The infiltrative dosing of a local anesthetic solution usually produces a burning sensation – not only because the release of the solution induces the release of pro-inflammatory mediators and sensitize the local nociceptors, but also because of the chemical (pH) and physical virtues of the liquid itself. In this sense, some studies indicate the use of a heated anesthetic solution as a valid and, moreover, non-operator-dependent solution, in reducing the painful symptoms. The subject is actually also debated in the medical field: Arndt (1983) does not find significant differences between solution at room temperature (21 ° C) and heated to body temperature (37 ° C), while Rogers (1989), in a study in the dental field, reports exactly the opposite.
In comparison with other surgical disciplines that commonly use local infiltrative anesthesia, dentistry is distinguished by the availability of the pharmacological molecule in the format of the cartridge.
The manufacturers expressly state that the local anesthetic cartridge should be kept away from light and at a temperature not exceeding 25°C, so it is usually placed in a drawer, ready for use. The works to which reference has been made so far instead put the threshold of increased effectiveness at physiological body temperature or even above it, in a range between 37 and 42 ° C. (FARENHEIGHT IS USED IN THE USA INSTEAD OF CENTIGRADE TEMPERATURES)
Wishing to provide an update, possibly definitive, of the evidence in the dental field, Aravena and colleagues (2018) prepared a randomized clinical trial, split-mouth, double-blind, which compares the dosage, in the maxillary arch, of anesthetic (lidocaine 2%) at room temperature (21 ° C) and heated to 42 ° C. The work involved a total of 72 volunteers (51 males) aged between 18 and 29 years (22 on average). The experimental design is simple and intuitive. The blind operator delivers the first cartridge, at room temperature or heated, already mounted on a syringe with a 30 Gauge short needle, and delivers half of the content (0.9 mL) to the muco-buccal fold, at a rate of 0.15 mL/sec. Immediately afterward, a second examiner gave the subject, who in turn ignored the temperature of the liquid, a 100 mm VAS scale, requesting to quantify the pain perceived during the injection. The test is repeated after a week , on the contralateral side and at a different temperature. The 42°C group provided an average VAS score of 15, significantly lower than the 35.3 of the control group.
The Authors also provided two possible physiological explanations for the phenomenon: an increase in the fluidity of the lipid membrane, which would facilitate the spread of the drug molecules, or the involvement of TRPV1 channels, the same channels that respond to capsaicin, the molecule responsible for the hotness of chili peppers.