Reflex is a highly stereotyped automated response to a specific stimulus. Masticatory reflexes are a type of stretch reflexes brought about by activation of muscle spindles in the muscles associated with the Mandibular Jaw. There are multiple types of Jaw reflexes which are seen during normal speech, any trauma, chewing etc.
Types of Jaw Reflexes:
- Jaw Closing Reflex / Jaw Jerk Reflex
- Jaw Opening Reflex
- Jaw Unloading Reflex
- Tooth Contact Reflexes
- Horizontal Jaw Reflexes
Jaw Closing Reflex / Jaw Jerk Reflex:
- A stretch reflex similar to knee-jerk reflex
- It is a monosynaptic reflex generated by stretching muscle spindles in the masseter muscle
- Latency period 7-12ms
- Demonstration: A sharp downward tap on the chin when the mandible is held loosely in the rest position results in contraction of the masseter muscle to bring the teeth into occlusion
Jaw Opening Reflex:
- Polysynaptic reflex
- Occurs as a result of mechanical or electrical stimulation of the lips, oral mucosa or teeth
- A slight opening movement occurs due to inhibition of activity in the mandibular elevators without simultaneous contraction of the depressors
Jaw Unloading Reflex:
- It is a protective reflex that occurs when the jaw is suddenly unloaded
- Eg: When a hard substance or food comes between occlusion while mastication.
- This reflex is seen when the food or substance suddenly breaks or slips or collapses, this reflex prevents the jaws from closing with a force and thus prevents any injury or damage to the teeth etc.
- This is due to reflex inhibition of elevators & reflex excitement of jaw depressors
- Due to receptors in periodontal ligament
- Protects teeth from damage
Tooth Contact Reflex:
- Reflex changes that occur in the elevator muscles when the upper & lower teeth are snapped together
- There is transient activation followed by a silent period & then a phase of increased & decreased activity in the elevators
- No effects on the depressors
Horizontal Jaw Reflexes:
It is also called as Horizontal Mandibular reflex which is seen when a labiolingual force is applied to the maxillary central incisor resulting in a lateral movement of the mandible to the contralateral side.
- Lateral, protrusive & retrusive reflex mandibular reflexes
- The reflex is known to be initiated by a rapidly adapting periodontal receptor
Thank you! This is a really useful article.
Hey! Can you please include diagrams? As we have to include it in our answers. Thank you!
Will try and include diagrams which need to be drawn specifically for this purpose.
Steve Weeks, DDS says
I’m remembering the “jaw-unloading reflex” differently. An example of the jaws being suddenly unloaded would be when biting on a carrot and the carrot suddenly yields. Without the protective reflex, the teeth would smash into each other. The reflex inhibits the jaw closers and activates jaw openers. I’d have to find my (30-year-old) notes or a text to find a drawing. Thanks for reminding me of neuroanatomy!
Thanks for correcting me, guess I got it mixed up. Corrected the content in the post.