Stable region for maxillary dental cast superimposition in adults, studied with the aid of stable miniscrews

Impact of the superimposition reference area on intraoral scanning accuracy in a partially dentate maxilla

STATEMENT OF PROBLEM

The alignment of 3-dimensional (3D) files involves selecting a reference area before performing a local best fit alignment during the digital scan superimposition and is essential for comparing digital scans. Scan alignment relies on both reference area location and the alignment algorithm. However, a consensus on the impact of different reference areas on intraoral scanning accuracy is lacking.

PURPOSE

The purpose of this in vitro study was to assess the impact of 3 superimposition reference areas on the accuracy of 3 intraoral scanners for a partially dentate maxilla.

MATERIAL AND METHODS

A Kennedy class II resin cast was scanned using 3 intraoral scanners (Primescan, TRIOS 3, and Emerald) outputting 30 digital scans (10 per scanner). Test scans from intraoral scanners were subsequently compared with a reference digital standard tessellation language file generated by a laboratory scanner with validated accuracy. The files were superimposed using best fit alignment for each intraoral scanner using 3 different superimposition reference areas (whole region of interest, palate, and all teeth). Accuracy was assessed by using a 3D analysis program (Geomagic Control X; 3D systems) for each scanner at 4 preselected areas. Test and reference scan differences were depicted on color maps and quantified via root mean square deviations. Differences were analyzed using regression analysis with the post hoc student t test and Bonferroni correction (α=.05).

RESULTS

The TRIOS 3 and Emerald produced positive deviations in the palatal color maps, whereas Primescan produced more uniform color maps, regardless of the superimposition strategy used. Primescan exhibited the best accuracy (trueness and precision) in both palatal and bounded edentulous areas, regardless of the superimposition reference area. The TRIOS 3 recorded the highest distal extension trueness (ranging from 42.9±7.7 µm to 65 ±19.5 µm), and Primescan achieved the highest precision (ranging from 28.5 ±9.8 µm to 48.9 ±16.9 µm), regardless of the superimposition area. Emerald demonstrated the highest teeth trueness (ranging from 31.6 ±6.8 µm to 69.6 ±11.5 µm), while Primescan produced the highest precision (ranging from 17.9 ±6.1 µm to 30.7 ±9.2 µm), regardless of the reference area used.

CONCLUSIONS

The chosen reference area for best fit alignment significantly influenced digital scan accuracy (P<.001). Primescan displayed the highest palatal and bounded edentulous area accuracy, with TRIOS 3 recording the highest distal extension trueness. Emerald recorded the highest teeth trueness and Primescan recorded the highest distal extension and tooth precision. All conclusions were independent of the superimposition strategy used.

Effect of low-level laser therapy on en masse retraction in females with bimaxillary dentoalveolar protrusion : A single-center randomized clinical trial

BACKGROUND

Acceleration of tooth movement has gained remarkable attention during the last decade. The aim of this study was to evaluate the effect of low-level laser therapy (LLLT) on en masse retraction of upper anterior teeth in adult women with bimaxillary dentoalveolar protrusion.

MATERIALS AND METHODS

In this two-arm parallel trial, 36 women with bimaxillary dentoalveolar protrusion were randomly divided into two equal groups. Eligibility criteria included class I Angle molar relationship, good general and oral health as well as no systemic disease or syndrome. Four temporary anchorage devices (TADs) were used in the upper and lower arches for anchorage purposes. A 0.019×0.025-inch stainless steel wire with crimped hooks just distal to the maxillary canines was inserted. Nickle titanium (NiTi) closed coil springs (200 g/side) were employed for en masse retraction following extraction of the first premolars. In the laser group (LG), retraction of the upper anterior teeth was done along with the application of LLLT on days 0, 3, 7, and 14 after extraction and then repeated biweekly until the end of retraction. Retraction was completed without LLLT application in the nonlaser group (NLG). Data concerning the rate of retraction as well as first molars and anterior positional changes were gained from digitized models and cone beam computed tomography (CBCT) scans taken just before extraction and at the end of retraction. Treatment-associated pain and root resorption were evaluated using visual analogue scale (VAS) and CBCT scans, respectively.

RESULTS

Four patients dropped out prior to follow-up. The duration of retraction was 10.125 ± 2.876 and 13.643 ± 3.455 months in the LG and NLG, respectively. The LG showed a statistically significant faster rate of en masse retraction (0.833 ± 0.371 mm/month) compared to the NLG (0.526 ± 0.268 mm/month; P ≤ 0.035). The observed root resorption was significantly less in the LG (P ≤ 0.05) with comparable pain scores in both groups.

CONCLUSIONS

Within the constraints of the parameters of the LLLT used in the current study and despite the statistically significant results on the rate of en masse retraction and the associated root resorption, LLLT did not demonstrate a clinically relevant effect that justifies its use to enhance en masse retraction.

NAME OF THE REGISTRY

Clinicaltrials.gov TRIAL REGISTRATION NUMBER: NCT05183451 DATE OF REGISTRATION: January 10, 2022, "Retrospectively registered" URL OF TRIAL REGISTRY RECORD: https://www.

CLINICALTRIALS

gov/study/NCT05183451.

Superimposition of virtual models using palatal rugae and maximum habitual intercuspation

INTRODUCTION

The superimposition of 3 dimensions (3D) digital models has been increasingly used for evaluating dental changes resulting from orthodontic treatment, and different superimposition techniques have been described. Although the maxilla has areas with greater stability for superimposition, such as the palatal rugae, there is still no reliable method for superimposing models of the lower arch.

OBJECTIVE

Therefore, this article aims to describe a technique for superimposing virtual models.

METHODS

To evaluate pre- and post-orthodontic treatment changes, the Geomagic Qualify 2013 software (3D Systems®, Rock Hill, South Carolina, USA) was used, with reference points in the maxilla, including the rugae and a reference area in the palate and midpalatal raphe. The lower arch was superimposed using the maximum habitual intercuspation (MHI) model as reference.

RESULTS AND CONCLUSION

3D models superimposition using palatal rugae and MHI occlusion seems to offer satisfactory results in the interpretation of clinical changes at different follow-up moments in terms of development and/or orthodontic treatment.

Evaluation of the success of predicted dental changes with clear-aligner treatment: A pilot study

Objective

This pilot study concerned evaluation of the success of predicted dental changes in patients presenting with Class I malocclusions who were submitted to treatment aligners, using the superimposition.

Methods

The digital models were superimposed and analyzed using 3DSlicer 5.0 software. Treatment and predicted changes regarding horizontal and vertical linear displacements, mesiodistal rotations, and incisor buccolingual tipping were quantified. The success rates were calculated by dividing the mean treatment change amount by the predicted change amount.

Results

Lower-incisor intrusion was the most accurate of the predicted vertical displacements (86.96 %), and buccal expansion of upper canines (99.32 %) and mesial translation of the lower incisors (98.57 %) were the most accurate horizontal linear displacements. The predicted rotation was achieved with the highest accuracy for lower incisors (75.69 %). Incisor buccolingual tipping success rates ranged between 45.78 % and 69.31 %. Low accuracy of predicted changes was found for upper-molar extrusion (10.23 %) and constriction (8.91 %). However, minimal corrections in these directions were planned.

Conclusions

Dental changes for all regions of maxillary and mandibular arches could be evaluated. High success rates were observed for most of the movements planned for ClearCorrect aligner therapy.

Compliance and side effects of tongue stabilizing device in patients with obstructive sleep apnea

OBJECTIVE

To evaluate the long-term effectiveness, compliance, and side effects of tongue stabilizing devices (TSDs).

METHODS

Thirty-nine patients were followed up after 12 and 30 months. The subjective effectiveness was assessed using the Epworth Sleepiness Scale (ESS), the Functional Outcomes Sleep Questionnaire (FOSQ-10), the Chalder Fatigue Scale (CFQ), and a sleep-related quality of life questionnaire (QoL). Compliance and side effects were assessed.

RESULTS

At 12-months, 35.9% of patients confirmed continuing the therapy, compared to only 15.4% of patients at 30 months. At 30 months, a significant average improvement of ESS (2.0 ± 2.8) was observed compared to baseline levels in six patients. Six patients demonstrated an average increase in blood pressure. The most frequently reported side effects were mouth dryness and excessive salivation. The 3D analysis revealed small tooth movements.

CONCLUSION

The TSD therapy demonstrated a good long-term subjective effectiveness against OSA but had a relatively low treatment acceptance rate.

Biomechanical model registration for monitoring and simulating large orthodontic tooth movements in the maxilla and mandible

PURPOSE

Superimposition of digital dental-arch models allows quantification of orthodontic tooth movements (OTM). Currently, this procedure requires stable reference surfaces usually only present in the maxilla. This study aimed to investigate the accuracy of a novel superimposition approach based on biomechanical principles of OTM and the equilibrium of forces and moments (EFM)-applicable in both jaws-for monitoring and simulating large OTM.

METHODS

The study included 7 patients who had undergone extraction of the first (PM1-Ex) or second (PM2-Ex) premolar in each quadrant. Digital models taken at start and end of the T‑Loop treatment phase were superimposed by applying 3 EFM variants differing in the number of teeth used for registration. Maxillary OTM results for EFM were validated against those for a conventional surface registration method (SRM). In an additional case study, OTM were simulated for PM1-Ex, PM2-Ex and non-extraction treatment strategies.

RESULTS

The EFM variant that included all teeth of the dental arch achieved the highest accuracy, with median translational and rotational OTM deviations from SRM of only 0.37 mm and 0.56°, respectively. On average, retracted canines and first premolars were distalized by 3.0 mm, accompanied by 6.2° distal crown tipping and 12.2° distorotation. The share of space closure by molar mesialization was 19.4% for PM1-Ex quadrants and 34.5% for PM2-Ex quadrants.

CONCLUSION

EFM allows accurate OTM quantification relative to the maxillary and mandibular bases even in challenging situations involving large OTM. Superimposition of malocclusion and setup models enables realistic simulation of final tooth positions. This may greatly enhance the value of digital setups for decision-making in orthodontic treatment planning.

Comparison between 2D cephalometric and 3D digital model superimpositions in patients with lateral incisor agenesis treated by canine substitution

INTRODUCTION

This study aimed to assess the reliability of measurements obtained after superimposing 3-dimensional (3D) digital models by comparing them with those obtained from lateral cephalometric radiographs in patients with lateral agenesis space closure by mesialization.

METHODS

Data were collected from premaxillary and postmaxillary dental casts and lateral cephalometric radiographs of 26 patients presenting lateral incisor agenesis and treated with rapid maxillary expanders and space closure by mesialization of the lateral sectors. Sagittal and vertical movements of the incisors and the maxillary molars were evaluated with lateral cephalometric radiographs and digitized 3D models superimposed on the palatal area. Paired sample t tests were used to determine if any significant difference existed between the 2 measuring techniques and between 2 different localizations of superimpositions.

RESULTS

Cephalograms and 3D digital model measurements were statistically similar in molars and incisor movements according to anteroposterior and vertical planes. Regarding incisor movements in the anteroposterior plane, measurements derived from second ruga 3D models were significantly greater than those derived from third ruga 3D digital models.

CONCLUSIONS

The 3D model superimposition method using the palate as a reference area is clinically reliable for assessing anteroposterior and vertical tooth movement as cephalometric superimposition in patients treated with rapid maxillary expanders and space closure by mesialization.

Vertical changes in the hard tissues after space closure by miniscrew sliding mechanics: a three-dimensional modality analysis

OBJECTIVES

This study aimed to investigate vertical changes in the maxillary central incisor and the maxillary first molar, along with alterations in the mandibular plane angle during space closure using miniscrew sliding mechanics.

METHODS

Twenty adult patients treated at Peking University Hospital of Stomatology between 2008 and 2013 were included. Digital dental models and craniofacial cone-beam computed tomography (CBCT) scans were obtained at the start of treatment (T0) and immediately after space closure (T1). Stable miniscrews were used for superimposing maxillary digital dental models (T0 and T1), and vertical changes in the maxillary first molar and the maxillary central incisor were measured. Three-dimensional changes in the mandibular plane were assessed through CBCT superimposition.

RESULTS

The maxillary central incisor exhibited an average extrusion of 2.56 ± 0.18 mm, while the maxillary first molar showed an average intrusion of 1.25 ± 1.11 mm with a distal movement of 0.97 ± 0.99 mm. Additionally, the mandibular plane angle decreased by an average of 0.83 ± 1.65°. All three indices exhibited statistically significant differences.

CONCLUSION

During space closure using the miniscrew sliding technique, significant changes occurred in both the sagittal and vertical dimensions of the upper dentition. This included extrusion of the maxillary central incisors, intrusion of the maxillary first molars, and a slight counterclockwise rotation of the mandibular plane.

Effect of clear aligner attachment design on extrusion of maxillary lateral incisors: A multicenter, single-blind randomized clinical trial

INTRODUCTION

Extrusion of maxillary lateral incisors during aligner treatment is a difficult movement to achieve accurately. Despite recommendations regarding attachment design, few studies and no prospective trials compare predictability among attachments. This study aimed to compare the efficacy between optimized and horizontal attachment designs for achieving maxillary lateral incisor extrusion during clear aligner treatment.

METHODS

The study included maxillary lateral incisors in 3 orthodontic practices requiring at least 0.3 mm of extrusion during the first series of 20-25 aligners in patients aged ≥16 years who were scheduled to begin clear aligner treatment (Invisalign; Align Technology, San Jose, Calif). Teeth were randomly assigned to receive optimized (O), rectangular horizontal nonbeveled (H), rectangular horizontal incisally-beveled (HIB), or rectangular horizontal gingivally-beveled (HGB) attachments. After the first series, a blinded evaluator measured extrusion using superimpositions with initial and predicted models. Linear models determined the difference in the predicted extrusion percentage achieved on the basis of attachment design. Other covariates were patient age, sex, number of trays, and self-reported compliance.

RESULTS

Forty patients (74 teeth) were enrolled, and 38 patients (71 teeth) completed the study. Intraexaminer and interexaminer reliability for extrusion measurements was high (intraclass correlation coefficient, 0.985 and 0.991, respectively). The achieved extrusion was significantly less than predicted (mean, 73%; P <0.0001). The average achieved extrusion was 62%, 79%, 78%, and 78% for O, H, HIB, and HGB attachments, respectively, with H significantly more effective than O (P = 0.0403). Horizontal attachments (H, HIB, and HGB combined) were significantly more effective than O attachments (P = 0.0060), with an average difference in achieved extrusion of 14% of the predicted amount (95% confidence interval, 4-23; estimated 76% vs 62%). Horizontal attachments were an estimated 22% more effective than O attachments for extruding maxillary lateral incisors.

CONCLUSIONS

Horizontal attachments are more effective than O attachments for predicted maxillary lateral incisor extrusion between 0.3 and 2.5 mm. The 3 horizontal attachment designs evaluated performed similarly for achieving predicted extrusion.

TRIAL REGISTRATION

This randomized clinical trial was registered and reported at clinicaltrials.gov (NCT04968353).

PROTOCOL

The protocol was not published before trial commencement.

FUNDING

This study was funded in part by the Alexander Fellowship of the Virginia Commonwealth University School of Dentistry, the Southern Association of Orthodontists, and the Virginia Orthodontic Education and Research Foundation. No funding source influenced the study design, the collection, analysis or interpretation of data, writing of the report, or the decision to submit the article for publication.

Are palatal rugae reliable markers for 3D superimposition and forensic human identification after palatal expansion? A systematic review

OBJECTIVES

Palatal rugae are periodic structures situated in the palatal mucosa, often used as landmarks for human identification and superimposition of digital dental models. This review aims to collect the current evidence regarding whether orthodontic palatal expansion could affect the stability of the palatal rugae and to give preliminary guidelines.

MATERIALS AND METHODS

A systematic review of the literature was performed in the scientific databases Pubmed; Embase; WoS; and Cochrane. Grey Literature was also sought (clinicaltrial.gov; ICTRP; AHRQ; INAHTA). The search protocol, was registered in PROSPERO (N*208722). Data extraction comprised: year of publication, journal, sample size, characteristics of the experimental and control group, type of expander, expansion protocol, rugae classification, measurement method on casts, time between casts, method error, rugae change, morphology change and overall outcome. Risk of bias of the included articles was evaluated with the Newcastle-Ottawa Scale.

RESULTS

A total of 12394 manuscripts were retrieved after duplicate removal. From these, nine articles were finally included for data extraction. three studies scored as low risk of bias, two as medium and four as high.

CONCLUSIONS

The morphology of the palatal rugae can be modified by palatal expansion techniques, especially by rapid maxillary expansion. The first rugae is the most stable along with the points close to the palatal midline, which should be used as a reference both for manual or semi-automatic superimpositions. Human identification and serial superimpositions based on palatal rugae should not be carried immediately post expansion and be taken in consideration with caution in patients who underwent prior palatal expansion.

Quantifying maxillary anterior tooth movement in digital orthodontics: Does the choice of the superimposition software matter?

BACKGROUND

To compare the agreement between predetermined angular and linear tooth movement measurements processed with three digital model registration software packages.

METHODS

Twenty maxillary intraoral pretreatment scans of patients undergoing clear aligner therapy were randomly selected. Digital setups were generated using OrthoAnalyzer Clear Aligner Studio software to serve as the reference standard. Both pretreatment scans and setups were converted to STL files and exported to Geomagic, OrthoAnalyzer-Model Set Compare, and Compare model registration software packages. The amount of tooth movement of the maxillary incisors and canines was calculated in six degrees of freedom.

RESULTS

Statistical significance of the obtained results was expressed at P < 0.01 to account for multiple comparisons. The maxillary central incisors showed the highest agreement for torque and rotation as measured by all software programs. Lateral incisors showed the least agreement in linear movements as measured by Geomagic and Compare, and for tip as measured by Geomagic and OrthoAnalyzer. Maxillary canines had the highest agreement for all linear movements as measured by Geomagic and Compare, and tip as measured by Geomagic and OrthoAnalyzer. Geomagic showed excellent agreement for all measurements except for torque, whereas Compare showed excellent agreement only for rotation and linear measurements. OrthoAnalyzer showed moderate agreement for all measurements except for rotation, which showed good agreement.

CONCLUSIONS

Maxillary central incisor measurements showed higher agreement compared with measurements of the maxillary lateral incisors and canines. Although none of the software showed poor agreement, Geomagic seemed to have the highest accuracy.

Natural reference structures for three-dimensional maxillary regional superimposition in growing patients

BACKGROUND

Assessment of growth-related or treatment-related changes in the maxilla requires a reliable method of superimposition. Such methods are well established for two-dimensional (2D) cephalometric images but not yet for three-dimensions (3D). The aims of this study were to identify natural reference structures (NRS) for the maxilla in growing patients in 3D, opportunistically using orthodontic mini-screws as reference; and to test the applicability of the proposed NRS for maxillary superimposition by assessing the concordance of this approach with Björk's 'stable reference structures' in lateral projection.

METHODS

The stability of the mini-screws was tested on longitudinal pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images by measuring the distance changes between screws. After verifying the stability of the mini-screws, rigid registration was performed for aligning the stable mini-screws. Then, non-rigid registration was used to establish the dense voxel-correspondence among CBCT images and calculate the displacement of each voxel belonging to the maxilla relative to the mini-screws. The displacement vectors were transformed to a standardized maxillary template to categorize the stability of the internal structures statistically. Those voxels that displaced less relative to the mini-screws were considered as the natural reference structures (NRS) for the maxilla. Test samples included another dataset of longitudinal CBCT scans. They were used to evaluate the applicability of the proposed NRS for maxillary superimposition. We assessed whether aligning the maxilla with proposed NRS is in concordance with the maxillary internal reference structures superimposition in the traditional 2D lateral view as suggested by Björk. This was quantitively assessed by comparing the mean sagittal and vertical tooth movements for both superimposition methods.

RESULTS

The stability of the mini-screws was tested on 10 pairs of pre- and post-orthodontic cone-beam computed tomography (CBCT) images (T1: 12.9 ± 0.8 yrs, T2: 14.8 ± 0.7 yrs). Both the loaded and the unloaded mini-screws were shown to be stable during orthodontic treatment, which indicates that they can be used as reference points. By analyzing the deformation map of the maxilla, we confirmed that the infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than  1 cm distal to incisor foramen except the palatal suture) were stable during growth. Another dataset of longitudinal CBCT scans (T1: 12.2 ± 0.63 yrs, T2: 15.2 ± 0.96 yrs) was used to assess the concordance of this approach with Björk's 'stable reference structures'. The movement of the maxillary first molar and central incisor showed no statistically significant difference when superimposing the test images with the proposed NRS or with the classic Björk maxillary superimposition in the lateral view.

CONCLUSIONS

The infraorbital rims, maxilla around the piriform foramen, the infrazygomatic crest and the hard palate (palatal vault more than 1 cm posterior to incisal foramen except the palatal suture) were identified as stable regions in the maxilla. These stable structures can be used for maxillary superimposition in 3D and generate comparable results to Björk superimposition in the lateral view.

Treatment effects after maxillary expansion using invisalign first system vs. acrylic splint expander in mixed dentition: a prospective cohort study

BACKGROUND

Invisalign First System (First) is a new type of orthodontic appliance for maxillary arch expansion in mixed dentition children. Till now, few studies have evaluated the expansion effects of First versus other appliances. What's more, most studies of arch expansion did not include a natural group to rule out growth effects. This prospective cohort study aimed to evaluate the dental and dentoalveolar effects using First or acrylic splint rapid maxillary expander (RME) in adolescents excluding growth factors.

MATERIALS AND METHODS

After screening by strict inclusion criteria and propensity score matching (PSM), fifty-one patients were included: First group (n = 17), RME group (n = 17), and natural growth (NG) group (n = 17). Nine indicators including dental arch width, dentoalveolar arch width, and inclination of the molars were measured on digital dental casts at baseline (T0) and six-month follow-up (T1). Paired t-tests were used for intra-group results, and two-sample independent t-tests were used for inter-group comparisons.

RESULTS

There was no significant increase in all indicators within six months in the NG group (p > 0.05). In the First group and RME group, all width indicators were significantly increased after treatment (p < 0.05). The RME group exhibited greater expansion than the First group in intercanine width, first interpremolar width, second interdeciduous molar width, first intermolar width, arch perimeter, intercanine dentoalveolar width, intermolar dentoalveolar width, and inclination of the molars (p < 0.05). Whereas, there was no significant difference in arch depth between the two treated groups.

CONCLUSIONS

Both First and RME can expand the maxillary arch in mixed dentition. In case of mild to moderate maxillary transverse deficiency (MTD), Invisalign First System could be a reasonable option. RME shows significant better efficiency of dental arch expansion than First, recommended for patients with severe MTD.

TRIAL REGISTRATION

This prospective study was registered on ClinicalTrials.gov (01/02/2022, registration number: ChiCTR2200056220). The trial was approved by the Ethical Committee of the Hunan Xiangya Stomatological Hospital Central South University (20,200,088), and informed consent was obtained from all subjects and their legal guardian(s).

A retrospective study of the accuracy of Invisalign Progress Assessment with clear aligners

The objective of this study was to detective the accuracy of model superimposition and automatic analysis for upper and lower dentition width in Invisalign Progress Assessment during the process of clear aligners. 19 cases were included in this study. Pre-treatment dental cast (T0) and post-treatment dental cast after staged treatment (T1) were available for three-dimensional model superimposition. Subsequently, movements of maxillary teeth in the horizontal plane (cross-section) after staged treatment and width of upper and lower dentition were measured by three-dimensional model superimposition in the real world and Invisalign Progress Assessment separately. Consequently, the data collected from these two methods were compared. In Invisalign Progress Assessment, movements of maxillary teeth in the horizontal plane after staged treatment was 2.31 (1.59,3.22) [median (upper quartile, lower quartile)] millimeter (mm), while in three-dimensional model superimposition, the result was 1.79 (1.21,3.03) mm. The difference between the two groups is significant (P < 0.05). Intercanine width upper, intermolar width upper, intercanine width lower, and intermolar width lower were 36.55 ± 2.76 mm, 56.98 ± 2.62 mm, 28.16 ± 1.85 mm, 53.21 ± 2.72 mm separately in Invisalign Progress Assessment and were 36.48 ± 2.78 mm, 56.89 ± 2.58 mm, 28.05 ± 1.85 mm, 53.16 ± 2.64 mm separately in three-dimensional model analysis, which was no significant difference among these groups (P > 0.05). The data from Invisalign Progress Assessment was not in parallel with what was achieved from model superimposition with palate as a reference completely. The accuracy of model superimposition in Invisalign Progress Assessment needs further investigation, whereas the accuracy of model analysis in Invisalign Progress Assessment was accurate. Thereby, results from Invisalign Progress Assessment should be interpreted with caution by the orthodontist in the clinic.

Effectiveness of clear aligners in achieving proclination and intrusion of incisors among Class II division 2 patients: a multivariate analysis

BACKGROUND

The predictability of incisor movement achieved by clear aligners among Class II division 2 patients is poorly understood. The aim of this retrospective study was to determine the effectiveness of clear aligners in proclining and intruding upper incisors and its influencing factors.

METHODS

Eligible patients with Class II division 2 malocclusion were included. For clear aligner therapy, three types of incisor movements were designed: proclination, intrusion and labial movement. Pre-treatment and post-treatment dental models were superimposed. The differences between predicted and actual (DPA) tooth movement of incisors were analyzed. Univariate and multivariate linear regression were used to analyze the potential influencing factors.

RESULTS

A total of 51 patients and their 173 upper incisors were included. Actual incisor proclination and intrusion were less than predicted ones (both P < 0.001), while actual labial movement was greater than predicted one (P < 0.001). Predictability of incisor proclination and intrusion was 69.8% and 53.3%, respectively. Multivariate linear regression revealed that DPA of proclination was significantly positively associated with predicted proclination (B = 0.174, P < 0.001), ipsilateral premolar extraction (B = 2.773, P < 0.001) and ipsilateral canine proclination (B = 1.811, P < 0.05), while negatively associated with molar distalization (B = - 2.085, P < 0.05). The DPA of intrusion was significantly positively correlated with predicted intrusion (B = 0.556, P < 0.001) while negatively associated with labial mini-implants (B = - 1.466, P < 0.001). The DPA of labial movement was significantly positively associated with predicted labial movement (B = 0.481, P < 0.001), while negatively correlated with molar distalization (B = - 1.004, P < 0.001), labial mini-implants (B = - 0.738, P < 0.001) and age (B = - 0.486, P < 0.05).

CONCLUSIONS

For Class II division 2 patients, predicted incisor proclination (69.8%) and intrusion (53.3%) are partially achieved with clear aligner therapy. Excessive labial movement (0.7 mm) of incisors may be achieved. Incisor movement is influenced by predicted movement amount, premolar extraction, canine proclination, molar distalization, mini-implants and age.

Maxillary molar distalization with a 2-week clear aligner protocol in patients with Class II malocclusion: A retrospective study

INTRODUCTION

This study aimed to investigate the efficacy of molar distalization with or without anterior teeth retraction.

METHODS

Forty-three patients who received maxillary molar distalization with clear aligners were retrospectively enrolled and further divided into 2 groups: a retraction group (with maxillary incisor retraction ≥2 mm in ClinCheck) and a nonretraction group (without anteroposterior movement or with the labial movement of the maxillary incisor in ClinCheck). Pretreatment and posttreatment models were collected and laser-scanned to obtain the virtual models. Three-dimensional digital assessments of molar movement, anterior retraction and arch width were analyzed in the reverse engineering software Rapidform 2006. To calculate the efficacy of tooth movement, the achieved tooth movement assessed on the virtual model was compared with the predicted tooth movement in ClinCheck.

RESULTS

The achieved efficacy rates of molar distalization for the maxillary first and second molars were 36.48% and 41.94%, respectively. There was a significant difference in molar distalization efficacy between the retraction group (31.50% at the first molar and 35.63% at the second molar) and the nonretraction group (48.14% at the first molar and 52.51% at the second molar). In the retraction group, the efficacy of incisor retraction was 56.10%. The efficacy of dental arch expansion was more than 100% at the first molar levels in the retraction group and at the second premolar and first molar levels in the nonretraction group.

CONCLUSIONS

There is a discrepancy between the outcome and the predicted maxillary molar distalization with clear aligners. The efficacy of molar distalization with clear aligners was significantly affected by anterior teeth retraction, and the arch width significantly increased at the premolar and molar levels.

Predictability of Maxillary Molar Distalization and Derotation with Clear Aligners: A Prospective Study

Clear aligners are employed daily for the treatment of Class II malocclusions, when a valid option involves distalization and derotation of the upper first and second molars. Evidence regarding the predictability of these movements is slight, and the treatment outcome that clinicians plan may not be achieved. Therefore, the purpose of this study is to assess the accuracy of distalization and derotation with clear aligners. Geomagic Control X, a 3D quality control software, was used to superimpose digital models of the pre-treatment, post-treatment, and virtual plan (ideal post-treatment) measurements of 16 patients (4 M, 12 F; mean age 25.7 ± 8.8 years). Linear and angular measurement tools were used to calculate the amount of tooth movement prescribed and achieved. Distal displacement of the buccal cusps had an overall accuracy of 69% for the first molar and 75% for the second molar. The accuracy of molar derotation was higher for the first molar (77.5%) than for the second molar (62.7%). The aligners were not able to achieve 100% of the ideal post-treatment result; thus, planning of refinements is often needed. However, clear aligners can be regarded as a valuable option for the distalization of first and second molars.

Changing clear aligners every 10 days or 14 days ? A randomised controlled trial

Objectives:

To compare 10-day and 14-day change regimens to achieve orthodontic tooth movement (OTM) in patients wearing clear aligners and to determine their subsequent pain perception.

Material and methods:

A total of 175 clear aligner patients were assessed for eligibility. Seventy-two patients were randomly assigned to a 10-day group (N = 36) and a 14-day group (N = 36) and were instructed to change the appliances every 10 or 14 days, respectively. OTM efficacy and OTM variation between the actual and predicted OTM digital models measured by shell-to-shell deviation, as well as pain perception determined by a visual analog scale (VAS), were assessed at T0 (baseline, before the placement of the aligners), T1 (stage 8, after completion of aligners #8), and T2 (stage 16, after completion of aligners #16).

Results:

The 10-day and 14-day groups showed similar OTM efficacy at both T1 and T2 for all types of tooth movements (p > 0.09 for all) and similar OTM shell-to-shell deviation at T1 (p = 0.06) and T2 (p = 0.22). The two groups also had similar VAS scores of pain perception throughout the study (p > 0.05 for all).

Conclusion:

The 10-day and 14-day groups showed similar tooth movement and pain perception, suggesting that the clear aligners may be changed every 10 days without a significant compromise in the clinical efficacy of OTM and patient comfort.

Trial registration:

ChiCTR, ChiCTR-IOR-15007532. Registered 17 November 2015, https://www.chictr.org.cn/showproj.aspx?proj=12500

Accuracy of integration of dental cast and cephalograms compared with cone-beam computed tomography: a comparative study

This study proposes a method that integrates maxillary dental cast and cephalograms and evaluates its accuracy compared with cone-beam computed tomography (CBCT) scans. The study sample comprised 20 adult patients with records of dental casts, cephalograms, and craniofacial CBCT scans. The maxillary dental cast was integrated with lateral and frontal cephalograms based on best-fit registration of palatal and dental outline curves from dental cast with cephalogram tracings. Linear measurement was conducted to assess the intra- and inter-examiner reproducibility of the proposed integration method using intraclass correlation coefficients; linear and angular measurements were conducted to assess its accuracy with CBCT scans as a standard reference. Paired t test, one sample t test, and mean ± standard deviation of the absolute value of difference were used to compare the integrated images and CBCT. The integration method showed good intra- and inter-examiner reproducibility (intraclass correlation coefficients > 0.98). The differences in linear and angular measurements between the integrated images and CBCT were not statistically significant but with a large deviation. When absolute value of difference was computed, the linear distance error was 0.51 ± 0.34 mm, the tooth point coordinate errors in X, Y and Z axes were 0.22 ± 0.22, 0.38 ± 0.32 and 0.21 ± 0.21 mm, respectively; the angular error in pitch, roll and yaw of the dental cast was 0.82 ± 0.51, 0.92 ± 0.59 and 0.80 ± 0.41 degree, respectively. The proposed method for integration of dental cast and cephalograms showed good reproducibility and acceptable accuracy compared with CBCT. It could be helpful for researchers to study three-dimensional tooth growth changes using the existing craniofacial growth data especially cephalograms.

The predictability of orthodontic tooth movements through clear aligner among first-premolar extraction patients: a multivariate analysis

BACKGROUND

The purpose was to determine the predictability of tooth movements through clear aligner among premolar extraction patients and to explore the effects of various factors on tooth movements.

METHODS

A total of 31 extraction patients (10 males and 20 females; age 14-44) receiving clear aligner treatment (Invisalign) were enrolled in this study. The actual post-treatment models and pre-treatment models were superimposed using the palatal area as a reference and registered with virtual post-treatment models. A paired t test was used to compare the differences between actual and designed tooth movements of maxillary first molars, canines, and central incisors. A multivariate linear mixed model was performed to examine the influence of variables on actual tooth movements.

RESULTS

Compared to the designed tooth movements, the following undesirable tooth movements occurred: mesial movement (2.2 mm), mesial tipping (5.4°), and intrusion (0.45 mm) of first molars; distal tipping (11.0°), lingual tipping (4.4°), and distal rotation of canines (4.9°); lingual tipping (10.6°) and extrusion (1.5 mm) of incisors. Age, crowding, mini-implant, overbite, and attachments have differential effects on actual tooth movements. Moreover, vertical rectangular attachments on canines are beneficial in achieving more predictable canine and incisor tooth movements over optimized attachments. Lingual tipping and extrusion of incisors were significantly influenced by the interaction effects between incisor power ridge and different canine attachments (p < 0.05).

CONCLUSIONS

Incisors, canines, and first molars are subject to unwanted tooth movements with clear aligners among premolar extraction patients. Age, crowding, mini-implant, overbite, and attachments influence actual tooth movements. Moreover, vertical rectangular attachments on canines are beneficial in achieving more predictable incisor tooth movements over optimized canine attachments.

Validation of three-dimensional digital model superimpositions based on palatal structures in patients with maximum anterior tooth retraction following premolar extraction

Objective

This study aimed to evaluate the superimposition accuracy of digital modes for measuring tooth movement in patients requiring anterior retraction after premolar extraction based on the proposed reference regions.

Methods

Forty patients treated with bilateral maxillary first premolar extraction were divided into two groups: moderate retraction (< 7.0 mm) and maximum retraction (≥ 7.0 mm). Central incisor displacement was measured using cephalometric superimpositions and three-dimensional (3D) digital superimpositions with the 3rd or 4th ruga as the reference point. The Wilcoxon signed-rank test and linear regression analyses were performed to test the significance of the differences and relationships between the two measurement techniques.

Results

In the moderate retraction group, the central incisor anteroposterior displacement values did not differ significantly between 3D digital and cephalometric superimpositions. However, in the maximum-retraction group, significant differences were observed between the anteroposterior displacement evaluated by the 3rd ruga superimposition and cephalometric methods (p < 0.05).

Conclusions

This study demonstrated that 3D digital superimpositions were clinically as reliable as cephalometric superimpositions in assessing tooth movements in patients requiring moderate retraction. However, the reference point should be carefully examined in patients who require maximum retraction.

Digital model superimpositions: are different software algorithms equally accurate in quantifying linear tooth movements?

Background

To evaluate the accuracy of three different 3D digital model registration software packages for linear tooth movement measurements, with reference to a 3D digital virtual setup (DS).

Methods

Twenty maxillary and mandibular pre-treatment scans of patients undergoing clear aligner therapy were used. Digital Setups were generated from pre-treatment scans using OrthoAnalyzer software. Both the pretreatment digital scans (T1) and Digital Setups (T2) were converted to STL files to be imported to the three studied software packages: Geomagic, OrthoAnalyzer and Compare. Linear changes in tooth positions were calculated for all the registered pairs.

Results

The change in tooth position was compared between the calculated tooth movement using each of the registration software packages versus the actual generated tooth movement from the Digital Setups. Continuous data was expressed as mean and standard deviation. Intraclass Correlation Coefficients for agreements between Digital Simulation and each software was used. Intra and Inter-examiner reliabilities were also assessed using Intraclass Correlation Coefficients. Significance of the obtained results was expressed at p ≤ 0.01. Geomagic software showed agreements > 0.90 for maxillary linear tooth movements and between 0.75 and 0.90 for mandibular measurements. OrthoAnalyzer software showed agreements between 0.50 and < 0.75 for maxillary and mandibular measurements. Compare software showed agreements > 0.90 for maxillary and mandibular linear tooth movements, indicating the best consistency.

Conclusions

Compare and Geomagic software packages consistently showed maximum accuracy in measuring the amount of tooth movement in the maxillary arch compared to the reference standard. Compare software showed the highest agreements in the mandibular arch. None of the three studied software packages showed poor agreement with the Digital Setup across all tooth movement measurements. Buccolingual tooth movements showed the highest agreements amongst linear measurements.

TIP, TORQUE & ROTATIONS: How accurately do digital superimposition software packages quantify tooth movement?

Background

To investigate the accuracy of three different 3D digital model registration software for tip, torque and rotation measurements, with reference to a 3D digital virtual setup. Twenty maxillary and mandibular pre-treatment scans of patients undergoing clear aligner therapy were used. Digital setups were generated from pre-treatment scans using a tooth movement software. Both the pretreatment digital scans (T1) and digital setups (T2) were converted to STL files to be exported to the 3 studied software that employed: (1) Semiautomatic best fit registration (S-BF), (2) Interactive surface-based registration (I-SB), and (3) Automatic best fit registration (A-BF) respectively. Changes in tip, torque and rotation were calculated for all the registered pairs.

Results

The change in tooth position was compared between the calculated tooth movement using each of the registration software packages versus the actual generated tooth movement from the digital setups. Continuous data was expressed as mean and standard deviation. Intra Class Correlation Coefficient for agreement between digital simulation and each software was used. Intra and Inter-examiner reliabilities were also assessed using Intra Class Correlation Coefficient. Significance of the obtained results was expressed at p ≤ 0.01. Semiautomatic best fit registration software showed excellent agreement (> 0.90) for all tooth movements, except for good agreement for torque (0.808). Interactive surface-based registration software showed moderate agreement for all measurements (0.50 and < 0.75), except for good agreement for rotation (0.783). Automatic best fit registration software demonstrated excellent agreement (> 0.90) for rotation, good agreement for tip (0.890) and moderate agreement for torque (0.740).

Conclusions

Overall, semiautomatic best fit registration software consistently showed excellent agreement in superimpositions compared to other software types. Automatic best fit registration software consistently demonstrated better agreement for mandibular superimpositions, compared to others. Accuracy of digital model superimpositions for tooth movements studied in superimposition studies, can be attributed to the algorithm employed for quantification.

Evaluation of the stability of the palatal rugae using the three-dimensional superimposition technique following orthodontic treatment

OBJECTIVES

To determine the uniqueness and stability of the palatal rugae after orthodontic treatment.

METHODS

Cast models of untreated subjects (n=50) were obtained twice at intervals of 8-30 months. Cast models of patients who received non-extraction (n=50) and extraction (n=50) orthodontic treatment were obtained before and after treatment at intervals of 11-41 months and 14-49 months, respectively. All 300 cast models were scanned digitally. The palatal rugae were manually extracted and transformed into 3D point clouds using reverse engineering software. An iterative closest point (ICP) registration algorithm based on correntropy was applied, and the minimum point-to-point root mean square (RMS) distances were calculated to analyze the deviation of palatal rugae for scans of the same subject (intrasubject deviation [ISD]) and between different subjects (between-subject deviation [BSD]). Differences in ISD between each group and the deviation between ISD and BSD of all 150 subjects were evaluated.

RESULTS

Significant differences were found in the 150 ISD and 1225 BSD in each group, as well as the 150 ISD and 11175 BSD across all groups. The mean values of ISD in untreated, non-extraction and extraction group were 0.178, 0.229 and 0.333 mm, respectively. When the first ruga was excluded in the extraction group, the mean ISD decreased to 0.241 mm, which was not significantly different from that in the non-extraction group (p=0.314).

CONCLUSIONS

Orthodontic treatment can influence the palatal rugae, especially in cases of extraction. Furthermore, variation mainly existed in the first ruga in cases of extraction. However, palatal rugae are still unique and may be used as a supplementary tool for individual identification.

CLINICAL SIGNIFICANCE

This study indicates that palatal rugae might be applied in the evaluation of orthodontic tooth movement and forensic individual identification. The registration algorithm based on correntropy provides a credible, precise, and convenient method for palatal rugae superimposition.

Effect of vibration on orthodontic tooth movement in a double blind prospective randomized controlled trial

The purpose of the present study was to investigate the effect of vibration on orthodontic tooth movement and safety assessment based on our previous basic research in animal experiments. A double-blind prospective randomized controlled trial using split-mouth design was conducted in patients with malocclusion. The left and right sides of maxillary arch were randomly assigned to vibration (TM + V) and non-vibration (TM) groups. After leveling, vibrations (5.2 ± 0.5 g-forces (gf), 102.2 ± 2.6 Hertz (Hz)) were supplementary applied to the canine retracted with 100 gf in TM + V group for 3 min at the monthly visit under double-blind fashion, and the canine on the other side without vibration was used as TM group. The amount of tooth movement was measured blindly using a constructed three-dimensional dentition model. The amount of canine movement per visit was 0.89 ± 0.55 mm in TM group (n = 23) and 1.21 ± 0.60 mm in TM + V group (n = 23), respectively. There was no significant difference of pain and discomfort, and root resorption between the two groups. This study indicates that static orthodontic force with supplementary vibration significantly accelerated tooth movement in canine retraction and reduced the number of visits without causing side effects.

Class III malocclusion with traumatic unilateral maxillary central incisor loss treated using orthodontic miniscrews: a case report

The present article reports the successful non-extraction orthodontic treatment using miniscrew anchorage in a patient who presented with maxillary left central incisor loss and unstable jaw movements. The chief complaints of the 23-year-old female patient were her protruding teeth and crowding of the mandibular anterior segment. The patient lost her maxillary left central incisor as a result of a traumatic injury during childhood. However, the crown was saved and attached to the adjacent teeth. The patient was diagnosed with a skeletal Class III and Angle Class III dental malocclusion. The jaw movements determined by a 6 degrees of freedom jaw movement recording system were unstable and irregular. Miniscrew anchorage was applied for distalisation of the maxillary right dentition and the mandibular dentition during non-extraction treatment. The maxillary left dentition was mesialised using miniscrew anchorage to close the space as a result of the lost maxillary left central incisor. After an active treatment duration of 36 months, the patient achieved a Class II molar relationship on the left side, a Class I on the right side, an optimal overjet and overbite, and a pleasing facial profile. Despite the asymmetric molar relationships, functionally stable and smooth jaw movements were established. The skeletal, occlusal and functional stability remained satisfactory after a 2-year retention period. In conclusion, miniscrew anchorage was valuable in supporting asymmetric tooth movement during non-extraction appliance treatment in a patient who presented with traumatic unilateral tooth loss.

A new protocol to accurately track long-term orthodontic tooth movement and support patient-specific numerical modeling

Numerical simulation of long-term orthodontic tooth movement based on Finite Element Analysis (FEA) could help clinicians to plan more efficient and mechanically sound treatments. However, most of FEA studies assume idealized loading conditions and lack experimental calibration or validation. The goal of this paper is to propose a novel clinical protocol to accurately track orthodontic tooth displacement in three-dimensions (3D) and provide 3D models that may support FEA. Our protocol uses an initial cone beam computed tomography (CBCT) scan and several intra-oral scans (IOS) to generate 3D models of the maxillary bone and teeth ready for use in FEA. The protocol was applied to monitor the canine retraction of a patient during seven months. A second CBCT scan was performed at the end of the study for validation purposes. In order to ease FEA, a frictionless and statically determinate lingual device for maxillary canine retraction was designed. Numerical simulations were set up using the 3D models provided by our protocol to show the relevance of our proposal. Comparison of numerical and clinical results highlights the suitability of this protocol to support patient-specific FEA.

Mini Hyrax vs Hyrax expanders in the rapid palatal expansion in adolescents with posterior crossbite: a randomized controlled clinical trial

PURPOSE

The aim of this study was to compare the dental effects, impact on quality of life, and pain perception of adolescents wearing Mini Hyrax and Hyrax expanders in rapid palatal expansion.

METHODS

Thirty-four adolescents aged 11 to 16 years, with maxillary transverse deficiency (unilateral or bilateral posterior crossbite), were randomly allocated into two groups, Mini Hyrax group and Hyrax group (1:1 ratio). Dental effects were evaluated by digitally superimposed pretreatment and postretention three-dimensional intraoral scans on the palatal rugaes using the software 3DSlicer. Impact on quality of life was assessed with the OHIP-14 questionnaire applied in the pretreatment, posttreatment and postretention. Visual analog scale was applied 24, 48, and 72 h and 7 days after the first activation of the expander.

RESULTS

Thirty of the 34 adolescents recruited completed the study. There were no statistically significant differences in dentoalveolar effects between groups. OHIP-14 scores across time among Mini Hyrax wearers were similar to those of the Hyrax wearers. The inter-group comparisons showed no difference between groups with respect to the OHIP-14 scores in posttreatment and postretention (p > 0.05). There were no differences in pain perception between groups. Considering intra-group comparison, the reduction in pain perception among adolescents in the Mini Hyrax group was gradual. Among adolescents in the Hyrax group, a statistically significant reduction between 48 and 72 h was observed.

CONCLUSION

There were no significant differences in dental effects, impact on quality of life and pain perception between adolescents wearing Mini Hyrax and Hyrax expanders in rapid palatal expansion.

PASS versus MBT™ for evaluation of anchorage control in three-dimensional measurements: a randomized controlled trial

BACKGROUND

Growth and development might lead to anchorage loss during orthodontic treatment, such as the mesial drift of molars, the compensation characteristics of upper molars following mandibular growth, or the angulation of molars before treatment. Different anchorage reinforcement devices have been developed to prevent mechanical anchorage loss, but the anchorage loss resulting from physiological factors should also be taken into account.

OBJECTIVE

To explore the efficacy of a new strategy to control physiologic anchorage compared with that of the conventional straight-wire appliance.

TRIAL DESIGN

Randomized controlled trial (RCT).

METHODS

Participants of Han ethnicity were randomized into the physiologic anchorage spee-wire system (PASS) group or McLaughlin-Bennett-Trevisi (MBT™) straight-wire group by minimization random allocation. The eligibility criteria were patients with a Class I or II molar relationship, permanent dentition (11-35 years old), fixed appliances involving the extraction of at least two upper first premolars, and medium or maximum anchorage requirements. Pre-treatment and post-treatment dental casts were scanned into digital casts and measured using a blinded method. Mesial displacements of the upper first molars were considered as the primary outcome for evaluating anchorage control. Measurements were taken for subgroups based on age.

RESULTS

Data from 60 participants were analysed. The baseline characteristics were not significantly different between groups. Mesial displacement of the upper first molar (in mm) was 2.96 ± 1.52 in the PASS group and 2.70 ± 1.66 in the MBT group (P = 0.521). The variation in incisor torque was -6.94 ± 6.35 degree in the PASS group and -11.76 ± 7.65 degree in the MBT group (P = 0. 010). The incisor retraction (in mm) was 4.24 ± 1.99 and 5.67 ± 2.27 in the PASS and MBT groups, respectively (P = 0.012). Adverse effects were not documented in any patient.

LIMITATION

The study was a single-centre study.

CONCLUSIONS

Compared with the MBT group, the PASS group without additional anchorage devices could attain well anchorage control by considering the dentoalveolar compensation of anchor teeth.

REGISTRATION

This RCT was registered at the Chinese Clinical Trial Registry (Chictr.org.cn) ChiCTR-TRC-13003260.

Comparison of achieved and predicted crown movement in adults after 4 first premolar extraction treatment with Invisalign

INTRODUCTION

In this study, we compared achieved and predicted crown movements of maxillary and mandibular first molars, canines, and central incisors in adults after 4 first premolar extraction treatment with Invisalign.

METHODS

Seventeen adult patients who received 4 first premolar extraction treatment with Invisalign and completed the first series of aligners were included. Superimposition of pretreatment and actual posttreatment dental models was acquired using registrations of pretreatment and posttreatment craniofacial models on the basis of bone surfaces and registrations of craniofacial and dental models on the basis of dental crown surfaces, respectively. Superimposition of pretreatment and predicted posttreatment models was acquired from ClinCheck software. Achieved and predicted 3-dimensional crown movements of maxillary and mandibular first molars, canines, and central incisors were then compared using the paired t test.

RESULTS

Relative to predicted changes, first molars achieved greater mesial displacement, mesial tipping, and buccal inclination in both the maxilla and mandible, greater intrusion in the maxilla, and greater mesial-lingual rotation and less constriction in the mandible. Canines achieved greater distal tipping in both the maxilla and mandible, less retraction in the maxilla, and greater lingual inclination and extrusion in the mandible. Central incisors achieved greater distal tipping and lingual inclination and extrusion in both the maxilla and mandible and less retraction in the maxilla.

CONCLUSIONS

Tooth crown movements were not fully achieved as predicted following Invisalign treatment. Differences focused on mesial tipping, buccal inclination, mesial displacement, and intrusion of the first molars, as well as distal tipping, lingual inclination, insufficient retraction, and intrusion of the canines and central incisors.

Intraoral scanners for capturing the palate and its relation to the dentition

Proper superimposition of intraoral scan generated 3D models enables detailed assessment of soft and hard tissue surface changes. This requires accurate 3D models and stable structures as superimposition references. In the maxilla, different reference areas have been proposed, mostly located at the palatal region. In this in vivo study we evaluated the precision of two intraoral scanners (TRIOS 3, 3Shape and CS 3600, Carestream) at the maxilla, focusing on the palate itself and also on its spatial relation to the dentition, following palatal superimposition. Precision was tested through the superimposition of repeated scans on the palate and the dental arch. Overall, the median precision of both scanners was high (< 0.1 mm). Scanner precision was comparable when the palatal area was tested individually. However, TRIOS 3 showed higher precision regarding the assessment of the dental arch, following superimposition of repeated models on the palate (median difference: approximately 40 μm). In few cases, local areas of higher imprecision were present for both scanners, exceeding 0.3 mm. Thus, scanner precision seems to be high in small, but slightly reduced considering larger areas, with differences between scanners. However, the effect on individual tooth position relative to the palate was for both scanners limited.

Is Continuous Eruption Related to Periodontal Changes? A 16-Year Follow-up

The aims of this study were to 1) determine if continuous eruption occurs in the maxillary teeth, 2) assess the magnitude of the continuous eruption, and 3) evaluate the effects of continuous eruption on the different periodontal parameters by using data from the population-based cohort of the Study of Health in Pomerania (SHIP). The jaw casts of 140 participants from the baseline (SHIP-0) and 16-y follow-up (SHIP-3) were digitized as 3-dimensional models. Robust reference points were set to match the tooth eruption stage at SHIP-0 and SHIP-3. Reference points were set on the occlusal surface of the contralateral premolar and molar teeth, the palatal fossa of an incisor, and the rugae of the hard palate. Reference points were combined to represent 3 virtual occlusal planes. Continuous eruption was measured as the mean height difference between the 3 planes and rugae fix points at SHIP-0 and SHIP-3. Probing depth, clinical attachment levels, gingiva above the cementoenamel junction (gingival height), and number of missing teeth were clinically assessed in the maxilla. Changes in periodontal variables were regressed onto changes in continuous eruption after adjustment for age, sex, number of filled teeth, and education or tooth wear. Continuous tooth eruption >1 mm over the 16 y was found in 4 of 140 adults and averaged to 0.33 mm, equaling 0.021 mm/y. In the total sample, an increase in continuous eruption was significantly associated with decreases in mean gingival height (B = -0.34; 95% CI, -0.65 to -0.03). In a subsample of participants without tooth loss, continuous eruption was negatively associated with PD. This study confirmed that continuous eruption is clearly detectable and may contribute to lower gingival heights in the maxilla.

Assessment of reference areas for superimposition of serial 3D models of patients with advanced periodontitis for volumetric soft tissue evaluation

AIM

This study aimed to determine the optimal reference area for superimposition of serial 3D dental models of patients with advanced periodontitis.

MATERIALS AND METHODS

Ten pre- and post-periodontal treatment 3D models (median time lapse: 13.1 months) of patients with advanced periodontitis were acquired by intraoral scanning. Superimposition was performed with the iterative closest point algorithm using four reference areas: (A) all stable teeth, (B) all teeth, (C) third palatal rugae and (D) the whole model. The superimposition accuracy was evaluated at two stable evaluation regions using the mean absolute distance and evaluated with two-way ANOVA and post-hoc multivariate model. The intra- and inter-operator reproducibility was calculated by intraclass correlation coefficient (ICC).

RESULTS

Superimposition accuracy evaluated at stable tooth evaluation region were 71 ± 29 μm, 73 ± 21 μm, 127 ± 52 μm and 113 ± 53 μm for areas A, B, C and D, respectively. All reference areas showed similarly high ICC values >0.990, except for reference area C showing ICC of 0.821 (intra-operator) and 0.767 (inter-operator) for tooth evaluation area.

CONCLUSIONS

Area A and B provide the highest accuracy for superimposition of serial 3D dental models acquired by intraoral scanning of patients with advanced periodontitis.

Assessment of techniques used for superimposition of maxillary and mandibular 3D surface models to evaluate tooth movement: a systematic review

BACKGROUND

Superimposition of three-dimensional (3D) digital models offers great opportunities to assess tooth movement during time. In the literature, several superimposition techniques are described.

OBJECTIVES

To summarize and critically assess the available evidence from studies on serial digital 3D dental model superimposition.

SEARCH METHODS

MEDLINE via Ovid and PubMed, EMBASE via Ovid, Cochrane Register of Diagnostic Test Accuracy Studies, and Google Scholar were searched with no time limit (last update: December 2018). Hand and unpublished literature searches were also performed.

SELECTION CRITERIA

Studies of any design that had a sample size ≥5 and tested superimposition of serial 3D digital dental models to assess tooth movement were included.

DATA COLLECTION AND ANALYSIS

Study selection, data extraction, and risk of bias assessment were performed independently by the authors.

RESULTS

Twelve studies met the eligibility criteria. The total risk of bias (QUADAS-2 tool) of 10 studies was high, whereas only 2 studies had unclear bias. Ten studies had high and two studies low overall applicability concerns. From these, one study tested the mandibular alveolar bone area, three studies the rugae area, nine studies a larger palatal area, and two studies the incisive papilla area. The high heterogeneity in samples, outcomes, and methods did not allow for synthesis of a considerable amount of studies in any case.

LIMITATIONS

The high heterogeneity among studies and the limited evidence did not allow for solid conclusions.

CONCLUSIONS AND IMPLICATIONS

The following areas of the maxilla could provide reliable outcomes: (1) the medial two-thirds of the third rugae and the area 5 mm dorsal to them and (2) an area including all rugae, with the lateral margins located at least 5 mm from the gingival margins and a distal margin that does not extend beyond the first molars. No recommendation is possible for other regions of the mouth. There is an urgent need for further research in the field.

REGISTRATION

PROSPERO (CRD42019124365).

The influence of the model superimposition method on the assessment of accuracy and predictability of setup models

INTRODUCTION

The aim of this study was to evaluate the influence of different superimposition methods on the accuracy and predictability of conventional and virtual diagnostic setups.

MATERIALS AND METHODS

Ten finished cases were used to make a conventional setup and a virtual setup. Second molars were not moved in the two setup situations to allow a reference for superimposition. Conventional and virtual setups were superimposed and compared by second molar registration and the whole surface best fit method (WSBF). Conventional and virtual setups were compared to the posttreatment models with WSBF and palatal rugae best fit (PRBF). Anterior, intermediate, and posterior regions of the dental arches were compared. The paired t-test was used to compare the mean differences between conventional and virtual setups, posttreatment models and both conventional and virtual setups by the WSBF method, and between maxillary posttreatment and virtual setup models using the WSBF and PRBF methods.

RESULTS

Conventional and virtual setups differed depending on the two superimposition methods used. Superimposition of the posttreatment models and both setups using WSBF presented no statistically significant differences. There were statistically significant differences between posttreatment and virtual setup models using WSBF and PRBF superimposition methods.

CONCLUSIONS

The model superimposition method influenced the assessment of accuracy and predictability of setup models. There were statistically significant differences between the maxillary posttreatment and virtual setup models using the WSBF and the PRBF superimposition methods. It is important to establish stable structures to evaluate the accuracy and predictability of setup models.

Palatal rugae positional changes during orthodontic treatment of growing patients

OBJECTIVES

To investigate the anteroposterior and vertical changes of the median rugae area, which is commonly used as dental model superimposition reference, relevant to its underlying skeletal structures.

SETTINGS AND SAMPLE POPULATION

Retrospectively collected pre- and post-treatment cephalometric radiographs and 3D digital dental models of 24 orthodontic patients (age at treatment start: 12.26 ± 0.83 years; assessment period: 2.13 ± 0.68 years) were analysed. All had mild to moderate malocclusions that were treated non-extraction with full fixed appliances.

MATERIAL AND METHODS

The incisive papilla and rugae points were placed on the dental models that were then registered to the cephalometric radiographs. Afterwards, the radiographs were superimposed on Sella, ANS-PNS, and through a maxillary structural method. The vertical and horizontal movements of the papilla and the rugae points, as well as of a central incisor, were measured (Viewbox 4 software).

RESULTS

The incisive papilla and the three rugae points remained stable anteroposteriorly, but moved downwards in the vertical dimension (approximately 1-2 mm), in a similar manner (P > .05). However, the anteroposterior position of the papilla and the first rugae points were affected by changes in anterior tooth position and inclination (P < .05).

CONCLUSION

Both the second and third rugae can be used as superimposition references for tooth movement assessment. The use of the papilla and the first rugae area is not recommended, because they are affected by tooth movement. The outcomes of a palatal superimposition are comparable to those of a maxillary skeletal superimposition in the anteroposterior, but not in the vertical dimension.

Accuracy and reliability of maxillary digital model (MDM) superimposition in evaluating teeth movement in adults compared with CBCT maxillary superimposition

Superimposition of 3D maxillary digital dental models of different time points based on palatal vault region has been used to evaluate tooth movement during orthodontic treatment. This study evaluated the accuracy and reliability of 3D maxillary digital model (MDM) superimposition in adults by comparing it with CBCT maxillary superimposition. In CBCT maxillary superimposition, voxel-based superimposition was firstly conducted, and MDMs were matched with corresponding CBCT models (CBCT-MDM superimposition). MDM superimposition (palatal vault regional superimposition) were performed on another pair of pre- and posttreatment MDMs. The position and orientation of upper first molars (U6s) and upper central incisors (U1s) on the posttreatment MDMs were compared to assess the accuracy of the MDM superimposition methods. The reliability was validated in both MDM superimposition and CBCT maxillary superimposition. In terms of accuracy, the average linear deviations in U6 and U1 positions were less than ± 0.3 mm, the average angular deviations of U6s and U1s were less than ± 0.2°, both have no significant difference from zero. The ICCs for MDM superimposition ranged from 0.85 to 0.99. The ICCs for CBCT-MDM superimposition were larger than 0.99 in all items. MDM superimposition was an efficient, accurate and reliable method for evaluating teeth movement in adults, although its reliability is slightly lower than CBCT maxillary superimposition.

3D-analysis of unwanted tooth movements despite bonded orthodontic retainers: a pilot study

Background

Recently, reports of unwanted tooth movements despite intact orthodontic bonded retainers have increased. These movements are not subject to relapse but are classified as a new developed malocclusion. The aims of the present pilot study were to analyze the prevalence of unwanted tooth movements despite intact bonded cuspid-to-cuspid retainers and to identify possible predisposing factors.

Materials and methods

Plaster casts of all patients finishing orthodontic treatment during three consecutive years were assessed before treatment (T0), after multibracket appliance debonding (T1) and after two years of retention (T2). After multibracket appliance treatment, all patients received a cuspid-to-cuspid flexible spiral wire retainer bonded to each tooth of the retained segment in the upper and lower jaw. The study group (SG) consisted of 44 patients (16 male, 28 female) with tooth movements (T1–T2) of the retained segment despite intact bonded cuspid-to-cuspid retainer and the control group (CG) of 43 patients (19 male, 24 female) without unwanted tooth movements. The casts of the SG were digitized, superimposed and measured. Using the Chi-square test, Fisher´s exact test and Mann–Whitney-U-test (p < 0.05), mandibular plane angle, incisor proclination, oral dysfunctions or habits (T0) and intercanine distance, overjet and interincisal relationship (T0, T1, T2) were compared between SG and CG.

Results

The prevalence of patients with unwanted tooth movements in one or both jaws was 27.0%. Maxillary retainers were affected more often (20.9%) than mandibular retainers (14.1%). The median amount of tooth movements was 0 to 0.66 mm with large interindividual variations. Oral dysfunctions or habits at T0, such as a lack of interincisal contact at all time points, were associated with unwanted tooth movements.

Conclusion

Unwanted tooth movements occurred more often with maxillary than mandibular retainers. Patients with oral dysfunctions/habits and without interincisal contact had a higher prevalence of unwanted tooth movements.

Assessment of the Stability of the Palatal Rugae in a 3D-3D Superimposition Technique Following Slow Maxillary Expansion (SME)

The Palatal Rugae are considered a useful human identification marker for both orthodontists and forensic personnel. The principal aim of the present study was to evaluate the stability of palatal rugae with a 3D-3D superimposition procedure following Slow Maxillary Expansion (SME), in order to assess whether they kept their uniqueness and validity for human identification, even after a specific dental treatment. For this purpose, a sample of 27 digital dental models - belonging to growing patients (13 males and 14 females), aged between 8.5 and 15 years, who underwent SME therapy - was retrospectively studied and compared with a control group of 27 untreated subjects - (13 males and 14 females). Digital dental models were obtained pre-treatment and at device removal; both were processed by means of an intraoral scanner. A superimposition procedure was thus performed to reach the minimum point-to-point distance between two models of palatal rugae. Intra- and inter-observer differences were statistically analyzed by paired Wilcoxon test and Intra-class Correlation coefficient (ICC), showing values larger than 0.93. There was no difference in Root-Mean-Square (RMS) values between untreated control subjects and subjects treated with Leaf Expander (p = 0.062). A RMS value of 0.43 was the threshold to distinguish the pooled group (“Untreated” and “Leaf”) from any mismatch. According to the obtained results, this study failed to reject the null hypothesis and presented no differences between the RMS values of the Test group and the RMS values of the untreated control group. This work highlighted the usefulness of 3D superimposition procedure for purposes of human identification, in subjects undergoing dental treatment. However, keeping in sight the forensic use of this technique as a helpful probation element in court, further studies should be performed to confirm these findings.

Reliability and validity of miniscrews as references in cone-beam computed tomography and intraoral scanner digital models: study on goat heads

Background

Miniscrews have been used to superimpose three-dimensional (3D) craniofacial images as well as explore stable structures in jaws. Our purpose was to evaluate the reliability and validity of linear and angular measurements made with miniscrews on a 3D cone-beam computed tomography (CBCT) at two voxel sizes and compared to models created by an intraoral scanner (IOS).

Methods

Altogether, 64 miniscrews were placed in 12 goat jaws. The jaws were scanned by CBCT machine at 0.12 mm and 0.3 mm voxels and by the IOS. Linear and angular measurements between miniscrews on CBCT at the two voxel settings and the IOS were compared with actual measurements and with each other.

Results

An intra-and inter-class correlation of 0.961–1.000 were obtained by each method. Linear measurements showed significant overestimations of 0.27 ± 0.24, 0.14 ± 0.22 and 0.15 ± 0.26 mm, and angular measurements showed non-significant differences of 0.11 ± 1.97°, 0.15 ± 2.79° and 0.41 ± 2.34° for the CBCT at 0.12-mm, 0.3-mm voxels and the IOS, respectively. Equal magnification of linear measurements was on homolateral and contralateral sides using CBCT, whereas significantly greater magnification on the homolateral side than on the opposite was observed using the IOS. There was no significant difference with angular measurements between digital CBCT models at two voxels and IOS. In addition, all angular measurements were comparable to actual measurement results.

Conclusions

Miniscrews in CBCT and IOS are reliable and clinical valid when used as a reference measuring tooth movement. However, when miniscrews are involved in high precision measurement in CBCT or IOS image, systematic error should be taken into consideration. When comparing CBCT images, using the same voxel size is recommended for miniscrew related measurements to reduce error.

Three-dimensional analysis of tooth movement in Class II malocclusion treatment using arch wire with continuous tip-back bends and intermaxillary elastics

Objective

The aim of this study was to analyze three-dimensional (3D) changes in maxillary dentition in Class II malocclusion treatment using arch wire with continuous tip-back bends or compensating curve, together with intermaxillary elastics by superimposing 3D virtual models.

Methods

The subjects were 20 patients (2 men and 18 women; mean age 20 years 7 months ± 3 years 9 months) with Class II malocclusion treated using 0.016 × 0.022-inch multiloop edgewise arch wire with continuous tip-back bends or titanium molybdenum alloy ideal arch wire with compensating curve, together with intermaxillary elastics. Linear and angular measurements were performed to investigate maxillary teeth displacement by superimposing pre- and post-treatment 3D virtual models using Rapidform 2006 and analyzing the results using paired t-tests.

Results

There were posterior displacement of maxillary teeth (p < 0.01) with distal crown tipping of canine, second premolar and first molar (p < 0.05), expansion of maxillary arch (p < 0.05) with buccoversion of second premolar and first molar (p < 0.01), and distal-in rotation of first molar (p < 0.01). Reduced angular difference between anterior and posterior occlusal planes (p < 0.001), with extrusion of anterior teeth (p < 0.05) and intrusion of second premolar and first molar (p < 0.001) was observed.

Conclusions

Class II treatment using an arch wire with continuous tip-back bends or a compensating curve, together with intermaxillary elastics, could retract and expand maxillary dentition, and reduce occlusal curvature. These results will help clinicians in understanding the mechanism of this Class II treatment.

Three-dimensional analysis of the physiologic drift of adjacent teeth following maxillary first premolar extractions

We assessed the three-dimensional (3D) pattern of the physiologic drift of the remaining adjacent teeth after premolar extraction due to orthodontic reasons and the associated factors. Data were collected from 45 patients aged 17.04 ± 5.14 years who were scheduled to receive a fixed appliance after maxillary premolar extraction. Seventy-five drift models were obtained and digitalized via 3D scanning. The average physiologic drift duration was 81.66 ± 70.03 days. Angular and linear changes in the first molars, second premolars, and canines were measured using the 3D method. All the examined teeth had tipped and moved towards the extraction space, leading to space decreases. Posterior teeth primarily exhibited significant mesial tipping and displacement, without rotation or vertical changes. All canine variables changed, including distal inward rotation and extrusion. The physiologic drift tended to slow over time. Age had a limited negative effect on the mesial drift of posterior teeth, whereas crowding had a limited positive effect on canine drift. Thus, the mesial drift of molars after premolar extraction may lead to molar anchorage loss, particularly among younger patients. The pattern of the physiologic drift of maxillary canines can help relieve crowding and facilitate labially ectopic canine alignment, whereas canine drift is accelerated by more severe crowding.

The effect of regular dental cast artifacts on the 3D superimposition of serial digital maxillary dental models

Superimpositions of serial 3D dental surface models comprise a powerful tool to assess morphological changes due to growth, treatment, or pathology. In this study, we evaluated the effect of artifacts on the superimposition outcome, using standard model acquisition and superimposition techniques. Ten pre- and post-orthodontic treatment plaster models were scanned with an intraoral scanner and superimposed using the iterative closest point algorithm. We repeated the whole process after manual removal of plaster artifacts, according to the current practice, as well as after re-scanning the cleaned models, to assess the effect of the model acquisition process derived artifacts on the superimposition outcome. Non-parametric multivariate models showed no mean effect on accuracy and precision by software settings, cleaning status (artifact removal), or time point. The choice of the superimposition reference area was the only factor that affected the measurements. However, assessment of individual cases revealed significant differences on the detected tooth movement, depending on artifact removal and on the model acquisition process. The effects of all factors tended to decrease with an increase in the size of the superimposition reference area. The present findings highlight the importance of accurate, artifact-free models, for valid assessment of morphological changes through serial 3D model superimpositions.

Superimposition of 3D maxillary digital models using open-source software

Historically, whether for research purposes or clinical monitoring, orthodontic evaluation of dental movements has been done using plaster study models and two dimensional (2D) radiographs. However, new frontiers for the diagnosis, planning and outcome assessment of orthodontic treatments have arisen, due to the revolutionary digital tools which enable a three dimensional (3D) computerized analysis of dental movements by means of digital models. However, the software for 3D analysis are often costly, resulting in limited access to orthodontists. The present study aims to describe, through a clinical case presented to the Brazilian Board of Orthodontics and Dentofacial Orthopedics, a method for the superimposition of maxillary digital models using an open-source software to evaluate dental movements.

Deviations in palatal region between indirect and direct digital models: an in vivo study

Background

Studies focusing on accuracy of intraoral digital models in the palatal region are scarce. The present study aimed to investigate the influence of different scanning sequences on palatal trueness and to assess deviation and distribution character of trueness in palate.

Methods

Overall, 35 participants accepted three types of procedures to acquire upper digital models. Indirect models digitalised from plaster models were considered as the reference. Two direct digital models were acquired using TRIOS 3 POD intraoral scanners, namely Groups Tr1 and Tr2, wherein intraoral scanning differed in terms of palatal scanning sequences. Based on a modified dental-level superimposition method, 3D measurements of trueness in palate and palatal vault region (PVR) for palatal stable regional superimposition in Groups Tr1 and Tr2, respectively, were performed. Absolute deviations were measured for trueness, while signed deviations were analysed for shape distortion. Colour-coded maps were used for quantitative analysis of deviation distribution pattern. Paired t test was used to analyse differences in palatal trueness between different scanning sequences. One-way repeated-measures analysis of variance and Bonferroni test were used to compare trueness measurements among different superimposition methods. Intraclass correlation coefficient (ICC) was used to verify reproducibility of the proposed method.

Results

Palatal trueness in Group Tr1 (118.59 ± 37.67 μm) was slightly less accurate than that (108.25 ± 33.83 μm) in Group Tr2 (p = 0.012 < 0.05). Trueness of PVR in Groups Tr1 (127.35 ± 54.11 μm) and Tr2 (118.17 ± 49.52 μm) did not differ significantly (p = 0.149). Moreover, no significant difference was noted in distortion of the palatal region and PVR in Groups Tr1 and Tr2 (p = 0.582 and 0.615, respectively). A similar pattern of palatal trueness was noted in a majority of participants (22/35). For 3D palatal trueness measurement, there were different applications for different superimposition methods. ICC for the proposed method was > 0.90.

Conclusions

Scanning sequences can affect palatal trueness. Palatal scanning should be initiated at the palatal side of the posterior teeth where the initial scan begins. For 3D PVR superimposition, distal boundary of the selected region should be adjusted mesially whilst referring to intraoral digital models.

Trial registration

The trial has been registered (registration No: R000039467, Trial ID: UMIN000034617, date of registration: 2018/10/24‘retrospectively registered’).

Does anchorage loss differ with 0.018-inch and 0.022-inch slot bracket systems?

OBJECTIVES

To compare maxillary first molar anchorage loss between 0.018-inch and 0.022-inch slot fixed appliance systems.

MATERIALS AND METHODS

Patients requiring bilateral maxillary premolar extractions (n = 74) within a randomized clinical trial comparing the effectiveness of 0.018-inch and 0.022-inch slot MBT bracket systems (3M-Unitek, Monrovia, Calif) were included. Three-dimensional pre- and posttreatment digital models were landmarked and measured (R700 scanner and OrthoAnalyzer software, 3Shape, Copenhagen, Denmark). Anteroposterior position of the first molars was measured using the third medial rugae point as a reference. Anchorage loss (AL) represented the subtraction of the posttreatment distance from the pretreatment distance for both anchorage loss right (ALR) and left (ALL) sides. The values were then compared using a two-way analysis of variance.

RESULTS

There were 41 and 33 cases for the 0.018-inch and 0.022-inch bracket slot systems, respectively. The baseline characteristics were similar between groups, except for the presence or absence of anchorage devices (P = .050). For the total sample: 0.018-inch ALR = 3.86 mm, ALL = 3.30 mm and 0.022-inch ALR = 3.73 mm, ALL = 3.47 mm (P = .970). There was also no significant difference between the 0.018-inch and 0.022-inch groups when subjects with anchorage devices were excluded (P = .383).

CONCLUSIONS

Bracket slot size does not influence maxillary molar anchorage loss during orthodontic treatment.

Comparison of achieved and predicted tooth movement of maxillary first molars and central incisors: First premolar extraction treatment with Invisalign

OBJECTIVES

To compare achieved and predicted tooth movements of maxillary first molars and central incisors in first premolar extraction cases treated with Invisalign.

MATERIALS AND METHODS

The present study included 30 patients who received maxillary first premolar extraction treatment with Invisalign. The actual posttreatment model was registered with the pretreatment model on the palatal stable region and superimposed with the virtual posttreatment model. Achieved and predicted tooth movements of maxillary first molars and central incisors were compared using paired t-test. Linear mixed-effect model analyses were used to explore the influence of age (adolescents vs adults), attachment (G6-optimized vs 3-mm vertical, 3-mm horizontal, and 5-mm horizontal), and initial crowding on the differences between predicted and achieved tooth movement (DPATM).

RESULTS

First molars achieved greater mesial tipping, mesial translation, and intrusion than predicted. Central incisors achieved less retraction and greater lingual crown torque and extrusion than predicted. Adolescents showed greater DPATM in the mesiodistal translation of first molars and labiolingual translation of central incisors and smaller DPATM in the occlusogingival translation of the first molars and crown torque of the central incisors than adults. The 3-mm vertical attachment group showed greater DPATM in the mesiodistal translation of the first molars vs the G6-optimized attachment group. Initial crowding had an inverse correlation with DPATM in angulation and mesiodistal translation of the first molars.

CONCLUSIONS

First molar anchorage control and central incisor retraction were not fully achieved as predicted in first premolar extraction treatment with Invisalign. Age, attachment, and initial crowding affected the differences between predicted and achieved tooth movement.