Background

Dental morphology and practice class is an essential part of the dentistry curriculum. This course provides theoretical and practical instruction on the morphology, function, and direct carving of tooth structure [1, 2]. The conventional teaching method involves theoretical learning followed by tooth carving based on the principles learned. Students use two-dimensional (2D) tooth images and plastic models to carve teeth on wax or plaster blocks [3,4,5]. Understanding tooth morphology is essential in prosthetic treatment and the creation of dental restorations in clinical practice. The proper relationship between the antagonist and proximal teeth, as indicated by their shape, is critical for maintaining occlusion and alignment stability [6, 7]. Although the dentristry curriculum helps students gain a comprehensive understanding of tooth morphology, they still face difficulties during the tooth carving process associated with conventional practice.

Beginner students in dental morphology practice face challenges interpreting and reproducing 2D images in three-dimensional (3D) form [8,9,10]. Tooth shapes are typically represented in 2D drawings or photographs, leading to difficulties in visualizing tooth morphology. Moreover, the pressure to complete tooth carving quickly within limited time and space, coupled with the use of 2D images, makes it difficult for learners to conceptualize and visualize 3D shapes [11]. Although plastic tooth models, available as partial completion or final form displays, aid learning, they have limited use, as commercialized plastic models are typically predefined and restrict practice options for instructors and learners alike [4]. Furthermore, these practice models are held by educational institutions and cannot be personally owned by students, leading to increased pressure to complete the pieces within the allotted class time. Instructors often guide a large number of students during the practice process, usually relying on conventional practice methods, which can lead to prolonged waiting times for instructor feedback on intermediate carving steps [12]. Therefore, a supplementary carving guide medium is needed to facilitate tooth carving practice and mitigate the limitations posed by plastic models.

Augmented reality (AR) technology has emerged as promising tool for enahncing learning experiences. By superimposing digital information onto the real environment, AR technology can provide learners with a more interactive and immersive experience [13]. According to Garzón [14], who drew on 25 years of experience in educational classification of AR spanning the first three generations, the use of cost-effective mobile devices and applications in 2nd generation AR (via mobile devices and applications) has significantly improved educational characteristics. Upon creation and installation, the mobile application enables the camera to recognize and display additional information about recognized objects, thereby enhancing user convenience [15, 16]. AR technology operates via quick response code or image marker recognition through a mobile device camera, displaying superimposed 3D information upon detection [17]. By manipulating the mobile device or image marker, users can easily and intuiviely observe and comprehend the 3D structure [18]. In the review of Akçayır and Akçayır [19], it was found that AR enhances “enjoyment” and succeeds in “raising the level of engagement” in pedagogy. Nevertheless, the technology can be “difficult for students to use” and result in “cognitive overload” due to data complexity, making supplementary learning guidance necessary [19,20,21]. Therefore, efforts must be made to enhance the educational value of AR by improving usability and reducing task complexity overload. These factors must be considered when creating educational media for tooth carving practice using AR technology.

To effectively guide learners in tooth carving using AR media, a sequential process should be followed. This approach can help reduce variation and facilitate skill mastery [22]. Novice carvers can improve the quality of their work by following a digital step-by-step tooth carving process [23]. Indeed, a step-by-step learning method has been shown to be effective in acquiring carving skills within a short period of time and minimizing errors in the final wax form for restorations [24]. In the field of dental prosthetics, subdividing the engraving process applied to the tooth surface is an effective way to help learners enhance their skills [25]. The present study aims to develop a mobile-friendly AR-based tooth carving practice tool (AR-TCPT) and evaluate its user experience. Furthermore, the study compares the user experience of AR-TCPT with that of a conventional plastic model for tooth carving, with the goal of assessing the potential of AR-TCPT as a practice tool.

Methods

Research design

The AR-TCPT was developed using AR technology for mobile devices. The tool was designed to create 3D models of the maxillary canine, maxillary first premolar, mandibular firt premolar, and mandibular first molar in a stepwise manner. Initial 3D modeling was completed using 3D Studio Max (2019, Autodesk Inc., USA), whereas final modeling was performed using the Zbrush 3D package (2019, Pixologic Inc., USA). Image markers were produced using Photoshop software (Adobe Master Collection CC 2019, Adobe Inc., USA) and were designed for stable recognition by mobile cameras, achieving a five-star rating in the Vuforia engine (PTC Inc., USA; http://developer.vuforia.com). The AR application was implemented using the Unity engine (2019.3.12., Unity Technologies, USA) and subsequently installed and operated on a mobile device. To evaluate the effectiveness of the AR-TCPT as a practice tool for tooth carving, a control group and experimental group were formed by randomly selecting participants from a class of dental morphology practice in 2023. Participants in the experimental group used the AR-TCPT, whereas those in the control group used the plastic model from a Tooth Carving Step Model Kit (Nissin Dental Inc., Japan). After completing the tooth carving task, user experiences for each practice medium were investigated and compared. The order of the research design is presented in Fig. 1. The study was conducted with the approval of the Institutional Review Committee of Namseoul University (IRB No: NSU-202210-003).

Fig. 1
figure 1

Development and user evaluation of an educational tool for tooth carving practice

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3D modeling following the tooth carving stages

3D modeling was used to display the morphological features of the teeth’s prominent and depressed structures on the mesial, distal, buccal, lingual, and occlusal surfaces in a sequential manner during the carving process. The teeth were modeled in 16 steps for the maxillary canine and maxillary first premolar, 13 steps for the mandibular first premolars, and 14 steps for the mandibular first molars. The primary modeling depicted the parts to be deleted and preserved, following the order of the tooth pieces, as shown in Fig. 2. The final modeling sequence of teeth is presented in Fig. 3. In the final modeling, the texture, ridges, and depressed structures of teeth were described, and pictorial information was included to guide the carving process and highlight structures requiring careful attention. At the beginning of the carving stage, each surface was color-coded to indicate its direction, and the wax block was marked with solid lines to indicate the parts to be removed. The mesial and distal surfaces of the teeth were marked with red dots to identify tooth contact points, which were to be preserved as prominences and not removed during the carving process. On the occlusal surfaces, red dots marked each cusp as preserved, and a red arrow indicated the carving direction during wax block carving. The 3D modeling of preserved and removed parts allowed for confirmation of the morphology of removed parts in the subsequent step of wax block carving.

Fig. 2
figure 2

Primary modeling for creating three-dimensional objects in the step-by-step tooth carving process. a: mesial aspect of the maxillary first premolar; b: slightly superior and mesiolabial aspect of the maxillary first premolar; c: mesial aspect of the maxillary first molar; d: slightly superior and mesiobuccal aspect of the maxillary first molar. B, buccal; La, labial; M, mesial

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Fig. 3
figure 3

Three-dimensional (3D) objects representing the step-by-step tooth carving process. This photograph shows completed 3D objects following the maxillary first molar modeling process and provides detailed information and textures for each sequential step. The second 3D modeling data include the final 3D object augmented in the mobile device. The dotted line indicates equal divisions of the tooth, and a separate piece indicates that it must be removed before including a piece containing a solid line. The red 3D arrow indicates the direction of tooth carving, the red circle on the distal surface represents the contact area of the tooth, and the red cylinder on the occlusal surface indicates the cusp. a: Dotted line, solid line, red circle on the distal surface, and steps indicating the wax block to be separated. b: Approximate completion of the maxillary first molar. c: Detailed view of the maxillary first molar, with the red arrow indicating the direction of tooth carving and the separated piece, red cylindrical cusp, and shape of the solid line indicating the part to be carved on the occlusal surface. d: Completed maxillary first molar

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Image markers and implementation of AR

To facilitate the recognition of sequential carving steps using a mobile device, four image markers were prepared for the mandibular first molar, mandibular first premolar, maxillary first molar, and maxillary canine. The image markers were designed using Photoshop software (2020, Adobe Co., Ltd., San Jose, CA), and they distinguished each tooth using a circle–number symbol and a background of repeated patterns, as shown in Fig. 4. The Vuforia engine (AR marker production software) was used to produce high-quality image markers, and after evaluating the single image type recognition rate with five stars, the image markers were designed and saved using the Unity engine. The 3D tooth model was step-by-step linked to the image marker, and its position and size were determined based on the marker. Using the Unity engine, and Android application that could be installed on mobile devices.

Fig. 4
figure 4

Image markers. These photographs show the image markers used in this study, which are recognized by the camera of the mobile device according to the type of tooth (number in each circle). a: Mandibular first molar; b: mandibular first premolar; c: maxillary first molar; d: maxillary canine

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Recruitment of participants

Participants were recruited from the first-year dental morphology practice class at the department of dental hygiene at Seoyeong University in Gyeonggi-do. Potential participants were informed of the following: (1) participation was voluntary, without financial or academic grade reward; (2) the control group would use a plastic model while the experimental group would use the AR mobile application; (3) the experiment would take place over three weeks and involve carving three teeth; (4) Android users would receive an application installation link, whereas iOS users would be lent Android devices with AR-TCPT installed; (5) AR-TCTP would function in the same manner in both systems; (6) the control and experimental groups would be randomly assigned; (7) tooth carving would take place in separate labs; (8) after completion of the experiment, a survey consisting of 22 items would be conducted; and (9) the control group could use the AR-TCPT after the experiment. In total, 52 participants volunteered, and online consent forms were obtained from each participant. The control group (n = 26) and experimental group (n = 26) were randomly assigned using the random function in Microsoft Excel (2016, Redmond, the USA). Figure 5 shows the participant recruitment and experimental design in a flowchart.

Fig. 5
figure 5

Research design for investigating the experiences of participants using plastic models and augmented reality applications

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Participant user experiences and comparative questionnaire

The experimental and control group carved three teeth each for three weeks, beginning on March 27, 2023, using the AR-TCPT and plastic model, respectively. Participants carved premolars and molars, including the mandibular first molar, mandibular first premolar, and maxillary first premolar, all with complex morphological features. The maxillary canines were not included in the carving. Participants were given a weekly time limit of 3 h to carve one tooth. After completing one tooth, the plastic model and image marker of the control and experimental groups, respectively, were retrieved. The 3D object of the tooth was not augmented via the AR-TCTP without image marker recognition. To prevent the use of other practice tools, the experimental and control groups practiced tooth carving in separate spaces. Feedback on tooth shape was provided for three weeks after the experiment concluded to limit the influence of instructor guidance. After completing the mandibular first molar carving in the third week of April, a questionnaire survey was conducted. The modified questionnaire of Saunders et al. [26] with 23 questions was used by Alfalah et al. [27] to assess the differences in heart shape between practice tools. However, in the present study, one item for direct manipulation per layer was excluded from the questionnaire items of Alfalah et al. [27]. The 22 items used in the current study are presented in Table 1. In the control and experimental groups, Cronbach’s α values were 0.587 and 0.912, respectively.

Table 1 Questionnaire items for comparing experiences of the control group (plastic model) and experimental group (AR-TCPT)
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Statistical analysis

SPSS statistical software (v25.0, IBM Co., Armonk, NY, USA) was used for data analysis. A significant two-tailed test was conducted at a significance level of 0.05. Fisher’s exact test was used to analyze general characteristics, such as gender, age, place of residence, and tooth carving experience, to confirm the distribution of these characteristics between the control and experimental groups. The survey data did not follow a normal distribution (p < 0.05), as evidenced by the results of a Shapiro–Wilk test. Therefore, the nonparametric Mann–Whitney U test was used to compare the control and experimental groups.

Results

The tools used by the participants for tooth carving practice are depicted in Fig. 6. Figure 6a shows a plastic model, and Fig. 6b–d shows the AR-TCPT used on a mobile device. The AR-TCPT used the device’s camera to recognize the image marker and display an augmented 3D tooth object on the screen, which participants could manipulate and observed in real-time. The mobile device’s next and previous step buttons allowed for a detailed observation of tooth carving steps and the morphological features of teeth. To carve the tooth, the AR-TCPT users compared the augmented 3D tooth model on the screen with a wax block in a sequential manner.

Fig. 6
figure 6

Tooth carving practice. This photograph shows a comparison between conventional tooth carving practice (TCP) using a plastic model and step-by-step TCP using an augmented reality-based tool. The learner can observe the carving step in three dimensions by pressing the next step and previous step buttons. a: Plastic model from a tooth carving step model kit. b: TCP using the augmented reality-based tool in the first stage of the mandibular first premolar. c: TCP using the augmented reality-based tool in the final stage of the mandibular first premolar. d: Process of identifying ridges and grooves. IM, image marker; MD, mobile device; NSB, next step button; PSB, previous step button; SMD, stand of mobile device; TC, tooth carver; W, wax block

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The randomly allocated participants in the two groups showed no significant differences in gender, age, place of residence, and tooth carving experience (p > 0.05). The control group comprised 96.2% females (n = 25) and 3.8% males (n = 1), whereas the experimental group solely consisted of females (n = 26). The control group had 61.5% (n = 16) 20-year-old participants, 26.9% (n = 7) 21-year-old participants, and 11.5% (n = 3) ≥ 22-year-old participants, whereas the experimental group comprised 73.1% (n = 19) 20-year-old participants, 19.2% (n = 5) 21-year-old participants, and 7.7% (n = 2) ≥ 22-year-old participants. In terms of the place of residence, 69.2% (n = 18) of the control group lived in Gyeonggi-do, whereas 23.1% (n = 6) lived in Seoul. In contrast, 50.0% (n = 13) of the experimental group lived in Gyeonggi-do, whereas 46.2% (n = 12) lived in Seoul. The percentages of the control group and the experimental group living in Incheon were 7.7% (n = 2) and 3.8% (n = 1), respectively. Out of the control group, 25 participants (96.2%) had no prior tooth carving experience. Similarly, 26 participants (100%) in the experimental group had no prior experience in tooth carving.

Table 2 presents the descriptive statistics and statistical comparisons of responses to the 22 survey items between the groups. The responses to each of the 22 items in the questionairre differed significantly between groups (p < 0.01). Compared with the control group, the experimental group had a higher mean score for 21 questionnaire items. Only in question 20 (Q20) of the questionnaire did the control group score higher than the experimental group. The difference in mean scores between groups is visually depicted in the bar chart in Fig. 7. Table 2; Fig. 7 also show the evaluation results of user experience for each item. In the control group, the highest-rated item was Q21, whereas the lowest-rated item was Q6. In the experimental group, the highest-rated item was Q13, whereas the lowest-rated item was Q20. As shown in Fig. 7, the largest difference in mean values between the control and experimental groups was observed in Q6, whereas the smallest difference was in Q22.

Table 2 Comparison of all questionnaire item responses between the control and experimental groups
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Fig. 7
figure 7

Comparison of questionnaire scores. Bar chart comparing the mean scores of the control group using the plastic model and the experimental group using the augmented reality application. AR-TCPT, augmented reality-based tooth carving practice tool

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Discussion

AR technology has become increasingly popular in various areas of dentistry, including clinical aesthetics, maxillofacial surgery, restorative techniques, dental morphology and implantology, and simulation [28,29,30,31]. For instance, Microsoft HoloLens provides advanced AR tools that augment dental education and surgical planning [32]. Virtual reality technology also provides a simulated environment for dental morphological education [33]. Although advanced hardware-dependent head-mounted displays for these technologies are not yet widespread in dental education, AR mobile applications can enhance clinical application skills and help users quickly understand anatomical structures [34, 35]. AR technology can also increase students’ motivation and interest in learning dental morphology, providing a more interactive and engaging learning experience [36]. AR learning tools help students visualize complex dental procedures and anatomy in 3D [37], which is critical for understanding tooth morphology.

The effect of 3D-printed plastic tooth models on tooth morphology education has been superior to that of textbooks with 2D pictures and explanations [38]. However, digitization of education and technological advancements have made it imperative to introduce various devices and technologies in health and medical education, including dental education [35]. Instructors face challenges teaching complex concepts in a rapidly evolving and dynamic field [39], and using a variety of practice media, in addition to traditional plastic models of teeth, is necessary to aid students in tooth carving practice. Therefore, the present study introduced a practice tool, the AR-TCPT, that ultizes AR technology to aid dental morphology practice.

Investigating the user experience of AR applications is crucial for understanding the factors that impact media utilization [

Conclusions

In conclusion, this study demonstrated the potential of the AR-TCPT as a practice tool for tooth carving, as it provided an innovative and interactive learning experience for students. Compared with the conventional plastic model group, the AR-TCPT group showed significantly higher scores in user experience, including benefits such as quick comprehension, improved learning, and reduced reliance on textbooks. With its familiar technology and ease of use, the AR-TCPT offers a promising alternative to conventional plastic tools and may assist beginners struggling with 3D carving. However, further research is required to evaluate its educational efficacy, including its effects on individual carving abilities and quantitative evaluations of carved teeth.