Perception of Pain Intensity and Quality in Patients Treated with Conventional Fixed Orthodontic Appliances Versus Clear Removable Aligners: A Pilot Study

1.1. Background

According to the International Association for the Study of Pain, pain is defined as “an unpleasant sensory and emotional experience associated with, or resembling, actual or potential tissue damage” [1]. Pain is frequently associated with dental care, with orthodontics being one of the procedures known to aggravate lingering pain and discomfort that may last for days or weeks [2, 3]. Regardless of the techniques and modalities used, most studies have shown that the majority of patients report peaking pain and discomfort during the first few days after orthodontic adjustment visits [2, 3]. Pain has also been reported as a dominating reason for orthodontic treatment discouragement and non-compliance [4].

Orthodontic appliances, either fixed or removable, represent foreign objects introduced to a physiologically and neurologically sensitive area of the body [5]. The mechanisms whereby the application of orthodontic forces causes pain are still not fully understood. However, these two interrelated and dependent biological events are outcomes of a cascade of self-limiting inflammatory, vascular, neural, cellular, and immunological reactions that act in an orchestrated manner [6]. It is important to bear in mind that the association between the orthodontic force being applied and the subsequent pain is not proportionally correlated [7]. This reflects the complexity and multidimensionality of pain perception that can be influenced by several factors, such as fear, culture, and past experience [8-10].

Shape memory polymers, used in the removable aligners, are innovative contemporary materials with the capacity to have their shape modified by external stimuli while maintaining the ability to revert back to their original forms. This emerging technology has been widely utilized in the field of medicine, including regenerative medicine, neuro medicine, orthopedics, and drug delivery systems, given their biocompatibility with human tissues, biodegradability, cost-effectiveness, and ease of fabri- cation. With the increased demand for aesthetic orthodontic appliances nowadays, the use of clear removable aligners has gained great popularity. Despite the minor oral constraint reported by patients (i.e., slight and temporary speech and swallowing difficulties), clear removable aligners are deemed aesthetic and non-restrictive for patients’ diet and oral hygiene practice [11]. Regardless, investigations providing a head-to-head comparison of pain perception between patients receiving conventional fixed orthodontic appliances and clear removable aligners using validated and reliable pain inventories remain scarce.

1.2. The Validated Arabic Version of the Short-form McGill Pain Questionnaire

The McGill Pain Questionnaire (MPQ), developed and published by Melzack in 1975, has revolutionized pain research [12]. It upgraded pain investigations from being limited to measuring pain intensity and included multi- dimensional pain descriptors to illustrate sensory, affective, and evaluative qualities of the pain experience. The modified short-form MPQ (SF-MPQ) is a shorter version of the original MPQ that was developed later to evaluate the sensory and affective qualities of pain [13]. Iwasakia et al. validated the use of MPQ in measuring orthodontic pain by modifying the original form [13]. Fifteen descriptors with 4-point Likert severity response scale (i.e., no pain, mild, moderate, severe) were incorporated, and the pain perception was quantified by the total score of those 15 descriptors. Only 11 descriptors of the 15 descriptors were discriminating for orthodontics (i.e., pressure, aching, throbbing, tight, strange, pulling, uncomfortable, sore, frustrating, annoying, miserable). Satpal S. Sandhu et al. confirmed the two-factor structure of the SF-MPQ, as proposed by Iwasaki et al. 2013 [13]. Hence, two dimensions, the sensory and affective model of the SF-MPQ, seem to be the most appropriate and informative in assessing orthodontic pain [14].

The Arabic version of the SF-MPQ was developed and validated by Terkawi et al. [15]. A two-stage systematic translation process was undertaken. A backward trans- lation back to the English language was accom- plished and validated against the original SF-MPQ to ensure that the translated Arabic questionnaire reflected the same item content as the original English questionnaire. For all translators (English and Arabic), the source language of the questionnaire was their mother tongue, and they were totally unaware of the concepts being explored in the SF-MPQ.

1.3. Aims of the Investigation

This investigation aimed to provide a head-to-head comparison of the perception of pain intensity using the validated Arabic version of the modified SF-MPQ in patients treated with fixed orthodontic appliances and those treated with clear removable aligners. The secondary aim was to investigate the pattern and quantity of analgesics use immediately after orthodontic adjust- ment visits and correlate this with the intensity and quality of the perceived pain.

2.1. Ethical Considerations

Ethical review was conducted in accordance with the Declaration of Helsinki [16] and approved by the King Abdul Aziz University Faculty of Dentistry Research Ethical Committee (Proposal #183-12-20; Approval #4263833; Date: January 17, 2021). The pain question- naire was accompanied by a cover letter to explain the purpose of the investigation to the participants, reassure respondents of the confidentiality of their responses and obtain their informed consent. Participation in the study was voluntary, and a consent form was obtained from all participants prior to accessing the pain questionnaire.

2.2. Participant Recruitment

This is a prospective observational investigation comparing self-reported pain intensity and pain quality by patients receiving conventional fixed orthodontic appliances versus clear removable aligners. Study parti- cipants were recruited from the Department of Orthodontics at the University and from the orthodontics practice at one private clinic. Patients were identified through the CPT codes registered in the electronic billing system and the electronic medical charts of the identified patients were reviewed to confirm their potential eligibility to be considered in the study. The study team personally approached all participants once they arrived at their orthodontics visits. The investigation details were provided to the participants and their permissions for voluntary enrollment were obtained.

2.3. Inclusion and Exclusion Criteria

The inclusion criteria of the subjects were 1) patients currently undergoing orthodontic treatment, 2) patients aged 15-65 years old, and 3) patients with no previous orthodontic therapy. Exclusion criteria included 1) patients with a history of clinically confirmed neurological, rheumatological, or psychological disorders (per physi cian’s report), 2) patients with preexisting chronic orofa cial pain condition (either odontogenic or non-odonto genic), 3) patients on continuous analgesic, steroid, or neurological therapies, and 4) patients who were unable to read, understand and/or fill out the modified SF-MPQ.

2.4. Study Design and Data Collection

Participants in this investigation were divided into two comparison groups: Group 1 (G1), defined as patients treated with fixed orthodontic appliances, and Group 2 (G2), defined as patients treated with clear removable aligners. For the sake of standardization, all removable aligners were constructed by Invisalign^®. The web link for the pain questionnaire was sent to the participants’ mobile devices twice, once at baseline (i.e., at the beginning of the adjustment orthodontic visit before changing the wires, in the conventional fixed appliances group, or switching to a new tray, in the removable clear aligners group) and once at 24-hour post-adjustment visit to collect follow up data. Study identification numbers were provided for each participant to link the answers of both the baseline and the post-adjustment visit SF-MPQ.

Demographic data, including participants’ gender, age, and level of education, were collected. The modified SF-MPQ included three components 1) an 11-point Numeric Pain Rating scale (NPRS) to measure current pain intensity, 2) a measure of severity for 10 qualitative pain descriptors (i.e., pulsating pain, electrical pain, stabbing pain, sharp pain, pressure pain, bite, and touch pain, exhausting pain, disgusting pain, scary pain, and miserable pain) reported on NRS as zero= no pain, 1-3= mild, 4-6= moderate, or 7-10= severe, 3) Present Pain Index (PPI) to determine the overall pain severity over the past 24 hours (reported as “no pain”, “mild”, “discom- forting”, “distressing”, “horrible”, “excruciating”), and 4) history of analgesic medications used (i.e., type and frequency).

However, contraction pain in SF-MPQ is not related to orthodontic pain, so it was eliminated from this study.

2.5. Study Outcomes

The primary outcomes included: 1) changes in pain intensity defined as mean difference of the NPRS score (ΔNPRS) from baseline to 24-hours post-adjustment, 2) changes in the frequency of reported severity of the 10 qualitative pain descriptors (i.e., no pain, mild, moderate, severe) from baseline to 24-hours post-adjustment, and 3) changes in the frequency of reported overall PPI over the past 24 hours (no pain, mild, discomforting, distressing, horrible, excruciating,). The secondary outcome was the difference between the two groups in the types and frequency of analgesics used post-adjustment visits.

2.6. Statistical Analysis

Standard descriptive statistics included means and standard deviations as well as frequencies for the measured variables. The bivariate analysis included a t-test and a Chi-square test. Data were analyzed using IBM SPSS statistical software (IBM Corp. Released 2011. IBM SPSS Statistics for Macintosh, Version 20.0. Armonk, NY: IBM Corp.). The significance level was set at α = 0.05.

Sample size calculation was done using G power, with a power (1- β) set at 0.90 and α=0.05 (2-tailed), determining a total sample of 172 with 86 subjects per group. Due to the availability of subjects and to ensure that we were able to detect a medium to small effect size, it was decided to go with a total sample of 200 with 100 subjects per group.

3.1. Demographic Characteristics

The total sample size was 209 subjects: 104 in G1 (fixed orthodontic appliances) and 105 in G2 (clear removable aligners). Nine subjects, 4 in G1 and 5 in G2 were lost on follow-up (i.e., they did not provide responses for the post-adjustment visit questionnaire). The mean age of the entire sample was 25 years old (SD±5.7), with 111 (55.5%) males and 89 (44.5%) females. Sixty-four (32%) had a high school degree or less, 110 (55%) had a bachelor's degree, and 26 (13%) had a master's degree or higher. Table 1 depicts the demographic characteristics of all study participants.

3.2. Reporting of Pain at Baseline

At baseline (prior to the adjustment orthodontic visit), no statistically significant difference in the NPRS was detected between G1 and G2 (p=0.19) (Table 2). Similarly, the frequency of reporting of SF-MPQ pain descriptors did not show statistically significant differences in the perception of pulsating pain, sharp pain, pain on biting and touching, exhausting pain, disgusting pain, and severe pain (Table 3). Only four of the SF-MPQ pain descriptors showed statistically significant differences in the frequency of reporting between the two groups at baseline. Higher reporting of “no pain” in electrical pain, stabbing pain, and scary pain descriptors was detected in G2, while the reporting of “no pain” in the pressure pain descriptor was more significant in G1. Adversely, the reporting of mild or moderate pain was higher in G1 for electrical, stabbing, and scary pains, while pressure pain was significantly more frequent in G2 [electrical pain (p= 0.005), stabbing pain (p=0.03), pressure pain (p=0.006), and scary pain (p=0.035)] (Table 3). There were no statistically significant differences in the frequency of the overall PPI severity between the two groups (Table 4).

3.3. Reporting of Pain at 24-hour Post-orthodontic Adjustment Visit

The mean NPRS values at 24-hour post-adjustment orthodontic visit showed significantly higher pain intensity in G1 (3.87±1.93) compared to G2 (2.09±1.84) (p<0.0001). Comparing the mean change in NPRS from baseline and post-adjustment visit (ΔNPRS) demonstrated a statistically significant difference between G1 (3.15±2.47) and G2 (1.58±1.74) (p<0.0001) (Table 2).

There was a statistically significant difference in the frequency of SF-MPQ pain descriptors reporting between G1 and G2, with more pain associated with G1. The frequency of reporting mild to moderate pulsating pain, electric pain, stabbing pain, sharp pain, and severe pain were significantly higher in G1 compared to G2 (p<0.0001). Similarly, bite and touch pain, exhausting pain, and disgusting pain were significantly higher in G1 compared to G2 (p=0.001, p= 0.004, p <0.0001, respectively). Conversely, there were no statistically significant differences between the two groups in the perception of pressure pain (p=0.160) (Table 3).

In regard to the overall PPI, no pain was reported in 6% in G1 versus 29% in G2. Similarly, mild overall pain was reported in 44% of G1 compared to 55% in G2. On the other hand, 33% in G1 versus 10% in G2 described the pain as discomforting, 10% in G1 versus 7% in G2 described the pain as distressing, and 7% in G1 versus only 1% in G2 described the pain as horrible. None of the participants in the two groups described the pain as excruciating (Table 4).

3.4. History of Pain Medication Intake

Analgesic medications were categorized into two groups: paracetamol and NSAIDs. Before the orthodontic adjustment visit, only 2 participants in G1 reported taking pain medications prior to the orthodontic adjustment visit (one paracetamol and one NSAID). At the 24-hour post-adjustment visit, 34 participants in G1 and only 8 participants in G2 reported the use of analgesic medications (p<0.0001). The type of analgesics and frequency of intake are detailed in Table 5.