Dooley Noted: 11/21/2015



In a recent NKT study group, we discussed how overbite (jaw retrusion) and underbite (jaw protrusion) can affect the intrinsic and extrinsic core systems, creating global compensations in the kinetic chain.



The lateral and medial pterygoids are the chief muscles of protrusion of the mandible. The superficial head of the masseter acts as a secondary synergist to their action.





Protrusion = Pterygoids

(Remember that the Ps go together!)



Protrusion = forward shifting of the mandible



*This causes the center of mass to shift ANTERIORLY, down-regulating posterior chain core.



The temporalis muscle is the chief of retrusion, or taking the jaw posteriorly into its anatomical position and the some. The deep head of the masseter acts as a secondary synergist to its action.







Retrusion = Temporalis



Retrusion = backward shifting of the mandible



*This causes the center of mass to shift POSTERIORLY, down-regulating recruitment of anterior chain core muscles.



Because the TMJ has more proprioception per surface area than any other joint in the human body, you will go where your jaw shifts you to go. If the body perceives a missing link in motor control, it will go to the jaw to compensate, since the jaw muscles and joint capsule are innervated by Midpons (mandibular division of trigeminal nerve).



*Remember: Pons and cerebellum are both metencephalon in embryonic development, so one brother compensates when another loses motor control.)



When the jaw shifts, the center of mass shifts. This will down-regulate recruitment of the opposite side core in the sagittal plane.



Commonly down-regulated structures by jaw protrusion:



1. Posterior chain intrinsic core = multifidii, internal abdominal oblique, lumbar erector spinae, posterior pelvic floor



2. Posterior chain extrinsic core = latissimus dorsi, gluteus maximus, quadratus lumborum



Commonly down-regulated structures by jaw retrusion:



1. Anterior chain intrinsics: transversus abdominis (TVA), anterior pelvic floor muscles

(Think Temporalis and TVA both start with T!)



2. Anterior chain extrinsics: deep neck flexors, obliques, rectus abdominis



Common secondary compensators that may be masked by jaw protrusion/retrusion:



1. For protrusion: upper and lower posterior chain muscle recruitment

– Look for tight, over-recruited toe flexors, tibialis posterior, soleus, gastrocs, hamstrings, upper trapezius, levator scapula



2. For retrusion: upper and lower anterior chain muscles

– Look for tight, over-recruited ankle dorsiflexors, peroneals, quads, scalenes

Example: If you are endlessly stretching your calves thinking they are shutting off gluteal control, this may be a secondary compensation for a hiding jaw compensation in the sagittal plane.



This can be pterygoids shifting the jaw forward into protrusion, shifting the perceived center of mass forward and down-regulating gluteal recruitment.



Please consider assessing the overbite and underbite if sagittal plane core control becomes an issue.



Also: get the tongue on the roof of the mouth and don’t let the teeth touch when doing, well, anything involving core – especially under heavy load.



Know where your jaw is positioned.



Get assessed. Get corrected.



As always, it’s your call.



– Dr. Kathy Dooley