T-Scan Novus System Application—Digital Occlusion Analysis of 3D Printed Orthodontics Retainers

Abstract

(1) Background: This study aims to evaluate the occlusal force distribution across different quadrants during the placement of orthodontic retainers fabricated using a biocompatible material via digital design. (2) Materials and Methods: A cohort of 21 patients in the retention phase following orthodontic treatment was included in this study. Intraoral scans were obtained using Trios color (3Shape). For retainer fabrication, the splint studio module of the 3Shape design software was utilized. Occlusal evaluation was performed using T-Scan Novus (Tekscan). The Kolmogorov–Smirnov test, Wilcoxon signed ranks test, and Mann–Whitney U test were used for statistical analysis. (3) Results: The digital design set evenly distributed contacts on all occluding surfaces. These contacts, uniform in area, turned out to be uneven in pressure: right distal—37.14%, right frontal—11.4%, left frontal—11.46%, and left distal—39.99%. (4) Conclusions: The results of the study indicate that the digital design workflow has the capability to achieve uniform contact distribution by area. However, despite the achievement of uniform contact distribution, the study found that there was an unequal distribution of occlusal forces. Specifically, the distal sections of the teeth experienced significantly higher loading compared to the frontal sections.

1. Introduction

Retention is the final phase that follows orthodontic treatment, aimed at maintaining tooth alignment and preventing relapse, which commonly occurs to varying extents [1]. Due to the diversity of orthodontic presentations, there is no single optimal retention protocol, and approaches are tailored based on pretreatment characteristics, treatment-induced changes, and general patient characteristics [2]. Retainers can be classified into two main types: fixed and removable [3]. Among these, passive Hawley-like removable appliances are increasingly popular and reliable in maintaining the desired occlusion. Variations include the removable Wrap Around appliance, which is an original version of the Hawley plate with modifications such as the Adams clasps; translucent retainers like Astics, which provide an aesthetic Hawley-type option; reinforced removable retainers that feature a metal grid reinforcing the acrylic base. Vacuum-formed retainers are easy to manufacture and prescribe [4]. In Switzerland, a survey revealed that most orthodontists place a bonded retainer in the upper and lower arches, except when the upper arch has undergone expansion during treatment or when extractions have been performed in the upper arch, in which cases a combination of fixed and removable retainers is used. Opinions differ on the recommended number of hours for wearing removable retainers and the duration of the retention phase [5]. In a comparative study focusing on linear transpalatinal measurements, 3D-printed retainers were found to be more accurate and reliable than vacuum-formed retainers [6].

Digitalization has become an integral part of dentistry, permeating various aspects of dental practice. The initial step in the digital workflow involves obtaining a digital model through the utilization of three-dimensional (3D) scanning technologies and converting physical models into digital computer-aided design (CAD) files [7]. The application of 3D scanning in dentistry offers several advantages, such as rapid production with customized design, enhanced patient comfort, time and cost efficiency, improved procedure planning, multi-angle visualization of dental anatomy, and increased treatment success rates [8].

To achieve a fully digital protocol, specific devices are required, including an intraoral scanner, a T-Scan system, and dental software. The T-Scan system, integrated into the digital workflow, allows for the detection of occlusal contacts, while the intraoral scanner captures the occlusal surfaces. Alignment of the three-dimensional occlusal surface with T-Scan registration enables the projection of occlusal forces onto the patient’s occlusal surfaces, facilitating the assessment of occlusal forces over time. This integration demonstrates the feasibility of incorporating different tools and software into a comprehensive dental digital workflow [9].

The evolution of the T-Scan system from its initial generation to the latest version has revolutionized occlusal analysis. The 8th generation, released in 2012, simplified the user interface, presenting occlusal contacts in a dynamic movie format with color-coded three-dimensional or two-dimensional (2D) graphics. This version provided insights into the percentage of force per tooth, along with analytic software displaying the center of force (COF) and COF trajectory, enabling a comprehensive understanding of the overall balance of occlusion [10]. The T-Scan system’s desktop changes in T-Scan 8 and T-Scan 10 have enhanced the visualization and functionality of the software. In T-Scan 8, important desktop changes include an enlarged Force vs. Time Graph, providing easier visualization of color-coded force and timing lines. Additionally, the introduction of a rotating 3-Dimensional ForceView window allows for improved visualization of moving individual force columns during movie playback. The rotating 3-D ForceView enables clinicians to adjust the window’s orientation to eliminate overlapping rising and falling force columns, optimizing the viewing experience [11].

T-Scan 10 introduces new software features accessible through the expanded desktop Toolbar. These features allow doctors to import and export patient data, generate reports, attach notes and photos, and create MP4 files of the scan. Furthermore, clinicians can import intraoral digitally-impressed .stl files of a patient’s arch and overlay them with T-Scan force data. These robust capabilities empower clinicians to efficiently diagnose and treat patients using objective and comprehensive force and timing data [12].

In terms of occlusal thickness, patients typically perceive occlusal registration strip thickness ranging from 12.5 to 100 µm. For occlusal analysis, the foils used should be thinner than the patient’s perception, with a thickness below 21 µm. T-Scan sensors, on the other hand, have a thickness of 60 µm. They consist of a coordinate system with 1500 sensitive receptor points made of conductive ink, which exhibit elastic deformation [13,14]. It’s important to note that the T-Scan system may have certain non-sensible areas due to its constructional features. The system’s most sensitive area can measure forces from 0.1 kg to 2.1 kg, making it more suitable for recording within lower load ranges. While the system has some reproducibility disadvantages, it contributes to the quantitative evaluation of occlusal contacts for diagnosis and treatment purposes [15]. However, it is worth mentioning that the T-Scan system may record fewer occlusal contacts than are actually present [16]. The maximum clenching forces of the masticatory muscles recorded by the T-Scan system tend to be located in centric occlusion at the third molars in a complete dentition of 32 teeth and at the second molars in a dentition of 28 teeth [17].

Regarding retainers, thermoformed retainers have the same thickness in all directions, and preliminary contacts often occur, mainly in the distal area. In this study, we specifically investigated printed retainers with digitally distributed balanced contacts. The digital design allows for an even distribution of contacts during placement. The purpose of this study is to determine whether the force of the contacts is evenly distributed. The study examines the distribution of occlusal forces by quadrants during the placement of orthodontic retainers printed from a biocompatible material.

2. Materials and Methods

The study involved a sample of 21 patients who were in the retention phase after orthodontic treatment. The sample consisted of 10 male and 11 female patients, with a mean age of 19.71 ± 6.27 years. The age range of the patients was between 15 and 35 years, with 76.2% of them being under 18 years old.

2.1. Study Design

To capture intraoral images of the upper and lower jaws, as well as the right and left bite, an intraoral scan was conducted using the Trios color (3Shape, Copenhagen, Denmark, 2014) imaging system. The digital models obtained from the scan were utilized to design the retainer using 3Shape design software (Splint studio software, 3Shape, Copenhagen, Denmark, 2023), as shown in Figure 1. For the fabrication of the retainer, the 3D printing technique was employed. Biocompatible resin OrthoClear (Nextdent, Soesterberg, The Netherlands) was chosen as the material for the retainer, as depicted in Figure 2. This resin is specifically formulated to be compatible with oral tissues, ensuring a safe and comfortable fit for the patient [18]. The retainers were made using the Nextdent 5100 3D printer, which is of the same brand (Nextdent, Soesterberg, The Netherlands).

To evaluate the occlusion, the T-Scan Novus system (Tekscan, Norwood, MA, USA, 2018) was used. The pressure-sensitive sensor of the T-Scan Novus system was placed between the dental arches, with a marker positioned between the upper central incisors. The patient was seated upright, and the sensor was positioned horizontally. The patient was instructed to close their teeth in tight contact. Three consecutive measurements were taken, with the first serving as a training trial to ensure proper performance by the patient and the subsequent two measurements used for analysis. The arithmetic averages of the two consecutive measurements were calculated for each patient.

To enable a precise comparison between the intraoral images obtained from the Trios color scanner and the T-Scan system, the intraoral images were imported into the T-Scan system prior to analysis. The licensed software version 10.0.40 (T-Scan 10) was used for data analysis [T-Scan™ v10 Software, Tekscan, Norwood, MA, USA, 2018]. The software facilitated the division of the dental arches into quadrants, automatically calculating the percentage force distribution within each quadrant. The study focused on the distribution of maximum intercuspidation by quadrants.

2.2. Statistical Analysis

Quantitative data are presented as mean ± SD or median (25th–75th percentile). Deviations from a Gaussian distribution were tested using the Kolmogorov–Smirnov test. Counts and percentages were used for categorical variables. The Wilcoxon signed ranks test was used to examine the difference in force distribution between the left and right distal zones, as well as between the left and right frontal zones. The Mann–Whitney U test was used to compare the force distribution between men and women. The significance level was assumed to be p < 0.05. Microsoft Office 2016 was used for tables and figures. Statistical analysis was conducted using the SPSS statistical software version 23 [IBM SPSS Statistics, New York, NY, USA, 2020].

To illustrate the findings, a clinical case of a 21-year-old patient who underwent orthodontic treatment involving both dental arches, including the positioning of impacted teeth and subsequent leveling with a pre-adjusted edgewise bracket system, was presented. This case serves as a visual representation of the study’s outcomes.

3. Results

At the beginning of orthodontic treatment, 14 patients had Angle Class I malocclusion, while 7 patients had Angle Class II malocclusion. Among the patients, 14 of them (66.7%) received orthodontic treatment without the need for tooth extractions, while 7 patients (33.3%) required extractions. The detailed distribution of patients based on Angle classification and extraction requirement is presented in

Table 1. Demographic and Clinical characteristics of the patients included in the study.

Demographic and Clinical Characteristics	Subjects N = 21
Age(years)	19.71 ± 6.27 *
Gender
Male	10 (47.6%)
Female	11 (52.4%)
Angel Class
Class I	14 (66.7%)
Class II	7 (33.3%)
Surgical treatment
Extraction	7 (33.3%)
Non-extraction	14 (66.7%)

* Mean ± SD.

:

The orthodontic treatment for the patients included in the study had an average duration of 28.57 (±4.61) months. When analyzing the data by gender, the average age of male patients was 17.80 (±2.57) years, while the average age of female patients was 21.45 (±8.12) years. The average treatment duration for male patients was 29.4 (±5.97) months, while for female patients, it was 27.82 (±3.02) months.

3.1. Digital Design

The digital design of the retainer was created using 3Shape software, specifically the splint studio module. The first step in fabricating the retainer, which was a modified splint, involved establishing an occlusal plane. This plane clearly demonstrated the proper leveling of the incisal edges and the tubercle tops, as depicted in Figure 3.

Several parameters were selected for the retainer design. The thickness of the retainer was set at 0.7 mm, while the laterotrusus value was set to 0 mm. The occlusal distance between the upper and lower jaws may vary based on protrusion. To maintain the existing occlusal relationships, both values were kept within a range of no more than 1 mm (0.7 to 1.1 mm). In the specific case presented, a 1 mm protrusion and a 1.1 mm gap between the jaws were observed. The software marked these values and adjusted the ratio between the upper and lower tooth arches, as shown in Figure 4.

After establishing the occlusal plane, two additional steps were taken in the retainer design process. The first step involved selecting the insertion direction, followed by delineating the boundaries of the future retainer. Subsequently, the occlusal surface was chosen. In the case of a retention apparatus, it is preferable for the retainer to have contact with the opposing teeth. This contact helps prevent the growth of the opposing teeth, and therefore, the retainer should be worn for at least 16 h a day. The software generated a color map indicating the areas of tight contacts that the retainer would have with the opposing teeth. The densest contacts, which had an added negative value, were marked in red, as shown in Figure 5. It was also possible to outline these contact areas, as depicted in Figure 6. The software acknowledged the thin design of the retainer, with an option for a minimal thickness of 0.5 mm. The system provided a warning about the potential risk of perforation in areas opposite sharp tubercles. In Figure 5 and Figure 6, these areas are indicated by the dark red color. Based on previous experience, the “accept” function was preferred over the “correct” function, indicating that the design was considered suitable [19].

3.2. Clinical Research

After 3D printing the retainer, the supports were removed from the occlusal surface, and it was polished. Due to the high precision of the tooth surfaces, no adjustment was required. Digital measurement of occlusion was performed during the initial placement of the retainer. The same clinician performed scans with both the intraoral scanner and the T-Scan Novus system.

Once the finished retainer framework was placed on the upper dentition, a digital measurement of the occlusion was taken using the T-Scan Novus system. The T-Scan system provides a color map based on the pressure detected by the sensor, corresponding to the force of contacts between the teeth. The color markings in the map indicate the strength of the contacts, with strong contacts represented by violet and red colors, followed by yellow, green, and weak contacts shown in blue. By pre-importing the intraoral images captured by the Trios color scanner, the software accurately positions the contacts on the tooth surfaces, ensuring that they are placed in their correct locations. This integration of data from the intraoral images and the T-Scan system facilitates a more precise analysis of the occlusion and the distribution of forces within the dental arches, Figure 7.

Although the distribution of contacts across different areas of the dentition was found to be uniform, there were variations in the strength of these contacts. The dentition was divided into four zones: two frontal zones and two distal zones, specifically right distal, right frontal, left frontal, and left distal. A predominance of contact strength in the distal area was observed. The overall distribution of contact force by zone can be seen in

Table 2. The percentage force distribution in the frontal and distal zones of the study group.

Zone		Median	IQR (Q1–Q3)	Minimum	Maximum	z	p
Distal	left (%)	40.60	37.50–42.35	35.40	45.40	−2.416	0.016
	right (%)	36.80	35.55–38.90	33.80	40.40
Frontal	left (%)	11.60	10.60–12.30	8.20	14.35	−0.261	0.794
	right (%)	11.60	10.23–12.70	6.80	14.60

. A Wilcoxon signed-rank test indicated a significant difference between the distribution forces of the left and right distal zones (z = −2.416, p = 0.016). We observed a significantly higher percentage of force distribution in the left distal zones compared to the right distal zones. However, there was no statistically significant difference in force distribution between the left frontal zone and the right frontal zones (z = −0.261, p = 0.794).

The sex distribution of contact force by zone is demonstrated in

Table 3. Force distribution by sex.

Zone	Sex	Median (Q1–Q3)	U	p
Right Distal Zone	male female	36.70 (35.31–37.95) 38.15 (35.55–39.60)	44.00	0.468
Right Frontal Zone	male female	11.60 (10.34–12.71) 12.35 (9.95–12.80)	50.00	0.756
Left Frontal Zone	male female	11.88 (10.25–12.85) 11.60 (10.60–12.20)	50.00	0.756
Left Distal Zone	male female	41.00 (37.10–42.55) 39.20 (37.80–42.35)	45.00	0.512

. There was no statistically significant difference between men and women in the right distal zones (p = 0.468), right frontal zones (p = 0.756), left distal zones (p = 0.512), and left frontal zones (p = 0.756).

A Wilcoxon signed-rank test was used to compare the distribution forces between the left and right distal zones in both men and women. We found a significant difference between the distribution forces of the left and right distal zones (z = −2.091, p = 0.037) in men. However, we did not find a significant difference between the distribution forces in women.

3.3. Main Results

Based on the obtained results, the following conclusions can be drawn:

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The T-Scan system has provided evidence that the projected absolute uniformity of contacts is accompanied by varying strength. This indicates that although the contacts may appear visually similar, they exert different levels of force;

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The strong contacts identified by the T-Scan Novus align with the expected locations as determined by the digital design, specifically in the left and right molars. This suggests that the digital software accurately predicted and represented the areas of strong contact;

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The T-Scan Novus has detected weaker contacts or the absence of contacts in the frontal region, contrary to the expectations set by the digital design;

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This indicates that the frontal contacts, as designed in the digital software, may not be adequately registered or may be weaker in reality, according to the T-Scan system’s measurements.

4. Discussion

The use of 3D-printed aligners and retainers is expected to replace traditional vacuum-formed ones due to their superior mechanical strength qualities. 3D-printed retainers offer increased accuracy and reliability compared to vacuum-formed retainers [6]. It is important to note that differences in the thickness of the samples can affect their elastic and strength properties. For example, specimens with the largest thickness (1.2 mm) exhibit the highest average flexural modulus, deformation, creep, and strength. On the other hand, samples with an average thickness of 1 mm have the lowest modulus of elasticity [20]. In addition to their mechanical properties, 3D-printed retainers provide several advantages, including a simplified laboratory protocol, time and cost savings, and precise design [19]. While 3D-printed retainers may show a larger deviation from the original reference models compared to conventional vacuum-molded retainers, they still provide measurements within 0.5 mm, which is considered clinically sufficient [21]. Modern methods of remote monitoring systems, such as dental monitoring, have also been implemented in standard orthodontic care. These systems allow for the tracking and control of the fit of the retainer and the oral hygiene of the patients [22,23]. Studies have shown that dental monitoring can significantly reduce the number of in-office visits by 1.68-3.5 visits and may contribute to improved aligner fit [24].

In Paradowska-Stolarz’s study on the mechanical characteristics of different materials, several dependencies were observed. BioMed Amber was found to be the most stable material in the compression test, showing minimal changes in its structure. On the other hand, IBT exhibited the lowest stability, indicating that it may be more suitable for the preparation of imprecise medical elements or auxiliary tools. Dental LT Clear, on the other hand, did not show any changes in texture after the compression test [25]. In a comparative study on BioMed Amber and Dental LT Clear, it was found that both materials are rigid and stable in properties. However, BioMed Amber demonstrated higher resistance to compression, while Dental LT Clear exhibited higher resistance to tensile forces [26]. The mechanical properties of 3D-printed occlusal splints are influenced by factors such as the method of post-curing, water storage, and thickness of the printing layer. Post-curing with a combination of heat and light can improve the mechanical properties and conversion rate of 3D-printed occlusal splints. Decreasing the thickness of the printing layer can increase flexural strength and surface hardness [27]. Furthermore, the printing angle of 3D-printed occlusal splint materials affects their polishability and surface hardness. Materials printed at 0° angle produce the highest gloss and lowest surface roughness, requiring no additional polishing. However, materials printed at 45° and 90° angles may require polishing with burrs, pumice stone, and high gloss to reduce surface roughness due to the layered structures created during printing [28].

The strength of distal contacts has been shown to be significant in natural dentition [17]. In a prospective study evaluating the number of contacts in centric occlusion during retention with thermoplastic retainers, it was observed that the expected increase in occlusal contacts did not occur at the end of the retention period with thermoplastic retainers, as they cover the occlusal surfaces of the teeth. However, both ideal and non-ideal posterior contacts increased in the long term, with the number of non-ideal contacts being more prevalent than ideal contacts [29]. Another study evaluating the use of a multi-layer clear retainer through T-Scan evaluation found that occlusal force decreased in the anterior dentition and increased in the posterior dentition [30].

Comparing retainer patients (using removable Hawley retainers and maxillary and mandibular retainers) with control subjects with normal occlusions, it was observed that both retention procedures allowed relative vertical movement of the posterior teeth. However, the number of posterior segment contacts increased more in the fixed retainer group compared to the Hawley and control groups at the end of retention [31]. When utilizing digitally designed constructions, the expectation is to achieve evenly spaced contacts. However, in cases with minimal interocclusal distance, areas of excessive proximity may be observed, particularly against sharp tubercles. Previous experience suggests that following the software’s warning regarding minimal thickness and ensuring uniform thinness of the material, preliminary contacts may be present and need to be manually adjusted after testing in the patient’s mouth [19].

Differences between the digital design and the actual outcome can be attributed to several factors. One such factor is the thickness and deformation of the sensor when the occlusion is closed. Foils with a thickness of less than 21 µm lack plastic deformation and are suitable for occlusal analysis. However, the T-Scan sensor used in this study has a thickness of 60 µm and may experience deformation during maximal intercuspidation. This difference in thickness can contribute to variations between the digital design and the actual occlusal contacts recorded by the T-Scan system [13,14]. It is important to note that the T-Scan system may record fewer occlusal contacts compared to the actual number of contacts present. This is due to the presence of non-sensible zones in the sensor, which may result in missed contact points. Therefore, the recorded contacts may not fully represent the complete occlusal contact pattern [15,16].

Another potential source of error is the positioning and removal of supports by the dental technician during the fabrication of the retainer. Despite meticulous removal and polishing, there is a possibility of altering occlusal features, which can impact the accuracy of the digital design compared to the actual clinical outcome [32,33]. These factors should be taken into consideration when interpreting and comparing the digital design with the actual clinical outcome. It is important to acknowledge the limitations and potential sources of error in order to make informed conclusions based on the results.

5. Research Limitations

The present study had several limitations that should be considered. Firstly, the sample size consisted of only 21 patients, all of whom underwent treatment using the straight wire technique.

Operator experience was found to be an important factor when evaluating intraoral scanners. It was observed that the experience of the operator influenced the overall assessment of these scanners. Therefore, the findings of this study may be influenced by the operator’s proficiency and expertise in using the intraoral scanner [34].

Another potential limitation of intraoral scans is the size of the scanner head. The conical shape of the head can make it challenging to access posterior molar areas, particularly in adolescents with smaller oral cavities. This limitation may affect the accuracy and completeness of the intraoral scans in capturing the entire dentition [35].

While efforts were made to address these limitations and improve clinical skills, it is important to recognize that higher-quality studies with larger sample sizes and standardized protocols are needed to ensure reliable and valid results. Conducting such studies is essential for orthodontists to make informed decisions in their clinical practice and to advance the field of orthodontics [36].

Another limitation of the study relates to the technical characteristics of the T-Scan device used. Although the T-Scan sensors are designed to be as thin as possible (0.1 mm) to meet technological requirements, they are still relatively thicker compared to occlusal indicators like articulating silk. Thinner occlusal registration materials have been found to yield more consistent records of contact points. The thicker sensors used in the T-Scan system can be susceptible to damage when concentrated forces are applied to a small area, such as a sharp tooth cusp. Additionally, the T-Scan system is more accurate in reproducing occlusal interferences when they exceed 0.6 mm in dimension [10]. The present report evaluates 3D-printed orthodontic retainers. Future studies are needed to test other important specific characteristics such as flexural strength [37], fatigue [38], roughness [39], and color stability [40] in order to complete the knowledge about these emerging materials.

To ensure greater reliability of the results, one clinician performed both the intraoral imaging and the digital examination of the occlusion. This approach minimizes inter-operator variability and enhances consistency in data collection and analysis.

6. Conclusions

In conclusion, the study findings indicate that while digital designs can successfully achieve uniform and balanced occlusal contact points, they do not necessarily result in an even distribution of forces across the teeth. The study observed a significant difference in the loading of the distal sections compared to the frontal sections, despite attempts to achieve a uniform design. This highlights the importance of not only achieving balanced contacts in digital design but also ensuring an even distribution of forces.

The T-Scan system proved to be a valuable tool for evaluating and improving occlusal force distribution. By utilizing this system, clinicians can enhance their treatment planning and achieve more effective outcomes in dentistry. However, further research and advancements are necessary to refine the digital design process and achieve a more balanced distribution of occlusal forces. By addressing these limitations and striving for more precise and balanced force distribution, clinicians can improve the long-term stability of orthodontic treatments and enhance patient outcomes. Continued research and advancements in digital design and occlusal analysis will contribute to the ongoing evolution and optimization of orthodontic practices.