INTRODUCTION

How well a patient adheres to the clinician's wear-time prescription is essential to the success of orthodontic treatment with removable appliances.^1,2 This statement holds true of the active phase of treatment and the subsequent retention phase. The wear-time requirements reported in the literature are standard protocols, which were defined by clinicians empirically. Some of these standard protocols for removable appliances vary greatly, ranging from strictly overnight use to almost 24 hours a day.^3–7 Many patients will not properly adhere to their clinician's instructions for wear times, cleaning, maintenance, and/or activation of removable appliances, and similar considerations apply to the requirements for inter- or intramaxillary elastics during fixed treatment.⁸ Given the substantial number of those not adhering to their wear-time prescription, numerous studies have been conducted to identify patient-level parameters that affect compliance.^9–15

Expectations are that compliance can be optimized by encouraging patients to select their own preferred color(s) and inlay motifs for their dental appliances. Even a commercial smartphone app for dental appliances has been introduced, allowing patients to configure their own removable appliances from an assortment of 14 colors, six glitter effects, and 38 inlay motifs.¹⁶ Yet no objective evidence has ever been provided that these hopes for better cooperation are actually justified.

Compliance research used to be hampered until recently by a total lack of objective measuring techniques, so that indirect methods were used exclusively. Meanwhile, this situation has changed with the recent introduction of a microsensor (TheraMon) that allows wear times to be routinely tracked without causing any complications.^17,18 Thus, electronic wear-time tracking can be used to investigate, for the first time, how custom-colored appliances would affect patient compliance. The goal was to document and statistically analyze wear times and wear behavior during the active phase of treatment with colored removable appliances that featured a built-in sensor, factoring in patient-related parameters (age and gender) and appliance type.

MATERIALS AND METHODS

Color Selection and Appliance Fabrication

Each patient was able to choose from 11 different colors for their appliances, ranging from traditional to more trendy with “disco glitter” effects. Once selected, the same color was used throughout the 90-day study period. Table 1 shows how similar colors were pooled into six basic groups (black, blue, green, yellow, pink, red). The neon colors were pooled with their basic colors, so that the yellow group, for example, included neon yellow, yellow, and orange. Figure 1a shows a functional appliance fabricated in neon green, which was a popular choice among the patients (also note the incorporated wear-time sensor). Alternatively, it was also possible for the patients to have multicolored appliances created by combining two to four single colors. Figure 1b shows a functional appliance for which two single colors were combined. All multicolored appliances were pooled into a single group in its own right. An additional option was to incorporate glitter particles into the appliances (these were not considered in the analysis). All appliances were created using a two-component cold-curing resin (Orthocryl, Dentaurum, Ispringen, Germany) suitable for the “salt-and-pepper” and the “doughing” technique.

Table 1 Selectable Colors and Pooled Color Groups for Analysis

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Data Preparation and Statistical Analysis

Wear times were evaluated in TheraMon software for Microsoft Windows (version 2.1.0.13) by viewing patient-based graphs of daily wear hours, mean wear time over the selected period, and median wear time determined in previous studies (9.0–9.7 hours).^14,20 For each patient, the daily wear time estimated from the regression at 45 days was used. For complete records, this is the mean wear time; regression imputes for missing data and additional estimate of the change of wear time within the study interval. Patients were defined as “continuous” or “discontinuous” users based on having worn their appliances on ≥96% or ≤95% of all treatment days, respectively (Figure 2a,b). Those having worn their appliances for a median of <6 h/d were defined as “noncompliers” (Figure 2c). The patient data were manually categorized in the TheraMon software and cross-checked in a spreadsheet (Microsoft Excel) that included, for each patient, pseudonymized personal data, wear-time data, color of appliance, and type of appliance. The patient data were transferred from a TheraMon database backup to a SQL server database, and R statistical software²¹ and SQL scripts were used. Wear-time differences between color groups were analyzed by pairwise t tests and Tukey correction for multiple comparisons with the “multcomp” package.²²

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RESULTS

Patient Demographics

Figure 3 illustrates the age and gender distribution of the included patients. While the boys were apparently somewhat older than the girls at the outset of treatment, this difference was not statistically significant.

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Patient-Selected Colors

This study shows that 63% of children aged 4 to 14 years preferred single colors and only 37% multiple colors for their appliances. Glitter effects selected by 18 patients could not be considered in the statistical analysis and hence should be regarded merely as a trend. None of the patients opted for uncolored appliances. Table 2 discloses how the analyzed color groups were related to age, gender, and appliance type. Single colors of the blue group were selected by 26 patients, thus being the most prevalent choice. Older boys (11–14 years) more than younger children and girls preferred blue colors. Appliance type (plate or functional) played a minor role in this preference for blue colors. Single colors of the yellow and green groups were, more or less regardless of age, chosen by similar numbers of patients overall, even though green colors were considerably more popular among the boys. Pink, defined as a separate color group, was the preferred choice by younger girls (4–10 years) but was not favored by any boys. Two older (11–14 years) boys were the only patients to select black, so that this color was excluded from further analysis.

Table 2 Distribution of Patient-Selected Colors for Removable Appliances Related to Age, Gender, and Appliance Type

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Color-Related Wear Times

Median wear times

Figure 4 illustrates the median wear times per patient per day plotted against age. Note the wide dispersion of these median values. Hence, despite the fact that all patients had freely selected the color of their removable appliances, the wear times ranged all the way from overcompliance to noncompliance. Only a few patients, however, actually heeded the prescribed wear time of 12 to 16 hours, and fewer still exceeded this prescription. A considerable minority wore their appliances <6 h/d and were, by this definition, classified as noncompliers. As apparent from Table 3, most patients wore their appliances for a median of 9.2–11.2 h/d based on the various color groups. The two boys who had selected black wore their appliances for only ≈50% of the prescribed wear time (6.1 hours instead of 12), which bordered on noncompliance. The best median wear times (≈11 h/d) were recorded for 39 patients who had chosen a green or blue single color, accounting for one-third of the total sample (n = 117), with older (11–14 years) boys being the largest subgroup. The poorest median wear times (≈9 h/d) were recorded for the patients in the pink and red groups, with younger (4–10 years) girls being the largest subgroup. These differences did not imply any significant effects of color selection on wear times.

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Table 3 Patient-Selected Colors as Reflected in Wear Times and Wear Behavior^a

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Trends during treatment

Among the boys, the median wear times were initially better and then decreased as the treatment proceeded; this downward trend was more notable with single color than with multicolored appliances. Conversely, the median wear times in the pink and red groups were initially poorer and improved into the treatment. Figure 4 illustrates the finding of an age-related deterioration of wear times, which is consistent with previous studies.

Color-Related Wear Behavior

Noncompliers

Table 3 summarizes findings of wear behavior, which were quantified in addition to the daily wear times through microelectronic tracking of each patient. Noncompliers were defined as wearing their appliances for a median of <6 h/d, which applied to 8%–33% of patients in the various color groups. These percentages of noncompliers were especially high in the red (33%) and yellow (27%) and especially low in the green (8%) and blue (12%) groups.

Continuous vs discontinuous users

This additional distinction in wear behavior was made after excluding the noncompliers. In the various color groups, 83%–91% of these patients had worn their appliances continuously (on ≥96% of treatment days), whereas 9%–17% had worn their appliances discontinuously (on ≤95% of treatment days). Continuous users accounted for 91% of patients in the yellow, for 87% in the blue, for 86% in the pink and multicolored, and for 83% in the green and red groups. According to the statistical analysis, however, color selection did not make a significant difference in continuous vs discontinuous wear behavior.

Trends during treatment

In addition to changes in the patients' wear times as such, their wear behavior was also found to change as the treatment proceeded. Figure 5 illustrates, based on two examples of continuous users who had both selected blue for their appliances, how the median wear times might increase (left) or decrease (right) on a case-by-case basis during the observation period. Similar observations were made with discontinuous users. While changes in wear times were very commonly recorded over the observation period, changes in wear behavior were less frequent.

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DISCUSSION

While numerous findings have been reported regarding patient compliance over the years, the vast majority of these have exclusively been based on empirical data. Investigations into patients' wear times and wear behavior in particular have, with very few exceptions, lacked a technological basis for objective experimental measurements.²³ Against this background, and even though colored appliances have been commercially available for years and are routinely used in clinical practice, what the color of a removable appliance can do for patient compliance has always remained an open question.

The present study revealed that, in descending order of popularity, the patients favored multicolored followed by blue, yellow, green, red, pink, and black single-color appliances. Color selection did not, however, significantly differ by age or gender. This ranking of preferred colors for appliances clearly differs from the results of an early empirical study on the same topic published half a century ago.²⁴ At that time, red was considered the most desirable color, followed by blue, yellow, and green. Hence, these color decisions are driven not so much by personality structures as by current trends. By deciding self-reliantly on the color of their removable appliances, the young patients are taking an important first step toward accepting their treatment. Because only colorful appliances with patient-selected colors are used where the study was conducted, a control group receiving a prescribed “standard” color appliance was not possible, which could be one of the limitations of the study. For future studies, however, it would be helpful to form an “uncolored appliances” control group.

This study does not confirm the assumption that self-reliant color selection may boost young patients' willingness to wear their appliances. Most of the patients did not adhere to the prescribed wear schedule of 12–16 hours a day. They all used appliances featuring their preferred color, and yet there were distinct differences in compliance, as reflected by wear times and wear behavior. The median wear time determined (10.25 hours, with an interquartile range of 7.9 to 11.8 hours) was slightly higher compared with previously reported median values of 7.75,²⁵ 7.9,²⁶ 9,^20,27, 9.5,²⁸ or 9.7¹⁴ hours. Continuous and discontinuous users, but also noncompliers, were noted in all color groups and even across appliances of exactly the same color. All patients knew that their wear time was tracked with a microsensor. However, the impact of this awareness on patients' compliance is controversially discussed in the literature.²⁶ Recent investigations have shown that treatment of noncompliers who wear their appliance for less than 6 hours a day will meet with little, if any, success.²⁵

The patient-selected coloring of appliances in this study did not prevent noncompliance and did not demonstrably modify any increases or decreases in wear times seen during the observation period. Neither did the colored appliances reverse the general trend for wear times to decrease as the treatment proceeded. However, none of the observed differences in wear times and wear behavior were statistically significant, with the only exception being a significant age-related decrease in median wear times. Multicolored appliances did not promote compliance in a way that would justify their more extensive laboratory requirements and higher cost compared with single-color appliances.

Compliance with wearing removable appliances is known to be a function of complex interactions between competing beneficial and adverse parameters. Hence, appliances fabricated in patient-selected colors should be regarded as just another parameter, which, although not essential to compliance, will be mildly conducive, similar to rewarding compliance with little gifts.²⁹ Much stronger effects should be expected from factors such as personalizing the wear-time prescription, the duration of treatment, or the patient's stage of life, personality structure, and familial/social environment. Compliance is, for that matter, determined to a large extent by the clinician-patient relationship. Studies have indicated that this relationship and the place of treatment will make a much greater difference to compliance than a patient's color preference for appliances.^14,15

CONCLUSIONS

• It is not possible to guess or predict compliance based on a patient's color preference for appliances, nor does the color preference make a statistically significant difference to wear times or wear behavior over the course of treatment.

• As a general rule, the colored appliances are worn for a median of 9–11 h/d. Colored appliances cannot ensure the success of treatment; treatment success is put at risk by noncompliers. Similar median wear times are achieved by continuous and discontinuous wearing of appliances.