RESUMO
Objectives: The aim of the present investigation was to study the effects of NaOCl and glutaraldehyde pretreatment on surface topography of denting and microtensile bond of resin-based composite to dentin
Materials and methods: For SEM examination, a three-millimeter thick dentin discs from the middle third of the crowns of 30 human first molar teeth were obtained. The samples were divided into three group [n=10], relative to the pretreatment utilized i.e., washing only, 2.5% NaOCl or 2% glutaraldehyde. Each group was further subdivided into two subgroups [n=5], relative to the washing used i.e., water or ethanol. Pretreated dentin surfaces were subjected to SEM examination. For microtensile bond strength test, the occlusal surfaces of 30 human first molar teeth were ground flat to the middle third of the crowns. The samples were divided according to the grouping system mentioned before and then bonded with the ethanol based Excite adhesive and restored with the Tetric-ceram hybrid dental composite cores. All samples were sectioned to 1mm[2] sticks and subjected to microtensile bon strength test
Results: SEM results revealed, regardless the washing material used, 2% glutaraldehyde pretreatment of dentin had minimal effects on smear layer removal but it resulted in raising of the collagen fibers at orifices of the dentinal tubules. 2.5% NaOCl pretreatment resulted in complete removal of the smear layer, blugs and collagen fibers at the dentinal tubule orifices. Statistical analysis of the microtensile bond strength values revealed that both pretreatment materials improved the bond strength to dentin, with significant values when water washing was used. Ethanol washing showed significant improvement in the bond strength among all the tested groups
Conclusions: Under the conditions of the present investigation the following conclusions were evident: Washing of cavities with ethanol before acid-etching, although does not affect the dentin surface topography, will enhance sealing and bonding of ethanol based adhesive systems to tooth structures. Pretreatment of dentin with 2% glutaraldehyde, is a promising approach for cavity disinfection, improvement of sealability of restorations and dentin desensitization. Pretreatment of dentin with 2% glutaraldehyde followed by washing with ethanol will enhance excellent sealing. Regarding to its effects on the surface topography of dentin and surface tension of fluids, 2.5% NaOCl application may be considered a new approach to dentin conditioning. In deep cavities, the surface topographic changes found with 2.5% NaOcl pretreatment, although improve bonding to dentin, when followed by acid-etching may invite chemicals used in adhesion steps and restoration to the dental pulp
RESUMO
Statement of problem: New dental materials and techniques have been introduced in the past few years of fabricate all ceramic crowns with improved strength, biocompatibility and better fit. However poor marginal fit still considered a common disadvantage of these esthetic crowns
Purpose: This study investigated the influence of different luting agents and thermalcycling on the microleakage of recently developed all-ceramic crowns
Materials and Methods: A hundred twenty human maxillary premolars were prepared for all-ceramic crowns with the following preparation criteria: 6-degree axial taper, 1.5 mm shoulder finish line placed 0.5 mm occlusal to the CEJ, 2 mm occlusal reduction and occluso-gingival height of 5 mm. prepared teeth were restored with Empress 2 all-ceramic crowns. Six luting agents [Superbond C and B; [SB], Rely X ARC; [RX], Mirage FLC; [MF], GC Fuji CEM; [FC], ProTec CEM; [PT] and Zinc phosphate cement; [ZP]] were used for cementation [n=20]. After 1-week storage in water, half of the specimens of each group [n=10] were thermal cycles for 70000 cycles. Specimens were then immersed in 50 wt% aqueous solution of silver nitrate for 2 hours. Each specimen was embedded in clear acrylic resin and aqueous solution of silver nitrate for 2 hours. Each specimen was embedded in clear acrylic resin and sectioned mid mesiodistally and buccolingually using Isomet 1000 Precision Saw. For each section the degree of microleakage was graded 0, 1, 2, 3 or 4 starting from the cervical margin using a stereomicroscope at 150 X original magnification. The Kruskal-Wallis test was used first to detect overall significance, followed by Mann-Whitney U tests to identify which pairs of groups had significant differences [alpha = 0.5]
Results: Thermalcycling significantly increased the degree of microleakage for all test groups at tooth/cement [T/C] and ceramic/cement [C/C] interfaces as follow, ZP [T/C, P = 0.0002], [C/C, P=0.0001]; PT [T/C, P = 0.0003], [C/C, P= 0.004]; FC, [T/C, P = 0.001], [C/C, P= 0.003]; SB, [T/C, P=0.002], [C/C, P=0.001]; RX, [T/C, P = 0.004], [C/C, P=0.011] and MF, [T/C, P = 0.008], [C/C, P = 0.009]. However adhesive resin cements and the paste form of hybrid glass ionomer cement significantly decreased the degree of microleakage compared to zinc phosphate cement [P<.05]Conclusion: There was a significant increase in the degree of microleakage after thermal cycling for all test groups at both tooth/cement and ceramic/cement interfaces. Adhesive resin cements and the past form of hybrid glass ionomer cement decreased the degree of microleakage
Clinical implications: Within the limitations of this in vitro study, the use of adhesive resin cements with a compatible dentin bonding agent and the paste form of hybrid glass ionomer cement are preferred for cementation of Empress 2 all ceramic crowns. These luting agents could improve the longevity of Empress 2 all-ceramic crowns