ABSTRACT
Resin based fissure sealants are currently used widely in clinical practice. Their longevity is controversial because of many variables in the oral environment such as temperature shifts and chemical changes. In the oral cavity, many solutions [water, food substances] could potentially affect the behavior of materials. Citric acid and lactic acid which simulate certain vegetables, fruits, candy and syrup could produce certain degree of softening of restorative resin's. The resin matrix becomes also softened with exposure to plaque organic acids of dental plaque in patients mouth. Various forms of rinses have been used for many years, some contain alcohol, while others contain no alcohol. Very little work specifically related to fissure sealants in such media. So, the primary goal of this study was to test the hypothesis that immersion in various media as food simulating liquids, mouth rinses and fluoride gels might affect the micro hardness of fissure sealants. Two different fissure sealants [Admira seal and Helio seal] were used in this study. Specimens were prepared by using a plastic ring mold with internal dimension 6 mm in diameter and 3 mm in height. Specimens were immersed in test media citric acid, lactic acid, alcoholic mouth wash, non alcoholic mouth wash, stannous fluoride gel and neutral sodium fluoride gel. Artificial saliva was used as control. Micro- hardness were recorded, analyzed and compared in various media. From the results of our study, it can be concluded that: within the limits of this study, Vickers micro-hardness of test materials varied according to the immersion media. In general, Admira seal displayed greater resistance to lactic acid, non alcoholic mouth wash and neutral sodium fluoride gel; however a specific pattern of softening susceptibility was identified relative to alcoholic medium. Helio seal exhibited more resistance in alcoholic medium. Overall , because of the increased consumption of low pH soft drinks by children and improper use of mouth washes, our results suggest that a similar process may occur clinically which affect the longevity of the fissure sealant materials
ABSTRACT
Statement of problem: Because water sorption of acrylic resins is accompanied by volumetric change, it is a physical property of importance. As a residual monomer leaches into the oral fluids causes tissue irritation, low solubility of these resins is desired
Purpose: This study was made to compare the water sorption and solubility of four different types of acrylic resins using injection molding technique in comparison with heat cured acrylic resin using compression molding technique
Results: All injection processed resins exhibited less water sorption than the compression processed resin [control group]. No significant difference was noted in the water sorption of all injection processed resins. Microwave polymerized acrylic resin [Acron MC] showed significant increase in the solubility value than the other tested acrylic denture base resins
ABSTRACT
Physical and mechanical properties of resins are of a great concern, and many approaches have been used to strengthen acrylic resin dentures. This study measured the effect of addition of rubber modified- montmorillonite [MMT) composite by different ratios to heat cured acrylic resin on the micro-hardness, Young's modulus, surface roughness and glass transition temperature. Fifteen acrylic resin test specimens were prepared and reinforced with rubber modified MMT (1% composite, 1% composite with double rubber content and 3% composite). The control group consists of five specimens with no reinforcement. These specimens were tested as regard; -micro-hardness, Young's modulus, surface roughness and glass transition temperature. The results of the present study demonstrated that, Vickers hardness values of acrylic resin denture base were decrease after addition of rubber MMT -composite at any ratio. The Young's modulus after addition of 3% rubber MMT-composite was nearly similar to that of control group. While adding 1% composite and 1% composite with double rubber content produce significant reduction in the Young's modulus values. As regards to surface roughness there was significant increase in the surface roughness after addition of 3% composite. Furthermore there was significant elevation of the glass transition temperature after addition of 3% rubber MMT-composiu;. While the glass transition temperature of the other ratios were nearly similar to that of the control group
ABSTRACT
Statement of Problem: One of the most critical steps of the ceramic restoration technique is cementation. Mechanical stress before the resin cement reaches a certain degree of polymerization can displace or even fracture the restoration
Purpose of Study: This is in vitro study conducted to evaluate the bond between ceramic and dentin or core material, using two luting resin cements, also evaluated the degree of conversion after curing through different ceramic thickness
Materials and Methods: for shear bond test: 30 non-restored human molars and premolars and 30 cylindrical shapes of composite core materials were randomly divided into 12 groups. The two resin luting cements tested were "Rely -X with Scotch bond multi purpose" and "Admira cement with Admira bond". A total of 40 ceramic discs [2 and 3mm] were etched, silane coated and then bonded to a flat dentin and core surface with luting cements associated with adhesive system and then photoactivated. For degree of conversion test;- C = C converted to C... C were determined with infrared spectroscopy [FTIR] after light polymerization curing through Mylar sheet which served as control group. 2 mm and 3 mm ceramic thickness
Results: For the control groups when the cement cured without ceramic spacer, the shear bond strength is greater than other groups cured through ceramic discs. Both dual cure cement" Rely-X and light cure cement "Admira" give nearly similar results. The bond strength of resin cements to dentin is slightly higher than that bonded to core material. The degree of conversion of both tested luting cement show significant reduction as a function of ceramic thickness. It is important to be noted that there is no significant correlation between the degree of conversion and shear bond