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Published in final edited form as: Clin Oral Investig. 2025 Dec 9;30(1):6. doi: 10.1007/s00784-025-06657-y

Three-dimensional assessment of tooth movements in clear aligner treatment of moderate and severe crowding

Margaret Eason 1, Sandra Khong Tai 2, Charlene Tai Loh 2, Aron Aliaga del Castillo 1, Rodrigo Teixeira 3, Nathan Hutin 1, Gaëlle Leroux 1, Marcela Lima Gurgel 1, Claudia Trindade Mattos 4, Antonio Carlos de Oliveira Ruellas 5, Mary Barkley 1, Eric Hannapel 1, Lucia Cevidanes 6
PMCID: PMC13630423  NIHMSID: NIHMS2209136  PMID: 41364276

Abstract

Objectives

To evaluate angular and linear tooth movements following orthodontic treatment for correction of moderate to severe crowding using clear aligner therapy (CAT).

Materials and methods

This retrospective study included 46 patients treated with clear aligners in permanent dentition for correction of moderate to severe crowding. Twenty-three patients (6 males, 17 females; mean age 20.0 years) were treated with premolar extractions and 23 patients (8 males, 15 females; mean age 17.3 years) were treated without premolar extractions. Three-dimensional tooth linear and angular displacements were quantified in the pre- and post-treatment digital dental models superimposed using the Slicer Automated Dental Tools module of 3D Slicer software (www.slicer.org). Generalized estimation equations were used for group comparisons (p < 0.05).

Results

CAT correction of moderate to severe crowding with premolar extraction led to significant retroclination of upper and lower incisors (upper: −6.71° ±7.79, P < 0.001 and lower: −5.11° ±8.49, P < 0.001). Anchorage control in extraction cases was limited, with approximately equal molar mesialization and incisor lingualization. In non-extraction cases, crowding was corrected through arch expansion with flaring of incisors. Vertical changes were similar between groups.

Conclusions

CAT of moderate to severe crowding without extraction led to arch expansion and proclination of incisors. In contrast, premolar extraction cases often presented incisor retroclination and molar mesial tipping, requiring careful biomechanical management.

Clinical relevance

These findings help clinicians plan treatments, manage patient expectations, and anticipate side effects, enabling the use of proper strategies and resources to optimize outcomes in both extraction and non-extraction cases.

Keywords: Clear aligner therapy, Tooth movement, Extraction, Non-extraction, 3D analysis

Introduction

Clear aligner therapy (CAT) has revolutionized orthodontic treatment, evolving from a solution for mild Class I crowding cases to a versatile solution for managing various malocclusions, including those necessitating premolar extractions [1, 2]. This evolution, propelled by technological advancements and a growing preference for esthetic treatment modalities, underscores the importance of comprehensively understanding CAT’s biomechanical principles and its effectiveness across different orthodontic scenarios [3].

Premolar extraction cases present unique challenges in CAT, primarily related to the management of tooth movements during the closure of extraction spaces [4]. Although CAT permits meticulous planning of posterior anchorage and incisor torque through virtual simulations, actual treatment outcomes may deviate from these initial projections [3, 4]. Recent findings highlight discrepancies in planned versus achieved tooth movements, including suboptimal anchorage outcomes, diminished incisor retraction, and unanticipated molar tipping [4]. CBCT-based studies have confirmed these deviations, demonstrating limited control of buccolingual inclination, root angulation, and space closure mechanics when compared to fixed appliances [3].

These deviations are attributed to various factors, such as the physical properties of clear aligners, which may undergo deformation during space closure, potentially affecting torque control and promoting undesirable tooth movements [4]. Moreover, the predominance of tipping movements in CAT can result in excessive mesial tipping of posterior teeth and distal tipping of anterior teeth during extraction space closure [5]. Recent data have also reported uncontrolled root positions adjacent to extraction sites and variability in canine retraction efficiency, even when optimized attachments and staging protocols are used [6, 7]. Such challenges are not unique to clear aligners and are also observed with conventional fixed appliances, particularly in maintaining effective mechanics during space closure, ensuring proper anchorage control and preventing unwanted tooth tipping [8]. In response to these challenges, technological innovations like Align Technology’s SmartForce and SmartStage systems have been developed to enhance attachment design for better canine retraction and molar control [9]. Nevertheless, the efficacy of these improvements in facilitating precise tooth movements, especially in extraction cases, continues to be a topic of discussion among orthodontists.

Given the complexities inherent in precisely evaluating tooth movements in CAT, especially in the context of extraction scenarios, this study seeks to advance our comprehension of the treatment of moderate to severe crowding by employing a sophisticated approach. Landmark-based superimposition techniques frequently fall short, primarily due to substantial modifications at extraction sites and potential shifts in reference areas like the palatal rugae throughout the course of space closure. These limitations underscore the necessity for more advanced and validated automated methods [10], capable of accurately superimposing digital dental models (DDMs) at various stages of treatment.

Therefore, the objective of this study is to quantitatively evaluate the three-dimensional tooth movements associated with the correction of moderate to severe crowding in premolar extraction and non-extraction cases treated with clear aligner therapy (CAT), using an automated digital model superimposition technique. The research hypothesis is that extraction and non-extraction protocols in CAT exhibit distinct patterns of tooth movement and biomechanical control, particularly in anchorage loss, incisor retraction, and posterior tipping. Through an in-depth analysis of tooth movements in both treatment approaches, this investigation seeks to contribute insights that inform treatment planning, protocol refinement, and patient communication.

Materials and methods

This retrospective study was approved by the Ethics Research Committee of University of Michigan (HUM00222995). The sample consisted of patients treated with clear aligners between 2016 and 2022 at a single orthodontic practice in British Columbia, Canada . The inclusion criteria included patients with initial (T1) and final (T2) digital dental models (DDMs) obtained from an iTero intraoral scanner, presence of moderate to severe crowding (4–7 mm arch length discrepancy), and molar relationship in Class I or Class II. Exclusion criteria consisted of treatment starting prior to 2014 (SmartTrack material and extraction G6 protocol were not introduced yet), missing final DDMs, Class III malocclusion, history of fixed appliance treatment, spacing present prior treatment, multiple missing teeth and excessive upper anterior lingual crown tip.

In total, 46 patients were selected and divided into two groups: 23 patients (6 males and 17 females, mean initial age of 20.0 years ± 10.5) who performed CAT with premolar extractions, and 23 patients (8 males and 15 females, mean initial age of 17.3 years ± 5.8) who received non-extraction CAT. The mean treatment duration was 43.0 ± 9.7 months in the extraction group and 32.3 ± 15.9 months in the non-extraction group. Patients treated with extractions received a mean of 116.6 ± 32.6 aligners over an average of 3.1 ± 1.2 refinement stages. In the non-extraction group, patients received 88.3 ± 37.6 aligners and underwent 2.9 ± 1.5 refinements. The digital treatment plans for the extraction sample consisted of both optimized G6 protocol attachments and 3 mm horizontal and vertical conventional attachments. Consideration was given to the anchorage planned in the initial digital treatment plan for the patients treated with premolar extraction. In the upper arch, 14 cases were planned with maximum, 7 cases with moderate, and 2 cases with reciprocal anchorage. In the lower arch, 9 cases were planned with maximum, 12 cases with moderate, and 2 cases with reciprocal anchorage. When determining the overall anchorage planned for each dental arch, the quadrant with the minimum planned anchorage was used as the reference.

The Slicer Automated Dental Tools module from 3D Slicer version 5.6.0 open-source software (www.slicer.org/) was used to perform artificial intelligence-based automatic segmentation of DDMs, orientation, landmark location, and quantification of the 3D displacements. The flow of image process is represented in Fig. 1. After de-identified the DDMs, crown segmentation was performed using the DentalModelSeg AI-based tool [11]. Individual teeth were then identified, as well as the centroids (constructed from center of occlusal surface of first molars as well as center of incisal edge of the right central incisor). Orientation were performed using Automated Standardized Orientation (ASO) AI-based tool [10]. The maxillary models were oriented automatically using the centroid of the first molars and upper right central incisor. Transformation matrix of upper arch applied to lower arch in occlusion. The lower arch was oriented to the upper arch in occlusion. DDMs at baseline (T1) and post-treatment (T2) were used for 3D superimposition. Automatic registration was performed with A-Reg IOS [10]. For upper arch, the region of the palate that avoids the first rugae and proximity with the gingival margins was used as a reference to registered T2 at T1 DDMs. This transformation was then applied to the lower arch, maintaining the dental arches in occlusion. This approach was used because no stable regions of reference existed in the lower arch due to the automatic trimming of the mucogingival line during the iTero intraoral scan for most cases. Automated Landmark identification (ALIIOS) was used to identify five landmarks on each tooth on both T1 and T2 models [12]: (1) center of occlusal surface/incisal edge. (2) midbuccal cervical region. (3) midlingual cervical region. (4) most mesial point on occlusal surface. (5) most distal point on occlusal surface. If necessary, the landmarks were then manually adjusted for a single examiner. The mid distance at the cervical level of each tooth using the midbuccal and midlingual points was then automatically computed to estimate dental long axes from the occlusal to the midcervical points [13]. To quantify the changes from T1 to T2 DDMs, Automated Quantification of 3D Components (AQ3DC) was used [14]. Seven measurements were made for each tooth, consisting of three angular and four linear measurements. The angular measurements included buccolingual inclination (torque) and mesiodistal angulation (tip), which were measured in the 3D space as the angles between the dental long axes formed by landmark #1 and the mid cervical point; and rotation, which was measured as the angle between the lines made by landmarks #4 and #5 at T1 and T2. The linear measurements included antero-posterior, vertical, and transverse tooth movements, as well as the total scalar displacement of landmark #1 between T1 and T2 [14].

Fig. 1.

Fig. 1

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Workflow for the preparation and analysis of digital dental models (DDMs) using AI-based tools from the DentalAutomatedTools module in 3D Slicer. (A) Automated segmentation of intraoral scans using the DentalModelSeg module. (B) Automatic orientation of the segmented models via the ASO-IOS tool. (C) Automated identification of the palatal rugae region (butterfly patch) for maxillary model registration. (D) Automated landmark identification on intraoral scans (ALIIOS) for quantifying tooth movements, with landmarks placed on the occlusal surface, incisal edge, and cervical regions. (E) Automated quantification using AQ3DC and data tabulation for statistical analysis

To evaluate tooth movements between the extraction and non-extraction groups, the data were categorized by arch (maxillary or mandibular) and by segment (anterior or posterior). The anterior segment included incisors and canines, while the posterior segment comprised second premolars, first molars, and second molars. An exception was made in the four cases involving extraction of second premolars: in these cases, the first premolars were classified as part of the anterior segment.

Intra-rater reliability of a single observer was tested by repeating the adjustment of the landmarks on 30% of the sample. It was tested using an Intraclass Correlation Coefficient (ICC) with an absolute agreement at a 95% confidence interval. Bland-Altman plots were also used to evaluate the intra-rater reliability. Normal distribution was verified using Shapiro-Wilk test. Descriptive statistics and generalized estimation equations were used to analyze the data sets. All the statistical analyses were performed using IBM SPSS Statistics software (version 29.0.2.0).Box plots were used to give visual representation of results. The level of statistical significance was set at α = 0.05. Results with p-values less than 0.05 were considered statistically significant.

Results

The intra-examiner correlation was excellent for all measurements, with the ICC coefficient ranging from 0.94 to 1.00. Bland Altman plots also demonstrate high agreement (Fig. 2A-F). An effect size analysis was performed for all variables using Cohen’s d, based on the observed mean differences and pooled standard deviations between the extraction and non-extraction groups. The effect sizes ranged from −2.03 to 2.77, indicating a moderate to large effect and supporting the adequacy of the sample size to detect clinically relevant differences.

Fig. 2.

Fig. 2

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Bland-Altman plots demonstrating high agreement between repeated measurements of tooth movements based on landmark placement on DDMs. The plots show the differences between two sets of measurements (y-axis) against the means of the two measurements (x-axis) for various tooth movement parameters. The horizontal lines represent the mean difference (solid line) and 95% limits of agreement (dashed lines). The tight clustering of data points around the mean difference line, with the majority falling within the 95% limits of agreement, indicates strong reproducibility of the landmark-based measurement technique on DDMs

Descriptive statistics of T1 and T2 angular and linear movements of extraction and non-extraction groups, the mean change between each group, with standard deviations and intergroup difference p-values determined using generalized estimation equations are reported by each arch and segment in Table 1. Significant differences between extraction and non-extraction groups were found. In extraction cases, the incisors in both arches exhibited significant retroclination with no torque control (upper arch, mean of −6.71° ±7.79, P < 0.001 and lower arch mean of −5.11° ±8.49, P < 0.001). Anchorage control was limited, leading to approximately equal amounts of molar mesialization and incisor lingualization. In the upper arch, the mean mesialization of posterior teeth was 3.94 ± 1.87 and the mean lingualization of anterior teeth was −3.19 ± 1.98. In the lower arch, the mean mesialization of posterior teeth was 2.83 ± 2.48 and the mean lingualization of anterior teeth was −2.81 ± 2.46. Mesial rotation of posterior teeth was greater in extraction group (upper arch, mean of 3.69° ±6.95, P < 0.001 and lower arch mean of 3.01° ±7.92, P < 0.001). Vertical changes were similar between groups.

Table 1.

Comparison of tooth movement in extraction and non-extraction orthodontic treatment with clear aligners

Measurements Extraction group Non-Extraction group P value
Mean change (SD) Mean change (SD)
BuccoLingual Angulation (°)
Upper Posterior Teeth 0.43 (± 7.29) 5.56 (± 11.80) < 0.001 *
Lower Posterior Teeth 5.65 (± 8.35) 5.59 (± 7.85) 0.969
Upper Anterior Teeth −6.71 (± 7.79) −1.97 (± 5.36) < 0.001 *
Lower Anterior Teeth −5.11 (± 8.49) 1.12 (± 6.98) < 0.001 *
MesioDistal Angulation (°)
Upper Posterior Teeth 4.07 (± 8.71) −0.74 (± 6.33) < 0.001 *
Lower Posterior Teeth 0.60 (± 10.83) 1.07 (± 9.36) 0.764
Upper Anterior Teeth −3.07 (± 7.21) −0.85 (± 4.97) < 0.001 *
Lower Anterior Teeth −2.54 (± 7.09) 0.82 (± 4.75) < 0.001 *
Rotation (°)
Upper Posterior Teeth 3.69 (± 6.95) 0.17 (± 8.34) 0.013 *
Lower Posterior Teeth 3.01 (± 7.92) −0.12 (± 8.27) 0.007 *
Upper Anterior Teeth −2.36 (± 10.18) −2.77 (± 15.57) 0.780
Lower Anterior Teeth −0.02 (± 12.73) −2.19 (± 13.66) 0.201
Antero-Posterior (mm)
Upper Posterior Teeth 3.94 (± 1.87) 0.00 (± 0.75) < 0.001 *
Lower Posterior Teeth 2.83 (± 2.48) 0.64 (± 1.31) < 0.001 *
Upper Anterior Teeth −3.19 (± 1.98) 0.14 (± 1.20) < 0.001 *
Lower Anterior Teeth −2.81(± 2.46) 1.06 (± 1.65) < 0.001 *
Vertical (mm)
Upper Posterior Teeth 0.36 (± 1.18) 0.58 (± 0.98) 0.411
Lower Posterior Teeth −0.63 (± 1.35) −0.43 (± 1.22) 0.558
Upper Anterior Teeth 1.37 (± 1.81) 1.11 (± 1.32) 0.474
Lower Anterior Teeth −0.60 (± 1.75) −0.97 (± 1.38) 0.419
Transverse (mm)
Upper Posterior Teeth −0.22 (± 0.95) 1.13 (± 0.98) < 0.001 *
Lower Posterior Teeth 0.18 (± 1.45) 1.05 (± 1.41) < 0.001 *
Upper Anterior Teeth −0.12 (± 1.38) −0.23 (± 1.10) 0.237
Lower Anterior Teeth 0.16 (± 1.39) 0.00 (± 1.58) 0.053
3D Displacement (mm)
Upper Posterior Teeth 4.31 (± 1.72) 1.77 (± 0.98) < 0.001 *
Lower Posterior Teeth 3.73 (± 2.13) 2.29 (± 1.28) 0.003 *
Upper Anterior Teeth 4.17 (± 1.93) 2.12 (± 1.09) < 0.001 *
Lower Anterior Teeth 3.98 (± 1.86) 2.60 (± 1.53) < 0.001 *
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BL Ang: (−) Lingual and (+) Buccal crown tip; MD Ang: (−) Distal and (+) Mesial crown tip; Rotation: (−) Distal and (+) Mesial crown rotation; AP: (−) Posterior and (+) Anterior crown movement; Vertical: (−) Intrusion and (+) Extrusion; Transverse (Posterior teeth): (−) Lingual and (+) Buccal crown movement; Transverse (Anterior teeth): (−) Mesial and (+) Distal crown movement

*

Statistically significant at P <0.05

Figure 4A to C illustrates angular changes observed in extraction cases and Figure D to non-extraction cases. Figure 5 illustrates the variability of molar mesialization control in two extraction cases planned with maximum anchorage (5 A and 5B), as well as treatment outcomes for a non-extraction case (5 C).

Fig. 4.

Fig. 4

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(A) Mesiodistal angulation, demonstrating molar tipping in extraction cases. (B) Buccolingual angulation of anterior teeth, showing incisor retroclination in extraction cases. (C) Buccolingual angulation of posterior teeth in non-extraction cases, indicating arch expansion through buccal crown tipping. (D) Buccolingual angulation of posterior teeth in extraction cases

Fig. 5.

Fig. 5

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Variability in molar mesialization and treatment outcomes in clear aligner therapy. (A, B) Two extraction cases planned with maximum anchorage, demonstrating different degrees of molar mesialization. (C) A non-extraction case showing the actual treatment outcome compared to the planned outcome. The superimpositions are for visualization purposes only and the study did not measure the predicted tooth movements from the digital treatment plan

Discussion

This study’s results reveal the variability in achieving precise tooth movements in moderate and severe crowding cases treated with clear aligners with premolar extraction and non-extraction cases. By employing advanced 3D superimposition techniques, this study underscores the critical need for precise anchorage management in the biomechanics of extraction scenarios, towards achieving the desired orthodontic outcomes. These findings are crucial for clinicians in planning treatment, setting patient expectations, and understanding potential side effects to utilize appropriate resources and strategies to achieve the desired outcomes in both extraction and non-extraction scenarios.

Our results are consistent with previous research evaluating the effects of premolar extraction treatment with clear aligners [4, 15]. The observed retroclination of incisors in the extraction group (Fig. 4B) aligns with the treatment goals for cases with significant initial protrusion. However, the ability of clear aligners to maintain adequate incisor torque control during retraction has been questioned [16, 17]. This is likely due to the mean change of 5.56° in the maxillary posterior buccolingual angulation in the non-extraction group (Fig. 4D), compared to 0.43° in the extraction group (Fig. 4C). However, considering that arch expansion with clear aligners is primarily achieved through crown buccal angulation rather than bodily movement [15, 18–21], further investigation into long-term stability is warranted to optimize treatment outcomes.

The statistically significant differences in mesiodistal angulation between extraction and non-extraction groups corroborate prior reports of undesired tipping during space closure with clear aligners [4, 20]. Clear aligner therapy often results in greater tipping movements compared to bodily tooth movement, especially in the closure of extraction spaces [6]. Our findings highlight the need for refinements in clear aligner biomechanics [5, 23–32], including optimizing the points of force application [22] and incorporating auxiliaries such as elastics and power arms [21], to minimize adverse crown angulations. While no significant differences were observed in rotation in anterior teeth, the trend towards mesial-in rotation of posterior teeth in extraction cases may indicate the need for studies on strategies for improving posterior rotational control.

It is noteworthy that no significant differences were observed in the vertical changes between extraction and non-extraction groups. This finding is particularly interesting, as one might expect the overbite to deepen more in extraction cases due to the mechanics of space closure [33]. However, our results indicate that the amount of upper incisor extrusion in the extraction group (1.37 ± 1.81 mm) was not significantly different from the non-extraction group (1.11 ± 1.32 mm). These findings suggest effective vertical control of the incisors during clear aligner therapy, even in extraction cases. The ability to maintain adequate vertical control of the incisors in extraction cases is a notable advantage of clear aligners, as it can help prevent unwanted deepening of the overbite and maintain facial esthetics [34]. This vertical control may be attributed to the inherent properties of clear aligners, such as the full-coverage design and the ability to incorporate intrusive forces through strategic attachment placement and aligner design [35].

A key finding from our study is that premolar extraction cases treated with clear aligners tend to exhibit reciprocal space closure, regardless of whether moderate or maximum anchorage is planned. The mean molar mesialization in extraction cases of 3.94 ± 1.87 mm and 2.83 ± 2.48 mm in the maxillary and mandibular arches, respectively, underscores the importance of setting realistic expectations and communicating potential discrepancies between virtual simulations and actual outcomes to patients [4]. The greater mesialization observed in the maxillary arch likely stems from its anatomical characteristics that render it more susceptible to anchorage loss [36]. As seen in Fig. 5, results can vary greatly, emphasizing the role of individual case characteristics and initial crowding in determining successful molar anchorage. These findings confirm the conclusions of Dai et al. [4]. The clinical significance of tooth movements differs notably between extraction and non-extraction cases due to inherent biomechanical and anatomical factors. In extraction cases, tooth movement typically involves space closure characterized by greater retraction and often tipping of anterior teeth, as well as mesial movement of posterior teeth into the extraction spaces. This results in distinct directional and magnitude patterns compared to non-extraction cases, where arch expansion and slight proclination or bodily movement may predominate. Our findings align with these biomechanical expectations, underscoring the need for tailored treatment planning and biomechanical control in extraction cases to optimize outcomes. Recognizing these tendencies allows clinicians to adapt their treatment strategies accordingly.

Our findings raise several questions that warrant further investigation. How can clear aligner protocols be optimized to enhance the predictability of tooth movements in extraction cases? What specific biomechanical strategies, such as auxiliaries or modified attachment designs, can be employed to improve anchorage control and minimize undesired tipping? While our study focused on dental anchorage, retraction, and angulation, a comprehensive assessment of overall clinical outcomes would benefit from additional metrics such as occlusal results, treatment efficiency, and patient satisfaction. Future prospective studies should aim to address these factors for a more holistic evaluation of clear aligners in managing extraction cases.

The present study contributes to our understanding of the biomechanical complexities and potential discrepancies between virtual simulations and clinical realities in the treatment of moderate to severe crowding with clear aligners. The demonstrated differences in tooth movement between premolar extraction and non-extraction cases highlight the importance of individualized treatment planning. By harnessing the capabilities of advanced 3D analysis and remaining cognizant of the intricacies involved in space closure and tooth movement control, clinicians can refine their treatment planning, patient communication, and evidence-based decision-making to optimize outcomes. As orthodontic technology and techniques continue to advance, embracing these findings and pursuing continued research will be instrumental in pushing the boundaries of what is achievable in complex cases. This study has limitations inherent to its retrospective design. These limitations should be considered when interpreting the results, and future randomized clinical studies with controlled samples are needed to confirm and expand upon these findings. While the digital treatment plans for extraction cases included anchorage preparation strategies such as optimized G6 attachments, vertical and horizontal rectangular attachments, and programmed distal tipping of molars, the retrospective nature of this study limited our ability to extract precise values for overcorrection (e.g., degrees of programmed tip or torque) from the aligner setup software. Moreover, auxiliary mechanics such as the use of Class II elastics were not consistently documented in the patient records. The significant molar mesialization and incisor retroclination observed in our sample, consistent with previous studies, underscore the clinical challenges of anchorage control in extraction cases treated with clear aligners. These results highlight the need for prospective studies that incorporate detailed records of digital plan parameters and auxiliary mechanics to improve predictability of treatment and refine aligner biomechanics.

Conclusions

Clear aligners therapy of moderate and severe crowding with premolar extractions exhibited greater challenges in controlling buccal inclination, anterior torque, and mesiodistal tip management, with notable retroclination of the incisors and mesial tipping of molars. Clinicians should anticipate and carefully manage the biomechanical limitations associated with tooth movement control.

Supplementary Material

Supplementary Material

The online version contains supplementary material available at https://doi.org/10.1007/s00784-025-06657-y.

Fig. 3.

Fig. 3

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Boxplots comparing tooth movements between extraction (yellow) and non-extraction (blue) groups treated with clear aligners, categorized by arch (upper or lower) and segment (anterior or posterior teeth). The boxplots display the distribution of angular measurements, including (A) mesiodistal angulation, (B) buccolingual angulation, and (C) rotation, as well as linear measurements, including (D) vertical changes, (E) transverse displacements, and (F) overall 3D displacements. Negative and positive values represent specific directional changes as detailed in Table. Dots represent outliers. Note the differences in tooth movement patterns between extraction and non-extraction groups, with statistically significant differences (P<0.05) indicated in Table

Acknowledgements

This work was supported by NIDCR R01DE024450.

Funding

This work was supported by NIDCR R01DE024450.

Footnotes

Ethical approval This study was approved by the Ethics Research Committee of University of Michigan (HUM00222995).

Informed consent Not applicabe.

Competing interests The authors declare no competing interests.

Data availability

No datasets were generated or analysed during the current study.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Material
NIHMS2209136-supplement-Supplementary_Material.pdf (162.5KB, pdf)

Data Availability Statement

No datasets were generated or analysed during the current study.

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