Effect of three common hot beverages on the force decay of orthodontic elastomeric chain within a 28-day period: An in vitro study.

Objective: This study aimed to assess the effects of commonly consumed hot drinks on the force decay of orthodontic elastomeric chains. Methods: This in vitro experimental study evaluated 375 pieces of elastomeric chains with six rings placed on a jig. Four rings were stretched by 23.5 mm corresponding to the approximate distance between the canine and the second premolar. Fifteen pieces served as reference samples at time zero, and 360 pieces were randomized into four groups: control, hot water, hot tea, and hot coffee. Each group was further divided into six subgroups (n = 15) according to the different exposure periods. The specimens in the experimental groups were exposed to the respective solutions at 65.5°C four times per day for 90 seconds at 5-second intervals. The control group was exposed to artificial saliva at 37°C. The force decay of the samples was measured at 1, 2, 7, 14, 21, and 28 days using a universal testing machine. Data were analyzed using repeated-measures analysis of variance. Results: Maximum force decay occurred on day 1 in all groups. The minimum force was recorded in the control group, followed by the tea, coffee, and hot water groups on day 1. At the other time points, the minimum force was observed in the tea group, followed by the control, coffee, and hot water groups. Conclusions: Patients can consume hot drinks without concern about any adverse effect on force decay of the orthodontic elastomeric chains.

Perceptions of mandibular asymmetry among orthodontists, oral and maxillofacial surgeons, and laypersons.

Background: Facial asymmetry is one reason orthodontic patients seek treatment. This study assessed the effect of mandibular asymmetry on facial esthetics and treatment needs perceived by laypersons, orthodontists, and maxillofacial surgeons. Materials and Method: In this descriptive cross-sectional study, the frontal image of a model was captured and symmetrized from the facial midline using Adobe Photoshop software. The mandible was rotated 0°-8° with 1° intervals. Images were presented to 41 laypersons, 39 orthodontists, and 29 surgeons using an online questionnaire. The observers rated each image's esthetics with a 0-100 Visual Analog Scale and determined their treatment need by choosing one of the following three choices: No need for treatment, needs treatment, acceptable, but better to be treated. Analysis of variance for repeated measurements model. The regression method, Kruskal-Wallis analysis, was used for statistical analysis and the level of significance was set as P < 0.05. Results: The images with 0° and 1° rotation received the highest esthetic rates among all three groups, while the images with 8° rotation were the least attractive ones. Furthermore, the image esthetic ratings significantly affected their treatment need. Mandibular asymmetry diagnosis threshold was 1° for orthodontists, and 3° for both laypersons and surgeons. The treatment need threshold was 5°, 6°, and 7° for surgeons, orthodontists, and laypersons, respectively. Conclusion: The esthetics of images decreased when mandibular asymmetry increased. Treatment need was also related to increased asymmetry. Orthodontists were the most sensitive group in diagnosis, while surgeons were the most sensitive ones when it came to treatment.

Systematic review of preventive and treatment measures regarding orthodontically induced white spot lesions.

White spot lesions (WSLs) are one of the most common adverse effects following comprehensive fixed orthodontic treatment. The purpose of this review was to evaluate recent studies addressing the prevention and treatment of these lesions. Electronic databases were searched for English-written studies published between 2015 and October 2020 involving randomized clinical trials aiming at prevention or treatment of orthodontically induced WSLs using the following keywords in their title or abstracts: randomized clinical trial OR randomized controlled trial AND white spot OR caries OR demineralization OR decalcification OR remineralization. From the 23 papers which met the inclusion criteria, 11 were on preventive methods, while 12 addressed treatment protocols. However, most of the reviewed studies had a high risk of bias. The results of this review strongly support the importance of oral hygiene observation in preventing WSLs. Sodium fluoride varnish 5% was confirmed to be effective in the treatment of these lesions, as well as in the prevention of WSLs in patients with suboptimal oral hygiene. In addition, immediate CO2 laser irradiation after bonding can effectively prohibit formation of WSLs during orthodontic treatment. The literature also illustrates a promising masking effect of resin infiltration for the treatment of WSLs. However, little scientific evidence supports the effectiveness of Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) against WSLs, although more clinical trials with long-term follow-up are needed. Oral hygiene maintenance is crucial in the prevention of WSLs, and 5% sodium fluoride varnish and CO2 laser irradiation are recommended in patients with compromised oral hygiene. In the case of WSL formation, fluoride varnish and resin infiltration are effective treatment modalities.

Evaluation of the flexural strength of orthodontic acrylic resin incorporated with propolis nanoparticles: an in vitro study.

AIM: Nanopropolis has become the subject of interest in medicine and dentistry as a natural product due to its outstanding properties, particularly antimicrobial activity. This study aimed at investigating the effect of nanopropolis on flexural strength of polymethyl methacrylate (PMMA).

Shear Bond Strength of Orthodontic Brackets Bonded with a Self-Adhering Composite in Dry and Saliva-Contaminated Conditions.

OBJECTIVES: The purpose of this study was to evaluate the effect of saliva contamination on shear bond strength (SBS) of orthodontic brackets bonded by a self-adhering composite compared with a conventional adhesive. MATERIALS AND METHODS: This in vitro, experimental study investigated 40 human premolars. The teeth were randomly divided into four groups based on the adhesive type and bonding condition: (I) Vertise Flow composite without saliva contamination (VF), (II) Vertise Flow composite with saliva contamination (VF/S), (III) Transbond XT composite without saliva contamination (TXT), and (IV) Transbond XT composite with saliva contamination (TXT/S). After the preparation step, brackets were bonded to the buccal surface of the teeth, and samples were mounted in acrylic blocks, incubated at 37°C for 24 hours, and underwent thermocycling between 5- 55°C. Next, the SBS was measured by a universal testing machine. Data were analyzed by ANOVA and Tukey's test. P<0.05 was considered statistically significant. RESULTS: ANOVA showed a significant difference in SBS among the groups (P<0.001). The highest SBS was achieved in the TXT group (26.63±9.09 MPa), followed by TXT/S (13.69±4.23 MPa), VF/S (3.68±1.49 MPa), and VF (3.04±1.73 MPa). CONCLUSION: Saliva contamination did not have a significant effect on SBS of brackets bonded with Vertise Flow. However, it did not provide acceptable bond strength for orthodontic bracket bonding in the clinical setting.

Factors Influencing the Accurate Identification of Written Minimal Pairs with Graphemic Similarity: Evidence from Persian-Speaking Children and Adults.

In this study, we compared children's and adults' ability to accurately identify target words in written minimal pairs (WMPs) with graphemically similar letters while accounting for factors such as gender, similarity of the middle letter in WMPs, mono- versus dimorphemic WMPs, number of syllable, homography, and imageability. Fifty children and fifty adults were exposed to a distractor stimulus as a pre-mask, followed by the target, and then a post-mask stimulus. Subsequently, the corresponding WMPs including the target word and its graphemically minimal contrast were presented to the participants to obtain their reaction time (RT) in accurately identifying the target word. Results demonstrated that children tend to slow down their reaction as a compensatory strategy to circumvent their less mature knowledge of graphophonic units/morphemes to achieve accuracy during word recognition. In addition, among all controlled factors, children's RT was significantly influenced by similarity of the middle letter in the WMPs. Adults' RT, however, was influenced by factors such as gender, similarity of the middle letter in WMPs, and homography.

Shear bond strength of metallic orthodontic brackets to zirconium crowns treated by sandblasting compared to enamel using a universal adhesive: An in vitro study.

OBJECTIVES: Orthodontic brackets are increasingly bonded to the surface of zirconium crowns due to the growing aesthetic demands in adults' restorations. Therefore, providing a reliable bond between these substrates is of great importance. This study aimed at investigating the shear bond strength (SBS) of orthodontic metal brackets bonded to zirconium treated by sandblasting. In addition, the value was compared with SBS between metal brackets and enamel. MATERIALS AND METHODS: Samples were divided into three groups including first premolar enamel specimens (n=20), untreated zirconium blocks (n=20) and sandblasted zirconium blocks (n=20). Enamel specimens underwent etching and bonding procedures using 37% phosphoric acid and 3M™ Scotchbond™ Universal adhesive. Zirconium blocks were randomly allocated to two groups. The first group was prepared by sandblasting with 50µm aluminium oxide particles (Al2O3) under 4 bars pressure followed by bonding brackets with 3M™ Scotchbond™ Universal adhesive. Metal brackets were also bonded to the untreated zirconium group using the same adhesive. All samples underwent thermocycling, and SBS was calculated using a universal testing machine with a crosshead speed of 1mm/min. Data were analysed using One-way Anova and Tukey's tests. RESULTS: The highest SBS was recorded in sandblasted zirconium group (26.17±8.22MPa) followed by enamel group (23.667±7.00MPa) and untreated zirconium group (11.49±7.00MPa). There was a significant difference between the SBS of untreated zirconium and that of two other groups. CONCLUSION: Perfect SBS was achieved by sandblasting pre-treatment, comparable to that of enamel. Therefore, sandblasting of zirconium crowns is recommended prior to bonding orthodontic brackets.

Antibacterial properties of an acrylic resin containing curcumin nanoparticles: An in vitro study.

Background. Microbial accumulation is still a significant problem with removable acrylic appliances. This study aimed to assess the antimicrobial properties of a self-cured acrylic resin containing curcumin nanoparticles (CNPs). Methods. This in vitro study used 48 acrylic discs containing 0.5%, 1%, and 2% CNPs. The antimicrobial properties of the discs against Streptococcus mutans, Streptococcus sanguinis, Lactobacillus acidophilus, and Candida albicans were evaluated using disc agar diffusion (DAD), eluted component, and biofilm inhibition tests. The growth inhibition zones were measured, and the colonies were counted after 1, 3, and 7 days. Results. DAD test showed that none of the curcumin nanoparticle concentrations caused growth inhibition zones for any microorganisms. All the concentrations were effective against all four microorganisms in the biofilm inhibition test except 0.5% for L. acidophilus. In the eluted component test, solutions containing 2% concentration had maximum growth inhibition of all the groups at all time intervals. An increase in curcumin nanoparticle concentration from 0.5% to 1% was effective only against C. albicans. Conclusion. Generally, CNPs in all concentrations were effective against the biofilms of all four microorganisms assessed in this study. Therefore, incorporating 2% CNPs into acrylic resin seems suitable for clinical use.

Comparative evaluation of the shear bond strength of ceramic brackets of three different base designs bonded to amalgam and composite restorations with different surface treatment.

BACKGROUND: Nowadays, due to the increasing number of adult orthodontic applicants, who also have multiple dental restorations, it is important to have the ability to bond an orthodontic appliance to restoration surfaces. OBJECTIVES: The aim of this paper was to determine the shear bond strength of ceramic brackets of 3 different base designs bonded to amalgam and composite restorations after using different surface treatment methods in vitro. MATERIAL AND METHODS: In an in vitro study, the surfaces of 180 amalgam and composite specimens were prepared by using sandblasting and the erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser irradiation. Ceramic brackets of 3 base designs, including Star, Cross and Slot, for upper central teeth were bonded to amalgam and composite surfaces by using Transbond™ XT Light Cure Adhesive. All specimens were incubated at a temperature of 37°C for 1 week, and then subjected to shear bond strength tests after 1,000 cycles of thermal cycling. The bond strength of the groups was analyzed by means of the one-way and two-way analysis of variance (ANOVA), and the comparison of the 2 groups was made with Tukey's test. Residual adhesives were also determined by a 4-part criterion (0-3) in different groups and the results were analyzed with the χ2 test. RESULTS: There was a significant difference in the shear bond strength of brackets of 3 base designs bonded to amalgam and composite surfaces with different surface treatment. CONCLUSIONS: According to the results of this study, all surface treatment methods and different bracket base designs were able to provide sufficient shear bond strength on composite and amalgam surfaces. As far as the bracket base design is concerned, the use of each of the 3 base designs in the amalgam group brought desirable results in terms of the adhesive remnant index (ARI) and shear bond strength values; the use of the Star base design in the composite group proved to be suitable.

Antimicrobial Properties of Acrylic Resin Incorporated with Propolis Nanoparticles.

Objectives: One of the main problems with polymethyl methacrylate (PMMA) used for the fabrication of oral removable appliances is plaque accumulation due to surface porosities. Incorporation of antimicrobial agents in this material might help tackle this problem. The aim of this study was to evaluate the antimicrobial activity of PMMA acrylic resin incorporated with propolis nanoparticles (PNPs). Materials and Methods: Antimicrobial properties of acrylic resin incorporated with PNPs were assessed against Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), Lactobacillus acidophilus (L. acidophilus) and Candida albicans (C. albicans). Acrylic discs were fabricated in four groups: A control group without PNPs and three experimental groups containing 0.5%, 1% and 2% concentrations of PNPs. Disc agar diffusion (DAD) test was performed to determine the antimicrobial effects of PNPs by measuring the microbial growth inhibition zones on Muller-Hinton agar plates. The eluted components test evaluated the viable counts of microorganisms in liquid medium after 24 and 72h. Finally, biofilm inhibition test assessed the efficacy of PNPs for inhibition of biofilm formation. P<0.05 was considered significant. Results: The acrylic discs failed to produce microbial inhibition zones in the DAD test. Discs containing 1% and 2% nanoparticles showed anti-biofilm effects on all four microbial species. The colony counts of all microorganisms significantly decreased following exposure to liquids containing nanoparticles after 24 and 72h in eluted component test. Conclusion: PMMA acrylic discs incorporated with PNPs presented some antimicrobial properties against S. mutans, S. sanguinis, L. acidophilus, and C. albicans. Objectives: One of the main problems with polymethyl methacrylate (PMMA) used for the fabrication of oral removable appliances is plaque accumulation due to surface porosities. Incorporation of antimicrobial agents in this material might help tackle this problem. The aim of this study was to evaluate the antimicrobial activity of PMMA acrylic resin incorporated with propolis nanoparticles (PNPs). Materials and Methods: Antimicrobial properties of acrylic resin incorporated with PNPs were assessed against Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), Lactobacillus acidophilus (L. acidophilus) and Candida albicans (C. albicans). Acrylic discs were fabricated in four groups: A control group without PNPs and three experimental groups containing 0.5%, 1% and 2% concentrations of PNPs. Disc agar diffusion (DAD) test was performed to determine the antimicrobial effects of PNPs by measuring the microbial growth inhibition zones on Muller-Hinton agar plates. The eluted components test evaluated the viable counts of microorganisms in liquid medium after 24 and 72h. Finally, biofilm inhibition test assessed the efficacy of PNPs for inhibition of biofilm formation. P<0.05 was considered significant. Results: The acrylic discs failed to produce microbial inhibition zones in the DAD test. Discs containing 1% and 2% nanoparticles showed anti-biofilm effects on all four microbial species. The colony counts of all microorganisms significantly decreased following exposure to liquids containing nanoparticles after 24 and 72h in eluted component test. Conclusion: PMMA acrylic discs incorporated with PNPs presented some antimicrobial properties against S. mutans, S. sanguinis, L. acidophilus, and C. albicans.

Evaluation of the Effect of Propolis Nanoparticles on Antimicrobial Properties and Shear Bond Strength of Orthodontic Composite Bonded to Bovine Enamel.

OBJECTIVES: We aimed to investigate the effects of propolis nanoparticles (prpNPs) on antimicrobial property and shear bond strength (SBS) of orthodontic composite bonded to bovine enamel. MATERIALS AND METHODS: Sixty bovine teeth were randomly divided into five groups (n=12). PrpNPs were prepared at concentrations of 0% (control), 1%, 2%, 5%, and 10% in Transbond XT composite to bond stainless steel brackets to the teeth. SBS between brackets and teeth was measured using a universal testing machine. After debonding, the adhesive remnant index (ARI) on bracket bases was measured. In the microbial test, composites with the aforementioned concentrations of prpNPs were cured in metal discs. The bacteria included Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), and Lactobacillus acidophilus (L. acidophilus), and antimicrobial effects of prpNPs were investigated by anti-biofilm, disc agar diffusion and eluted component tests. RESULTS: The 10% prpNPs group showed the lowest SBS. Colony growths of S. mutans and S. sanguinis at all concentrations (except for 1%) was significantly lower than the control group. L. acidophilus colony growth was significantly reduced at 5% and 10% concentrations. Growth inhibition zone developed at 2%, 5%, and 10% concentrations for S. mutans and S. sanguinis. The lowest numbers of S. mutans and S. sanguinis colonies at all concentrations were observed on day 15. L. acidophilus colonies decreased significantly at all concentrations (except for 1%) until day 30. CONCLUSION: Nano propolis has a significant antimicrobial effect at 2% and 5% concentrations, and the SBS is maintained within the acceptable clinical range.

Assessment of hair nickel and chromium levels in patients with a fixed orthodontic appliance: a systematic review and meta-analysis of case-control studies.

INTRODUCTION: The metals nickel (Ni) and chromium (Cr) can cause immunological sensitivity and adverse biological and cytotoxic effects. AIM: To evaluate hair levels of these metals in patients undergoing fixed orthodontic treatment compared with controls. MATERIAL AND METHODS: Five databases - PubMed, Web of Science, Scopus, Cochrane Library, and ScienceDirect - were searched up to January 2018 for evaluation of the hair levels of nickel and/or chromium in patients undergoing fixed orthodontic treatment. To assess the study quality, the Newcastle-Ottawa Scale was used (NOS), and to compare hair Ni and Cr levels in the cases compared with the controls, a random-effects meta-analysis was performed by Review Manager 5.3 using standard mean differences (SMDs) and 95% confidence intervals (CIs). RESULTS: Out of 38 studies in the databases searched, 6 studies were included in the meta-analysis. The pooled SMD of hair Ni levels between the cases and controls was 0.95 µg/g (95% CI: -0.09, 1.99; p = 0.07), which showed that the Ni level was similar in the cases compared with the controls, and that for hair Cr levels was 0.88 µg/g (95% CI: -0.45, 2.21; p = 0.20), so the Cr level was similar in the cases compared with the controls. CONCLUSIONS: The slightly elevated hair levels of Ni and Cr in patients undergoing fixed orthodontic treatment suggest that changing the components of fixed orthodontic appliances can be considered as an acceptable solution in the future.

Evaluation of the relationship between crown size and root canal morphology of mandibular incisors by cone beam computed tomography (CBCT).

BACKGROUND: The main reason for the failure of endodontic therapy is the incomplete knowledge about the anatomical variation of root canals. One of the most important factors that leads to the failure of root canal treatment, is missed and untreated major root canals. OBJECTIVE: with respect to the complexity of mandibular incisors treatment and high prevalence of the second canal, and the possibility of the relationship between the crown size and the extra canal in these teeth, the aim of this study was to determine the relationship between crown size and root canal morphology in mandibular incisors with CBCT. METHODS: In this cross-sectional study, mandibular permanent incisors were randomly collected in Qazvin City, Iran, and were mounted in eight ternary groups on a plastic slot, using putty molding material. After preparation of Scot view, the samples were scanned by CBCT NewTom 5G. Afterward, the mesiodistal and buccolingual dimensions were measured by the software's measurement tool with a precision within tenths of a millimeter. In the next stage, a multi-planar option and 400% magnification tool of the software were utilized to study axial and cross sectional views of each tooth to determine canal type. Data were analyzed employing one-sample Kolmogorov-Smirnov, Levene, independent- samples t-test and Roc curve by SPSS version 20. RESULTS: The majority of mandibular incisors have a single canal (63.9% of them had type I canal system). In addition, 36.1% of the roots had two canals, among which, type III was the most common. The mean of maximum mesiodistal and buccolingual diameters in type III was significantly bigger than that in type I (p<0.05), but the means of crown size in the two canal types were not significantly different. CONCLUSION: Despite increase in mesiodistal and buccolingual dimension in two canal mandibular incisors with type III canal system, their crown sizes (M-D/F-L index) were not significantly different, in comparison to single canal incisors.

Evaluation of the antibacterial activity of a conventional orthodontic composite containing silver/hydroxyapatite nanoparticles.

BACKGROUND: One of the most important complications of fixed orthodontic treatment is the formation of white spots which are initial carious lesions. Addition of antimicrobial agents into orthodontic adhesives might be a wise solution for prevention of white spot formation. The aim of this study was to evaluate the antibacterial properties of a conventional orthodontic adhesive containing three different concentrations of silver/hydroxyapatite nanoparticles. METHODS: One hundred and sixty-two Transbond XT composite discs containing 0, 1, 5, and 10 % silver/hydroxyapatite nanoparticles were prepared and sterilized. Antibacterial properties of these composite groups against Streptococcus mutans, Lactobacillus acidophilus, and Streptococcus sanguinis were investigated using three different antimicrobial tests. Disk agar diffusion test was performed to assess the diffusion of antibacterial agent on brain heart infusion agar plate by measuring bacterial growth inhibition zones. Biofilm inhibition test showed the antibacterial capacity of composite discs against resistant bacterial biofilms. Antimicrobial activity of eluted components from composite discs was investigated by comparing the viable counts of bacteria after 3, 15, and 30 days. RESULTS: Composite discs containing 5 and 10 % silver/hydroxyapatite nanoparticles were capable of producing growth inhibition zones for all bacterial types. Results of biofilm inhibition test showed that all of the study groups reduced viable bacterial count in comparison to the control group. Antimicrobial activity of eluted components from composite discs was immensely diverse based on the bacterial type and the concentration of nanoparticles. CONCLUSIONS: Transbond XT composite discs containing 5 and 10 % silver/hydroxyapatite nanoparticles produce bacterial growth inhibition zones and show antibacterial properties against biofilms.

Effect of Fixed Orthodontic Treatment on Salivary Flow, pH and Microbial Count.

OBJECTIVES: The present study was designed to evaluate the changes in saliva properties and oral microbial flora in patients undergoing fixed orthodontic treatment. MATERIALS AND METHODS: Two important saliva properties namely the salivary flow rate and pH as well as oral microbial flora were assessed in 30 orthodontic patients before starting fixed orthodontic treatment and after six, 12 and 18 weeks of treatment. Selective media, Sabouraud dextrose agar, Mitis salivarius agar and Rogosa agar were used for isolation of Candida albicans, Streptococcus mutans and Lactobacillus acidophilus, respectively. Statistical analysis was performed using Friedman and Dunn's tests. P< 0.05 was considered statistically significant. RESULTS: After six, 12 and 18 weeks of commencing fixed orthodontic treatment, the total colony counts of Candida albicans, Streptococcus mutans and Lactobacillus acidophilus showed a significant increase. The saliva pH decreased during the orthodontic treatment (P< 0.05) while the salivary flow did not change significantly. CONCLUSIONS: Fixed orthodontic treatment causes major changes in the saliva properties. The changes in oral microflora and saliva properties show the importance of caries preventive measures during orthodontic treatment.

The effect of the buccal corridor and tooth display on smile attractiveness.

AIMS: The aim of the present study was to evaluate the lay perception of the effect of the buccal corridor and amount of tooth-gingival display on the attractiveness of a smile in different facial types. MATERIALS AND METHODS: Using Adobe Photoshop CS3 software, frontal facial images of two smiling Iranian female subjects (one short-faced and one long-faced) were altered to create different magnitudes of buccal corridor display (5, 10, 15, 20 and 25%) and tooth-gingival display (2 mm central incisor show, 6 mm central incisor show, total central incisor show, total tooth show with 2 mm gingival show and total tooth show with 4 mm gingival show). Sixty Iranians (30 males and 30 females) rated the attractiveness of the pictures on a 1-5 point scale. RESULTS: Narrower smiles were preferred in long-faced subjects compared with short-faced subjects. Minimal tooth show was more attractive than excessive gingival display in short-faced subjects. There were no gender specific, statistically significant differences found in the ratings given by the lay assessors. CONCLUSIONS: Harmonious geometry of the smile and face in both the vertical and transverse dimensions influences smile attractiveness and this should be considered in orthodontic treatment planning.

Evaluation of shear bond strength of orthodontic brackets bonded with nano-filled composites.

OBJECTIVES: The purpose of this study was to evaluate the shear bond strength (SBS) of orthodontic brackets bonded with two types of nano-composites in comparison to a conventional orthodontic composite. MATERIALS AND METHODS: Sixty extracted human first premolars were randomly divided into 3 groups each containing 20 teeth. In group I, a conventional orthodontic composite (Transbond XT) was used to bond the brackets, while two nano-composites (Filtek TM Supreme XT and AELITE Aesthetic Enamel) were used in groups II and III respectively. The teeth were stored in distilled water at 37°C for 24 hours, thermocycled in distilled water and debonded with a universal testing machine at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI) was also evaluated using a stereomicroscope. RESULTS: AELITE Aesthetic Enamel nano-composite revealed a SBS value of 8.44±2.09 MPa, which was higher than Transbond XT (6.91±2.13) and Filtek TM Supreme XT (6.04±2.01). Statistical analysis revealed a significant difference between groups II and III (P < 0.05). No significant difference was found between groups I and III, and between groups I and II (P > 0.05). Evaluation of ARI showed that Transbond XT left fewer adhesive remains on teeth after debonding. CONCLUSION: Results of this study indicate that the aforementioned nano-composites can be successfully used for bonding orthodontic brackets.

Effect of silver nano particles on flexural strength of acrylic resins.

PURPOSE: Poly(methyl methacrylate), PMMA, is widely used for fabrication of removable orthodontic appliances. Silver nano particles (AgNps) have been added to PMMA because of their antimicrobial properties. The aim of this study is to investigate the effect of AgNps on the flexural strength of PMMA. METHODS: Acrylic liquid containing 0.05% and 0.2% AgNps was prepared for two kinds of acrylic resins: Rapid Repair &Selecta Plus. Two groups without AgNps were used as control groups. For each one, flexural strength was investigated via Three Point Bending method for the 15 acrylic blocks. Two-way ANOVA, one way ANOVA and Tukey tests were used for statistical analysis. RESULTS: Rapid Repair without AgNps showed the highest flexural strength. Addition of 0.05% AgNps to Rapid Repair, significantly decreased its flexural strength while, continuing the addition up to 0.2% increased it nearly up to its primary level. In contrast, addition of AgNps to Selecta Plus increased its flexural strength but addition of 0.05% nano particles was more effective than 0.2%. CONCLUSIONS: The effect of AgNps on flexural strength of PMMA depends on several factors including the type of acrylics and the concentrations of nano particles.

Effect of nicotine on orthodontic tooth movement in rats.

INTRODUCTION: Although the detrimental health effects of cigarettes are well known, many people, including some orthodontic patients, continue to smoke. Nicotine can affect bone resorption and apposition. Therefore, the aim of this study was to investigate the effect of nicotine on orthodontic tooth movement. METHODS: Thirty-two adult male Sprague-Dawley rats were randomly divided into 3 experimental groups and 1 control group. With the rats under general anesthesia, 5-mm nickel-titanium closed-coil springs were placed between the maxillary right first molars and first incisors. Injections of nicotine were administered daily for 13 days: group A, 0.5 mg per kilogram; group B, 0.75 mg per kilogram; and group C, 1 mg per kilogram. Group D, the control group, received injections of 0.1 mL of normal saline solution. At the end of the experimental period, the rats were killed, and interproximal tooth movements were measured. RESULTS: The mean amounts of tooth movement were 0.47 mm in group A, 0.62 mm in group B, 0.78 mm in group C, and 0.21 mm in group D. Statistical analysis with analyis of variance (ANOVA) test showed significant differences between all groups. The most movement occurred in group C, and group D had the least movement. CONCLUSIONS: Nicotine accelerates orthodontic tooth movement, and this effect is dose-dependent. Nicotine's role in accelerating tooth movement might be related to its effect of accelerating bone resorption.