Nanofillers can reduce enamel demineralization without compromising physical properties of the composite. The aim of this study was to evaluate shear bond strength (SBS) and antibacterial effects of an orthodontic composite after adding titanium oxide (TiO2) nanoparticles. Light cure orthodontic composite paste (Transbond XT) was blended with TiO2 nanoparticles. A total of 30 extracted premolars were randomly allocated into two groups of 15. In order to bond brackets, Transbond XT adhesive and nanocomposite were used in each group, respectively. SBS of two groups were determined, and the adhesive remnant index (ARI) scores were assessed. A total of 45 composite discs specimen were prepared. Of the 45 discs, 30 discs were made from nanocomposite and tested for antibacterial properties immediately and 30 days after curing by direct contact test. The antibacterial properties of the remaining 15 discs that were made from the conventional composite were tested immediately after curing as control group. Student's t-test and chi-square tests were used to analyse the data with the significance level of 0.05. No significant difference was found between SBS of conventional and nanocomposites, 24 hours after curing (P = 0.58). Chi-square test showed that ARI scores of two groups were not significantly different after debonding (P = 0.69). Comparison of antibacterial effects between conventional and nanocomposite demonstrated significant difference between two groups, with nanocomposites having a higher antibacterial activity (P = 0.03). Colony count revealed no significant difference in bacterial growth immediately and 30 days after curing in nanocomposite group. Adding TiO2 nanoparticles to orthodontic composite enhances its antibacterial effects without compromising the SBS.

In this study, shear bond strength (SBS) of metal orthodontic brackets to porcelain following conditioning by Er:YAG (erbium-doped yttrium aluminum garnet) and Nd:YAG (neodymium-doped yttrium aluminum garnet) laser in comparison to conventional methods was evaluated. One hundred glazed porcelain discs with an upper central shape were prepared and randomly assigned to five equal groups of 20. In the first group, samples were only deglazed and roughened by diamond burs. In the second group, after roughening and deglazing of porcelain samples, the samples were etched by 9.6% hydrofluoric acid for 4 min. Groups, 3, 4, and 5 were prepared by 0.8-W Nd:YAG laser, 2-W Er:YAG laser, 3-W Er:YAG laser for 10 s, respectively. Then, metal, mesh-based brackets were bonded to porcelain samples, and after being stored in distilled water for 24 h, debonding was carried out by a Zwick testing machine. ANOVA and Tukey tests were used to compare SBS in five groups. Mean SBS in groups 1 to 5 were 3.3 ± 1.6, 7.0 ± 2.1, 6.9 ± 2.7, 2.3 ± 1.1, and 3.7 ± 2.3 MPa, respectively. ANOVA test revealed a significant difference between five groups (p < 0.05). Although Tukey's test showed SBS in groups 2 and 3 were significantly higher than the other groups, they did not differ with each other significantly (p > 0.05). The results revealed that SBS of 9.6% hydroflouric acid and Nd:YAG Laser was in an acceptable range for orthodontic treatment. Nd:YAG laser was shown to be an acceptable substitute for hydrofluoric acid while Er:YAG laser with the mentioned power and duration was not a suitable option.

There is little information concerning the cytotoxic effects of no-mix and flowable adhesives used in orthodontics. The aim of the present study was to evaluate the cytotoxic effects of a no-mix (Unite), a light-cured (Tranbond XT), and a flowable (Denfil Flow) adhesives on human oral fibroblasts. Twelve discs of each adhesive were prepared and aged for 1, 3, 5, and 7 days in Dulbecco's Modified Eagle's Medium (DMEM). Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the difference between the groups was tested by analysis of variance and Tukey tests (α = 0.05). After 1 day of storage, the no-mix adhesive showed moderate cytotoxic effects (P < 0.05), while the light-cured and flowable adhesives were essentially non-cytotoxic. Ageing considerably reduced the cytotoxicity of the no-mix adhesive. On days 5 and 7 of the experiment, the cell viability of three adhesives did not differ significantly (P > 0.05), but cell viability was slightly reduced on day 7. Moderate cytotoxic effects of no-mix adhesive on the first day of the experiment suggest that care should be taken to protect dentists and patients when these adhesives are being handled. Despite higher resin components, the flowable adhesive showed excellent biocompatibility.

This study investigated the combined effect of fractional CO(2) laser irradiation and fluoride on treatment of enamel caries. Sixty intact premolars were randomly assigned into four groups and then stored in a demineralizing solution to induce white spot lesions. Tooth color was determined at baseline (T1) and after demineralization (T2). Afterwards, the teeth in group 1 remained untreated (control), while group 2 was exposed to an acidulated phosphate fluoride (APF) gel for 4 min. In groups 3 and 4, a fractional CO(2) laser was applied (10 mJ, 200 Hz, 10 s) either before (group 3) or through (group 4) the APF gel. The teeth were then immersed in artificial saliva for 90 days while subjected to daily fluoride mouthrinse and weekly brushing. Color examinations were repeated after topical fluoride application (T3) and 90 days later (T4). Finally, the teeth were sectioned, and microhardness was measured at the enamel surface and at 30 and 60 μ from the surface. In both lased groups, the color change between T1 and T4 stages (∆E(T1-T4)) was significantly lower than those of the other groups (p < 0.05). Laser irradiation followed by fluoride application (group 3) caused a significant increase in surface microhardness compared to APF alone and control groups (p < 0.05). Microhardness at depths of 30 and 60 μ was also significantly greater in group 3 compared to those of all other groups (p < 0.05). Application of a fractional CO(2) laser before fluoride therapy is suggested for recovering the color and rehardening of demineralized enamel.

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