Watch the lips.
Scissor technique is commonly used. Some of you are wired funny and use thumb under pointer finger. Still works. Use it
Others use the less invasive Chin Push. Teeth can be disgusting and gnarly.
And my friend, Jim Ducanto use of the Suction tip/modified Yankuer during his SALAD simulation in the vomiting manikin, has made me want to use suction device even more in patients who haven't vomited. Less use of my fingers and more safety for me when opening the patient's mouth.