Wassana Wichai

Cytotoxicity of Three Light-Cured Orthodontic Adhesives

Objective: The aim of this study was to evaluate the cytotoxic effects of three commercial light-cured orthodontic adhesives.Materials and methods: The potential cytotoxic effects of three types of orthodontic adhesives, Grengloo, Green Glue, and Transbond XT, were tested on L929 cell culture. The cell line was grown in 96-well tissue culture plates (1x105 cells/mm3). Thin resin discs weighing 0.4, 0.6, 0.8, 0.8, and 0.8 gram of each material were prepared and aged for 1, 3, 6, 8, and 10 days, respectively, in Minimum Essential Medium (MEM) at 37°C with 5% CO2 at 100% humidity. Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay according to ISO 10993-5: 2009 (E). The differences among the groups was statically analyzed by independent paired t-test (α = 0.05).Results: After 1 day of storage, all adhesive systems showed cytotoxic effects. However, ageing tended to considerably reduce the cytotoxicity of Green Glue. Grengloo was essentially non-cytotoxic day 3 onwards, while Green Glue and Transbond XT exhibited potential cytotoxicity at all times of the experiment. Conclusion: All tested light-cured orthodontic adhesives had cytotoxic potential during the first day. Grengloo had the highest cell viability, whereas, Green Glue had the lowest.

Degree of Conversion of Three Light-Cured Orthodontic Adhesives

Introduction: The aim of this in-vitro study was to analyze the polymerization ability of 3 light-cured orthodontic adhesives by determining the degree of conversion (DC). Materials and Methods: Fourier transform infrared spectroscopy (FTIR) was used to evaluate the DC after polymerization immediately, 1 day, 7 days, and 30 days. The adhesives investigated were Transbond XT (3M Unitek, USA), Grengloo (Ormco Corp., USA), and Green Glue (Hangzhou Biomaterials, China). Twelve stainless steel brackets (n=4) were used and the adhesives were cured with Bluephase G2 (Ivoclar Vivadent, Liechtenstein). The data were analyzed by Kruskal-Wallis test for comparing materials and Friedman test for comparing the time periods. Results: The DC values were significantly different among the materials and among the time periods. The highest DC in each period was obtained for Grengloo and the lowest DC was observed for Transbond XT. Thus, there were significant differences between the DC values of Grengloo and Transbond XT in each period. Among the time periods, DC% at T1 (Immediately) and T3 of the material were significantly different. The DC values of all adhesives increased extremely from immediately following curing to 1 day and then slightly increased from 1 day to 7 days. Conclusions: Grengloo showed the highest levels of DC at all tested periods. The percentage values of DC largely increased from immediately following curing to 1 day. This concluded that monomers in orthodontic adhesives kept converting even after completion of photoactivation.

Grain Structure and Surface Roughness of Four Commercial NiTi Orthodontic Archwires

This study investigated four commercially available NiTi orthodontic archwires from different manufactures for their grain structure and surface roughness.Four commercially available pre-formed NiTi orthodontic archwire (Ormco, Sentalloy, Highland and NIC) with diameter 0.016 x 0.022 inch2 were tested. The wire samples were polished and etched to evaluate the morphology and structure of wire surface. Each NiTi archwire was investigated under a reflected light microscope of an Optical Microscope to analyze its grain structure and size, in longitudinal surfaces. The surfaces of wire were qualitatively examined in the secondary electron mode at common magnification (500X). The surface roughness was also evaluated by a surface roughness tester. The descriptive statistic was evaluated the mean and standard deviation of surface roughness and Medcale T-Test was to test the mean difference of the surface roughness in each brands. This study showed an average grain size of 2-8 μm for each NiTi archwire. The wire surface of Ormco and Highland showed straiations along the longitudinal axes, however Sentalloy and NIC showed small pores on the wire surface. The surface roughness was 0.09 μm for Highland, 0.25 μm for Sentalloy, 0.28 μm for Ormco and 0.46 μm for NIC archwire. The Highland was smoothest and NIC was the roughest. There were in significant (p < 0.05) difference of surface roughness of each brands. The results showed that the four manufactures NiTi archwires were different in grain size, wire surface and surface roughness. During clinical application, these archwires may exhibit different mechanical properties, such as strength, hardness, ductity, and friction because of their microstructure.

Loading and Unloading Forces Following Addition of 5% Cu in Nickel-Titanium Alloy Used for Orthodontics

This study aims to address the amount of force delivered by a fabricated NiTiCu orthodontic wire with a ternary composition ratio of 46.0 Ni: 49.0 Ti: 5.0 Cu and to compare the results with a commercial NiTiCu35oC orthodontic archwire. Nickel (purity 99.9%), Titanium (purity 99.8%), and Copper (purity 99.9%) were used in this study with the atomic weight ratio 46.0 Ni: 49.0 Ti: 5.0 Cu. The elements were melted to form an alloy using an electrolytic arc furnace in argon gas atmosphere and homogenized at 800oC for 1 hr. The alloys were subsequently sliced into thin plates (1.5mm) by EDM wire cutting machine to obtain the specimens and were cold-rolled with 30% reduction followed by heat treatment in a furnace at 400oC for 1 hour. Then, the three newly fabricated NiTiCu specimens were cut in nearly identical wire sizes of 0.016 inch x0.022 inch. Commercial preformed Ormco NiTiCu35oC archwire with size 0.016 inch x 0.022 inches were used for comparative purposes. Three-point bending test was performed using a Universal Testing Machine to investigate the force of the load-deflection curve at oral temperature (36oC+ 1) with deflection points at 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5 mm. Descriptive statistics was used to evaluate each variable and independent t-test was used to analyze the differences between the groups. It was found that both NiTiCu wires presented typical superelastic properties as observed from the load-deflection curve. The average force was 341.70 g for loading, and 264.18 g for unloading for 46.0 Ni: 49.0 Ti: 5.0 Cu wire. Similarly, the values were 299.88 g for loading, and 201.96 g for unloading for Ormco NiTiCu35oC. There were significant differences (p<0.05) in mean loading and unloading forces between the two NiTiCu wires. The deflection forces in loading and unloading force for Ormco NiTiCu at each point were less than 46.0 Ni: 49.0 Ti: 5.0 Cu wire, except at the deflection point of 0.25 mm. Regarding the force difference between each deflection point of loading and unloading force, Ormco NiTiCu35oC exerted less force than 46.0 Ni: 49.0 Ti: 5.0 Cu wire, except at difference deflection at 1.5-1.25 mm of unloading force. However, there were still within the acceptable limits for orthodontic use. It is concluded that the fabricated ternary alloy of 46.0 Ni: 49.0 Ti: 5.0 Cu (atomic weight) with 30% reduction and heat treatment at 400oC for 1 hr. and Ormco 35oC NiTiCu presented the characteristics of both superelastic and shape memory in their wire form. The unloading forces of both NiTiCu wires were in the range of orthodontic use. This should be a good foundation for further studies towards development of new orthodontic NiTiCu archwires.

Shear Bond Strength and ARI Score of Chemically Cured Orthodontic Adhesive Resins

The purpose of this study was to compare shear bond strength and to evaluate Adhesive Remnant Index (ARI) score among three chemically cured orthodontic adhesive resins, namely Unite (3M Unitek, USA), Rely-a-Bond (Reliance, USA) and Ortho-Force (China). Materials and methods: Ninety extracted human maxillary premolars were randomly divided into 3 groups (30 teeth/group). Upper premolar metal brackets (Ormco, USA) were boned by using the following adhesive systems: Unite, Rely-a-Bond and Ortho-Force. After 24 hours, shear bond strength was tested by using a Universal Testing Machine with a crosshead speed of 0.5 mm/min. After debonding, all teeth and brackets were examined under 10-times magnification and scored by using Image-Pro Plus 7.0 software program. Results: One-way ANOVA followed by post-hoc Tukey HSD multiple comparison test showed a statistically significant (P<0.05) difference among groups. Ortho-Force had the lowest shear bond strength (17.53±3.60 MPa) and demonstrated statistically significant difference (P<0.05) from the other groups. The difference between Unite (22.40±3.11 MPa) and Rely-a-Bond (20.67±2.70 MPa) was not statistically significant. The bond failure sites were categorized according to the ARI, and the Chi-square test showed significant differences in the ARI scores (P<0.05) among all sample groups. The ARI score of 3 was found to be the most prevalent in Ortho-force (73.33%), followed by Unite (66.67%), and Rely-a-Bond (0%). In Rely-a-Bond group, ARI score of 1 was the most prevalent (66.67%). Only Unite had no residual adhesive left on tooth surface after debonding (6.67%). Conclusions: Unite and Rely-a-Bond produced greater shear bond strength than Ortho-Force. According to ARI score, Unite and Ortho-Force had a high frequency of all the adhesive remained on the tooth surface but Rely-a-Bond had high frequency of less than half the adhesive remained on the tooth surface.

Comparison of Mechanical Properties of Three Different Orthodontic Latex Elastic Bands Leached with NaOH Solution

Orthodontic elastic bands made from natural rubber continue to be commonly used due to their favorable characteristics. However, there are concerns associated cytotoxicity due to harmful components released during conventional vulcanization (sulfur-based method). With the co-operation of The National Metal and Materials Technology Center (MTEC) and Faculty of Dentistry Mahidol University, a new method was introduced to reduce toxic components by leaching the orthodontic elastic bands with NaOH solution. The objective of this study was to evaluate the mechanical properties of Thai and commercial orthodontic elastic brands (Ormco and W&H) leached with NaOH solution. Three elastic brands (N =30, size 1⁄4 inch ,4.5 oz.) were tested for mechanical properties in terms of initial extension force, residual force, force loss, breaking strength and maximum displacement using a Universal Testing Machine. The results showed that force loss significantly decreased in Thai-LEACH and W&H-LEACH, whereas the values increased in Ormco-LEACH (P<0.05). The data exhibited a significantly decrease in breaking strength with Thai-LEACH and Ormco-LEACH, whereas all 3 brands revealed a significantly decrease in maximum displacement with the leaching process (P<0.05). In conclusion, leaching with NaOH solution is a new method, which can remove toxic components from orthodontic latex elastic bands. However, this process can affect their mechanical properties. Leached elastic bands from Thai had comparable properties with Ormco and have potential to be developed as a promising product.

Influence of the cross-linking agent on mechanical properties of PMMA powder with compromised particle morphology

OBJECTIVE To investigate the effect of a cross-linking agent on the mechanical properties of self-cured orthodontic acrylic resin using PMMA powder (CPM-PMMA) with a compromised microstructure. MATERIALS AND METHODS The mechanical properties of three sample groups were investigated in this study: CPM-PMMA, orthocryl and orthoplast. CPM-PMMA powder was prepared by suspension polymerization. It was mixed with a commercially available liquid (orthocryl) to yield a test specimen and to compare its flexural properties and Vicker hardness with the two commercial products. Molecular weight and particle size distribution of all groups were examined. Particle morphology was observed using scanning electron microscopy (SEM) and optical microscopy (OM). RESULTS The average molecular weight of the CPM-PMMA powder was similar to that of the industrial products. Its particle size distribution was narrow and limited to large sizes (91.1-149μm). SEM and OM presented the compromise particle morphology. However, the flexural properties and Vicker hardness of CPM-PMMA powder mixed with orthocryl liquid showed no significant difference compared with orthocryl sample group. In addition, the CPM-PMMA had higher flexural properties than the orthoplast samples. CONCLUSIONS Although the CPM-PMMA powder presented a compromised particle morphology and narrow particle size distribution, when mixed with orthocryl liquid, the cured resin produced acceptable mechanical properties due to the large amount of cross-linking agent. This result could indicate that the mechanical properties of self-cured acrylic resins are mainly dependent on the amount of cross-linking agent in the liquid component.

Initial Tensile and Residual Forces of Pigmented Elastomeric Ligatures from Various Brands

This study aimed to investigate the initial tensile and residual forces of pigmented elastomeric ligatures (clear, pink, and metallic) from three commercial brands – Brand 1 (USA), Brand 2 (USA), and Brand 3(China). Twelve elastomeric ligatures of each brand and color were evaluated for initial tensile and residual forces after stretching for 28 days at 37°C by a Universal Testing Machine. The results showed that the highest initial tensile force was 14.78 N, 20.71 N, and 15.1 N for the metallic color of Brand-1, pink color of Brand -2, and metallic color of Brand -3, respectively. There were significant (p<0.05) differences in the initial tensile force of each brand, except clear and metallic color of Brand-1 & 3 and pink color of Brand-2 & 3. Similarly, among the pigmented ligatures from each brand, significant (p<0.05) differences were observed in the initial tensile force, except metallic color of Brand-1 & 3. Brand-3 had the highest residual force after 28 days, whereas the loss of force was 80-90% in Brand-1 & 2 and 20-30% in Brand-3. There were also significant (p<0.05) differences in the residual forces in each color and brand, except metallic color of Brand-1. In conclusion, there were significant differences in the initial tensile and residual forces among the three pigmented elastomeric ligatures of the three commercial brands.

Effect of the Addition of 3% Co in NiTi Alloy on Loading/Unloading Force

The study evaluated the loading-unloading force in the load-deflection curve of the fabricated NiTiCo and NiTi wires. Wire alloys with Nickel, Titanium, and Cobalt (purity-99.95%) with atomic weight ratio 47Ni:50Ti:3Co and 50.6Ni:49.4Ti were prepared, sliced, and cold-rolled at 30% reduction, followed by heat treatment in a furnace at 400oC for 1 hour. The specimens of wire size of 0.016 x 0.022 inch2 were cut and subjected to three-point bending test to investigate the load-deflection curve at deflection point 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5 mm. Descriptive statistic was used to evaluate each variables and independent t-test was used to compare between the groups. The results presented a load-deflection curve that resembled a typical superelastic wire. However, significant differences were seen in the loading-unloading forces between the two with an average loading force of 412.53g and 304.98g and unloading force of 292.40g and 208.08g for NiTiCo and NiTi wire, respectively. The force at each deflection point of NiTiCo in loading-unloading force was higher than NiTi wire. This study concluded that the addition of 3%Co in NiTi alloy can increase the loading-unloading force of NiTi wire but were within the range for orthodontic tooth movement.

Failure Site and ARI Score of Rebonded Brackets Using No-Mix Adhesive Resins

To evaluate failure sites and ARI scores of re-bonded brackets after debonding of three no-mix adhesive brands. 120 teeth were divided into 2 groups for bonded and rebounded (60 teeth/group) and 3 subgroups (20 teeth/subgroup) for three no-mix adhesive, System1+, Rely-a-bond, and Unite. Tooth surface and bracket base were inspected by low power light microscope (10X) after debonding. The failure sites were assessed and residual adhesives was recorded using the Adhesive Remnant Index (ARI). The failure sites were expressed in percentage and Chi-square was used to determine significant differences in the ARI scores among groups (p< 0.05). After rebonding brackets, the failure site of no mix adhesive in bonding were changed to cohesive layer in rebonding group except Unite adhesive. ARI scores of all adhesive were changed from score 2 in bonding group to score 3 in rebonding group after debonding bracket. There were significant (p<0.05) differences in the ARI scores between bonded and rebonded groups except Unite and System1+ and between Unite groups. The results showed that the failure site mostly changed to cohesive layer and ARI changed to Score 3 in three no-mix adhesives after debonding in rebonding brackets.