw. Preload is the squeeze that remains.

If the material under the screw slowly settles, the screw can lose some stretch, and the connection can lose some of its squeeze.

What changes when the screw bears on printed polymer?

In a conventional Ti-base configuration, the prosthetic screw bears on a metallic seat, and the titanium component provides the mating interface with the MUA. The restorative material is bonded to that component.

In a direct-to-MUA printed configuration without a metallic bearing insert, the screw head may load the printed restoration itself. Polymer then forms part of the structure compressed between the screw head and the abutment. These are different connection arrangements, not merely different component counts.^[9]

Removing the titanium base can eliminate a bonding interface and associated assembly steps. That is a legitimate workflow consideration, and directly connected printed interim techniques have been described for that purpose.^[8]

It does not establish that the printed configuration performs worse. It does mean that its behavior should not be assumed from a different assembly.

A titanium interface should not be treated as a guarantee, either. In an in vitro study of 30 temporary-cylinder, MUA, and implant assemblies, reverse-torque values generally declined over repeated tightening and removal cycles. The measured outcome was removal torque, not a direct continuous measurement of clamping force. Conventional assemblies also require careful interpretation of their mechanical behavior.^[3]

Why time and contact area matter

Polymers can respond to load over time.

Under sustained stress, deformation can increase: creep. When deformation is held constant, the stress required to maintain it can decrease: stress relaxation. A bolted joint is more complicated than either idealized condition because the screw and clamped material interact as forces and deformations change. Engineering investigations of polymer-containing composite joints examine how these behaviors contribute to preload relaxation.^[5]

Dental acrylic research offers relevant background, with an important qualification. Komiyama and Kawara studied residual stress relaxation associated with processing heat-activated denture-base resin and retaining it in a stone mold. Their work was not a test of a printed screw seat under clinical service conditions.^[4]

Composite-joint research addresses a different part of the question. Modeling work by Yang and colleagues links polymer-matrix creep to joint-level preload relaxation. That supports investigating the mechanism, but it does not supply a preload-loss value for a dental printed resin.^[6]

The distinction matters. A heat-processed denture-base resin, a printed restorative resin, and a fiber-reinforced engineering composite are not interchangeable test materials. Results must remain tied to the material, geometry, environment, and loading conditions studied.

Contact geometry adds another variable. For the same force, distributing that force over a greater effective bearing area lowers average contact stress. Real screw-seat contact is not uniform, however, and a larger visible screw head does not by itself establish how force is distributed through the seat. Composite-joint research has examined contact geometry as a contributor to relaxation behavior.^[6]

A broader or differently shaped seat can therefore have an engineering rationale. Its performance still needs to be evaluated with the intended material and assembly.

NASA provides a useful distinction

NASA's threaded-fastener standard treats short-term relaxation differently depending on the materials in the clamped joint. It permits a nominal allowance for all-metallic clamped parts, with qualifications, but calls for test-derived values when nonmetallic parts or coatings are involved. Expected preload loss from material creep is considered separately.^[7]

This is a spaceflight standard, not a dental protocol.

Its relevance is the approach to uncertainty: characterize the actual material-containing joint rather than transfer an assumption from an all-metal assembly.

It gives dentistry a reason to ask for the measurement. It does not predict the clinical answer.

What the dental evidence can tell us

A dental technique report by Raico Gallardo and colleagues describes fabricating an additively manufactured complete-arch interim prosthesis connected directly to MUAs. It documents a restorative workflow. It does not establish comparative retained preload after prolonged aging and loading.^[8]

A critical review of Ti-base-free MUA connections likewise describes limited, heterogeneous evidence across different restorative materials and designs. That broader literature should not be treated as validation of a specific printed-polymer screw seat.^[9]

The distinction between outcomes is equally important. Different tests answer different questions:

Removal torque can provide useful information, but it is not itself a direct force measurement. Methods that estimate preload from torque require additional information and assumptions; Hess and colleagues, for example, describe combining tightening torque, removal torque, and screw geometry.^[1]

Similarly, a fracture test that does not measure clamping force cannot, by itself, establish preload retention. A restoration could remain intact while experiencing localized deformation. Whether that occurs to a meaningful extent in a particular printed connection is something to investigate, not an outcome to presume.

That is the unresolved dental question.

What a meaningful comparison would measure

A useful investigation would begin with clearly defined, appropriately matched assemblies and measure both initial preload and retained preload over time.

The comparison should distinguish two objectives. One experiment might isolate the influence of the bearing material while controlling other variables. Another might compare complete systems, each using its intended screw and seat geometry. Those experiments would answer related, but different, questions.

A proposed protocol could track calibrated clamp force or screw strain after tightening, early settling, wet storage near body temperature, and controlled cyclic or thermal aging. It should report the initial and remaining forces, not only a percentage loss, and account for any influence of the measurement setup itself.

Resin formulation, processing, seat geometry, surface condition, and repeated assembly could then be examined systematically.

A result showing similar preload retention would be just as informative as a difference. And a laboratory difference would still need to be considered alongside functional and clinical outcomes before being assigned clinical significance.

What to ask before the next delivery

For clinicians and technicians evaluating a direct-to-MUA printed workflow, the practical question is specific:

Ask what was actually evaluated. Fabrication accuracy, fracture resistance, removal torque, direct preload retention, and clinical follow-up contribute different kinds of information.

Those questions do not justify changing torque values, component combinations, or processing protocols outside the applicable manufacturer instructions. They help identify what those instructions and supporting data establish, and what remains uncertain.

Following the prescribed tightening procedure remains essential. Understanding the clamping force that remains afterward is a further question.

For a full-arch provisional, that question belongs to the period when the patient is actually using the restoration.

This article is educational and does not replace clinical judgment, patient-specific treatment planning, or applicable manufacturer instructions. Engineering evidence discussed here supports mechanisms and research questions; it does not establish the clinical performance of an untested dental configuration.

References

1. Hess DP, Wadhwani CPK, Chung KH, Wee AG. A practical approach to determining screw preload in dental implant systems. Journal of Prosthetic Dentistry. 2026;135(5):901-903. doi:10.1016/j.prosdent.2025.08.022. Source

2. Chambers JA. Preloaded Joint Analysis Methodology for Space Flight Systems. NASA Technical Memorandum 106943. 1995. Source

3. Alhameed A, Sinha N, Thompson GA, Drago C, An H. In vitro study to analyze reverse torque values of attachment screws with multiple loosening and tightening preload cycles. Journal of Prosthodontics. doi:10.1111/jopr.13916. Source

4. Komiyama O, Kawara M. Stress relaxation of heat-activated acrylic denture base resin in the mold after processing. Journal of Prosthetic Dentistry. 1998;79(2):175-181. doi:10.1016/S0022-3913(98)70213-6. Source

5. Friedrich C, Hubbertz H. Friction behavior and preload relaxation of fastening systems with composite structures. Composite Structures. 2014;110:335-341. doi:10.1016/j.compstruct.2013.11.024. Source

6. Yang J, Ren Y, Song Y, Mu X, Sun Q, Yuan B. A novel strain-hardening viscoelastic-viscoplastic constitutive model: Application to preload relaxation prediction in composite bolted joints. Composite Structures. 2026;387:120352. doi:10.1016/j.compstruct.2026.120352. Source

7. National Aeronautics and Space Administration. NASA-STD-5020B: Requirements for Threaded Fastening Systems in Spaceflight Hardware. 2021; revalidated January 5, 2026. Table 1 and Appendix A.3. Source

8. Raico Gallardo YN, Kukunas S, Sukotjo C, Karayazgan B. Additively manufactured complete arch interim prosthesis directly connected to multiunit abutments: A dental technique. Journal of Prosthetic Dentistry. Published online August 10, 2026. doi:10.1016/j.prosdent.2026.07.020. Source

9. Mosaddad SA, Rodríguez-Pérez I, Pieralli S, Beuer F, Molinero-Mourelle P, Çakmak G. Titanium base-free multi-unit abutment connections: A critical review of prosthetic screw design, biomechanical behavior, and clinical performance. Materials. 2026;19(11):2212. doi:10.3390/ma19112212. Source