The Weather & Alginate impressions

If you've worked in dentistry long enough, you've probably noticed a strange pattern.
The weather changes dramatically, the temperature suddenly rises or drops, and within a day or two the phone starts ringing.

"The denture is tight."
"The tray doesn't seat."
"The crown seems slightly out."
"We've had to do far more adjustments than usual."

At Bremadent Dental Laboratory, we process thousands of cases every month, and over the years we've noticed this trend repeatedly. Whenever there is a sudden change in weather, particularly during heatwaves or cold snaps in the UK, there is often a noticeable increase in calls regarding the fit of appliances.

It isn't always the laboratory.

It isn't always the clinician.

Very often, the impression itself is the common denominator. Alginates are fantastic materials. They're quick, affordable, accurate when handled correctly and remain one of the most widely used impression materials in general dental practice. However, they are also incredibly sensitive to how they are mixed, stored, disinfected and transported.
Small changes can create surprisingly large dimensional differences.

Understanding those variables can save chairside time, reduce remakes and produce far more predictable results.

Why Does Weather Matter?
Alginates are hydrocolloid materials. That means they rely heavily on water during mixing and are affected by both temperature and moisture.

When temperatures change dramatically, the water used to mix the alginate often changes with it.
Many dental practices use tap water directly from the surgery sink. Depending on how the plumbing is configured, that water may be significantly warmer during a summer heatwave or much colder during winter.

We've even visited practices where the cold tap is supplied from pipework running externally before entering the building. On a freezing January morning or a hot July afternoon, the water temperature can be very different from what you might expect. Those few degrees matter.

Hot Water Can Speed Everything Up
Warmer water accelerates the chemical reaction within alginate.
That means:
• Shorter working time
• Faster setting time
• Less time to fully load and seat the tray
• Increased risk of distortion if the tray is not seated promptly

We've seen occasions where clinicians are caught out because they're following exactly the same routine they've used all year, yet the alginate suddenly feels as though it's setting before they've even reached the patient's mouth.
Nothing else has changed. Except the weather.

Cold Water Isn't Always Better
The opposite can happen in winter. Very cold water slows the setting reaction. While this may sound helpful, it also means:
• Longer time in the mouth
• Increased chance of movement before set
• Greater patient discomfort
• Increased likelihood of distortion if the tray is disturbed

Again, nothing is technically "wrong." The impression material is simply behaving differently because the mixing water has changed temperature.

It's Not Just Temperature
Weather often gets blamed, but in reality it usually exposes other small inconsistencies that already exist within the impression process.

When several minor variables occur together, the final impression may no longer be dimensionally stable enough to produce a highly accurate appliance. Over the years we've identified several common causes.

Incorrect Powder and Water Ratios
It can be tempting to estimate. One slightly rounded scoop. A little extra water. Half a scoop because it "looks about right."

Unfortunately alginates are formulated to work within very specific powder-to-water ratios. Too much water produces a weaker mix with increased shrinkage. Too little water creates a thicker mix that may not fully capture detail.
Always follow the manufacturer's recommended ratios.

Not Shaking the Container Before Use
This is one that surprises many people. During storage and transport, heavier particles within the alginate powder naturally settle towards the bottom of the container.

If the tub or bag isn't shaken thoroughly before first use, the composition of the powder changes throughout the container.

Early mixes may contain different proportions of fillers and reactants compared with the final scoops. Most manufacturers actually recommend gently rolling or shaking the container before opening. It's a thirty-second job that can improve consistency enormously.

Using Expired Alginates
Every material has a shelf life. Once alginate passes its expiry date, moisture absorption and chemical degradation begin affecting performance. Setting times become less predictable. Surface detail may reduce. Dimensional stability may change.

Always rotate stock and avoid using materials beyond their recommended expiry date.

Poor Mixing Technique
Whether mixing by hand or using an automatic mixer, consistency matters. Incomplete mixing leaves powder pockets throughout the impression. Over-mixing may reduce working time. Under-mixing can weaken the structure and reduce accuracy. A smooth, creamy consistency without dry particles is always the goal.

Disinfecting for Too Long
Disinfection is essential. No laboratory wants an impression that hasn't been disinfected correctly.
However, over-disinfection can be equally problematic. Many impression materials have recommended immersion times. Leaving alginate immersed significantly longer than advised allows additional water absorption or dehydration depending on the disinfectant used. Either can affect dimensional stability.
Always follow both the alginate manufacturer's guidance and the disinfectant manufacturer's instructions.

Using the Wrong Disinfectant
Not every disinfectant is compatible with every impression material.
Some solutions can alter the surface, affect dimensional stability or interfere with gypsum pouring.
Compatibility matters. If in doubt, check the manufacturer's recommendations rather than assuming all disinfectants behave the same.

Delayed Pouring
Alginates are designed to be poured as soon as reasonably possible. Although many modern formulations advertise extended stability, every hour introduces additional opportunity for dimensional change.

If impressions must be transported to your dental laboratory, proper storage becomes even more important.
A damp environment is not the same as soaking the impression. Likewise, allowing impressions to dry out on a windowsill or dashboard is equally problematic.

Poor Tray Selection
An excellent alginate cannot compensate for an unsuitable tray.

• Insufficient clearance.
• Lack of adhesive.
• Tray flexure.
• Overfilled trays.

All can contribute towards distortion before the impression even reaches the laboratory.

Patient Movement
Sometimes the simplest explanation is the correct one.

• Talking.
• Swallowing.
• Moving.
• Removing the tray too early.
  
  

These seemingly minor events can create distortions that only become obvious once the appliance has been manufactured.

When the Laboratory Spots a Pattern
One of the advantages of processing thousands of impressions every month is that patterns become easier to recognise.
If several practices suddenly begin reporting fitting issues during the same week, we naturally investigate.

• Has a material changed?
• Has a process altered?
• Has equipment been recalibrated?

Quite often, after speaking with clinicians, we discover the timing coincides perfectly with an unexpected heatwave or sudden cold spell.

It's rarely one catastrophic error. More often it's several tiny variables aligning at exactly the wrong time.

Practical Tips for Consistent Alginates
If you want more predictable impressions throughout the year, consider the following checklist:
• Use room-temperature water rather than relying on seasonal tap water.
• Follow the manufacturer's powder-to-water ratios exactly.
• Shake or roll new alginate containers before first use.
• Check expiry dates regularly.
• Mix consistently every time.
• Use compatible disinfectants.
• Follow recommended disinfection times.
• Pour impressions promptly.
• Store impressions correctly during transport.
• Ensure trays are rigid, well-fitting and properly adhesive coated where required.
• Review technique whenever the weather changes significantly.

Small Details Produce Predictable Dentistry
In dentistry, success rarely comes from one big thing. It comes from hundreds of small things done consistently well.
An alginate impression may only take a few minutes to make, but those few minutes determine everything that follows.
When clinicians understand how environmental conditions influence impression materials, many unnecessary adjustments, remakes and frustrations can be avoided.

The next time the British weather decides to surprise us, and let's face it, that's fairly often, it may be worth checking the temperature of the mixing water before assuming the laboratory has made a mistake.
Sometimes the smallest variable explains the biggest mystery.

At Bremadent Dental Laboratory, we believe predictable outcomes begin long before a model is poured. By working together and understanding how impression materials behave, we can reduce remakes, improve consistency and ultimately provide a better experience for both clinicians and patients.

We provide a trusted laboratory service delivering consistent quality, saving chairside time, and supporting predictable patient outcomes.

📞: 0208 520 8528 

 📧: [email protected] 

📍: 25A St James Street, London, E17 7PJ