Introduction

Dental caries is a common problem in young children. Often, more than one tooth is affected and several treatment sessions are needed. Although use of anaesthetics can lead to a relatively painless dental procedure, the delivery of local anaesthetic solutions and the needle puncturing the mucosa is known to be uncomfortable. Besides pain and discomfort, the prospect of an injection can also provoke anxiety, particularly in children. Research shows that about 14% of Dutch children between 4-11 years are dentally anxious and the strongest fears are associated with injections.1,2 One of the systems developed to minimise pain and discomfort during local anaesthesia injection is the Wand® system. The Wand® device is a computer-automated injection system that provides a precise injection flow-rate, regardless of tissue resistance.4

In previous studies with children, divergent results are found with the Wand®. Some showed lower pain ratings for injections with the Wand® in comparison with injections with the traditional syringe5,6 and another study7 reported lower pain ratings upon anaesthetic solution depositing using the Wand® system but similar pain ratings for needle insertion. In addition, there are also studies reporting no difference between the two injection methods, the Wand® system and the traditional syringe.8

In our earlier study we found that low anxious children showed less pain related behaviour when injected with the Wand® compared with the traditional syringe.10 No research has been done so far to study the effect of the Wand® on the pain behaviour of children over sequential treatment sessions. Therefore, to study if the positive effect of the Wand® on low anxious children persists over treatment sessions, the aim of the present study is to compare the pain and distress response of children receiving a local anaesthesia injection using a computerised device (Wand®) with the response of children receiving an injection using a traditional syringe over two sequential treatment sessions. Furthermore, it was studied whether the response to the two injection techniques was related to the child's dental anxiety level.

Material and methods

Subjects

A total of 152 children were asked to participate, however, three children could not be included in the study because their parents did not give permission to videotape the treatment session and two children because the parents did not have sufficient knowledge of the Dutch language to fill out the questionnaire. Therefore, this study was conducted among 147 children. Children were selected as a convenience sample ie all children that came for treatment during the study period and who met the selection criteria were selected. Selection criteria included: need for two subsequent treatment sessions requiring local anaesthesia, age between 4-11 years and no suspected or known developmental delay. All patients were treated by two paediatric dentists in a specialised dental care clinic. For 20 children only their first treatment session could be included due to rescheduling of the second appointment (Fig. 1).

Figure 1
figure 1

Flow diagram of the progress through the phases of the trial

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Ethical approval was obtained from the University Ethics Committee and the Interuniversity Dentistry Research School (IOT) at the Academic Centre of Dentistry Amsterdam. Written parental consent was obtained by the researchers before every individual treatment. The authors have no connection with the manufacturers of the Wand®.

Methods

Each child was randomly assigned to either the Wand® (n = 71) or the traditional injection (n = 76) condition based on a randomisation list generated by SPSS (SPSS Inc, 12.0, Chicago, USA). To avoid possible preference of two dentists, they were required to decide on the tooth to be treated before the anaesthetic condition was revealed. For the Wand® injections one of three insertion techniques was used after application of topical anaesthetic (benzocaine) with a cotton role, according to the manufacturer's instruction: the anterior middle superior alveolar injection (AMSA) or palatal anterior superior alveolar injection (PASA) for maxillary teeth and the periodontal ligament (PDL) for maxillary teeth or the mandible. Traditional anaesthesia was performed after topical anaesthetic (benzocaine) had been applied with a cotton role, according to the manufacturer's instruction, in the area of the injection site. For maxillary teeth, buccal or palatal injection sites were used, whereas in the mandible only the mandibular block anaesthesia was given.

All treatments were videotaped and analysed by two independent observers: an advanced psychology student and an advanced dental student. Both observers were extensively trained using videotapes not included in the study.

Measurements

Pain related behaviour: Five different pain related behaviours were each recorded as present or absent for every 15 second interval of the entire injection period: 1. Body movement, movement of greater than 15 cm of an extremity or turning of the body; 2. Muscle tension, clear tension in the hands (white knuckles) or tension of the body; 3. Crying or screaming; 4. Verbal protest; and 5. Bodily resistance, when it was needed to hold the child. For all of the five behaviours the occurrence is summed and divided over the number of intervals to calculate the mean score of the pain related behaviours.

Distress: The behavioural response of children in dentistry is often a mixture of anxiety and pain,11 therefore it was decided to also assess distress behaviour. The distress behaviour was measured using Venham's (modified) clinical rating of anxiety and cooperative behaviour. The scale consists of six points: 1) relaxed, 2) uneasy, 3) tense, 4) reluctant, 5) resistance, and 6) out of contact or untreatable. The scale has an established reliability and validity.12,13 The Venham scores for all 15 second intervals are summed and divided over the number of intervals to calculate a mean distress score.

Self-reported pain: The pain experience of the child was measured using a modified version of the visual rating scale (VRS). The scale resembled a thermometer and consisted of 11 points running from 0 = no pain to 10 = worst pain possible. Parallel to the scale six faces were presented, expressing different levels of pain/distress so young children could point out the face matching their own level of pain/distress.14

Dental anxiety: To assess the general level of dental anxiety of the child the parent was asked to complete the Dental Subscale of the Children's Fear Survey Schedule CFSS-DS on behalf of their child. The CFSS-DS has been extensively validated and consists of 15 items, related to various aspects of dental treatment and each item can be scored on a 5-point scale 1) 'not afraid at all', to 5) 'very afraid'. Total scores thus range from 15-75. Previous research has indicated scores below 32 as non-clinical.2

Procedure

Each treatment session was videotaped from the start until the end of the local anaesthesia (the needle leaving the mouth). This phase was divided into 15 second intervals and for each interval the observers coded the occurrence of the five pain related behaviours and gave a distress score on the Venham scale. After the dental injection, when the child was calm (eg after a sip of water), the dentist presented the modified VRS to the child and read aloud the standardised instructions. Next the child was asked to point out his or her level of pain on the scale. While the child was treated the parents filled out the CFSS-DS. As part of the routine in the dental clinic parents were not present during treatment.

A reliability analysis was done using 20 cases from a training-video. Results showed a good agreement between two observers (Interclass correlations: 0.98 Venham scale and 0.93 pain related behaviours). The videotapes from the study were evaluated by both observers independently and in case of disagreement a final rating was reached by joint decision.

Statistical methods

Independent t-tests (injection time, age, CFSS-DS score) and Chi2 tests (gender, experience with injection) were used for the randomisation check. Differences between the experimental and control group on a set of dependent variables were analysed using a multivariate analysis with dental anxiety as covariate. Sequential effects between the first and second treatment session were calculated using a repeated measure analysis.

Results

The study was conducted among 147 children (71 girls) aged 4-11 years (mean age 6.4 years, SD 1.7). In Table 1 the results are shown for the randomisation check. No difference was found between the participants receiving the injections with the Wand® (n = 71) and the participants receiving the injections with the traditional syringe (n = 76) regarding age, gender, dental anxiety level and earlier experience with dental anaesthesia injections. The time taken for an injection with the Wand®, however, was on average three times longer (mean 153.3 SD 33.7 seconds) than the time needed with the traditional syringe (mean 47.8 SD 22.3 seconds) (t(144) = -22.46, p <0.001).

Table 1 Randomisation check
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The mean CFSS-DS score for the total group was 30.33 (SD 11.24) and 38% (n = 53) of the children had a CFSS-DS score above 32 which means that these children suffer to some degree of dental anxiety. The mean CFSS-DS score for the highly anxious children (HAC) was 41.77 (SD 9.14) and the mean CFSS-DS score for the low anxious children (LAC) was 23.24 (SD 5.06).

Injection on the first treatment session

A multivariate analysis was done (MANCOVA) with injection technique (Wand, traditional) and level of dental anxiety (high, low) as independent variable, with mean Venham score, mean number of pain related behaviours and self reported pain score as dependent variables and location of the injection (upper or lower jaw) as covariate. The results showed no main effect for the injection technique (F(3,133) = 0.77, p = 0.51). There was no difference for the mean Venham score, the mean number of pain related behaviours or the self-reported pain score between children injected with the Wand or the traditional injection on the first treatment session. In addition, there was a significant main effect for the level of dental anxiety (F(3,133) = 6.50, p <0.001). Subsequent univariate analysis showed that in the total group highly anxious children had a higher mean Venham score (F(1,135) = 13.44, p <0.001) displayed more pain related behaviours (F(1,135) = 10.15; p = 0.002) and gave a higher self-reported pain score (F(1,135) = 1245, p = 0.001) than low anxious children (for means see Table 2). The location of the injection was not a significant covariate (F(3,133) = 1.35, p = 0.26).

Table 2 Mean and standard deviation for the mean Venham scores, mean number of pain related behaviours and self-reported pain during the first treatment session
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Injection on the second treatment session

A multivariate analysis was done (MANCOVA) with injection technique and level of dental anxiety as independent variable, with mean Venham score, mean number of pain related behaviours and self reported pain score over the second treatment session as dependent variables and location of the injection (upper or lower jaw) as covariate. The results showed no main effect for injection technique (F(3,112) = 0.46, p = 0.71) or for level of dental anxiety (F(3,112) = 1.15; p = 0.33) and location was no significant covariate (F(3,112) = 0.37, p = 0.78). Thus there was no difference for the mean Venham score, the mean number of pain related behaviours or the self-reported pain score for children injected with the Wand or the traditional injection on the second treatment session (for means see Table 3).

Table 3 Mean and standard deviation for the mean Venham scores, mean number of pain related behaviours and self-reported pain during the second treatment session
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Sequential dental visits

Subsequently three repeated measures analysis were done for: mean Venham score, mean number of pain related behaviours and self-reported pain over the first and second treatment session with injection technique and level of dental anxiety as fixed factors. The analyses for both the mean Venham score (F(1,117) = 0.33, p = 0.57) and the mean number of pain related behaviours (F(1,117) = 0.65, p = 0.42) showed no significant results. The analyses for the self reported pain showed a significant main effect for level of dental anxiety (F(1,120) = 5.26, p = 0.024); low anxious children had a significant increase in their pain report from the first (mean 2.19 SD 2.50) to the second (mean 3.43 SD 3.27) injection. No other significant effects were found.

Discussion

During the first and second treatment session no significant difference was found between the self-reported pain and distress reaction of children to an injection with the Wand® or the traditional technique. Furthermore, the level of dental anxiety was not of influence on the pain and distress response to the two injection techniques. High and low anxious children responded similarly to an injection with the Wand technique or the traditional technique. The results of the current study could not replicate the finding of our previous research where the level of dental anxiety was found to be of influence.10

When comparing the response of high and low dentally anxious children in the total group, the level of dental anxiety was found to be of influence on children's response. During the first injection highly anxious children reported more pain or displayed more distress and pain behaviour than low anxious children. The reaction of highly anxious children suggests that they lack sufficient coping strategies resulting in, eg more crying, movement and verbal protest. A study on coping strategies and dental anxiety showed that highly anxious children tend to use more behavioural (destructive) and less cognitive coping strategies.15 Highly anxious children seem to be sensitised before being referred to the paediatric dentist and exposed to the actual treatment. The same study on coping found that children who had experienced pain during a previous dental treatment had a higher level of dental anxiety than children who had not experienced pain during a previous dental treatment.15 Perhaps, more treatment sessions are necessary in order to habituate highly anxious children to a mild pain stimulus or more specific techniques are needed like teaching children how to cope with dental injections.

Furthermore, low anxious children tend to report more pain after the second injection than after the first injection. This could mean that these children get sensitised during the first treatment session perhaps as a result of underestimation of the amount pain.

A study on the pain felt after ear piercing showed children who under-predicted their pain on the first ear expected and reported significantly greater pain when the second ear was pierced in comparison with over-predictors or children who accurately predicted the pain for the first ear. It seems recommendable to encourage children to expect realistic rather than minimal amounts of pain.16

Overall, the dentists participating in this study are specialised paediatric dentists with many years of experience in delivering local anaesthesia injections. As a result, they seem to be able to do a good job with both techniques. Besides, topical anaesthesia was used before all injections so pain during needle insertion was minimal.

The injection time of the Wand® was much longer than that of the traditional method so children who are already reacting negatively to an injection seem to be longer in distress with the Wand® system.

Some limitations of the present study must be taken into account. First of all, this study is done with a referred population with a relatively large proportion of dentally anxious children, therefore, caution must be taken when generalising the results. Further studies seem necessary to analyse in more detail when the Wand technique is to be preferred over the traditional injection technique. Variables as injection site, volumes of aesthetic fluid and dental treatment could be of importance. It also seems useful to use a less anxious study population since this is found to be of great influence on children's response to a local anaesthesia injection. In addition, further studies seem necessary to get an insight into the response pattern of children on sequential dental visits.

To conclude, the current study could not clarify the divergent results found in former studies with the Wand®. It does seem that the level of dental anxiety is of greater influence on children's reaction than the injection technique. Therefore, it is of great importance to the dentist to know the level of dental anxiety of the patient in order to help them tailor their treatment to the needs of their paediatric patients.