Submasseteric Infection: A Rare, Deep Space Cheek Infection Causing Trismus. 
Submasseteric space infections are rare at any age but particularly so in primary school children.  The origin of the infection is usually odontogenic, from pericoronitis in a third molar.  Submasseteric inflammation is a deep facial space inflammation, often progressing to mature abscess, and usually misdiagnosed as staphylococcal or streptococcal lymphadenitis or pyogenic parotitis.  The hallmark of a masticatory space infection is trismus.  The cardinal signs of this infection include a firm mass in the body of the masseter muscle with overlying cellulitis with trismus.