Abstract
Anxious people tend to overestimate the intensity of aversive events such as fear and pain. When an aversive event has been experienced personally, prediction is based on experience and is possibly less subject to bias due to anxiety. Therefore, it was hypothesized that subjects will overestimate fear of specific dental pains relative to subjects who experienced the pain or procedure personally. Samples of highly anxious dental patients (n = 48), patients waiting for periodontal treatment (n = 56), and psychology freshmen (n = 262) completed a measure of dental anxiety and the Fear of Dental Pain (FDP) questionnaire. All FDP items were extended with the question whether the subject ever experienced the pain personally (yes or no). Less fear was reported when the pain had been experienced personally, with the exception of the sample of highly anxious dental patients. The results suggest that fear of dental pain is a highly important covariate in dental pain research.
INTRODUCTION
Fear of dental pain is a highly relevant concept in dental pain research and, moreover, in dentistry (van Wijk and Hoogstraten, 2003). Whereas anxiety and fear can be seen as a state of distress in anticipation or in the presence of a perceived danger, respectively, fear of pain can be seen as a state of distress related to a very specific type of stimulus, namely, pain (Gower, 2004). Research suggests that anxious people tend to overestimate anticipated pain (Arntz et al., 1994). Moreover, individuals tend to overestimate the intensity of aversive events in general, including such events as fear (Rachman and Bichard, 1988; Rachman, 1994) and pain (Rachman and Arntz, 1991). Therefore, people who are predisposed to respond fearfully to pain are at an increased risk of ending up in a vicious circle of anxiety, fear of pain, and avoidance of dental treatment.
An example of overestimation of pain related to dental procedures concerns endodontic therapy. In a survey about opinions regarding endodontic therapy, it appeared that people who personally experienced root canal therapy were 4 to 5 times more likely to describe the procedure as painless (Public Communications Inc., 1984), relative to people who did not experience the procedure. Moreover, a study by Rousseau et al.(2002) showed that patients reported more pain during extraction than during root canal therapy. In fact, 92% of patients undergoing root canal therapy reported less or much less pain than expected. The question is the extent to which this overestimation of pain is present on a wider variety of painful dental experiences.
We undertook the present study to test four specific hypotheses. Because dental pain can induce anxiety, and anxiety leads to overestimation of (dental) pain, it is assumed that an overestimation of either the pain, or the fear of it, is particularly present in a group with subjects scoring high on dental anxiety, such as highly anxious dental patients (I). In fact, if fear of dental pain is exacerbated by the current level of dental anxiety, one may expect that a reduction of dental anxiety is associated with lower levels of fear of dental pain (II). In addition, we included a sample of patients receiving painful dental treatment, to test the hypothesis that fear of dental pain is associated with more pain during treatment (III). Finally, if a subject has experienced a certain dental treatment personally, the amount of pain is no longer only an estimate and should therefore be less subject to bias from anxiety. Therefore, it was hypothesized that subjects will overestimate fear of specific dental pains relative to subjects who experienced the pain or procedure personally (IV).
MATERIALS & METHODS
Subjects
Three samples were used. In sample 1, subjects (N = 60), with a mean age = 41.5 yrs for the men and 36.8 yrs for women, were highly anxious dental patients (33 females) treated at the Dental Fear Clinic (SBT) at the ACTA. In sample 2, subjects (N = 60), with a mean age = 45.6 yrs for the men and 44.3 yrs for women, were patients (36 females) waiting for periodontal probing for the assessment of pocket status. In sample 3, subjects (N = 309) were psychology freshmen (209 females), with a mean age = 21.2 yrs for the men and 20.1 yrs for women. Only subjects who completed all relevant questionnaires were included in the analysis, that is, 48 highly anxious dental patients, 56 periodontal patients, and 262 psychology students. The study design was approved by the Netherlands Institute for Dental Sciences (IOT) for samples 1 and 2, and by the Department of Psychology for sample 3. All subjects participated on a voluntary base, were able to stop at any given point, and were given the opportunity to receive information regarding the aim and general outcome of the study.
Fear of Dental Pain
The Fear of Dental Pain questionnaire (FDP; van Wijk and Hoogstraten, 2003), which was developed as a dental equivalent of the Fear of Pain Questionnaire (FPQ-III; McNeil and Rainwater, 1998), consists of 18 items describing more or less painful dental experiences. Subjects are asked to think about the pain an event might cause and to indicate the amount of fear they feel associated with that event. Answers are scored from 1 (no fear at all) to 5 (extreme fear) and are summed to derive the FDP score (range, 18–90). Examples of items are: receiving a root canal treatment, having a tooth pulled, and being drilled in the jawbone. For the present study, each item was extended with the question: ‘Did you experience this yourself, yes or no?’
Dental Anxiety
The S-DAI is a short version of the Dental Anxiety Inventory (Stouthard, 1989), which has been shown to be reliable and valid (Aartman, 1998). It contains 9 items that are answered on a five-point Likert-type scale. An example is, ‘I become nervous when the dentist invites me to sit down in the chair’.
Pain Experienced
Within the sample of periodontal patients, the amount of pain felt during the periodontal probing procedure was assessed according to a Numerical Rating Scale (NRS) (0, no pain at all, to 10, worst possible pain; Turk and Melzack, 1992).
Procedure
The highly anxious dental patients from sample 1 completed the questionnaires (S-DAI and FDP) at some point during their anxiety treatment (which consisted of several sessions). To apply for this anxiety treatment, these patients had completed the S-DAI once previously (before the first session took place). As such, a delta anxiety score was calculated (dental anxiety at start of treatment minus dental anxiety at present) for these patients and was related to their current level of fear of dental pain.
The periodontal patients in sample 2 were about to be probed for the assessment of pocket status. They completed the S-DAI and FDP before being probed, and afterwards they were asked to rate the painfulness of the probing procedure on a NRS.
The students from sample 3 completed the S-DAI and FDP as part of a course requirement.
Statistical Analysis
We performed multivariate analysis of covariance and independent-sample t tests to test for equality of means. Pearson’s correlation coefficient was used as a measure of linear association. Sample size was based on the fact that the mean score of a sample approximates a normal distribution for n > 30 (Central Limit Theorem, Lyupanov; see van den Brink and Koele, 1996). We doubled this number for samples 1 and 2, to increase statistical power and to allow for assessment of gender differences and comparison of subjects who did and those who did not experience some painful events personally.
RESULTS
Anxiety and Fear of Dental Pain
Mean scores, standard deviations, and internal consistency were calculated for the total sample, for separate samples, and for gender separately (Table 1). We performed an initial MANOVA to analyze group differences (sample, gender) on the dependent variables (dental anxiety, fear of dental pain). An expected multivariate main effect was found for sample, F (4, 722) = 35.03, p < 0.001, resulting from a much higher mean FDP (mean difference = 23.6, confirming hypothesis I) and S-DAI score from the highly anxious dental patients. In addition, the student sample scored significantly higher on mean FDP scores than did the periodontal patients, but not on the S-DAI. A multivariate main effect for gender was also found, F (2, 361) = 4.85, p < 0.008, resulting from a higher mean score for women on the FDP and S-DAI. However, subsequent t tests within samples revealed no differences for gender within the student sample. No significant interaction was present. A second MANOVA was performed with age as a covariate. A main effect was found for sample, F (4, 718) = 31.93, p < 0.001, and for gender, F (2, 359) = 3.84, p < 0.022. Age was significantly related to the FDP score, but not to the S-DAI. The result showed that this relation accounted for the differences in FDP score between students and periodontal patients mentioned in the initial MANOVA.
For the sample of highly anxious dental patients, a delta anxiety score (anxiety at start minus anxiety at present) was calculated and related to their current level of fear of dental pain. A strong negative correlation was found, r = −0.64, p < 0.01 (n = 22), indicating that higher reductions of dental anxiety were associated with lower levels of fear of dental pain (confirming hypothesis II).
Fear of Dental Pain and Pain
For the sample of periodontal patients, Pearson’s correlation was calculated between fear of dental pain, and the pain felt during the probing procedure. Mean pain during probing was 2.75 (on a 0–10 NRS, SD = 2.46). A moderate correlation was found, r = 0.45, p < 0.001 (n = 55), suggesting that higher levels of fear of dental pain are associated with more pain felt during probing (confirming hypothesis III). Interestingly, dental anxiety was not related to the amount of pain felt, r = 0.11, p < 0.43.
Experience with Dental Pain and Fear of Dental Pain
For all FDP items, mean difference in item score was calculated between subjects who answered that they did experience the particular item personally and those who did not (Table 2).
In addition, multiple independent t tests were performed on the mean difference in item scores between subjects with and those without personal experience on that item. The results are presented for all subjects together and for samples separately (Table 2). For all subjects, 8 items showed a positive significant difference, indicating less fear for pain when subjects had experienced the pain personally. Only one item showed a negative difference (higher score for the experience group). So, the general trend appears to be that subjects overestimate their fear of pain when they have not actually experienced the particular pain itself (confirming hypothesis IV). All but one of the differences was in the expected direction. Within the student sample, the effect of overestimation (without personal experience) was even stronger. Ten items showed significant differences; none of the significant differences was negative. Within the sample of periodontal patients, the effect seems somewhat more modest. Only 3 items showed significant differences. Obviously, the skewed distribution of experience on some items, and the smaller sample size of the periodontal patients, prevented us from finding more differences. Finally, within the sample of highly anxious dental patients, most item differences are negative and of a magnitude comparable with those in the other samples.
DISCUSSION
Subjects tend to overestimate their fear of dental pain when they have not actually experienced the particular pain itself. This result was reversed within the sample of highly anxious dental patients in whom personal experience with an item led to higher fear of dental pain for that item. For the sample of periodontal patients, higher levels of fear of dental pain were associated with more pain felt during probing. For the sample of highly anxious dental patients, stronger reductions in dental anxiety were associated with lower levels of fear of dental pain.
Our results support the findings from a recent study (Klages et al., 2004) showing that subjects in general expect more pain than they experience, and that this effect is stronger in a group with higher dental anxiety scores. The fact that the opposite result was found in the sample of highly anxious dental patients needs attention. The most obvious explanation is that highly anxious dental patients must have had a strongly negative experience, resulting in a higher ‘fear of dental pain’ score. Whereas ‘normal’ subjects overestimate their fear of dental pain, which is, in a sense, protective (it can hardly be any worse), highly anxious dental patients seem to have experienced reality to be even worse than they expected (for reasons unknown to us, i.e., not necessarily the amount of pain). Indeed, as stated in the INTRODUCTION, an early negative dental experience is probably the most stated single cause for dental anxiety (Locker et al., 1996 , 1999). It is therefore reasonable to find that at least part of the experience with dentistry, within a group of highly anxious dental patients, has been traumatic.
The results, moreover, showed that highly anxious dental patients with the strongest reduction of dental anxiety also showed the lowest ‘fear of dental pain’ scores. This suggests that dental anxiety is at least partly responsible for the level of fear of dental pain within a person. The latter is obvious, since research suggests that anxious people tend to overestimate pain (Arntz et al., 1994). However, the result from the present study must be interpreted with some caution. We could obtain the necessary information for only 22 highly anxious dental patients.
Within the sample of periodontal patients, the results showed that higher levels of fear of dental pain were associated with more pain felt during periodontal probing. Interestingly, dental anxiety was not related to the amount of pain felt, while fear of dental pain was, despite the fact that the two are strongly related. This suggests that, beyond the part explained by dental anxiety, fear of dental pain may well be directly related to the amount of pain experienced during a stressful event.
To conclude, the results from this study support the assumption that people who are predisposed to respond fearfully to pain are at an increased risk of ending up in a vicious circle of anxiety, fear of pain, and avoidance of dental treatment. Other possible consequences are that patients who are fearful of dental pain may need more anesthesia or different anesthetic procedures. One can even imagine that a person extremely fearful of pain should be treated with an anxiolytic (for instance, ‘laughing gas’) to reduce the level of fear or arousal, before the dentist commences with the actual anesthetic procedure. Future research will be aimed at reducing fearful expectations regarding dental pain (the FDP questionnaire) and investigating whether this has any effect on the pain experience.
Mean Scores (with Standard Deviation) and Reliability [Cronbach’s alpha]
Mean Differences on Item Score, Overall and Within Samples between Subjects Who Experienced the Item Personally and Subjects Who Did Not
Footnotes
Acknowledgements
This study was supported by ACTA and the Netherlands Institute for Dental Sciences (IOT). The authors thank Dr. P. Makkes from the Stichting Bijzondere Tandheelkunde (SBT) and Prof. Dr. U van der Velden from the Department of Periodontology at ACTA.