Chemical stability of Bioglass in simulated oral environment

Statement of Problem: bioglasses are a series of biocompatible dental materials, which are considered as light conducting inserts in resin composite restorations. Consequently, their chemical stability is more essential when they are used in conjunction with resin composite

Objectives: the aim of this study was to evaluate and compare the chemical stability of Bioglass with dental porcelain and resin composite by determining the amount of released K[+], Na[+], Ca[2+] ions and silicone elements from these materials as a result of exposure to tested solutions with different pH levels including: Sodium Bicarbonate [SB, [pH=9.2]], Sodium Buffer Lactate [SBL, [pH=2.4]], Acetic Acid [AA, [pH=2.4]], and Distilled Water [DW, [pH=6.2]]

Materials and Methods: in this experimental study, forty 2.0 × 4.0 cylindrical rods for each tested material group [Dental porcelain, Resin composite and Bioglass] were prepared. They were divided into four subgroups of 10 rods each, which immersed in one of the four testing solutions in a designated container. The containers were stored at 50 [degree]C and 100% humidity for one week. The released ions were measured by using a spectrophotometer [[micro]g/cm[2]/ml]. The data were statistically analyzed by nonparametric Kruskal-Wallis H test

Results: it was observed that the tested materials released ions at different levels of concentration. The significant amounts of Sodium, Calcium, and Silicon ions release were measured in Bioglass subgroups in all the tested solutions [p < 0.001]. Potassium ion release from dental porcelain was the largest in all solutions except for AA in which Bioglass had the greatest potassium ion release [p < 0.001]

Conclusions: a greater structural instability was observed for Biogalss group than dental porcelain and resin composite in testing solutions with different pH levels

[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

[ in vitro evaluation on shear bond strength of three resin luting cement systems in bonding of base metal alloy and ceramco and inceram porcelains to dentin]

Developed synthetic resin cement are recommended for cementation of crown and bridges. Bonding of adhensive resins to ceramic, metal, enamel and dentin is an important factor for a successful clinical restoration. The purpose of this study was to determine the shear bond strength of 3 luting cement systems [Dual cure, self Cure and resin modified glass inomer] for bonding the base metal alloy, Ceramco and Inceram porcelain to dentin. In this experimental study, 90 extracted human teeth were prepared and buried in self cure acrylic resin while the buccal surface remained out of the acrylic material. The enamel of the buccal surface were removed and a flat surface was obtained on the dentin. Thirty blocks of base metal alloy, Ceramco laminate porcelain and Inceram were prepared with the dimensions of 6x4x2mm, and divided into 3 subgroups. Each subgroup was cemented with C and B Metabond, Panavia F and Rely X to dentin. After that, they were thermocycled between 5°C to 50°C for 500 cycles, the shear bond strengths were measured in an universal testing machine. Finally, the specimens were inspected under a stereomicroscope with a magnification of 40 to determine the modes of failure. The data were analysed using SPSS software [2-way ANOVA, Duncan's test and Fisher's Exact test]. Maximum shear bond strength in bonding of 3 experimental plates to dentin with 3 adhesive resin systems are as follows: Panavia F for base metal plates [15.316 +/- 2.925 MPa], C and B Metabond for Ceramco porcelains [11.789 +/- 1.730 MPa] and Inceram porcelains [10.512 +/- 3.249 MPa]. Within the limitation of this study, the best cement for cementation of base metal plates was Panavia F or C and B Metabond cement. Among these three evaluated cements,C and B Metabond cement proved to be better for cementation of Ceramco porcelains to dentin and C and B Metabond or Panavia F for cementation of Inceram plates to dentin

[Effect of different surfactant solutions with and without EDTA on dentin surface free energy]

Increase in surface free energy of tooth activates enamel and dentin to enhance surface wettability and optimize adhesion. The purpose of this study was to evaluate the effect of different surfactant solutions with and without EDTA during preparation on dentin surface free energy. In this in vitro study, 88 selected molar teeth were cut in occlusal one-third of the crown and a flat dentin surface was obtained. Surfactant solutions with five different HLB [Hydrophil-Lipophil Balance] were selected and the flat dentin surfaces were abraded with a commercial high-speed cylindrical diamond bur while rinsing with the solutions. Two control groups were selected, including negative control [cutting with air-water spray], positive control [cutting with air-water spray and etching with phosphoric acid]. The study was carried on by depositing drops of two different liquids including distilled water [polar liquid] and methylene iodide [non-polar liquid] on the different treated surfaces and taking photographs of the drops by means of a digital camera. The contact angles were measured with AutoCad software. The surface free energy of dentin was then calculated using Fowkes equation. After selection of the most effective solution, a higher concentration was applied to determine the effect of concentration on surface free energy. After determining the effective concentration, the combined solution of surfactant and EDTA was evaluated. Data analysis was done by ANOVA and Duncan test with 95% signifieance level. The SEM study was done to evaluate smear layer formation in the specimens. The results revealed that use of surfactant on dentin surface decreased the surface energy while the surfactant with EDTA caused a significant increase in the surface energy compared to surfactant solution alone [Pvalue<0.05]. This increase in energy was equal to that of negative control. SEM study revealed that using surfactant with or without EDTA, removes the smear layer incompletely. 1] Surfactant solutions without EDTA decrease dentin surface energy at the same level of positive control group. 2] The result of measuring surface energy in negative control group and in the groups using this combined solution was identical with surface tension of water [72.8 j/m[2]]

[ effect of different thinknesses of some restorative materials, tooth structures and air on light intensity reduction: a laboratoary evaluation]

The minimum acceptable light intensity for light cure systems is 233mW/Cm2. This intensity is acceptable just for curing the surface of composite and is not acceptable for the deeper areas. Light intensity decrease after passing through different thicknesses of tooth structures and dental materials can affect the degree and depth of polymerization of light cure materials. The purpose of this study is evaluation of light intensity decrease after passing through different thicknesses of dental structures, light activated hybrid and microfilled composites, light activated glass ionomer, bioglass, dental porcelain and also air. Six groups each containing five samples including hybrid composite, microfilled composite, glass ionomer, dental porcelain, bioglass and dental structures in five thicknesses from 1 up to 5 millimeter were prepared. The intensity of curing light was measured by radiometer after passing through samples and the air. Rate of light intensity reduction reduces dramatically after passing through different thicknesses of dental porcelain, tooth structures, microfilled composite, hybrid composite, bioglass, glass ionomer and air respectively. The reduction rates for dental porcelain, tooth structures, microfilled composite, hybrid composite, bioglass, glass ionomer and air with 1.0 mm thickness are 88,80,78,68,47,44 and 0.7 percent respectively .As thickness increases, reduction of light intensity increases. Higher light intensity reduction occures after passing through dental porcelain and the lower occures within air. 1. Application of light cure material in less than 1 .mm thickness could have better results due to polymerization. 2. for light cure glass ionomer it is acceptable to cure only for one millimeter thickness. 3. For bioglass as a light coducting insert and material, the acceptable curing depth is up to 3mm. So higher light curing intensity is suggested for different sizes and thickness of these inserts. 4. For other materials and tooth structures even after passing through 1mm thickness, the adequate intensity is not aquired. So units with the ability of producing higher intensity radiation patterns are suggested. 5. The reduction rate of light intensity due to different distances is considerably lower than when light is passed through different thicknesses of dental materials and tooth structures

Evaluation and comparison of effect of different irradiation patterns and new suggested light exposure pattern on microleakage of composite resin restorations

There is a significant relationship between polymerization rate and polymerization shrinkage stress in restoration. The more the polymerization rate is, the shorter viscoplastic phase of the composite would be, leaving no time for the composite to flow and consequently sudden hardening of the composite occurs. This leads into severe shrinkage stresses followed by composite detachment from cavity walls resulting in microleakage within restoration and tooth. The aim of this study was to suggest a new method of light exposure pattern for composite curing and evaluation of its effect on enamel and dentinal microleakage in respect to some other light exposure patterns. In this exprimental invitro study, flat tooth sections, 40 dentinal and 40 enamel samples were etched and Dentin Bonding Agent [DBA] [Excite] was applied according to the manufacturer's instruction. While placed on the samples, one bulk Tetric ceram A3 composite was inserted in to a 2x2 mm polyethylene cylindrical mould. Samples were divided into dentinal and enamel groups of ten and light cured with Astralis 7 light exposure patterns including HIP [High Intensity Program], LOP [Low Intensity Program], PUL [Pulse Program] and SUP [Suggested Progressive Program] for 80 seconds. After curing, thermocycling, dye penetration and medial sectioning, samples were observed under a scaled reflective microscope for microleakage measurement. The data were analysed statistically using One-Way and Two-Way ANOVA and Duncan test through SPSS software. There was a significant difference in microleakage between enamel samples. The microleakage rate was the highest in HIP group while no microleakage was detected in the other groups. The degree of microleakage in dentin samples was significantly less in SUP group than the others but there was no significant difference between the other groups. 1. The least dentinal microleakage occurred with application of suggested progressive program [SUP] compared to other testing groups. 2. Like LOP and PUL light exposure patterns, no enamel microleakage occurred with SUP application. 3. Enamel microleakage was detected in HIP group which had higher light intensity