Sensation Related to Local Anesthesia Injected
Pain
at Varying Temperatures Devereaux S. Peterson, D.M.D., M.Ed., M.S.D.* and Daniel R. Kein, D.D.S.**
ABSTRACr
The purpose of the study was to determine whether local anesthetic solution warmed to body temperature (37 C) produced less pain on injection than an anesthetic solution injected at room temperature (210 C) and to determine which solution resulted in quicker anesthetic onset. It was foiund that the subjects experienced no difference in pain during injection of warm and cold anesthetic solution given respectively in the maxillary buccal sulcus area. The time of anesthetic onset was also not influenced by solution temperature. Introduction One ofthe primary patient management difficulties facing dentists is patient fear of pain during local anesthetic injection. Investigators have experimented with various techniques designed to reduce pain on injection in order that subsequent injections do not continue to be so anxiety producing, i.e., topical anesthetics, slow injection, smaler gauged needles, pressure anesthesia, etc. Some individuals also recommend warming local anesthetic solutions to body temperature prior to injection to reduce pain, and heating devices toward that purpose are presently being marketed. Bennett' stated that temperature changes could induce pain and that the change must be of sufficient intensity to excite the pain receptor free nerve endings. Some other individuals have concluded from this that warming local anesthetic solution to body temperature will help decrease injection pain by reducing temperature alterations in the tissue after the injection so that pain receptors are not stimulated. However, Monheim2 believed this procedure was unnecessary since tissue fluids presumably buffer the solution quickly. In any case, little empirical study has been done which directly relates pain during injection with the temperature of anesthetic solution. Oikarinen, et al3 investigated subjects' perceptions of room temperature and body temperature anesthetic during injection into the buwcal submucosa and fiund that the subjects experienced these solutions as being at body temperature regardless of whether the solution was warmed or not. Although these authors believed the implication 164
of their study was that warming the solution was not indicated as a pain preventive, their studies did not actually relate a pain response to the solution temperature. There is also a body of opinion which proposes that warming local anesthetic solution to body temperature hastens anesthetic onset.4 No substantiating studies regarding anesthetic temperature and anesthetic onset were found in the dental literature. Purpose: The purpose ofthis study was to determine whether anesthetic solution warmed to body temperature produced less pain on injection than an anesthetic solution injected at room temperature and to determine which solution resulted in quicker anesthetic onset. Material and Methods: Sixteen female subjects, with noncomplicating medical histories, participated in the experiment. Their average age was twenty-two, ranging from nineteen to twenty-nine. The informed consent of all human subjects who participated in the experimental investigation reported or described in this manuscript was obtained after the nature of the procedures and possible discomforts and risks had been fully explained. Each subject was given an infiltration injection in the buccal sulcus of the maxillary right and left premolar regions, one with local anesthetic solution slowly warmed to thirty-seven degrees centigrade, with the temperature maintained in a thermostaticaly heated bath, and the other at twenty-one degrees centigrade. The sequence of injections was randomized to account for the anticipatory effects on the subject's anxiety over the second injection. Double blind conditions were ensured, since neither the patient nor the dentist administering the injection knew which solution was heated. One operator adm stered all the injections to tMott Children's Health Center/Hurley Medical Center Flint,
Mchigan
*DireCtr, Pedonontic Residency Program
**Second Year Resident in Pedodontics
SEPrTEBER-OCToBER, 1978
standardize injection technique as much as possible. The entire content ofthe cartridge was injected during a standardized period of thirty seconds for each
TABLE 1 Pain Responses Versus Temperature of Anesthetic Solution
injection.
The anesthetic used was XylocaineR hydrochloride 2 percent with epinephrine, 1:100,000. The syringes were disposable (MonojectR) with twenty-seven gauge one-inch needles. No topical anesthetic was given in order to avoid its possible interference with the subject's pain perception. The subjects were asked to report their perceived pain response according to the following scale, which was adapted from Chaves:5 0 -no pain 1 slight pain 2 - moderate pain 3 - severe pain The subjects were instructed to distinguish between pain on insertion of the needle through the mucosa and the injection of solution and to report their pain response only as it related to the actual injection of anesthesia. Five seconds after needle entry into tissue, the injection of solution was initiated and the subject was so informed. The subjects were asked to report their pain sensations immediately after initiation of injection and after termination of injection. The subjects were also asked to record in minutes the onset of anesthesia after each injection. The statistical tests used were Chi-square for the pain data and the students' t-test for the onset data.
Results: The subjects' reports ofpain, during the initiation of the injection and after termination of injection (see Table 1) showed no consistent differences in pain perception between the warm and the cold anesthetic. The Chi-square analysis was made by compressing the cells for slight pain, moderate pain, and severe pain to avoid violation of the Rule of Five.6 Chi-square values of 1.46 and 0.52 resulted for reports of pain on initiation of injection and pain at termination of injection respectively, neither of which approached acceptable statistical confidence levels. The mean time of anesthetic onset between the warm and cold anesthetic solutions was 1.375 minutes and 2.000 minutes respectively. However, t-test comparisons demonstrated no statistically significant relationship between anesthetic temperature and speed of anesthetic onset (t = 1.316). Discussion:
The results of this study demonstrate that heating local anesthetic solutions to body temperature to reduce pain during local anesthetic injection is unnecessary. In fact, it is interesting to note that four out ofthe five responses of moderate pain (see Table 1), which was the severest pain category reported by subjects in this study, resulted from injections of warm anesthetic solution. Comparisons ofanesthetic solution temperature and onset time probably deserve further study, at least to SEPTEMBER-OCTOBER, 1978
Temperature of
Anesthetic
Pain Response During Initiation of the Injection No Slight Moderate Severe Pain Pain Pain Pain
Warm (37 C)
Cold(21°C) Temperature of
Anesthetic
Warm (37° C)
Cold(21°C)
9 6
6 9
1 1
0 0
Pain Response at Termination of the Injection No Slight Moderate Severe Pain Pain Pain Pain
9 7
4 9
3 0
0 0
settle basic research questions in this area. Although the results of this study demonstrated no clear statistical relationship between the two, certain trends emerged that pointed to a possible association between warm anesthetic solution and quicker anesthetic onset. For example, eight of the sixteen subjects reported faster onset after injection of warm anesthetic solutions as opposed to only one who reported the reverse (the remainder reported equal times for anesthetic onset). If this trend held constant in studies using more subjects, statistical significance might be attained with similar statistical means resulting from this study, since the t-test is influenced toward probability in studies with larger sample sizes. However, such results would admittedly be of limited practical value, since the mean difference between anesthetic onset for warm and cold solutions in this studv was only 0.625 minutes (about 37.5 seconds), a time differential which has obvious limitations for practical importance in clinical settings.
Conclusions: The results of this study indicate that no benefit is gained in terms ofreduction of pain or clinically meaningfil speed of anesthetic onset by heating local anesthetic solutions to body temperature prior to injection. REFERENCES 1. Bennett C R Monheim's local anesthesia and pain control in dental practice ed. 6. St. Louis CV Mosby 1978. 2. Monheim M Local anesthesia and pain control ed. 4 St. Louis CV Mosby 1969. 3. Oikarinen V J Ylipaavalniemi P Evers H Pain and temperature sensations related to loci analgesia Int J Oral Surg 4:151 1975. 4. Adriani J The pharmnacologgy ofanesthetic drugs ed 5 Springfield C Thomas 1970. 5. Chaves J F and Barber T X Cognitive strategies, experimenter modeling, and expectation in the attenuation ofpain. J Abn Psydv 83:356 1974. 6. Chikton N W Design and analysis in dental and oral research Phila J B Lippinontt 1967.
165
Pain
at Varying Temperatures Devereaux S. Peterson, D.M.D., M.Ed., M.S.D.* and Daniel R. Kein, D.D.S.**
ABSTRACr
The purpose of the study was to determine whether local anesthetic solution warmed to body temperature (37 C) produced less pain on injection than an anesthetic solution injected at room temperature (210 C) and to determine which solution resulted in quicker anesthetic onset. It was foiund that the subjects experienced no difference in pain during injection of warm and cold anesthetic solution given respectively in the maxillary buccal sulcus area. The time of anesthetic onset was also not influenced by solution temperature. Introduction One ofthe primary patient management difficulties facing dentists is patient fear of pain during local anesthetic injection. Investigators have experimented with various techniques designed to reduce pain on injection in order that subsequent injections do not continue to be so anxiety producing, i.e., topical anesthetics, slow injection, smaler gauged needles, pressure anesthesia, etc. Some individuals also recommend warming local anesthetic solutions to body temperature prior to injection to reduce pain, and heating devices toward that purpose are presently being marketed. Bennett' stated that temperature changes could induce pain and that the change must be of sufficient intensity to excite the pain receptor free nerve endings. Some other individuals have concluded from this that warming local anesthetic solution to body temperature will help decrease injection pain by reducing temperature alterations in the tissue after the injection so that pain receptors are not stimulated. However, Monheim2 believed this procedure was unnecessary since tissue fluids presumably buffer the solution quickly. In any case, little empirical study has been done which directly relates pain during injection with the temperature of anesthetic solution. Oikarinen, et al3 investigated subjects' perceptions of room temperature and body temperature anesthetic during injection into the buwcal submucosa and fiund that the subjects experienced these solutions as being at body temperature regardless of whether the solution was warmed or not. Although these authors believed the implication 164
of their study was that warming the solution was not indicated as a pain preventive, their studies did not actually relate a pain response to the solution temperature. There is also a body of opinion which proposes that warming local anesthetic solution to body temperature hastens anesthetic onset.4 No substantiating studies regarding anesthetic temperature and anesthetic onset were found in the dental literature. Purpose: The purpose ofthis study was to determine whether anesthetic solution warmed to body temperature produced less pain on injection than an anesthetic solution injected at room temperature and to determine which solution resulted in quicker anesthetic onset. Material and Methods: Sixteen female subjects, with noncomplicating medical histories, participated in the experiment. Their average age was twenty-two, ranging from nineteen to twenty-nine. The informed consent of all human subjects who participated in the experimental investigation reported or described in this manuscript was obtained after the nature of the procedures and possible discomforts and risks had been fully explained. Each subject was given an infiltration injection in the buccal sulcus of the maxillary right and left premolar regions, one with local anesthetic solution slowly warmed to thirty-seven degrees centigrade, with the temperature maintained in a thermostaticaly heated bath, and the other at twenty-one degrees centigrade. The sequence of injections was randomized to account for the anticipatory effects on the subject's anxiety over the second injection. Double blind conditions were ensured, since neither the patient nor the dentist administering the injection knew which solution was heated. One operator adm stered all the injections to tMott Children's Health Center/Hurley Medical Center Flint,
Mchigan
*DireCtr, Pedonontic Residency Program
**Second Year Resident in Pedodontics
SEPrTEBER-OCToBER, 1978
standardize injection technique as much as possible. The entire content ofthe cartridge was injected during a standardized period of thirty seconds for each
TABLE 1 Pain Responses Versus Temperature of Anesthetic Solution
injection.
The anesthetic used was XylocaineR hydrochloride 2 percent with epinephrine, 1:100,000. The syringes were disposable (MonojectR) with twenty-seven gauge one-inch needles. No topical anesthetic was given in order to avoid its possible interference with the subject's pain perception. The subjects were asked to report their perceived pain response according to the following scale, which was adapted from Chaves:5 0 -no pain 1 slight pain 2 - moderate pain 3 - severe pain The subjects were instructed to distinguish between pain on insertion of the needle through the mucosa and the injection of solution and to report their pain response only as it related to the actual injection of anesthesia. Five seconds after needle entry into tissue, the injection of solution was initiated and the subject was so informed. The subjects were asked to report their pain sensations immediately after initiation of injection and after termination of injection. The subjects were also asked to record in minutes the onset of anesthesia after each injection. The statistical tests used were Chi-square for the pain data and the students' t-test for the onset data.
Results: The subjects' reports ofpain, during the initiation of the injection and after termination of injection (see Table 1) showed no consistent differences in pain perception between the warm and the cold anesthetic. The Chi-square analysis was made by compressing the cells for slight pain, moderate pain, and severe pain to avoid violation of the Rule of Five.6 Chi-square values of 1.46 and 0.52 resulted for reports of pain on initiation of injection and pain at termination of injection respectively, neither of which approached acceptable statistical confidence levels. The mean time of anesthetic onset between the warm and cold anesthetic solutions was 1.375 minutes and 2.000 minutes respectively. However, t-test comparisons demonstrated no statistically significant relationship between anesthetic temperature and speed of anesthetic onset (t = 1.316). Discussion:
The results of this study demonstrate that heating local anesthetic solutions to body temperature to reduce pain during local anesthetic injection is unnecessary. In fact, it is interesting to note that four out ofthe five responses of moderate pain (see Table 1), which was the severest pain category reported by subjects in this study, resulted from injections of warm anesthetic solution. Comparisons ofanesthetic solution temperature and onset time probably deserve further study, at least to SEPTEMBER-OCTOBER, 1978
Temperature of
Anesthetic
Pain Response During Initiation of the Injection No Slight Moderate Severe Pain Pain Pain Pain
Warm (37 C)
Cold(21°C) Temperature of
Anesthetic
Warm (37° C)
Cold(21°C)
9 6
6 9
1 1
0 0
Pain Response at Termination of the Injection No Slight Moderate Severe Pain Pain Pain Pain
9 7
4 9
3 0
0 0
settle basic research questions in this area. Although the results of this study demonstrated no clear statistical relationship between the two, certain trends emerged that pointed to a possible association between warm anesthetic solution and quicker anesthetic onset. For example, eight of the sixteen subjects reported faster onset after injection of warm anesthetic solutions as opposed to only one who reported the reverse (the remainder reported equal times for anesthetic onset). If this trend held constant in studies using more subjects, statistical significance might be attained with similar statistical means resulting from this study, since the t-test is influenced toward probability in studies with larger sample sizes. However, such results would admittedly be of limited practical value, since the mean difference between anesthetic onset for warm and cold solutions in this studv was only 0.625 minutes (about 37.5 seconds), a time differential which has obvious limitations for practical importance in clinical settings.
Conclusions: The results of this study indicate that no benefit is gained in terms ofreduction of pain or clinically meaningfil speed of anesthetic onset by heating local anesthetic solutions to body temperature prior to injection. REFERENCES 1. Bennett C R Monheim's local anesthesia and pain control in dental practice ed. 6. St. Louis CV Mosby 1978. 2. Monheim M Local anesthesia and pain control ed. 4 St. Louis CV Mosby 1969. 3. Oikarinen V J Ylipaavalniemi P Evers H Pain and temperature sensations related to loci analgesia Int J Oral Surg 4:151 1975. 4. Adriani J The pharmnacologgy ofanesthetic drugs ed 5 Springfield C Thomas 1970. 5. Chaves J F and Barber T X Cognitive strategies, experimenter modeling, and expectation in the attenuation ofpain. J Abn Psydv 83:356 1974. 6. Chikton N W Design and analysis in dental and oral research Phila J B Lippinontt 1967.
165
