Evaluation of the antimicrobial effect of conventional and nanosilver-containing varnishes on oral streptococci

Statement of the Problem: Nanosilver particles have the potential to serve as a bactericidal agent because of the inherent antimicrobial influences of silver ion. The literature confirmed that specific micro-organisms, especially streptococci, have an important role as an etiological factor for caries

Purpose: The aim of this study was to evaluate the antimicrobial effect of conventional and nanosilver-containing varnishes on oral streptococci

Materials and Method: Pure cultivations of Streptococcus mutans and Streptococcus salivarius were prepared on blood agar media. Thereafter, 0.5 McFarland standard of recently grown bacteria in normal saline was prepared and the bacteria were cultivated monotonously on the culture medium surface by applying a swab. Different concentrations of nanosilver varnishes were prepared in the Mueller- Hinton broth medium in the test tubes and equal amounts of 0.5 McFarland suspension of all the tested bacteria were added separately to all test tubes. A tube without varnish was included as the control sample. The tubes were kept at 37°C for 24 hours, then cultured to determine the numbers of bacteria in each tube by counting colonies. The numbers of bacteria in tubes with varnish were compared to the numbers of bacteria in the tube without varnish. In the instance of observing any reduction in the growth, the minimum inhibitory concentration for growth in the tube with varnish was determined

Results: Nanosilver varnish had an antimicrobial effect on S. mutans and S. salivarius. S. salivarius was more susceptible than S. mutans to the nanosilver varnish

Conclusion: Based on the results of this study, nanosilver varnishes can be used under amalgam restorations to reduce microbial population and subsequently preventing the recurrent caries

[Comparison of the effects of microfilled and hybrid composite resin restorations on the fracture resistance of extensively weakened teeth]

Composite resins can play an important role in dentin support and enamel strength via bonding to tooth structure. The purpose of this study was to compare the effects of hybrid and microfilled composite restorations on the fracture resistance of extensively weakened teeth. In this case control study 40 intact maxillary premolars were mounted in transparent acrylic resin blocks. The samples were divided into 4 groups [n=10 each]. Group PC comprised of intact teeth, without preparation and restoration. In other three groups MOD preparations with constant depths and converged walls toward occlusal surfaces were prepared. Group NC composed of teeth with preparations but without any restoration. Group HR included prepared and restored teeth using a hybrid composite and Group MR contained prepared and restored samples with a microfilled composite. Samples were thermocycled [500 cycles in 5-55°C], then were placed under compressive loads in a universal testing machine, and the curves were drawn with a software called Test Xpert. Mean fracture resistance in HR, MR, PC, and NC groups were 48.1010, 59.1773, 83.1420, and 21.9220, respectively. There was a statistically significant difference among the groups [P<0.05]. The increasing effect of microfilled group on the fracture resistance of restored teeth is significantly more than that of hybrid group

Retention of creative pin placement vs. traditional method in human mandibular molar teeth [in vitro]

Extensive caries restoration has always been considered as one of dental issues. To resolve this problem different methods have been suggested such as dentinal pins.Previous clinical studies revealed that the use of retentive pins, faces numerous risks [pulp exposure, dentin cracks, root perforations, etc]. Introducing of bonding and composite systems, resulted in minimized mechanical retention for cavity preparation. Advantages of amalgam restorations such as simplicity of use, better mechanical properties, suitable clinical longevity and being less costly sustained its use in practice. On the other hand, caries removal usually results in a cavity form with small undercuts. So if we fill these small undercuts with [Bonding and Composite], then insertion of pins in this base, could be considered as a safe way for obtaining retention. The purpose of this study was comparing the retention of creative pin placement [using composite] to the retention of traditional method. In this experimental study thirty sound human mandibular molar teeth free from decay and restoration were selected. The occlusal surface of samples was removed up to 3mm above CEJ. Teeth were divided in 2 groups: Group A: [N=15] T.M.S Minim pin inserted in dentin at 2mm depth. Group B: [N=15] One layer of composite [1mm] bond to flat occlusal surface of teeth and then the pin was inserted in it at 2mm depth so only 1mm of pin placed into dentin. Group C: [N=15] cylinders of composite were prepared [height=5mm, dimension= 8mm] and pin was inserted in them at 2mm depth. The retention of pins was determined under tensile force with Zwick universal testing machine and data was charted by Test Xpert. 10-11 program. Data were analyzed by variance analysis [ANOVA] and L.S.D test. The ANOVA showed: a statistically significant difference between all groups. [p< 0.05] The L.S.D test showed: - No significant difference between A and B. [p> 0.05] - Significant difference between A, B and C. [p< 0.05]. The highest tensile strength belonged to group A. there was no significant difference between group A and B. So by using this technique 1mm depth of pin in dentin can result as same retention as 2mm depth. The lowest tensile strength belonged to group C

Comparison of direct and indirect composite resin restorations effect on the fracture resistance of maxilly premolars [an in vitro study]

One of the problems involved in the restoration of extensive cavities is loss of the fracture resistance of the remaining tooth structure to withstand masticatory forces. But possible reinforcement of remaining tooth structure has been increased by the use of adhesive restorative materials. Tooth reinforcement may be affected by the different physical properties of direct and indirect composite resin restorations. So, theaim of this study was tocompare direct and indirect composite resin restorations effect on the fracture resistance of maxillary premolars with mesio-occluso distal [MOD] cavities. In this experimental [in vitro] study, 24 human maxillary premolars free of any caries, restoration or crack, which had been extracted in a 6 month period, were selected and MOD cavities with the bucco- lingual extension equal to two third of intercuspal distance were prepared on them all. The teeth were divided randomly in 3 groups including A [8 teeth and direct restoration group], B [8 teeth and indirect restoration group] and C [8 teeth and preparation without restoration group] and were undergone fracture test with universal testing machine. Variance and Tukey tests were used for analysis of results; the level of significance was set at 0.05. The mean fracture resistance was!314.75 +/- 332.26, 1192.25 +/- 352.45 and 382.45 +/- 142.51 for direct restoration, indirect restoration and preparation withoutrestoration groups,respectively. There was no significant difference between A and B groups [P=0.60], whereas the differences were significant between A and C groups [P=0.00] and also B and C groups [P=0.00]. According to the present study, both direct and indirect composite restorations cause increase in the fracture resistance of teeth and so can have an important role in extensive cavities

[ in-vitro comparison between antimicrobial activity of nanosilver and chlorhexidine against streptococus sanguis and actinomyces viscosus]

The antimicrobial activity of silver nanoparticles has been investigated in medical fields in recent years, but its effect on dental plaque micro-organisms has not been studied. The aim of the present study was to evaluate the in vitro antimicrobial properties of nanosilver on two dental plaque microorganisms and to compare it with chlorhexidine. In this experimental study, antibacterial effects of silver nanoparticles and chlorhexidine against Streptococus sanguis and Actinomyces viscosus were determined by minimum inhibitory concentration [MIC] and minimum bactericidal concentration [MBC] using microdilution method. Each experiment was repeated at least five times to ensure the accuracy of testing. Results showed that the MIC of soluble silver nanoparticles and chlorhexidine for Streptococcus sanguis were 16 and 256 microg/ml, respectively. Soluble silver nanoparticles had an MIC of 4 and chlorhexidine had an MIC of 64 micro g/ml for Actinomyces viscosus. The MBC of soluble silver nanoparticles and chlorhexidine for Streptococcus sanguis were 64 and 512 microg/ml, respectively and for Actinomyces viscosus these figures were 16 and 102 microg/ml, respectively. Silver nanoparticles have strong antibacterial activity against Streptococus sanguis and Actinomyces viscosus which was achieved by lower doses in comparison to chlorhexidine mouthwash

[Evaluation of the effect of nanohydroxyapatite on erosive lesions of the enamel of permanent teeth after exposing to soft beer [In vitro]]

Consumption of acidic carbonated beverages is the most important etiologic factor for dental erosion. Studies show that nano hydroxyl apatite can remineralize initial caries lesions. The aim of this study was to determine the effect of that nano hydroxy apatite on the micro hardness of enamel of permanent third molar after exposing to soft beer. This in vitro study was done on 18 permanent third molars without caries and crack. After measurement of the micro hardness of the teeth, these teeth were placed in the 40 cc of Delester and secondary micro hardness of them were measured. Then the teeth were divided in to two groups randomly and were exposed to nano hydroy apatite in treatment group and tap water in control group and finally micro hardness of the teeth was determined. Changes in micro hardness was analyzed with paired t test in each group and ANOVA between groups. The results showed that micro hardness of 18 samples after exposing to lemon Delester -Behnoosh- reduced to 92.5% of primary micro hardness and paired t test showed that this is significant statistically [P=0.009]. Micro hardness of 9 samples in water group after exposing to water was 99.3% of secondary micro hardness and paired t test showed there is not significant statistically [P=20.6]. Micro hardness of 9 samples in nano hydroxy apatite after exposing to nano hydroxy apatite was 98.2% of secondary micro hardness and paired t test showed there is significant statistically [P=0.012]. Based on the results of this study nano hydroxyl apatite can remineralize erosive lesion on the enamel of permanent teeth resulting from exposing to lemon Delester

effect of antioxidant agents on shear bond strength of composite and bleached enamel

Several studies have shown a reduction in enamel bond strength when the bonding procedure is carried out immediately after vital bleaching with peroxides. The purpose of this study was to compare the effects of antioxidant agents [sodium ascorbate, sodium sulfite] and delayed bonding on shear bond strength of composite resin to enamel after bleaching with two different concentrations of carbamide peroxide. In this in-vitro study, 100 human premolars were collected and randomly divided into 10 groups. The investigation was conducted in two parts according to bleaching agent and elapsed time after bonding. In part I, bleaching wras with 35% carbamide peroxide [Opalescense Quick] for 30 minutes was performed. In part II, bleaching was performed with 15% carbamide peroxide [Opalescense Regular] for 6 days and 6 hours for each case. The teeth in both parts were divided in 5 groups: 1: No Bleaching-Bonding [control] 2: Bleaching-Bonding 3: Bleaching-Sodium ascorbate-Bonding 4: Bleaching-Sodium sulfite-Bonding 5: Bleaching-Saliva immersed [for 3 weeks]-Bonding After bonding and thermocycling [1000 cycles between 5-55°C] and 7 days of storage, shear bond strength was measured in all specimens. Groups differences were analyzed by using Kolmogrove Smirnov, one way NOVA and Sheffe tests. Statistical analysis indicated that treatment with antioxidant agents after bleaching with carbamide peroxide can cause such a compromised bonding comparable to the control group [p>0.05]. Antioxidant treatment can severely decrease the bonding strength