As for how the 2013 injury impacted his appearance so many years later, he explained to Men's Health that it related to his masseter muscles overcompensating for the injured muscles in his face, combined with his temporary failure to continue with physical therapy.
The masseter muscles, the ones used for chewing among other things, work alongside the other muscles of the face “like a symphony,” according to the Neighbors star. After his accident, those masseter muscles had to pick up some of the slack to compensate for the injured ones. As a result, Efron has had to work with a specialist and do physical therapy for his jaw. However, back in 2021, Efron took some time off from physical therapy while in Australia, which accounts for his change in appearance at that time.
“The masseters just grew,” he explained, “They just got really, really big.”