Can chewing on only one side cause facial asymmetry?

Yes, chewing on only one side over a long period can contribute to facial asymmetry. Only the chewing muscles on the side you use develop, so the left and right muscles differ in size, and strain accumulates on one jaw joint, making pain or joint noises more likely. What matters is identifying the cause: people often avoid one side because of a cavity, a missing tooth, or pain, so that cause has to be treated before the habit can change. However, if your jaw already makes noises or opening your mouth is uncomfortable, you should have a TMJ examination.