The effectiveness of Virtual Reality for dental pain control: A case study.

HUNTER G. HOFFMAN^ac*, AZUCENA GARCIA-PALACIOS^d, DAVID R. PATTERSON^b, MARK JENSEN, THOMAS FURNESS III^a, and William F. Ammons, Jr.^e

keywords: dental pain, virtual reality, presence, analgesia, distraction, attention

The effectiveness of Virtual Reality for dental pain control: A case study.

Reduction of pain and distress during dental/periodontal procedures would likely increase the frequency of visits of avoidant patients. Fear-related behaviors are considered the most difficult aspect of dental patient management, and can interfere with good dental care.^1,2,3 Fear of dentists dental work has been associated with the amount of pain experienced at the dentist.^4,5,6 For example, the two most common dimensions of dental injection fear are "pain of injection" and "fear of bodily injury from injection"³. Direct experience is the most common origin of dental fears.^7,8 Furthermore, many patients with dental fears only go to the dentist when they have a painful tooth⁹, increasing the chances that their dental visit will involve pain.

In a recent survey of randomly selected college students at the University of Washington, 19% of the students reported dental anxiety¹⁰, and the prevalance and unhealthy avoidance is similar in a representative sample of the Seattle community¹¹. Techniques such as cognitive behavioral treatments,^{12 ,14} nitrous oxide, and intravenous sedatives administered during dental treatments¹⁵ have been found to minimize patient pain and discomfort during dental care.

Distracting patients with a movie has been shown to help reduce pain during gastrointesinal endoscopies¹⁶, and during wound care of severe burn patients¹⁷. Although to our knowledge, no controlled experiments have been published, there is considerable anecdotal evidence that dental patients feel less pain while watching a movie, and some dentists use such distraction in everyday practice for fearful or avoidant patients.

Immersive virtual reality (VR) has proved effective for distracting burn patients from pain and anxiety during burn wound care and physical therapy^18,19 and during laboratory studies of pain²⁰. Researchers¹⁸ found immersive VR was dramatically more effective at reducing pain during staple removals from a burn skin graft than a Nintendo64 video game control group. VR reduced the amount of time [not clear why amount of time is underlined here] burn patients spent thinking about their pain and/or wound care procedures. Another study used no distraction (conventional treatment) for the control condition. Burn patients undergoing physical therapy for severe burn wounds estimated they spent approximately 75% of the therapy session thinking about their pain or /the procedure. When these same patients went into virtual reality, they spent only about 25% of the time thinking about their pain or /the procedure ²¹. Whether VR analgesia generalizes to procedural pain populations from etiologies other than burns is an important clinical(?)medicalquestion in this line of research.

The present study explored whether VR analgesia generalizes to procedural dental/periodontal pain in patients with adult periodontitus. Periodontitis is a chronic progressive disease that affects the gums, ligament and bone around the teeth. It is characterized by the development of inflammation in the gingiva that subsequently extends, resulting in the resorption of alveolar bone. This bone resorption and the migration of the attachment of the periodontal ligament on the root of the tooth results in the formation of a space, the periodontal pocket. This pocket is a pathological site filled with large numbers of microorganisms (plaque), inflammatory cells, exudate, and tartar that is attached to the exposed root of the mouth. Gentle probing or brushing commonly causes bleeding.²² Scaling and/or root planing is the most common non-surgical treatment for periodontitis. During this procedure the dentist or dental hygenist uses various sharp instruments to scrape the deposits of bacterial plaque and calculus off the tooth and out of the pocket.²³ Periodontal scaling and root planing, which can be quite painful for patients with moderate/advanced adult periodontitis, frequently requires the use of local anesthetic or nitrous oxide.

Using a within-subjects design, we tested the degree to which pain associated with periodontal scaling was reduced by distracting patients with immersive virtual reality or a movie relative to a no-distraction control. The amount of decay (and hence painfulness) often varies from one part of the mouth to another, within a single patient. The relatively short treatment durations used helped equate the degree of decay of the areas scraped for each of the three conditions. Care was taken to select areas of the mouth that would have been "equally painful" for each of the 3 conditions if no distraction had been given. The two patients with periodontitis were selected because they reported severe pain with periodontal scaling in the past, and each of the two patients had shown problematic avoidance of periodontal care on previous occassions. [Dave’s emial point about the lack of pain with ususal teeth cleaning care will be raised in the readers’ minds here. Most people have their teeth cleaned without muhc pain. Need to make some comment about why these particular patients would normally feel pain here, like the comment you made in response to Dave’s quiery.]

Patients answered 6 pre-treatment questions consisting of the 4 Dental Anxiety Scale questions²⁴ as well as two other questions rating anxiety and desire to avoid periodontal treatments. The Dental Anxiety Scale has been shown by Coreh²⁴ to have high test-retest reliability, and validity. After reading the introduction to the experiment each patient sat in the dentist chair and had periodontal scaling in three conditions (e.g., no distraction, watching a movie, or virtual reality). The patient’s self-ratings of pain and presence were the primary dependent variables. Ratings were administered after each experimental treatment during a brief (approximately 2 minute) pause in dental care. At each pause (once after dental care with VR, once after dental care while watching the movie, and once after dental care with no distraction), patients completed several retrospective pain ratings. Patients gave ratings using 0 — 10 scales (see appendix) with labels on the scale indicating that 0 = ‘none,’ 1 — 4 = ‘mild,’ 5 — 6 = ‘moderate,’ and 7 — 10 = ‘severe,’ pPatients rated their WORST PAIN, AVERAGE PAIN, how UNPLEASANT was dental care, how much their teeth/gums BOTHERED them during the cleaning procedure, and HOW MUCH TIME THEY SPENT THINKING ABOUT THEIR PAIN during the session. Patients in the VR were also asked the following ratings using labeled 0 to 10 scales: To what extent (if at all) did you feel nausea as a result of experiencing VR? While experiencing VR, to what extent did you feel like you went into the virtual world? How real did the objects in the virtual world seem to you? Hendrix and Barfield²⁵ describe several studies showing the reliability of a similar subjective measure of presence. Patients also filled out similar ratings after the movie condition.

A Silicon Graphics Octane MXE with Octane Channel Option (www.sgi.com) was coupled with a V8 VR helmet (www.virtualresearch.com) to create an immersive, 3-D, interactive, computer-simulated environment. Eyepieces on the helmet were circular and had 60 degree diagonal field-of-view per eye. Patients had the illusion of flying through SnowWorld, a virtual environment created with Creator^TM modelling software and VEGA^TM development software from www.MultiGen.com. SnowWorld depicts an icy 3-D virtual canyon with a river and waterfalls (see Figure 1). The patient’s view followed a pre-programmed path through the world, and they could "look around" the virtual world using an ordinary mouse to change gaze direction (without affecting the direction they went in SnowWorld). Patients shot snowballs at snowmen and igloos by aiming with their gaze (via the mouse) and pressing the spacebar on a keyboard to shoot. The snowballs exploded with animations and 3-D sound effects on impact. Patient One participated in 3 conditions of equal duration during periodontal scaling on areas of their mouths with equivalent degrees of decay, as did Patient Two. The three conditions were 1) VR, 2) a movie (patients watched the Humphrey Bogart movie "Casablanca" while wearing special personal movie viewing glasses) and 3) was "no distraction". Both patients had seen the classic movie before, helping make what they saw during the brief clip meaningful with the intention of enhancing the patient’s illusion of presence (see Hoffman et al.,¹³⁾. Patient One spent 2.5 minutes in each of the three treatment conditions. Patient Two spent 5 minutes in each treatment condition. Periodontal scaling can be painful for patients with adult periodontitis.

On the pre-test screening, Patients were asked to "Rate the anxiety you expect to experience during the dental procedure". On a scale from 0 to 100, where 0 = not at all and 100 = very much so, patient One circled 60, patient Two circled 20. Patients were also asked to "Rate how much you would like to avoid undergoing the dental treatment". On a scale from 0 to 100, where 0 = not at all and 100 = very much so, patient One circled 100, patient Two circled 70. Using Corah’s Dental Anxiety Scale²⁴, patient One showed a dental fear score one standard deviation above the standardized median (suggesting the patient had some fear but was not clinically phobic). Patient Two’s dental fears were about average overall (i.e., no indications of dental fear for patient Two). [Wait, the heading says patient one, and the results include both patients??]

As shown in Figure 2, according to 0-10 subjective pain ratings, for patient One, the mean pain ratings were in the severe range while watching a movie (7.2) or during no distraction (7.2) but were in the mild pain range (1.2) during the VR condition. The patient’s pain scores decreased for sensory pain (worst pain and average pain), and for affective pain ratings (unpleasantness). The patient showed a large drop in bothersomeness and reported spending spent much less time thinking about his dental pain while in VR compared to watching the movie. More specifically, during dental care, the patient reported spending "most of the time" thinking about his pain while watching the movie, and "some of the time" thinking about his pain while in immersive VR (SnowWorld). As predicted, on a scale from 0 to 100 with 100 = high, the patient rated his sense of presence much higher in VR than in the movie condition (60 vs. 0 respectively), and he rated the realism of objects higher in VR than for the movie (30 vs. 0 respectively). Simulator sickness was zero for both conditions. Watching a movie did not reduce the pain of patient One. The patient reported that the movie image on his TV glasses was not high enough resolution, and this may have contributed to the finding that (contrary to our prediction of modest pain reduction), the movie had no analgesic effect for Patient One.

The results for patient Two are shown in Figure 3. According to 0-10 subjective pain ratings with labels, Patient Two reported mild to moderate pain with no distraction (mean = 4.4), mild pain while watching the movie (3.3) and essentially no pain while in VR (0.6) during his periodontal scaling. In VR the patient’s pain scores decreased for sensory pain (worst pain and average pain), and for affective pain ratings (unpleasantness). The patient showed a large drop in bothersomeness and spent much less time thinking about his dental pain while in VR compared to watching the movie, and compared to no distraction. As predicted, on a scale from 0 to 100 with 100 = high, the patient rated his sense of presence much higher in VR than in the movie condition (70 vs. 10 respectively), yet he rated the realism of objects higher for the movie than for VR (50 vs. 40 respectively). Simulator sickness was zero for both the movie and VR conditions.

These two cases provide preliminary evidence that entering a virtual environment can help control dental/periodontal pain during a non-surgical treatment for periodontitis. The first patient’s pain ratings showed considerable reduction while in VR relative to movie and no distraction control conditions. While in VR, the patient’s pain scores decreased dramatically for sensory pain, and affective pain, and he showed a large reduction in the amount of time spent thinking about his pain during periodontal scaling.

The second patient also had periodontitis. Although the pattern of results was less dramatic than Patient One, Patient Two also reported showed decreases drops in pain during VR relative compared to the movie control condition. Although VR was more effective than the movie for Patient Two, the movie did appear to provide some pain reduction compared to no distraction.

VR systems provide computer-generated sensory input to several senses (e.g., sight and sound). Such converging stimulation(?)evidenceevidence from multiple senses, and the interactive nature of the experience, can make the virtual world presented difficult for the brain to ignore. Immersive VR is uniquely effective for giving participants the illusion of going into the virtual environment. This sense of presence is the essence of immersive VR²⁶. Researchers²⁷ speculate that the strength of the illusion of presence in the virtual world reflects the amount of attention drawn into the virtual environment. The effectiveness of VR distraction treatment may depend on how present patients feel in the virtual environment. The illusion of presence in VR was relatively high for both patients, especially considering that this is the first use of immersive VR for pain control that did not permit head motion of the patients. Unlike previous studies treating severe burn patients,^18,19 in the present study, patients kept their heads still and used the mouse to look around in the virtual world.

Both patients in this study reported that VR reduced their awareness of dental pain. Both also reported that they were They appeared to be so absorbed in SnowWorld that they did not think often about their pain while in VR. VR and the movie control condition differed with respect to the patient’s ability to see the treatment room, instruments, or the dentist’s light. When watching the movie, patients could still see the real world. In VR, patients could not see the real world. The patient’s inability to see the dental hygenist and scaling instruments may be one advantage of VR.

Simulator sickness is a form of motion sickness characterized by an increase in nausea²⁸. Simulator sickness was not a problem in this study, nor has it been a problem in any of our other research on VR analgesia. We have specifically designed our VR hardware and software to minimize simulator sickness. We also pre-tested the VR worlds on healthy undergraduate volunteers, and have monitored patients closely (e.g., a nausea rating after every VR session). Simulator sickness but should be monitored closely in any medical use of VRshould be monitored in any medical application of virtual reality. It is more likely to be a problem with longer exposure durations, (e.g., > 20 minutes). Patients with severe susceptibility to motion sickness should not use VR (approximately 3% of the population). Frequent breaks can reduce the likelihood of simulator sickness, but it is best to stop a person early if they begin to show symptoms. The earlier it is stopped, the less severe the symptoms, and the sooner the symptoms go away.

Demand Characteristics, Both patients and researchers were aware of the experimental conditions and this is a factor that could have influenced their scores on all the measures. Although difficult to achieve in clinical settings, double blind experimental designs are needed. In double blind studies, neither the researchers nor the patients know exactly what experimental condition the subject is in on any given test. Such a study would reduce the plausability of a demand characterististics or /placebo effects as explanations for the efficacy of VR pain control. For example, the experimenter interacting with the patient and the patient may both be unaware that another group of patients is receiving a different (e.g., less distracting) experimental condition. One example of such a design …. Such a study would reduce the plausability of demand characterististics or placebo effects as explanations for the efficacy of VR pain control.

Figure 2.

Figure 3.

References

2. Corah, NL, O’Shea, RM, Ayer, WA. Dentists’ management of patient’s fear and anxiety. JAADA 1985:110(5):734-6.
3. Milgrom, P., Coldwell, S.E., Getz, T., Weinstein, P., Ramsey, D.S. Four dimensions of fear of dental injections. JADA, 1997; 28, 756-762.

5. Rate your AVERAGE PAIN during the most recent session:

8a. How real did the virtual objects seem to you?