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