For information regarding impressions air entrapment, refer to the following:

• Definition
• Causes
• Solutions

Definition

Air entrapment in impressions is when there are pockets of air within the impression material which distort the accuracy of the impression.

Causes

Air entrapment in impressions can be caused;

• When dispensing the material, if you're not careful.
• If you lift the tip of the gun while dispensing.
• Inadequate preparation of impression material

Solutions

Try the following actions to prevent air entrapment in impressions:

• Cleaning the teeth and gum tissue before impressing to remove plaque, fluid, and other buildup creates a clean slate for the PVS material.
• Also, if you've already taken multiple impressions on the same patient in one sitting, be sure to clean the teeth before re-impressing each time. This improves detail and prevents air entrapment. 
• To prevent air entrapment, keep the tip of the gun down and dispense the material evenly, as demonstrated in this tutorial and video.
• Seat the tray gradually from anterior to posterior or vice versa depending on your preferred technique to allow air to escape as the tray is being seated.