[Microleakage evaluation of silorane-based composites versus low shirinkage methacrylate-based composites]

Determining the best restorative material to decrease microleakage in class V restorations is of great importance in operative dentistry. The aim of this in-vitro study was to evaluate the microleakage of silorane-based composites compared to low shrinkage methacrylate-based composites in class V restorations. In this in vitro study, class V cavities were prepared on the buccal and lingual surfaces of 24 human premolars and molars [48 cavities]. The specimens were divided into four groups of 6[12 cavities] as follows: group 1 [LS System Adhesive, Primer and Bond + Filtek P90], group 2 [Kalore-GC+ Clearfil SE bond], group 3 [Clearfil SE bond + Grandio] and group4 [Clearfil SE bond + Aelite LS Posterior]. All the specimens were thermocycled for 2000 cycles [5-50°C]. The teeth were then immersed in 0.5% basic fuchsin dye for 24 hours at 37°C, sectioned and observed under stereomicroscope. Data were analyzed using Kruskal-Wallis and Wilcoxon tests at a P<0.05 level of significance. There were no significant differences in microleakage among the four groups at the occlusal margin [P>0.05]. But, there were statistically significant differences in microleakage between Silorane and Aelite at the gingival margin [P<0.05]. Statistically significant differences were also found in microleakage between occlusal and gingival margins [except for Kalore and Silorane] [P>0.05] Silorane was not superior to the conventional low shrinkage methacrylate-based composites except for Aelite in terms of microleakage

[Comparison of temperature rise in silorane-based and methacrylate-based composites cured by LED and Argon laser]

Temperature rise occurs during photoactivation of dental composites due to the exothermic polymerization reaction and different curing units. The aim of this study was evaluation of temperature rise in two kinds of composites with different curing units. In this experimental study, five samples of each composite resin [Filtek Z250, Filtek P90] were placed in two-millimeter deep Teflon molds which were 4mm in diameter. Curing was done from top surface with LED, high power LED and argon laser and temperature was recorded by a thermometer placed under the samples. After reaching room temperature, samples were cured and the temperature was recorded again. The time of maximum temperature was also recorded. The data were analyzed by two-way ANOVA and Tukey HSD. Composites and curing units had statistically significant influence on the temperature rise [p<0.001] Silorane-based composites showed significantly higher temperature rise than methacrylate-based ones. A significantly lower rise in temperature occurred when illumination was performed by argon laser. There was no significant difference in temperature rise between the two types of LEDs. The type of composite had no effect on the time of maximum temperature and in all samples the maximum temperature was recorded at the beginning of irradiation. Silorane-based composites showed higher temperature rise than methacrylatebased ones. Argon laser revealed less heat than LEDs. The maximum temperature rise was recorded at the beginning of irradiation

Effect of the thermal and mechanical load cycling on microleakage of packable composite resin

Some studies have reported packable composite has good mechanical properties including less stress, polymerization shrinkage and lower coefficient in thermal expansion, but it's adaptation to cavity walls is not so good. This study evaluated the thermal cycling and Mechanical loading on microleakage of packable composite using in-vitro method. Forty eight bovine incisors were selected; Cl II cavity preparations were performed. The teeth were etched with 37% phosphoric acid. After etching, the teeth were rinsed with distilled water and dried with cotton pellet. Single bond [3M] adhesive system was applied next according to the manufacturer's instructions. The surface was light-cured [Intensity 520 MW/cm[2] and the cavities were filled with P 60 composite [3M]. The teeth were randomly divided into two groups and two subgroups [n=12]. Each group was treated with different thermal and mechanical load cycling. The entire surface of each tooth was coated with three layers of Nail polish, except for the 1- mm width around the cervical margin. The teeth were immersed in 2% fushin solution for two hours and then embedded in acrylic resin. Then they were hemi-sectioned longitudinally in a mesio-distal direction through the center of the restoration. The half tooth specimens were evaluated according to the amount of dye microleakage by means of a 40xmagnification. Statistical analysis was conducted using SPSS software, and Kruskal-Wallis test. No significant difference was detected between the four groups [P>0.05]. According to the results of this study, thermo cycling and mechanical loading showed no effect on microleakage

[Antiviral effects of different sterilization and disinfection methods on internal tubes of dental handpiece]

Dental handpieces are the most commonly used instruments in dentistry and their cross contamination is very high due to their direct contact with blood and saliva. The purpose of this study was to evaluate the antiviral effects of formalin tablets and autoclave on internal lumens of dental handpieces. This experimental study was designed in order to evaluate the effect of different materials and methods of sterilization and disinfection on virus elimination from internal spaces and interior chambers of dental turbines. Four study groups were composed of: 1] Vacuum autoclave, 2] Non vacuum autoclave, 3] Ten Para Formaldehyde tablets, and 4] Twenty Para Formaldehyde tablets. Nine turbines were tested in each group after preliminary washing, drying and autoclaving. The internal tubes and spaces were then contaminated with Polio and Herpes Simplex virus type I. Antiviral agents and devices were used according to the manufacturers' instructions. Two cell culture samples were obtained from each handpiece, after washing them with sterile distilled water and MEM [Minimum Essential Medium]. In each group one handpiece was designated as control. The culture results were recorded after one week. Autoclaving was perfectly effective on both Polio and Herpes Simplex virus type I in all groups [vacuumed, non-vacuumed, with or without lubricant]. Formalin tablets were 100% effective only on polio virus, and in the 20 tablet group turbines without lubricant. These tablets killed the Herpes Simplex virus in all groups. According to the results of this study, autoclaving is the best method of virus elimination in dental handpiece

[EDTA dentin conditioning and Micro-shear bond strength using SE and SEM]

The main objective of using adhesive material is the improvement of restorative materials bonding to dentin surface in clean environment. The aim of this study was to investigate the effect of EDTA on bond strength of composite resin to dentin surface when used at different times and concentrations prior to application of adhesive systems by employing Scanning Electronic Microscope [SEM]. A total of 100 dentin samples were prepared from 50 human premolars. These samples were divided into two groups according to bonding type [Clearfil SE Bond =group I, Futurbond NR=group II] and each one was classified 5 subgroups according to time and concentration of EDTA as follows: 1 - Control. 2- EDTA 15%, 30 seconds. 3 - EDTA 15%, 60 seconds. 4 - EDTA 24%, 30 seconds. 5 - EDTA 24%, 60 seconds. These samples were conditioned and composite cylinders were adhered to them. After 500 cycles of thermocycling, the testing for micro-shear bond strength was conducted on these samples. Another 10 samples were demineralized for 30 seconds with 6NHCL and deproteinized with 2.5% Naocl for 10 minutes, air dried with desiccators and viewed under SEM. Data were analyzed using one-way as well as three-way ANOVA and Tukey tests. The mean Micro-shear bond strength in group I [Clearfil SE bond] were: 31.88 [ +/- 13] for subgroup 1, 28.4 [ +/- 13] in subgroup 2, 29.8 [ +/- 9] in subgroup 3, 29.2 [ +/- 11] in subgroup 4, and 32.7 [ +/- 12] in subgroup 5. The mean Micro-shear bond strength in group 2 [Futurbond NR]: were: 22.6 [ +/- 10] for subgroup 1, 28.5 [ +/- 9] in subgroup 2, 27.3 [ +/- 10] subgroup 3, 32.4 [ +/- 15] in subgroup 4, and 31.1 [ +/- 14] in subgroup 5. There were no significant differences between the samples conditioned and the ones not conditioned with EDTA, time and the concentration of EDTA applied and also the two bonding types. EDTA conditioning prior to use of the two bonding agents under investigation in this study did not improve the bonding strength of the self etch systems, neither did the time and the concentration of EDTA applied

[Evaluation of disinifecting of 5% sodium hypochlorite solution diluted to 2:100 along with the use of disposable covers on HBV contaminated dental office surfaces and equipments]

The efficiency of disinfecting materials and procedures in removal of contamination from dental surfaces and equipments is essential. In authors' previous study, daily use of 2:100 dilution of 5% sodium hypochlorite in water and disposable covers were recommended since HBV contamination was found on semi-critical parts of the operative dentistry department. The aim of this study was to evaluate the HBV contamination following application of the recommended procedures. The study was conducted in two parts. In the first cross-sectional part, samples were collected from 17 sites of dental surfaces. In the second interventional part samples were collected from 10 sites of 9 dental and 3 sites of 2 light cure units, before and after disinfection with 5% sodium hypochlorite solution diluted to 2:100. Sterile cotton swabs moistened with sterile BSAS [Bovcine Serum Albumin in Sodium Chloride] solution were used for sampling. Samples were tested by PCR technique in Pasteur Institute, Iran. None of the samples collected in the first part of the study showed contamination. In the second part of the study, from 96 samples taken from various parts of dental and light cure units, before and after disinfecting, there was only on HBV contaminated site before disinfection which showed not contamination after disinfection. Based on the results of this study, disinfecting procedure with 5% sodium hypochlorite solution diluted to 2:100 along with using disposable covers is effective in preventing HB contamination

Effect of three filler types on mechanical properties of dental composite

Despite the improvements achieved in the field of dental composites, their strength, longevity, and service life specially in high stress areas is not confirmed. Finding better fillers can be a promising step in this task. The purpose of this study was to investigate the effect of the filler type on the mechanical properties of a new experimental dental composite and compare these with the properties of composite containing conventional glass filler. Experimental composites were prepared by mixing silane-treated fillers with monomers, composed of 70% Bis-GMA and 30% TEGDMA by weight. Fillers were different among the groups. Glass, leucite ceramic and lithium disilicate were prepared as different filler types. All three groups contained 73% wt filler. Comphorquinone and amines were chosen as photo initiator system. Post curing was done for all groups. Diametral tensile strength [DTS], flexural strength and flexural modulus were measured and compared among groups. Data were analyzed with SPSS package using one-way ANOVA test with P<0.05 as the limit of significance. Results: The results showed that the stronger ceramic fillers have positive effect on the flexural strength. Ceramic fillers increased the flexural strength significantly. No significant differences could be determined in DTS among the groups. Flexural modulus can be affected and increased by using ceramic fillers. Flexural strength is one of the most significant properties of restorative dental materials. The higher flexural strength and flexural modulus can be achieved by stronger ceramic fillers. Any further investigation in this field would be beneficial in the development of restorative dental materials

[Role of cusp coverage in the protection of unsupported enamel in posterior composite restorations]

Background and aim: removal of unsupported enamel is one of Block's important principles in cavity preparation. The aim of this study was to determine the effect of bonding materials in the protection of unsupported enamel and sound tooth structure

Materials and Methods: in this study, 30 sound mandibular molars were selected. After cusp reduction, a 3mm depth occlusal cavity with walls consisting of pure unsupported enamel of 3mm height, was prepared. The samples were divided into two groups. In the first group, the cavities were filled by composite. In the second group, the cavities were filled like the first group and the unsupported enamel surfaces were then etched extending 2mm buccocclussally and enamel dentin bonding was applied. These surfaces were finally covered by composite and light cured. The compressive strength of both groups were evaluated by an instron machine

Results: date were subjected to t-student test for analysis. The mean required force to break unsupported enamel was 3440N/mm2 in the first group and 4213N/rnm2 in the second group showing the effective role of etching and buccal coverage of enamel in the protection of remaining weak enamel

Conclusion: the findings of this study suggest that the application of adhesives and coverage of the buccal surfaces support the weak enamel and dentin walls