Dental Local Anesthesia

The Gate control theory of pain in 1965 was proposed by Melzack and Wall where as Dolscheider in 1894 proposed the Pattern theory/ Descartes in 1644, which came up with the specificity theory of pain.

The first method affects pain perception where as the 3^rd method affects pain reaction. The 2^nd method is affected by both pain perception and reaction, indicating the dual nature of pain.

Mandibular nerve is the largest of the three divisions of the trigeminal nerve, consists of two roots, a large sensory root and a small motor root. The ophthalmic nerve is the smallest of the three and is a sensory nerve.

The nerve block method of securing regional anesthesia consists of depositing a solution in proximity to a main nerve trunk and thus preventing afferent impulses from travelling centrally beyond the point.
The block has no effect on hemostasis in the area as it is not a local infiltration.

Nasociliary nerve is the 3^rd main branch of the ophthalmic division. It enters the orbit through the superior orbital fissure. The branches of this nerve are divided into those arising in the orbit, in the nasal cavity and on the face.

The intraligamentary technique is a type of local infiltration technique to provide a single tooth anesthesia.

The solution is deposited alongside the periosteum and not above the periosteum. The success of these injections depends on the diffusion of the anesthetic solution through the periosteum and into the underlying bony structure to come in contact with the nerves therein.

While these theories help to explain the mechanism of action of local anesthetic agents, none can be considered conclusive. Their exact mechanism of action is still unknown.

In 1973, Gow Gates described the true mandibular nerve block by depositing anesthetic solution at the neck of the condyle. A single injection provides hard and soft tissue anesthesia of the mandible to the midline.

Lidocaine undergoes biotransformation in the liver but in toxic doses, it first produces stimulation then depression of the CNS. In toxic overdose cases, convulsions may be induced, hypotension and cardiovascular collapse and respiratory arrest.

The lingual nerve gives off branches to the interior alveolar nerve and contributes many sensory fibres to the mucous membrane of the floor of the mouth and gingival on the lingual surface of the mandible.

Sodium bisulphate is added to dental cartridges that contain vasoconstrictor to enhance an adequate shelf life. In the presence of oxygen, the sodium bisulphate is converted to sodium bisulphate, thus sparing oxidation of the vasoconstrictor.

The first toxic symptom of all synthetic local anesthetics is usually manifested by signs and symptoms of CNS stimulation such as restlessness leading to convulsions. The stimulating phase is usually followed by depression, which if severe can cause death.

When not accompanied by a vasoconstrictor, all local anesthetic agents can produce vasodilation. This action tends to increase their rate of absorption from the injection site, a feature that not only decrease the duration of action but also elevates the blood level, thus increasing the likelihood of producing toxicity.

When the patient is sitting in the dental chair, the brain is placed in a superior position and is the most susceptible to the reduced blood volume flow resulting in syncope. This is a form of neurogenic shock and is caused by cerebral ischemia secondary to vasodilation with a corresponding drop in blood pressure.