How Wide Can You Open?
Here is a suggestion: Every time you see a patient measure their interincisal opening. Normal opening is over 40-45mm, and most adults open 45-55mm.This measurement is a great “icebreaker”, meaning you do not have to touch a (usually) apprehensive patient, as most folks are not afraid of a ruler. Be jovial when you tell them their measurement (most cheeseburgers are over 45mm thick). Most importantly, repetitive charting of interincisal opening is an objective record for current and future assessment of jaw function. If someone cannot open comfortably to at least 40mm, then it is time to look for the problem that restricts jaw movement. The causes of limited opening are generally categorized as intracapsular or extracapsular, problems from within or outside the temporomandibular joints, respectively. But, that is a topic for another time. Meanwhile, keep a ruler on your tray table!
Why Can’t I Open My Jaw?
Most adults have an interincisal opening of 45-55mm. The causes of limited opening are generally categorized as intracapsular or extracapsular, problems from within or outside the temporomandibular joints, respectively. Further, restricted jaw opening may or may not be painful. The most common intracapsular causes of limited jaw opening are 1), TMJ strain, sprain, and edema (SPE)of the TMJ ligaments (including the capsule), and 2), meniscus (disc) dislocations. Acutely, the swelling and inflammation within the TMJ capsule is painful, particularly during condylar translation. Preauricular intracapsular pain limits jaw movement to 20-30mm. The diagnostic dilemma is that SPE and acute meniscus dislocations have the same symptoms of pain and restricted jaw opening. Chronic meniscus dislocations usually limit jaw opening to 30-35mm because, as edema subsides and the pain decreases, the patient will stretch the TMJ ligaments/disc anteriorly. So, condylar translation improves. Some people with dislocated discs can open over 40mm because they have severely stretched the TMJ ligaments and displaced/deformed their disc(s). An accurate diagnosis is made with a cinematic TMJ MRI scan. Masticatory muscle trismus is the most common extracapsular source of limited jaw opening. Trismus is a tonic contraction of the muscles of mastication, usually from trauma or irritation of the muscle(s). Trauma from dental injections often cause muscle trismus: Inferior alveolar block (medial pterygoid), poster superior alveolar block (lateral pterygoid). Mandibular third molar extraction (anterior temporalis), and mandibular ramus fractures (masseter and medial pterygoid) cause direct traumatic trismus. Infections cause noxious chemical irritation of all muscles contacting bacteria and purulence. Limited jaw opening from an odontogenic infection is a red flag warning that aggressive treatment is needed because the patient’s life is being threatened! When someone tells you that they “have a small mouth”, or that their jaw hurts and they can’t open…get out your ruler, measure their jaw opening! Think intracapsular, extracapsular, or both! There are other reasons for limited jaw opening…but that is a topic for another time.