What you need to know about injections/local anaesthesia – Part III

1. Extraction and odontectomy
2. Alveoloplasty and alveolotomy
3. Incision and drainage of abscess
4. Cavity preparation in deeper cavities
5. Pulp procedure
6. Periodontal and gingival surgery
7. Cyst enucleation and marsupialization
8. Removal of small benign growth and salivary stones
9. Relief from denture sore spots

10. Treatment of trismus
11. Diagnostic test for various facial pain esp. trigeminal neuralgia
12. As a treatment therapy for trigeminal neuralgia
13. In radiography when patient is gagging.
14. For anesthesia of oral cavity and jawbones in treatment of fractures
1. Fearful and apprehensive patients
2. Allergy to LA solution
3. Acute infections, fear of needle contamination and spread of infection
4. Mentally retarded, uncooperative or very young children
5. When anatomic anomalies make anesthesia difficult or impossible
6. Hyperthyroidism
7. Liver disorders
8. Renal disorders
9. Cardiac patients
10. Uncontrolled diabetic patients
11. Patients with any internal hemorrhage
12. Major oral surgical procedure

1. Patient is awake and cooperative
2. Patient does not have to omit the previous night meals as in GA
3. No trained person required
4. Negligible incidence of morbidity
5. Patient can leave the dental clinic unescorted


1) Non Disposable:
– Breech – loading, metallic, cartridge type, Aspirating.
– Breech – loading, Plastic, cartridge type, Aspirating.
– Breech – loading, metallic, cartridge type, Self Aspirating.
– Pressure Syringe.
– Jet Injector.
2) Disposable Syringes
3) Safety Syringes
4) Computer Controlled Local Anesthetic Device (CCLAD)

Permits the anesthetic solution to travel from the syringe into the tissues surrounding the needle tip.
 Bevel (Long, Medium & Short)
 Shaft
 Hub
 Syringe Adapter


The principle of infiltration analgesia is the injection of anesthetic solution very near the actual area to be treated and relying upon the solution diffusing or infiltrating to the sensory nerves so that conduction pain impulses prevented.

Main types

 Submucous and Supraperiosteal







Control of intra-op hemorrhage

Soft tissue manipulation is associated with hemorrhage esp. when tissues are not healthy.

LA with vasodilating properties proves to be counterproductive

Hence addition of vasoconstrictors is beneficial

Epinephrine is the drug of choice.

Excessive use may cause rebound bleeding


Long duration procedures

During longer duration procedures (2 hours or more) bupivacaine a long acting LA is preferred.

However, according to Danielsson bupivacaine has long duration of action when used for regional nerve block (Int. J. Oral  Maxillofac Surgery 15,119 -126,1986)

But its duration of action when used as supraperiosteal injection is somewhat shorter even than that of lidocaine with epinephrine

Post op analgesic period of bupivacaine is 8 hrs in mandible and 5 hrs in maxilla

Post-procedural pain control

Long acting LA’s offer a means to achieve post op pain control with minimal risk of developing adverse reactions unlike opiod analgesics

                  Often intermediate LA used intra-op and long acting LA at the end of the procedure

However this is contraindicated in children and physically and mentally incapacitated patients 



Centbucridine – most of the research in relation to this drug has been conducted in India by Gupta et al, Suri et al.

 It is a quinolone derivative, 5 – 8 times more potent than Lidocaine.

Does not affect the CVS and CNS adversely

Only trial in dentistry showed it to be as effective in 0.5% concentration, as Lidocaine 2% (Vachrajani et al)


 Ropivacaine – Long acting amide. It is prepared as an isomer while all other amide linked anesthetics are available as racemic mixture

It has a greater margin of safety between convulsive and lethal doses, it is less dysrhythmogenic, has a shorter half life and decreased cardiotoxicity than bupivacaine.


EMLA – 5% Lidocaine and 5% prilocaine (25mg/kg) in a oil in water emulsion

It could to some extent eliminate the use of needle esp. for minor procedures.


pH alterations– by Addition of sodium bicarbonate

Addition of CO2

CO2   diffuses through the nerve membrane and decreases the intracellular pH and increases the intracellular concentration of RNH+

Thus the anesthtetic becomes concentarated within the nerve trunk (ion trapping). This increases the duration of anesthesia

However the drug must be administered shortly after mixing with CO2


Hyaluronidase– addition of this increases both the onset and area of anesthesia.

Duration of anesthesia is slightly decreased

It should be added to anesthetic cartridge just before administration


Ultra long-acting LA- Tetrodotoxin and Saxitoxin are highly toxic, hence their use is not advocated


Slow release of LA for patients with chronic pain, where prolonged analgesia has been desired

2 diff approaches have been tried:

Insertion of bupivacaine into egg phospholipid and cholesterol liposomes

Incorporation into polylactic acid microspheres


Other methods of inducing local anesthesia

Electronic dental anesthesia (EDA)

Mechanism of action of EDA can be explained by the gate control theory. Vibrating, pulsating, twitching stimulates the large A fibres, which activates the inhibitory interneuron and closes the gate. Pain impulses produced by scalpel or high speed drill are transmitted via the smaller fibres which come on the closed gate and their conduction is blocked

Also the blood levels of serotonin, endorphins and enkephalins are increased, these act like systemic analgesics decreasing the pain perception of the patient

EDA has been used with great success in nonsurgical periodontics.

EDA can be used for obtaining pain control during LA administration. This    produces excellent soft tissue anesthesia…study by Meechan et al.

The elevated levels of serotonin and β-endorphin levels after EDA reduces pain in post op period.

It can be used for reversing local anesthesia in patients with risk of post-op anesthetic complications.

Contraindications of EDA:

Cardiac pacemakers

Neurological disorders


Very young pediatric patient

Older patients with senile dementia

Language communication difficulties






Bleeding disorders – aspiration is a must, avoid nerve blocks, infiltration and intraligamentary injections preferred.

Congestive heart failure – Decreased liver perfusion leading to increase in half life, therefore increased chance of toxicity

Myocardial infarction – treatment avoided for 6 months, limited use of vasoconstrictor (0.04 mg).

Thyroid disease – avoid epinephrine

Hypertensive patients – BP to be checked before every appointment.

Renal diseases – decreased clearance, therefore, high level of anesthetics in blood hence, increased chance of toxicity

Atypical plasma cholinesterase – avoid ester linked LA

Malignant hyperthermia – was thought to be precipitated by amide linked Las however there is no concrete proof to the same

Methhemoglobinemia – caused due to the major metabolite of prilocaine i.e. orthotoluidone. Hence used cautiously in susceptible patients.


Drug interactions

Cimetidine  It competes with lidocaine for binding with hepatic oxidative enzymes

Suphonamides – ester linked LA thought to decrease their bacteriostatic action

Opioid analgesics– may increase the risk of LA overdose

Tricyclic antidepressants – Enhances the CVS actions of exogenously administered vasopressors leading to hypertensive crisis

Nonselective betablockers– cause  increase in BP and reflex bradycardia if given along with vasopressors

General anesthetic – esp. halogenated general anesthetics increase risk of cardiac dysrhythmias

Cocaine – it itself causes massive vasoconstriction and deprives the heart of oxygen. Hence Local anesthetic agents without a vasopressor preferred in these cases

For complications of LA, refer to :  http://www.intelligentdental.com/2011/10/22/complications-of-injections-part-1/