Nothing’s worse than ordering a custom night guard and realizing it doesn’t fit. The truth? 80% of the time, it all comes down to the impression.
At Sentinel Mouthguards, we’ve helped thousands of customers protect their smiles with custom-fit night guards. Along the way, we’ve reviewed more than 5,000 dental impressions — each one unique, but many sharing the same challenges.
Today, we’re sharing what we’ve learned. By looking at the most common impression mistakes (anonymized, of course), we can show you how to avoid them and ensure your guard fits comfortably from the very first try.
The Top Impression Mistakes We See
1.Too Shallow Overall — Especially the Back Molars
The #1 issue we encounter is impressions that don’t capture the full depth of the teeth. Sometimes it’s just the molars, sometimes it’s the entire tray being too shallow. Without a deep enough impression, your guard won’t “lock in” properly, which can make it feel loose or unstable.
Tip: Submerge your teeth evenly and fully into the putty, making sure those back molars are seated all the way down. Hold steady for the full 3 minutes while the putty sets.
2. Putty Timing — Too Soon or Too Late
Another very common issue is removing the tray before the putty has hardened fully, which causes distortion. On the flip side, if the putty is left too long before inserting, it can harden mid-process and prevent a full impression.
Tip: Once the two putty colors are fully mixed, you have about 30–45 seconds to load the tray and begin your impression. Then, stay still for the entire 3 minutes to let the material set completely.
3. Incomplete Mixing (White Streaks Left in Putty)
When the base and catalyst aren’t blended fully, streaks of unmixed putty remain. This can cause soft spots or weak areas in the impression, which distort the details of your teeth.
Tip: Knead the two putty colors together until you see one solid, uniform shade with no streaks before loading the tray
4. Off-Center or Uneven Impressions
Alignment issues are another culprit. Sometimes the tray isn’t centered, so one side of the teeth is captured better than the other. Other times, customers push one side up before the other, creating an uneven balance.
Tip: Practice with an empty tray before mixing the putty so you know how to center it properly. When taking the impression, use a mirror for alignment and apply even pressure across both sides.
Why These Issues Matter
Even small errors in your impression can make a big difference in how your guard feels:
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Shallow impressions = loose or unstable fit
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Poor timing = distorted shape
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Incomplete mixing = weak or inaccurate details
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Uneven alignment = tightness or imbalance on one side
A perfect-fitting night guard starts with a precise impression — it’s the foundation we build on.
How We’ve Got You Covered
Every impression that arrives at our lab is carefully inspected by our technicians. If something looks off, we’ll reach out and, if needed, send a complimentary redo kit. Your comfort and protection come first, always.
✅ Example of a Great Impression
Notice how:
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Every tooth, front to back, is fully captured.
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The molars are deep and well-defined.
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There are no white streaks, bubbles, or distortions.
This is the foundation of a perfectly fitting guard.
❌ Common Impression Mistakes
1. Too Shallow (Especially Molars)
The #1 mistake we see is not pressing deeply enough. Sometimes the molars are missing detail, sometimes the entire tray is too shallow. Without depth, the guard won’t “lock in” properly.
2. Distortion Detected
Distortion happens when the tray shifts, the putty is removed too early, or the material pulls away unevenly as it sets. Even small movements during the 3-minute setting time can warp the impression, which changes the shape of the final guard.
Research shows that movement or uneven pressure during the impression setting phase can introduce distortion—even subtle shifts can affect accuracy significantly.
Tip: Submerge your teeth evenly and firmly into the putty. Hold steady for the full 3 minutes.
✅ Quick Checklist: Before You Begin
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🌀 Mix completely — knead the putty until it’s one uniform color (no white streaks).
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🪞 Center the tray — use a mirror to align before pressing.
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🦷 Submerge evenly — press straight down so front and back teeth are fully captured.
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⏱ Hold steady — stay still for the full 3 minutes while the putty sets.
💡 Pro Tip: Practice with an empty tray first so you feel confident when it’s go time.
🧐 What If My Dental Impression Isn’t Good Enough?
Great question — and one we get often. Here’s what happens behind the scenes at Sentinel:
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Initial Review by Our Lab Techs
Every impression we receive is visually inspected right away. Our technicians look for signs of distortion, pulling, shallow molars, or uneven alignment. -
Manual Logging (Yes, We’re Old School 👴)
We also keep a handwritten log of every impression we receive. It may sound old-fashioned, but it’s part of how we ensure no detail slips through the cracks. -
Digital Scanning & 3D Modeling
Once approved, your impression is scanned into our digital system. From there, we create a precise 3D model of your teeth, which is reviewed a second time before moving to production. -
Final Check Before Printing
If everything looks good, your design goes to our 3D printer (or lab team for handmade guards) to begin the build process.
🚨 But what if something’s not right?
If we see distortion, shallowness, or anything that would affect the fit of your guard, we’ll send you an email right away and ship a complimentary redo kit — no extra cost, no hassle.
Your comfort and protection always come first. 💚
❓ Frequently Asked Questions
Q: What if I mess up twice?
No worries — we’ve got you covered. Every order includes one complimentary redo kit, but if you need additional kits, we offer them at a low cost. Our goal is to make sure you end up with a guard that fits comfortably, no matter how many tries it takes.
Q: How long do redo kits take to arrive?
Once we identify that you need a redo kit, we ship it out right away. Most customers receive theirs within 2–5 business days depending on location.
Q: Will I be charged for a redo kit?
Your first redo kit is completely free. If you need extra kits beyond that, they can be purchased easily through our website.
Q: Do I need to send back my bad impression?
Nope! You can discard the unsuccessful putty and tray. We’ll send you a fresh kit with everything you need to try again.
Q: How will I know if my impression is good?
Our lab technicians review every impression before it goes into production. If we notice an issue — like shallow molars, distortion, or alignment problems — we’ll reach out right away with next steps and, if needed, send a complimentary redo kit.
Want peace of mind even sooner? 📸 Feel free to email us a photo of your impression before mailing it back. Our team will give you quick feedback so you’ll know whether it’s good to go.
The Bottom Line
Taking a great impression isn’t complicated, but it does take care and attention to detail. By avoiding the four most common mistakes — shallow depth, poor timing, incomplete mixing, and uneven alignment — you’ll ensure a smoother process and a better fit.
Every great night guard starts with a great impression. Take 10 minutes today, and we’ll handle the rest — your comfort is guaranteed.
💚 Ready to get started? Order your custom impression kit today and protect your smile with a guard designed just for you.