Effect of Elastomeric Module Degradation and Ligation Methods on Kinetic Friction between NiTi or Stainless Steel Wires and Stainless Steel Brackets.

Objectives: The reduction of resistance to sliding between the archwire and bracket promotes more seamless tooth movement, leading to a faster and improved orthodontic treatment experience. This research aimed to examine how the degradation of elastomeric modules, different ligation methods, bracket-wire angle, and wire type (nickel titanium, NiTi or stainless-steel, SS) impact the kinetic friction resulting from the interaction between NiTi or SS archwires and SS brackets. Materials and Methods: The current in vitro study was conducted on nine groups, including NiTi and SS archwires with three types of ligations (O-ring, figure of 8, and SS wire ligature) and two bracket-wire angles (0˚ and 10˚). The kinetic friction in each group was measured using a Universal Testing Machine at four time intervals: baseline, day one, week one, and week four. Repeated measures ANOVA, Mauchly test of sphericity followed by the Greenhouse-Geisser test, and relevant post hoc tests were used for statistical analysis (P<0.05). Results: The authors found a decrease in kinetic friction in all types of ligations, which confirmed the effect of time on the degradation of ligation modules. The kinetic friction of figure of 8 ligations was higher than both O-ring and SS wire ligations. No difference was observed between O-ring and SS wire ligations. Furthermore, the bracket-wire angle did not affect friction. Conclusion: The authors suggest that the use of figure of 8 ligations in NiTi and SS wires should be limited due to their high friction and replaced with other types of ligations, if possible.

Antimicrobial and Mechanical Properties of Orthodontic Acrylic Resin Containing Zinc Oxide and Titanium Dioxide Nanoparticles Supported on 4A Zeolite.

Polymethyl methacrylate (PMMA) is widely used to manufacture removable orthodontic appliances. However, since the porous structure, cold-curing acrylic resins are susceptible to bacterial adhesion and colonization. The aim of this study was to investigate the antibacterial and mechanical properties of a cold-curing PMMA resin containing ZnO and TiO2 nanoparticles supported on the 4A zeolite. ZnO and TiO2 nanoparticles supported on the 4A zeolite were synthesized. Nanoparticles were added in three compositions as ZnO/4A, TiO2/4A, and ZnO/TiO2/4A at 2wt% and 4wt% concentrations to cold-curing acrylic resin powder (SR Triplex® Cold Ivoclar Vivadent AG, FL-9494 Schaan/Liechtenstein). X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were performed to investigate the nanocomposite characteristics. A direct test method was used to assess the antibacterial properties against Streptococcus mutans, Klebsiella pneumoniae, and Escherichia coli. The surface roughness of acrylic samples was measured with a profilometer. Flexural strength was evaluated by a three-point bending test, and one-way ANOVA and Tukey's post hoc tests were used for statistical evaluation of the data. A p value of less than 0.05 was considered statistically significant. XRD confirmed the accurate crystalline structure of synthesized nanoparticles; FE-SEM images showed nanoparticle dispersion within polymerized acryl. The addition of 2 and 4 wt% of ZnO/4A, TiO2/4A, and ZnO/TiO2/4A caused colony reduction in all types of tested microorganisms more than 99% and 100%, respectively. The mean flexural strengths of acrylic specimens containing 2wt% and 4wt% of synthesized nanoparticles were significantly lower than those of the resin without nanoparticles. Fabricated samples showed favorable antibacterial properties but decreased flexural strength.

A Novel Developed Bioactive Composite Resin Containing Silver/Zinc Oxide (Ag/ZnO) Nanoparticles as an Antimicrobial Material against Streptococcus mutans, Lactobacillus, and Candida albicans.

AIM: The objectives of this study were to develop a new bioactive composite resin containing silver/zinc oxide (Ag/ZnO) nanoparticles and investigate the effects on mechanical, cytotoxic, biocompatibility, and antimicrobial properties. MATERIALS AND METHODS: Disc-shaped specimens were prepared from composite with and without nanoparticles in separate culture media containing Streptococcus mutans, Lactobacillus, and Candida albicans. Bracket bonding evaluation was performed on composite without nanoparticles (O), composite containing ZnO (Z) nanoparticles, composite containing ZnO nanoparticles and silver ions (A&Z), and composite containing Ag/ZnO nanoparticles (AZ) synthesized using optical precipitation. RESULTS: Composite resin with nanoparticles (AZ, A&Z, and Z) showed significant antimicrobial properties (P < 0.05). The mean shear bond strength of A&Z composite resin (13.61 ± 0.73 MPa) was significantly less than that of conventional composite resin (19.03 ± 4.12 MPa) (P < 0.05). In addition, the mean shear bond strength of AZ composite resin (20.49 ± 1.03 MPa) was significantly higher than that of Z (16.35 ± 1.03 MPa) and A&Z composite resins. CONCLUSIONS: Incorporation of ZnO nanoparticles and their compounds into orthodontic composite resins induced antibacterial properties against oral pathogens, and of all these nanoparticles, the AZ group exhibited the best antimicrobial activity and highest shear bond strength.

Influence of Physical Dimension and Morphological-Dependent Antibacterial Characteristics of ZnO Nanoparticles Coated on Orthodontic NiTi Wires.

White spot lesions (WSLs) are one of the adverse effects of fixed orthodontic treatments. They are the primary sign of caries, which means inhibiting this process by antibacterial agents will reverse the procedure. The current study tested the surface modification of nickel-titanium (NiTi) wires with ZnO nanoparticles (NPs), as antimicrobial agents. As the morphology of NPs is one of the most critical factors for their properties, the antibacterial properties of different morphologies of ZnO nanostructures coated on the NiTi wire were investigated. For the preparation of ZnO nanostructures, five coating methods, including chemical vapor deposition (CVD), chemical precipitation method, polymer composite coating, sol-gel synthesis, and electrospinning process, were used. The antibacterial activity of NPs was assessed against Streptococcus mutans by the colony counting method. The obtained results showed that all the samples had antibacterial effects. The antibacterial properties of ZnO NPs were significantly improved when the specific surface area of particles increased, by the ZnO nanocrystals prepared via the CVD coating method.

Comparison of radiographic changes in the alveolar crest after extraction of fully and partially erupted premolars during orthodontic treatment: A retrospective analytical study.

Background. The alveolar process plays an essential role in providing dental support and gradually disappears with tooth loss. Space deficiency can cause one premolar to remain semi-erupted adjacent to a fully-erupted premolar. During orthodontic treatment, each of these premolars can be extracted. This retrospective study aimed to compare radiographic changes of the alveolar crest due to orthodontic movements of fully-erupted and semi-erupted premolars into the extraction sites before and after treatment. Methods. The patients were divided into the fully-erupted premolar extraction (first) group and the semi-erupted premolar extraction (second) group. The distance between the cementoenamel junction (CEJ) and the alveolar crest, from the distal aspect of the canine to the mesial aspect of the first molar, was measured on panoramic radiographs of 78 patients (39 from each group) before and after treatment with a digital caliper. Changes in the alveolar crest were compared between the two groups. Finally, the height differences of the alveolar crest in mesial and distal aspects of the remaining premolars in both groups were calculated at the end of treatment. Descriptive statistical analyses and paired and independent t tests were used in the study. Results. The distance from the CEJ to the alveolar crest at mesial and distal aspects in the first group and the distal aspect of the extraction site in the second group increased significantly. However, changes at the mesial aspect were not significant in the second group. Comparing the alveolar crest height between the two groups and between the mesial and distal aspects of the remaining premolar tooth indicated no significant differences. Conclusion. No significant difference was observed between the extraction of a fully-erupted or semi-erupted premolar to obtain greater alveolar height.

Arch width changes in patients with Class II division 1 malocclusion treated with maxillary first premolar extraction and non-extraction method.

BACKGROUND: The aim of this study was to determine arch width changes during maxillary first premolars extraction and non-extraction treatment in patients with Class II division 1 malocclusion. MATERIAL AND METHODS: Dental casts of 91 Class II division 1 patients (36 males and 55 females) were evaluated. The minimum age of the subjects at the beginning of treatment was above 16 years. 48 patients were treated with extraction of the maxillary first premolars and 43 patients were treated without extraction. Pre- and post-treatment maxillary and mandibular inter-canine and inter-molar arch widths were measured. RESULTS: At the end of treatment, maxillary and mandibular inter-canine widths of both groups increased significantly. The maxillary inter-molar width decreased in the extraction group and increased in the non-extraction group. The mandibular inter-molar width increased significantly in both groups. No significant differences were observed between males and females. CONCLUSIONS: The results of this study indicated that there was a tendency for an increase in arch width during both the extraction and non-extraction treatment except maxillary inter-molar width in the extraction cases. Key words:Dental arch, malocclusion, angle Class II, tooth movement, extraction.

Comparison of multiple rebond shear strengths of debonded brackets after preparation with sandblasting and CO2 laser.

Background. Failure of orthodontic bracket bonds is a common occurrence during orthodontic treatment. Different techniques have been suggested in the literature to remove resin residues from the bracket bases and enamel surfaces to prepare the surfaces again after debonding. This study attempted to compare multiple rebond shear strengths (SBS) of debonded brackets following preparation with sandblasting and CO2 laser. Methods. The brackets were bonded on 30 human and bovine maxillary central incisors using self-curing composite resin. SBS was measured using Hounsfield testing machine. The brackets were rebonded for two other times after composite resin residues on their surfaces were removed, either with air abrasion or CO2 laser. The debonded brackets and enamel surfaces were also evaluated after each debonding procedure under a stereomicroscope in order to determine adhesive remnant index (ARI). SBS of debonded brackets after each step were compared between sandblast and CO2 laser groups. Results. We observed significant differences in SBS values between pre-recycling and first (P = 0.04), second (P = 0.007) and third recycling (P = 0.007) with laser. Recycling with sandblasting resulted in a decrease in SBS after the first and second recycling procedure; however, the SBS increased after the third recycling procedure, with no significant differences. Conclusion. SBS of brackets after recycling with sandblasting and laser beams was not significantly different, and both were at a favorable level. However, repeating the recycling procedure with sandblasting resulted in more favorable SBS compared to laser.

Zinc-oxide nanocoating for improvement of the antibacterial and frictional behavior of nickel-titanium alloy.

AIM: To fabricate a friction-reducing and antibacterial coating with zinc oxide (ZnO) nanoparticles on nickel-titanium (NiTi) wire. MATERIALS & METHODS: NiTi orthodontic wires were coated with ZnO nanoparticles using the chemical deposition method. Characteristics of the coating as well as the physical, mechanical and antibacterial properties of the wires were investigated. RESULTS: A stable and well-adhered ZnO coating on the NiTi wires was obtained. The hardness and elastic modulus of the ZnO nanocoating were 2.3 ± 0.2 and 61.0 ± 3.6 GPa, respectively. The coated wires presented up to 21% reduction in the frictional forces and antibacterial activity against Streptococcus mutans. ZnO nanocoating significantly improved the surface quality of NiTi wires. The modulus of elasticity, unloading forces and austenite finish temperature were not significantly different after coating. CONCLUSION: This unique coating could be implemented into practice for safer and faster treatment to the benefit of both patient and clinician.

The effect of ZnO nanoparticle coating on the frictional resistance between orthodontic wires and ceramic brackets.

Background. Any decrease in friction between orthodontic wire and bracket can accelerate tooth movement in the sliding technique and result in better control of anchorage. This study was carried out to evaluate frictional forces by coating orthodontic wires and porcelain brackets with zinc oxide nanoparticles (ZnO). Methods . In this in vitro study, we evaluated a combination of 120 samples of 0.019×0.025 stainless steel (SS) orthodonticwires and 22 mil system edgewise porcelain brackets with and without spherical zinc oxide nanoparticles. Spherical ZnOnanoparticles were deposited on wires and brackets by immersing them in ethanol solution and SEM (scanning electronmicroscope) evaluation confirmed the presence of the ZnO coating. The frictional forces were calculated between the wiresand brackets in four groups: group ZZ (coated wire and bracket), group OO (uncoated wire and bracket), group ZO (coatedwire and uncoated bracket) and group OZ (uncoated wire and coated bracket). Kolmogorov-Smirnov, Mann-Whitney andKruskal-Wallis tests were used for data analysis. Results. The frictional force in ZZ (3.07±0.4 N) was the highest (P <0.05), and OZ (2.18±0.5 N) had the lowest amount of friction (P <0.05) among the groups. There was no significant difference in frictional forces between the ZO and OO groups (2.65±0.2 and 2.70±0.2 N, respectively). Conclusion . Coating of porcelain bracket surfaces with ZnO nanoparticles can decrease friction in the sliding technique,and wire coating combined with bracket coating is not recommended due to its effect on friction.

Effect of surface treatment with sandblasting and Er, Cr: YSGG laser onbonding of stainless steel orthodontic brackets to silver amalgam

Objectives: Satisfactory bonding of orthodontic attachments to amalgam is a challenge for orthodontists. The aim of this in vitro study was to compare the shear bond strength of stainless steel orthodontic brackets to silver amalgam treated with sandblasting and Er,Cr:YSGG laser. Study Design: Fifty-four amalgam discs were prepared, polished and divided into three groups: In group 1 (the control group) the premolar brackets were bonded using Panavia F resin cement without any surface treatment; in groups 2 and 3, the specimens were subjected to sandblasting and Er, Cr:YSGG laser respectively, before bracket bonding. After immersing in distilled water at 37°C for 24 hours, all the specimens were tested for shear bond strength. Bond failure sites were evaluated under a stereomicroscope. Data was analyzed using one-way ANOVA and a posthoc Tukey test. Results: The highest and lowest shear bond strength values were recorded in the laser and control groups, respectively. There were significant differences in mean shear bond strength values between the laser and the other two groups (p<0.05). However, there were no significant differences between the sandblast and control groups(p=0.5).Conclusions: Amalgam surface treatment with Er,Cr:YSGG laser increased shear bond strength of stainless steel orthodontic brackets (AU)

Bolton’s intermaxillary tooth size ratios among Iranian schoolchildren

Objectives: The aims of the present study were to determine anterior and total tooth-width ratios in a representativeIranian sample in Tabriz city and compare them with the Bolton standards. Study design: A total of 54 Iranianschoolchildren (12-14 years old) in Tabriz were examined. Alginate impressions were taken for subjects andpoured by the dental stone. The mesiodistal widths of the teeth were measured using a digital caliper. The overalland anterior Bolton’s intermaxillary tooth size ratios for each model pair was calculated. Results: There were nosignificant differences (p > 0.05) between the right and left sides of the dental arch and a symmetry in size exists.There were no significant differences between genders for all teeth measured except for the maxillary centralincisors, maxillary canines and mandibular canines. Anterior and overall Bolton ratios for males were 77.72±0.25and 92.44±0.19 and for females were 78.48±0.30 and 92.45±0.23 percent, respectively. There were no statisticallysignificant differences between males and females for the anterior and overall ratios. The anterior and overall Boltonratios among Tabrizian schoolchildren were 78.10±0.28 and 92.24±0.21 percent, respectively. There was nostatistically significant difference between these ratios and those were found in the Bolton study. Conclusion: Nosignificant differences between the mesiodistal sizes of contralateral teeth were observed and a symmetry in sizeexists. There were no significant differences in the mesiodistal sizes of similar teeth between males and femalesexcept for the maxillary central incisors, maxillary canines and mandibular canines. Significant differences inBolton ratio between males and females, and examined population (student from Tabriz, Iran) and the Bolton’sweren’t observed either (AU)

Effect of chin position on natural head orientation reproducibility

Background and aims: Establishment of natural head position (NHP) in radiography or photography by estimation,which is called natural head orientation (NHO), has been recently advocated by various studies. This studyaimed to determine the effect of chin position on the accuracy and reproducibility of NHO in a more realisticway.Materials and Methods: NHP-based digital photographs of 33 adults with normal profile were modified usingthe computer software Supper-Goo and Photoshop technique to produce 99 profile images in three groups withnormal, forward and backward chin positions. The reconstructed images were presented to three observers whorotated the images through a circular hole on a computer monitor. The horizontal angle was read on screen andrecorded whenever they found the best horizontally-oriented face. This was performed at four intervals: T0: baseline;T1: after 5 minutes; T2: after one week; and T3: one month after baseline.Results: After orientation, the mean orientation angles were 0.19° ± 1.39, 0.20° ± 1.53 and - 0.31° ± 1.38 for thenormal, forward and backward chin groups, respectively. T-test did not show any significant differences in NHOand NHP among the three groups of chin position: P values of 0.17, 0.19, and 0.26 for normal, forward, and backwardchin positions, respectively. However, one-way ANOVA demonstrated significant differences in the NHObetween the normal and backward, and backward and forward chin groups. The obtained reproducibility rate ofNHO calculated via Med-Calc 8.1 online software for T0, T1, T2 and T3 intervals was more than 60%, which isregarded significant in medical studies.Conclusion: Natural head position could be created with great reproducibility through orientation of profile imagesin different chin positions. NHO is under the influence of chin position; however, this influence is not clinicallysignificant (AU)

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Bolton's intermaxillary tooth size ratios among Iranian schoolchildren.

OBJECTIVES: The aims of the present study were to determine anterior and total tooth-width ratios in a representative Iranian sample in Tabriz city and compare them with the Bolton standards. STUDY DESIGN: A total of 54 Iranian schoolchildren (12-14 years old) in Tabriz were examined. Alginate impressions were taken for subjects and poured by the dental stone. The mesiodistal widths of the teeth were measured using a digital caliper. The overall and anterior Bolton 's intermaxillary tooth size ratios for each model pair was calculated. RESULTS: There were no significant differences (p > 0.05) between the right and left sides of the dental arch and a symmetry in size exists. There were no significant differences between genders for all teeth measured except for the maxillary central incisors, maxillary canines and mandibular canines. Anterior and overall Bolton ratios for males were 77.72±0.25 and 92.44±0.19 and for females were 78.48±0.30 and 92.45±0.23 percent, respectively. There were no statistically significant differences between males and females for the anterior and overall ratios. The anterior and overall Bolton ratios among Tabrizian schoolchildren were 78.10±0.28 and 92.24±0.21 percent, respectively. There was no statistically significant difference between these ratios and those were found in the Bolton study. CONCLUSION: No significant differences between the mesiodistal sizes of contralateral teeth were observed and a symmetry in size exists. There were no significant differences in the mesiodistal sizes of similar teeth between males and females except for the maxillary central incisors, maxillary canines and mandibular canines. Significant differences in Bolton ratio between males and females, and examined population (student from Tabriz, Iran) and the Bolton's weren't observed either.

Effect of chin position on natural head orientation reproducibility.

BACKGROUND AND AIMS: Establishment of natural head position (NHP) in radiography or photography by estimation, which is called natural head orientation (NHO), has been recently advocated by various studies. This study aimed to determine the effect of chin position on the accuracy and reproducibility of NHO in a more realistic way. MATERIALS AND METHODS: NHP-based digital photographs of 33 adults with normal profile were modified using the computer software Supper-Goo and Photoshop technique to produce 99 profile images in three groups with normal, forward and backward chin positions. The reconstructed images were presented to three observers who rotated the images through a circular hole on a computer monitor. The horizontal angle was read on screen and recorded whenever they found the best horizontally-oriented face. This was performed at four intervals: T0: baseline; T1: after 5 minutes; T2: after one week; and T3: one month after baseline. RESULTS: After orientation, the mean orientation angles were 0.19°±1.39, 0.20°±1.53 and -0.31°±1.38 for the normal, forward and backward chin groups, respectively. T-test did not show any significant differences in NHO and NHP among the three groups of chin position: P values of 0.17, 0.19, and 0.26 for normal, forward, and backward chin positions, respectively. However, one-way ANOVA demonstrated significant differences in the NHO between the normal and backward, and backward and forward chin groups. The obtained reproducibility rate of NHO calculated via Med-Calc 8.1 online software for T0, T1, T2 and T3 intervals was more than 60%, which is regarded significant in medical studies. CONCLUSION: Natural head position could be created with great reproducibility through orientation of profile images in different chin positions. NHO is under the influence of chin position; however, this influence is not clinically significant.