Keywords

1 Introduction

Orthodontic field goes continuously towards innovation and well-being. Among the possible research directions, that to UX concerns can take an important role in developing innovative devices from the designers, engineers, dentists, dental technicians and patients’ points of view. Our research group, composed by heterogeneous competencies ranging from conceptual design to orthodontics, rapid prototyping and UX design/evaluation, developed a functional orthodontic appliance for the correction of skeletal class II malocclusions.

UX concerns spread over the whole development process; nevertheless, this paper focuses on two phases: the data collection before starting the development and the evaluation of the design results. The UX concerns developed through the involvement of the Quality Function Deployment and the irMMs-based UX evaluation method 2.0, including the meQUE questionnaire 2.0.

Data collection highlighted customers’ requirements that, in turn, allowed leading the design effort towards the correct goals and performing at best the benchmark of existing functional orthodontic appliances. The evaluation of the design results verified the achievement of the goals and gave suggestions for possible improvements.

The paper runs as follows. The background section contains an overview on functional orthodontic appliances, as well as the description of the Quality Function Deployment method and of the irMMs-based UX evaluation method 2.0. The research activities section describes the two phases this work focuses on. The discussion section reasons about the results of the product evaluation and the conclusions close the paper, together with some perspectives for future work.

2 Background

2.1 Functional Orthodontic Appliances

Functional orthodontic appliances are devices used to correct malocclusions [1, 2]. These devices control and modify opening-closing patterns to adapt condyle shapes. They are placed inside the mouth; the therapy usually lasts from six months to two years. Among the different types of malocclusions defined by E. Angle [2], class II malocclusion is a deviation - either aesthetic, functional or both, from the ideal occlusion (mandible retruded respect to the maxilla).

It is acknowledged that the main issue for good medical results with these devices is the patient’s compliance, especially because the treatment takes place with children [2]. Therefore, these devices are classified into non-compliance and compliance [1,2,3]. The first ones refer directly to fixed devices, usually cemented on the patients’ teeth, all of this forcing full-time wear during therapy; the second ones refer to removable devices, more comfortable because they can be taken out while eating, etc.

Different kinds of devices exist, from Herbst [4] to MARA [5], Jasper Jumper [6], Forsus [1], Twin Block [7], Bionator and Frankel [2, 3]. Herbst and Twin Block are the most used as fixed and removable devices, respectively. Figure 1 depicts them.

Fig. 1.
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The most used fixed and removable devices: Herbst (a) and Twin Block (b).

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Herbst is a bilateral joint with a telescopic mechanism usually welded to orthodontic bands. Twin Block is a bilateral joint as well; it consists of acrylic inclined blocks. The other kinds of devices are redesigns aimed at resolving the drawbacks reported by these two main devices like the fact that size and shape can cause lack of compliance with patients and can make sores in the soft tissues of the mouth, hygiene can be affected due to plaque accumulation, positioning/removal procedures can be difficult and/or hurting and that most of the times the treatment effectiveness is quite moot [2, 8,9,10].

2.2 Quality Function Deployment

Quality Function Deployment (QFD) is a well-known method to understand the design problem and collect and organize data for the design process [11]. The method consists of a series of steps to translate qualitative information, the customers’ requirements, into quantitative parameters, the engineering requirements. The House of Quality (HoQ) data structure collects the data and makes them easily accessible to the downstream design phases. The HoQ is suitable for systematic design and can work in synergy with other design tools such like morphology and TRIZ [12, 13].

At the beginning, data about users and about products similar to the one under development are collected, evaluated and rated. The identification of the customers represents the first step. Then, customers’ requirements are described, translated into design requirements and evaluated through questionnaires. Meanwhile, a competitors’ benchmarking is performed; existing products are identified and evaluated against the requirements in order to highlight satisfaction degrees. The results of these evaluations allow focusing on the most interesting competitors’ product solutions and ranking the design requirements to distribute the design efforts as effectively as possible. It is worth to say that UX concerns are getting more and more importance among the customers’ requirements.

2.3 IrMMs-Based UX Evaluation Method 2.0

The irMMs-based UX evaluation method 2.0 (irMMs method, hereafter) quantifies the UX of products [14]. The core of the irMMs method exploits interaction related Mental Models (irMMs) and evaluate the UX by comparing what is expected (before the interaction) to what is real (thanks to the interaction). The irMMs method reached the release 2.0 thanks to the addition of the meQUE questionnaire 2.0.

The irMMs are cognitive processes that users generate in their mind before to act in order to satisfy a specific need in a specific situation of interaction. They consist of lists of users’ meanings and emotions, including users and products’ behaviors determined by these meanings and emotions [15]. The generation of an irMM develops through five steps, based on the Norman’s model of the seven stages of the action cycle [16].

The adoption of the irMMs method happens through user tests. Users generate their irMMs respect to a specific need to satisfy and compare these irMMs to the real interaction with the product. The adoption generates two lists of positive and negative UX aspects that describe the strong points and the criticalities of the experience, respectively. More specifically, the irMMs method consists of three sections that differ in the knowledge about the product of the users who undergo the tests. The first section considers users who do not know the product at all; they generate their irMMs based on previous experiences with different products only. This is the absolute beginners (AB) section. The second section considers again users who do not know the product; nevertheless, before the generation of the irMMs (and before to know the need to satisfy) they are allowed to interact freely with the product for some time. This is the relative beginners (RB) section. Finally, the third section considers users who already know the product. This is the relative experts (RE) section. Figure 2 summarizes the four phases of the irMMs method adoption: input setting, material and environment setup, test execution and data analysis. The tests for the three sections can run in parallel, providing that no influences among them happen in the meantime.

Fig. 2.
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The irMMs method adoption.

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As soon as the tests come to the end, the evaluators generate the UX aspects thanks to some precise rules [14]. After that, the evaluators classify the UX aspects against the interaction topics they refer to (specific procedures, product components, etc.) and, for each topic, they split the UX aspects t into positive and negative and order them against the number of occurrences and the impact. If an UX aspect refers to product characteristics rarely involved in the interaction, its impact will be low; on the contrary, if the UX aspect deals with core procedures determining the cognitive compatibility of the product with the users’ problem solving processes, the impact will be higher.

The irMMs method exploits the meCUE questionnaire 2.0 (meCUE, hereafter) to deepen the UX analysis from different points of view. This questionnaire provides a quantitative UX evaluation starting from the Components model of User Experience (CUE model) of Thuring and Mahlke [17]. As shown in Fig. 3 this model considers the perceptions of instrumental and non-instrumental product qualities and the emotional reactions as main components of the UX. The meQUE maps the CUE model into five modules named instrumental product qualities, non-instrumental product qualities, emotions, consequences of use and overall evaluation.

Fig. 3.
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CUE model and meCUE questionnaire.

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The integration of the meQUE in the irMMs method, proposed by Filippi and Barattin is summarized in Fig. 4 [14]. White boxes represent those activities of the irMMs method that remain as they are; four grayed boxes contain activities modified and seven grayed boxes with bold text indicate the new activities added by the integration. The integration implies changes in phase two (material and environmental setup), changes and additions in phase three (test execution) and additions in phase four (data analysis).

Fig. 4.
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The integration of the meQUE in the irMMs method [14].

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3 Research Activities

The design process considered here consisted of four stages: observation, ideation, prototyping and testing [16]; Clearly, UX concerns were present throughout. Nevertheless, this paper considers them in those two activities where they had the heaviest impact, the data collection in the observation stage - before starting the development of the device, and the evaluation of the design results - named product evaluation - in the prototyping and testing stages. The QFD and irMMs method were involved, respectively. All of this is depicted in Fig. 5.

Fig. 5.
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The two activities where UX concerns had the heaviest impact, together with the tools used to manage them.

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The description of the two activities occurs in the following.

3.1 Data Collection

The QFD analysis considered three kinds of customers, differently involved from the UX point of view. Three dentists, two dental technicians and five patients expressed their expectations using questionnaires. In addition, four among the most relevant competitors were evaluated focusing on the satisfaction of the customers’ requirements: Herbst (labeled as Comp1 in the following), MARA (Comp2), Jasper Jumper (Comp3) and Forsus (Comp4). The dentists, as orthodontics specialists, performed this evaluation and found that no system satisfied the customers’ requirements in full; for this reason, space for improvement was reputed to exist. Table 1 and Table 2 contain the result of the data collection. Table 1 shows the customers’ requirements together with the relative importance, all of them classified by use phase. Table 2 shows how much the competitors satisfied the customers’ requirements. This quantification uses a 1-5 scale, where 1 represents “not satisfy” and 5 is “completely satisfy”.

Table 1. Customers’ requirements with relative importance, classified by use phase.
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Table 2. Results of the benchmarking of the competitors.
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The QFD analysis had a two-face result. From one hand, the ordered pieces of information in the HoQ allowed getting the clear picture of the requirements of all the customers and, consequently, generated the bases for the UX evaluation that occurred in the other activity this research focuses on. On the other hand, the QFD analysis gave precious indications for the development process in terms of priorities, aspects to focus on, quantitative targets to aim at, etc.

Regarding the first result, the UX-related requirements highlighted thanks to the QFD involvement can be summarized as follows.

  • UX-Req1. Minimizing interfering with daily activities (speaking, eating, etc.) (highlighted by patients).

  • UX-Req2. Being robust (dentists and dental technicians).

  • UX-Req3. No injuring and/or harmful (patients).

  • UX-Req4. Being good-looking (small, almost invisible, etc.) (patients).

  • UX-Req5. Easy to mount and fix (possibly cemented to the teeth) (dentists).

For what concerns the second result, designers had quite precise indications to carry their work on, focusing on the engineering requirements of real interest. The main ones were as follows.

  • Ind1. Maximize robustness.

  • Ind2. Minimize volume.

  • Ind3. Minimize contact with soft tissues.

  • Ind4. Minimize sharp geometries.

  • Ind5. Minimize the number of pieces.

Designers tried to satisfy the customers’ requirements with activities optimized by following these indications. The device was designed starting from a free-form, patient-specific concept developed in a previous study [18]. Once designed, the device was prototyped using a 3D printer, together with a pair of sample dental arches, in order to make the tests of the irMMs method feasible. Figure 6 shows the result of the designers’ effort, represented both digitally and physically.

Fig. 6.
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The digital (a) and physical (b) representation of the developed device.

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Four pieces, two for the left and two for the right side, compose the device. Each side consists of three zones: the mechanism, the basements and the connections (Fig. 6a shows them. The mechanism zone, designed on the specific patient’s corrected mandible path obtained by elaborating data from video tracking, consists of a spherical pin in the lower side (mandibular side), which slides on a guide surface in the upper side (maxillary side), to accomplish the correction in a smooth way. The two basements (upper and lower sides) are the second zone and consist of an offset of the shape of the second premolar and first and second molar; these teeth are those the two basements will be cemented to. The third zone consists of free forms connecting the basements to the mechanism; their definition aims at minimizing the volume and at being as smooth as possible.

Designers were quite sure about the satisfaction of the customers’ requirements for the following reasons.

  • UX-Req1. The interocclusal positioning of the device parts should guarantee freedom of movements. Rounded edges and variably sloped contact surfaces should increase comfort, allowing painless daily use of the device and avoiding the mechanism to get stuck.

  • UX-Req2. The four monolithic device pieces should increase robustness and avoid unexpected failures. The mechanism concept was chosen as simple as possible for the same reason, in accordance with Comp2, the best competitor from this point of view.

  • UX-Req3. The smooth free forms surfaces spread over the device should make it safe for the patients, avoiding injuries and any other disease. All of this is helped also by the interocclusal position since this reduces the amount of material in contact with the soft tissues of the mouth.

  • UX-Req4. Reduced volume and interocclusal positioning should make the device almost invisible; consequently, patients should be more prone to accepting it.

  • UX-Req5. The offset solution mimicking the teeth shape of the basements should make the device implant straightforward.

Now, designers’ belief needed to be checked against the final users’ opinion. This is why the second activity of interest in this research, the product evaluation, took place.

3.2 Product Evaluation

The UX evaluation occurred through the four phases of the irMMs method adoption cited in the background section. How these phases occurred here is described in the following.

Input Setting.

The product was the device just developed. The need was “implant it”, if the user was a dentist or a dental technician, and “use it”, if he/she was a patient”. All sections (AB, RB and RE) were considered. Nineteen users (seven AB, six RB and six RE) were involved, selected among dentists, dental technicians and patients, all of them showing different levels of knowledge about class II malocclusions and other solutions available on the market. Finally, three evaluators took part in the tests, two designers and one UX specialist.

Material and Environment Setup.

Physical models of the new device as well as of the upper and lower dental arches (Fig. 6b) were prepared to allow RB users getting confident with the product and all users performing the tests. User guides were customized focusing on the aspects highlighted by the QFD analysis during the data collection.

Test Execution.

At the beginning, the device was briefly described to the users, without showing the prototype. This description allowed them to express their expectations as mental models. After that, users compared their expectations with the actions allowed by the prototypes they interact with and with the feedback coming from them. All the tests ran smoothly. They took 25 min each in average. Figure 7 shows two photographs taken during the test of an RE user.

Fig. 7.
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Photographs taken during the test of an RE user.

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Data Analysis.

At the end, the content of nineteen user guides (every user reached the end of the test and filled one guide) was available for reasoning about the UX of the device. Figure 8 reports what was expected (before the interaction with the prototypes) and what had been real (after the interaction), all of this for every section (AB, RB and RE) and classified against the five modules of the meQUE. It is worth to say that data from AB users before the interaction refer only to emotions because of the irMMs method functioning.

Fig. 8.
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Result of the meQUE, before and after the interaction with the prototypes.

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The evaluators used these data to generate the lists of UX aspects, as expected by the irMMs method. The lists contain 9 positive and 35 negative UX aspects. The UX aspects are not reported here for space reason. Some of them are cited in the following to support the discussion.

4 Discussion

At first, the comparison between the data collected in the two moments allows making some considerations.

  • The UX of the device was better than expected for every section for every module of the meQUE. The expected UX described in the mental models has always been overcome during the interaction with the device. The only exception regarded the meaning for the RB users. All of this lets start thinking about a good result of the design activities.

  • The RE users were those who showed the major differences between the “before” and the “after”. Since RE users should be the sternest judges, once again all of this witnesses the goodness of the device from the UX point of view.

  • Regarding the modules of the meQUE, those with higher values on average referred to instrumental and non-instrumental product qualities (module I and module II). The device was reputed as particularly good for what concerns usefulness and usability, as well as visual aesthetics, status, commitment and meaning.

  • Emotional reactions (module III) and consequences of use (module IV) had lower values, although a meaningful difference exist between the “before” and the “after”. Nevertheless, it is quite difficult to associate positive emotions, intentions to use in the future, etc., to these kinds of devices; therefore, this result was somehow expected.

  • The overall evaluation was very low in the mental models (“before”) and the real interaction (“after”) increased it just a bit. Probably, negative emotions and the reluctance to use these devices in general, influenced the judgment negatively.

The availability of the lists of UX aspects allowed verifying the effectiveness of the designers’ effort in satisfying the customers’ requirements (expectations) collected thanks to the QFD exploitation in the data collection phase and summarized in Sect. 3.1. These customers’ requirements are recalled in the following, together with some reasoning about design drawbacks and possible suggestions for further device improvements.

  • UX-Req1. Minimizing interfering with daily activities (speaking, eating, etc.). Despite the interocclusal positioning and the use of rounded edges and variably sloped contact surfaces, users felt the prototype quite uncomfortable and interfering with daily activities. For example, a negative UX aspect reported “the upper part of the device is ok but that spherical pin at the bottom is something my tongue cannot stop to interfere with” or “I am not sure I can bite properly with these smooth surfaces”.

  • UX-Req2. Being robust. The users perceived the robustness assurance guaranteed by the four pieces only partially. One of the negative UX aspects, expressed by an RE dental technician, was “I don’t think that that pin is strong enough to withstand the forces occurring during mandible movements, its size should be increased”.

  • UX-Req3. No injuring and/or harmful. The device shape, as well as its positioning, made the users quite confident about using it safely. Nevertheless, some perplexities arose, like that expressed in the negative UX aspect “the freedom in the mandible movement (mouth opening without constraints) is of course something good; nevertheless, I feel that this freedom increases the risk to bite my tongue or the inside of my cheeks” or in another negative UX aspect “I think that the part of the device devoted to fixing is too thin. To me, the device risks to slip away more than often”.

  • UX-Req4. Being good-looking (small, almost invisible, etc.). People who used such kinds of devices in the past appreciated the design effort towards aesthetics and non-invasiveness. Only one user was a bit disappointed as witnessed by his negative UX aspect “that spherical pin is horrible. To me, people I could talk with can see it and think that I have something wrong in my teeth”. Moreover, several users highlighted the importance of the color choice.

  • UX-Req5. Easy to mount and fix (possibly cemented to the teeth). Dentists and dental technicians expressed no remarks from this point of view during the evaluation. This because the cemented device was somehow an explicit request. Conversely, some patients complained about this. For example, a negative UX aspect was “I expected an innovative device, easy to put on and off. Instead, it is only another fixed device” and another negative UX aspect was “it is not so simple to position as it seems”.

5 Conclusions

This research addressed the importance of UX concerns in developing functional orthodontic appliances. The discussion section should have made clear this importance, both in terms of indications for an effective development and of suggestions for possible improvement of the design results. The device developed during this research seems to answer to the customers’ requirements better than other existing devices.

The research activities in the near future will focus on the suggestions for possible improvements. A new release of the device, lighter and even more non-invasive than the current one will be developed. Overall, particular attention will be paid in trying to substitute the spherical pin, disagreeable to many users during the tests, with something arising more confidence about strength, safety and non-invasiveness. The result will undergo the irMMs method adoption, involving different dentists, dental technicians and patients.