1. Aims and objectives To discuss different types of periodontal receptor and their properties function of the sensory receptors in the periodontium differences in periodontal innervation compared with other sites Learning outcomes - you should be able to: demonstrate an understanding of the innervation, projection pathways, and sensory receptor properties in the periodontium by written or diagrammatic explanation discuss similarities and differences in skin and periodontal innervation

2. Lecture outline Periodontal receptor types - anatomy/structure - distribution Primary afferents- site of cell bodies and central projections - methods of study - CV and receptor properties Modulation of receptor function Functional importance- sensory discrimination - reflexes - mastication - salivation - nociception

3. Tooth support mechanisms and periodontal innervation What is the nature of periodontal innervation? Why are there periodontal mechanoreceptors? What do they do? Is the innervation in the periodontium different from other sites?

4. Periodontal receptor types - human studies difficult as tissue fixation often poor - animal tissues monkeydogcat ratmouseguinnea pig ferretmolehedgehog Extremely confused picture until resolved by radiolabelling studies (Byers)

5. Periodontal innervation - structure/anatomy free nerve endings unmyelinated C and myelinated A  axons specialised endings (Ruffini-like/Type II SA) myelinated A  axons How can we study the function of these afferents?

6. Primary afferent fibres Peripheral nerve Trigeminal ganglion Mesencephalic nucleus A  30-80ms -1 low threshold mechanoreceptors A  5-30ms -1 high threshold mechanoreceptors C0.5-2ms -1 nociceptive postganglionic sympathetic

7. force X compression tension buccal lingual Units become more SA moving towards apex Receptors evenly distributed around root but more are in apical third Cash & Linden, 1982

8. challenged by Loescher & Robinson, 1989 Two groups of units - SA and RA No relationship between SA/RA and position in rel n to fulcrum From Loescher & Robinson, 1989

9. Majority respond to tension Direction of sensitivity not evenly distributed around tooth - more sensitive to distolingual displacement Therefore higher proportion of receptors in this region? From Loescher & Robinson, 1989 91 units, lower left canine Radius = 18 units

10. Low threshold mechanoreceptors A  fibres Irrespective of site of recording - both RA and SA Are there receptor differences? no conclusive evidence anatomy - Ruffini endings and free nerve endings found in all areas of periodontium - more in apical third Directional sensitivity more located in distolingual areas?

11. normal adequate stimulus - displacement of tooth ? Force or movement? Periodontium is viscoelastic - force and displacement vary in health and disease. respond to tension rather than compression (cf. Ruffini) Man can detect forces of 0.5gm (1-2g), displacements 2- 5µm Project to V ganglion or V MSN - ?significance V ganglion  V sensory n.  sensation? V MSN  V motor n.  reflex control of jaw muscles? Low threshold mechanoreceptors

12. Mesencephalic nucleus Primary afferent cell bodies BUT in the midbrain Muscle spindles Golgi tendon organs Periodontal afferents Sutural afferents Motor nucleus  &  motor neurones to Masseter Temporalis Ant belly digastric Lat & med pterygoid

13. High threshold mechanoreceptors A  & C fibres 5-30ms -1 0.5-2ms -1 Very little experimental evidence because: smaller axons smaller cell bodies adequate stimuli - noxious

14. CVs >2.5ms -1 <30ms -1 7/9 respond to mech stim 2/8 respond to heating 4/6 respond to cold 2/7 respond to KCl  behave as nociceptors Mengel et al, 1994

15. From Jyvasjarvi et al., 1988

16. High threshold mechanoreceptors and nociceptors Very little currently known A  and C fibres present Adequate stimulus - noxious difficult to apply to receptive fields where are the cell bodies?

17. Modulation of receptor function Symp stim inhibits mechanoreceptor activity (50% units) Blocked by  receptor antagonist Not blood flow dependent Why?

18. Functions of periodontal receptors 1. Sensory discrimination Forces on teeth Forces exerted by jaw muscles Oral discrimination food texture preparation for swallowing 2. Reflex control of masticatory muscles and tongue Eating Speech jaw opening reflex

19. Reflex control of masticatory muscles Reflex responses are critically dependent on:- species nature of stimulation SLOW PUSH A  low threshold S.A. response Excites jaw closers LIGHT TAP BRISK TAP A  low threshold R.A. response ?A  ?C higher threshold Inhibits jaw closers No activity in jaw openers Inhibition of jaw closers Excitation of jaw openers

20. Functions of periodontal receptors 3. Reflex control of salivation Rabbits and humans Unilat. chewing = unilat. salivation Stimulation from perio not as important as gustatory input 4. Nociception Inflammation BUT in full tooth loss there is no dramatic loss of function

21. Inflammation and the periodontium Periodontitis acute periapical periodontitis chronic periodontitis Orthodontic tooth movement acute inflammation and bone resorption pain

22. Tooth support mechanisms and periodontal innervation What is the nature of periodontal innervation? specialised and free nerve endings, low and high threshold mechanoreceptors, nociceptors Why are there periodontal mechanoreceptors? What do they do? Reflexes, sensory discrimination, nociception Is the innervation in the periodontium different from other sites? Ruffini endings but RA and SA properties Inflammation