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Pain related to mandibular block injections and its relationship with anxiety and previous experiences with dental anesthetics

Open AccessPublished:January 24, 2012DOI:https://doi.org/10.1016/j.oooo.2011.08.006

      Objective

      Anesthetic injections should reassure patients with the prospect of painless treatment, but for some patients it is the main source of their fear. We investigated pain resulting from mandibular block injections in relation to anxiety and previous experience with receiving injections.

      Study Design

      Patients (n = 230) filled out questionnaires before oral surgery. They were then asked to raise their hand when they felt pain as a result of the injection. The injection was administered, and pain intensity (11-point numeric rating scale) and pain duration (in seconds) was measured.

      Results

      In general, patients expected (mean 4.2, SD 2.7) significantly more pain than they experienced (2.4 ± 2.2). About 8.3% of patients reported a score in the range of 7 to 10. On average, pain lasted for 6.2 seconds (range 1-24.5 s), ∼36% of patients raised their hand for ≤2 seconds, and 14.6% raised their hand for ≥10 seconds. Pain was significantly positively associated with anxiety and the way previous injections were experienced.

      Conclusions

      Mandibular block injections can be considered to be mildly painful, with pain lasting only a few seconds. The pain experience of a mandibular block seems only partly dependent on experienced anxiety and previous experiences with receiving injections.
      The fact that local anesthesia is available should comfort patients by providing them with the knowledge that they will not feel pain during dental procedures. In practice, this does not hold true. First of all, not all dental apprehension and anxiety is driven by pain expectations.
      • de Jongh A.
      • Muris P.
      • ter Horst G.
      • Duyx M.P.
      Acquisition and maintenance of dental anxiety: the role of conditioning experiences and cognitive factors.
      Many patients are anxious about receiving injections. For example, in The Netherlands an estimated 16.1% of patients report fear of injections, and ∼1% of the population suffers from injection phobia.
      • Oosterink F.M.
      • de Jongh A.
      • Hoogstraten J.
      Prevalence of dental fear and phobia relative to other fear and phobia subtypes.
      It may be that patients who are fearful of dental injections have had negative experiences involving injections and belief that injections will be quite painful for them. Indeed, the 2 most commonly reported factors underlying fear of injections are fear of pain and fear of bodily injury.
      • Milgrom P.
      • Coldwell S.E.
      • Getz T.
      • Weinstein P.
      • Ramsay D.S.
      Four dimensions of fear of dental injections.
      Therefore, although anesthetic injections should reassure patients with the prospect of painless treatment, for some patients these injections are the source of their anxiety or fear.
      A number of factors are related to the level of pain felt during dental injections. These may include, among others, type of anesthetic fluid, amount of injected anesthetic fluid, injection rate, location of injection, expertise of the dentist, use of surface anesthesia, and methods of injection (traditional syringe or computerized anesthetic delivery systems, such as the Wand).
      • van Wijk A.J.
      • Hoogstraten J.
      Anxiety and pain during dental injections.
      Besides procedural factors, psychologic factors appear to play an important role in the perception of pain as well, most notably anxiety or fear. Anxiety is an anticipatory emotional state that serves to prepare an organism for a (perceived) threat or danger. Cognitive processes play a role in the evaluation of this threat,
      • Lazarus R.S.
      • Folkman S.
      Stress, appraisal and coping.
      • Eli I.
      Oral psychophysiology: stress, pain, and behavior in dental care.
      such as knowledge, beliefs, and the way in which we seek, process, and store information. Usually, knowledge, expectations, and beliefs are acquired through experience. However, sometimes these are based on inaccurate information rather than personal experience. One example concerns endodontic therapy (ET). A recent study showed that ET was ranked third out of 68 anxiety provoking dental stimuli.
      • Oosterink F.M.
      • de Jongh A.
      • Aartman I.H.
      What are people afraid of during dental treatment? Anxiety-provoking capacity of 67 stimuli characteristic of the dental setting.
      In other words, ET has a reputation of being very painful in the perception of the general public. In the light of Litt's remark that “What seems to account for the high prevalence of dental fear is the perception that dental procedures are painful,”
      • Litt M.D.
      A model of pain and anxiety associated with acute stressors: distress in dental procedures.
      ET is a dental procedure for which this holds true. In contrast, research shows that people who experienced ET personally are actually quite positive about it.
      • LeClaire A.J.
      • Skidmore A.E.
      • Griffin Jr, J.A.
      • Balaban F.S.
      Endodontic fear survey.
      In one study, we showed that giving positive (yet correct) information about ET led to a reduced fear of pain associated with ET.
      • van Wijk A.J.
      • Hoogstraten J.
      Reducing fear of pain associated with endodontic therapy.
      Apparently, information affects knowledge, expectations, and beliefs, resulting in reduced fear. Moreover, people who do not have experience with certain dental procedures still form expectations about it. The problem is that such estimation is subject to anxiety, and people usually overestimate fear or pain for procedures they did not experience themselves.
      • van Wijk A.J.
      • Hoogstraten J.
      Experience with dental pain and fear of dental pain.
      In the present study, we investigated pain related to mandibular block injection. Mandibular block injection was chosen for a number of reasons. All such injections are given in the same location, using the same anesthetic solution and the same injection volume. In addition, mandibular block is administered on a large scale to relatively young people undergoing third molar extraction (TME) who are typically quite anxious (about TME) and may have different experiences with receiving dental injections. Therefore, the general aim of this study was to investigate pain as a result of mandibular block injections. Our results may be used to provide a more accurate estimate to (fearful) patients of what to expect from mandibular block injections. Earlier research suggests that anxious patients generally feel more pain of longer duration as result of an oral injection, compared with less anxious patients.
      • van Wijk A.J.
      • Hoogstraten J.
      Anxiety and pain during dental injections.
      • van Wijk A.J.
      • Makkes P.C.
      Highly anxious dental patients report more pain during dental injections.
      In addition, earlier results
      • van Wijk A.J.
      • Hoogstraten J.
      Anxiety and pain during dental injections.
      suggest that previous experience with dental injections may be predictive for how future injections are experienced. Therefore, we tested 2 hypotheses: 1) Patients with negative experiences regarding dental injections report increased anxiety and pain compared with patients reporting positive experiences; and 2) anxiety is positively associated with pain as a result of the injection.

      MaterialS and Methods

      Participants

      Patients attending the department of Oral and Maxillofacial Surgery in the Amstelland Hospital (Amstelveen, The Netherlands) who required a mandibular block injection before treatment were eligible to participate in this study. Inclusion criteria were the ability to read, understand, and fill out questionnaires and willingness to participate. Data collection took place from June 4, 2010, to June 16, 2010. The study was performed with the understanding and written consent of each subject and according to the ethical principles described in the Declaration of Helsinki.

      Anxiety and pain measurement

      An 11-point numeric rating system scale (NRS) was used to measure preinjection anxiety and expected pain as a result of the injection. Pain experienced during the injection was rated on an 11-point NRS ranging from 0 (no pain) to 10 (extreme pain). Pain duration was measured using a stopwatch. Anxiety experienced during the injection was also rated.

      Dental injection

      The anesthetic injection was standardized as much as possible. None of the patients received topical anesthesia. All of the patients received the same amount (1.7 mL) of anesthetic fluid (articaine hydrochloride/ephinephrine) in the same location (mandibular block). Injections in all of the patients were administered using the same type of needle (27 gauge). Three highly experienced oral and maxillofacial surgeons (OMSs) gave the injections and performed subsequent surgeries.

      Fear of dental pain

      Fear of dental pain was measured by using the short Fear of Dental Pain Questionnaire (s-FDPQ).
      • van Wijk A.J.
      • McNeil D.W.
      • Ho C.J.
      • Buchanan H.
      • Hoogstraten J.
      A short English version of the fear of dental pain questionnaire.
      This questionnaire consists of 5 items rated on a 5-point scale ranging from 1 (no fear at all) to 5 (extreme fear), yielding a total score range of 5-25. Subjects were asked to rate the amount of fear of pain related to each item, e.g., “receiving root canal treatment.” Cronbach alpha was 0.89 in the present study and scores were distributed normally.

      Dental anxiety

      Dental trait anxiety was measured using the Dental Anxiety Scale.
      • Corah N.L.
      Development of a dental anxiety scale.
      The questionnaire consists of 4 items, each rated on a 5-point scale, yielding a total score range of 4 to 20. Cronbach alpha was 0.89 in the present study, and the data were somewhat skewed to the right.

      Experience with dental injections

      To form an impression of previous experience patients had with injections, a number of different questions were used.
      • Matthews D.C.
      • Rocchi A.
      • Gafni A.
      Factors affecting patients' and potential patients' choices among anaesthetics for periodontal recall visits.
      One item asked about previous experience with dental injections (yes/no). Three items were used to assess previous experience with dental injections in terms of confidence in the injection (how well did it work for you), pain felt during injections (how much pain did you feel), and anxiety related to injections (how did it make you feel). One item was used to assess anxiety regarding future injections (if you go to the dentist tomorrow, how would that make you feel?). Answers were given on a 5-point answer scale.

      Procedure

      Before treatment, eligible patients were informed in the waiting room about the study and asked to participate on a voluntary basis. On agreement, an informed consent form was signed. Next, patients were told that the aim of the study was to investigate pain as a result of dental injections. Next, patients filled out all questionnaires. After being seated in the operating chair/surgery room, patients were instructed to raise their hand when feeling pain as a result of the injection, and to lower their hand when the pain stopped. An independent research assistant measured pain duration with a stopwatch. After the patient's hand was lowered, pain intensity was indicated on an NRS. Instructions on asking for participation and raising the hand were written down in a protocol that was used for each patient.

      Statistical analysis

      Distributions of categoric variables were analyzed with the χ2 test. Independent mean scores were compared with the independent-samples t test. The Pearson correlation was used as a measure of linear association, and forward stepwise multiple regression analysis was used as a predictive model. The level of significance was set at alpha .05.

      Results

      A total of 230 patients were included in the study. There were 121 male (mean age 41.9 years, SD 18.1) and 109 female (mean age 36.9 years, SD 19.1) patients. Male patients were slightly older: t(228) = 2.04; P < .05. The majority of patients came to the department for surgical third molar removal (84.4%), another 9.1% required apical surgery, and 6.5% were there for other procedures (13 different procedures, mostly related to implant placement). A total of 49 patients did not participate, because they were either too anxious (n = 13), they did not feel like it (n = 6), the questionnaire was too long (n = 5), they missed treatment (n = 8), they did not receive a mandibular block but a local anesthetic (n = 5), or because treatment was canceled (n = 12). Treatment was carried out by the 3 oral surgeons as follows: OMS1 29%, OMS2 60.2%, and OMS3 10.8%.

      Pain as a result of injection

      The following results are presented in Table I. Mean pain intensity as a result of the mandibular block injection was 2.6 (SD 2.2). Mean expected pain intensity was rated significantly higher than experienced pain. About 1 in 5 patients expected pain to be in the range of 7-10. Only 19 patients reported that the experienced pain was in the range of 7-10. Of the 46 patients who expected pain to be >6, only 6 actually reported experiencing pain ≥6.
      Table IMean scores, standard deviation, and score distribution for anxiety, pain intensity, and pain duration
      MeanSDScore 0-6Score 7-10
      Preinjection anxiety4.32.774.5%25.5%
      Expected injection pain4.22.380.1%19.9%
      Experienced injection pain2.62.291.7%8.3%
      Experienced anxiety3.22.783.5%16.5%
      Duration injection pain—total sample; n = 2301.4 s3.5
      Duration injection pain—hand raisers: n = 615.3 s5.1
      Regarding duration of pain, only 61 patients raised their hand (see Discussion). Patients who did raise their hand did so, on average, for 5.3 seconds (SD 5.1) with a range of 1-24.5 seconds. A total of 36.1% raised their hand for ≤2 seconds, and 14.6% raised their hand for ≥10 seconds. For the group of hand raisers, the correlation between pain intensity and duration was r = .47.

      Experience with dental injections

      Our first hypothesis was that patients with negative experiences regarding dental injections would report increased anxiety and pain with respect to the injection. Only 10 patients (4.3%) had never experienced an injection in the mouth. Regarding the other 221 patients, 91.9% indicated that anesthetic injections worked usually or always well for them. Another 6.3% could not remember, and 1.4% indicated that injections only worked slightly for them. When asked to think about their last injection, 8.1% reported having felt severe to very severe pain. Regarding their last injection, 18.6% reported having felt anxious, and another 9% indicated having felt very anxious. When patients were asked how they would feel if they had to undergo an anesthetic injection the next day when visiting the dentist, 15.2% said that they would be anxious and another 6.5% very anxious.
      Patients with different dental needle experiences were compared regarding preinjection anxiety, expectations about pain, experienced anxiety, and experienced pain. Patients who reported “I cannot remember” were excluded for analysis regarding the respective item. An overview of mean scores is presented in Table II. In summary, all analysis of variance (ANOVA) were significant (P < .05). The general trend was that more negative dental experiences were associated with more (anticipated and experienced) pain and anxiety (Table II), thereby confirming our first hypothesis. Patients without previous extractions expected significantly more pain (5.9 vs. 4.7) as a result of the extraction (t(228) = −2.80; P = .006) but did not differ on anxiety before the injection (5.3 vs. 4.7).
      Table IIExperience with dental injections compared with mean (anticipated and experienced) anxiety and pain scores
      QuestionAnswerInjection anxietyExpected painExperienced anxietyExperienced painn
      MSDMSDMSDMSD
      DNE2
      P < .05(analysis of variance).
      Always3.922.763.942.392.792.582.472.03124
      Usually4.082.493.832.183.052.602.422.1859
      Reasonably5.762.265.381.945.052.894.262.7221
      Total4.162.684.062.323.102.692.642.21204
      DNE3
      P < .05(analysis of variance).
      Very severe6.633.505.633.355.754.654.004.244
      Severe4.712.845.502.313.152.512.542.0314
      Average5.402.345.561.994.402.583.752.1367
      Mild3.652.363.531.852.482.482.132.0877
      No pain3.333.172.571.932.232.451.941.7841
      Total4.302.734.182.303.182.722.692.22203
      DNE4
      P < .05(analysis of variance).
      Very relaxed0.300.951.301.640.501.270.901.1010
      Relaxed2.371.982.931.891.481.651.781.5966
      Neutral4.081.824.172.052.752.082.622.1677
      Quite anxious6.591.535.771.736.181.973.902.2841
      Very anxious8.151.185.852.395.352.783.802.6720
      Total4.242.704.122.323.142.702.632.21214
      DNE2, “How well does an anesthetic injection usually work for you?” DNE3, “Thinking about your last injection, how much pain did you feel?” DNE4, “Thinking about your last injection, how anxious were you?”
      low asterisk P < .05 (analysis of variance).

      Anxiety, expectations, and experience of pain

      Our second hypothesis was that anxiety is positively associated with pain from the injection. Correlations between the expected and experienced anxiety and pain measures are presented in Table III. Pain experienced during the injection correlated most strongly with anxiety experienced during the injection. Preinjection anxiety was more strongly correlated with expectations about pain and anxiety rather than the actual experience itself. The best predictor for pain during the injection, after anxiety during the injection, was the “fear of dental pain” score.
      Table IIIPearson correlation between all anxiety and pain measures
      1234567
      1Preinjection anxiety
      2Expected injection pain0.72
      3Anxiety for treatment0.850.67
      4Expected treatment pain0.570.660.67
      5Experienced injection pain0.470.470.420.43
      6Experienced injection anxiety0.750.620.700.510.64
      7FDP0.710.590.750.640.490.67
      8DAS0.690.460.660.410.300.590.66
      Some of our patients reported feeling substantial pain as a result of the injection. A number of stepwise regression analyses were performed to determine which variables would predict experienced pain intensity. In short, pain intensity could be predicted significantly (F4,180 = 26.47; P < .001) based on s-FDPQ score (b = 0.14), anticipated pain (b = 0.21), age (b = −0.02), and gender (0.65): R = .61; adjusted R2 = .36. Thus, about 36% of variance in pain could be explained by the variables in the regression analysis. A much larger part remained unexplained. However, these analyses confirmed our second hypothesis. We may add that female patients (mean 5.3, SD 2.5) scored significantly higher than male patients (mean 3.4, SD 2.6) on pain intensity: t(228) = −5.6; P < .001.

      Exploratory analyses

      The following analyses were to contrast the results of the preceding section. The sample was divided based on pain intensity: low pain (NRS <7) and high pain (NRS >6). Low and high pain was significantly associated with gender (χ2(1) = 5.7; P < .02), resulting from a relatively large number of women in the high pain group (14 out of 19). In addition, 16 out of 19 patients in the high pain category were treated by the same OMS. As such, low and high pain showed a trend toward being associated with a specific OMS (χ2(2) = 5.1; P = .079; Table IV). We grouped together the 2 other OMSs (with a total of 3 patients in the high pain group) and performed the comparison again. This yielded a significant result (χ2(1) = 5.01; P = .025), suggesting that one of the surgeons had relatively more patients in the high pain group than the other 2. A similar result was seen when comparing the mean pain intensity and pain duration scores between the OMSs. A trend was observed regarding pain intensity (F2,227 = 2.84; P = .06), resulting from a relatively higher score from OMS II. For pain duration, a significant difference was found (F2,228 = 3.10; P = .047), resulting from a longer mean duration of pain from OMS III. The OMS variable did not add unique variance to the prediction of pain intensity or pain duration.
      Table IVMean scores and standard deviation of pain intensity and pain duration for each surgeon separately, along with distribution of patients in the low or high pain category across oral surgeons
      OMSPain duration (s)
      Total sample (n = 230).
      Pain duration (s)
      Sample of hand raisers (n = 61).
      Pain intensity (NRS)Low pain nHigh pain n
      nMSDnMSDMSD
      I671.012.73164.224.272.141.81652
      II1381.303.00374.904.062.872.3612216
      III252.996.5289.358.822.262.03241
      OMS, Oral maxillofacial surgeon; Low pain, NRS score <7; High pain, NRS score >6.
      low asterisk Total sample (n = 230).
      Sample of hand raisers (n = 61).
      To conclude, if the mean pain intensity score associated with each OMS weighs equally heavy, the overall mean pain intensity changes from 2.6 to 2.4 and mean pain duration (for the hand raisers) changes from 5.6 to 6.2 seconds.

      Discussion

      In the present study, we examined 230 oral surgery patients regarding pain intensity and pain duration as a result of a mandibular block injection. In general, patients expected significantly more pain than they experienced, a result in line with earlier studies.
      • Arntz A.
      • van Eck M.
      • Heijmans M.
      Predictions of dental pain: the fear of any expected evil, is worse than the evil itself.
      Mean pain intensity was 2.4, and mean pain duration was 6.2 seconds. As such, a mandibular block injection can be considered to be a mildly painful experience lasting only a few seconds. These results can be used to accurately inform fearful patients about what to expect from mandibular block injections, hopefully resulting in reduced fear and anxiety. Most patients (and readers) will agree with this notion (i.e., mildly painful), because it is likely to be in agreement with their personal experiences or beliefs. Only a small part of the patients reported feeling substantial pain (>6 on an NRS). Regression analyses showed that fear of dental pain, expected pain, age, and gender were significant predictors of pain intensity. However, these results should be interpreted with caution, given that 16 out of 19 patients in the substantial pain group (>6 on an NRS) received injections from the same OMS. Another influential factor was previous experience with dental injections. Our results showed that more negative experiences with injections were related to more anticipated and experienced anxiety and pain. This is largely in line with earlier research.
      • de Jongh A.
      • Olff M.
      • van Hoolwerff H.
      • Aartman I.H.
      • Broekman B.
      • Lindauer R.
      • et al.
      Anxiety and post-traumatic stress symptoms following wisdom tooth removal.
      Regarding duration of pain, only 61 patients raised their hand. Upon asking, many patients admitted that they forgot to raise their hand, either as a result of anxiety or because the time between giving the instruction and the actual injection was too long. In other words, the group of non–hand raisers consisted of patients who did not consider the injection to be painful enough to raise their hand and patients that considered the injection to be painful but who forgot to raise their hand. Unfortunately, this finding invalidates pain duration in the present study to an unknown extent. That is, subjects who were so anxious that they forgot to raise their hand may differ substantially from the ones who did respond. In this sense, results may change when nobody “forgets” to raise their hand. Future studies that include pain duration as a dependent variable should either improve the instructions to the patient or should consider giving (or repeating) the instruction just before the injection. Another difficulty is that raising the hand could be a visual cue for the surgeon. In other words, a surgeon can “decide” to lower the injection rate (which strongly affects the pain felt) when seeing the hand go up. In the present study, however, the oral surgeons were not motivated to make a “good impression,” because they were not aware of any comparisons that might be made. In addition, when the injection is given, the surgeon is focused on the injection area, the needle and insertion procedure, and applying pressure to deliver the anesthetic. In other words, there is not much opportunity for the surgeon to use the hand as a feedback mechanism to alter the injection speed. Nevertheless, for future studies, a button that can be pressed to measure duration of pain would minimize the possibility of such an effect.
      Although previous experience with dental injections was associated with anticipated and experienced anxiety and pain, it was not possible to predict, based on the measures used in this study, which patients would experience the mandibular block injection as substantially painful (NRS >6). In a future study, physiologic measures (heart rate, galvanic skin response, respiration, and skin temperature) and additional psychologic measures (introversion/extraversion) will be included to examine whether this prediction can be improved and to assess to what extent the subjective outcomes correspond with the physiologic response of patients experiencing the injection as substantially painful.
      In conclusion, mandibular block injections can be considered to be mildly painful, with pain lasting only a few seconds, for the majority of patients. The pain experience is partly dependent on experienced anxiety and previous experiences with receiving injections and partly dependent on the surgeon providing the injection. Only a minority of patients reported feeling substantial pain as a result of the injection.

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