سال:1397 | دوره: | شماره: |تعداد مقالات:6

Poly (methyl methacrylate) (PMMA) is the most common material used to fabricate complete and partial dentures. Despite its desirable properties, it cannot fulfill all mechanical requirements of prosthesis. Flexural fatigue due to repeated masticatory and high-impact forces caused by dropping are the main causes of denture fractures. In the past, different reinforcing agents such as rubbers, macro fibers, and fillers have been employed to improve the mechanical properties of denture base resins. Development of Nano dentistry has introduced new approaches for reinforcement of dental materials. Interest in nanostructure materials is driven by their high surface area to volume ratio, which enhances interfacial interaction and specific new biological, physical, and chemical properties. Researchers to reinforce PMMA resins have used Nanoparticles (Nps) which were comprised of silver, Titania (TiO2), zirconia (ZrO2), alumina, and ceramic. Although different reports describe the use of nanofiber and nanotubes in dental composites, few studies have evaluated the reinforcement potential of nanofiber and nanotubes in PMMA denture base resins. The current article aims to review the different attempts to enhance the mechanical properties of denture base materials. We also focus on recent advances and potential future developments for reinforcement of the PMMA acrylic resins.

Statement of problem: Numerous studies report significant changes in tooth color that occur during orthodontic treatment. The adverse effects of bleaching procedures during orthodontic treatments have not been studied comprehensively.Objectives: This study investigated the effects of two methods of dental bleaching on the degree of microleakage beneath orthodontic brackets.Materials and Methods: We selected 45 extracted premolar teeth and bonded them to orthodontic brackets. These teeth were stored in normal saline for 24 hours and the rmocycled. We randomly divided the samples into 3 groups of 15 teeth per group. The first group (control) received no bleach treatment; the second group (office bleaching) was treated with 35% hydrogen peroxide (Whiteness HP Maxx); and the third group (home bleaching) was treated with 22% carbamide peroxide (Whiteness Perfect). The apices were sealed with sticky wax, rinsed in tap water, and air-dried. We applied nail varnish to the entire surface of each tooth, except for an area approximately 1 mm away from the brackets. The samples were immersed in basic fuchsine and cleaned after 24 hours. Microleakage was determined by direct measurement using a stereomicroscope. Kruskal-Wallis and Dunn post-hoc statistical tests, and SPSS software were used for statistical analysis. The significance level was set at P≤0.05.Results: The office bleaching group had significantly more microleakage scores under the brackets at both the occlusal (P=0.04) and gingival (P=0.040) margins of the brackets compared to the home bleaching group. The home bleaching group showed statistically more significant microleakage scores than the control group in both the gingival (P=0.006) and occlusal (P=0.014) margins of the brackets.All three groups had statistically more significant microleakage at the gingival margins of the brackets than the occlusal margins.Conclusions: Office bleaching caused the most microleakage under the brackets and home bleaching caused more microleakage than the control group. We observed more microleakage at the gingival margins of the brackets compared to the occlusal margins.

Statement of problem: Secondary dental caries is a common clinical finding in composite restoration. The development of a bactericidal dental adhesive provides a promising method to reduce the risk of secondary caries.Objectives: This study aimed to assess the antibacterial activity of silver (Ag) and titanium dioxide (TiO2) nanoparticles incorporated into an experimental dentin bonding agent formulation.Materials and Methods: Ag and TiO2 nanoparticles at 0.05, 0.1, 0.2, 0.5, and 1 wt% concentrations were incorporated into the adhesives. The suspensions were sonicated to ensure homogenous dispersion of nanoparticles in the adhesive system. Formulation was composed of acetone, 2, 2-bis [4- (2-hydroxy-3-methacryloxypropoxy) phenyl] propane (Bis-GMA), 1, 6-bis- [2-methacryloyloxyethyl carbonyl amino] -2, 4, 4-trimethylhexane (UDMA), trimethylolpropane trimethacrylate (TMPTMA), 2-hydroxyethyl methacrylate (HEMA), and photoinitiator, with polyvinylpyrrolidone (PVP) as the stabilizer.We counted the colony-forming units (CFU%) of two cariogenic bacteria, Streptococcus mutans (S. mutans)and Lactobacillus acidophilus (L. acidophilus), that were exposed to the powdered light cured adhesive specimens. The effects of various concentrations of each nanoparticle were compared by one-way ANOVA, followed by the post hoc Bonferroni test.Results: All samples exhibited definite antibacterial activity (P<0.05) compared to the control specimens. The Ag nanoparticle samples showed higher antibacterial properties compared to the TiO2 nanoparticle samples. Increasing the concentration of nanoparticles resulted in significant differences in bactericidal properties, with the exception of 0.2 to 0.5 wt% Ag nanoparticle specimens exposed toS. mutans and the 0.2 to 0.5 wt% TiO2 nanoparticle specimens exposed to L. acidophilus.Conclusions: These metal-based nanoparticles exhibited dose-dependent bactericidal activities. The Ag nanoparticles had higher antibacterial activity compared to the TiO2 nanoparticles. Incorporation of these nanoparticles into dental adhesives is a promising way to reduce the risk of secondary caries. However, further clinical evaluations should be performed.

Statement of problem: prophylactic removal of the impacted lower third molar (ILTM) is controversial and accompanying pathologic conditions play an important role.Objectives: The aim of the present study is to evaluate the prevalence of commonly found pathoses associated with ILTM in relation to angulation and impaction depth in cone beam computed tomography (CBCT).Materials and Methods: We evaluated CBCT of 500 ILTMs from 235 females (57%) and 177 males (43%) for the presence of caries on the second and third molars, external root resorption (ERR) of the second molar, and follicular spaces (FS)>5 mm in diameter in relation to angulation and impaction depth according to Pell and Gregory and Winter’s classifications, respectively.Results: We observed that 55.6% of ILTM had at least one detectible lesion.ERR was the most frequent pathologic condition (31.2%), followed by caries on the second (26%) and third (13.4%) molars, and FS>5 mm (2.4%). ERR was the only pathology influenced by angulation. There was significantly more ERR in mesioangular ILTMs (40.5%, P<0.001). Most ERR occurred in direct contact with the third molar. Class C showed a lower risk for second and third molar caries (P<0.001), but higher risk for ERR (P=0.008) and FS> 5 mm (P=0.035). There were more caries on the second molar (P=0.013) and FS>5 mm (P<0.001) in class III.Conclusions: Prophylactic removal of ILTMs (especially in mesioangular or horizontal impactions) could be suggested considering the potential for pathologic changes in ILTMs and the propensity for these teeth to cause ERR in second molars.

Statement of problem: Dental caries is a common infectious disease induced by Streptococcus mutans (S. mutans).Objectives: Due to the high incidence rate of dental caries and iron deficiency in the Iranian population, we have conducted this study to analyze the effects of iron acetate and iron sulfate on controlling the growth of S. mutans.Materials and Methods: In this in vitro study, we evaluated the antibacterial effects of iron sulfate and iron acetate on S. mutans by the disk diffusion method, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). The results were compared to those for 0.2% chlorhexidine and penicillin as the controls.Results: Iron sulfate had higher MIC and MBC values compared to penicillin and chlorhexidine (P<0.001). Iron acetate MIC and MBC values did not significantly differ with penicillin and chlorhexidine. The iron sulfate inhibition zones at the 25 and 50 mg/mL doses were more than those of iron acetate.Conclusions: Iron sulfate and iron acetate solutions can inhibit the growth of S. mutans. Hence, different compounds that contain iron salts such as toothpastes, mouth washes, and food supplements can be produced to prevent dental caries and iron deficiency.

Statement of problem: The bonding of fiber post to resin core or root dentin is challenged by limited penetration of resin material to the polymeric matrix of fiber posts.Objectives: The purpose of this study was to investigate the effect of Er, Cr: YSGG on micro push-out bond strength of glass fiber posts to resin core material.Materials and Methods: We used 2 commercially available fiber posts, Exacto (Angelus) and White Post DC (FGM), which had similar coronal diameters. Specimens of each fiber post (n=36) were randomly divided into three subgroups (n=12 posts per group) according to different surface treatment methods: control (no surface treatment), irradiation by 1W Er, Cr: YSGG, and irradiation by 1.5W Er, Cr: YSGG. A cylindrical plastic tube was placed around the post. Resin core material was filled into the tube and cured. Coronal portions of the posts were sectioned into 1-mm-thick slices. Then, the specimens were subjected to a thermocyling device for 3000 cycles. The micro push-out test was carried out using a Universal Testing Machine. Data were analyzed using one-way ANOVA followed by Tukey’s HSD post hoc test to investigate the effect of different surface treatments on each type of fiber post.Results: The 1.5W Er, Cr: YSGG laser statistically reduced micro push-out bond strength values in the Exacto groups (P<0.05). However, there was no significant difference between the control and 1W Er, Cr: YSGG groups. We observed no significant difference among different surface treatment methods in the White post DC groups (P>0.05). Mode of failure analysis showed that mixed failure was the predominant failure type for all surface treatment groups.Conclusions: The beneficial effect of Er, Cr: YSGG laser application could not be confirmed based on the results of this in vitro study. Er, Cr: YSGG laser could not significantly enhance the bond strength values. However, the 1.5W laser statistically decreased micro push-out bond strength in the Exacto fiber posts.