Periodontal receptorsPeriodontal receptors are present in the Periodontal are present in the Periodontal ligament.ligament.

The receptors in PDLThe receptors in PDL

record sense of :record sense of :

1- Touch1- Touch

2- Pain2- Pain

3- Pressure3- Pressure

The PDL also containsThe PDL also contains

proprioceptorsproprioceptors giving giving

information concerninginformation concerning

movements & positions .movements & positions .

Types of receptors present in PDL:

1- Nociceptors for pain1- Nociceptors for pain which preceive painful stimuli which result in both pain preception & reflex responses by rapidly opening of the mouth.

2-mechano receptors2-mechano receptors which respond to physical deformation of the plasma membrane caused by touch and pressure .

3- mechano receptors for proprioception3- mechano receptors for proprioception detect tooth contact during function & reflexly controls the mandibular movement & play an important role in the control of masticatory cycle .

Due to the presence of receptors in the PD membrane , small forces applied on the teeth may be identified , for ex., the presence of a very thin (10-30µm) metal foil (strip) placed between the teeth during occlusion can readily be identified. Mechanoreceptors are activated by tooth movements as little as 1-3 microns .

Also the movements which brings the teeth of the mandible in contact with the occlusal surfaces of the maxillary teeth is arrested reflexively &altered into on opening movement if an inert particle is detected in the chew . Thus, the receptors in the PDL together with proprioceptors in muscles & tendons, Play an essential part in the regulation of chewing movements & chewing forces.

Innervation of PDL:

The PDL is abundantly supplied with sensory The PDL is abundantly supplied with sensory nerve fibers capable of transmitting nerve fibers capable of transmitting tactiletactile , , pressurepressure & & painpain sensation by the trigeminal sensation by the trigeminal pathway in to their trophic center in the pathway in to their trophic center in the semilunar semilunar ganglionganglion..

WWhile the hile the proprioceptive proprioceptive nerves have the trophic nerves have the trophic center in the more centrally positioned center in the more centrally positioned mesencephalic nucleus .mesencephalic nucleus ...

Nerve bundles pass in to the PDL from the periapical area & through channels from the alveolar bone follow the course of the blood vessels.

They are divided into single myelinated fibers which ultimately lose their myelin sheath & end in one of these types of neural terminations

Types and distribution of neural Types and distribution of neural termination in PDLtermination in PDL

. . 1-Free endings have a tree like configuration which include nociceptors (pain receptors) ,that carry pain sensation through a small diameter nerve fibers.

2-Ruffini-like mechano receptors ,are flatted, elongated capsule containing a few nerve fibers, they respond tonically to heavy continuous touch or pressure located primarily in apical area.

3-Tactile ( meissners) corpuscles also mechano receptors , are tall , ovoid –to pear shaped consist of 2 or 3 nerve fibers , and are phasic receptors for light touch , texture and low frequency vibration , are found mainly in the mid root area.

The periodontal ligament is richly innervated by mechano receptors whose cell bodies are located either in:

Trigeminal ganglion (TG).Trigeminal ganglion (TG). Mesencephalic (MS) trigeminal nucleusMesencephalic (MS) trigeminal nucleus.

Both are sensitive to stretch of ligament induced by tooth movement , but they are different in

Thresh.Thresh. Central connections.Central connections. Functional significanceFunctional significance ..

MS &TG receptors in PDL has a different MS &TG receptors in PDL has a different distribution in the PDL ,in distribution in the PDL ,in CAT teethCAT teeth shows shows thatthat

Mechano receptors with bodies in MS are Mechano receptors with bodies in MS are unevenlyunevenly distributed between the fulcrum & distributed between the fulcrum & apex of the tooth.apex of the tooth.

Mechano receptors with bodies in TG are Mechano receptors with bodies in TG are distributed distributed more equallymore equally between the fulcrum between the fulcrum & apex of the tooth.& apex of the tooth.

Adaptation of the mechano receptors:Adaptation of the mechano receptors:

1- Rapidly adapting receptors1- Rapidly adapting receptors are loosely attached to the surrounding tissue & slippage occurs during sustained displacement of the tissue .They could function to signal initial contact with food or opposing teeth .

2- Slowly adapting receptors2- Slowly adapting receptors are those which are more firmly attached to the surrounding tissue .They are useful for discriminating tooth stimulated ,the stimulus direction ,intensity &change of pressure applied to the tooth.

Slowly adapting receptors are subjected to force only just above threshold , behave like rapidly adapting receptors.

Distribution of mechanoreceptors :Distribution of mechanoreceptors :

AA total of 127 periodontal mechanoreceptor neurons are dissected from the inferior alveolar nerve in 9 cats

Of these Of these 105105 are classified as are classified as slowly adaptingslowly adapting PD mechanoreceptors in that , they are PD mechanoreceptors in that , they are responded to both phasic & sustained responded to both phasic & sustained components of a force applied to the tooth components of a force applied to the tooth crown.crown.

Twenty two Twenty two are classified as are classified as rapidlyrapidly adaptingadapting PD mechanoreceptorsPD mechanoreceptors they are responded they are responded while the force is being applied but does not while the force is being applied but does not continue to fire during a sustained force.continue to fire during a sustained force.

Of these 127 PD Mechanoreceptors , 30situated within labial part of the PDL.

The 23slowly adapting receptors are in the apical third of the ligament.

The 7 rapidly adapting receptors are closure to the fulcrum than to the apex.