Arch Expansion Research Articles

Study on the decay laws and deterioration mechanism of mechanical properties of cement-stabilized gravel under water-heat-salt coupled conditions

A new type of asphalt pavement disease, known as arch expansion, has appeared in the saline soil regions of Northwest China. The emergence, as well as the evolution of the disease, is strongly related to the distribution of sulfate. However, the decay of Cement-stabilized gravel (CSG) mechanical properties is closely related to the onset and development of arch expansion. The relationship between CSG mechanical strength and salinity in the arch expansion area is analyzed based on field investigations to systematically study the mechanical property degradation law and mechanism of CSG. The mechanical strength and deterioration patterns of CSG with different coupling conditions were investigated. The mineral composition and micromorphology of the erosion products were analyzed. The results show that the mechanical properties of CSG in the area of the arch deteriorate more than those in the regular section. The mechanical strength of the specimens initially containing salt and partially immersed in salt solution decayed most severely. In terms of the deterioration mechanism of mechanical strength of CSG, the water-heat-salt erosion process is also divided into two parts, including the formation stage of gypsum and ettringite, the stage of C-S-H decomposition and thaumasite formation, respectively. The degradation mechanism of CSG is a combination of physical and chemical erosion.

Predictability of Maxillary Expansion with Invisalign® First: Treatment Planning vs. Outcome

The aim of this study is to retrospectively investigate the predictability of maxillary arch expansion with Invisalign ® First in mixed dentition. In a sample of 64 treated patients, 3D digital models from the ClinCheck® software were compared with post-treatment digital models. Predicted maxillary expansion was related to the final outcome of expansion. At the cuspidal level, there was observed a predictability of 59.68% for deciduous canines, 63.77% for first deciduous molars, 66.99% for second deciduous molars, and 55.61% for first permanent molars. At the gingival level, there was observed a predictability of 49.87% for deciduous canines, 53.11% for first deciduous molars, 53.36% for second deciduous molars, and 45.16% for first permanent molars. The difference between the predicted and achieved expansion was statistically significant (p < 0.05). Within the present limitations, our results suggest that, with Invisalign® First, it is possible to expand the upper arch in mixed dentition in an effective and predictable way. Clear aligners could represent a new and valid alternative for arch expansion in growing patients.

Comparative Experimental Evaluation of Orthodontic Appliances for Maxillary Arch Expansion.

Background/Objectives: The orthodontic treatment of posterior crossbite using appliances for gradual maxillary expansion is crucial to ensure proper transversal jaw relationships as much as occlusal functionality. The aim of this study was to analyze forces and torques generated by different appliances for maxillary expansion. Methods: Measurements were conducted for the Wilson® 3D® Quadhelix (WQH) and Wilson® 3D® Multi-Action Palatal Appliance (WPA) across various sizes and compared to the Remanium® Quadhelix (RQH). Activations were set to 8 mm for the WQH and RQH and 6 and 8 mm for the WPA. Rotations and root torque were simulated via an activation of 10° for arches. A total of eight test series were conducted. Results: The WPA displayed the highest force and torque values for all movements, far surpassing recommended guideline values (expansion 8.5->15.0 N/46.3-86.5 Nmm, rotation 3.1-6.1 N/40.7-61.4 Nmm, torque 3.9-5.1 N/22.4-29.7 Nmm), and the WQH displayed the lowest values (expansion 2.7-12.6 N/11.1-39.6 Nmm, rotation 0.1-1.7 N/23.0-32.2 Nmm, torque 0.9-2.9 N/3.4-10.5 Nmm). Appliances with the smallest transverse dimensions exhibited the highest force and torque maxima. Conclusions: This study underscores the importance of understanding biomechanical principles in orthodontics for minimizing unintended tooth movements, providing detailed insights into the force systems of appliances acting in the transverse plane, and establishing a foundation for future clinical investigations to validate these in vitro findings.

Effectiveness of dental arch expansion in the orthodontic treatment with clear aligners: a scoping review.

The clinical protocol and effectiveness of dental expansion with Clear Aligner Therapy (CAT), especially among adults is still unclear. There is a need to map and explore knowledge gaps of dental expansion with CAT among children and adults. This scoping review explores the extent and depth of the available literature regarding the effectiveness and predictability of CAT in performing orthodontic expansion in both children and adults. The following databases were consulted as sources of information: PubMed, MEDLINE, Embase, Web of Science, Scopus, LILACS, COCHRANE Library, and ProQuest Dissertations & Thesis, in which the search was limited to studies on children or adults requiring transverse arch expansion and using clear orthodontic aligners. Two independent reviewers assessed the citations and extracted data, which was then synthesized in a narrative format. Over all, 698 citations were retrieved, and 33 were included. Among these, 3 were systematic reviews, 4 were cohort studies, 2 were case-control studies, and 24 were case series. Eighty-five percent of the included studies were published in the last 5 years. Despite different protocols and measurement methods, aligners were effective for arch expansion in adults and children, and the expansion predictability was greater for the lower arch than for the upper arch. The evidence suggests that arch width increment is more predictable in the premolar region and less predictable in the canine and second molar areas, with high variability across studies. Orthodontic aligners have demonstrated effectiveness in expanding arches in both adults and children. However, the literature suggests a decrease in arch width toward the posterior region, and there is no evidence of skeletal gains. To provide more conclusive evidence, randomized controlled clinical studies are warranted. This review was registered in the Open Science Framework database (DOI: https://doi.org/10.17605/OSF.IO/6EG8F).

Effect of time between archwire changes on intended dentoalveolar expansion in orthodontic patients treated with fixed appliances : Aprospective controlled clinical trial.

To analyze the effects of the time span between archwire changes on the amount of transverse dental arch expansion. The design was aprospective, controlled clinical trial. Randomization was performed by computer-generated allocation tables. In all, 35patients were evaluated in three groups treated with fixed appliances and the same four sequential leveling archwires, however, with different replacement periods: 28days (4-week [4W] group), 56days (8-week [8W] group), and 84days (12-week [12W] group). Digital models were measured before the treatment (T0) and at the end of the evaluation period (T1) by ablinded operator with OrthoAnalyzer® software (3-Shape, Copenhagen, Denmark) and compared using MANOVA. Amultiple linear regression was also used to evaluate the influences of age, initial dental crowding, incisor inclination, and facial pattern on the amount of expansion. Mean expansion was 2.77 ± 0.84 mm (upper arch) and 3.12 ± 0.88 mm (lower arch) in the 12Wgroup; 1.96 ± 0.82 mm and 2.27 ± 0.96 mm in the 8Wgroup, and 1.11 ± 0.93 mm and 1.32 ± 0.91 mm in the 4Wgroup, respectively for the upper and lower arches. The amount of expansion varied significantly between the groups in the area of the canines, first premolars, and second premolars for both arches. Expansion was less in older patients. Initial dental crowding, incisor inclination and facial pattern had no influence on dental expansion. Longer time spans between archwire changes provided greater amounts of expansion, while age is inversely related, with younger patients expressing greater amounts of expansion. The results also suggest that the expansion provided by the fixed appliances is expressed mainly in the canine and premolar areas.

Impact of Invisalign® first system on molar width and incisor torque in malocclusion during the mixed dentition period.

In orthodontic treatment of patients during the mixed dentition period, arch expansion and opening deep overbite are one of the objectives to achieve proper alignment of the teeth and correction of sagittal and vertical discrepancies. However, the expected outcomes of most therapeutic regimens are not clear, making it impossible to standardize early treatment effects. Therefore, this study was designed to evaluate the impact of the Invisalign® First System on the dental arch circumference and incisor inclination in patients during the mixed dentition period. A total of 21 children during the mixed dentition period (10 females and 11 males, with an average age of 8.76 years) were included in this study. The patients received non-extraction treatment through Invisalign® First System clear aligners, and no other auxiliary devices were used except Invisalign® accessories. Subsequently, the cooperation degree of patients during treatment and the oral measurement parameters at the beginning (T1) and the end (T2) of treatment were collected. All patients showed moderate/good cooperation degree during treatment. Besides, horizontal width of the maxillary first molar increased significantly; the designed arch expansion was 4.1 mm (±1.4 mm), while the actual arch expansion was 3.0 mm (±1.7 mm). Furthermore, the torque expression rate of upper anterior teeth reached 56.53%. Invisalign® First System clear aligners can effectively correct the teeth of patients during the mixed dentition period, widen the circumference of dental arch, and control the torque of incisors.

Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study.

The objective of this study was to investigate the biomechanical effects of different tooth movement patterns and aligner thicknesses on teeth and periodontal tissues during maxillary arch expansion with clear aligners, to facilitate more precise and efficient clinical orthodontic treatments. Three-dimensional models including teeth, maxilla, periodontal ligament, and aligner were constructed and subjected to finite element analysis. Tooth displacement trends and periodontal ligament stresses were measured for seven tooth displacement patterns (divided into three categories including overall movement of premolars and molars with gradually increasing molar expansion in each step; distributed movement of premolars and molars; and alternating movement between premolars and molars at intervals) and two aligner thicknesses (0.5mm and 0.75mm) during maxillary arch expansion with clear aligners. When expanding the maxillary arch with clear aligners, the effective expansion of the target teeth mainly showed a tilting movement trend. Increasing the amount of molar expansion increased the buccal displacement of the first molar but decreased the buccal displacement of the premolars. The mean buccal displacement of the target teeth was greater in the posterior teeth interval alternating movement group (0.026mm) than in the premolar/molar distributed movement group (0.016mm) and the overall movement group (0.015mm). Increasing aligner thickness resulted in greater buccal displacement of the crowns and increased stress on the periodontal ligaments. Increasing the amount of molar expansion reduces the efficiency of premolar expansion. Alternating movement of premolars and molars at intervals achieves a higher arch expansion efficiency, but attention should be paid to the anchorage of adjacent teeth. Increasing the thickness of the aligner increases the expansion efficiency but may also increase the burden on the periodontal tissues.

Evaluation of Mandibular Projection in Class II Division 2 Subjects Following Orthodontic Treatment Using Clear Aligners.

The purpose of this study was to evaluate the mandibular growth and/or projection following maxillary incisor proclination, overbite correction, and maxillary dentoalveolar expansion without the use of any class II mechanics, in growing class II division 2 patients treated with clear aligners. Before and after treatment cone-beam computed tomographic (CBCT) generated lateral and posteroanterior cephalograms of thirty-two patients with skeletal class II division 2, 16 in the treatment group and 16 in the untreated group, were reviewed to evaluate treatment-related changes. Upper incisors were proclined and protruded, as well as upper arch expansion and overbite correction were performed as part of their regular treatment. Cephalometric analysis was performed to evaluate skeletal and dental changes. Unpaired statistical t-tests were performed to determine if significant skeletal class II correction was achieved in the treatment group. In the treatment group, after treatment, the upper incisors became more proclined and protruded, and the inter-molar width increased while the overbite was reduced compared to the control group. An increase in skeletal mandibular growth and forward projection was also observed, thus contributing to an improvement of the sagittal skeletal relationship as evidenced by ANB and Wits values compared to the control group. A combination of upper incisor proclination, correction of deep overbite, and maxillary dentoalveolar expansion using clear aligners appears to contribute to an improvement of the skeletal class II relationship in growing patients with class II division 2. This study shows that unlocking the mandible by correcting a deep overbite, proclining upper incisors, and expanding the upper arch in growing class II division 2 patients can improve skeletal class II using clear aligners. How to cite this article: Mirzasoleiman P, El-Bialy T, Wiltshire WA, et al. Evaluation of Mandibular Projection in Class II Division 2 Subjects Following Orthodontic Treatment Using Clear Aligners. J Contemp Dent Pract 2024;25(4):295-302.

Comparison of transverse dimensional and incisor changes between wide and narrow orthodontic archwires: a randomized controlled trial.

To clinically compare the effects of broader archwires to standard archwires, using conventional brackets in both cases, on the transverse and incisor changes in maxillary and mandibular arches during leveling and alignment. Fifty-two patients presenting with crowding were allocated into two groups; one group received the broad Damon archwires while the other received standard 3M OrthoForm III Ovoid archwires. All participants were treated with conventional brackets using similar archwire sequences (0.014, 0.018, 0.016 × 0.022/0.016 × 0.025, 0.019 × 0.025 NiTi/CuNiTi archwires). Digital casts were obtained from alginate impressions before treatment (T0) and six weeks after inserting 0.019 × 0.025 NiTi archwires (T1). Pretreatment (T0) and post-alignment (T1) lateral cephalograms were obtained for each patient. The primary outcomes were the changes in the transverse arch dimensions and incisor inclination. The secondary outcomes were the horizontal and vertical linear changes in incisor position. Complete data were collected for 47 patients. There was a significant increase in arch width during treatment within each group, except for upper inter-molar width in 3M group (P = 0.071). Damon wire induced a statistically significant increase in maxillary inter-second premolar width (P = 0.042), and mandibular inter-first premolar (P = 0.043), inter-second premolar (P = 0.008) and inter-molar widths (P = 0.033) compared to 3M group. The increase in incisor proclination and the linear change in incisor position were significant within each group, with less mandibular incisor proclination (P = 0.004) and horizontal advancement (P = 0.038) in the Damon group. Damon archwires created a comparatively greater increase in the maxillary inter-second premolar width and the mandibular inter-first premolar, inter-second premolar, and inter-molar widths, and less proclination and horizontal advancement in mandibular incisors. The study provides invaluable evidence that using broad archwires with self-ligating brackets is the reason behind any greater expansion observed in this system rather than the unique mechanical and biological features exerted by the self-ligating system. Our results suggest that Damon archwire might be a better alternative compared to the narrower standard archwires that are usually used with conventional brackets, especially in the mandibular arch, in cases where mild to moderate crowding is planned to be resolved with a non-extraction approach. However, as arch expansion in the absence of posterior crossbites raises the question of long-term stability, the reported advantage of the use of wide wires should be interpreted with caution and should be considered in the retention phase, bearing in mind that achieving a good post-treatment occlusion is important for enhancing post-treatment stability.

Comparison of the Haas Expander and the Elastodontic Device for the Resolution of Transverse Discrepancies in Growing Patients: A Single-Centre Observational Study

Background: This study aimed to compare the clinical outcomes of using two different devices to treat upper palatal discrepancies evaluated with a digital intraoral scanner. Methods: A total of 64 patients were enrolled and treated with either an elastodontic expansion device (32 patient test group, 16 females and 16 males, mean age 7.08 ± 0.44) or Haas expander (32 patient control group, 16 females and 16 males, mean age 7.32 ± 0.50). The two groups exhibited similar orthodontic features. The orthodontic criteria were: skeletal class I relationship; molar class I relationship; complete eruption of upper sixths; presence of unilateral or bilateral cross bite. All dental casts were examined and subsequently scanned with an intraoral scanner (I-Tero) pre-treatment (T0) and 12 months after the onset of therapy (T1) to assess the distance between the decidous upper canines (ICW, intercanine width) and the distance between the mesiopalatal cusps of the upper first molars (IMW, intermolar width). For statistical analysis, the t-test for continous variables and the chi-square test for categorical variables were used, respectively. Results: There were no statistically significant differences between the mean and SD of the expansions that resulted from the Haas expander and the elastodontic devices (Haas expander vs. Eptamed: ICW_T1 (Haas) = 42.34 (3.09), ICW_T1 (Eptamed) = 42.69 (2.77); p = 0.743; IMW_T1 (Haas) = 34.22 (2.29), IMW_T1 (Eptamed) = 34.00 (2.56); p = 0.800). The two devices were similarly effective. Conclusions: Elastodontic devices and the Haas expander can successfully help the orthodontist to conduct upper arch expansion treatment. However, elastodontic devices are more comfortable during the resolution of palatal discrepancies compared to palatal expander devices.

Vertical and transverse treatment effects of Invisalign First system compared to Hyrax maxillary expanders with fixed appliances in mixed dentition patients.

To compare vertical and transverse changes in mixed dentition patients treated with the Invisalign First System (IFS) to those treated with a banded hyrax expander with fixed appliances (Hyrax) and control groups, and to assess the efficiency rate of dental arch expansion with IFS. The study included 80 mixed dentition patients, with 40 in each group (IFS and Hyrax) and 40 controls from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection. Skeletal and dental vertical dimension changes and arch width changes between pretreatment (T1) and posttreatment (T2) were evaluated. Age at T1, time interval (T1-T2), sex, and Angle class did not significantly differ among the groups. Mandibular plane angle changes showed a similar reduction for the control and IFS groups, with no changes in the Hyrax group. However, the differences among the three groups did not reach statistical significance (P = .06). The Hyrax group showed significantly greater expansion in maxillary intermolar width compared to the IFS group, 4.4 vs 2.5 mm, respectively. The efficiency of maxillary expansion using IFS ranged from 52.3% to 76.87%. During the mixed dentition stage, no significant changes occurred in vertical dimensions among the control, Hyrax, and IFS groups. Although there was a trend suggesting a greater reduction in mandibular plane angle in the IFS group compared to the Hyrax group, this may not be clinically significant given the less than 1° difference. IFS can be a viable option for addressing mild arch width deficiencies, with a predictable increase in intermolar width of approximately 2.5 mm.

Comparison of Dentoalveolar Expansion with Clear Aligners by Using Two Different Treatment Protocols in the Early Mixed Dentition: A Retrospective Study

Objectives: To evaluate the effect of different expansion protocols on tooth movements during maxillary arch expansion with Invisalign First System® (IFS) in the mixed dentition. Materials and Methods: This study was conducted using digital models of 20 patients treated with sequential expansion (MFE, mean age: 7.88±0.60; 9 girls, 11 boys) and 20 patients treated with simultaneous expansion (SIE, mean age: 7.94±0.51; 12 girls, 8 boys) acquired before (T0) and after (T1) treatment. Maxillary parameters were measured on each model at T0 and T1. Mann Whitney U tests were used for comparisons between groups, and Wilcoxon tests were used for the analysis of intra-group. Results: In both groups, the greatest increase of maxillary arch width (AW) was determined at both the cusp tips and gingival levels of the upper first deciduous molars followed by the second deciduous molars and by the deciduous canines (p < 0.01). The lowest increase of AW was found in the at the permanent first molars (p < 0.01). Conclusion: Both protocols with IFS can be considered effective in patients in early mixed dentition. The greatest increase was detected at the level of the upper first deciduous molars, whereas the least increase was observed at the level of the first permanent molars. Key Words: Clear Aligners, Invisalign® First system, Mixed dentition

Modalities used to gain space in dental arch

Most of orthodontic patients seek treatment to improve their facial and dental esthetics which is compromised due to variety of malocclusions. Malocclusion can be caused by skeletal or dental factors. Dental malocclusion includes crowding, spacing, increased overjet, and overbite, rotations of teeth etc. Correction of some malocclusions like crowding and increased overjet needs space in the dental arch. There are various methods for creating space in the dental arch such as proximal stripping, distalization of molars, extractions, expansion of arch, and proclination of anterior teeth, and derotation of posterior teeth. In this article, we will briefly discuss about these methods.

Miniscrew anchorage versus Class II elastics for maxillary arch distalization using clear aligners.

To identify whether intramaxillary miniscrew anchorage could achieve a better maxillary arch distalization effect in clear aligner treatment compared to Class II elastics. Thirty adult patients with Class II dentition who were treated with whole maxillary arch distalization using clear aligners were collected. Either intramaxillary miniscrew anchorage (miniscrew group, n = 17) or intermaxillary Class II elastics (Class II elastic group, n = 13) were used to support maxillary arch distalization. Three-dimensional predicted and achieved displacements, and angular changes of maxillary posterior teeth and anterior teeth, were measured and compared. The achieved distalization efficiency was 36.2%-43.9% in the posterior teeth and the retraction efficiency was 36.9%-49.4% in the anterior teeth. No statistically significant differences were found in maxillary arch distalization efficiency between the groups. The miniscrew group achieved less incisor extrusion and posterior tooth distal tipping than the Class II elastic group. Both groups achieved comparable arch expansion, posterior tooth buccal inclination, and anterior tooth lingual inclination. Intramaxillary miniscrew anchorage and intermaxillary Class II elastics achieved comparable efficiency in maxillary arch distalization. However, the miniscrew anchorage showed better vertical control in anterior teeth and mesiodistal tipping control in posterior teeth.

The Common Retention Practices Among Orthodontists from Different Countries.

To investigate the most common retention practices, factors influencing the retention protocol, and the differences among orthodontists regarding retention practices. An online validated questionnaire was anonymously sent to 3,000 orthodontic residents and clinicians. The survey consisted of 19 questions regarding the participants' demographics, prescribed retention appliances, factors affecting retention appliance choices, and adjunctive retention procedures. Descriptive statistics, Chi2 and Kendall's Tau-b tests were applied. Five hundred fifty-five orthodontic residents and clinicians, 53.3% males and 46.7% females, completed the survey, indicating a response rate of 18.5%. Although participants' demographics, type of treatment and pre-treatment malocclusion influence the choice of retention protocols, thermoplastic retainers (TR) were the most popular retention regime for the maxillary arch for both adults (47.4%) and adolescents (42.3%). Bonded retainers (BR) were the favored option for the mandibular arch (44.9% of adults and 40.7% of adolescents). The degree of arch expansion (64.1%) and the degree of interdigitation (50.1%) after treatment were the most influential factors for the choice of the preferred type of retainers by the respondents. 68.6% of the participants thought professional retention guidelines would be useful. Thermoplastic retainers were the most common retention appliances for adults and adolescents in the maxilla. At the same time, BR was the most favored retainer in the mandibular arch, with clinical experience, practice setting, and malocclusion- and treatment-related factors influencing the type of the chosen appliance. The demographic differences and the uneven participation in the survey need to be considered while interpreting the findings of this study.

Orthodontic considerations in hypodivergent craniofacial patterns

This article examines the characteristics of hypodivergent craniofacial patterns and explores treatment modalities in response to these features. It discusses the impact of robust masticatory muscles, which produce heavy occlusal forces. In addition, it examines the use of Botox or splints to reduce gonial angles in individuals with a square face. A nonextraction treatment approach supported by temporary skeletal anchorage devices is recommended; however, if anatomical limitations persist, extraction may be necessary when arch expansion, molar distalization, incisor proclination, or interproximal reduction cannot create the necessary space. In hypodivergent cases where a nonextraction approach is impractical, a single-arch extraction strategy may be considered to prevent a reduction in the vertical dimension. Emphasizing esthetics, particularly maxillary incisor display, a protocol of total arch extrusion of the maxillary dentition assisted with temporary skeletal anchorage device, bite raisers, and interarch elastics is suggested.

Descriptive analysis of the cases published in the Align® Global Gallery.

Social media enhanced access to information, making it easier to share dental treatments. This study aimed to conduct a descriptive analysis of the clinical cases published on the Align® Global Gallery platform. A retrospective cross-sectional study of 1,582 cases was conducted, data extracted referred to the following basic information: case number; patient's age; reported gender; Invisalign® package modality; treatment time; aligner exchange protocol; total number of aligners per arch; type of retainers, and inclusion of initial and final panoramic and cephalometric radiographs. The majority were young (mean age 24.6 years, SD = 11.6), female patients (69.1%) with Class I malocclusion (39.4%) and crowding (77.9%). Comprehensive treatment was common (66.5%), with an average treatment time of 18 months (SD = 8.56; 95% CI = 17.6-18.5), with the most frequently reported aligner exchange protocol being 7 days (49.5%), with an average of 50.6 aligners in the upper arch (SD = 26.9; 95% CI = 49.2-51.9), and 48.7 in the lower arch (SD = 26.1; 95% CI = 47.4-50.0). Arch expansion (66.9%) and interproximal reduction (59.7%) were common approaches, while extractions were rare (4.3%). In most cases, initial lateral cephalometric (80.4%) and panoramic (93.3%) radiographs were presented. However, the final radiograph count dropped, with lateral cephalometric at 69.2%, and panoramic at 82.2% of cases. Cases in the Align®Global Gallery mostly feature Class I patients with crowded teeth, treated with expansion and interproximal reduction. The absence of standardized information and post-treatment data restricts the applicability of these findings to broader Invisalign® treatment trends.

Accuracy of arch expansion with two thermoplastic materials in Invisalign® patients: EX30® and SmartTrack®.

The purpose of this retrospective study was to compare accuracy of arch expansion using two different thermoplastic materials in Invisalign aligners: EX30® (Polyethylene Terephthalate Glycol, or PETG) and SmartTrack® (polyurethane). The study sample comprised 65 adult patients consecutively treated with Invisalign from two private practices: group 1 - treated with EX30® (358 teeth) and group 2 - treated with SmartTrack® (888 teeth). Six hundred and twenty-three measurements were assessed in three digital models throughout treatment: model 1 - initial, model 2 - predicted tooth position, and model 3 - achieved position. Sixteen reference points per arch were marked and, after best alignment, 2 points per tooth were copied from one digital model to another. Linear values of both arches were measured for canines, premolars, and first molars: on lingual gingival margins and cusp tips of every tooth. Comparisons were performed by Wilcoxon and Mann-Whitney test. Both termoplastic materials presented significant differences between predicted and achieved values for all measurements, except for the lower molar cusp tip in the SmartTrack® group. There is no statistical difference in the accuracy of transverse expansion between these two materials. Overall accuracy for EX30® aligners in maxilla and mandible were found to be 37 and 38%, respectively; and Smarttrack® presented an overall accuracy of 56.62% in the maxilla and 68.72% in the mandible. It is not possible to affirm one material expands better than the other. Further controlled clinical studies should be conducted comparing SmartTrack® and EX30® under similar conditions.

Does the trimline extension and attachment size affect maxillary arch expansion in clear aligner therapy ? A finite element study

Abstract Objective Using finite element analysis (FEA), the aim of the present study was to evaluate the effects of different aligner trimline extensions and attachment sizes on maxillary first and second molars under expansive forces delivered by clear aligner therapy Methods The study utilised 3 mm and 4 mm horizontal rectangular attachments on the maxillary first and second molars. Two main models were created: a High and Flat Trimline Aligner (HTLA), and a Low and Flat Trimline Aligner (LTLA). Six distinct model variations were created for the analysis: (1) LTLA and no attachment (NA), (2) LTLA and 3 mm horizontal rectangular attachment (3HA), (3) LTLA and 4 mm horizontal rectangular attachment (4HA), (4) HTLA and NA, (5) HTLA and 3HA, (6) HTLA and 4HA. Results In all models, the crowns of the maxillary molars exhibited buccal displacement, whereas the root displayed palatal displacement. The LTLA-NA model had the greatest displacement of all models, whereas the HTLA-4HA model had the lowest displacement. The greatest PDL stress value was identified in the coronal third region of the palatal root of the molars. Conclusion Buccal tipping of the molars was observed during aligner expansion in all models. By increasing the attachment size and heightening the aligner trimline extension, the occurrence of buccal tipping was significantly reduced.

The predictability of arch expansion with the Invisalign First system in children with mixed dentition: a retrospective study.

This study aimed to quantify the predictability of arch expansion in children with early mixed dentition treated with the Invisalign First® system and evaluate the clinical factors for the predictability of arch expansion. Pretreatment, predicted and posttreatment digital models from Invisalign's ClinCheck® software were obtained for 90 children with mean (standard deviation) age of 8.42 (0.93) who planned arch expansion. Arch width measurements were collected using Invisalign's arch width table. The predictability of expansion was calculated by comparing the amount of expansion achieved with the predicted expansion. Linear regression analysis was used to evaluate clinical factors associated with predictability of expansion. The predictability of the expansion of the maxillary teeth was as follows: 71.1% primary canines (n = 55), 67.5% first primary molars (n = 46), 65.2% second primary molars (n = 79), and 53.4% first permanent molars (n = 90); the predictability of the expansion of the mandibular teeth was 81.1% primary canines (n = 31), 81.2% first primary molars (n = 51), 77.8% second primary molars (n = 80), and 69.4% first permanent molars (n = 90). The predictability of arch expansion was significantly higher in the mandibular arch compared to the maxillary arch and significantly lower in the permanent first molar than in the other primary teeth. Predictability decreased significantly as the amount of predicted expansion per aligner increased in the upper and lower permanent first molars, primary second molars, and upper primary canines. Predictability significantly increased when buccal or palatal attachments were placed on the bilateral side compared to cases without attachment at the upper permanent first and primary second molars. The predictability of arch expansion using the Invisalign First® system varies according to arch and tooth type. The amount of predicted expansion per aligner and the number of attachments to the maxillary teeth are potential clinical factors that can affect the predictability of expansion.