ABSTRACT
Objectives: to evciluate the microstructure of the recently developed glass ceramic [Leucite-Egypt] using scanning electron microscope and its shear bond strength to commercially available nickel chromium alloy
Materials and methods: for microstructure investigation four metal discs in dimension 3mm in diameter and 1.5mm in thickness [nickel chromium] were cast, 2 for each ce-rami: material [Leucite-Egypl and Vita company]. Both ceramic materials were fused [3mm in diameter and 2mm in thickness] according to manufacture instruction. They were examined by scanning electron microscope [SEM] at different magnification. For shear bond strength testing, ten cylindrical metal specimens [35mm in length and 4.5mm in diameter] were prepared five for each ceramic material. The ceramic materials were applied in dimension 8mm in height and 1mm in thickness, all specimens were subjected to shear bond strength testing in a universal testing machine. Data were collected, tabulated and statistically analyzed using Student t test
Results: SE micrographs revealed that the two tested materials composed of two phases, grayish white leucite crystals in dark gray vitreous glassy phase. The scanning electron micrographs of Leucite-Egypt ceramic were characterized by the presence of microcracks as well as the presence of the two crys-tallographic forms, tetragonal form and metastable cubic form. No statistically significant differences were found between the mean shear bond strength values of the two tested materials. Further studies are recommended to investigate the strength properties of Leucite-Egypt by different rate of cooling
ABSTRACT
Objectives: the purpose of this study was to determine the effects of a home bleaching agent on the color stability and the surface texture of Duceram feldspathic porcelain, Duceram LFC and IPS Empress 2
Materials and Methods: Fifteen ceramic specimens were constructed. Five for each of Duceram feldspathic porcelain, hydrothermal Duceram LFC and IPS Empress 2. All specimens were subjected to spectrophotometric analysis of color parameters, image analysis of surface roughness and scanning electron microscopic evaluation before and after exposure to bleaching agent Zoom
Results: The three tested ceramic materials showed significant increased in the color change as well as the surface roughness after each bleaching step. Duceram LFC exhibited the highest color change and surface roughness throughout the test. An acceptable color change [A E<2] was observed with Duceram after first bleaching step and also with IPS Empress 2 after first and second bleaching step. Results also demonstrated that IPS Empress 2 specimens recorded the lowest Ra values throughout the test. Scanning electron microscopic evaluation revealed that the bleached specimens showed various degree of surface roughness and irregularities as a result of degradation of glass phase in the different ceramic materials. Further researches are required to confirm these re-suits clinically
ABSTRACT
Objectives: To investigate and compare the color stability of two brands of hybrid resin composites, namely; Filtek Z/250 and Tetric Ceram, after being illuminated with ion argon laser, light- emitting diodes [LED] and halogen light curing units [LCU], after storages in coffee at time intervals one week and three weeks
Materials and Methods: From each material, 15 discs were prepared and equally divided into three groups. Composite disc specimens were cured by ion argon laser, LED and halogen LCU. Color coefficients [CIE L*a*b*] were measured by a double beam ultraviolet visible spectrophotometer, immediately after curing and after storage in coffee for one and three weeks period
Results: All tested specimens showed color changes after one week, irrespective of the curing technique [deltaE 1.8-5.4]. After three weeks storage period, the halogen light cured specimens showed the highest significant change in the mean deltaE values, whereas, the laser cured specimens showed the least mean deltaE scores for both tested materials. Significantly lower mean deltaE values were noted with the Tetric Ceram LED cured specimens compared to their halogen light cured counterparts. On the other hand, for the halogen tight cured specimens, Z/250 specimens exhibited better color stability than the Tetric Ceram specimens did. The depth of cure, as well as the slower rate of curing, improve the color stability of resin-based composite. For halogen light curing units, resin-based composites with higher inorganic filler content are recommended, to obtain better color stability
ABSTRACT
Objectives: the purpose of this study was threefold; firstly; to determine and compare the fracture resistance of sound, class II prepared and restored human maxillary premolars with five different bonded resin- composite, ceromer and ceramic inlays, using mechanical testing and finite element analysis [FEA]. Secondly; Check the validity of the numerical model as a successful non destructive technique for teeth analysis by comparing the obtained numerical data to the experimental data. Thirdly; to assess the-stress distribution and maximum tensile stresses, using a three- dimensional FEA, in class II prepared and restored human maxillary premolars with the aforementioned five inlays
Materials and Methods: Forty two sound human maxillary premolars were selected, cleansed, scrubed and embedded in self-curing acrylic resin blocks. Teeth were randomly assigned into seven groups six teeth each. Group I comprised unprepared and unrestored teeth [controls]. Group II comprised teeth that were class II prepared but not restored. In groups III-VII, standardized class II cavity preparations were performed and restored with five different bonded inlays; resin-composite [Filtek Z/250]. Ceromer [Targis], fired porcelain [Vita Dur Alpha], CAD/CAM [Cerec 1] and copy-milled [Celay] respectively. All inlays were cemented with dual-component composite-resin based luting material [Panavia 21, Lot 31113; Kurary Co. Ltd]. All specimens were subjected to a compressive axial load on a universal testing machine [Lloyd testing machine, England], with a 5 KN compressive load cell and a constant rate of loading 0.5 mm/ mm, by means of a steel bar [8 mm in diameter]. The bar was centralized to the occlusal surface, parallel to the long axis of the tooth and contacted the buccal and palatal cuspal slopes beyond the margins of the preparations/restorations. The compression load was applied until the specimen fractures. The fracture load values were recorded in [KN] at the moment of fracture. Data was tabulated and statistically analyzed. For the FEA, a maxillary first premolar was three dimensionally modeled. The model symbolized the tooth with its different components [enamel, dentin, etc], the restoration, the resin cement, the acrylic resin block and the applied load. The properties of the restoration were varied to cover all used inlays. The cement thickness was also varied. A 170 N static load simulating the working load on the tooth was applied in a way similar to that applied during the mechanical testing
Results: Class II cavity preparation in maxillary premolars significantly decreased the tooth resistance to fracture. The fracture resistance of teeth restored with Filtek Z/250, Targis and Cerec inlays was not statistically significantly different from that of sound tested teeth, yet, the sound tooth fracture resistance was not re-established. Teeth restored with laboratory fired ceramic inlays showed significantly the lowest mean fracture load compared with machinable ceramics and other tested inlays. The fracture load numerical data was consistent with the experimental data in this study. Results of FEA stress distribution and maximum tensile stresses assessment within the tooth and the different inlays, implicate that the modulus of elasticity and the tensile strength of the inlay material influence the mode of fracture of restored teeth. The finite element analysis can be considered as a reliable non destructive method for assessment of the tensile stress distribution within the restored teeth and also as a predictor of the fracture load
Recommendations: Further studies are needed to determine the role of the resin cement properties under machinable ceramic inlays in improving the fracture resistance of teeth
ABSTRACT
Objectives: To evaluate two different feldspathic porcelain materials, namely: Vita Dur Alpha and VitaVM7; firstly by examination of the surface morphology of unetched and etched specimens using scanning electron microscopy [SEM], secondly by studying their chemical compositional element concentration using energy dispersive X-ray [EDX] analysis, thirdly by studying their surface hardness property and finally by determining their shear bond strength to dentine after two hydrofluoric acid etching durations [5 and10 seconds]
Materials and Methods: Twenty specimen discs for each material were prepared and randomly assigned into four groups according to the following experimental protocol: Surface morphology and elemental analysis assessment, microhardness and shear bond strength testing
Results: The surface morphology showed that the two tested materials have a two-phase structure with a major amount of leucite crystals in a glassy vitrous phase. The two phases are more homogeneously distributed in VitaVM7. In Vita Dur Alpha, microcracks were observed in the glassy matrix within the leucite crystals. The surface morphology produced by different hydrofluoric acid [HF] duration [5 and 10 seconds], followed a distinct pattern for each tested material. The pattern was more evident in the VitaVM7 etched specimens. More intense surface disruption was seen in the 10 second-etched specimens. Results of the EDX analysis revealed the presence of considerable amount of alkali metal ions in both tested materials, which were slightly higher in Vita Dur Alpha. VitaVM7 was characterized by having higher silica content. No statistical significant difference was found between the mean VHN values of the two tested materials. There was statistical significant difference between the mean shear bond strength values of the two tested materials regardless of the etching duration. The 10-second etched VitaVM7 yielded the highest mean shear values, whereas, the 10-second-etched Vita Dur alpha yielded the least mean shear values
Conclusions: Differences in ceramic microstructure and ceramic composition are controlling factors in the development of micromechanical retention produced by etching and chemical adhesion mediated by silane. Structure homogeneity did not significantly decrease the hardness of the tested ceramic materials. Hydrofluoric acid etching for 10 seconds does not seem to be the method of choice for conditioning ceramics having inhomogeneous phase distribution and high alkali content. The data provided by the EDX analysis coupled with the information from the SEM elucidated the results obtained from the mechanical testing
ABSTRACT
Anstract: The purpose of this study was twofold, first to evaluate the effect of 50% hydrogen peroxide bleaching agents on surface morphology, ultra-structure of resin-dentin interface and the shear bond strength of resin composite to dentin. Second, to evaluate the effect of application of two different forms of antioxidants on the bleached dentin surface on the fore mentioned properties. One adhesive system [Dentastic Uno]. Epic TMPT microfilled composite. 50% bleaching gel and two antioxidants namely sodium ascorbate and vitamin C were used in this study. 56 intact maxillary first premolars were used. The teeth were equally divided into four groups, fourteen specimens each. Group I was directly bonded with composite resin without bleaching, group II was subjected to bleaching prior to composite bonding, whereas group III and IV were treated with sodium ascorbate and vitamin C antioxidants respectively after bleaching then bonded with resin composite. The teeth were examined by SEM to investigate dentin surface topography and resin- dentin interface. All samples were also subjected to shear bond strength testing using a universal testing machine
Results: The unbleached specimens showed adequate removal of the smear layer with effective opening of the dentinal tubules. The hybrid layer revealed a uniform distribution with resin tags positively extending in the demineralized dentin. On contrary, the bleached specimens showed the presence of smear layer and no opened dentinal tubules were evident. This resulted in forming thin, irregular and crumbly hybrid layer, with less resin tags extensions in dentinal tubules. SEM of cut dentin surface treated with sodium ascorbate after hydrogen peroxide bleaching, showed adequate removal of smear layer with a well distinct hybrid layer similar to that of control group. While the SEM of cut dentin surface treated with vitamin C after bleaching, showed a well established smear layer with no evidence of etching. The hybrid layer was very thin with few and short resin tags. The mean and standard deviation values of shear bond strength in MPa indicated that the least mean shear bond strength value was shown by the bleached dentin group[4.56 MPa] while the highest mean shear bond strength value [14.45 MPa] was shown by the unbleached group. There was insignificant difference between the sodium ascorbate treated group and the unbleached control group
Conclusions: Hydrogen peroxide bleaching dramatically affects the dentin surface morphology, the hybridization quality as well as the shear bond strength of resin bonded composite to dentin. Application of sodium ascorbate as a biological antioxidant reverses the oxidation effect of hydrogen peroxide bleaching on dentin surface topography and restores the compromised shear bond strength. Different chemical formulations of antioxidants produced various interfacial structures of bleached dentin and finally the shear bond strength of composite to dentin is intimately related to the quality of hybrid layer and the resin tag infiltration