Assalaamu alaykum. Can I pray with my retainers inserted in my mouth? I have been having pronunciation issues ever since I adjusted my jawline, and due to the shape of the retainers, they may actually make it easier for me to pronounce my words.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

It is permissible for you to pray with the retainers in your mouth, and your prayer is valid without any dislike involved, especially given that they help you pronounce the letters correctly, as you mentioned. Some scholars held that it is disliked for the praying person to hold something in his mouth during the prayer. However, this is interpreted as to mean when it hinders proper pronunciation. If it does not hinder proper pronunciation, then it is not disliked.

The Maaliki scholar Al-Kharashi said in his commentary on Mukhtasar Khaleel:

"It has been stated in Al-Mudawwanah that (Imaam) Maalik held that it is disliked for the praying person to put a dirham or dinar or anything in his mouth during the prayer. Ibn Al-Qaasim said that if the person does so, he is not obliged to repeat the prayer. Sanad said that holding the dirham in one's mouth may or may not hinder proper pronunciation; so those whose pronunciation is affected should avoid it. A similar opinion was narrated by Ash-Shabeebi, interpreting the view in Al-Mudawwanah to mean that it is disliked for the person whose pronunciation is affected, apart from others."

Allah knows best.