Variability of slot size in orthodontic brackets

The Mechanical and Clinical Properties of Customized Orthodontic Bracket Systems-A Comprehensive Review

The rise of computer-aided design and computer-aided manufacturing (CAD/CAM) and 3D printing technologies in orthodontics has revolutionized the development of customized labial and lingual bracket systems with a variety of materials, which offer potential advantages over traditional orthodontic brackets. To highlight the current state of knowledge regarding the mechanical and clinical properties of CAD/CAM and 3D-printed custom bracket systems, we conducted a comprehensive search across the PubMed, Embase, Cochrane Library, Web of Science, and Scopus databases to identify relevant articles published before April 2024. Mechanical (including fracture toughness, hardness, modulus of elasticity, frictional resistance, slot accuracy, torque transmission, and shear bond strength) and clinical (including treatment efficiency and duration, cost, and comfort) properties were compared between traditional and customized orthodontic bracket systems in the current review. Our findings suggest that customized brackets have the potential to increase bracket slot precision, reduce treatment time, and offer cost-efficiency. However, it is worth noting that the advantages and disadvantages of customized bracket systems vary depending on the bracket material and the manufacturing methods, warranting comprehensively controlled investigations in the future.

Precision of slot widths and torque transmission of in-office 3D printed brackets : An in vitro study

PURPOSE

To investigate a novel in-office three-dimensionally (3D) printed polymer bracket regarding slot precision and torque transmission.

METHODS

Based on a 0.022″ bracket system, stereolithography was used to manufacture brackets (N = 30) from a high-performance polymer that met Medical Device Regulation (MDR) IIa requirements. Conventional metal and ceramic brackets were used for comparison. Slot precision was determined using calibrated plug gages. Torque transmission was measured after artificial aging. Palatal and vestibular crown torques were measured from 0 to 20° using titanium-molybdenum (T) and stainless steel (S) wires (0.019″ × 0.025″) in a biomechanical experimental setup. The Kruskal-Wallis test with post hoc test (Dunn-Bonferroni) was used for statistical analyses (significance level p < 0.05).

RESULTS

The slot sizes of all three bracket groups were within the tolerance range according to DIN 13996 (ceramic [C]: 0.581 ± 0.003 mm; metal [M]: 0.6 ± 0.005 mm; polymer [P]: 0.581 ± 0.010 mm). The maximum torque values of all bracket-arch combinations were above the clinically relevant range of 5-20 Nmm (PS: 30 ± 8.6 Nmm; PT: 27.8 ± 14.2 Nmm; CS: 24 ± 5.6 Nmm; CT: 19.9 ± 3.8 Nmm; MS: 21.4 ± 6.7 Nmm; MT: 16.7 ± 4.6 Nmm).

CONCLUSIONS

The novel, in-office manufactured polymer bracket showed comparable results to established bracket materials regarding slot precision and torque transmission. Given its high individualization possibilities as well as enabling an entire in-house supply chain, the novel polymer brackets bear high potential of future usage for orthodontic appliances.

A scanning electron microscopy investigation of the precision of three orthodontic bracket slot systems

OBJECTIVE

One of the most imprortant factors in achieving ideal teeth positions is the precision of the slot dimensions of orthodontic brackets into the archwires are inserted.This study aimed to assess the accuracy of the dimensions of orthodontic bracket slots and molar buccal tube apertures and to compare them with the specifications provided by the manufacturers.

METHOD

A total of sixty brackets and ten molar buccal tubes with varying slot heights were examined using a scanning electron microscope from the mesial side. The dimensions and morphology of these bracket slots and buccal tubes apertures were assessed using the AutoCAD Software. A one-sample t-test was conducted to compare the measurements with the values provided by the manufacturer.

RESULTS

The findings of the present study indicated that the height of the measured bracket slots and buccal tube apertures dimensions were significantly larger than the actual dimensions and exhibiting divergent walls. On the other hand, the depth of the brackets slots showed significantly smaller values than the actual one.

CONCLUSION

A need for careful consideration when selecting a commercially accessible brand for everyday use is essential as certain materials may not meet acceptable standards.

Dimensional accuracy, mechanical property, and optical stability of zirconia orthodontic bracket according to yttria proportions

This in vitro study evaluated comprehensively the performances of zirconia brackets with varying yttria proportions in manufacturing advanced orthodontic brackets. Three experimental groups of zirconia brackets were fabricated using yttria-stabilized zirconia (YSZ) materials with different yttria proportions-3 mol% yttria (3Y-YSZ), 4 mol% yttria (4Y-YSZ), and 5 mol% yttria (5Y-YSZ) (Tosoh Ceramic, Japan). A polycrystalline alumina ceramic bracket (3M™ Clarity™ Advanced, MBT 0.022-in. slot) was employed as the control group. Morphological properties, including slot surface structure and dimensions, were examined using scanning electron microscopy and surface profiler analysis. Manufacturing accuracy was assessed with root mean square calculations of trueness and precision. Mechanical properties were tested, encompassing static and kinetic frictional resistance (FR) and fracture strength. Optical stability was evaluated through 20,000 cycles of thermocycling and a 7-day immersion in various coloring agents. Within the limitations of this study, zirconia brackets containing 3 to 5 mol% YSZ presented enhanced reliability in terms of dimensional accuracy and demonstrated favorable optical stability. Notably, owing to its advantageous mechanical properties, the 3Y-YSZ variant showed remarkable potential as an advanced material for fabricating orthodontic brackets.

Evaluating orthodontic bracket slot dimensions and morphology: A narrative review

The current article aims to review the previous studies that measure the orthodontic bracket slot dimensions and geometry. Searches in different databases, including PubMed Central, Science Direct, Wiley Online Library, the Cochrane Library, Textbooks, Google Scholar, and Research Gate, in addition to a manual search, were performed about the methods of assessing orthodontic bracket slot dimension up to March 2023. The irrelevant and duplicate studies were eliminated, leaving 35 studies for this narrative review. The findings indicate that the slots are oversized with diverging walls in most studies. Manufacturers must respect the standards during manufacturing brackets and adhere to the actual dimensions and tolerance values.

An Evaluation of the Accuracy and Precision of Ceramic Orthodontic Bracket Slot Dimensions Utilizing Micro-Computed Tomography (Micro-CT)

This study's aim is to determine the accuracy and precision of the bracket slot height in MBT 0.022″ ceramic brackets. Five brackets from 11 different systems (n = 55) were scanned using micro-computed tomography (micro-CT). The slot height was measured at the face (external) and base (internal) of the slot. Data were analyzed using a One-Sample t-Test, and a Paired t-Test. The lowest external height was seen in OrthoCare Purity^® at 0.02264″ (2.9%), and the greatest in TOC Ghost Advanced^® at 0.02736″ (24.4%). The lowest internal height was seen in Forestadent Glam^® at 0.02020″ (-8.2%), and the greatest in TOC Ghost Advanced^® at 0.2547″ (15.8%). OrthoCare Purity^® measurements corresponded most closely with the expected measurements. TP InVu^® was found to be the most precise bracket for external height (range = 0.00043″) and American Orthodontics 20/40^® for internal height (range = 0.00028″). In assessing slot geometry, all brackets demonstrated a higher mean external slot height compared to the internal measurements at the base of the bracket. Orthodontic bracket slots are larger than expected and slot parallelism was not observed in any bracket brand tested. Similarly, slot dimensions are imprecise where two 'identical' brackets have different slot sizes. The clinician should, therefore, assume that play is most likely higher than expected.

Comparative evaluation of different debonding and reconditioning methods for orthodontic ceramic brackets regarding effectiveness for reuse : An in vitro study

PURPOSE

To investigate the reusability of ceramic brackets in terms of shear bond strength, friction behavior, slot dimension, fracture strength, and color stability.

METHODS

A total of 90 conventionally debonded and 30 by an Er:YAG laser debonded ceramic brackets were collected. All the used brackets were inspected under a stereomicroscope at 18 × magnification and sorted according to their adhesive remnant index (ARI). Five groups were formed (n = 10): (1) new brackets as a control group, (2) flamed and sandblasted, (3) flamed and acid bathed, (4) laser-reconditioned, and (5) laser-debonded brackets. The bracket groups were tested regarding different properties such as shear bond strength, friction behavior, slot size, fracture strength, and color stability. Analysis of variance (ANOVA) and nonparametric Kruskal-Wallis tests were used for statistical analysis (significance level: p < 0.05).

RESULTS

Shear bond strength values of the acid reconditioned brackets were significantly lower (8.0 ± 3.1 MPa) compared to the control group (12.9 ± 2.9 MPa). Laser-reconditioned (32.8 ± 2.7%) and laser-debonded (30.9 ± 2.4%) brackets showed the lowest force loss due to friction (control group 38.3 ± 3.0%). No significant differences were observed between groups regarding slot size and fracture strength. All groups had color differences of [Formula: see text]< 10. Scanning electron microscope images and ARI scores indicated that most of the residues on the bracket bases were removed.

CONCLUSION

All reconditioning methods yielded adequate results regarding bracket properties. Yet, focusing on the need to protect the enamel and the bracket base, laser debonding seems to be the most suitable method for reconditioning ceramic brackets.

Comparison of the sliding resistance between three models of self-ligating ceramic brackets: An in vitro and micro-morphological study

OBJECTIVE

The main objective of our study was to compare a new model of self-ligating ceramic bracket (Clarity™ Ultra by 3M™), to its competitors by evaluating their resistance to sliding during an in vitro simulation of canine retraction.

MATERIAL AND METHODS

The sample consisted of 120 brackets (30 brackets in each group: Victory Twin Series LP™, Clarity Ultra™ by 3M™, Damon Clear 2™ by Ormco™ and Empower™ 2 Clear by American Orthodontics™). Canine retraction was simulated using a universal testing machine connected to a software that measured the average sliding resistance (ASR) for each group. Five brackets from each group were randomly selected and observed under a digital optical microscope at ×50 magnification. ANOVA test and Tukey's analysis were carried to detect statistically significant differences between the groups' sliding resistance values, at the risk of α=0.05.

RESULTS

Measured ASR values of control group (metallic Victory Twin) were the highest ones (70.55g), followed by 3M™ (33.22g) then Damon™ (6.72g) and AO™ (5.49g) (P-value<0.0001). Through microscopic observations, we found that the 3M™ bracket has the lowest percentage of slot chamfering (8%) compared to the other brackets (12%). The 3M™ bracket also has the widest slot followed by AO, and then Damon™. All three bracket types have oversized slots compared to the manufacturer's description, the least oversized being the 3M™ bracket, followed by AO™ and then Damon™. 3M™ and Damon™ brackets have covers that concealed the entire wire in the vertical dimension whereas the AO™ bracket has a curvilinear cover that only shields the gingival part of its slot. Wire-play is zero for the 3M™ group, and 0.1mm for the other two groups.

CONCLUSION

Clarity Ultra™ ceramic bracket produced by 3M™ does not perform well against friction forces compared to its competitors and that is due to its micro-morphological characteristics.

Super-elasticity in vitro assessment of CuNiTi wires according to their Austenite finish temperature and the imposed displacement

OBJECTIVES

To assess the super-elasticity of CuNiTi wires (Ormco, Glendora, Calif) according to their Austenite finish temperature (Af) and to the imposed displacement. The secondary objective was to compare the wire dimensions with the stated measurements and to study interbatch variability.

MATERIALS AND METHODS

10 types of CuNiTi wires (Ormco, Glendora, Calif) (n = 350) were investigated at 36 ± 1°C, with conventional brackets (Victory Series, 3M Unitek, Monrovia, Calif). Tensile test with coronoapical displacement ranging from 1 to 5 mm of the canine bracket was imposed. The wire dimensions were initially measured from two batches (n = 10).

RESULTS

Dimensional heterogeneity varied by ± 2.00% compared to the manufacturer's data, and even up to 5.54% for 0.014-inch CuNiTi (P = .00069). However, all unloading forces were reproducible. In decreasing order, the forces delivered by a CuNiTi 27 were greater than those with CuNiTi 35 and 40. The super-elasticity was expressed only for displacements of 1 to 2 mm, at best up to 3 mm for 0.014-inch CuNiTi 27.

CONCLUSIONS

The value of Af as well as the amount of imposed displacement seem to influence the expression of the super-elasticity of CuNiTi wires and the amount of corrected malocclusion. Among the tested wires, under these experimental conditions, 0.014-inch wire could be suitable as a first archwire. CuNiTi 35, therefore, seems to offer the best compromise among the force level, the expression of super-elasticity and the amount of malocclusion correction.

Compliance with the ISO 27020:2019 norm of a sample of currently available preadjusted Orthodontic bracket systems. Are the actual dimensions as expected?

Background

Determine the exact slot dimension of a sample of a MBT prescription stainless steel conventional brackets from different manufacturers to compare the actual values with the nominal ones declared by the manufacturers and to verify the compliance with tolerance limits given by the ISO 27020:2019. Different batches from each manufacturer were evaluated to determine whether or not they are different in size. In addition, the geometry of the slot walls was assessed.

Methods

360 stainless steel preadjusted orthodontic brackets of 12 different manufacturers were assessed. All brackets had a nominal slot size of 0.022 by 0.028 inches, belonged to the right upper central incisor, and were fabricated with the metal injection molding technique (MIM). For each manufacturer, three different manufacturing batches were evaluated. Brackets were coded using a single-blind design.

Results

All bracket systems in the study group except one displayed a statistically significant difference with the nominal declared value, although only four of the systems did not comply with the tolerance limits established by the ISO 27020:2019. In most of the systems, the slot height was oversized when compared to the nominal one. A significant interbatch variability was found in most of the evaluated systems. Most of the brackets walls were divergent.

Conclusions

The dimensional accuracy of commercially available metal brackets is not guaranteed. The respect for the norm should be enforced as well as the quality controls along the manufacturing process since orthodontic brackets are a precision medical device.