Loading is defined as the application of a mechanical load or force to something. A loading test in musculoskeletal tissues looks into the response of muscle strength with examiner's resistance to movement. In the case of the joints, the use of orthopedic maneuvers will provide useful information about function and presence of inflammation.
Each muscle responds different to loading. Here some examples:
Masseter and anterior temporalis muscles:
- Contraction of the muscle might increase the pain.
- A painful masseter might produce ipsilateral deflection.
Lateral Pterygoid muscle (inferior belly):
- Biting in maximum intercuspidation will stretch the muscle and might produce pain.
- Protrusion with resistance will contract the muscle and might produce pain.
Lateral Pterygoid muscle (superior belly):
- Biting in maximum intercuspidation will stretch the muscle and might produce pain.
- Protrusion with resistance will NOT produce pain.
Medial Pterygoid muscle:
- Palpation will refer pain to posterior area of the mouth, throat and ear.
- Biting in maximum intercuspidation will contract the muscle and might produce pain.
- Opening wide (stretch) will deflect to contralateral side and produce pain.
There are 3 basic orthopedic maneuvers for the TMJ:
- Distraction: The two bonny structures of the TMJ are manually (and gently) separated by pulling towards protrusive. This helps to identify the strength of muscles and ligaments.
- Compression: The two bonny structures of the TMJ are manually (and gently) compressed by retruding the jaw. This helps to identify the presence of inflammation in retrodiscal tissues (retrodiscitis).
- Lateral or medial distraction/ compression: by manually moving the jaw horizontally, the examiner might identify the presence of a dislocated disk or muscle guarding.
Barrientos E, Pelayo F, Tanaka E, Lamela-Rey MJ, Fernández-Canteli A, de Vicente JC. Effects of loading direction in prolonged clenching on stress distribution in the temporomandibular joint. J Mech Behav Biomed Mater. 2020 Dec;112:104029. doi: 10.1016/j.jmbbm.2020.104029. Epub 2020 Aug 11. PMID: 32827997.