Here is the step by step fitting instruction: https://www.oralmart.com/how-to-mold-a-mouthguard/

Absolutely!! We would Love to Send You a Replacement!

While some customers with braces try to make it work, our sports mouth guards are actually NOT recommended for use with braces.

Yes! There are 2 different sizes (Adult Size & Kids Size).
Adult Size : 2.26 in. (W) x 2.15 in (L) x 0.81 in. (H)
Kids Size: 2.14 in. (W) x 1.78 in (L) x 0.73 in. (H)

But dimensions above probably don’t mean much if you don’t know the size of your or your kid’s mouth. We have sold many mouth guards so below is what the customers told us based by their experiences.

Kids mouth guard is Mostly for Age 12 & Below
Adult mouth guard is Mostly for Age 13 & Up
Also, female adults with smaller mouth could go with youth size.

No problem. We will send you one as a replacement. Sometimes there is a learning curve when it comes to molding a mouth guard.

Normally, if you kid can’t get a tight fit, it’s one of the reasons below.

1) Is water hot enough? (Boil the water to the boiling point and then turn off the stove.) 

2) Heat mouth guard long enough? (Keep it on the boiled water for 40 seconds)
3) Bite down hard enough? (Bite down harder and deeper for more grip)
4) Step 5 helps too. Press mouth guard against teeth from the side for more grip. 

If you could you provide us the pictures of the 2 molded mouth guards, I will have my team look into them and get back to you with our advice for better molding experience.

Personalizing mouth guards involves more work so we don’t customize it at this moment.

Most sports mouth guards are for upper teeth only. I believe Shock Doctor has some double mouth guards for both upper and lower teeth.

I am sorry but we don’t sell double mouth guard at this moment.

You can re-mold it for a few times. Please make sure you don’t over-boil it and watch the video we created for boiling the mouth guard correctly. If you feel that the mouth guard is kind of out of shape after a few tries, please let us know and we would love to send you a replacement so you can start from scratch. Or if you don’t think it’s going to work for you, please provide your order ID and we would issue you a full refund once we hear from you.

FAQ #1: Youth mouth guards are bigger after fitting. (It may look small to you BEFORE fitting. Please follow the step-by-step guide.)
FAQ #2: The Size Suggestion by “Age” is “ESTIMATE”. Kids ages between 11 and 15 could go either way. If you really can’t make a decision, please try the youth one and see if it covers the molar teeth by checking the teeth marks on the inner gel.
FAQ #3: For kids under 5 years old, dual-layer mouth guards may be too bulky. You may need to trim the ends of the kids mouth guard to make sure it fits comfortably and doesn’t irritate the back of your kid’s mouth (Yes! Extra work might be needed). Please consult your kids’ dentist before purchase or try out clear mouth guards (5 PACK) which is totally trimmable.
FAQ #4: The gap for the front teeth is small for tighter fit. The teeth marks don’t have to be exactly on the gap. As long as the teeth stay on the inner gel, it would be fine. After putting in the boiled water for 35 ~ 40 seconds, the inner gel will be very soft and ready to mold. You kids can easily bite through the small gap at the front.

Fitting Issue? Can’t Get Snug Fit?

There are a few possible reasons you couldn’t get a snug fit.
Water was not hot enough. (Make sure you bring water to the boil before turning off the stove.)
Didn’t put mouth guard in the hot water long enough (35-40 seconds for Oral Mart mouth guard.) 
Put in cold water for too long. This step is to prevent a burning mouth. Putting the mouth guard in cold water for too long dramatically affect the fitting performance. Do a quick tap water dunk or wave in the air for at least a few seconds.
Other than biting deeper into the inner gel (It’s totally fine to bite through the inner gel.), please push the outer wall towards your upper teeth and gums to create more grips.
5 Easy Steps to Fit Your Oral Mart Sports Mouth Guard Right
https://www.oralmart.com/how-to-mold-a-mouthguard/