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Orthodontic Materials: Properties and Effectiveness of Use

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Biomaterials".

Deadline for manuscript submissions: 10 November 2025 | Viewed by 8059

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Special Issue Editors

Dr. Matthias Mertmann

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Guest Editor

Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU, 80336 Munich, Germany
Interests: material science; biomechanics; brackets; NiTi alloys

Prof. Dr. Andrea Wichelhaus

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Guest Editor

Department of Orthodontics and Dentofacial Orthopedics, LMU University Hospital, LMU, 80336 Munich, Germany
Interests: orthodontic research; biomechanics; material science; mechano-biology; genetics

Special Issue Information

Dear Colleagues,

The use of materials in orthodontic research and clinical applications has shifted focus from traditional metal-based appliances towards laser-sintered metallic devices, polymeric foils, and printable plastics, e.g., for use in aligners. To date, questions about sustainability and environmental footprints need to be considered and addressed scientifically, together with equally important aspects of patients’ benefits, comfort, and possible side effects.

This Special Issue collects research papers discussing new developments in orthodontic material science and their application in treatment systems. This comprises papers that discuss mechanical properties and the simulation of forces and moments in clinical application and in vivo studies. In addition to material science, papers that detail environmental aspects and sustainability are also invited.

Dr. Matthias Mertmann
Prof. Dr. Andrea Wichelhaus
Guest Editors

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Keywords

orthodontics
metals
mechanical properties
simulation
brackets
aligner
treatment system
sustainability
environmental effects
retention
surface structure
adhesion
polymers
clinical studies
3D printing
laser sintering
CAD–CAM retainer

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Published Papers (7 papers)

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Research

10 pages, 819 KiB

Open AccessArticle

Influence of Printing Orientation on Surface Roughness and Gloss of 3D Printed Resins for Orthodontic Devices

by Cecilia Goracci, Carlo Bosoni, Patrizia Marti, Nicola Scotti, Lorenzo Franchi and Alessandro Vichi

Materials 2025, 18(3), 523; https://doi.org/10.3390/ma18030523 - 23 Jan 2025

Viewed by 877

Abstract

The study aims to assess the effect of printing orientation on surface roughness and gloss of resins for 3D printing of aligners. Squared specimens (14 × 14 × 4 mm) were printed using Dental LT Clear (Formlabs, Somerville, MA, USA; LT) or Tera Harz TC-85 DAC (Graphy, Seoul, Republic of Korea; TC) with different orientations: 0° (horizontal), 90° (vertical), and as per the manufacturer’s recommendation (40° for LT, 60° for TC). A profilometer was used to measure roughness (Ra) in µm, while gloss was recorded in gloss units (GU) with a glossmeter. The collected data were statistically analyzed. Material type did not significantly influence roughness, while print orientation was an influential factor, with the orientation recommended by the manufacturer yielding the roughest specimens. Vertical printing resulted in significantly higher roughness than horizontal. Material type was a significant factor for gloss, with TC exhibiting significantly higher gloss than LT. Print direction significantly influenced gloss, with vertical printing resulting in the highest gloss. The finding of higher roughness for vertical prints can be explained by the presence of a greater number of layers. The superior gloss exhibited by TC regardless of print angulation could be related to the effective cleaning of uncured resin by centrifugation and to the high degree of monomer conversion in nitrogen atmosphere. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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15 pages, 3540 KiB

Open AccessArticle

Dynamic Reconstruction of the Nickel Ions’ Behavior in Different Orthodontic Archwires Following Clinical Application in an Intraoral Environment

by Mirela Georgieva, George Petkov, Valeri Petrov, Laura Andreeva, Jorge N. R. Martins, Velizar Georgiev and Angelina Stoyanova-Ivanova

Materials 2025, 18(1), 92; https://doi.org/10.3390/ma18010092 - 29 Dec 2024

Cited by 1 | Viewed by 833

Abstract

Rationale: Orthodontic archwires undergo chemical and structural changes in the complex intraoral environment. The present work aims to investigate the safe duration for intraoral use (related to the nickel release hypothesis) of different types of nickel-containing wires. By analyzing how the nickel content (NC) varies over time, we aim to provide practical recommendations for the optimal use of said archwires. Materials and Methods: Our analysis focuses on the following nickel-containing archwires: stainless steel, Ni-Ti superelastic, heat-activated NiTi and CuNiTi, and multi-force archwires. The studied archwires of each type were divided into three groups: group 1, as received; group 2, retrieved after intraoral exposure for less than 6 weeks; group 3, used for more than 8 weeks. To assess NC, measurements using scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and laser-induced breakdown spectroscopy (LIBS) were performed in multiple regions of each wire. Statistical analysis of the measured values using one-way ANOVA and multiple group comparisons showed significant differences in nickel content between groups. The dynamic behavior of the statistical results for NC was then modeled using logistic regression and fitted with cubic splines. Conclusions: The proposed behavior model, with further refinement, could enable orthodontists to make informed, patient-specific decisions regarding the safe and effective use of orthodontic floss. The overall conclusion of the study is that due to stability, SS-CrNi, HA-Ni-Ti with Cu, and TriTanium^TM are suitable for long-term use, and due to higher nickel release, Ni-Ti-Superelastic, HA-Ni-Ti without Cu, and Bio-Active^TM are better for short- to medium-term use. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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10 pages, 987 KiB

Open AccessArticle

Assessment of Change in Enamel Color and Surface Hardness Following the Use of ICON Resin Infiltration and Remineralizing Agent: An In Vitro Study

by Naif Almosa, Khalid Alaman, Fares Alkhudairi, Muhannad Alhaqbani, Mohammed Alshalawi and Rahaf Zawawi

Materials 2024, 17(24), 6030; https://doi.org/10.3390/ma17246030 - 10 Dec 2024

Viewed by 860

Abstract

This study aimed to evaluate the change in enamel color and surface micro-hardness following the use of resin-infiltration concept material (ICON) and casein phosphopeptide-amorphous calcium fluoride phosphate (CPP-ACFP) remineralizing agent. Fifty-four extracted human third molars were collected and randomly divided into three groups: group A: control with no surface treatment; group B: treated using ICON; and group C: treated using CPP-ACFP. The change in color and micro-hardness of the enamel surface were measured using spectrophotometer and Vickers hardness number, respectively. The measurements were taken at three timelines; baseline (BL), after demineralization (DM), and after surface treatment (TX). The three groups showed no significant differences in enamel color change after demineralization (p < 0.05). However, after surface treatment in relation to the baseline, groups B and C had a significant increase in color change compared to the control group (p < 0.05), and group B showed a statistically significant increase in enamel color changes compared to group C. Additionally, all groups exhibited a significant reduction in enamel micro-hardness after demineralization in comparison to their baseline (p < 0.05). Group C showed a significant increase in micro-hardness after surface treatment compared to groups A and B (p < 0.05), while group B showed a significant decrease in enamel micro-hardness compared to groups A and C (p < 0.05). These findings suggest that teeth treated with CPP-amorphous calcium fluoride phosphate (CPP-ACFP) show a significant improvement in enamel surface color after demineralization compared to the teeth treated with resin infiltration (ICON) and the non-treated teeth. Additionally, enamel surfaces treated with CPP-ACFP show significant enamel hardness regaining, while resin infiltration (ICON) compromises enamel surface hardness. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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14 pages, 924 KiB

Open AccessArticle

Wear Behavior and Water Sorption of Additively Manufactured Resin-Based Splint Materials

by Johann Wulff, Cordula Leonie Merle, Sebastian Hahnel and Martin Rosentritt

Materials 2024, 17(23), 5880; https://doi.org/10.3390/ma17235880 - 30 Nov 2024

Cited by 1 | Viewed by 784

Abstract

3D printing as an additive manufacturing method has proven to be of great interest for the computerized production of oral splints. Various parameters must be taken into consideration when assessing the durability of oral splints in a wet environment, such as the mouth. The aim of this in vitro study was to assess the wear behavior and water sorption of two 3D-printed splint materials depending on their building orientation and post-processing parameters. The parameters considered included the type of post-polymerization and the type of cleaning utilized after printing. The average wear depth was between −421.8 μm and −667.5 μm. A significant influence of the building orientation (p < 0.001) but not of the material (p = 0.810), cleaning (p = 0.933), or post-polymerization (p = 0.237) on wear was demonstrated. The water sorption ranged between 13.8 μg/mm³ and 30.3 μg/mm³, featuring a significant dependency on material and building orientation but not on cleaning (p = 0.826) or post-polymerization (p = 0.343). Material and fabrication methods should be carefully selected, because the type of material and building orientation affect the wear and water sorption of additively manufactured splint materials. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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15 pages, 2513 KiB

Open AccessArticle

In Vitro Investigation Using a New Biomechanical Force–Torque Analysis System: Comparison of Conventional and CAD/CAM-Fixed Orthodontic Retainers

by Francesca Thaden, Linus Hötzel, Hisham Sabbagh, Matthias Mertmann and Andrea Wichelhaus

Materials 2024, 17(19), 4916; https://doi.org/10.3390/ma17194916 - 8 Oct 2024

Viewed by 1117

Abstract

(1) Background: After more than a decade since their first description, Inadvertent Tooth Movements (ITMs) remain an adverse effect of orthodontic retainers without a clear etiology. To further investigate the link between ITMs and the mechanical properties of different retainers, the response upon vertical loading was compared in three retainer types (two stainless steel and one nickel–titanium). The influence of different reference teeth was also considered. (2) Methods: Three retainers (R1, R2, R3) were tested in a newly developed biomechanical analysis system (FRANS). They were bonded to 3D-printed models of the lower anterior jaw and vertically displaced up to 0.3 mm. Developing forces and moments were recorded at the center of force. (3) Results: The vertical displacement caused vertical forces (Fz) and labiolingual moments (My) to arise. These were highest in the lateral incisors (up to 2.35 ± 0.59 N and 9.27 ± 5.86 Nmm for R1; 1.69 ± 1.06 N and 7.42 ± 2.65 Nmm for R2; 3.28 ± 1.73 N and 15.91 ± 9.71 Nmm for R3) for all analyzed retainers and with the R3 retainer for all analyzed reference teeth, while the lowest Fz and My values were recorded with the R1 retainer. (4) Conclusions: Displacements of 0.2 mm and larger provided forces and moments which could be sufficient to cause unwanted torque movements, such as ITMs, in all analyzed retainers. Clinicians must be mindful of these risks and perform post-treatment checkups on patients with retainers of all materials. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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15 pages, 4986 KiB

Open AccessArticle

Relevant Aspects in the Mechanical and Aging Degradation of NiTi Alloy with R-Phase in Endodontic Files

by Patricia Sánchez, Benedetta Vidi, Cristina Rico, Jesús Mena-Alvarez, Javier Gil and Juan Manuel Aragoneses

Materials 2024, 17(13), 3351; https://doi.org/10.3390/ma17133351 - 6 Jul 2024

Viewed by 1065

Abstract

One of the most important challenges in endodontics is to have files that have excellent flexibility, toughness, and high fatigue life. Superelastic NiTi alloys have been a breakthrough and the new R-phase NiTi alloys promise to further optimize the good properties of NiTi alloys. In this work, two austenitic phase endodontic files with superelastic properties (Protaper and F6) and two austenitic phase files with the R-phase (M-wire and Reciproc) have been studied. The transformation temperatures were studied by calorimetry. Molds reproducing root canals at different angles (30, 45, and 70°) were obtained with cooling and loads simulating those used in the clinic. Mechanical cycles of different files were realized to fracture. Transformation temperatures were determined at different number of cycles. The different files were heat treated at 300 and 500 °C as the aging process, and the transformation temperatures were also determined. Scanning and transmission electron microscopy was used to observe the fractography and precipitates of the files. The results show that files with the R-phase have higher fracture cycles than files with only the austenitic phase. The fracture cycles depend on the angle of insertion in the root canal, with the angle of 70° being the one with the lowest fracture cycles in all cases. The R-Phase transformation increases the energy absorbed by the NiTi to produce the austenitic to R-phase and to produce the martensitic transformation causing the increase in the fracture cycles. Mechanical cycling leads to significant increases in the transformation temperatures M_s and A_f as well as R_s and R_f. No changes in the transformation temperatures were observed for aging at 300 °C, but the appearance of Ni₄Ti₃ precipitates was observed in the aging treatments to the Nickel-rich files that correspond to those with the R transition. These results should be considered by endodontists to optimize the type of files for clinical therapy. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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11 pages, 6782 KiB

Open AccessArticle

Effect of the Height of a 3D-Printed Model on the Force Transmission and Thickness of Thermoformed Orthodontic Aligners

by Omar Ghoraba, Christoph Bourauel, Mostafa Aldesoki, Lamia Singer, Ahmed M. Ismail, Hanaa Elattar, Abdulaziz Alhotan and Tarek M. Elshazly

Materials 2024, 17(12), 3019; https://doi.org/10.3390/ma17123019 - 20 Jun 2024

Viewed by 1795

Abstract

This research aims to investigate the influence of model height employed in the deep drawing of orthodontic aligner sheets on force transmission and aligner thickness. Forty aligner sheets (Zendura FLX) were thermoformed over four models of varying heights (15, 20, 25, and 30 mm). Normal contact force generated on the facial surface of the upper right central incisor (Tooth 11) was measured using pressure-sensitive films. Aligner thickness around Tooth 11 was measured at five points. A digital caliper and a micro-computed tomography (µ-CT) were employed for thickness measurements. The normal contact force exhibited an uneven distribution across the facial surface of Tooth 11. Model 15 displayed the highest force (88.9 ± 23.2 N), while Model 30 exhibited the lowest (45.7 ± 15.8 N). The force distribution was more favorable for bodily movement with Model 15. Thickness measurements revealed substantial thinning of the aligner after thermoforming. This thinning was most pronounced at the incisal edge (50% of the original thickness) and least at the gingivo-facial part (85%). Additionally, there was a progressive reduction in aligner thickness with increasing model height, which was most significant on the facial tooth surfaces. We conclude that the thermoplastic aligner sheets undergo substantial thinning during the thermoforming process, which becomes more pronounced as the height of the model increases. As a result, there is a decrease in both overall and localized force transmission, which could lead to increased tipping by the aligner and a diminished ability to achieve bodily movement. Full article

(This article belongs to the Special Issue Orthodontic Materials: Properties and Effectiveness of Use)

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