The patient’s side: Willingness-To-Pay index for computerized anesthesia

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Dino Re, Sabrine Fessi*, Gabriele Augusti, Davide Augusti | Department of Oral Rehabilitation, Istituto Stomatologico Italiano, University of Milan, Italy
*Riyadh Colleges of Dentistry & Pharmacy, Riyadh, Kingdom of Saudi Arabia



Best protocols and techniques for improving dental anesthesia need to be elucidated. The objectives of this study were to evaluate, through a visual analog scale (VAS), pain levels and discomfort produced by a computer-controlled local anesthesia delivery and evaluate the willingness to pay (WTP) values of a patients’ population interested in this technology.

Materials and methods

A group of 50 adult patients undergoing dental restorative procedures, and previously treated with a conventional anesthesia infiltration technique, were recruited for this study. For all subjects a computerized injection technique (The Wand® STA; Milestone Scientific Inc.) was used before starting clinical treatments by the same investigator. The sensation of pain during injection was scored by VAS scale; WTP data were collected through an individually delivered questionnaire. VAS and WTP values, associations with socio-demographic parameters (Mann-Whitney and Kruskal-Wallis tests) and potential correlations between variables (chi-square test in contingency tables) were revealed by statistical analysis.


Minimal discomfort was reported using the tested device (overall VAS mean value: 1.6 ± 2.2). A trend towards higher VAS levels was found in the lower arch (1.8 ± 2.5) with respect to the upper arch (1.3 ± 1.8) (p=0,4); 58% of the subjects were willing to pay an additional fee to receive a minimally-invasive anesthesia (median WTP value of 20€); patients who strictly followed recall programs (every 3 months) allocated superior amounts of money to the selected technique for pain control.


Considering the previous experiences of the population treated with conventional local anesthesia, the computer-based device tested demonstrated low pain ratings during injection procedures. More than half of the patients were willing to pay an additional fee to receive local anesthesia using a computer-controlled device.

Keywords: Additional fee, Computerized device, Dental anesthesia, Pain, Willingness-to-pay.


The successful management of pain during dental procedures has always been a challenge in everyday practice; computer-controlled delivery of local anesthetics might substitute traditional injection techniques in a variety of clinical scenarios. For example, intra-ligamental computerized local anesthesia was found to be as effective as a traditional block of the inferior alveolar nerve for several endodontic therapies (1-4). Computerized injection techniques have also been effective during dento-alveolar surgery, like exposure and extraction of palatally impacted canines (5). From the patient’s perspective, a number of studies have reported low levels of anxiety and pain perception (during both needle insertion and delivery) with the aid of computerized devices (4, 6, 7).
In the last years, the validation of new medical approaches or technologies should take into consideration the patient’s domain (8); in other words, the overall assessment of a treatment would be incomplete if only the strictly clinical biological/physiological outcomes or numerical data regarding its efficacy/success were analyzed; asking what are the expectations of patients, their degree of acceptance and satisfaction with different modalities for pain control would allow a better understanding of the effectiveness of our therapies and their impact on patients’ oral health and well-being in a broad sense (9). From a methodological point of view, in order to better understand subjects’ inclinations toward new injection techniques and/or devices, patients could be invited to indicate how much money they would be willing to pay to undergo a specific procedure, thus receiving the benefits or otherwise avoiding the negative effects of a clinical condition. The variable Willingness To Pay (also known as WTP index) expresses the strength/magnitude of preference for treatment, or the economic value that the patients assigned to its benefits and the maximum amount of money they are willing to spend (10). In medicine, WTP is a well-established index and it has been used to evaluate pharmacological therapies (like administration of anticoagulants in cardiovascular diseases) (11), interventions for lifestyle modifications in subjects affected by diabetes mellitus (12) or recovery programs in cases of drug abuse (13). WTP has also been applied extensively to evaluate the preference of patients for treatments indicated in infective (HIV) (14) or neoplastic diseases (pulmonary malignancy) (15). The measurement of patient preferences by WTP index might be helpful when dealing with decisions in health economics (16).
The aim of this study was to evaluate the impact of a computer-controlled device for dental anesthesia on a population of adult patients; in particular, the main objective was to analyze the strength of preference, expressed according to the WTP method, against an alternative technique for delivering anesthetic injections. At the same time, discomfort levels produced by the automatic device were recorded and correlated to socio-demographic variables.


Materials and methods

  1. Fifty patients attending a private dental clinic were recruited for this study; the sample comprised 25 men and 25 women (age range: 18-73 years). The purposes of our investigation were explained to the participants; informed consent and approval were obtained. The inclusion criteria were good general health (ASA I-II), having received a local, traditional, intra-oral anesthetic injection less than 6 months earler; patients requiring an entire nerve block (i.e: inferior alveolar nerve block) as a last procedure for pain control were excluded. Moreover, systemic diseases or medications directly or indirectly affecting the neurological condition or altering pain perceptions led to exclusion of the subject from the study. The injections and delivery of anesthetic solutions using the tested computerized technology (The Wand®, Milestone scientific Inc., Livingstone, USA) were always performed by the same dentist, who had extensive previous experience with the device. Manufacturer’s recommendations and materials were followed to obtain proper pain control.
    Briefly, for all cases, a single-tooth intraligamental (or periodontal ligament) anesthesia was delivered with needle (STA® Bonded Handpiece, Milestone scientific Inc.; 30 Gauge, ½ inch needle size) insertions at two sites of the interested tooth (mesial and distal line-angles). Penetration along the gingival sulcus and advancement to the periodontal ligament were carried out keeping the bevel of the needle towards the root surfaces, at an approximate 30-45° angulation. Flow rates and pressures of injection were guided and controlled by the device itself. Fifteen minutes after administration of the anesthetic solution, and just before starting the planned dental treatment, a two-parts questionnaire-delivered survey was carried out. The first part of the survey was to be filled by the dentist with technical data regarding treatment: involved tooth, type of procedure, drug for anesthesia and number of dental carpules used. The second part was aimed to the patient: personal information including name, age, gender, level of education and income range, as well as details about oral hygiene were recorded. Finally, patients were asked the following.
    1) To objectively evaluate the perceived discomfort through a pain VAS scale (0-10).
    2) To qualitatively specify their feelings about the computerized injection technique when compared to the last traditional injection they had received (“I have felt more-same-less discomfort than the last time”).
    3) To determine the maximum amount of money they would be willing to pay to receive a computer-mediated anesthetic technique. The WTP questions were framed in the form of a bidding game (or system of the offer) (8): starting from a basis of 10€, each patient was invited to raise or drop the price to 10€ currency units. Minimum and maximum economic limits were set corresponding to 0€ and 50€, respectively. For each new figure given, an increase or reduction in price was offered to determine the expenditure deemed appropriate by the patient.
    The study population was subjected to descriptive statistical analysis using a professional software (SPSS Statistics 19, IBM Corp.). The median WTP values, expressed in euros, were calculated in relation to socio-demographic parameters. Variations of WTP values associated with categorical variables were analyzed using the Mann–Whitney U-test (dummy variables) and Kruskal–Wallis (multiple variables). Medians were also calculated for the obtained VAS scores and their potential associations with clinical (i.e: upper/lower arch, tooth type) or patient-related variables were assessed (Mann-Whitney U-test).



The demographic profile of the respondents is provided in Table 1; the participants exhibited good attitudes towards oral health, declaring to visit their dentist regularly (90% of check-ups every 6-12 months).

Table 1 Demographic and clinical profile of the participants (n=50)

Most of the patients received computer-controlled anesthesia in order to accomplish an operative dentistry procedure: in most cases (44/50; 88%), fillings (due to dental caries) or tooth preparations for an indirect restoration (inlays/onlays; or temporary crowns) were carried out. Other cases included in-depth oral hygiene with scaling and root planing (3/50), endodontic therapy and tooth extraction (2/50).
The anesthetic of choice was Articaine®, with variable amounts of vasoconstrictor (1:100.000 or 1:200.000); one single cartridge was used for all cases, with the exception of the endodontic therapy that required an additional intrapulpar injection (one plus one cartridges).
Distribution of VAS scores is also available in Table 1; the overall mean VAS score was relatively low (1.6 ± 2.2), with values of 1.6/10 and 1.7/10 for women and men, respectively (p=0.8). While higher VAS scores were revealed before starting some specific procedures like endodontics (4.5/10) and surgery (2.4/10), no significant differences were found among treatment categories (p=0.6). Moreover, a trend towards higher VAS levels was found in the lower arch with respect to the upper arch (1.8 vs 1.3; p=0.4).
Positive feelings about the computer-delivered anesthesia were reported: 86% of participants declared less discomfort than that perceived during their last traditional procedure for pain control. 58% of patients of our sample would like to pay an additional fee for a modern anesthesia technique: in particular, a median WTP value of 20€ (first quartile: 20€; second quartile: 30€) – as an additional sum of money to the standard cost of the therapy – was found. The obtained WTP median values (25th and 75th percentiles also reported) divided in relation to the categorical variables are represented in Table 2; a specific trend was found looking at categories of dental check-ups, with higher WTP values for patients with the highest frequency of visits (3 months follow-ups programs; median WTP value of 35€).

Table 2 Willingness-To-Pay expressed in Euro (median value (25th, 75th percentiles)) for the tested computerized anesthesia


Computerized device and needle phobia

A number of studies on the origins of fear of dental treatment have been published (17-19); most of them indicated needle phobia as the primary etiological factor, potentially leading to an avoidance of care behavior. While some authors have proposed an evolutionary or genetic origin for needle phobia (20), the fear of injections frequently arises after a negative experience at a physician’s or dentist’s office. According to a study by Ost (21), 56% of subjects who have injection phobia could trace their fear back to a negative conditioning from a health care experience; moreover, 24% of the subjects could trace their phobias to having seen another child, often a sibling, experiencing a negative event (i.e painful or traumatic) associated to needles. Based on these studies, the availability of a computerized device for delivering a minimally invasive, less traumatic dental anesthesia – linked with less discomfort/pain during injection – might be extremely helpful for the prevention of needle phobia. In subjects already suffering of needle phobia, the computerized device could be a measure for re-education and desensitization through new positive exposures to dental injections.

VAS scores
Our study substantially confirmed low levels of discomfort associated with the tested technology, as we found mean VAS scores in the range of 0.1-2.4/10 (75% of cases).
For a comparison of values, McPherson et al. (6), using a 100mm VAS scale, have reported scores of 38.9-38.7mm/100mm for larger and standard-bore needles, respectively, when using traditional syringes and injection techniques for the inferior alveolar nerve block. In the same study, VAS scores of about 35mm/100mm were found for a traditional injection technique during anesthesia of the long buccal nerve (6). In our study, 86% of patients declared less discomfort than that perceived during their last traditional procedure for pain control. This result, although nearly unanimous, should be interpreted cautiously: despite a restricted interval of 6 months was selected, the recall of an event might be influenced by time elapsed and/or complex memory elaborations. A factor involved on pain during traditional anesthesia is the pressure of the liquid injected into the tissues; an extremely slow, drop-by-drop, computer-controlled release of anesthetic solution might reduce discomfort associated with stretching of soft tissues. According to Nusstein et al. (7), significantly more pain was found for solution deposition with a conventional syringe (42% on a Heft-Parker VAS scale) than that produced by the Wand Plus® injection technique (25%), for anterior middle superior alveolar anesthesia (AMSA). The type of dental procedure to be carried out should not have direct influence on pain sensation at injection sites; however, we recorded higher VAS scores in patients undergoing dento-alveolar surgery (extraction) or endodontics. A possible explanation is that increased levels of anxiety or stress might also increase pain thresholds in these specific patients.

WTP values and factors of influence
More than half (58%) of the studied population agreed to pay an additional sum of money (median WTP value of 20€) for the minimally invasive anesthesia; this result might further confirm acceptance of the patients and the positive, direct experience with the proposed form of pain control. Subjects demonstrating no concerns for an additional fee might have also recognized the technological value of the computerized device or the additional training/skills of the dentist related to the learning curve with a modern, non-traditional device. In a different study on WTP index regarding prosthetic restorations in the single-tooth gap (8), the authors found positive, significant association of WTP values with the importance assigned by the patients to oral care. In the current study a similar trend was found. In fact, patients who strictly followed recall programs and check-ups (every 3 months) would allocate a higher amount of money to receive the computerized anesthesia. It is reasonable to think that people who really take care and have a positive attitude about their oral health are more willing to accept new pain control technologies, especially after having experienced them.
As stated by Locker at al., the first barrier to treatment, although this is of proven effectiveness in restoring oral health and well-being, could be represented precisely by a high economic cost (22). A number of patients refused to address additional money to the cost of the therapy (in order to get the computerized anesthesia), despite our initial offer was set to a small amount of 10€; in our analysis the income variable was not related to WTP values, but a larger sample might have detected a different association. Reasonably, patients that fall in groups with high or low economic possibilities are able to invest higher or lower amounts of money, respectively, for the treatment they pursued.

Limitations of the study
More patients should be enrolled in future studies to further evaluate their feelings and clinical responses to the computerized device; moreover, correlations between anxiety/stress levels along with the psychological status of the patients and pain perception at injection sites should be explored. Finally, the best approach for WTP elicitation (23), the proper amount of information that should be provided to participants about the tested technology (comprehensiveness of the scenario), or the potential influence of psychological variables on recorded WTP values are interesting topics that should be deeply investigated.

Within the limitations of this study, the computer-based device tested demonstrated low pain ratings during single-tooth anesthesia used for several dental clinical treatments and applied to different areas of the mouth; most of the participants (86%) declared less perceived discomfort with respect to their last traditional procedure for pain control.
More than half of the patients were willing to pay an additional fee (median WTP value of 20€) to receive minimally-invasive local anesthesia.

Study financing
The Authors declare that they have not received funding for the present study.
Conflict of interest
The Authors declare that they have no conflict of interest.


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