effect of microwave disinfection on dimensional stability and flexural strength of acrylic resins

Several studies have evaluated the effect of microwave radiation on physical properties of acrylic resins. However, due to the recent introduction of heat-cure and cold-cure acrylic resins into the dental market and rapid popularity of cold-cure resins with less distortion in denture base, the present study sought to assess the effect of microwave disinfection on dimensional stability and flexural strength of two recently introduced heat-cure [Ivoclar] and cold-cure [FuturaGen] acrylic resins. In this laboratory study, acrylic models were fabricated of an edentulous maxillary model using Ivoclar and FuturaGen acrylic resins. Three reference points were marked on the model: two in the back and one in the front of the edentulous arch. These reference points were used for the measurement of dimensional stability in the anteroposterior and cross-arch dimensions. Ten specimens of each acrylic resin were not disinfected. Ten samples were subjected to two 3 min cycles of microwave disinfection with 600 watt power. Distances between the reference points were measured by a Profile Projector. To evaluate flexural strength, a metal mould measuring 64x10x3.3 mm was used for the fabrication of resin specimens. Similar to what was done for dimensional stability testing, 10 specimens of each acrylic resin were not disinfected and 10 other samples were subjected to 3-point bending test after disinfection. Data were compared and statistically analyzed using Mann-Whitney U test. The mean difference in anteroposterior and cross-arch dimensions revealed that two cycles of microwave disinfection of Ivoclar and FuturaGen acrylic resins did not have a significant effect on their dimensional stability [P>0.017]. The mean and standard deviation of the flexural strength of FuturaGen acrylic resin before and after disinfection was 76.86 +/- 16.80 and 70.18 +/- 8.48, respectively. These values for Ivoclar acrylic resin were 85.92 +/- 12.23 and 81.91 +/- 6.59, respectively. Two cycles of disinfection with microwave did not cause a significant effect on flexural strength of the two understudy acrylic resins [P>0.05]. Two cycles of microwave disinfection had no negative effect on dimensional stability or flexural strength of FuturaGen and Ivoclar acrylic resins

effect of 15% carbamide peroxide bleaching on the shear bond strength of composite to enamel

Carbamide peroxide bleaching has been implicated to adversely affect the bond strength of composite to enamel. The purpose of this study was to evaluate the effect of carbamide peroxide bleaching on the shear bond strength of composite to bleached enamel bonded with a three step total etch system; Scotchbond Multipurpose [SBMP], and two simplified all-in-one systems; Prompt L-Pop [PLP] and i bond. Seventy two human molar teeth were randomly assigned to three control and three experimental groups. The experimental groups were subjected to a%15 carbamide peroxide bleaching system. Twenty four hours later, all the control and experimental groups were bonded with cylinders of composite, using three dental bonding agents. After thermocycling, shear bond strengths were determined by a universal testing machine. The data were evaluated using one way ANOVA and Duncan tests [P < 0.05]. The composite bond strengths of SBMP were 19.52 +/- 15.21 MPa to the unbleached and 7.95 +/- 4.16 MPa to the bleached enamel. For PLP, the unbleached enamel exhibited bond strengths of 9.6612.89 MPa and, the bleached one showed a bond strength value of 5.3910.66 MPa. For i-bond the composite bond strengths were 11.46 +/- 4.31 MPa to the unbleached and 6.41 +/- 2.01 MPa to the bleached enamel. There was a statistically significant difference between the shear bond strength of the control and experimental groups of each dental bonding agent [SBMP, P < 0.001, PLP, P < 0.001, i bond: P = 0.002]. Bleaching with 15% carbamide peroxide used in this study reduced the bond strengths of the composite to the enamel bonded with a three step total etch and two simplified one step all-in-one dental bonding agents

Bioactive glass nanopowder for the treatment of oral bone defects

Osseous defects around dental implants are often seen when implants are placed in areas with inadequate alveolar bone, or around failing implants. Bone regeneration in these areas using bone grafts or its substitutes may improve dental implants prognosis. The aim of this study was to prepare and characterize the bioactive glass nanopowder and development of its coating for treatment of oral bone defects. Bioactive bioglass coating was made on stainless steel plates by sol-gel technique. The powder shape and size was evaluated by transmission electron micropscopy, and thermal properties studied using differential thermal analysis [DTA]. Structural characterization techniques [XRD] were used to analyze and study the structure and phase present in the prepared bioactive glass nanopowder. This nanopowder was immersed in the simulated body fluid [SBF] solution. Fourier transform infrared spectroscopy [FTIR] was utilized to recognize and confirm the formation of apatite layer on prepared bioactive glass nanopowder. The bioglass powder size was less than 100 nanometers which was necessary for better bioactivity, and preparing a homogeneous coating. The formation of apatite layer confirmed the bioactivity of the bioglass nanopowder. Crack-free and homogeneous bioglass coatings were achieved with no observable defects. It was concluded that the prepared bioactive glass nanopowder could be more effective as a bone replacement material than conventional bioactive glass to promote bone formation in osseous defects. The prepared bioactive glass nanopowder could be more useful for treatment of oral bone defects compare to conventional hydroxyapatite or bioactive glass

[ effect of polishing time on the shear bonding strength of resin composite and composer to dentin]

Suitable bond strength between tooth and restorative material is one of the most important factors in durability of restoration. The polishing of a restoration should be performed when the bond strength will not be influenced by the stress that is produced by the mechanical procedure of polishing. The aim of this study was to evaluate the effect of polishing time on the shear bond strength of resin composite and compomer to dentine of tooth. The aim of this study was to evaluate the effect of polishing time on the shear bond strength of resin composite and compomer to dentin of tooth. Truncated cone cavities were prepared in the horizontal coronal occlusal dentinal sections of 48 human molar teeth. Specimens were randomly divided in 4 experimental groups. The specimen cavities of group 1 and 2 were filled with resin composite and the specimen cavities of group 3 and 4 were filled with compomer. The specimens of group 1 and 3 were polished immediately after filling the cavities by restorative material and the specimens of group 2 and 4 were polished after 24 hours storage of samples in normal saline at 37 C. All of the specimens were stored in normal saline at 37 C for one week. The push out test was used to evaluate the shear bond strength of resin composite and compomer to dentin and the mean values of shear bond strength of the four groups were determined. The results were analyzed with ANOVA and Duncan tests. The results showed statistically significant differences between the mean shear bond strength values of group 1 and 3, group 2and 3, and groups 3and 4. Group 4 possessed the highest shear bond strength while group 3 possessed the lowest shear bond strength. It was concluded that hygroscopic expansion of compomer and improvement of bond strength of the compomer during the storage time due to delayed polishing increases the shear bond strength between compomer and dentin. On the other hand, since the type of setting reaction of the resin composite is polymerization, the time of polishing had no significant influence on the shear bond strength between resin composite and dentine

Effect of different blood contaminated adherent surface treatments on shear bond strength of compomer and composite resin to dentin, using a self etching adhesive

Blood contamination is a common problem in dentistry that can decrease bond strength dramatically which may be affected by methods of decontamination as well. The aim of this study was to evaluate and compare the influence of blood contamination on shear bond strength of composite and compomer to dentin using Prompt L-Pop as an adhesive system. Also, to assess the effectiveness of different surface treatments on the bond strength. In this experimental study, 120 molar teeth were sectioned to provide flat occlusal dentinal surfaces. Specimens were embedded in acrylic resin with the flat surface exposed. The dentinal expose surfaces were polished to 600 grit. The teeth were randomly divided into five groups of twelve specimens [F1-F5] for compomer material and five other groups [Z1- Z5] for composite resin. After application of Promt L-Pop to dentinal surfaces of specimens, the surfaces in all groups, except for F1 and Z1, [as controls] were contaminated with human blood and then one of the following surface treatments was applied. Groups F2 and Z2 without any treatment, groups F3 and Z3 rinsing with water, groups F4 and Z4 rinsing with water and reapplication of adhesive, groups F5 and Z5 rinsing with NaOCl and using Prompt L-Pop again. Restorative materials were applied to treated surfaces using plastic molds. After thermocycling, shear bond strengths, mode of failures and morphology of dentin-material interfaces were evaluated. The data were statistically analyzed using Factorial analysis of Variance, One-Way ANOVA, Duncan, T-student and Chi-Square tests with P<0.05 as the limit of significance. Compomer showed statistically significant higher bond strength in comparison to composite [P<0.001]. Duncan test showed significant differences between all compomer groups, except between groups F4 and F5, and between all composite groups except for groups Z1 and Z4 and for groups Z2 and Z3. Based on the findings of this study, shear bond strength of compomer material was significantly higher than composite. Blood contamination reduced bond strength, but rinsing contaminated dentin with water or NaOCl and reusing Prompt L-Pop increased bond strength in both materials

Comparative evaluation of the initial corrosion of four brands of high copper dental amalgams

Statement of Problem: Many attempts have been made in order to evaluate the amalgam corrosion behavior as an indicator of biocompatibility

Purpose: The aim of this study was to evaluate and compare the initial corrosion of four different brands of dental amalgams

Materials and Methods: Four different types of commercial high copper dental amalgam were studied. A special mold was used and twenty-one samples of each type of commercial dental amalgams were prepared. X-ray diffraction technique was used to investigate the microstructure of freshly prepared specimens. Electrochemical potentiodynamic tests were performed in physiological solutions in order to determine and compare the corrosion behavior of freshly prepared sample of four brands of dental amalgams. The physiological solutions were the Ringer's solution and physiological normal saline. Five replicate tests on each group of specimens were performed. Tafel extrapolation and linear polarization methods determined corrosion potentials and corrosion current densities. The mean value and standard deviations of the results were calculated. The mean values were statistically compared by ANOVA and Duncan methods at 95% level of confidence

Results: Gamma-2 phase was present in freshly prepared sample of each type of commercial amalgam. The results showed statistically significant differences between the mean corrosion current density values of freshly prepared sample of four brands of amalgams [P<0.05]. The freshly prepared specimen of Sybraloy dental amalgam possesses the higher initial corrosion resistance than the other three, and Cinaalloy dental amalgam possesses the lowest corrosion resistance. This trend is independent to the type of physiological environment

Conclusion: Initial corrosion resistance of each type of commercial dental amalgam is much less than its corrosion resistance that could be obtained after one week. From the viewpoint of the corrosion behavior as an indication of biocompatibilty and for prediction of biocompatibily of the amalgam restoration, it is necessary to pay attention to the initial corrosion of dental amalgam

review on dental amalgam corrosion and its consequences

Dental amalgam is still the most useful restorative material for posterior teeth and has been successfully used for over a century. Dental amalgam has been widely used as a direct filling material due to its favorable mechanical properties as well as low cost and easy placement. However, the mercury it contains raises concerns about its biological toxicity and environmental hazard. Although in use for more than 150 years, dental amalgam has always been suspected more or less vigorously due to its alleged health hazard. Amalgam restorations often tarnish and corrode in oral environment. Corrosion of dental amalgam can cause galvanic action. Ion release as a result of corrosion is most important. Humans are exposed to mercury and other main dental metals via vapor or corrosion products in swallowed saliva and also direct absorption into blood from oral mucosa. During recent decades the use of dental amalgam has been discussed with respect to potential toxic effects of mercury components. In this article, the mechanisms of dental amalgam corrosion are described and results of researches are reviewed. It finally covers the corrosion of amalgams since this is the means by which metals, including mercury, can be released within oral cavity

Effect of the type of restorative material on bonding efficacy and microleakage of a self-etching adhesive system

Background: prompt L-Pop is a self-etching dentin adhesive, which is recommended to use with both compomers and composite resins. The aims of this investigation were to determine and compare the microleakage, shear bond strength, and shear push out strength of composite and compomer to dentin with application of Prompt L-Pop as adhesive system

Methods: after application of Prompt L-Pop on the occlusal dentinal surfaces of 24 intact molar teeth, the specimens were divided into two groups [n=12]. Composite resin[Filtec Z250] and compomer [F2000] were used to dentinal surfaces of group 1 and 2 respectively, using a plastic mold. Twenty-four truncated cavities were prepared in 24 horizontal occlusal coronal dentinal wafer. After application of Prompt L-Pop, the specimens divided into two groups [n=12], and the cavities in group 1 and 2 were filled with composite and compomer respectively. After application of Prompt-L-Pop on the surfaces of 20 class V cavities, the cavities were randomly divided into two groups [n=10], and were restored with composite resin and compomer respectively. The bond strength values and microleakage scores of groups were evaluated

Results: compomer material revealed more but not statistically significant different means [SD] of shear bond strengths [Mpa] and shear push out strength [MPa]. There were no significant differences in enamel and also dentinal microleakage scores, between two groups [p>0.05]

Conclusion: improving bonding efficacy and microleakage result of compomer in this study, would be because Prompt LPop is a water based material and therefore chemically more compatible with hydrophilic restorative materials, such as compomers

[ effect of an adhesive system, surface roughness and irregularities on shear bond strength of repaired amalgam]

When an amalgam restoration fails, the repair of existing amalgam restoration with fresh amalgam can be a practical alternative to the replacement of entire restoration. In most studies the bond strength of fresh amalgam to old amalgam is reported lower than the old amalgam itself. Therefore, the purpose of this study was to compare the effect of using adhesive system with surface irregularities and roughness on shear bond strength between fresh and set [old] amalgam. Fifty acrylic cylinders were made and a cavity preparation [6mm diameter by 2 mm high] was made in each cylinder. Forty cavities were filled with amalgam, level with cylinders surface and ten cylinders [control group =Group 1] were filled 5mm higher than the surface of cylinder using split die. After aging of all samples in water at 37°C for 14 days, the first 40 samples were divided into 4 groups and were repaired with fresh amalgam in the following manner. Group 2: with surface irregularities and roughness, group 3: using Panavia F, without surface irregularities and roughness, Group 4: using cement and surface irregularities and roughness, group 5: without cement and without surface irregularities and roughness. After storage in water at 37°C for 7 days, the shear bond strengths of groups were tested. Mean shear bond strengths and standard deviations [MPa] for groups were: in Group 1 [control]: 36 +/- 4.8, Group 2: 31.26 +/- 2.70, Group 3: 8.07 +/- 1.34, Group 4: 13.05 +/- 1.83 and in Group 5 no bond was seen. ANOVA revealed statistically significant difference among groups Duncan test indicated that there was a significant difference between each group with the other one. Results of this study didn't reveal any advantages for using Panavia F to increase the bond strength. According to the results obtained from making surface roughness and irregularities compared to the control group, this procedure can be suggested for repairing broken amalgam as an acceptable procedure

[Knowledge and attitude of hygeine instructors in the schools of Isfahan about oral hygiene]

Since hygiene instructors can play important role in promoting and following oral hygiene instructions in schools, it was decided to investigate hygiene instructors knowledge and their attitudes about oral hygiene. This was qualitative-descriptive cross sectional study. Information was gathered by questionnaire containing 25 questions about knowledge and 8 questions about attitude. 188 hygiene instructors were selected randomly among 278 hygiene instructors present in primary schools in Isfahan. After questionnaires were approved by specialists, they were completed by hygiene instructors. The data were analyzed by SPSS software program and statistical analysis was carried out with analysis of Variance, T-test, ANOVA and Spearman correlation. The average of perssonals knowledge was 18.53 +/- 2.78 and domain was 11 to 24 [Total mark: 25]. The average of their attitude was 25.7 +/- 2.7 [Total mark: 32]. The T-test didn't show any relationship between attitude, knowledge and educational degree [i. e. Diploma VS bachelor degree]. There was no relationship between work experience and educational degree work experience and attitude, knowledge and attitude. The average of perssonals' knowledge showed statisfactory results and positive attitude. Periodic instructions and supervising hygiene inctructors in school can improve students' oral hygiene in school and this in turn can create healthier students overall