Evidence
Scientific research has been carried out showing the benefits of not only chewing gum, but mastic gum.
Research suggests that chewing only 5 minutes a day can increase bite force significantly.
Mastic Gum Studies/Articles/Books
A pilot study of the effect of masticatory muscle training in facial growth in long-face children:
https://core.ac.uk/download/pdf/85222094.pdf
Page 43: https://books.google.co.uk/books?id=V9YaCgAAQBAJ&dq=info:V6lAHbHqP1AJ:scholar.google.com/&lr=
Mastic gum is recommended in the book 'Breath' by James Nestor
Chewing Gum Studies/Articles
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5893462/
https://news.stanford.edu/2020/07/21/toll-shrinking-jaws-human-health/
https://www.sciencedaily.com/releases/2019/05/190531100544.htm
Page 23, Table 2: http://www.pps.org.pk/PJP/12-1/Amer.pdf
https://www.science.org/doi/10.1126/sciadv.abn8351
https://apm.amegroups.org/article/view/107169/html
Masseter Recovery