ABSTRACT
Objective: To evaluate the fit of crowns constructed from metal ceramic nicke-chromium alloy, gold electroformed and Cerec 3 restoration systems
Materials and methods: A total of thirty crowns were fabricated in this study: two main groups: fifteen anterior and fifteen posterior crowns. Each group was divided into three subgroups, each of five crowns were designed as follows: five nickel-chromium ceramo-metallic crowns, five gold electroformed ceramo-metallic crowns and five Cerec 3 [all-ceramic] crowns. The vertical gap distance defined as the marginal opening between the prepared die margin and the most apical surface of the cast crowns was measured before and after porcelain application using a traveling microscope
Results: for the metal ceramic crowns before porcelain application both systems showed clinically accepted range of marginal gap but the gold-electroformed system showed better marginal fit. After porcelain application the metal ceramic systems showed distortion in marginal fit than before porcelain application. The gold-electroformed anteriors system was significantly distorted more than the nickel-chromium and Cerec 3 systems. The posterior crowns were insignificantly different from each other and within the clinical acceptable range for marginal gap
Conclusion: 1- The posterior crowns are within the clinical acceptable range for marginal fit for all systems before and after porcelain application. 2- The nickel-chromium and the gold-electroformed systems are within the clinical acceptable range for marginal fit before porcelain application. 3- The high temperature used during the firing of porcelain affect the marginal fit of a metal-ceramic restorations. 4- The distortion in the marginal fit of anterior crowns was pronounced for the gold-electroformed system after porcelain application. 5-CAD/CAM [Cerec 3] crowns represent good technology compare to other fabricated techniques
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
Purpose: To investigate the influence of the fillers on the shear bond strength of hybrid and nan-ofilled resin based restorative materials bonded with unfilled and filled bonding agents to dentin substrate
Materials and Methods: Two types of resin based restorative materials; hybrid and nano-filled composites; and two types of bonding agent systems; unfilled and filled bonding agents; were used in this study. A total of twenty specimens for shear bond strength testing were prepared, ten for each restorative material. Five specimens of each group were bonded with unfilled bonding agent, whereas the other five were bonded with filled bonding agent. The specimens were then subjected to shear bond strength test and scanning electron micrograph characterization of the hybrid layer morphology
Results: When comparing the two types of resin based restorative materials; nanofilled composite showed always higher shear bond values than the corresponding hybrid ones. However, no significant difference was found. But when comparing the two types of the bonding agent systems the composites bonded with the unfilled bonding agent recorded higher values than the corresponding ones bonded with the filled bonding agents. This was significant only with the nanofilled composite [P < 0.05] scanning electron [SE] microscopic examination confirmed the obtained results
Conclusions: 1-The incorporating filler characteristics; loading and size distribution; in resin based restoration influence their shear bond strength. 2- The optimal adaptation of the unfilled bonding agent system to the dentin is a contributing factor in improving their shear bond strength. 3- The incorporating fillers in the bonding agent system has a negative effect on the of shear bond strength
ABSTRACT
This work investigated the effect of glass fiber reinforcement on the flexural behavior of the acrylic resin denture base material. The flexure strength, modulus of elasticity and deflection of the denture base material with and without fiber reinforcement were compared. The effect of fiber sil-anation on those properties was also investigated
Materials and methods: Fifty-five specimens were prepared according to ADA specifications and the material was manipulated according to the manufacturer's instruction. One percent of different glass fiber length and distribution [unsilanated aYid silanated]: chopped, short, long, woven fine and woven coarse, were packed in the specimen. Specimens were wet stored at 37°C for 48 hours prior to testing on a tensometer under three-point loading. With the knowledge of the load at failure, transverse strength, modulus of elasticity and deflection were calculated. Results of nonreinforced and reinforced [unsilanated and silanated] groups were tabulated and statistically analyzed. It was found that fiber reinforcement improved both flexure strength and modulus of elasticity and reduced deflection compared to the non reinforced control group. The long fiber showed the highest flexure strength and modulus of elasticity with the least deflection. Fiber silanation showed a percentage increase in the flexure strength and the modulus of elasticity and a percentage decrease in the deflection compared to the unsilanated fiber
ABSTRACT
The aim of this study determines the optimum repair material and technique for a broken conventional acrylic resin denture base in terms of its bending properties. Fifty five rectangular specimens [65x10x2.5 mm in dimensions] were fabricated; twenty specimens were fabricated from the repairs materials [heat cured, self cured, high impact and light cured acrylic resin]. Thirty five specimens were fabricated from clear heat cured acrylic resin and cut perpendicular along the midline into two halves where the inner corners were rounded to be repaired with different repair materials. Two surface pretreatments were used prior to repair: the monomer for three minutes and the methyl-ene chloride for five seconds. All specimens were stored in distilled water for forty eight hours before bending testing under four point loading. It was found that the specimens repair with heat cured acrylic resin pretreated with methylene chloride as well as high impact acrylic resin pretreated with its monomer gave the highest results. The least strength was obtained with light cured acrylic resin repair material
ABSTRACT
Objectives: To show the depth of fluoride uptake by the tooth structure from a restorative and dentine bonding agent material using a wavelength dispersive X ray analysis [WDX] at Oum, lOOum and 200um from the surface of a restoration, as well as the degree to which the dentine bonding agent prevented the passage of this fluoride released
Material and methods: Six human premolars teeth scadueled to be extracted for orthodontic treatment were used in this study. Two it was filled with the Rite-Dent composite, while the distal cavity was filled with the Dyract AP composite. Half of the teeth was filled with both composites directly without the use of bonding agent. The other half was subjected to the routine bonding technique. All teeth were stored in distilled water at 37°C for one month before they were tested. The fluoride concentration was measured using wavelength dispersive x-ray analysis [WDX] at Oum, l00microm and 200um from the surface of a restoration
Results: At Oum the cavities restored with Dyract AP with and without the application of adhesive Prim and Bond NT gave the highest fluoride uptake values and are insignificantly different from each other while that restored with Rite-Dent composite with and without application of adhesive were insignificantly different from each other and gave a lower values. At 100 um and 200microm the cavities restored with Dyract AP without the application of adhesive was significantly different from all cavities and gave the highest fluoride uptake values. Conclusion: 1- The amount of fluoride uptaked by the tooth structure depend upon the fluoride present in the restoration as well as the ability of the dentine to uptake this fluoride. 2- The concentration of fluoride uptaked by the tooth structure dropped as the sites were moved further away from the cavity wall. 3- The dentin bonding agent systems do not prevent the passage of fluoride to the tooth structure