STRATEGIES TO IMPROVE LOCAL ANESTHESIA
Warming or cooling Some researchers recommend warming local anesthetic solutions to decrease injection pain, while others believe it offers no benefits (Davidson & Boom, 1992). Suggested mechanisms of action for this phenomenon include: increased solubility of the solution; nociceptor stimulation, based on the belief that cold is more painful than warm; and changes of the pKa to create a more basic form of the anesthetic to decrease latency (Finsen, 2017; Martin, Jones & Wynn, 1996). Recently, Gumus and Aydinbelge conducted a double-blind, split-mouth clinical study comparing the pain perception of room temperature (21°C) versus warmed (37°C) articaine in children aged 5-8 years (Gumus & Aydinbelge, 2020). One hundred subjects received a maxillary buccal infiltration and the results showed a statistically significant reduction in pain perception and heart rate when the warmed local anesthetic was used. Practitioners can use low-tech methods for warming a dental local anesthetic cartridge before injection - placing in in a cup Vibration and distraction Melzack and Wall described Gate Control Theory in 1965 as a pain-modulating system in which a neural “pain gate” present in the spinal cord can open and close, thereby modulating the perception of pain (Melzack & Wall, 1965). Some nerve fibers in the body transmit pain (e.g., Type A delta and Type C dorsal root fibers), while others can transmit touch or pressure (e.g., Type A beta fibers). In situations where both painful and pressure stimuli are felt, the dual transmissions of sensations race to the brain to be interpreted, each by different nerve tracks. According to the Gate Control Theory if a non-painful stimulus reaches the brain first, neural gates will close and the non-painful stimulus will override the painful stimulus thereby decreasing the perception of pain. The smaller, unmyelinated Type A delta and Type C nerve fibers which transmit pain sensations are susceptible to nerve block via local anesthetics. Larger, myelinated Type A beta fibers transmit touch, temperature, and pressure sensations, and these impulses are transmitted faster than unmyelinated nerve fibers. Type A beta fibers can be stimulated by wiggling the patient’s cheek during local anesthetic administration or when using a vibrating device. Literature on the use of vibrating devices to improve patient comfort during local anesthesia administration is generally positive but is equivocal (Nanitsos, Vartuli, Forte, Dennison & Peck, 2009; Nasehi, Bhardwaj, Kamath, Gadicheria & Pentapati, 2015; Shaefer, Lee & Anderson, 2017). Three examples of vibrating devices are: a vibrating device that snaps on to the barrel of an existing metal syringe (VibraJect ® Injection Comfort System, https://www.physicsforceps.com/ vibraJect-comfort-solution); a cordless, and a rechargeable handheld wand featuring tips that vibrate (DentalVibe ® . https:// www.dentalvibe.com/); and transcutaneous electronic nerve Buffering Alkalinization of dental local anesthetics or buffering to raise the pH of these acidic solutions is a well-documented technique that results in clinical benefits such as decreased injection pain, reduced onset time, and the need for less overall volume of local anesthesia (Cepeda et al., 2015; Goodchild & Donaldson, 2016; Kattan, Lee, Hersh & Karabucak, 2019; Goodchild & Donaldson, 2019). The pH range of commercially available local anesthetic solutions containing a vasoconstrictor such as epinephrine is between 3 and 5, and this low pH may contribute to injection- site pain and slow onset (Whitcomb, Drum, Reader, Nusstein & Beck, 2010). To mitigate the adverse effects of these acidic local anesthetic solutions, the addition of 8.4% sodium bicarbonate to alkalinize or buffer these solutions closer to physiologic pH has been extensively studied in dentistry and medicine (McKay, Morris & Mushlin, 1987; Stewart, Chinn, Cole & Klein, 1990; Capogna, Celleno, Laudano & Giunta, 1995; Curatolo, et al.
of warm water or holding it in the hand for a few minutes to warm it via body heat. Cartridge warming devices can also be used to achieve a recommended temperature of 37 to 43°C for the warmed cartridge contents (Aravena, Barrientos, Troncoso, Coronado, & Sotelo-Hitschfeld, 2018; Lundbom, et al., 2017). Although research on cooling local anesthetics is scarce and less compelling, a study by Dabarakis et al examined the effect of temperature on the onset and duration of pulpal anesthesia using 3% mepivacaine (Dabarakis, Tsirlis, Parisis & Tsoukalas, 2006). Following injection of mepivacaine at room temperature (20°C) or cooled (4°C), there was no statical difference in the onset of anesthesia among the subjects but the cooled anesthetic showed a statistically significant increase in duration (29% increase). Measurement of injection pain was not an outcome of the study, however the authors stated, “the majority of our subjects mentioned experiencing more pain during the cold injection.” stimulation (TENS) units which pass a high-frequency, low- voltage, electric current between two electrodes to activate the Type A beta fibers, sending signals to the brain that block or scramble normal pain signals. A study by Ching et al, compared pain rating scale measurements in a split-mouth study in 36 adolescent patients aged 10 to 17 (Ching, Finkelman & Loo, 2014). Each patient received two infiltration injections, one of the injections involved the use of a vibrating device and immediately after the amount of discomfort was rated from 0 to 10 using the Wong-Baker FACES Pain Rating Scale. The median difference between pain felt by the two groups was two, with 17 of the patients reporting zero pain on injection, compared to only 3 by the control group. The authors concluded that most subjects (83%) reported significantly less pain than in the control group. This study supports the earlier work of Nanitsos where it was concluded that, “applied vibration decreases pain associated with a local anesthetic injection,” however, in this study the vibration stimulus was applied extra orally by the patient during the time of the injection (Nanitsos, Vartuli, Forte, Dennison & Peck, 2009). A study by Shaefer used the Symptom Severity Index (SSI) including a Visual Analog Scale (VAS) to not only evaluate pain, but to inquire about the experience of the injection with the practitioner using a vibrating device (Shaefer, Lee & Anderson, 2017). In 60 subjects receiving a IANB injection there was a significant difference in both SSI scores (intensity of discomfort, unpleasantness, and how easy it was to endure the injection) and VAS. The authors concluded the vibrating device, “reduced pain from dental anesthesia when used with injections that are routinely difficult for patients to tolerate,” such as the inferior alveolar nerve block. 1998; Cepeda et al., 2015; Kattan, Lee, Hersh & Karabucak, 2019). Buffering or alkalinization of these solutions drives the stoichiometric relationship toward more uncharged local anesthetic molecules in situ. As these molecules are lipid soluble, they readily cross lipid membranes, resulting in faster, more profound, and more effective local anesthesia clinically. The results of a recent systematic analysis showed that buffered local anesthetics are more effective than nonbuffered local anesthetics when used for mandibular or maxillary anesthesia in pulpally involved teeth, and that buffered local anesthetics have 2.29 times greater likelihood of achieving successful anesthesia (Kattan, Lee, Hersh & Karabucak, 2019). On the horizon, FDA approval is being sought for new buffered local anesthetics which promise to overcome the current barrier to adoption of buffered local anesthetics, which is admixture at
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