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2007| January-March | Volume 10 | Issue 1
July 31, 2008
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The role of oxygen inhibited layer on the shear bond strength of composites - An in-vitro evaluation
Seema Merwade, Jagadish
January-March 2007, 10(1):1-4
Light or chemically cured dental composite resins leave a soft, sticky superficial layer upon polymerization. The layer is commonly referred to as Oxygen Inhibited Layer and it is always present when a composite or bonding resin is polymerized in air. For years. it
wa s believed that Oxygen Inhibited Layer is required before adding more layers of bonded composite. But reports on how Oxygen Inhibited Layer affects the bond strength have been inconsistent and contradictory. The aim of the present study was to compare the shear bond strengths of composite composite bonded specimens prepared with or without Oxygen Inhibited Layer. The shear bond strengths were tested using Universal Testing Machine. The results of the present study show that the presence of Oxygen inhibited layer increases the shear bond strength values at the interphase of incrementally built 2 layer composite specimens. Within the limitations of the present study, it can be conclusively stated "a higher shear bond strength results from Oxygen Inhibition on the surface layer of composite".
Metal collars - are they serving any purpose?
Sameer Goyal, PV Shyamala, Revathi Miglani, L Lakshmi Narayanan
January-March 2007, 10(1):14-18
The purpose of this study was to investigate the fracture resistance of endodontically treated teeth with uniform and non-uniform ferrule configurations. Root canal treatment and post space was performed in fifty extracted intact, non carious human maxillary central incisors and were divided into 5 groups of 10 specimen each i.e. Group I -- No contra bevel (No core ferrule), Group 11 - contra bevel <2mm(core ferrule <2mm), Group III - 2mm contra bevel (2mm core ferrule), Group I V - contra bevel >2mm (core ferrule >2mm). Group V - Nonuniform contra bevel (Non uniform core ferrule). Crown preparation was done in a standardized manner in all the specimen. Based on the groups varying core ferrule height was given in all the specimen. Wax patterns were made, invested and casted. Cast posts were then luted followed by crown cementation and then tested in universal testing machine at a cross head speed of 2.5mm/min and the load was applied to the lingual edge at 45° angle to the long axis of the tooth. It was concluded that contra-bevel / core ferrule does not further enhance the fracture resistance.
Remineralization of enamel sub-surface lesion using casein phosphopeptide amorphous calcium phosphate (CPP-ACP) - a quantitative energy dispersive X-ray analysis (EDAX)
Mithra N Hegde, Shishir Shetty, Deepak Pardal
January-March 2007, 10(1):19-25
This study aimed at quantitatively evaluating the remineralization potential of casein phosphopeptide -amorphous calcium phosphate (CPP-ACP) paste on artificial enamel sub-surface lesion using Energy Dispersive X-rayAnalysis (EDAX). 60 enamel specimens were prepared from extracted human molars. All specimens were evaluated for mineral (calcium and phosphorous) content (wt %) using EDAX. The specimens were placed in demineralizing solution for 48 hrs to produce artificial carious lesions. Mineral content was again measured using EDAX. The specimens were then randomly assigned to 3 study and 1 control group (incubated in artificial saliva after demineralization), in which each group except the control was treated with remineralizing paste (10 % CPP-ACP paste) for 1. 5 and 10 days twice daily for 3 minutes, followed by incubation in artificial saliva at 370°C The control group received no treatment with remineralizing paste. After the remineralization treatment mineral content (wt %) of samples was measured using EDAX. The study groups showed an increase in the mineral content as compared to demineralized samples. No change was seen in the control group. 10 % CPPACP paste could significantly remineralize the artificial enamel sub-surface lesion in vitro and the remineralization potential was dose dependent with.
Effect of pre and post operative bleaching on microleakage of amalgam and composite restoration using 10% carbamide peroxide - an invitro study
Asha Sarah Jacob, NM Dhanya Kumar
January-March 2007, 10(1):33-37
Background and objectives:
The purpose of this study was to evaluate the effect of pre and post operative bleaching with 10% carbamide peroxide on marginal leakage of amalgam and resin composite restorations.
Three groups were made using 30 extracted, caries free and restoration free molars (n = 10). In the preoperative group, bleaching was performed with 10 % > carbamide peroxide, followed by the placement of resin composite and amalgam restorations on class V cavity preparations. In the post operative group, bleaching was performed after the resin composite and amalgam restorations were fabricated. The third group served as a control in which no bleaching was performed. Dye penetration was used for evaluation of marginal leakage.
In post operatively bleached teeth, statistical analysis revealed significant difference between the control and experimental groups for resin composite restorations, but in amalgam restorations there were no significant difference. In preoperatively bleached teeth marginal leakage scores of the resin composite restorations in the experimental group were significantly higher than the control group, but no significant difference was observed between amalgam and resin composite restorations. No significant difference were found between experimental and control groups of amalgam restorations.
Interpretation and Conclusion:
Bleaching with carbamide peroxide may after the marginal leakage of resin composite restoration, but amalgam restorations are not affected adversely in vitro.
Effect of Rewetting agents on the shear bond strength of different bonding agents when applied on dry dentin
Abhishek Bansal, Vasundhara Shivanna
January-March 2007, 10(1):26-32
Background and Objectives:
The objective of this study was to compare shear bond strength of the three bonding agents containing different concentrations of water when applied over the etched dentin surfaces under different conditions like dry, wet (control subgroup) or dry and rewetted with different rewetting agents like Aqua Prep and Gluma desensitizer.
The study samples comprised of the buccal and lingual surfaces of 60 extracted human molars that were ground to expose the dentin. The teeth were randomly assigned to three groups depending upon the different bonding agents (Multipurpose Scotch bond, Single Bond, Prime and Bond NT)Further each group was divided into four subgroups depending upon the different etched dentin surface conditions i.e. dry, wet (control subgroup), dry and rewetted with different rewetting agents that received the following treatment. In all the three groups, the dentin surface was etched with 35% phosphoric acid for 15 seconds and the treated surface was rinsed thoroughly with water followed by the application of respective bonding agents according to manufacturers instructions and light cured under different etched dentin surface condition like dry, wet or dry and rewetted with aquaprep and Gluma desensitizer. Each major group was further divided into 4 subgroups of 10 samples each depending upon different etched dentin surface conditions. The specimens were stored in distilled water at 37
C for 24 hours and the shear bond strength was tested by lowering the knife edge chisel at a cross head speed of l mm/minute. The data was analysed with One way ANOVA test and post hoc Tukey test.
The highest mean shear bond strengths were obtained (in order) on dentin that was re-wetted with Gluma desensitizer, rewetted with Aquaprep or in wet dentin substrate condition, differences between these surface conditions were not statistically significant for either material.
Interpretation and Conclusion:
The use of dentin bonding agents containing different percentage of water should be considered according to different dentin substrate conditions i.e. dry or wet. Use of rewetting agents may be beneficial when dentin was over dried after acid etching and rinsing, and when less percentage of water concentration dentin bonding
used in such situation.
Fourier transform infrared spectroscopic evaluation - Degree of conversion of a packable, hybrid and flowable composite resin cured using a light transmitting post
Sridhar Vishnu, Sowmya Natesh Kumar, Deivanayagam Kandaswamy, Nagendrababu Venkateshbabu
January-March 2007, 10(1):38-42
The introduction of light transmitting post paved the way for the composite resin to invade the root canal systems. Aim of the study was to evaluate the degree of conversion of a flowable, hybrid and packable composite resin after polymerizing the resin by using light transmitting post by using the Fourier transform infrared spectroscopy. Packable composite resin showed significantly lower degree of conversion values when compared to hybrid and flowable at the apical and middle third. Coronal third showed better conversion than middle third and apical third. Even though degrees of conversion values in the apical samples were low they fall well within the range of 50 - 70% which is considered adequate. A higher degree of conversion can be obtained for hybrid and flowable resin composite up to 14 mm length, if a light transmitting post is used along with an increased light curing time of 4 minutes.
Effect of cyclical lateral forces on microleakage of cervical resin composite restorations
Ryan Francisco Alberto, Ida de Noronha de Ataide
January-March 2007, 10(1):5-13
The purpose of this in-vitro study was to compare the amount of microleakage occurring in cervical restorations in groups of extracted teeth restored with four different types of resin composite materials, representing four basic categories widely used by restorative dentists today. This comparison was made, both with and without the application of cyclic lateral forces. A testing instrument developed specifically to reproduce cyclic lateral forces was utilized. The amount of microleakage that occurred was compared, both with and without the application of the forces. Within the limitations of the study, we found that the packable and the hybrid resin composite material exhibited significantly more leakage than either the flowable or the microfilled resin composite. This was observed in both the fatigued and the non-fatigued specimens. This finding supported the theory that the lower modulus of elasticity of flowable and microfilled resin composites allows more flexure of the restoration during the flexure of the tooth, that results from its reciprocal movements. The non-fatigued specimens restored with flowable and microfilled resin composite material had less microleakage than did those restored with the hybrid resin composite material. The findings in the study supported the possibility that lower modulus of elasticity of the microfilled and flowable resin composite materials may have some beneficial effects in reducing the stress placed on the adhesive bond at the resin tooth interface during the polymerization phase.
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