How Much Does Zirconia Shrink During Sintering?

 

 

If you mill a zirconia crown from a pre-sintered disc, the dimensions you see before sintering are not the dimensions you will have after sintering.

The difference is not small.

For conventional CAD/CAM zirconia, a linear shrinkage of roughly 19–21% is commonly reported for 3Y-TZP materials, while some studies and technical sources report broader ranges depending on the material and manufacturing method. A 2025 study examining seven zirconia CAD/CAM materials reported typical linear shrinkage of around 19–21% for 3Y-TZP and approximately 18–19% for some 4Y- and 5Y-based materials.

That means a zirconia restoration designed to finish at 10 mm cannot simply be milled at 10 mm and placed into a furnace.

The pre-sintered restoration has to be larger.

There is another point that is easy to miss.

A statement such as "zirconia shrinks by 20%" does not mean that the CAD software simply makes the restoration 20% larger.

The calculation is based on the relationship between the pre-sintered dimension and the final dimension.

For laboratories working with zirconia every day, understanding this difference is more useful than remembering a single shrinkage percentage.

What Does 20% Linear Shrinkage Actually Mean?

Let us use a simple example.

Suppose a zirconia test specimen is:

100 mm before sintering

After sintering, it becomes:

80 mm

The linear shrinkage is:

(100 − 80) / 100 × 100% = 20%

So the material has a 20% linear shrinkage.

Now look at the problem from the opposite direction.

Suppose the final restoration needs to have a particular dimension of 10 mm.

If the material shrinks by 20%, the pre-sintered dimension needed to produce 10 mm after sintering is:

10 ÷ 0.80 = 12.5 mm

So the milled dimension would need to be approximately 12.5 mm, not 12 mm.

This distinction matters.

A 20% shrinkage rate does not correspond to simply adding 20% to the final dimension.

The compensation factor is effectively the inverse of the remaining dimension.

For a linear shrinkage of 20%:

Shrinkage factor = 1 / (1 − 0.20) = 1.25

For a linear shrinkage of 21%:

1 / (1 − 0.21) ≈ 1.266

For a linear shrinkage of 19%:

1 / (1 − 0.19) ≈ 1.235

A zirconia manufacturer's CAM data may therefore appear as a number around 1.2–1.3 rather than as a simple "20% shrinkage" statement.

The exact format depends on the CAM system and manufacturer.

Why Does Zirconia Shrink by So Much?

The dimensional change comes from densification.

A pre-sintered zirconia blank contains a compacted zirconia structure that still has considerable internal pore space. During final sintering, the material becomes much denser.

As the internal spaces are reduced and the particles move closer together, the external dimensions decrease.

The material is not simply "losing 20% of its size."

Its density is changing at the same time.

One 2024 study examining three commercial dental zirconia groups reported linear shrinkage values of approximately 20.27%, 20.74%, and 19.58%. The corresponding volumetric shrinkage values were approximately 49.37%, 48.5%, and 48.27%. The study also reported substantial increases in relative density after sintering.

These numbers provide a useful way to understand the relationship.

A roughly 20% reduction in each linear dimension can correspond to almost a 50% reduction in volume.

Using a simplified example:

A cube measuring:

100 × 100 × 100 mm

has a volume of:

1,000,000 mm³

If every linear dimension decreases by 20%, the final dimensions become:

80 × 80 × 80 mm

The final volume is:

512,000 mm³

That is a volume reduction of:

48.8%

So when a laboratory hears "20% linear shrinkage," it should not interpret that as a small dimensional adjustment.

It represents a substantial change in the material's geometry.

Is 20% the Standard Shrinkage for All Zirconia?

No.

For laboratories and distributors, this is an important distinction.

There is no universal zirconia shrinkage number that applies to every disc on the market.

Different materials can have different shrinkage behavior.

A 2025 study published in Materials investigated seven zirconia CAD/CAM materials, including conventional 3Y-TZP, 5Y-TZP, and several strength-gradient multilayer zirconias.

The researchers found that the zirconia material itself had the strongest influence on measured shrinkage, with a reported partial eta-squared value of 0.893 in the global analysis. The study also noted typical linear shrinkage values around 19–21% for 3Y-TZP and approximately 18–19% for some 4Y- and 5Y-based materials.

These findings are useful when comparing zirconia products.

Two discs may both be described as "multilayer zirconia," but that does not mean their dimensional compensation should be identical.

The material composition, powder characteristics, manufacturing process, pressing conditions, and pre-sintered density can all influence the final shrinkage.

For a laboratory, the practical rule is simple:

Use the shrinkage information supplied for the actual zirconia product and, when applicable, the actual batch.

Do not replace it with a generic 20% value.

The Manufacturing Process Before Sintering Also Matters

The shrinkage number is related to how the zirconia blank is manufactured before it reaches the milling machine.

Zirconia powder can be compacted using different forming processes, and the resulting green or pre-sintered body can have different density and pore distributions.

A study on dental machinable zirconia examined the effect of compaction pressure on sintering behavior.

The researchers reported that linear shrinkage decreased from 24.54% at 50 MPa compaction pressure to 20.9% at 400 MPa in the tested material system. They also found that higher compaction pressure affected sintering behavior and machinability.

This example shows that shrinkage is not determined by the furnace alone.

The thermal cycle is only one part of the process.

The condition of the zirconia before it enters the furnace has already been established by the powder formulation and manufacturing process.

For a zirconia manufacturer, this means shrinkage has to be controlled upstream.

For a distributor, a technical datasheet showing "20% shrinkage" is more useful when the supplier can explain how that value was measured.

How Is the Shrinkage Factor Determined?

In a controlled manufacturing environment, shrinkage can be measured using a known geometric specimen.

For example, a manufacturer can prepare a specimen with a known pre-sintered dimension, sinter it under a defined program, and then measure the final dimension.

The linear shrinkage can be calculated as:

Linear shrinkage (%) = (L₀ − L₁) / L₀ × 100

where:

L₀ = pre-sintered length

L₁ = final sintered length

For example:

Pre-sintered length = 20.00 mm

Sintered length = 15.90 mm

Linear shrinkage:

(20.00 − 15.90) / 20.00 × 100 = 20.5%

The corresponding compensation factor would be approximately:

1 / (1 − 0.205) = 1.258

This is the type of calculation behind the dimensional compensation used in CAD/CAM workflows.

In actual manufacturing, the procedure can be more controlled than this simple example. Multiple specimens may be measured, and manufacturers may monitor different dimensions and different batches.

The number should come from measurement.

It should not simply be estimated from the expected density.

Why Batch-Specific Shrinkage Can Matter

Multilayer zirconia makes this issue more complicated.

A multilayer disc may contain different zirconia compositions or strength/translucency zones across its thickness.

If different areas of the disc do not have exactly the same shrinkage behavior, dimensional control becomes more complicated.

The 2025 study mentioned earlier specifically investigated strength-gradient multilayer zirconia and measured specimens taken from different positions within the discs. The researchers examined whether horizontal and vertical positions affected shrinkage and compared several commercially available materials. The material type had the strongest influence in their overall analysis.

For manufacturers, this is one reason batch testing matters.

For laboratories, it also explains why "multilayer" should not automatically be treated as a purely cosmetic shade feature.

There may be material changes through the disc that need to be considered during production.

If a supplier provides a single shrinkage value for a multilayer disc, the distributor should be able to explain whether that value represents the whole disc, a particular layer, or a batch average.

Does Shrinkage Occur Equally in Every Direction?

For conventional pressed CAD/CAM zirconia, the material is generally manufactured to have a relatively uniform structure, and many systems are designed around relatively uniform linear shrinkage.

But "relatively uniform" should not be interpreted as "mathematically identical at every point."

A particularly useful 2017 study looked at the relationship between measured shrinkage and the fit of zirconia copings.

The researchers compared geometric test specimens with actual CAD/CAM-milled zirconia copings from three commercial materials.

They found statistical differences between manufacturer-reported shrinkage values and experimentally measured values, as well as differences between shrinkage measured from simple geometric specimens and shrinkage observed in the actual copings.

The study also reported that shrinkage in the copings was not completely uniform, and the measured internal fit differed from the internal space specified by the CAD/CAM software.

A laboratory is not sintering a perfect cube.

It is sintering a crown, bridge, coping, or another restoration with different wall thicknesses, curves, connectors, margins, and internal surfaces.

A material's shrinkage measured on a simple test specimen does not necessarily tell the entire story of how a complex restoration will behave.

Why Does Restoration Geometry Matter?

Imagine two zirconia restorations made from the same disc.

One is a relatively simple single crown.

The other is a long-span bridge with thin areas, thick connectors, and several units.

Both restorations use the same shrinkage factor.

That does not mean their dimensional changes will necessarily be identical in every region.

The geometry affects how the restoration is distributed through the material and how the final dimensions are measured.

This point was also seen in a 2020 study of yttria-stabilized zirconia copings.

The researchers evaluated six different coping designs and compared standard and fast sintering protocols.

After sintering, the copings showed average linear changes of about 1.32% under the standard protocol and 1.54% under the fast protocol when compared with the initial design parameters, with volumetric changes of about 3.82% and 3.90%, respectively. The study concluded that preparation design had a greater influence on dimensional changes than the difference between the standard and fast sintering protocols tested.

These numbers should not be confused with the roughly 20% shrinkage of the zirconia blank itself.

They are measurements of the dimensional change of the fabricated coping relative to the original design under the specific experimental setup.

This distinction matters when reading dental research.

Different studies may report "shrinkage" at different stages.

Not Every "Shrinkage Percentage" Means the Same Thing

When comparing technical documents or research papers, it is useful to check what the percentage actually refers to.

There are at least three different things that can be discussed:

Linear shrinkage

Change in one dimension.

Volumetric shrinkage

Change in total volume.

Dimensional change of a restoration

Change measured on the actual crown, coping, bridge, or other restoration compared with a reference design.

These values are not interchangeable.

For example, a material with approximately 20% linear shrinkage can show close to 49% volume reduction if the contraction is uniform in three dimensions.

That does not mean the restoration itself has a "49% shrinkage factor."

The terminology needs to be read carefully.

Why a Small Shrinkage Error Can Become a Real Fit Problem

Now consider a simpler production example.

Suppose the actual linear shrinkage of a zirconia material is:

20.0%

The correct compensation factor is:

1.25

Now suppose the CAM system is using a factor corresponding to:

19.0% shrinkage

The compensation factor would be:

1.235

The difference in compensation factor is only about:

0.015

That may look insignificant.

But if the final target dimension is 20 mm:

Using the 20% value:

20 × 1.25 = 25.00 mm

Using the 19% value:

20 × 1.235 ≈ 24.70 mm

The difference in the pre-sintered target dimension is approximately:

0.30 mm

Three-tenths of a millimeter is not a huge number for a zirconia disc.

But for a dental restoration, especially around a margin or internal surface, a dimensional difference of this scale can matter.

Shrinkage data should therefore not be treated as a rough reference number.

The closer the production system is to its intended dimensional accuracy, the more relevant the compensation data becomes.

What Happens If the Wrong Shrinkage Factor Is Entered?

This is one of the first things I would check if a laboratory reports that the fit of a new zirconia material is different from its previous material.

Suppose the zirconia manufacturer states a linear shrinkage of 20.2%.

The laboratory imports the new material into its CAM software but continues using the previous supplier's compensation value.

The milling itself may look completely normal.

There may be no obvious problem during machining.

The issue only becomes visible after sintering.

Depending on the direction and size of the compensation error, the final restoration can be:

slightly too large;

slightly too small;

different from the expected internal fit;

or inconsistent when compared with the CAD reference.

At that point, the operator may first suspect the milling machine.

But the milling machine may have performed exactly as programmed.

The problem can be the material parameter.

A new zirconia product should therefore be treated as a new material system during validation, even if its appearance and disc dimensions look almost identical to the previous product.

What Should a Laboratory Do When Changing Zirconia Brands?

A simple checklist is useful here.

Before putting a new zirconia disc into regular production, check:

1. Shrinkage factor

Ask the supplier for the actual linear shrinkage or CAM compensation value.

2. Measurement method

Ask how the value was obtained.

Was it measured from cubes, bars, discs, or actual restorations?

3. Batch information

Find out whether the value is fixed for the product or supplied batch by batch.

4. Sintering program

Use the program recommended for that specific material.

5. CAD/CAM compatibility

Confirm that the compensation format matches the CAM software being used.

6. Validation sample

Before large-scale production, mill a small number of representative restorations and evaluate their dimensions after sintering.

This does not require a complicated laboratory experiment.

A laboratory can start with a known crown design, keep the milling parameters unchanged, and compare the final restoration with the reference.

The purpose is to find out whether the new material behaves as expected before it becomes part of routine production.

What Should a Distributor Ask the Zirconia Manufacturer?

Distributors often focus on strength, translucency, shades, disc sizes, and price.

Those are all reasonable questions.

If the product will be sold to professional dental laboratories, shrinkage data should also be part of the technical discussion.

I would ask the manufacturer:

What is the linear shrinkage range?

Is the shrinkage value batch-specific?

What test method is used?

Is the number measured before and after final sintering?

What compensation factor should be entered into the CAM software?

Is the factor different for different zirconia grades?

Do multilayer discs use one compensation value across the whole disc?

What happens if the laboratory uses a different furnace program?

Has the shrinkage factor been validated on actual CAD/CAM restorations?

These questions are more useful than simply asking whether a disc has "high strength" or "high translucency."

A distributor does not need to perform material science testing personally.

But having the right technical questions makes it easier to distinguish between a product with documented manufacturing control and one that only has a marketing datasheet.

What About a 98 mm Zirconia Disc?

Here is another practical example.

Suppose a zirconia disc has a nominal diameter of:

98 mm

And suppose its measured linear shrinkage is:

20%

If the shrinkage were uniform across the diameter, a simplified calculation would give:

98 × 0.80 = 78.4 mm

after sintering.

That does not mean a dental laboratory should use 98 mm as a final usable restoration dimension.

It simply illustrates the scale of the dimensional change.

In real CAD/CAM production, the disc is used as a pre-sintered blank from which restorations are milled with compensation already applied.

The software is not trying to preserve the original 98 mm diameter.

It is compensating for the material's expected contraction.

The shrinkage factor is therefore part of the digital manufacturing data rather than an optional note.

Does a Higher Shrinkage Number Mean a Worse Zirconia?

No.

A 20.5% shrinkage material is not automatically better or worse than a 19.5% material.

The number itself does not tell us:

strength;

translucency;

aging behavior;

milling quality;

surface quality;

or clinical performance.

Shrinkage is primarily a dimensional processing parameter.

What matters to the laboratory is whether the shrinkage is:

known, consistent, measurable, and correctly compensated.

A material with a predictable 20.5% shrinkage can be easier to work with than a material advertised with a lower shrinkage value but poor batch consistency.

For production, predictability is more useful than a single attractive number.

Why Manufacturers Should Monitor Shrinkage During Production

From the manufacturing side, shrinkage is something that needs to be controlled before the product reaches the laboratory.

If the pre-sintered density changes, the sintering behavior can change.

If the powder characteristics change, the final dimensional behavior may change.

If pressing conditions change, the blank may respond differently during sintering.

A zirconia manufacturer therefore cannot simply measure shrinkage once and assume the same number will remain valid forever.

The 2011 study on compaction pressure provides a good example of this relationship. Changing compaction pressure from 50 MPa to 400 MPa in the tested zirconia system was associated with a change in measured linear shrinkage from 24.54% to 20.9%.

These exact values should not be taken as representative of commercial dental discs today.

What the study demonstrates is more basic:

The physical state of the pre-sintered body influences how much it contracts during final sintering.

For manufacturers, that makes dimensional control part of material production rather than something left to the dental laboratory.

Why Multilayer Zirconia Deserves Extra Attention

Multilayer zirconia has become common in digital dental workflows.

From the laboratory's perspective, it is convenient because one disc can contain different optical or mechanical zones.

From a dimensional-control perspective, however, multilayer materials require more information.

If the layers have different compositions or powder characteristics, their shrinkage behavior needs to be characterized.

The 2025 study of seven zirconia materials specifically included several strength-gradient multilayer products and examined shrinkage at different positions in the discs. The researchers emphasized the importance of checking shrinkage behavior when using these materials because variations could affect the dimensional accuracy of restorations.

For a laboratory buying multilayer zirconia, I would therefore ask one additional question:

Is the stated shrinkage factor representative of the whole disc, or is it based on a particular layer or test position?

That question is easy to ask and can reduce uncertainty later.

What About 3D-Printed Zirconia?

The shrinkage discussion becomes more complicated when zirconia is produced by additive manufacturing.

The forming process is different, so the pre-sintered body may have a different internal structure and shrinkage pattern.

A 2025 study comparing milled and 3D-printed zirconia specimens reported approximately 26% shrinkage along all axes for the subtractively processed group, while the 3D-printed cubic specimens showed approximately 19.88%, 21.99%, and 20.02% shrinkage along the X, Y, and Z axes in the tested setup.

These results should not be used to say that 3D-printed zirconia always shrinks less than milled zirconia.

The study used particular materials and processing conditions.

The useful point is that manufacturing method can change shrinkage behavior.

As dental laboratories begin to encounter more additively manufactured zirconia, the assumption that one shrinkage model applies to every zirconia production method becomes less useful.

A Better Way to Look at Shrinkage

When I discuss zirconia shrinkage from an R&D perspective, I prefer not to ask:

"How many percent does zirconia shrink?"

A more useful question is:

"How does this specific zirconia behave under its specified processing conditions?"

That question contains several smaller questions:

What is the pre-sintered density?

What is the measured linear shrinkage?

How consistent is it between batches?

Is the shrinkage isotropic?

Does the material have different layers?

How was the shrinkage measured?

What compensation factor should be used?

Which sintering program was used during validation?

Has the value been checked on actual restorations?

Once these questions are answered, the percentage itself becomes much more meaningful.

What Should a Buyer Look for on a Zirconia Datasheet?

If you are a laboratory owner, purchasing manager, or distributor comparing zirconia products, I would not look only at the headline specifications.

A useful technical sheet should give you enough information to understand how the material will behave in your digital workflow.

At minimum, look for:

Parameter	Why it matters
Linear shrinkage	Determines dimensional compensation
Shrinkage factor / CAM factor	Used by CAD/CAM software
Sintering schedule	Connected with the reported material properties
Zirconia type	Helps identify the material system
Batch information	Useful when investigating dimensional changes
Disc dimensions	Needed for CAM setup and production planning
Density information	Helps understand the pre-sintered and final material state
Recommended milling system	Helps avoid parameter mismatches
Recommended sintering furnace conditions	Useful when validating a new material

A datasheet does not need to be complicated.

But the shrinkage information should be clear enough that a technician does not have to guess which number belongs in the CAM software.

The Number Matters, But Consistency Matters More

A laboratory can work with 19%, 20%, or 21% linear shrinkage.

The exact number is not the only issue.

What matters is whether the number is known and whether the actual material behaves close to that value under the intended production conditions.

For example, if a manufacturer states a 20.0% shrinkage factor and production measurements remain close to that value from batch to batch, the laboratory can build a stable workflow around it.

If one batch behaves like 19.5%, another like 21%, and another like 22%, the problem becomes much harder to manage.

The laboratory may start adjusting milling parameters when the actual issue is material variation.

Dimensional consistency is therefore one of the less visible but important parts of zirconia manufacturing.

Final Thoughts

So, how much does zirconia shrink during sintering?

For conventional dental CAD/CAM zirconia, around 19–21% linear shrinkage is a useful reference range for many 3Y-TZP materials, while published studies show that actual values vary with material composition, manufacturing process, pre-sintered condition, and measurement method. Some studies report values outside this range as well.

There is no single "zirconia shrinkage number."

A 20% linear shrinkage means that 100 mm becomes approximately 80 mm. It also means that achieving a final 10 mm dimension requires a pre-sintered dimension of about 12.5 mm under a simplified uniform-shrinkage model.

That difference is why CAD/CAM compensation is necessary.

Research has also shown that the measured shrinkage of actual zirconia restorations may not perfectly match values obtained from simple geometric specimens or manufacturer-reported values. Differences in material and restoration geometry can affect the final result.

For laboratories, the practical approach is to treat shrinkage data as part of the zirconia's technical specification.

When changing materials, check the CAM factor.

When a new batch produces unexpected dimensional changes, check the material and batch information before changing the milling strategy.

When buying from a new supplier, ask how the shrinkage was measured.

For distributors, do not stop at asking for strength and translucency data. Ask for the information that a dental technician actually needs to put the material into production.

A zirconia disc may look like a simple round blank when it arrives at the laboratory.

But its shrinkage behavior has already been influenced by everything that happened before that disc reached the milling machine.

For the manufacturer, controlling that behavior is part of producing a consistent material.

For the laboratory, understanding the number is part of producing a consistent restoration.