**5.7 Psychological factors**

Anxiety in the patient may also play a role in the local anesthetic failure. Clinicians who have worked with anxious patients know that they have a lower pain threshold and are more likely to complain about an unpleasant dental experience. The sight of a needle and the sound of the dental handpiece are frequently reported as causes of anxiety in patients. Furthermore, patients may be particularly apprehensive about root canal therapy.

### **5.8 Effect of inflammation on blood flow**

Inflammation has several additional consequences on the physiology of local tissues. Inflammatory mediators cause peripheral vasodilation, which increases the rate of systemic absorption, lowering the concentration of local anesthetics. Local anesthetics, in most circumstances, need formulation with vasoconstrictor drugs. Thus, this is a potentially relevant mechanism. Although regional variations in blood flow occur in inflamed dental pulp, little is known regarding inflammationinduced vascular alterations in periradicular tissue [21]. Furthermore, this vasodilation is likely to be confined and not seen at distant injection sites. As a result, compared to nerve block anesthesia, this concept may be more useful in understanding issues with infiltration anesthesia.

#### **5.9 Effect of inflammation on nociceptors**

Inflammation alters the production of many proteins in nociceptors, resulting in a rise in neuropeptides such substance P and calcitonin gene-related peptide. These neuropeptides have an essential role to perform have a role in regulating pulpal inflammation. Furthermore, tissue damage can change the composition, distribution, and activity of sodium channels expressed on the nociceptors. Inflammation's effect on these sodium channels might substantially impact local anesthetic failures [22].

#### **5.10 Tachyphylaxis**

Tachyphylaxis is a condition in which a receptor agonist medication causes a reduction in responsiveness to a subsequent dose of the drug. Because local

*Tackling Local Anesthetic Failure in Endodontics DOI: http://dx.doi.org/10.5772/intechopen.99316*

anesthetics are frequently used in conjunction with vasoconstrictors, the medication may remain in the tissue long enough to trigger tachyphylaxis at the sodium channel. This has been suggested as a factor in decreased anesthetic efficacy, particularly after many administrations [21].
