1. Oral surgery
Oral surgery
Local anesthesia
Local anesthesia

2. Terminology Anesthesia = Analgesia = Local anesthesia
General anesthesia
Sedation == general analgesia
Paraesthesia
Pain threshold

3. Local anesthesia Methods for inducing local anesthesia:
Mechanical trauma
Low temperature
Anoxia
Chemical irritant…….euginol
Neurolytic agent ……….alcohol
Chemical agent

4. Ideal properties of a local anesthetic agent
Preferable
Minimal allergisity
Adequate shelf life
Surface anesthesia
Easy to sterile
Mandatory
Potent and reliable
Reversible
Minimal toxicity(MOS)
Rapid onset
Acceptable duration
Non irritating
Stable in solution
Easily metabolized

5. Indications of local anesthesia
Diagnosis
Reduce or eliminate pain during dental treatment

6. Contraindications of local anesthesia
Systemic
Uncooperative patient like child
Uncontrolled hemorrhagic patient
Allergic patient to local anesthesia
Local
Patient received radiotherapy
Acute infection at injection site
Vascular abnormality at operation site

7. Contraindications of local anesthesia
Relative
Advanced liver disease
Thyrotoxic goiter
Uncontrolled cardiovascular disease

8. Advantages of local anesthesia
Simple technique
Minimal equipment
Transportable
Minimal contraindication
Hemorrhage could be controlled by vasoconstrictor
No airway impairment
Minimal postoperative care
No need for anesthetist
Duration could be controlled
Co-operative patient simplify the work

9. Disadvantages of local anesthesia
Difficult to achieve co-operation
Mechanical obstruction by large tongue or limited mouth opening
Failure due to anatomical variation or incomplete anesthesia
Prolonged parasthesia
Spread of acute infection

10. Mode of action of local anesthesia
Prevention of generation and or conduction of nerve impulse
Act as chemical roadblock between source of impulse and brain

11. Sensory neuron
Afferent neuron

12. Structure of nerve fiber
Nerve bundle of different fibers separated from other bundles by dens fibrous tissue
core fiber
Mantle fiber

13. Generation of nerve impulse
Resting membrane potential (RMP)
(-70) mv due to impermeability of membrane to sodium ion
Concentration of sodium ion is more in the extra cellular area
- 70 mv

14. Generation of action potential Threshold level (firing level)
Extra cellular
Na ++ K+
+35
Intracellular axoplasm
Threshold level (firing level)
--70
Potassium efflux
Repolarization
0.7 second
Sodium influx
Depolarization
0.3 second

15. Impulse propagation transmittion of nerve impulse along the neuron
Movement of the impulse along the axon:
Saltatory movement (jumping)
Creep conduction

16. Mode of action of local anesthesia
Local anesthetics interfere with propagation of the action potential by blocking the increase in sodium permeability during depolarization.
Depolarization inhibited
Firing level not reached
Action potential inhibited

17. Theories of action of local anesthesia
Acetylcholine theory
Calcium displacement theory
Surface charge theory
Membrane expansion theory
Specific receptor theory

18. Nerve Blockade Theories
Membrane expansion theory
Agent molecules must be lipid soluble
Membrane is “disordered”
Channel changes occur
Benzocaine as example for this theory

19. Membrane expansion theory
Extra cellular
Intracellular axoplasm
Membrane expansion theory

20. Nerve Blockade Theories
Specific Receptor Theory
Anesthetic agent receptor in channel
Accessed from intracellular side

21. Specific receptor theory
Extra cellular
Intracellular axoplasm
Specific receptor theory

22. H W Type of nerve fiber and their characteristic feature
Acupuncture as anesthesia in dentistry

23. Structure of local anesthesia3
Ester:
R —COO—R —N
R — Lipophilic aromatic residue. 1 2 1 R 4
R — Aliphatic intermediate connector. 2 R 3
R , R — Alkyl groups, occasionally 3 4
Amide:
R —NHCO—R —N 1 2
H. Constitute with N the hydrophilic
terminus. R 4
Example:
C H 2 5
H N—
—COO—(CH ) —N 2 2 2
C H 2 5
Exception:
Benzocaine, which lacks a substituted amino group

24. PH and local anesthesia
Dissociation constant PKa:
pH at which 50% of drug present in free base form and 50% in cationic form (water soluble)
Most local anesthetic Pka(7-9)
How can local anesthesia cross nerve membrane?
Local anesthetic solution prepared as weak acid form at 4-5 pH to prevent precipitation of free base in neutral solution, thus it present as cataionic form that must converted to base form to be lipid soluble and cross cell membrane

25. Buffering capacity

26. Local anesthetic agent after injection and with function of plasma buffering will dissociate into free base form and cataionic form
Free base form cross the cell membrane
After crossing the membrane an other dissociation occur and cataionc form resulted will bind the receptor

27. Onset (induction time)
Time from injection of local anesthesia to the sign of adequate surgical anesthesia achieved
Factors affect onset (induction time)
Concentration pH
PKa
Anatomical barrier
Lipid solubility

28. Recovery
Time from early sign appeared to the complete loss of all effects of drug occur
This results from reduced concentration of drug with no binding with the receptors

29. Diffusion from intranuronal tissue (mantle fiber)
Recovery time
Concentration gradient depleted by:
Dilution by interstitial fluid
Action of capillary and lymph
Absorption by other tissue
Hydrolysis of ester
Extraanuronal
Diffusion from intranuronal tissue (mantle fiber)

30. Protein binding capacity
Duration
Recovery slower than induction ?
Protein binding capacity
Protein binding
Vasoactivity
concentration
Vascularity of the site
Time from induction to complete recovery from local anesthesia
It depend on:

32. Principle of reinjection
After reinjection in prolonged procedure 2 situation may occur
Failure ??
Edema
Localized hemorrhage
Clot formation
Reduced pH (poor buffer capacity)
hypernatremia
Profound anesthesia:
Increase concentration gradient to mantle fiber then to the core fiber

33. Progression of local anestheticfunction
Dull pain
Temprature
Sharp pain
Touch
Deep pressure
Proprioception
Motor function

34. H. W.
Why infected area presents a poor site for action of local anesthesia